Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
2001-04-13
2003-02-18
Martin, David (Department: 2841)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S748000, C361S713000, C174S051000, C174S078000, C257S720000
Reexamination Certificate
active
06522555
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a circuit board on which various semiconductor devices or electronic components are to be mounted. Particularly, the present invention relates to a resin board (a thermally conductive board) with high heat dissipation that is suitable for use in the power electronics field and to a power module including the same.
2. Related Background Art
Recently, there have been demands for increases in density and improvements in function of semiconductors, as a higher performance and a smaller size are required in electronic equipment. Accordingly, smaller higher-density circuit boards on which such semiconductors are to be mounted also have been required. Hence, a design with consideration to heat dissipation of a circuit board has become important. As a technique of improving heat dissipation of a circuit board, a method employing an insulated metal substrate using a metal plate made of, for example, copper or aluminum instead of a conventional printed board formed of glass-epoxy resin has been known in which a circuit pattern is formed on one surface or both surfaces of the metal plate with an insulating layer interposed therebetween. When higher thermal conductivity is required, a board has been used in which a copper sheet is bonded directly to a ceramic board made of, for example, alumina or aluminum nitride. Generally, an insulated metal substrate is utilized for use with a relatively low power consumption. In this case, the insulated metal substrate is required to have a thin insulating layer to have an improved thermal conductivity. Accordingly, the insulated metal substrate has a problem in that a portion between the circuit pattern and the metal plate as a ground tends to be affected by noise easily, and also has a problem in withstand voltage.
In order to solve such problems, recently, a board has been proposed in which a composition containing a filler with high thermal conductivity added to a resin is combined with a lead frame as an electrode to form one body. For example, JP 10(1998)-173097 A proposes a board including such a composition. A method of manufacturing such a thermally conductive board is shown in
FIGS. 15A and 15B
. According to JP 10(1998)-173097 A, a mixed slurry containing at least an inorganic filler and thermosetting resin is used to form a film and thus a sheet-like thermally conductive resin composition
16
is produced. The composition
16
is dried and then is superposed with a lead frame
11
and a heat sink
13
as shown in FIG.
15
A. Next, as shown in
FIG. 15B
, they are heated and compressed and the composition
16
is cured to form an insulating layer
12
. Thus, a thermally conductive board
28
is produced.
In such a thermally conductive board and a power module including the same, generally a part of the wiring pattern is grounded to the heat sink according to electrical requirements such as reducing stray capacitance. In such a case, it is necessary to connect the wiring pattern and the heat sink outside the board and an additional step other than steps for component mounting is required.
FIG. 16
shows an example of the connection with the heat sink in such a case. According to this example, a part of the lead frame
11
is used as a grounding pattern
15
and a lead
29
is soldered to the grounding pattern
15
and the heat sink
13
to establish a ground connection. In the figure, numeral
12
indicates an insulating layer. In order to connect the wiring pattern and the heat sink outside the board, it also is necessary to place the grounding pattern at the periphery of the board. This is a constraint in pattern design, and the degree of freedom in circuit design has been decreased accordingly. Furthermore, there has been a problem in that the size of the board itself increases to allow the establishment of the connection.
SUMMARY OF THE INVENTION
The present invention is intended to solve the aforementioned problems in the conventional technique. It is an object of the present invention to provide a thermally conductive circuit board (hereinafter also referred to as “thermally conductive board”) with high heat dissipation, high conductivity, and high ground-connection reliability that are obtained by an electrical connection between a heat sink and a grounding pattern inside an insulating layer of the thermally conductive board and to provide a method of manufacturing the same. In addition, it also is an object of the present invention to provide a power module allowing its size to be reduced and its density increased using the thermally conductive board.
In order to achieve the above-mentioned object, a thermally conductive circuit board of the present invention includes an electrically insulating layer, an electrically conductive heat sink, and a lead frame as a wiring pattern. The electrically insulating layer is formed of a thermally conductive resin composition containing 70 to 95 wt. % inorganic filler and 5 to 30 wt. % resin composition containing at least thermosetting resin. The lead frame and the electrically insulating layer are provided with their surfaces flush with each other. A grounding pattern electrically connected to the heat sink inside the electrically insulating layer is present in an arbitrary position in the same plane as that in which the wiring pattern is formed.
A first method of manufacturing a thermally conductive circuit board with a grounding pattern connected to a heat sink according to the present invention includes:
(1) placing a metal pole in a desired place in an electrically conductive heat sink; and
(2) superposing a lead frame as a wiring pattern, a sheet-like thermally conductive resin composition made of 70 to 95 wt. % inorganic filler and 5 to 30 wt. % resin composition containing at least uncured thermosetting resin, and the heat sink sequentially with a portion of the metal pole protruding from the heat sink facing the sheet-like thermally conductive resin composition, and heating and compressing them,
so that (A) the metal pole is connected to the lead frame and the sheet-like thermally conductive resin composition is allowed to fill up to a surface of the lead frame or (B) a surface of the metal pole is allowed to be flush with the surface of the lead frame to be a part of the wiring pattern and the sheet-like thermally conductive resin composition is allowed to fill up to the surface of the lead frame, and
the thermosetting resin contained in the sheet-like thermally conductive resin composition is cured.
A second method of manufacturing a thermally conductive circuit board with a grounding pattern connected to a heat sink according to the present invention includes:
(1) processing an electrically conductive heat sink by extruding its desired portion to form a protrusion; and
(2) superposing a lead frame as a wiring pattern, a sheet-like thermally conductive resin composition made of 70 to 95 wt. % inorganic filler and 5 to 30 wt. % resin composition containing at least uncured thermosetting resin, and the heat sink sequentially with the protrusion of the heat sink facing the sheet-like thermally conductive resin composition, and heating and compressing them,
so that (A) the protrusion is connected to the lead frame and the sheet-like thermally conductive resin composition is allowed to fill up to a surface of the lead frame or (B) a surface of the protrusion is allowed to be flush with the surface of the lead frame to be a part of the wiring pattern and the sheet-like thermally conductive resin composition is allowed to fill up to the surface of the lead frame, and
the thermosetting resin contained in the sheet-like thermally conductive resin composition is cured.
A third method of manufacturing a thermally conductive circuit board with a grounding pattern connected to a heat sink according to the present invention includes:
(1) placing a metal pole in a desired place in a lead frame as a wiring pattern; and
(2) superposing the lead frame, a sheet-like thermally conductive resin composition
Hirano Koichi
Matsuo Mitsuhiro
Nakatani Seiichi
Yamashita Yoshihisa
Bui Hung
Martin David
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