Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
2000-10-12
2002-12-10
Lam, Cathy (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C428S901000, C174S255000
Reexamination Certificate
active
06492008
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a multilayer printed wiring board and, more particularly to a multilayer printed wiring board suppressing warping caused by temperature change and an electronic equipment using the multilayer printed wiring board.
A printed wiring board is composed of a composite insulation material formed of fiber woven cloth impregnated with a resin and a circuit pattern of electric conductor formed on the surface of the composite insulation material, and a multilayer printed wiring board is formed by laminating the printed wiring boards in multilayer. E-glass fiber of electric use is generally used for the cloth used for the composite insulation material. Quartz glass fiber or aromatic polyamide fiber is sometimes used for the cloth. A copper film or a copper film having nickel plate on the surface is used for the electric conductor.
The thermal expansion coefficient of the copper film of the electric conductor material is approximately 17×10
−6
(1/°C.), and the thermal expansion coefficient of the composite insulation material made of E-glass fiber and an epoxy group resin is approximately 11×10
−6
(1/°C.). The thermal expansion coefficients of the electric conductor material and the composite insulation material are different from each other as described above. Therefore, the thermal expansion coefficient in the surface direction of the multilayer printed wiring board made of the electric conductor material and the composite insulation material depends on a thickness of the electric conductor forming the circuit pattern and a ratio of the circuit pattern formed of the electric conductor covering the surface of the composite insulation material, that is, a covering ratio.
In general, the circuit patterns formed in the multilayer printed wiring board are not symmetric with respect to the central plane in the thickness direction of the multilayer printed wiring board. In the case where the thicknesses and the covering ratios on the both sides of the electric conductor layers composing the multilayer printed wiring board are asymmetric with respect to the central plane as described above, the thermal expansion coefficients in the surface direction of the electric conductor layers become asymmetric.
Therefore, when the multilayer printed wiring board receives a thermal effect during manufacturing, a warp occurs in the board. If there is a warp in the multilayer printed wiring board, trouble occurs in connecting electronic parts when the electric parts are soldered on the surface of the multilayer printed wiring board because displacement occurs in positional relationship between a junction formed in the part and a junction formed in the multilayer printed wiring board.
In general, the multilayer printed wiring board is formed by that a plurality of printed wiring boards having a circuit pattern on the surface of the composite insulation material are bonded using prepreg by heating at about 170° C. Therein, in a case where the thicknesses and the covering ratios on the both sides of the electric conductor layers composing the formed multilayer printed wiring board are asymmetric with respect to the central plane as described above, a warping deformation occurs in the multilayer printed wiring board due to the difference of the thermal expansion coefficients when the multilayer printed wiring board is cooled down to room temperature (20° C.) after being heated and bonded at 170° C. When electronic parts are soldered on the multilayer printed wiring board, the multilayer printed wiring board is heated up to 170° C. or higher. In that time, a warping deformation also occurs in the multilayer printed wiring board due to the difference of the thermal expansion coefficients.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a multilayer printed wiring board and an electronic circuit which are small in the warping deformation due to temperature change even if the thicknesses and the covering ratios on the both sides of the electric conductor layer are asymmetric with respect to the central plane. the present invention is characterized by a multilayer printed wiring board formed by laminating composite insulation layers and laminated bodies, the composite insulation layer being made of a cloth and a resin impregnated into the cloth, said laminated body being composed of electric conductor layers formed on a surface of the composite insulation layer, wherein a thermal expansion coefficient of the composite insulation layer having a higher covering ratio by the electric conductor layer is set to a value smaller than a thermal expansion coefficient of the composite insulation layer having a lower covering ratio by the electric conductor layer.
Further, a multilayer printed wiring board in accordance with the present invention is characterized by that a thermal expansion coefficient of the cloth in the composite insulation layer having a higher covering ratio by the electric conductor layer is a value larger than a thermal expansion coefficient of said the in the composite insulation layer having a lower covering ratio by the electric conductor layer.
Further, a multilayer printed wiring board in accordance with the present invention is characterized by that the electric conductor layer comprises an electric power supply layer and a signal layer, and a thermal expansion coefficient of at least one of the composite insulator layers in contact with the electric power supply layer is set to a value smaller than a thermal expansion coefficient of the composite insulator layer in contact with the signal layer.
Further, a multilayer printed wiring board in accordance with the present invention is characterized by that the electric conductor layer comprises an electric power supply layer having a covering ratio of 60 to 80%, preferably 65 to 75% and a signal layer having a covering ratio of 10 to 20%, and a thermal expansion coefficient of at least one of the composite insulator layers in contact with the electric power supply layer is within a range of 8.5 to 9.5×10
−6
/°C., and a thermal expansion coefficient of the composite insulator layer in contact with the signal layer is within a range of 10 to 12×10
−6
/°C., preferably 10.5 to 11.5×10
−6
/°C.
Further, a multilayer printed wiring board in accordance with the present invention is characterized by that the electric conductor layer comprises an electric power supply layer and a signal layer, and the cloth of at least one of the composite insulator layers in contact with the electric power supply layer is made of quartz glass, and the cloth of the composite insulator layer in contact with the signal layer is made of a glass having a thermal expansion coefficient larger than a thermal expansion coefficient of the quartz glass.
As the circuit layers in accordance with the present invention, 4 to 50 layers can be formed.
Further, the present invention is characterized by an electronic equipment comprising electronic parts mounted on a circuit connecting pad formed on a surface of the multilayer printed wiring board described above.
Particularly, in the present invention, a highly productive wiring board can be obtained by that the composite insulator layer is formed by using the same amount of cloth contained in each composite insulator layer and using a material having different thermal expansion coefficient for the cloth. Therefore, it is preferable that quartz glass is used for the composite insulator layer having a larger covering ratio and a glass having a thermal expansion coefficient larger than a thermal expansion coefficient of the quartz glass is used for the composite insulator layer having a smaller covering ratio.
An example of a manufacturing method of the multilayer printed wiring board in accordance with the present invention is as follows.
A sheet of inner prepreg is obtained by impregnating and applying an impregnating epoxy vanish into and to a sheet-shaped base material and by drying it at tempera
Amagi Shigeo
Murakawa Satoshi
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