Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
2000-12-01
2003-05-20
Lam, Cathy (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C428S344000, C428S901000, C174S255000, C174S263000
Reexamination Certificate
active
06565954
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a circuit board in which layers are electrically connected using a conductor such as a conductive paste and to a method of manufacturing the same.
BACKGROUND OF THE INVENTION
Recently, the applicant has proposed a multilayer circuit board in which layers are electrically connected using a conductive paste (in Japanese Patent No. 2,601,128).
FIG. 8
shows a method of manufacturing the multilayer circuit board. As shown in FIG.
8
(
a
), release films
501
made of polyester or the like are laminated on both surfaces of a porous substrate
502
obtained by impregnating aromatic polyamide fibers with a thermosetting epoxy resin. As shown in FIG.
8
(
b
), through holes
503
are formed at predetermined positions in the porous substrate
502
by a laser processing method. Then, the through holes
503
are filled with a conductive paste
504
as shown in FIG.
8
(
c
). As a filling method, the porous substrate
502
with the through holes
503
is placed on a table of a screen printing machine and the conductive paste
504
is printed directly from the top of one of the release films
501
. In this case, the release film
501
at the printed side serves as a print mask and to prevent the surface of the porous substrate
502
from being polluted. Then, the release films
501
are peeled off from both the surfaces of the porous substrate
502
. As a next step, metal foils
505
such as copper foils are laminated on both the surfaces of the porous substrate
502
. In this state, it is heated and pressurized, thus bonding the porous substrate
502
and the metal foils
505
as shown in FIG.
8
(
d
). In this process, the porous substrate
502
is compressed to be made thin. Simultaneously, the conductive paste
504
within the through holes
503
also is compressed, and a binder constituent contained in the conductive paste
504
is forced out, thus strengthening the adhesion between conductive constituents and between the conductive constituents and the metal foils
505
. As a result, the conductive material contained in the conductive paste
504
becomes dense, and thus layers are electrically connected to each other. After that, a thermosetting resin that is a constituent of the porous substrate
502
and the conductive paste
504
are cured. Finally, as shown in FIG.
8
(
e
), the metal foils
505
are selectively etched in a predetermined pattern, thus completing a double-faced circuit board.
However, in the aforementioned configuration and manufacturing method, when the through holes
503
are formed to be minute, the initial connection resistance increases and greatly varies. Further, the connection resistance varies depending on reliability tests such as a temperature cycling test or a pressure cooker test, which has been a problem. The problem is caused by the aspect ratio, which is the ratio of the diameter of the through holes
503
and the thickness of the porous substrate
502
, approaches 1 when the through holes
503
are formed to be minute, and therefore the compressibility required for stabilizing the electric connection cannot be obtained.
In the process of peeling off the release films
501
, when the through holes are decreased in diameter, the influence of the release film cannot be ignored at the ends of the through holes. In peeling off the release films, the conductive paste
504
is removed by the release films, thus preventing the through holes from being filled with the conductive paste, which has been another problem.
SUMMARY OF THE INVENTION
Bearing the aforementioned problems in mind, the present invention aims to provide a circuit board that enables minute via holes to be obtained with high reliability using a conductive material such as a conductive paste and a method of manufacturing the same.
In order to solve the aforementioned problems, in a circuit board of the present invention, through holes formed in a thickness direction of an electrical insulating substrate are filled with a conductor, and wiring layers formed on both the surfaces of the electrical insulating substrate in a predetermined pattern are electrically connected by the conductor. The circuit board is characterized in that adhesive layers are formed on both the surfaces of the electrical insulating substrate and at least one wiring layer is embedded in one of the adhesive layers. In such a configuration, the conductor within the through holes is compressed sufficiently and thus minute via holes can be formed with high reliability. That is to say, since at least one wiring layer is embedded in one of the adhesive layers, the conductor within the through holes is compressed sufficiently. As a result, a conductive constituent of the conductor becomes dense, thus enabling via-hole connection with a low initial connection resistance and high reliability,
It is preferred to use a conductive paste as the conductor, since a resinous constituent contained in the conductive paste is forced out from the through holes when the conductive paste within the through holes is compressed and the conductive constituent contained in the conductive paste becomes dense, thus obtaining the via-hole connection with a low initial connection resistance and high reliability more easily.
When the through holes in the topmost layer are covered with a wiring layer, the conductor filling the through holes is not exposed at the surface. Consequently, it is effective to provide such through holes to the top layer of a substrate.
When the wiring layers are formed so that a part of the respective through holes is exposed and such wiring layers are used as inner layers, landless via holes in which via holes are compressed by a smaller wiring than the diameter of the via holes can be obtained. Thus, further minute wiring can be formed.
When at least the surface of each wiring layer facing the through holes is processed to be rough, the contact area between the wiring layer and the conductor increases, and the adhesion between the wiring layer and the adhesive layer also is increased. Therefore, the process is effective for further improving the reliability of minute via holes.
A first method of manufacturing a circuit board according to the present invention comprises: providing through holes in an electrical insulating substrate having adhesive layers formed on its both surfaces; filling the through holes with a conductive paste; superposing a supporting base, on which a wiring layer has been formed in a predetermined pattern, at least on one surface of the electrical insulating substrate; embedding the wiring layer in an adhesive layer by compressing the electrical insulating substrate, on which the supporting base has been superposed, by heating and pressurization; and removing the supporting base while leaving the wiring layer. The method enables a circuit board with via holes having high reliability in connection with a minute wiring layer to be provided by such an easy method that the patterned wiring layer is supported by the laminated supporting base that is removed after press.
A second method of manufacturing a circuit board according to the present invention comprises: laminating release films, each of which has an adhesive layer on its one surface, on both surfaces of an electrical insulating substrate so that each surface of the electrical insulating substrate comes into contact with the adhesive layer; providing through holes in the electrical insulating substrate having the release films; filling the through holes with a conductive paste; peeling off the release films while leaving the adhesive layers in the electrical insulating substrate; superposing a supporting base, on which a wiring layer has been formed in a predetermined pattern, at least on one surface of the electrical insulating substrate; embedding the wiring layer in the adhesive layer by compressing the electrical insulating substrate on which the supporting base has been superposed by heating and pressurization; and removing the supporting base while leaving the wiring layer. This met
Andou Daizou
Higashitani Hideki
Nakamura Tadashi
Sugawa Toshio
Tsukamoto Masahide
Lam Cathy
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
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