EP1837419A1

EP1837419A1 - Matrix holder

Info

Publication number: EP1837419A1
Application number: EP07104744A
Authority: EP
Inventors: Daniel Sundqvist
Original assignee: Swedish Electroforming Technology AB
Current assignee: Swedish Electroforming Technology AB
Priority date: 2006-03-24
Filing date: 2007-03-23
Publication date: 2007-09-26
Also published as: SE529882C2; SE0600672L

Abstract

Device (10) for holding a disc-shaped element (12b, 12c) in an electroplating bath, such as a matrix disc for manufacturing press matrices for optically-readable discs. The device comprises a sealed cavity (24) delimited between a flat base plate (26b, 26c) and a backing piece (16), which cavity can be connected to a vacuum source via a connector (42) in the backing piece (16) and which cavity is in communication with holes (28, 28a) arranged around the periphery and in the centre of the base plate that connect the said cavity (24) to the side of the disc element (12a-c) that is not to be plated. The connector (42) is arranged in such a way that when it is disconnected from the vacuum source, it maintains a requisite negative pressure for holding the disc element (12b, 12c) against the flat base plate (26b, 26c) during the plating process.

Description

BACKGROUND TO THE INVENTION

1. Technical field

The present invention relates to a device for holding a thin disc-shaped element, in particular a matrix disc for manufacturing press matrices for optically-readable discs, such as CD and DVD discs, in an electroplating bath, and relates more specifically to a device of the type described in the preamble to Claim 1. The invention also relates to methods for fixing a disc element in a holder, which disc element is to be plated on one side in an electroplating installation.

2. Background art

Various means are already known for holding a disc element, that is to be electroplated, against a flat base in a holder, in order to achieve a plating layer of even thickness over the whole of the surface of the disc element. For example, according to a previously known solution, the disc element is held by means of a permanent magnetic platen, with the disc element being "drawn" against the platen. A disadvantage of this solution is that particles can be attracted by the magnetic platen and can cause difficulties in cleaning the platen before the disc element is placed upon it. In addition, any particles that remain on the platen can cause serious irregularities in the resulting plating layer on the disc element, with the result that this has to be rejected.
Attempts have been made to hold the disc element against a base in the holder by means of a vacuum. With this solution, a negative pressure acts on the side of the disc element that is not to be plated, with this negative pressure being maintained during the plating process by the suction side in the holder being permanently connected to the vacuum source that generates the negative pressure, via a pipe system that is located in components that are submerged in the electrolyte bath during the plating process. This results in problems in the form of a risk of leakage, whereby the electrolyte fluid can penetrate into the system and become contaminated.
US 5 552 975 describes electroplating of rigid silicon substrate plates, in which these are drawn by means of a vacuum against a flat base, over a sealing ring that is sandwiched between them. In order for the silicon substrate to be able to be pressed flat against the base, a sealing ring must first be pressed down into a circular groove in the base, for which purpose concentric evacuation grooves are formed in the base that is subjected to the vacuum. If a thin disc element of such a type that is described in the present invention were to be placed on such a device, circular grooves would appear on the upper side of the disc element, which is not acceptable.

DISCLOSURE OF INVENTION

It is an object of the present invention to avoid these problems and to propose an arrangement in which the plating equipment has a vacuum source that does not need to work continuously and remain in constant communication with the suction side via a pipe system that is subject to leakage in order to maintain a requisite negative pressure in the holder during the whole of the plating process, and in which the plating equipment has a vacuum-applying configuration that does not cause deformation of the thin disc element that is to be electroplated. For this purpose, the device according to the invention is characterized by the characteristics that are described in Claim 1. Thus, an arrangement is proposed that makes it possible to hold the disc element to the base in the holder in a way that is gentle and does not cause deformation and, at the same time, makes possible a momentary "charging" of a cavity in the holder with a negative pressure that is sufficient to hold the disc element against the base in a gentle way, after which the cavity in the holder is sealed off and disconnected from the vacuum source before the plating process commences. By this means, no continuous connection of the vacuum source to the said cavity in the holder is required during the plating process and accordingly the use is also avoided of a pipe system that can be subject to leakage in the plating installation.
According to a preferred embodiment of the device according to the invention, the hub and the connector are designed to be able to be docked with an external fixture or docking station, during the insertion and fixing of a disc element that is to be plated and during removal of a disc element after it has been plated, in which external fixture or docking station the hub can position the device in such a way that the connector can be connected to a nipple in the fixture that is in communication with the vacuum source or can be connected to the atmosphere. By this means, the device can easily be transported between the fixture and the plating installation with the disc element fixed in the holder in a "negative pressure-charged" state, without the device being connected to the vacuum source. According to an alternative embodiment, the device can be designed to be permanently fixed to the cathode shaft even during the insertion of a disc element that is to be plated, and during removal of a disc element from the device after it has been plated, whereby the device does not need to be moved between an external fixture and the cathode shaft of the plating installation. In order to hold a disc element in the device, a suitable negative pressure can thereby be applied on one side of the disc element by a temporary connection to a vacuum source, when the cathode shaft is raised up out of the electrolyte bath in the plating installation.
Suitable embodiments of the devices according to the invention are defined in the subsidiary claims relating to the device.
Alternative methods according to the invention for carrying out this concept are defined in the subsequent independent Claims 8 and 9.
The invention is described in greater detail below with reference to the attached drawings.

Brief description of drawings

Figure 1 shows a cross-sectional view of a device according to the invention for holding a disc-shaped element that is to be plated in an electroplating installation, with the device being mounted in an external fixture, and
Figures 2 a-c show three exploded views in perspective of components in the device for carrying out different phases of the plating process.

Modes for carrying out the invention

In Figure 1, a device according to the invention for holding a disc element 12b; 12c (see also Figures 2b-c) that is to be electroplated, is designated in general by the reference numeral 10, in particular a matrix disc for manufacturing press matrices for optically-readable discs, such as CD and DVD discs. The device 10 comprises a sleeve-shaped hub 14, that is designed as a guide for fitting the device on a rotating cathode shaft in an electroplating installation (not shown). The hub 14 is connected to a backing piece 16, to which is attached a current-transmitting platen 18, that has a flat base surface 20 and an upward-projecting outer circular edge 22. A plurality of cut-outs 24 are made in the platen 18, that form cavities from which air can be evacuated, as will be described in greater detail below. The base surface 20 forms a contact surface for a flat base plate 26b and c, that supports the disc element 12b, c that is to be plated, and that can consist of titanium. The current-transmitting platen 18 has, in addition, a central part 27 provided with internal threads for screwing the holder device 10 onto a threaded, current-supplying nose piece (not shown) on the cathode shaft.
In Figures 1, 2b and 2c, the disc element consists of a father matrix disc and mother matrix disc 12b and 12c respectively, while the disc element 12a in Figure 2a is a so-called glass master disc with a photo resist with a metallized upper layer on a glass disc. The base plate 26b and c has a plurality of through holes 28 (Figures 1, 2b and 2c) distributed around the periphery and in the central area, that connect the cut-outs 24 to the back of the disc element 12a-c that is to be plated. The base plate 26a for the glass master in Figure 2a can have a single central hole 28a for receiving a central projection that is frequently found on the underside of the glass disc.
As shown best in Figure 2a, which shows the holder components for the first plating phase for production of a press, matrix, in which a so-called father matrix 12b (Figure 2b) is built up on the glass matrix 12a, a circular current-transmitting element 30 is arranged to come into contact with the circular edge 22 of the current-transmitting platen 18 and also, with outer periphery of the metallized layer on the glass master 12a. A holding ring 32 can be fixed on the backing piece 16 by means of a plurality of rotating spring-loaded clamps 34, so that an inward-projecting collar 36 on the ring 32 can press the circular current-transmitting element 30 against the metallized layer of the glass master 12a in order to give this a negative charge during the plating. The hub 12, the backing piece 16 and the holding ring 32 are all made of an electrically-insulating material.
Figure 2b shows the holder components for manufacturing a mother matrix 12c (Figure 2c) in a second plating phase, on top of the father matrix 12b obtained in the first plating phase. For this purpose, the base plate 26b is used, that has a peripheral groove 38 for housing a plating bead that normally arises during the formation of the father matrix 12b. Finally, Fig. 2c shows the holder components for manufacturing a press matrix (not shown) (Figure 2c) in a third plating phase, on top of the mother matrix 12c obtained in the second plating phase, in which a plate 26b similar to the base plate 26c is used. It should be noted that the normally very thin father and mother matrices 12b, 12c can be held against the base plate 26b, 26c in such a way that they are flat and not deformed, by means of a sealing ring 33 (Figure 1) on the holding ring 32 acting on the side of the matrix that faces away from the base plate. Accordingly, the matrix does not need firstly to press down and be deformed by a sealing ring located inside and close to the vacuum-application points 28 on the matrices 12b, 12c.
As shown in Figure 1, where the disc matrix holder 10 is inserted in a hole 39 in a fixture 40 located outside the plating installation by means of the hub 14 acting as a guide element, a device 42 is arranged in the backing piece 16 for connecting the cavity 24 to an external vacuum source (not shown) for generating a requisite negative pressure in the cavity 24 for holding the disc element 12a-c flat against the base plate 26a-c, which negative pressure communicates with the back side of the disc element 12a-c that is to be plated via through holes 28, 28a in the base plate 26a-c. The device 42 comprises a manual or automatic shutting-off element 44 or valve, for example a non-return valve, and, in the docking position, is connected to a nipple 46 that is in communication with the vacuum source via a connector 48 in the fixture 40. After the disc element 12a-c has been placed on the base plate 26a-c and the holding ring 32 has been tightened, the cavity 24 is connected to the vacuum source so that the disc element 12a-c is drawn into close contact with the flat base plate 26a-c by means of the suction effect. Thereafter, the cavity 24 is sealed by means of the shutting-off element 44 prior to, or (when a non-return valve is used) in conjunction with, the matrix holder 10 being lifted up out of the fixture 40 that serves as a docking station and is screwed on to the cathode shaft in the plating installation. During the actual plating process, the cavity 24 in the matrix holder 10 is thus not connected to the vacuum source. After each plating phase, the matrix holder 10 is removed from the cathode shaft and reinserted in the fixture 40, whereupon the cavity 24 is connected to the atmosphere by the shutting-off element 44 in the connector 42 being opened. The matrix holder 10 can be provided with a negative pressure indicator 50 that provides a visual indication that there is the requisite negative pressure in the cavity 24.
In an alternative embodiment of the device according to the invention, it is possible to omit the fixture 40 and instead to let the disc holder device 10 remain on the end of the cathode shaft while inserting and removing a disc element. The insertion and removal of the disc element is carried out when the holder 10 and the cathode shaft are raised up from their submerged position in the electrolyte bach in the plating installation. A temporary connection of the cavity 24 in the holder to the vacuum source for drawing the disc element against the flat base 26a-c can then be carried out using a pipe (not shown) that does not extend down into the bath or through components that are submerged in the bath during the plating process, after which the cavity 24 is sealed and the pipe is disconnected from the holder before the holder is lowered into the bath to commence the plating of the disc element. After completion of the plating process and after the holder 10 and the cathode shaft have been raised up, the cavity 24 that is subjected to the negative pressure can be connected to the atmosphere by opening a valve (not shown), after which the holding ring 32 can be removed and the disc element can be taken out.
According to the invention, a matrix holder 10 is thus proposed that does not need to be kept continuously connected to a vacuum source during the plating process in order to hold a disc element flat against a base, but instead is "charged" with a negative pressure and sealed in an external fixture and is disconnected from the vacuum source before it is mounted on the cathode shaft and lowered into the plating bath. Alternatively, with the exception of the holding ring 32, the holder 10 can remain on the cathode shaft in the raised up position during the disc replacing procedure.

Claims

Device for holding a disc-shaped element (12a-c) in an electroplating bath, in particular a matrix disc for manufacturing press matrices for optically-readable discs, such as CD and DVD discs, comprising:
a hub (14) that can be fitted over a rotating cathode shaft in an electroplating installation,

a backing piece (16) connected to the hub (14),

a holding ring (32), that is connected to a peripheral part of the backing piece (16) in such a way that it can be removed, for clamping a circular electrical contact element (30) against an outer peripheral part of the disc element (12a-c),

an element (18) for transmitting electrical current between the cathode shaft and the electrical contact element (30),

a fixing device (27) for securing the device on the cathode shaft,

a flat base plate (26a-c) for the disc element (12a-c), and

a sealed cavity (24), delimited between the base plate (26a-c) and the backing piece (16), that is connected to a vacuum source in order to hold the disc element (12a-c) against the base plate (26a-c) by means of a negative pressure during the process of plating one side of the disc element,
characterized in that the base plate (26a-c) has a plurality of through holes (28) distributed around an outer peripheral area and at least one through hole (28, 28a) in a central area of the plate, which holes (28, 28a) connect the said cavity (24) to the side of the disc element (12a-c) that is not to be plated, and in that a connector (42) is integrated into the device (10), that communicates with the said cavity (24) and is able to be temporarily connected to the vacuum source in order to generate a required negative pressure in the cavity, with the connector (42) being arranged to be disconnected from the vacuum source prior to the commencement of the plating process when the cavity (24) is sealed off in order to maintain a requisite negative pressure in the cavity for holding the disc element (12a-c) against the base plate (26a-c) during the plating process.
Device according to Claim 1, characterized in that a plurality of through holes (28) are distributed around the central area of the plate.
Device according to Claim 1 or 2, characterized in that the hub (14) and the connector (42) are designed in such a way that, during insertion of a disc element that is to be plated and during removal of a disc element after it has been plated, they can be docked with an external fixture (40), in which the hub (14) can position the device in such a way that the connector (42) can, at the same time, be connected to a nipple (46) in the fixture (40) that is in communication with the vacuum source.
Device according to Claim 1 or 2, characterized in that it is designed to be permanently secured to the cathode shaft, even during insertion of a disc element that is to be plated and during removal of a disc element from the device after it has been plated.
Device according to any one of Claims 1-4, characterized in that the connector (42) is fixed to the backing piece (16).
Device according to any one of Claims 1-5, characterized in that the connector (42) comprises a non-return valve (44).
Device according to any one of Claims 1-6, characterized in that it is provided with a visual negative pressure indicator (50).
Method for fixing a disc element in a holder, which disc element is to be plated on one side in an electroplating installation, characterized in that the holder (10) is placed in a fixture (40), in that a cavity (24) in the holder is connected to a vacuum source in order to draw the disc element (12a-c) against a flat base (26a-c) in the holder at points around its outer periphery and at its central part, by the application of a required negative pressure on the other side of the disc element via the said cavity (24) in the holder, and in that the cavity is disconnected from the vacuum source, while the cavity is sealed off in order to maintain the requisite negative pressure in the holder to hold the disc in the holder under transportation of the holder between the fixture (40) and the plating installation and during the plating process therein.
Method for fixing a disc element in a holder, which disc element is to be plated on one side in an electroplating installation, in which, when the holder (10) is mounted on a cathode shaft, a cavity (24) in the holder is connected to a vacuum source in order to draw the disc element (12a-c) against a flat base (26a-c) in the holder by the application of a required negative pressure on the other side of the disc element via the said cavity (24) in the holder, characterized in that the disc element (12a-c) is pressed against the flat base (26a-c) at points around its outer periphery and at its central part, and in that, prior to the plating process commencing, the cavity (24) is disconnected from the vacuum source, while the cavity is sealed off in order to maintain the requisite negative pressure in the holder to hold the disc in the holder during the plating process.