Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
1998-10-06
2001-05-29
Lam, Cathy F. (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C174S073100, C174S255000
Reexamination Certificate
active
06238777
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a printed-circuit board.
2. Description of the Related Art
A structure for dispersing stress generated in a printed-circuit board has been disclosed, for example, in the Japanese Unexamined Patent Publication No. 6-85005. According to this structure, a resin having a coefficient of linear thermal expansion smaller than that of the printed-circuit board is filled in a gap between the printed-circuit board and a semiconductor chip mounted on the board, and expansion and contraction of the printed-circuit board is suppressed in accordance with a difference between a linear thermal expansion of the filled resin and of the printed-circuit board so that a thermal stress generated in the printed-circuit board is dispersed.
There are some problems, however, in the above structure as explained briefly below. That is, according to this structure, an effect of stress dispersion in the printed-circuit board is influenced by a state of the resin filled to the gap and a dispersion of the composition of the filled resin. As a result, cracks occur in a boundary portion between a conductive pattern (e.g., an electrode pattern) and an insulated layer. The above problem will be explained in detail with reference to
FIG. 4
below.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a printed-circuit board which can suppress an occurrence of cracks in the boundary portion under the conductive pattern in the insulating layer when the heat is applied to the printed-circuit board.
In accordance with the present invention, there is provided a printed-circuit board including: a plurality of insulating layers; a plurality of conductive patterns formed in each insulating layer; and a plurality of substantially closed and curved patterns each formed around the conductive patterns in each insulating layer, and each formed by a material having a coefficient of linear thermal expansion smaller than that of the insulating layer.
According to the above structure, when the heat is applied to the printed-circuit board, the thermal stress occurs in the boundary portion under the conductive pattern in the insulating layer due to the difference between the coefficients of linear thermal expansion. In the present invention, however, the thermal stress is dispersed in an area surrounded by the closed and curved pattern, based on an effect of a hydrostatic pressure due to the closed and curved pattern, so that the thermal stress becomes weak in the boundary portion. As a result, it is possible to prevent cracks in the boundary portion.
In a preferred embodiment, each closed and curved pattern is formed of the same material as that of each of the conductive patterns.
In another preferred embodiment, each closed and curved pattern is made of copper.
In still another preferred embodiment, when the coefficient of linear thermal expansion of each insulating layer is &agr;
1
, when the coefficient of linear thermal expansion of each conductive layer is &agr;
2
, and when the coefficient of linear thermal expansion of each closed and curved pattern is &agr;
3
, the following condition, i.e., &agr;
1
>&agr;
2
≧&agr;
3
, is satisfied.
REFERENCES:
patent: 3142610 (1964-07-01), Lowe
patent: 5165984 (1992-11-01), Schoenthaler
patent: 5354599 (1994-10-01), McClanahan et al.
patent: 5700549 (1997-12-01), Garant et al.
patent: 559151341 (1980-11-01), None
patent: 5-82929 (1993-04-01), None
patent: 06085005 (1994-03-01), None
Kondo Koji
Oda Ryuji
Denso Corporation
Lam Cathy F.
Pillsbury Madison & Sutro LLP
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