Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
1999-07-16
2001-11-20
Gaffin, Jeffrey (Department: 2841)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S258000, C174S260000, C174S256000, C361S751000, C361S760000, C257S713000, C257S669000
Reexamination Certificate
active
06320136
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application claims the priority of Application No. H11-15043, filed Jan. 25, 1999 in Japan, the subject matter of which is incorporated herein by reference.
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a layered printed-circuitboard, which is provided with a characteristic of high resistance to heat variation.
BACKGROUND OF THE INVENTION
In general, a printed circuit board is a flat board whose front contains slots for integrated circuit chips and connections for a variety of electronic components, and whose back is printed with electrically conductive pathways between the components.
A semiconductor apparatus is fabricated by mounting semiconductor integrated circuits onto a printed circuit board. Such a semiconductor apparatus hereinafter is called a “module”. In recent years, multi-layered structural type modules have been used to improve integration rate and high-frequency characteristics.
A conventional semiconductor apparatus (module) includes a semiconductor chip; leads connected at one end to the semiconductor chip; metal wires connected between the semiconductor chip and the leads; and a seal material (package). The seal material (package) may be made of epoxy resin or silicon resin to protect the semiconductor chip.
The module also includes a layered printed-circuit-board and pads, formed on the layered printed-circuit-board. The pads are electrically connected to the leads through conductive material paste (conductive adhesive), such as solder or silver paste.
Usually, the package has a thermal expansion coefficient of around 7×10
−6
/° C., while the layered printed-circuit-board has a thermal expansion coefficient of around 15×10
−6
/°C. It means that there is a lot of difference in thermal expansion coefficient between the package and the layered printed-circuit-board.
In fabrication process of a module (semiconductor device module), a temperature cycling test is carried out. According to such a temperature cycling test, the temperature atmosphere of the module is changed with a predetermined cycle. According to the conventional module, in the temperature cycling test, mechanical stress is concentrated at the conductive material paste, because of the difference of thermal expansion coefficient between the package and the layered printed-circuit-board. As a result, a crack may be made in the conductive material paste. Such a crack results in a disconnection, and therefore the module becomes inoperative.
For solving the above problems in a temperature cycling test, a printed circuit board having a low thermal-expansion-coefficient can be used. If such a printed circuit board is used, the costs for the module is increased.
OBJECTS OF THE INVENTION
Accordingly, an object of the present invention is to provide a layered printed-circuit-board having a high resistance to heat variation.
Another object of the present invention is to provide a semiconductor circuit module including a layered printed-circuit-board having a high resistance to heat variation.
Additional objects, advantages and novel features of the present invention will be set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, a printed circuit board, on which an electronic component with leads is mounted, includes a first conductive layer; an insulating layer formed on the first conductive layer; a second conductive layer formed on the insulating layer; and a buffer region. The second conductive layer is provided with pads to be connected to the leads of the electronic component. The buffer region has a thermal expansion coefficient lower than the first conductive layer and is arranged between the first conductive layer and the insulating layer to ease thermal expansion of the first conductive layer.
According to a second aspect of the present invention, a semiconductor circuit module includes a semiconductor package which contains a semiconductor chip therein and is provided with leads; and the layered printed-circuit-board described above. The semiconductor package is mounted on the layered printed-circuit-board, so that the leads of the semiconductor package are electrically connected thereto.
In the present invention, the first conductive layer may be made of copper. The buffer region may be located at an area corresponding to the pads of the second conductive layer. The buffer region may be a blank region, in which no conductive pattern is formed. The buffer region may be filled with a buffer material, such as silicon rubber.
The buffer region may be a buffer layer formed throughout on the first conductive layer. The buffer layer may be made of silicon rubber.
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Gaffin Jeffrey
OKI Electric Industry Co., Ltd.
Patel I B
Wenderoth , Lind & Ponack, L.L.P.
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