CA1193370A

CA1193370A - Interconnected printed circuit boards and method of connecting circuit boards

Info

Publication number: CA1193370A
Application number: CA000431299A
Authority: CA
Inventors: Hirofumi Matsumoto
Original assignee: Nippon Mektron KK
Current assignee: Nippon Mektron KK
Priority date: 1982-06-30
Filing date: 1983-06-28
Publication date: 1985-09-10
Also published as: DE3323469A1; US4550357A; GB2123224B; JPS594096A; GB2123224A; GB8317809D0

Abstract

INTERCONNECTED PRINTED CIRCUIT BOARDS AND
METHOD OF CONNECTING CIRCUIT BOARDS

Abstract of the Invention:
Interconnected printed circuit boards and a method of connecting different types of printed circuit boards is presented. The method is particularly well suited for connecting the circuit patterns of a flexible printed circuit board to the corresponding circuit patterns of a hard printed circuit board and is easily accomplished by the novel utilization of an electroconductive adhesive. The adhesive connection of the present invention also provides improved ease of separability of the connected circuit boards.

Description

INTERCONNECTED PRINI'ED CIRCUIT BOARDS AND
METHOD OF CONNECTING CIRCUIT BOARDS

Background of the Invention:
This invention relates to the structure of interconnected printed circuit boards of different kincls, and to a method of connecting different kinds of printed circuit boards. More particularly, this invention relates to a new and improved structure and method of connecting the circuit patterns of a flexible printed circuit board to the corresponding circuit patterns of a hard or rigid printed circuit board utilizing an electroconductive adhesive.
An enormous number of electronic devices require the concurrent u~e of both flexible and rigid or hard printed circult boards (pcb). Often these flexible and hard printed circui~ boards must be connected to each other within an electronic instrument~ Various methods have been proposed to effect a connection of this type such as soldering. Unfortuna~ely, all of the prior art connecting methods require highly skilled and time consuming t~chniques. Additionally, specially designed reinforcement structures for use in increasing -the reliabi]ity of the connection between the two patterns are often needed. As a consequence, many problems have arisen in utilizing the above discussecl methvds including high labor and material costs. A further problem is that ~he pfeviously used conrlecting methods are relatively permanent. Thus, if ~he connected printed circuit boards have to be separated, this separation proved to be troublesome and costly if it can be effected at all without destroyirlg one or both boards.

Summary of the Invention:
The above discussed and o~her problems of the prior art are overcome or alleviated by the structure and method of connecting printed circuit boards of the present invention. In accordance with the present inventiorl, an improved structure and method of connecting the circuit patterns of a flexible printe~ circuit board to the corresponding circuit patterns of a hard printed circuit board is achieved by use of an electroconductive adhesive.
The novel use of an electroconductive adhesive to connect different kinds of printed circuit boards provides a far more simplified connection structure and method tharl previously found in the prior art.
This simplified method results in lower production cost due to decreased material and labor cost as well as providing for ease of separation of the connected boards should any problem arise subsequent to the initial connection.
The above discussed and other advantages of the present invention will be apparent to and understood by those slcilled in the art from the following detailed description and drawings.

Brief Description of the Drawings:
Referring now to ~he drawings, wherein like elements are numbered alike in the several FI5URES:

3~

FIGI~RE l is a perspective view of a connection between a flexible printed circuit board and a hard printed circuit board i.n accordance with the present invention~
FIGURE 2 i,s arl enlarged cross-sectlonal elevation view of one interconnection of the circuit boards of FIGURE l~
FIGURE 3 is a planar view of a flexible printed circuit board in accordance with another embodiment of the present invention.
FIGURE 4 is an enlarged corss-sectional view of the circuit board of FIGURE 3 connected to a hard printed circuit board in accordance with a second embodiment of the method of the present invention.
FIGURE 5 is a cross-sectional elevation view of a connectiont similar to FIGURE 4, incorporating a reinforcement~

Description of the Preferred Embodiment:
Referring jointly to FIGURES l and 2, a connection made in accordarlce with a first embodiment of the present invention is shown. A flexible printed circuit board, shown generally at l, i,s comprised of an ,insulating base material 2 with a printed circuit pattern 3 thereon. A rigid or hard circuit board, shown generally at 6, is comprised of an insulating base material 7 with a circul-t pattern 8 thereon. The circuit patterns are adhesively/
mechanically and electrically interconnected by an electroconducti.ve adhesive 4, as best seen in FIGURE

2. In this embodiment the circuit elements 3 ex~end beyond the insulating base material 2, and the adhesive is initially applied to the underside of the elements 3.

3~

-4-In order to connect the circuit patterns 8 on the hardboard 6 to the respective and corresponding circuit patterns 3 on the flexible circuit board 1 electroconductlve adhesive 4 is applied to that portion of one or both circuii patterns to be connected. Next t a visual alignment of the correspondir~g patterns is made and finally the clrcuit patterns 3 and 3 are physically brought together and pressed so as to physically join and electrically connect the circuit patterns of the two different printed circuit boards to each other.
The novel structure and connecting method of the present invention provi.des a simple and inexpensive approach to connecting flexible circuit boards to hardboards which has heretofore been accomplished only by sophisticated and/or technical procedures.
Furthermore, unlike the prior connection techniques, with proper selecti.on oE adhesive material, the present invention allows for rel.atively easy removal of the adhesi.vely connected circuit boards by variou~
means of disengagement well known to those skilled in the art.
Referring now to FIGURES 3 and 4, a second embodiment of the present invention is shown wherein the end portion of the insulating base material 11 of flexible printed circuit board 10 is shaped like the teeth of a comb. The circuit patterns 12 which are attached to the base 11 extend out to the end of each particular tooth llA at the end of the base 1.1. An electroconductive adhesive 13 is applied to both the top surface of the ends of the circuit pattern 12 and to the bottom base material surface of each tooth llA
of the base 11D The tooth structure of the base 11 of FIGU~E 3 is provided in order to prevent the adhesive 13 from short~circu.iting adjoining circuit patterns 12.

7~D

After application of the adhesive 13 to the base teeth llA anci circuit patterns 12 3S described a~ove, the teeth :llA are bent back upon themselves r as sho~n in FIGURE 4, so ~hat the adhesive applied to the bottom surface of the teeth llA overlap and form a single integratecl or overlapping structure. A hard circuit board 14 having an insulating base material 15 wlth circult patterns 1~ thereon can then be adhes:ively connected to the flexible circuit board 10. As in the previous example shown in FIGURE 1 and 2, the respective circuit patterns 12 and 16 must be c~rresponding patterns. The conrlection is accomplished by visually matching up the respective circuit patterns 12 and 16 and su~sequerltly pressing the patterns 12 and the patterns 16 into physical and electrical contact through the electroconductive adhesive 13.
As previously noted in discussing the structure and methods of FIGURES 1 through 4, the present invention provides a structure and method of connection having low production cost, also being characteri~ed by ease of separation if a problem arises in one of the connected circuit boards.
The method of the present invention permits the connection between the respective, corresponding patterns to be relnforced by application of a nonelectroconductive adhesive tape over the adhesively connected patterns. This added reinforcement results in increased durability of the connection against vibration and other fatigue factor 5 .
Finally, lf a particular connectiorl between different circuit boards is of the type in which it is very unlikely that a subsequent separation will be needed, then a rnore permanent connection may be utilizeci in conjunction with the present invention as shown in FIGURE 5. In FIGURE 5, a connection accordirlg to FIGURE 4 has beem subsequently reinforced with solder 25. As shown, the circuit pattern 20 applied to insulatiny base material 19 of flexible circuit board 18 is adhesively conrlected by electroconduc-tive adhesive 24 to the circuit pattern 23 on base ma~erial 22 of hardboard 21 I~hus! the solder 25 acts to cômpletely and more permanently connect the correspondirlg pa~terns 20 and 23.
In accordance with the structure and method of the present invention9 the circuit patterns of flexihle and hard circuit boards can be simply and easily connected at low cost and little labor using an electroconductive adhesive~ These adhesively connected patterns are then easily separable ~fter the connection is obtained thereby providing an improved efficiency during inspections, part exchanges and repairs~
While preferred embodiments have been shvwn and described, various modifications and substitutions may be made thereto witho~t departiny from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustrations and not limitation.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

CLAIM 1. A method of connecting printed circuit boards including the steps of:
applying electroconductive adhesive to the ends of a first circuit pattern, said first circuit pattern being located on a first insulating base material, said first circuit pattern and first base material defining a first printed circuit board;
aligning the ends of said first circuit pattern with corresponding ends of a second circuit pattern said second circuit pattern being located on a second insulating base material, said second circut pattern and said second base material defining a second printed circuit board;
said first and second base materials being different materials; and bringing said corresponding ends of said first and second circuit patterns together under pressure to form physical and electrical connections.
CLAIM 2. The method of claim 1 including:
applying electroconductive adhesive to the ends of said second circuit pattern.
CLAIM 3. The method of claim 1 wherein:
said first printed circuit board is a flexible printed circuit board; and said second printed circuit board is a hard printed circuit board.
CLAIM 4. The method of claim 1 wherein:
said ends of said first circuit pattern extend outward from said first base material.
CLAIM 5. The method of claim 4 wherein:
said first base material has a tooth shape which corresponds to said outwardly extended ends of said first circuit pattern.
CLAIM 6. The method of claim 5 including:
bending each of said teeth downwardly to form a single overlapping structure.
CLAIM 7. The method of claim 6 including:
bending each of said teeth downwardly to form a single overlapping structure.
CLAIM 8. The method of claim 1 including:
applying electroconductive adhesive to part of said first circuit pattern and to part of said first base material; and bending said parts back upon themselves with the part of said first circuit pattern on the exterior side of the bend.
CLAIM 9. An interconnected circuit board array including:
a first circuit board having a first base material and a first circuit pattern of conductive elements thereon;
a second circuit board having a second base material and a second circuit pattern of conductive elements thereon corresponding to said first circuit pattern;
one of said base material being a flexible material defining its circuit board as a flexible circuit board and the other of said base materials being a hard material defining its circuit board as a hard circuit board; and electroconductive adhesive between said first and second circuit patterns forming a physical and electrical connection therebetween.
CLAIM 10. The array of claim 9 wherein:
said ends of said first circuit pattern extend outward from said first base material.
CLAIM 11. The array of claim 9 wherein:
said first base material has a tooth shape which corresponds to said outwardly extended ends of said first circuit pattern.
CLAIM 12. The array of claim 9 wherein:
said teeth are bent backward upon themselves, with the conductive elements on the outer side of the bend.