Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
2001-04-09
2003-04-15
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C428S325000, C428S329000, C428S330000, C428S461000, C174S255000, C174S258000
Reexamination Certificate
active
06548152
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a circuit substrate whose thermal radiation property is improved by a mixture of resin and inorganic filler. In particular, it relates to a high thermal radiation printed wiring board made of resin (thermally conductive substrate) for mounting electronic power devices.
BACKGROUND OF THE INVENTION
Recently, as high performance and miniaturization of the electronic apparatus have been required, high density and high performance semiconductors have been sought. Consequently, circuit substrates for mounting thereof have also been required to be small and of high density. As a result, it is important to design circuit substrates taking the thermal radiation property into consideration. A well known technique for improving the thermal radiation property of circuit substrates, while using a printed circuit board made of glass-epoxy resin, is to use, a metal base substrate having a metal, for example, aluminum etc. and form a circuit pattern on one face or both faces of this metal substrate with an insulating layer interposed in between the circuit pattern and the metal substrate. Moreover, when higher thermal conductivity is required, the metal base substrate is made of a copper plate, which is directly bonded to a ceramic substrate made of, for example, alumina or aluminum nitride. For an application requiring relatively small electric power, a metal base substrate is generally used. In this case, however, in order to improve the thermal conduction, the insulating layer must be thin. Therefore, as for the substrate of thin insulating layer, break down voltage is low, and the influence by the noise, too, is big.
It is difficult for the metal base substrate and ceramic substrate to satisfy both performance and cost requirements. Recently, an injection molded thermally conductive module has been suggested, where a thermoplastic resin composition containing inorganic filler is integrated with the lead frame of an electrode. This injection molded thermally conductive module has excellent mechanical strength in comparion with a ceramic substrate. However, due to the high viscosity of the thermoplastic resin, it is difficult to injection mold such a module with a high filler content, and so the thermal radiation property of module is poor. In particular, at the time of melting the thermoplastic resin at high temperature and kneading with filler, if there is too much filler, the melting viscosity is rapidly increased in a point that not only kneading but also injection molding is made impossible. Moreover, the filler serves as an abrasives to abrade the metallic mold, and, thus, reduces the life of the mold. Consequently, the content of the filler is limited, so that only lower thermal conductivity can be obtained as compared with the thermal conductivity of the ceramic substrate.
SUMMARY OF THE INVENTION
The object of the present invention is to overcome the above mentioned problems and to provide a sheet for a thermally conductive substrate in which an inorganic filler can be filled in a resin at a high filler loading to form a thermally conductive module by a simple method, having (a) approximately the same coefficient of the thermal expansion in the plane direction of the substrate as that of a semiconductor, and (b) excellent thermal radiation property; a method for manufacturing the above mentioned sheet for a thermally conductive substrate; a thermally conductive substrate using the above mentioned sheet; and a method for manufacturing this thermally conductive substrate.
In order to attain the objects, the sheet for the thermally conductive substrate of the present invention is a sheet mixture comprising 70 to 95 weight parts of inorganic filler and 5 to 30 weight parts of resin composition comprising at least thermosetting resin, hardener and hardening accelerator. This sheet mixture has a good flexibility in the half hardened state or partially hardened state. (Hereinafter, “B stage” will be used for the half hardened state or partially hardened state.) This sheet mixture of the thermally conductive substrate can be molded and processed into a predetermined shape due to the flexibility of the sheet. On complete hardening of the resin composition, the substrate can be made rigid with excellent mechanical strength.
It is preferable in the sheet for the thermally conductive substrate of the present invention that the half hardened state or partially hardened state has a viscosity in the range of 10
2
to 10
5
(Pa·s). By such a preferred embodiment, excellent flexibility and processing property can be provided, so that the sheet can be molded and processed into the predetermined shape. More preferably, the half hardened state or partially hardened state has a viscosity in the range of 10
3
to 10
4
(Pa·s). The viscosity of the sheet herein is measured by the following method: the apparatus used for measuring the elasto-viscosity was a “cone and plate” type dynamic measurement apparatus, MR-500, the product of Rhelogy Co., Ltd.; the sheet was processed into the predetermined size and sandwiched between the cone and plate having a diameter of 17.97 mm and cone angle of 1.15 deg.; sinusoidal oscillation was given to the sample in the twisting direction; and the difference in the phases of torque which was generated by the sinusoidal oscillation was calculated. Thus, the viscosity was measured. In the evaluation of the elasto-viscosity of the sheet of the present invention, the sinusoidal oscillation was a sine wave with a frequency of 1 Hz, the strain was 0.1 deg., the load was 500 g and the temperature was 25° C.
It is preferable in the sheet for the thermally conductive substrate of the present invention that 0.1 to 2 weight parts of solvent having a boiling point of not less than 150° C. is further added to 100 weight parts of total weight of inorganic filler and thermosetting resin composition. By this preferred embodiment, excellent flexibility and processing property can be provided.
It is preferable in the sheet for the thermally conductive substrate of the present invention that the solvent having a boiling point of not less than 150° C. is at least one solvent selected from the group consisting of ethyl carbitol, butyl carbitol and butyl carbitol acetate. By this preferred embodiment, the processing of the sheet material is easy, flexibility can be provided to the thermosetting resin at room temperature, and the viscosity of the sheet material for molding and processing can easily be controlled.
It is preferable in the thermosetting resin composition in the sheet for the thermally conductive substrate of the present invention to comprise:
1) 0 to 45 weight parts of a first resin that is solid at room temperature,
2) 5 to 50 weight parts of a second resin that is liquid at room temperature,
3) 4.9 to 45 weight parts of the hardener, and
4) 0.1 to 5 weight parts of the hardening accelerator
when the thermosetting resin composition is 100 weight parts. By such a preferred embodiment, excellent flexibility and processing property can be provided.
It is preferable in the sheet for the thermally conductive substrate of the present invention that the main component of the thermosetting resin that is solid at room temperature is one or more components selected from the group consisting of bisphenol A epoxy resin, bisphenol F epoxy resin and liquid phenol resin. By this preferred embodiment, the “B stage” resin has a long shelf life and the hardened resin has excellent electrical insulating property and mechanical strength.
It is preferable in the sheet for the thermally conductive substrate of the present invention that the main component of the thermosetting resin composition is at least one resin selected from the group consisting of epoxy resin, phenol resin and cyanate resin.
It is preferable in the sheet for the thermally conductive substrate of the present invention that the thermosetting resin composition comprises brominated multifunctional epoxy resin as a main component, bisphenol A novolak resin as a hardener, and imidazole a
Handa Hiroyuki
Nakatani Seiichi
Jones Deborah
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
Stein Stephen
LandOfFree
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