Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1997-04-11
2001-06-12
O'Neill, Michael (Department: 3713)
Metal working
Method of mechanical manufacture
Electrical device making
C029S825000, C029S829000, C029S844000, C029S847000, C156S051000, C156S052000, C156S053000
Reexamination Certificate
active
06243946
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an interlayer connection structure between conductive circuit layers disposed at one and the other surface sides of a circuit board.
2. Brief Description of the Related Art
Recently, electronic instruments have developed remarkably and electronic instruments of high degree of precision have been used in various fields. With the progress of this development, circuit boards to be used in such electronic instruments are required to have a high performance and a high efficiency. At the same time, such electronic instruments are required to be inexpensive.
As a circuit board, a rigid multilayer circuit board, flexible multilayer circuit board and a rigid/flexible multilayer circuit board as a combination thereof are mostly used. In such a multilayer circuit board, an interlayer connection is required. In order words, conductive circuits of the multilayer circuit board are required to be electrically connected together at predetermined spots.
FIG. 1
shows a process for an interlayer connection by a through-hole plating method which is most generally practiced. According to this method, as shown in
FIG. 1A
, a double face copper clad lamination substrate composed by joining copper foils
1
,
2
to opposite surfaces of an insulative sheet
3
is formed. Then, as shown in
FIG. 1B
, a part of this double face clad lamination substrate corresponding to a conductive circuit is drilled, for example, to form a hole therein. Thereafter, as shown in
FIG. 1C
, a copper plating
5
is applied to an inner wall surface of a drilled hole
5
. At this time, the copper plating
5
is applied also to the surfaces of the copper foils,
1
,
2
on the opposite surfaces of the insulative sheet
3
. Then, as shown in FIG. ID, a pattern is formed on each copper foil
1
,
2
by an ordinary photoetching process, so that conductive circuit layers
1
′,
2
′ are formed. This example is a method for manufacturing a double face circuit board The same is likewise applicable to a multilayer circuit board which is subjected to the drilling process and the copper plating process in which the above-mentioned drilling and copper plating processes are employed.
In such prior art devices as mentioned above, several thousands of holes free from burrs must be formed in the conductive circuit. Moreover, in some cases, a surface processing (smearing processing) must be performed with respect to the surface of the wall of each hole.
That is, because a large number of processing steps are required for the interlayer connection, those steps result in major factors for increasing costs. Moreover, because there is a provision of holes formed in the surface of the board, electrical parts can not be mounted thereon. This makes it difficult to mount such electrical parts in high density.
The present invention has been accomplished in view of the above-mentioned problems inherent in the prior art devices.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide an interlayer connection structure in a circuit board in which an interlayer connection can be made in a simple manner.
Another object of the present invention is to provide an interlayer connection structure in a circuit board which can be reduced in manufacturing cost.
A further object of the present invention is to provide an interlayer connection structure in a circuit board which can effectively fulfill the requirement for designing circuit pattern in high density.
A still further object of the present invention is to provide an interlayer connection structure in a circuit board in which electronic parts can be mounted in high density.
In order to achieve the above objects, there is essentially provided an interlayer connection structure in a circuit board characterized in that a local part of a conductive circuit layer disposed at one surface side of an insulative sheet is bent inwardly of the insulative sheet so that an apex of a projectingly bent portion is formed, and the apex of the projectingly bent portion is abutted with another conductive circuit layer disposed at the other surface side of the insulative sheet so that an interlayer connection is established therebetween.
From another aspect of the present invention, there is also provided an interlayer connection structure in a circuit board characterized in that a local part of a conductive circuit layer disposed at one surface side of an insulative sheet and a local part of another conductive circuit layer disposed at the other surface side are bent inwardly of the insulative sheet so that an apex of each projectingly bent portion is formed, and the apexes of the projectingly bent portions are abutted with each other so that an interlayer connection is established therebetween.
It is preferred that the apexes of the projectingly bent portions are fused together by means of a conductive paste or a metal having a low melting point, which is interposed between interfaces of the abutting portions.
The insulative sheet may be a thermoplastic resin, and the projectingly bent portion may be projected inside while the insulative sheet is locally plasticized.
The thermoplastic resin may be a liquid crystal polymer.
The above and other objects and attendant advantages of the present invention will become manifest to those skilled in the art from a reading of the following description and claims in conjunction with the accompanying drawings which constitute part of this specification.
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Suzuki Etsuji
Yamazaki Hidehisa
Yonezawa Akira
Nguyen Binh-An
O'Neill Michael
Wenderoth , Lind & Ponack, L.L.P.
Yamaichi Electronics Co. Ltd.
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