Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
2000-10-23
2003-05-27
Talbott, David L. (Department: 2827)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C361S813000
Reexamination Certificate
active
06570099
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a circuit board on which various types of semiconductor devices and electronic components are mounted. In particular, the present invention relates to a thermal conductive substrate that is constituted by a resin substrate with high heat-radiating characteristics suitable for a power electronics field, and to a method for manufacturing the same.
BACKGROUND OF THE INVENTION
Accompanying the request for high performance and miniaturization of electronic equipment in recent years, there has been a demand for high-density packaging of electronic components and semiconductors. Accordingly, it is more likely that heat generated from different components is concentrated, leading to a higher temperature. In order to release this heat from the equipment quickly, it is important to design the equipment considering heat radiation. Thus, circuit boards also need to have high heat-radiating characteristics.
In order to improve the heat-radiating characteristics of the circuit boards, there are conventional printed boards using glass-epoxy resin. On the other hand, metal-based circuit boards also have been suggested. The metal-based circuit board is produced in such a manner that circuit patterns are formed on one side or both sides of a metal plate such as copper or aluminum via an insulator layer. When still higher heat-radiating characteristics are required, a substrate that is formed by directly joining a copper plate to a ceramic substrate such as alumina or aluminum nitride is used. Generally, the metal-based circuit boards are used for applications requiring relatively small electric power. However, the insulator layer has to be thin to achieve high thermal conductivity. This causes problems in that the metal-base circuit boards are susceptible to noise between the insulator layer and the metal base and have low withstand voltage.
For the purpose of solving these problems, a substrate formed in the following manner has been suggested recently. That is, a composition produced by filling an inorganic filler having an excellent thermal conductivity in a thermosetting resin is integrated with a lead frame serving as an electrode, so as to obtain the substrate. The substrate using such composition is disclosed, for example, in JP 10 (1998)-173097 A.
FIG. 6
shows the method for manufacturing this thermal conductive substrate. First, a thermal conductive resin composition slurry containing at least the inorganic filler and the thermosetting resin is formed so as to obtain a thermal conductive green sheet
61
. This thermal conductive green sheet
61
is dried, then stacked onto a lead frame
62
as shown in FIG.
6
A. Subsequently, as shown in
FIG. 6B
, the thermal conductive green sheet
61
is cured by heating and pressing so as to be an insulator layer
63
containing a thermal conductive resin cured material. In this manner, a thermal conductive substrate
64
is completed.
When producing the substrate by such a method, in order to maintain high heat-radiating characteristics and withstand voltage of the thermal conductive substrate
64
and to increase the adhesive strength of the lead frame
62
serving as a wiring pattern to the insulator layer
63
, it is preferable that the thermal conductive resin composition constituting the thermal conductive green sheet
61
covers the end faces of the wiring pattern of the lead frame
62
. Thus, at the time of heating and pressing, the thermal conductive resin composition has to have the fluidity necessary for covering the end faces of the pattern of the lead frame
62
. On the other hand, in order to increase the thermal conductivity of the thermal conductive substrate, the higher ratio of the inorganic filler in the thermal conductive resin composition is effective. However, when the ratio of the inorganic filler increases, the fluidity of the thermal conductive resin composition decreases. This causes a problem in that it becomes difficult to cover the end faces of the lead frame with the thermal conductive resin composition. In addition, when the ratio of the inorganic filler increases, the organic constituent for maintaining adhesive characteristics between the thermal conductive resin compositions decreases. This causes a problem in that it becomes difficult to process the thermal conductive resin composition into a desired shape and to maintain and handle this shape.
SUMMARY OF THE INVENTION
It is an object of the present invention to solve the problems described above and to increase thermal conductivity of a substrate and, at the same time, maintain fluidity of a thermal conductive resin composition so as to cover the end faces of a lead frame with the thermal conductive resin composition in a portion where the lead frame is in contact with the thermal conductive resin composition, thereby maintaining high heat-radiating characteristics and reliability. It is a further object of the present invention to achieve easy handling of the thermal conductive resin composition, thereby making it easier to produce the substrate.
The above-described object can be achieved in the following manner.
First, a thermal conductive substrate of the present invention includes a first electrical insulator layer, a second electrical insulator layer, and a lead frame serving as a circuit pattern. The first electrical insulator layer is formed of a thermal conductive resin composition containing a thermosetting resin and an inorganic filler (hereinafter, also referred to as a reinforcing material), and is joined to the lead frame. The second electrical insulator layer is provided on a side of the first electrical insulator layer not in contact with the lead frame, and is formed of a thermal conductive resin composition containing the inorganic filler and a resin composition containing the thermosetting resin. The second electrical insulator layer has a higher thermal conductivity than the first electrical insulator layer.
Next, a first method for manufacturing the thermal conductive substrate of the present invention includes producing a first thermal conductive resin composition by mixing an inorganic filler and a resin composition containing a thermosetting resin that is not cured, producing a second thermal conductive resin composition having a higher thermal conductivity than the first thermal conductive resin composition by mixing the inorganic filler and the resin composition containing the thermosetting resin that is not cured, and stacking a lead frame, the first thermal conductive resin composition and the second thermal conductive resin composition in this order and integrating them by heating and pressing, as well as curing the thermosetting resin.
Then, a second method for manufacturing the thermal conductive substrate of the present invention includes processing a first thermal conductive resin composition that has been produced by mixing an inorganic filler and a resin composition containing a thermosetting resin that is not cured into a sheet, producing a second thermal conductive resin composition having a higher thermal conductivity than the first thermal conductive resin composition by mixing the inorganic filler and the resin composition containing the thermosetting resin that is not cured, processing the second thermal conductive resin composition into a layer having a substantially constant thickness and adhering the layer onto a heat-radiating board, and stacking a lead frame, the first thermal conductive resin composition and the heat-radiating board provided with the second thermal conductive resin composition in this order so that the first and second thermal conductive resin compositions contact each other and integrating them by heating and pressing, as well as curing the thermosetting resin.
Next, a third method for manufacturing the thermal conductive substrate of the present invention includes processing a second thermal conductive resin composition produced by mixing an inorganic filler and a resin composition containing a thermosetting resin that is not cured into a l
Handa Hiroyuki
Hirano Koichi
Matsuo Mitsuhiro
Nakatani Seiichi
Yamashita Yoshihisa
Merchant & Gould P.C.
Norris Jeremy
Talbott David L.
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