Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
2000-08-22
2004-06-29
Gibson, Randy W. (Department: 2841)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S760000, C361S720000, C361S748000
Reexamination Certificate
active
06757176
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to circuit boards, and more particularly, to increasing circuit board reliability.
BACKGROUND OF THE INVENTION
Printed circuit boards, which are used in the manufacture of electrical, mechanical, electro-mechanical, and other kinds of products, provide a substrate for mounting a die on which integrated circuits, such as processors, memories, and amplifiers, are fabricated.
FIG. 1
shows a cross-sectional view of a prior art ball-grid array (BGA) package
100
which includes printed circuit board
103
coupled to board
105
by solder balls
107
, and die
109
coupled to printed circuit board
103
by adhesive
111
and molding compound
112
.
A longstanding and unsolved problem with printed circuit boards in general and with BGA package
100
in particular is that printed circuit board
100
may develop a crack, such as crack
113
. Crack
113
destroys the structural integrity of BGA package
100
. Once the structural integrity of BGA package
100
is destroyed, unforseen stresses may break or damage electronic connectors, such as electronic connectors
115
and
116
, and as a result, any product in which BGA package
100
is incorporated may malfunction.
One method of solving problems associated with printed circuit board cracking and the resulting electronic connection failures is to include a second printed circuit board in the design of an electronic system. The second circuit board is a redundant printed circuit board which mirrors the operation of the primary board, so a system failure occurs only when both the redundant printed circuit board and the primary board fail at the same time. Unfortunately, this solution is very expensive and is cost effective only in systems, such as trains, airplanes, or spacecraft, where the cost of failure is high. For systems in which the cost of failure is low, redundant circuit boards are seldom used.
For these and other reasons there is a need for the present invention.
SUMMARY OF THE INVENTION
The above mentioned problems with cracking in circuit boards and other problems are addressed by the present invention and will be understood by reading and studying the following specification. A circuit board is described that includes embedded fibers, which strengthen the board, and a surface layer having a certain thickness range that inhibits the formation of cracks in the circuit board.
The present invention provides, in one embodiment, a circuit board including a core layer and a surface layer. A number of fibers are embedded in the core layer. The surface layer has a thickness which is between about 10% and about 30% of the circuit board thickness. Embedding fibers in the core layer increases the strength of the circuit board. A surface layer thickness of between about 10% and about 30% of the circuit board thickness inhibits the formation of cracks in the circuit board, which improves the reliability of circuits mounted on the circuit board and systems in which the circuit board is embedded.
In an alternate embodiment, the present invention provides a method of fabricating a circuit board having a circuit board thickness. The method includes forming a core layer including a number of fibers, and forming a surface layer on the core layer. The surface layer has a surface layer thickness that is between about 10% and about 30% of the circuit board thickness and is free of fibers.
REFERENCES:
patent: 2695351 (1954-11-01), Beck
patent: 3617613 (1971-11-01), Benzinger et al.
patent: 4886699 (1989-12-01), Carroll et al.
patent: 6127728 (2000-10-01), Juneja et al.
Du Yong
Jiang Tongbi
Bui Hung
Gibson Randy W.
Micro)n Technology, Inc.
Schwegman Lundberg Woessner & Kluth P.A.
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