US 3676914 A
The mask-frame subassembly of a color picture tube is made with the formed mask portion thereof imperforate and, therefore, a blank. Both surfaces of the blank are coated with a photosensitive resist and exposed through master patterns to create latent images of apertures to be formed in the blank. These images are developed and the mask blank is thereafter etched from both surfaces to produce an aperture pattern determined by that of the masters. The image area of the tube is screened through well-known photoprinting techniques in which a second master is employed to define and precisely locate the pattern of phosphor deposits. After screening, filming and aluminizing, the face panel section of the tube receives the aperture mask-frame subassembly and the tube processing then continues in conventional manner. In developing an aperture pattern in the mask blank and in screening the face panel, a system of studs and leaf springs or supports is employed to establish a coupling of kinematical design. This is characterized by unique positioning of the coupled elements with their geometric centers in a known reference location and makes possible interchangeability of masks and panels.
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United States Patent Flore 1 51 July 18, 1972 1 MANUFACTURE OF SHADOW MASK COLOR PICTURE TUBE Joseph P. Flore, Chicago, [11,
 Assignee: Zenith Radio Corporation, Chicago, 111.
 Filed: May 1, 1970  Appl. No.: 33,766
Primary Examiner-John F. Campbell Assistant Examiner-Richard Bernard Lazarus Attorney-Francis W. Crotty ABSTRACT The mask-frame subassembly of a color picture tube is made with the formed mask portion thereof imperforate and, therefore, it blank. Both surfaces of the blank are coated with a photosensitive resist and exposed through master patterns to create latent images of apertures to be formed in the blank. These images are developed and the mask blank is thereafter etched from both surfaces to produce an aperture pattern determined by that of the masters. The image area of the tube is screened through well-known photoprinting techniques in which a second master is employed to define and precisely locate the pattern of phosphor deposits. Afler screening, filming and aluminizing, the face panel section of the tube receives the aperture mask-frame subassembly and the tube processing then continues in conventional manner. In developing an aperture pattern in the mask blank and in screening the face panel, a system of studs and leaf springs or supports is employed to establish a coupling of kinematical design. This is characterized by unique positioning of the coupled elements with their geometric centers in a known reference location and makes possible interchangeability of masks and panels.
17 China, 16 Drawing figures Patented July 18, 1972 5 Sheets-Sheet l MoskBlonk Frome Forming Forming i i Oxidizing Oxidizing y Spring Ahoching HQ 2 MoskBlonk Frome Assembling i Master Stress Poi'iern Reiieving Phosphor Exposing 8 Screening Developing l V Oxide Filming Stripping 8i Erohing i i Aluminizing Blockening Mosk inserting Inventor Joseph P Here AHorne Patented July 18, 1972 3,676,914
5 Sheets-Sheet l;
Patented July 18, 1972 3,676,914
5 Sheets-Sheet 3 Inventor 4 JosephPFiore AHorn Patented July 18, 1972 3,676,914
5 Sheets-Sheet i Inventor Joseph P. Fiore Attorney n u a. u u o o n In l u a a o n u u o- 5 Sheets-Sheet f Patented July 18, 1972 Attorney iriventor Joseph P Fiore MANUFACTURE OF SHADOW MASK COLOR PICTURE TUBE BACKGROUND OF THE INVENTION The present invention is directed to an improved process for the manufacture of shadow mask color picture tubes. lt achieves a result that has long been desired, namely, interchangeability of masks and screen panels.
In processing tubes of the type under consideration, it is customary to determine the pattern and precise location of the phosphor deposits on the screen of the tube by exposing through the shadow mask a photoresist layer or other sensitized coating that has been applied over the screen. Such exposure establishes a latent image of the phosphor deposits which is then developed and, repeating this sequence each of three times, forms the familiar dot triads over the screen area of the tube. Each such triad comprises a dot of green, a dot of blue and a dot of red phosphor.
It is of critical importance to the successful operation of such a tube that the apertures of the mask, installed in the tube and through which color selection is achieved, be in precise alignment or registry with the dot triads of the screen otherwise color fringing or imperfections may be experienced. This is such a necessary relation that it has been obtained in prior manufacturing processes by temporarily installing a given shadow mask within the face panel during each of the three exposure steps of the screening process and by permanently positioning the same mask within the panel when screening has been completed. This practice is known as pairing and has become widespread in the commercial production of shadow mask tubes. By pairing" is meant an assignment of a particular shadow mask to a particular face panel section ofa tube. A severe limitation inherent in pairing is that the mask is referenced to the panel during screening and imposes its own peculiarities on the phosphor pattern of the screen structure. As a consequence interchangeability of masks and/or panels is impossible if color imperfections are to be avoided. As a general proposition, the cOlor-selection electrode or shadow mask is a working part of the tube and may not be compatible with screening requirements, as will become apparent presently in the discussion of black-surround and post-deflection-focus types of color tubes.
While the pairing technique may be, and in fact is, used suc cessfully in the commercial manufacture of shadow mask tubes, its limitations add to the cost, complexity and inconvenience of the manufacturing process. By way of example, if a tube has been completely screened and its mask suffers damage, such as denting or other deformation, all is lost and the screen processing must be undertaken again from the very beginning. This follows simply because the screen of the tube made in accordance with prior practices is uniquely identified with a particular mask and it is not feasible to substitute a different mask in the event of damage to the one that has been used in screening. A substituted mask will not have the precision of matching or registration with the screen required to achieve acceptable color fidelity in image reproduction. It will be self-evident that interchangeability of masks provides dramatic economies in manufacture. By way of illustration, where such interchangeability is possible, if a given mask becomes damaged, another may be substituted in its place in the tube in process or, in other words, the screen may be salvaged. Other attractive advantages include simplification in the screening process since screening may be accomplished without having to insert and remove the shadow mask from the face panel section several times and also the mask may be kept cleaner which is highly desirable.
One form of shadow mask that has been recently introduced commercially features phosphor dots of reduced diameter so that the dots are spaced from one another over the image area, rather than being in tangential contact as typified by the original commercial version of the tube. In its more recent form, the tube has light-absorbing material disposed in the spaces between, and on the screen area surrounding, the
phosphor dots giving rise to the popular description of a blacksurround tube. A tube of this type is described and claimed in U.S. Pat. No. 3,l46,368, issued on Aug. 25, I964 and assigned to the assignee of the present invention. The black-surround tube has decided advantages both in respect of brightness and contrast. It is, however, a comparatively difficult tube to manufacture particularly with regard to screening since it is necessary, in the preferred structure, to have the electron beams of the tube larger in size than the phosphor dots constituting the dot triads of the screen. A similar requirement with attendant manufacturing difficulties is presented with the so-called post-deflection-acceleration or focus type of shadow-mask tube. Were interchangeability of masks possible, and such is the contribution of the present invention, there is a very marked simplification in the manufacture of black-surround and post-deflectionfocus shadow-mask tubes.
Accordingly, it is an object of the invention to provide an improved process for the manufacture of shadow-mask color tubes.
It is another object of the invention to improve the manufacture of such tubes by avoiding one or more of the aforementioned difiiculties of prior processes.
it is a specific object of the invention to provide for interchangeability of masks and/or panels in the manufacture of shadow mask color tubes whether they feature black-surround and post-deflection-focus or not.
SUMMARY OF THE INVENTION The invention improves the manufacture of shadow-mask types of color picture tubes through a process one embodi ment of which includes the step of forming a mask-frame component or subassembly from a material that may be etched. The formed mask is imperforate and is configured to correspond substantially to the internal surface of the face panel section of the tube in process. The frame portion extends from the mask portion for securing the mask-frame subassembly in a predetermined position within the face panel section. Preferably, the mask-frame subassembly is first thermally treated for stress relief and then a coating of a sensitized resist is applied to at least one surface of the mask after which the mask-frame subassembly is supported in a predetermined alignment with a master pattern through which the mask blank coating is exposed to actinic energy to establish in the sensitized coating a latent image of a desired aperture pattern. This latent image is then developed and thereafter the mask blank is etched to create the desired aperture patterns.
In a complementary operation, a master pattern is also used to screen on the internal surface of the face panel section of the tube an interleaved series of deposits of different phosphor materials arranged with the deposits of any given phosphor material distributed in accordance with the aperture pattern that has been created in the mask. In screening, the panel is uniquely referenced to the master pattern, just as the mask blank was referenced to its master pattern in developing apertures in the mask, in order to achieve interchangeability of masks and panels. Finally, and after the screening has been accomplished, the mask-frame subassembly is installed in the face panel section of the tube.
In one specific and preferred embodiment of the invention the aperture pattern formed in the mask portion of the maskframe subassembly is determined by the master pattern but the relative sizes of the holes in the master and in the mask is determined by whether or not the screen is conventional or is to be for the black-surround or post-deflection-focus variety of shadow-mask tube. If it is of either the last two mentioned varieties, the individual apertures formed in the mask portion of the mask-frame subassembly are larger than those of the master pattern and are also larger than the phosphor deposits formed by screening the face panel with its master. Control of the mask aperture size in relation to its master and in relation to the phosphor dots of the screen is readily attained by adjustment of parameters of the exposing step as well be explained.
BRIEF DESCRIPTION OF THE DRAWINGS The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and ad vantages thereof, may be best understood by reference to the following description taken in connection with the accompanying drawings, in the several figures of which like reference numerals identify like elements, and in which:
FIGS. la-lc are sketches used in explaining a particular type of mechanical coupling system used in practicing the sub' ject invention to attain interchangeability;
FIG. 2 is a flow chart of process steps taken in the manufacture of a shadow mask color tube in accordance with the invention;
FIGS. 3a and 3b are sketches pertaining to mask and frame assembling;
HO. 4 is a sketch used in explaining a method of developing master patterns to be employed in preparing an aperture mask;
FIGS. Sa-Sd are detail but fragmentary views of process steps for forming an aperture pattern in the mask of the tube in process; and
FIGS. 6-7 are sketches pertaining to master pattern forming for, and for use in, screening.
Shadow-mask tubes come in a variety of sizes and shapes with phosphor deposits that may likewise be of different shapes. For example, a tube of a given screen dimension may be round or rectangular and the various phosphor materials may be applied in the form of strips or dots. Practice of the present invention is not dependent on such factors and it will be assumed, simply for convenience, that the tube under consideration is a 23-inch rectangular tube for which the screen is a multiplicity of phosphor clot triads distributed over the image area of its face panel section.
Structurally, tubes of the type in question are formed of envelopes that have two principal parts; a face panel section and a funnel section. The face panel section is rather like a flanged dish with a skirt or flange circumscribing a screen or image area which is to be screened with phosphor materials. For the additive type of color television system currently in commercial use the screen is a repeating pattern or an interlace of similar deposits of green, blue and red phosphor materials collectively defining phosphor dot triads. The funnel section has an enlarged end which matches, both as to dimension and configuration, the flange of the face panel section so that they may be sealed together by means of a sealing frit to constitute an envelope suitable for supporting a vacuum. The small end of the funnel section accommodates a neck which houses at least one electron gun but usually a cluster of three such guns is arranged to develop three electron beams that are directed and accelerated toward the screen of the tube. With the tube assembled, the shadow mask is interposed between the gun cluster and the screen, being very much closer to the latter. The apertures of the mask permit color selection by confining each of the three electron beams to impinge upon only the particular phosphor material to which any given beam has been assigned. In these respects the structure and operation of the tube are entirely conventional and need not be discussed in further detail.
The improved method of manufacturing shadow mask tubes has the desired attribute of interchangeability of shadow masks and face panels and comprises two series of processing steps that may progress independently of one another. One is forming of the mask-frame subassembly of the tube and the other is screening its image area. They will be considered in the recited order but first the matter of interchangeability deserves comment.
Let it be assumed initially that the mask-frame subassembly is prepared in the manner presently to be described to achieve interchangeability so that any one of a production lot is suitable for installation in a given tube being fabricated. Let it be further assumed that screening is perfonned in the conventional way except that a master mask, properly related to the mask-frame subassembly in respect of its aperture pattern, is temporarily installed within the face panel for each of the required three exposures utilized in defining the phosphor deposits that collectively constitute the image screen. In this case, interchangeability will be true of masks only and not of panels because, in the screening process, the exposure mask will have been referenced to the panel rather than to a reference that is meaningful to the mask-frame subassembly. Only half of the desired ultimate objective will have been attained. Preferably, in screening the panel is uniquely referenced to the master rather than vice versa so that interchangeability of panels as well as masks is achieved. The desired objective is accomplished by the use of a coupling system of kinematical design through which unique referencing is established in processing both the mask blank and the image screen of the face panel.
An understanding of such a coupling system may be derived from a consideration of FIGS. 10-11 in which it is assumed that a mask, represented by rectangle B, is to be uniquely cou pled and referenced to a face panel, represented by rectangle A, with their geometric centers superposed. A pair of locating pins 1 and 2 is first secured to one face on panel A at a distance x/Z from its horizontal centerline, where x is the height of mask B. A third locating pin 3 is affixed to the same face of panel A at a distance y/2 from its vertical centerline, where y is the width of mask B. These three pins establish a fixed or unique orientation if mask B is placed on panel A with three points of its periphery contacting pins 1-3 but the planar relationship of bodies A and B will not have been determined. For that purpose, three identical pads 4-6 are affixed to the same face of panel A to receive and support the periphery of mask B. With these pads in place, the bodies A and B are coupled with uniqueness as to planar position and orientation and this has been accomplished with six points of contact or coupling. Six is at once the minimal and adequate number of points to determine uniqueness and, while additional locating pins and pads may be employed for added mechanical strength, they are redundant so far as positioning is concerned. Of course, any added pins or pads must be compatible with the positioning established by the aforesaid six points.
Equivalent results may be obtained through the use of three coupling connections each of which provides two of the necessary six points, as explained in the text Procedures in Experimental Physics by John Strong, Prentice-Hall 1939 at page 585. It will be recognized that the leaf spring-stud coupling arrangement conventionally employed in shadow mask color tubes is of this type since the studs projecting inwardly of the face panel to support the mask are circular in cross section and the apertures provided in the leaf mounting springs of the mask are triangular in shape so that when received by the mounting studs each leaf spring and stud coupling defines two support points and collectively the three constitute the six points required for uniqueness. While prior tube structures utilize this kind of coupling arrangement, their processing has not been carried out in the manner necessary to achieve interchangeability. A novel process to secure such a result will be explained but attention is first directed to forming the maskframe subassembly.
To a considerable extent the mask-frame subassembly is manufactured in accordance with the method described in US. Pat. No. 3,35 l ,996, issued on Nov. l4, I967 and assigned to the assignee of the present invention. There is one most significant difference, however, in the two methods and it is this difference which makes interchangeability of masks realizable, whereas the method of the earlier patent is directed to masks used in the practice of pairing alluded to above. More particularly, the mask-frame subassembly of the patent features the formation of an apertured mask which is then united with a frame while in accordance with the present invention a mask blank which is imperforate, except possibly for locating holes in its peripheral portion, is formed with a frame after which the subassembly is further processed to develop a desired pattern of apertures in its mask. It is known that the mask and frame may be formed from a single blank of material or they may be fabricated separately and then combined in a subassembly. Either approach is acceptable although the latter is depicted in the flow chart of FIG. 2. Accordingly, a mask blank of suitable material is first formed to the configuration desired of the mask as used in the tube. The material chosen is one that lends itself to chemical milling, as by etching, and is usually a thin sheet of annealed steel of approximately 5 mil thickness. The blank is cut to a desired shape, that is to say, round or rectangular but rectangular for the case under consideration, and is heat treated and work hardened preparatory to being pressed into a desired form. Since the internal surface of the panel section of the tube is approximately a spherical section, the mask blank is given a similar configuration so that the mask, when finally positioned within the tube is in essentially parallel relation to the screen, that is to say, these components are positioned in parallel or in nested concentric relation. The mask may be die pressed or drape drawn in accordance with the apparatus and method of U.S. Pat. No. 3,296,850 issued on Jan. 10, 1967 and assigned to the assignee of the present invention.
Having formed the mask blank into a spherical section, it is degreased and blackened or oxidized to have radiation properties similar to those of a black body. A variety of processes are available for this purpose including chemical blackening and thermal blackening, the latter being accomplished by heating the mask blank for an appropriate period of time. For example, the mask may be heated to 600 degrees F. and the oxygen of the oven then purged and replaced by steam. The temperature is then increased to 1,000 degrees F. and retained for about minutes to oxidize or blacken the mask in an oxidizing atmosphere. An attractive advantage derived from thermal blackening at high temperature is added stability or contour control of the mask through stress relieving, that is to say, stresses that may have been introduced in the mask-blank forming are relieved by heat treating. Experience reveals that stresses in the mask after the mask-forming operation are responsible for instabilities and undesired changes in the mask contour leading to color contamination in the finished tube. This is avoided by stress relieving of the mask which is to be accomplished before joining the mask to its frame. Stress relieving may result from thermal oxidation or may be undertaken as a separate process step but in any event it is to be accomplished in preparing the mask for uniting with a frame.
The formed but imperforate mask blank is to be provided with a frame so that the mask-frame subassembly may be mechanically and permanently positioned within the panel section of the tube. As stated above, the flow chart of FIG. 2 contemplates forming the frame separately as by stamping from a sheet of cold rolled steel that is relatively thick and therefore mechanically much stronger than the mask. Typically, the frame is formed of 93 mil stock and it is dimensioned and configured in relation to the mask blank to facilitate their being assembled in telescoping or overlapping relation after which they may be welded to one another. One method of preparing the frame with its mounting springs is disclosed in U.S. Pat. No. 3,351,996 referred to above. Briefly, a frame of appropriate dimensions is stamped from a blank of steel and is then stamped or otherwise shaped into a desired configuration for uniting with the mask blank.
in accordance with another well-known method, the mask frame is formed from strip stock through a roll and forming process. After shaping, the frame preferably is stress relieved which may be done at a high temperature with a short time cycle or at a relatively low temperature but with a long time cycle. Assuming the frame material to have an annealing temperature of about L600 degrees F., stress relieving may be achieved by heating to L400 degrees F. for approximately minutes.
The formed frame is oxidized, as indicated in FIG. 2, and is then provided with leaf springs which are attached to the frame at one end and present triangularly shaped mounting apertures at the opposite end dimensioned to receive mounting studs projecting inwardly of the face panel section of the. tube to support the mask-frame in position. There are three or four such mountinG springs depending upon the choice that is made as between a three and four point suspension system. As explained, three are sufficient to the desired kinematical design and a fourth may be used but it must be compatible to the design created by the other three. For convenience, a three point suspension will be assumed. Of course, the overall dimensions of the mask-frame are less than the internal dimensions of the face panel to facilitate installing the mask in position. Accordingly, the mounting springs are shaped to extend away from the frame to which they are attached and to bridge the distance between the frame and the internal wall surfaces of the face panel. The chart of FIG. 2 indicates that the mounting springs are attached to the frame prior to assembling of the mask-frame subassembly. One may, if desired. attach the springs after the mask-frame subassembly has been prepared, but there is distinct preference to attaching the springs prior to fabricating the subassembly.
The sketch of FIG. 3a illustrates a preferred method of spring attachment, assuming that three leaf springs are to be employed. A fixture is provided having three studs 15 that are dimensioned and positioned to simulate a bogey face panel, that is to say, a panel which is perfect as to configuration and dimension of its component parts. The geometric center of the simulated panel is indicated by the cross in the figure. All three preformed leaf springs 14 are first assembled onto studs 15 by means of the triangular openings in the springs with the longitudinal axes of the springs coplanar with the axes of the studs. The frame B is now moved into position between the ends of springs 14 which are then welded to the frame. Experience shows that this operation may be conducted fast and with precision, assuring that the geometric center of frame B, coincides with that of the aforementioned simulated panel. Again, the kinematical coupling is relied on in achieving the desired relation or unique positioning of the frame to a simulated bogey panel.
The schematic diagram of FIG. 3b represents a formed but imperforate mask blank B, supported on a stationary bed 2 having a seat which matches the mask blank in conformation and suitable locating or positioning devices (not shown) for orienting the mask blank. A frame 8,, constructed in accordance with U.S. Pat. No. 2,897,392 issued July 28, i959 and assigned to the assignee of the present invention, and having mounting springs 14 attached as just described, is shown above mask blank 8,. Once again a fixture is used, having studs [5 to simulate a bogey panel and to receive leaf springs 14 of the frame. In forming the mask-frame subassembly, frame B telescopes with reference to the flange of mask blank B, and when in position with its mounting springs 14 engaging studs 15 its reference axis C coincides with reference axis D of the fixture, establishing a desired predetermined distance E from the crown at the center of the mask blank to the reference axis C of frame 8,. The telescoped parts are united by spot welding. This is a far more precise and manageable dimensioning procedure than is available if the springs are attached after the subassembly has been constructed.
in any event, the mask-frame subassembly with the mounting springs in position is made thermally stable by undergoing a final stress relieving step. This is particularly beneficial because, whether the telescoped mask and frame are in perfect alignment or suffer some slight misalignment in assembling, it is found that due to the difference in mass of these parts a stress condition is set up in the mask blank in the area close to and per force of the individual welds. Unless relieved by thermal treatment, such stress results in deformation or unwanted change in contour of the mask and color imperfections during tube operation. On the other hand, if the stress is relieved by heating to approximately 470 degrees C. for about 10 minutes, the mask exhibits its desired contour in stable operation of the tube, as required for optimized color reproduction. Accordingly, after the subassembly has been made, it is stress relieved to cause the mask-frame subassembly to be stable at temperatures encountered both in the succeeding processing steps of the tube and in its operation in the reproduction of images in simulated natural color.
Oxidizing of the mask-frame subassembly, whether the components thereof are treated separately as described or after the subassembly has been made, further contributes to thermal stability in the operation of the tube. It is known that a significant portion of the electrons in the three beams of the tube impinge upon and are intercepted by the mask. As a consequence, the mask experiences a substantial increase in tern perature and may dissipate as much as 45-50 watts. Stability of the structure in the face of such heat dissipation is enhanced by the oxidizing which causes the structure to have heat radiation properties similar to those of a black body.
The next step in the processing of the mask-frame is to provide in the formed mask blank a multiplicity of apertures of a desired shape, size and location to define a pattern of apertures appropriate to the operation of the tube in process. Since the tube under consideration has been assumed to be a rectangular tube with a dot-triad type of screen, the mask is to be provided with circular apertures distributed in a rectangular field. The mechanics of providing an aperture pattern in a mask blank, as such, are quite well known and include the steps of exposing and developing an image of the aperture pattern on the mask blank. For the process under consideration the exposure is through a master pattern by means of which the specifications of the aperture pattern of the mask are precisely determined. It is appropriate, for the sake of completeness, to consider an acceptable process for preparing such a master for exposing mask blank 8,.
The sketch of FIG. 4 represents an exposure system by means of which a bogey mask 8 is utilized in preparing a pair of masters M, and M to be used in developing aperture patterns in mask blanks which patterns accurately duplicate that of bogey mask B. The expression bogey mask" is here used to mean a mask with an aperture pattern that is optimum for image reproduction with a bogey screen in which the three dif ferent phosphor materials have been deposited to form a multiplicity of phosphor dot triads. It will have apertures of a desired size distributed over a rectangular field with uniform diameter or with a graded hole size, as desired. In many instances the hole size decreases with radial distance from the center of the mask.
The sketch of FIG. 4 shows bogey mask 8 supported by a fixture similar to that described in connection with FIG. 3a having studs dimensioned and positioned to simulate a bogey panel. These studs couple with the leaf mounting springs 14 of the mask B and support that mask in a uniquely determined position with its geometric center and that of the simulated panel disposed on the vertical axis of an optical projection system. Two additional support systems of kinematical design, very similar to that of FIG. 1c, are arranged on opposite sides of fixture 15 for the purpose of holding planar plates 17 and 17' of glass or the like in preselected exposure positions at chosen distances from bogey mask B and with their geometric centers aligned with that of the mask. The axial spacing of plates l7, 17' from mask B is not critical, it is selected from convenience and the parameters of the exposure step are adjusted to achieve a desired relation of the patterns M, and M established on plates 17 and 17' respectively, in respect of the aperture pattern of mask B. The coupling systems for plates l7, l7 individually have elements l6, 16' which may be similar to the pin and pad arrangement of FIG. la to be of kinematical design assuring that the geometric cen ters of the mater blanks are aligned on a common axis with that of bogey mask B.
The optical system of the exposure chamber represented by FIG. 4 includes a pair of light sources S, and S, as well as a curvilinear light reflector R. The reflector is constructed to the end that light source S, is imaged at point S, and vice versa, that is to say, and as represented by the broken construction lines of FIG. 4, a light ray issuing from source 8,, if permitted unimpeded travel to reflector R is reflected therefrom to the point 5,. And, likewise, a light ray from light source S, under the same conditions is reflected to the point 3,.
Each of plates I7, 17' bears a photosensitive coating on the surface thereof facing mask B and the coating may he a positive resist which has the property that, upon exposure to actinic energy, such as ultraviolet light from source S, or 8,, it is rendered soluble, whereas it is otherwise insoluble in a particular solvent. The exposure process for creating master patterns M, and M, is as follows: The blank 17' for master pattern M having been coated with a light sensitive resist. is placed on supports 16'; the blank I! for master pattern M, is temporarily removed from the projection system and light source S, alone is energized. Accordingly, an image of the aperture pattern of mask B is projected on the blank 17', creating therein a latent image of the desired master pattern M The blank 17' is now removed from the exposure chamber and the latent image is developed by washing with a solvent of the resist. Having thus prepared master pattern M plate 17 is installed in its coupling system 16 and light source S, is energized. The light from source S is projected from reflector R through mask B to blank 17 and a latent image of master pattern M, results. The plate is removed from the exposure chamber and treated with a solvent to develop master pattern M The described system features straight through projection since light sources S, and S, are imaged on one another and as a consequence master patterns M, and M not only accurately represent the aperture pattern of bogey mask B, but also are properly related to one another in position. It is noted in passing that Eastman Kodak Company markets graphic art plates that are sensitized and directly useable as plates l7 and 17.
Having prepared master patterns M, and M their use in the continued processing of the mask frame will be considered. If apertures are to be formed in the mask blank by etching from but a single side, it is only necessary to apply the photo or light sensitive coating to that side or surface of the blank, although it is preferred that both surfaces of the mask blank be coated and that etching be accomplished from both sides. Accordingly, both sides of the mask blank are coated with a photosensitive resist of the type which experiences a change in solubility upon exposure to actinic energy. Resists are either of the negative type which become insoluble in a solvent upon exposure or of the positive type which is normally insoluble but becomes soluble upon exposure. Either is suitable so long as the aperture pattern is projected from a positive or negative image chosen to meet the characteristics of the resist. It is convenient to use a positive resist which is normally insoluble in a solvent but which becomes soluble upon exposure to ultraviolet light. Resists of this character are commercially available; a typical one is Azo Plate Ill, distributed by Shipley Company Incorporated of Newtown, Massachusetts. The coated mask-frame is installed in the exposure chamber of FIG. 4 along with master patterns M, and M, and in substitution for bogey mask 8. Since the mask-frame in process is equipped with leaf mounting springs 14, identical to those of bogey mask 8, their coupling with studs 15 in the chamber supports the mask-frame in a unique exposure position which is precisely the same as the position previously occupied by bogey mask B. By virtue of the uniqueness in position, established through the use of a coupling system featuring kinematical design, the mask-frame is properly referenced as required for interchangeability. Its geometric center is positioned where the geometric center of bogey mask B was located in preparing master patterns M, and M Now, both light sources 5, and S, are energized, or alternatively they may function in sequence, to expose the concave surface of the mask-frame to master pattern M, and to expose the convex surface thereof to master pattern M Further details of the mask-frame processing are represented by the fragmentary views of FIGS. Sa-Sd.
FIG. 5a shows a fragment of mask blank B, with oxidized layers 12 and on its opposing surfaces and superposed layers or coating 13, 13a of a positive photosensitive resist.
The coating may be applied in any of a variety of ways such as flow coating, spraying, dipping and spinning, electrostatic spraying, etc. After the coating has been applied and dried, the mask blank is exposed through master patterns M and M,, as explained above, which determine the nature of the individual apertures and the aperture pattern to be developed in the mask blank.
It may be noted in passing that there is flexibility in the exposure step and in the master pattern utilized at the exposure step. While the mask blank to be exposed has been preformed to a spherical section, the master may be planar or other shape with its pattern of transparent portions and the optics of the light projection system arranged to project the desired image on the mask blank. For example, it may be convenient to form the master as a spherical section in order that it may be positioned essentially in nested concentric relation with the mask blank, between the light and mask blank during the exposure step. In the simplest case, where the mask blank has a single surface coated with a sensitized resist, the coating preferably is on the concave side and the blank may be supported above the master mask in an exposure chamber or lighthouse similar to that customarily employed in photoresist screening. Such a structure is described in US. Pat. No. 3,319,556, issued on May l6, I967, and assigned to the assignee of the present invention. Preferably, however, both surfaces of the mask blank bear a sensitized resist and it is exposed in a chamber like that of FIG. 4 so that both surfaces of the blank are exposed through the pair of master patterns M and M to establish latent images concurrently or sequentially, as desired, on both surfaces of the mask and in registration with one another.
Where the aperture mask is for a screen having a mosaic or triad arrangement of phosphor deposits, as has been assumed, the exposed areas of the sensitized coatings for each hole of the mask are as represented in FIG. 5a, wherein the concave surface of the mask blank has an annular elemental area l4 exposed through a hold of master M in coaxial alignment with a similar but larger area 140 on the obverse surface of the blank exposed through the corresponding hold of master M These elemental areas represent latent images of apertures that are to be chemically milled, by etching, in those portions of the blank surfaces which they overlie. Image 14a is made larger than image 14 simply because etching is more easily undertaken through the use of images of unequal size. These latent images 14, 14a are developed by washing the mask with the solvent of the sensitized material of coatings 13, 13a as a consequence of which the exposed elemental areas wash out, leaving in the coatings on the surfaces of the mask blank pairs of openings 15, 150. There is a pair of such openings for each aperture to be formed in the mask and the members of each pair are in registration with one another, that is to say, they are in radial alignment as illustrated in FIG. 5b. Having developed the series of openings I5, 150 in the sensitized coatings, the mask is heated to a temperature of approximately 250 degrees C. for 5 minutes in order to bake the remainder of the resist coatings.
The mask is next treated with a chemical stripper, as by flushing, dipping or spraying, for the purpose or removing the elemental portions of oxide layers 12, 120 which lie immediately under or are exposed through openings 15, 15a of the resist coatings. The stripper employed must be effective in removing oxide from the mask blank but it must not attack the residue of coatings 13, 13a. Hydrogen chloride is an acceptable stripper. It is desirable to strip the exposed portions of the oxide surfaces to facilitate etching since the oxide layers I2, 120 otherwise serve as a resist which is relatively insensitive to the etchant and impedes etching. After having stripped the exposed portions of the oxide layers, mask B is in the condition represented in FIG. 5c and is thereafter etched to develop the holes, such as hole 16 of FIG. 5d in the mask blank. For the usual mask material etching is readily accomplished with ferric chloride acid that is applied by spraying or dipping into a tank in which the etchant is circulated by ultrasonic action to improve uniformity of the etch. It is clear from the shape of aperture l6 that the blank preferably is etched from both surfaces. The convex side of the mask blank which has coating 13a is etched first to develop a large recess in blank B which does not break through the opposed surface, namely, that which bears resist coating 13. Etching from the obverse or concave side of the blank through opening l5 then causes aperture 16 to extend totally through blank 11 and determines its effective diameter d. The large diameter section of aperture 16 may be formed relatively quickly and removes the major portion of the elemental part of the mask blank required to mill aperture l6. The next etching step performed through opening 15 removes a minor part of the mask blank and, therefore, may be conveniently undertaken with adequate care and control as required to precisely dimension the hole diameter d.
The effective size d of blank aperture 16 is dictated by the character of the tube in process and is subject to control by adjusting the geometry of the exposure system. For the conventional shadow mask tube wherein the phosphor dots are in tangential contact with one another, all over the image area. the hole diameter d is relatively small to construct the electron beams passing through apertured mask B, to a diameter less than that of the phosphor dots. On the other hand, where the tube is of the black-surround or post-deflection-focus variety, the hold diameter d is comparatively large since for this case. as explained above, the electron beam is larger in diameter than the phosphor dots. A given set of masters M and M may be used in forming the aperture pattern in mask blank B for either type of tube. It is simply a matter of adjusting the process parameters so that the latent images 14, 140 formed on resist coatings [3, 13a by exposure through the master patterns are properly dimen-sioned.
In milling apertures 16 in mask blank 8,, the etchant attacks only the elemental surfaces of the mask blank that are exposed by holes 15, 15a because the other surfaces of the mask blank are protected by the residue of resist coatings 13, 13a. This is most advantageous in that a minimum of material is removed from the mask blank and that which is removed is confined to those elemental portions of the blank where it is desired that the apertures be formed. In other words, the mask retains maximum mechanical strength. When the etching has been completed, resist coatings 13, are removed by washing the mask with a solvent for the resist. For positive resists trichlorethylene is a suitable solvent and for negative resists, such as polyvinyl alcohol or fish glue, a caustic solution may be used. Now only the wall surfaces of apertures 16 represent exposed surfaces of the mask; the remainder of the mask blank is covered by oxide layers I2, 120. The apertured mask is then subjected to a chemical blackening which blackens the surfaces of the mask that had been exposed as a consequence of etching. This restores to the mask the black body properties that are desirable for heat dissipation purposes. The mask shall now have been completely processed and the maskframe subassembly is in condition for final installation into a face panel section of a shadow mask tube.
Of course, the face panel section of the tube in process must be screened before the mask-frame subassembly is to be installed. Screening has in common with the described process of forming the mask-frame, the step of exposing a sensitized layer or coating with actinic energy directed thereto through a master pattern but now to create a latent image of phosphor dots instead of a latent image of mask apertures. By exposing a sensitized layer that has been applied over the image area of the tube with a master pattern properly related, in specification and position relative to a fixed or known reference, to that employed in developing a pattern of apertures in the mask blank, as described above, the desired feature of interchangeability is attained. Consequently, the flow chart of FIG. 2 indicates that the master pattern is utilized in mask blank processing as well as in phosphor screening.
Here, again, there is process flexibility but at the sacrifice of some degree of interchangeability. More specifi-cally, in screening the face panel a plate bearing a master pattern, such as plate 17, may be equipped with mounting springs so that the master may be temporarily installed within the panel for the exposure step. Where this procedure is adopted, the master becomes referenced to the panel rather than having the panel referenced to a bogey mask or other fixed reference. As a con sequence interchangeability of panels is not achieved but interchangeability of masks is retained since, as explained, the mask blanks are all properly referenced to a bogey panel during the exposure step of mask-aperture forming. The preferred practice is to reference the panel to a bogey mask in screening to the end that complete interchangeability of masks and panels results. Before describing the screening steps, a procedure will be given for developing a series of master patterns for screening, appropriately derived from the same bogey mask B from which master patterns M and M, used in processing mask B were derived.
The apparatus employed is that of FIG. 6a which represents what is known in the tube art as a demountable and may be thought of as a simulated picture tube, differing therefrom in two material respects. First of all the envelope has a funnel portion 20 and a cap or face panel 21 that are not sealed to one another. Instead, they may be assembled on a temporary basis through a sealing joint well known to the art which so couples the components that the envelope may hold a vacuum essentially the same as that established in a finally evacuated picture tube. For the demountable this is accomplished by a connection 22 to a vacuum system which maintains the desired condition within the envelope. The small end of en velope section 20 has the usual gun cluster 23 and terminal base 24 through which operating potentials are applied to the electrode system of the device. Of course, a high voltage connection (not shown) is also provided for the purpose of applying final anode voltage of the proper value. In order to scan with the electron beams issued from gun cluster 23 a bogey yoke 25 is associated with envelope section 20 and the other accessories, including static and dynamic convergence are also provided. They constitute no part of the present invention and are well known so that for simplicity they have not been indicated in the sketch. Within the demountable there is supported a fixture again having studs I dimensioned and positioned to simulate a bogey panel. The same bogey mask B used in preparing masters M, and M described in connection with FIG. 4, is shown in position within the demountable, being supported in the usual way by its mounting springs 14 engaging fixture studs 15. Another fixture having studs I6 supports a conductive plate 18, again through a coupling arrangement of kinematical design so that the geometric centers of mask B and plate 18 are superposed or aligned along the electron optical axis of the demountable. The surface of plate 18 facing gun cluster 23 is covered with an electron sensitive coating, such as polyvinyl alcohol sensitized with ammonium dichromate.
With bogey mask B and plate 18 in position and with panel 21 removably sealed to the free end of envelope section 20, a vacuum is drawn in the demountable and the electrode system is energized so that electron beams may be developed. Three master patterns are required for screening, one for each color, and while processed individually the same steps are involved for each. Assume that the master pattern under discussion is for screening with green phosphor. In that case, only the gun of cluster 23 that corresponds to the gun of the tube in process assigned to excite the green phosphor dots of the screen is energized to issue an electron beam that is accelerated toward plate 18 and is permitted to reach there by traversing holes of bogey mask B. Concurrently, deflection signals are applied to yoke 25 and the electron beam scans a bidirectional raster on the mask to, in effect, project its aperture pattern onto the electron sensitive coating of plate [8, creating therein a latent image of that pattern. Thereafter, the vacuum is released, the demountable is opened and plate I8 is removed and rinsed with a solvent for its resist coating to develop the latent aperture pattern.
The next step, illustrated in the sketch of FIG. 6b, is simply a reduction of the aperture pattern established on plate IS in its transfer to another plate 18' in well-known fashion. There are two reasons for this image size reduction. Firstly, the distance 0 in FIG. 6a shows that plate 18 is spaced from bogey mask 8 in its exposure step by approximately the same distance that separates the mask from the image screen in the finished tube. Additionally, this reduction step may adjust for whatever position is desired of the screening master, between the light source and face panel, during the exposure step incident to screening with green phosphor.
The third step to be taken, as indicated in FIG. 6c, is projecting the image pattern from plate I8 onto a final green master pattern M by means ofa light source S:, and a correcting lens L which corrects for the fact the plates used in developing screening master M are planar whereas the screen surface of the face panel is a spherical section. This type of lens correction is well understood in the art and no difficulty would be experienced in designing a suitable lens for making the surface curvature correction under consideration. It is highly beneficial and distinctly preferred to employ a system of optical correcting lenses to impart to the master M all of the correcting or compensating effects which, under prior art practices, are introduced by means of correcting lenses in the screening exposure chambers. By preparing master M to incorporate such corrections in its aperture pattern, the master may be permanently installed in the screening exposure chamber and the correcting lens heretofore required in such chamber may be eliminated. Master pattern M may be used in screening with green phosphor but in any factory production a number ofexposure chambers are concurrently in use in screening face panels with green phosphor and, accordingly, a number of duplicates of master pattern M are produced by contact printing. One such master pattern is permanently installed in each exposure chamber utilized in the exposure step for processing with green phosphor.
A master pattern M for use in screening with blue phosphor is prepared in the same way and is duplicated for permanent installation in the blue exposure chambers. One difference in procedure is required, namely, the gun ofcluster 23 of the demountable to be energized in preparing master M is the one which corresponds to the gun of the tube in process assigned to excite blue phosphor dots. In like fashion, a screening master M for processing red phosphor is prepared and duplicated. In this case, the red gun of cluster 23 is energized and the remaining two are cut off.
Having prepared three master patterns M M M they are used in screening with their respective color phosphors in a process that is very similar to the prior art. Since the same process is practiced for each of the three different phosphor materials, it is sufiicient to consider only one in detail and this will be done in relation to the sketches of FIGS. 7a and 7b. The arrangement represented in FIG. 7a is the exposure chamber for green and has the usual source 30 of ultraviolet light which may expose the facepanel P of a tube in process through master pattern M supported between the light source and the panel. It will be observed that no correcting lens is included in the exposure chamber. Again, to preserve condi tions necessary to interchangeability of panels, master pattern M and panel P are engaged by coupling systems of kinematical design by which reference positions are established. More particularly, couplings 16 support the master pattern with its geometric center along the optical axis of the chamber. Similarly the support for panel P establishes its geometric center along the same reference axis. A suitable arrangement for that purpose is represented in FIG. 7b. The fixture for holding the panel in position, while satisfying the necessary requirements for mask and panel interchangeability, should simulate a bogey mask and the displacement required of the coupling elements to have the simulated mask engage the panel should also simulate the corresponding movement of the coupling element in the actual coupling of a mask to a panel. Since each mounting spring ofa mask is secured at one end to the mask and is free at the opposite end which has the aperture for engaging the panel stud, the displacement of the springs required to effect coupling is essentially a radial or curvilinear movement rather than a linear one. Consequently, the fixture of FIG. 7b is arranged to have three coupling elements of identical construction. Each includes a pivoted lever 32 having at one end a connection to the piston of an air cylinder 31 and carrying at its opposite end a triangularshaped aperture to engage stud 15 of panel P. When the cylinder is actuated, lever 32 is displaced about a centrally located pivot and the aperture is brought along an arcuate or radial path into engagement with stud is. As explained previously, each such spring has a minimum two-point contact with its associated stud and the family of three springs establishes the necessary six points for the unique positioning desired of panel P. The fixture comprised of the three levers 32 and their associated cylinders are installed to the end that the unique position of panel P is one in which its geometric center is in axial alignment with the geometric center of master pattern M It is desirable to minimize the weight of the panel to prevent damage to its studs and that may be easily accomplished by the use of counter-weight springs (not shown). For example, three springs may be positioned between the top surface of the exposure table and the free end of the flange depending from the face panel. These springs are to be dimensioned to have a net load of about one pound on the mounting studs.
ln processing face panel P with green phosphor, a photosensitive coating including particles of green phosphor in suspension is applied as a coating over the entire screen area of the panel and the panel is then installed in the exposure chamber by means of the fixture described in the preceding paragraph. ln screening, as in providing an aperture pattern in mask blank 3,, the nature of the resist employed is detennined by the character of the exposing energy, that is to say, whether it be light, an electron beam or whatever type of actinic energy is desired to be used. It is most convenient, however, to utilize a water soluble photosensitive resist in screening, such as polyvinyl alcohol (pva) sensitized with ammonium dichromate. The slurry coated panel having been positioned in the lighthouse is exposed by ultraviolet light through master mask M Since then sensitized coating of the panel contains green phosphor, the light source for this exposure chamber is positioned to simulate the electron gun of the tube in process that is assigned to excite the green phosphor dots. Exposure of the panel creates a latent image of the green phosphor dots, distinguishing these portions of the resist coating from the remainder thereof by the fact that the exposed elemental areas are rendered insoluble in water. The panel is removed from the exposure chamber and washed with water which develops the green phosphor dots on the image area.
The blue and red phosphor dots are established in essentially the same way but in each case the exposure, for convenience, is made in a light-house that is arranged for a particular color. The lighthouse for blue phosphor processing, for example, has a master pattern M B and its light source is positioned to represent the blue gun of the tube in process. In similar fashion, the lighthouse for processing red phosphor includes a master pattern M and its light source simulates the electron gun of the tube that is to excite the red phosphor. In the three exposure and developing steps interlaced deposits of green, blue and red phosphor dots are established on the image area of the face panel of the tube. These deposits are located with great precision over the image area by having them exposed to actinic energy through a carefully prepared master. importantly, in the exposure steps of screening the panel P is accurately referenced to its screening master rather than mounting the master within and, therefore, referencing it to the panel. By the same token, mask blank H is referenced to its master in similar fashion during mask exposure and complete interchangeability of masks and panels results.
The screening will be recognized as basically a well-known photoprinting method differing in certain important particulars from prior practices. Heretofore, a single mask was used both in screening and in achieving color selection in the finished tube. Since the one mask accomplished both functions, it was temporarily installed within the face panel section of the tube in process during the exposure step of each of the three different phosphors but was otherwise separated from the face panel during the other process steps required to make a complete screen although the mask always traveled with its assigned panel as is the custom in practicing pairing. in accordance with the present teaching, however, the aperture mask constituting a component of the tube is installed within a face-panel section only once, namely, when screening has been completed and just prior to sealing the face-panel section to a funnel section in forming the tube envelope. The obvious advantages in the change include, in addition to interchangeability, minimized possibility of damage to masks because their handling is drastically reduced and also the mask is kept clean during the tube processing. Another important change is that an exposure mask or master pattern is permanently installed in each exposure station and the panel is referenced to the expo sure table and, therefore, to the master rather than referencing the master to the panel by installing the master within the panel for exposure purposes.
The relative dimensions of the phosphor dots on the screen and the apertures of the mask to be installed in the tube in process are determined by the type of tube to be produced. If the tube is conventional, its phosphor dots are dimensioned to be in tangential contact with one another and the apertures of the mask are made smaller than the phosphor deposits so that the electron beams are smaller in dimension than the phosphor dots. When a beam is accurately registered on a phosphor dot, a peripheral portion of the dot is not energized and constitutes a guard band for assuring white field purity. For the black-surround of post-deflection-focus tube, however, the obverse size relation is adopted and the phosphor dots are, in fact, smaller in diameter than the electron beams. This result of controlled phosphor dot size is achieved conveniently by suitable dimensioning of the screening exposure chamber. For example, light source 30 includes a collimator and the size of its tip may be chosen to control the size of the phosphor dots. Other variables that may be adjusted to accomplish the same end include the size of the apertures or transparent portions of master M M, or M, as well as the spacing of the master from panel P. It is known that when the penumbra effect is utilized in determining phosphor dot size, some control is available by adjusting the intensity of the exposing light source and/or the duration of the exposure interval. It is preferred in production, however, to place minimal reliance on the penumbra effect and to achieve control of phosphor dot size by adjusting the geometry of the exposure set up, as described. This leads to better control and more uniformity in the screening process. Of course, for the blacksurround tube it is necessary to surround all of the phosphor dots with a light-absorbing material which may be accomplished by applying the surround material to the screen either before or after the phosphor dots have been formed as explained in Fiore et al. US. Pat. No. 3,146,368.
In one method of applying light-absorbing material to all portions of the screen other than those intended to receive phosphor deposits the screen is first coated with a clear pva and exposed in the manner of phosphor dot screening. In this case, however, the exposure and development establishes dots of clear pva on the screen, instead of phosphor dots, and if the process is carried out three times, each elemental screen area designated to receive phosphor will be protected by clear pva. After the light-absorbing layer has been applied, the pva is removed by a chemical stripper and screening may then proceed in the usual fashion. This procedure, involving three exposures, may be simplified by the present process featuring interchange-ability. For a black surround tube, the master employed in exposing the clear pva may have a pattern designed to expose at one time all of the elemental areas of the screen where the pva is to be retained and thus eliminate two exposures of the prior art. Such a master may be prepared for example in the apparatus of FIG. 6a by scanning plate 18 with beams from each of the three guns in cluster 23.
After the phosphors have been applied to panel P the screen is filmed in the usual way and then aluminized to provide for the screen a conductive backing layer of a diffusely reflective material for optimum brightness output. After aluminizing, the face panel section is ready for mask insertion and a mask, provided with an aperture pattern processed as described above so as to be precisely related to the pattern of phosphor deposits of the screen, is finally installed in the face panel section. From this point on the processing of the tube is continued in conventional manner, including the panel section with the conical or funnel envelope section, inserting the cluster ofelectron guns, processing them and so forth.
The master patterns used in processing the mask and in screening need not be made on substrates of the same material as the shadow mask made for installation in the tube being fabricated. The substrate material for the masters may be metal, plastic or glass. it is selected with these considerations in mind: it must be readily formed and milled to have the desired configuration and must be opaque but provided with a pattern or transparent portions, such as holes, of accurately controlled location, shape and dimension; and must have stability to retain its characteristics without alteration either during storage or in use when preparing shadow-mask subassemblies or screening the image area of a tube in process; and it must be compatible with precise and economical methods of duplication, such as contact printing. Presently, the preference is to planar glass. The shadow mask is chosen with generally the same considerations but additionally with the requirement that the material of the mask be compatible both with tube processing and operation. Since tube processing and operation involve high temperature conditions, as in bakeout and in beam scannin the mask has more severe requirements than the master which only has to stand the less rigid conditions of a lighthouse or exposure chamber. Accordingly, the mask is usually made of steel.
A number of benefits provided by the described process have been set forth above and need not be repeated. By adopting only that part of the procedure that results in interchangeable masks, but not interchangeable panels, there is a time consuming burden of continuously checking the master used in screening which is obviously undesirable. Moreover, since in such a case the master is supported within the panel during screening, undesirable limitations are imposed on the material of the master. For example, it could hardly be constructed of heavy plate glass.
Emphasis may be given to the fact that in the preferred embodiment the screening master is, in effect, made a part of the exposure chamber. Additionally, it may not be necessary to include a correcting lens in the optical system of that chamber because the necessary corrections may be built into the screening master.
While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.
I claim: 1. in the manufacture of a shadow-mask type of color cathoderay tube having a face panel section, the improvement which includes the following steps:
forming a mask-frame component comprising an imperforate mask portion of a material subject to etching configured to correspond substantially to the internal surface of said face panel section of the tube in process and further comprising a frame portion extending from said mask portion for securing the mask-frame component in a predetermined position within said face panel section;
applying to at least one surface of said mask portion a coat ing of a sensitized resist;
supporting said mask-frame component in predetermined alignment with reference to a first master having a predetermined pattern of transparent portions by an arrangement establishing at least six points of coupling between said mask-frame and said master to support said mask-frame and said master with their geometric centers aligned along a common reference axis;
exposing said coating to actinic energy through said master to establish in said coating a latent image of a desired aperture pattern;
developing said image and thereafter etching said mask portion to create therein said aperture pattern;
and producing a screened face panel from a screening master having a predetermined relationship to said first master so that any aperture mask processed from said first master is utilizable with any face panel processed from said screening master.
2. The improvement in accordance with claim 1 in which said mask portion and said frame portion are separately formed;
and said mask portion is stress relieved and then is united with said frame portion.
3. The improvement in accordance with claim 2 in which said mask-frame component is further stress relieved after said mask portion and said frame portion have been united to one another.
4. The improvement in accordance with claim 3 in which said mask portion and said frame portion are oxidized prior to the application of said resist coating;
and in which said mask is treated with an oxide stripper subsequent to said development step but prior to said etching step.
5. The improvement in accordance with claim 3 in which said frame portion is provided with leaf mounting springs and is stress relieved before being united with said mask portion.
6. The improvement in accordance with claim 1 in which a coating of said sensitized resist is applied to both surfaces of said mask portion;
said mask-frame component is supported in predetermined alignment with a pair of first masters positioned on opposite sides of said mask-frame component;
both coatings of resist are exposed through said pair of masters, respectively to establish said latent image;
said mask portion is etched from both sides to create said aperture pattern;
and said screening master has a predetermined relationship to one of said first masters.
7. The improvement in accordance with claim 6 in which said predetermined alignment is established by six point coupling arrangements which support said mask-frame component and both of said masters with their geometric centers aligned along a common reference axis.
8. The improvement in accordance with claim 7 in which said pair of masters is formed by a photoprinting process in which:
a. a bogey mask-frame is positioned in said predetermined alignment between a pair of substrates having sensitized surfaces facing said bogey mask-frame and (b) both of said surfaces are exposed to actinic energy directed thereto through said bogey mask frame.
9. The improvement in accordance with claim 1 which includes the following additional steps:
developing said screening master to have a preselected relationship to said first master through which said exposure step of said mask-frame takes place;
supporting said face panel referenced to said screening master in accordance with said predetermined alignment of said mask-frame component in relation to said first master;
and screening on said face panel a phosphor pattern determined by exposing said panel through said screening master.
10. The improvement in accordance with claim 9 in which said screening master is derived from the same bogey maskframe used in developing said first master.
1]. The improvement in accordance with claim it) in which said aperture pattern of said mask-frame is a multiplicity of substantially circular holes distributed over a generally rectangular field;
in which a family of three screening masters are developed from said bogey mask-frame, one for screening with each of green, blue and red emitting phosphors;
and in which said face panel is successively screened with each of said three screening masters to form a phosphordot triad screen on said panel.
12. The improvement in accordance with claim 11 in which said mask-frame component is installed within said face panel only after said panel has been screened through said three screening masters.
13. The improvement in accordance with claim 11 in which the screening of said face panel with any of said phosphors includes the step of removably supporting said panel in an exposure chamber in which the one of said screening masters associated with the phosphor being screened is permanently installed;
and in which said panel is referenced to said screening master in the manner in which said mask-frame component is referenced to its master during the exposure of said mask portion.
14. The improvement in accordance with claim 13 in which said screening master is derived from said bogey mask-frame through a process which incorporates correction factors in the pattern of said screen master which may be projected directly on said panel, without the imposition of a correcting lens, in the exposure of said panel.
15. In the manufacture of a shadow mask color tube, the improvements which includes the following steps:
forming a mask-frame having a mask portion of a material subject to attack by an etchant and characterized by the fact that the mask is a formed imperforate blank;
coating said mask with a sensitized resist;
supporting said mask-frame by an arrangement establishing at least six points of coupling between said mask-frame and a fixture with the geometric center of said mask disposed along a first reference axis;
similarly supporting a first master, representing the aperture pattern of a bogey mask-frame, by an arrangement establishing at least six points of coupling between said first master and said fixture with the geometric center of said first master on said first reference axis;
exposing said mask to actinic energy through said first master to create a latent image of an aperture pattern in said coating;
developing said latent image and then etching said mask to create said aperture pattern therein;
screening the face panel of said tube by:
a. coating the internal surface of the face panel with a sensitized resist;
b. supporting said panel by an arrangement establishing at least six points of coupling between said panel and another fixture so that the geometric center of said panel is disposed along a second reference axis;
c. similarly supporting a screening master, also represent ing the aperture pattern of said bogey mask-frame, by an arrangement establishing at least six points of coupling between said screening master and said other fixture with the geometric center of said screening master on said second reference axis, said second axis being equivalent to said first axis in that said first master and said screening master are both referenced to said bogey mask-frame; and
d. applying to said panel a phosphor pattern determined by exposing said panel to actinic energy through said screening master;
and finally installing said mask-frame in said panel. 7 16. The improvement in accordance with claim 15 in which both surfaces of said mask are coated with said resist;
a second master is supported as said first master but on the opposite side of said mask; both surfaces of said mask are exposed through said first and second masters, respectively, to create said latent image; and said panel is screened with green, blue and red emitting phosphors through repeating said steps (a) (d) three times but each time utilizing a screening master derived from said bogey mask frame and individual to an assigned one of said phosphors. 17. The improvement in accordance with claim 15 in which said mask-frame is stress relieved before being exposed to actinic energy.
Citas de patentes