JP2010239164A - Wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-cost wiring board having excellent heat radiating properties which may be manufactured with less number of processes. <P>SOLUTION: In a wiring board, a circuit pattern 3 is formed by laminating a copper foil to an insulating layer 2. A metal material is further laminated by a cold spraying method to the upper part of the circuit pattern 3 to increase thickness in order to form an upper circuit pattern 5. Accordingly, even when a power semiconductor 6 is mounted on this thick upper circuit pattern 5, thermal resistance can be reduced because the heat generated by a loss of the same power semiconductor can be diffused by the upper circuit pattern 5. Therefore, it is possible to constitute a wiring board having excellent heat radiating properties and showing remarkably less amount of thermal resistance in comparison with the wiring board of the related art not including the upper circuit pattern 5. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a wiring board, and more particularly to a wiring board that has excellent heat dissipation and can be applied to industrial power supply equipment.

  Semiconductor modules used for power supply devices are applied in a wide range from consumer equipment such as home air conditioners and refrigerators to industrial equipment such as inverters and servo controllers. In particular, an IGBT (Insulated Gate Bipolar Transistor) module equipped with a power semiconductor generates a large amount of heat, so that a metal base wiring board or a ceramic wiring board having excellent heat dissipation has been used.

FIG. 3 is a view showing a cross-sectional structure of a conventional metal base wiring board.
The metal base wiring board has a three-layer structure including a base metal 101, an insulating layer 102 formed on the base metal 101, and a circuit pattern 103 formed on the insulating layer 102. As the base metal 101, a metal having excellent heat dissipation such as an aluminum plate or a copper plate is used. The insulating layer 102 is made of an epoxy resin containing an inorganic filler such as SiO ₂ , Al ₂ O ₃ , or AlN.

  The circuit pattern 103 is usually made of copper foil, but in rare cases, aluminum foil may be used. The copper foil having a thickness of about 35 μm to 140 μm is usually used. This copper foil is processed into a predetermined circuit pattern by wet etching. In the case of a power semiconductor having a small current capacity of about 10 A and low heat generation, the power semiconductor is directly mounted on the circuit pattern 103 by soldering. When the current capacity of the power semiconductor is increased, the heat is spread on the circuit pattern 103 to reduce the thermal resistance, so that the thickness of the copper foil is about 140 μm. If 140 μm is insufficient, a thicker copper foil such as 200 μm or 250 μm is used. Furthermore, if the thickness of the circuit pattern 103 is 1 mm or more, for example, 3 to 4 mm, the heat spreader effect is exhibited, the heat generated in the power semiconductor spreads in the lateral direction, and the thermal resistance is greatly reduced.

  The insulating layer 102 used for the metal base wiring board needs to be excellent in insulation reliability and heat dissipation. Furthermore, the insulating layer 102 is also required to be excellent in stress relaxation properties, moisture resistance, heat resistance, and the like, and resin compositions suitable therefor are also known (see, for example, Patent Documents 1 to 3). ). Thus, the circuit pattern 103 is bonded to the base metal 101 via the insulating layer 102 having excellent heat dissipation, so that the metal base wiring board is used as a wiring board for mounting a high heat-generating component such as a power semiconductor. It has been.

However, in the case of an epoxy resin containing an inorganic filler such as SiO ₂ , Al ₂ O ₃ , AlN, etc., since the filling amount is limited, its thermal conductivity is currently about 7 to 10 W / m · K. Therefore, there is a limit to the current capacity of the power semiconductor module that can be applied, and at present, it can only be applied up to about 50 A class.

  On the other hand, in the case of a power semiconductor module with a larger capacity exceeding 50 A, a ceramic wiring board having a higher thermal conductivity of the insulating layer is used instead of a metal-based wiring board.

  4A and 4B are diagrams showing a cross-sectional structure of a conventional ceramic wiring board, in which FIG. 4A shows a ceramic wiring board and FIG. 4B shows a ceramic wiring board to which a base metal is bonded.

  The ceramic wiring board is configured by pasting circuit patterns 103 on both sides of a ceramic insulating plate 104. The ceramic insulating plate 104 is produced by kneading the raw material powder with a binder to form a sheet-like insulating plate called a green sheet and firing it at a high temperature. Thereafter, a copper foil or an aluminum foil for the circuit pattern 103 is bonded at a high temperature to form a wiring board. Furthermore, these ceramic wiring boards are usually bonded to a copper base metal 101 having a thickness of about 2 to 3 mm via a solder layer 105.

The ceramic insulating plate 104 is made of Al ₂ O ₃ , AlN, Si ₃ N ₄ or the like as a raw material. The thermal conductivity of the ceramic insulating plate 104 is about 20 W / m · K when the raw material is Al ₂ O ₃ , 160 to 180 W / m · K when the raw material is AlN, and Si ₃ N _{4 as} the raw material. In this case, it is about 80 W / m · K, which is 1 to 2 digits higher than the case where an inorganic filler is added to the epoxy resin.

JP 2002-12653 A JP 2002-76549 A Japanese Patent Application Laid-Open No. 2002-114836

  However, in the case of a metal-based wiring board, if the copper foil is thickened to reduce the thermal resistance, the etching time for processing the circuit pattern layer becomes longer in proportion to the thickness. There is a problem that the cost is significantly increased and the cost is significantly increased. Moreover, if the thickness of the circuit pattern layer is 3 to 4 mm, not only will it take a long time to melt copper, but the etching of the edge of the circuit pattern layer cannot be performed with high accuracy, so the etching process itself is realistic. Not.

  In the case of a ceramic wiring board, a ceramic insulating board is manufactured once, a circuit pattern layer is bonded thereto, etching is performed, and the ceramic wiring board thus manufactured is bonded to a base metal by soldering, etc. Since many man-hours are required, there is a problem that the price is high and it is difficult to reduce the price. Moreover, in the case of a ceramic wiring board, the copper foil for the circuit pattern cannot be made too thick. In order to enhance the heat spreader effect, a thick copper foil or copper plate may be attached, but the copper plate is bonded to the ceramic insulating plate at a high temperature of about 1000 ° C or higher. Will bend due to bimetal effect during cooling. Also, as described above, the thickness of the copper foil or the copper plate increases the etching processing cost significantly. Therefore, the thickness of the circuit pattern of the ceramic wiring board is currently only used to about 0.6 mm or less. Not.

  The present invention has been made in view of these points, and an object of the present invention is to provide a wiring board that can be manufactured with less man-hours, is inexpensive, and has excellent heat dissipation.

  In the present invention, in order to solve the above problems, in a wiring board in which a metal foil is bonded to an insulating plate and the metal foil is processed to form a circuit pattern, the circuit pattern is an upper part of a portion where a heat generating semiconductor component is mounted. In addition, a wiring board is provided in which the stacked circuit patterns are provided in a stacked manner.

  According to such a wiring board, a thicker stacked metal pattern is formed on the circuit pattern of the metal foil. As a result, if a power semiconductor is mounted on this thick stacked circuit pattern, the heat generated by the loss can be diffused in the thick stacked circuit pattern, so that the thermal resistance can be reduced, and the heat dissipation with low thermal resistance. An excellent wiring board can be configured.

Further, according to the present invention, the wiring board provided with the overlay circuit pattern is a metal base wiring board made of an inorganic filler-filled resin in which an insulating plate is bonded to a metal plate.
Furthermore, according to the present invention, the wiring board provided with the stacked circuit pattern is a ceramic wiring board in which the insulating board is a ceramic insulating board in which metal foil is bonded to both sides, and the raw material of the ceramic insulating board is Al ₂ O _3. , AlN, or Si ₃ N ₄ .

  Since the wiring board of the present invention can form a circuit pattern of metal foil at least partially thick, if a power semiconductor is mounted on this thick circuit pattern, the heat generated by the loss is thick. Since it can be diffused with a pattern, the thermal resistance can be reduced, and there is an advantage that it is possible to easily and inexpensively manufacture a wiring board having a low thermal resistance and excellent heat dissipation compared to conventional metal-based wiring boards and ceramic wiring boards. .

The manufacturing process of the wiring board of this invention, and the state of the completed power semiconductor module are shown, Comprising: (a) shows a metal base wiring board, (b) shows the formation process of the stacked circuit pattern by cold spray. (C) shows a state in which an upper circuit pattern is formed, and (d) shows a power semiconductor module in which a power semiconductor is mounted on the upper circuit pattern. It is explanatory drawing about the thickness of an overlaid circuit pattern. It is a figure which shows the cross-section of the conventional metal base wiring board. It is a figure which shows the cross-section of the conventional ceramic wiring board, Comprising: (a) shows a ceramic wiring board, (b) has shown the ceramic wiring board to which the base metal was joined.

  Hereinafter, as an embodiment of the present invention, with reference to the drawings, an example in which the present invention is applied to a metal-based printed wiring board in which a predetermined circuit pattern is formed by bonding a metal foil to an insulating layer and processing the metal foil. This will be described in detail.

  FIG. 1 shows a manufacturing process of a wiring board according to the present invention and a state of a completed power semiconductor module, wherein (a) shows a metal-based wiring board, and (b) shows the formation of an overlaid circuit pattern by cold spraying. (C) shows a state in which an overlaid circuit pattern is formed, and (d) shows a power semiconductor module in which a power semiconductor is mounted on the overlaid circuit pattern.

  As shown in FIG. 1A, the metal base wiring board has a three-layer structure in which an insulating layer 2 containing an inorganic filler is provided on a base metal 1 and a circuit pattern 3 is laminated thereon. ing.

  The circuit pattern 3 is usually made of copper foil. The circuit pattern 3 may be an aluminum foil instead of the copper foil. The copper foil bonded to the insulating layer 2 is processed into a predetermined pattern by wet etching to form a circuit pattern 3. Here, as the copper foil, a standard product having a thickness of about 35 μm to 140 μm is usually used. Further, the pattern width of the circuit pattern 3 is determined by the current capacity of the circuit, but considering the etching processing cost, the thickness of the copper foil is desirably as thin as possible.

  The metal base wiring board formed as described above is the same as the conventional metal base wiring board. However, in the wiring board according to the present invention, only a region in the circuit pattern 3 where heat dissipation is desired to be improved is partially provided. The thickness is increased. That is, as shown in FIG. 1B, a mask 4 having a hole having a shape corresponding to a region where the thickness is to be increased is disposed on the circuit pattern 3, and a cold spray method is applied from above. Then, the metal powder is sprayed at supersonic speed at room temperature, and the metal powder is laminated on the circuit pattern 3 to form the stacked circuit pattern 5 shown in FIG.

  Here, the cold spray method will be described. The cold spray method is regarded as one of the thermal spraying techniques. A gas having a temperature lower than the melting point or softening temperature of the thermal spray material is converted into a supersonic flow, and the thermal spray material particles are injected into the flow to accelerate. This is a technique for forming a film by colliding with a substrate at a high speed in a solid state. The feature of the cold spray method is that the temperature of the working gas for heating and accelerating the sprayed material particles is significantly lower than that of the conventional plasma spraying method, flame spraying method, high-speed flame spraying method and the like. Plasma spraying or the like requires a high working gas temperature of 2000 to 8000 ° C., but in the case of cold spray, a working gas of room temperature to about 600 ° C. may be used. The thermal spray material particles are allowed to collide with the base material at a high speed in a solid state without being heated so much, but when the critical velocity is reached, the base material and the thermal spray material particles are plastically deformed to form a film. Therefore, unlike other thermal spraying methods, it is possible to minimize oxidation and thermal alteration of the thermal spray material due to heat.

  The cold spray device branches high-pressure gas supplied from a gas source such as a cylinder into a powder supply device and a gas heater. Of these, the mainstream working gas flows through a coiled gas pipe heated directly or indirectly by an electric furnace or the like, is heated, is supplied to a spray gun, is accelerated by a supersonic nozzle, and is ejected.

  On the other hand, a part of the working gas is diverted to the powder supply device and flows into the back of the spray gun together with the spray powder as a carrier gas. Although the heating of the working gas may not be performed, the heating is advantageous in that it can increase the particle velocity and easily cause plastic deformation of the particles. Air, helium, or nitrogen is used as the gas.

  Here, a metal material having a particle diameter of 1 to 50 μm is used as the thermal spray material sprayed onto the circuit pattern 3. As the particle material, copper, aluminum, iron, titanium, molybdenum, nickel, or the like is used. Usually, copper or aluminum is used for the wiring board. These spray material particles are sprayed and deposited on the circuit pattern 3 through the mask 4 at a speed of 500 to 900 m / s at a distance of 10 to 50 mm, and as shown in FIG. As described above, the stacked circuit pattern 5 is formed on the circuit pattern 3. In order to obtain the required film thickness for the stacked circuit pattern 5, the sprayed material particles are sprayed for a predetermined time. The thickness of the stacked circuit pattern 5 is set in consideration of the loss generated in the power semiconductor. Although depending on the generated loss, the thickness of the effective overlay circuit pattern 5 is about 0.5 mm to 5 mm.

  A metal base wiring board having a three-layer structure in which the stacked circuit pattern 5 is directly bonded to the copper foil is manufactured by such a manufacturing process. Thereafter, the power semiconductor 6 is mounted on the stacked circuit pattern 5 stacked by cold spray. The power semiconductor 6 is usually joined to the stacked circuit pattern 5 by SnPb solder or SnAgCu solder.

  Finally, the power semiconductor 6 is connected to the external circuit by a wire 7 necessary for connection to an external circuit, and the power semiconductor module shown in FIG. In the case of a semiconductor element having a large current capacity such as the power semiconductor 6, an aluminum wire is usually used as the wire 7.

  Note that the upper circuit pattern 5 to be stacked by cold spray is formed only on the portion where the power semiconductor 6 that needs to dissipate the circuit pattern 3 is mounted, but may be formed on the entire surface of the circuit pattern 3.

Further, even with a copper material or other metal material laminated by cold spray, the thermal conductivity inherent to the material can be obtained.
Further, here, the case of a metal-based wiring board has been described as an embodiment of the wiring board, but the ceramic wiring board shown in FIG. 4 also has the same pattern on the circuit pattern 103 on the side where the power semiconductor is mounted. An overlaid circuit pattern can be formed by the manufacturing method described above.

Next, optimization of the thickness of the stacked circuit pattern 5 laminated on the circuit pattern 3 by cold spray will be described.
FIG. 2 is an explanatory diagram of the thickness of the stacked circuit pattern.

  The heat flow generated from the power semiconductor 6 usually has the property of spreading and spreading at an angle of 45 degrees. Therefore, if the distance a from the chip end of the power semiconductor 6 to the end of the upper circuit pattern 5 is equal to the total thickness b of the circuit pattern 3 and the upper circuit pattern 5, the heat spreader effect is maximized and the thermal resistance is increased. Can be greatly reduced. For this reason, it is not necessary to forcibly increase the width of the circuit pattern 3 and the upper circuit pattern 5 with respect to the size of the power semiconductor 6, and it is not necessary to increase the thickness of the upper circuit pattern 5 by force.

  From the above relationship between the width and thickness of the stacked circuit pattern 5, the distance a from the end of the power semiconductor 6 to be mounted to the end of the stacked circuit pattern 5 and the total thickness b of the circuit pattern 3 and the stacked circuit pattern 5 The ratio of 1 is optimal, but if it is in the range of 0.8 to 1.2, substantially sufficient thermal diffusivity can be obtained. If this is less than 0.8, sufficient thermal diffusibility may not be obtained, and if it exceeds 1.2, the effect will be saturated.

  In the above embodiment, the case where a metal foil such as copper is bonded to an insulating layer or a ceramic insulating plate and the metal foil is processed to form a predetermined circuit pattern is described in detail. Also, it can be applied to the adjustment of the thickness of the circuit pattern of the lead frame.

DESCRIPTION OF SYMBOLS 1 Base metal 2 Insulating layer 3 Circuit pattern 4 Mask 5 Overlay circuit pattern 6 Power semiconductor 7 Wire 101 Base metal 102 Insulating layer 103 Circuit pattern 104 Ceramic insulating board 105 Solder layer

Claims (6)

In a wiring board in which a metal foil is laminated to an insulating plate and a circuit pattern is formed by processing the metal foil,
The circuit board is characterized in that an upper circuit pattern is laminated on an upper part of a portion where a heat generating semiconductor component is mounted.   2. The upper circuit pattern according to claim 1, wherein a distance from an end of a semiconductor chip to be mounted to an end of the upper circuit pattern is equal to a total thickness of the circuit pattern and the upper circuit pattern. Wiring board.   The stacked circuit pattern has a ratio of a distance from an end of a semiconductor chip to be mounted to an end of the stacked circuit pattern and a total thickness of the circuit pattern and the stacked circuit pattern of 0.8 to 1.2. The wiring board according to claim 1, wherein the wiring board is in a range.   4. The wiring board according to claim 2, wherein the insulating board is a metal-based wiring board made of an inorganic filler-filled resin bonded to a metal plate. The insulating plate is a ceramic wiring board made of a ceramic insulating plate in which the metal foil is bonded to both sides, and the raw material of the ceramic insulating plate is one selected from Al ₂ O ₃ , AlN, and Si ₃ N _4. The wiring board according to claim 2 or 3, wherein   4. The wiring board according to claim 2, wherein the material of the upper circuit pattern is one selected from copper, aluminum, iron, titanium, molybdenum, and nickel.

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