JPH06334286A - Circuit board - Google Patents

Abstract

PURPOSE:To obtain a circuit board, excellent in thermal conduction and withstand voltage, that is specifically suitable for circuit boards for power modules by bonding metal foil circuits to both sides of a ceramic board with high thermal conductive organic adhesive. CONSTITUTION:Metal foil circuits 3 and 4 are obtained by plating both sides of a ceramic board 2 with Ni. If the ceramic board is an aluminum nitride board 16, the difference in thermal expansion coefficient is slight between the metal foil circuit 3 and 4 and silicon semiconductor, and their thermal conductivity is five to ten times that of alumina boards. This makes unnecessary heat spreaders that are conventionally required in mounting a power semiconductor chip 7 on an insulting aluminum board. In addition the title circuit board 3 and 4 allows a ceramic board 2 that facilitates mounting power semiconductor chips 7 and a board for controlling the power semiconductor chips 7 to be easily mounted on the same metal board by bonding or soldering without degrading heat dissipating property withstand voltage reliability. This makes the circuit board highly suitable for intelligent power modules.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit board excellent in thermal conductivity and withstand voltage, which is particularly suitable as a circuit board for a power module.

[0002]

2. Description of the Related Art In recent years, a power module incorporating a power semiconductor chip such as a power transistor has been used for a purpose of controlling a large amount of power such as an inverter, and the usage amount thereof has been rapidly increasing. In these power modules, an alumina metallized substrate has been conventionally used as a substrate on which a power semiconductor chip is mounted, but when assembled into a power module, the workability is poor and the cost is high. For this reason, in addition to heat dissipation and insulation properties, a thick copper foil-clad ceramic substrate using alumina or aluminum nitride, which has good assembly workability (for example, JP-A-56-16309).
No. 3, JP-A-3-18087) and insulating aluminum substrates (JP-A-58-48432) have come to be used.

As shown in FIG. 5, a thick copper foil-clad ceramic substrate is a ceramic plate 2 with a metal foil circuit 3 such as thick copper plated with Ni on a thick copper plate 1 plated with Ni.
Are joined by solder 5 on their entire surfaces. The thick copper plate 1 efficiently dissipates heat generated from the power semiconductor chip 7 via the ceramic plate 2 and also serves as a support plate for reinforcing the fragile ceramic plate 2.

[0004]

However, the use of such a thick copper plate not only hinders the weight saving of the module, but also the ceramic plate and the copper plate (for example, the coefficient of thermal expansion of copper is 16 ppm which greatly differs in thermal expansion coefficient). Alumina 7.3ppm / ° C / ° C, aluminum nitride 4.7pp
(m / ° C.) needs to be soldered over a wide area, and in the worst case, there is a fear of causing insulation failure due to cracking of the brittle ceramic plate.

Furthermore, since a high temperature is required for joining the ceramic plate and the metal foil circuit, and the connection between the power semiconductor chip and the metal foil circuit is an ultrasonic connection using a thick aluminum wire, the metal foil circuit is connected. However, there is a problem that Ni plating is required.

On the other hand, in the insulated aluminum substrate shown in FIG. 6, since the thick aluminum plate 20 functions as a heat dissipation and support plate, there is no problem as described above using the thick copper plate, but compared with the thick copper foil-clad ceramic substrate. However, since a thinner high-thermal-conductivity organic adhesive 10 is used, the withstand voltage characteristic is inferior, and a copper heat spreader 9 needs to be soldered in order to efficiently dissipate heat from the power semiconductor chip. there were.

[0007]

Means for Solving the Problems As a result of intensive studies to solve the problems of the thick copper foil-clad ceramic substrate and the insulating aluminum substrate, the inventors of the present invention have found that a metal foil circuit is provided on the back surface with a high thermal conductive organic system. A ceramic plate having good thermal conductivity, which is bonded using an adhesive, and a metal plate are joined using solder,
Furthermore, a method of bonding a metal foil circuit capable of ultrasonically connecting a power semiconductor chip and a metal foil circuit with a thick aluminum wire and capable of passing a large current on the ceramic plate with a high thermal conductive organic adhesive, etc. As a result, they have found that the above problems can be solved, and completed the present invention.

That is, a first aspect of the present invention is a circuit board characterized in that a metal foil circuit is adhered to both sides of a ceramic plate by a high thermal conductive organic adhesive, and a second aspect. Is a circuit board characterized in that a circuit board made of a ceramic plate having metal foil circuits adhered on both sides is joined to a partial surface or the whole surface of the metal plate by soldering.

The present invention will be described in more detail below. The present invention incorporates a method of bonding a metal foil circuit with a high thermal conductive organic adhesive while utilizing the high thermal conductivity, low thermal expansion property and high insulating property of a ceramic plate.

That is, in the present invention, the high heat conductive organic adhesive is used for bonding the ceramic plate and the front and back metal foil circuits.

The high thermal conductive organic adhesive (hereinafter often referred to as an adhesive) used in the present invention preferably has a thermal conductivity of at least 2 W / mK or more as a cured product. Adhesives having such characteristics include thermosetting resins such as epoxies, silicones, urethanes, polyimides, polyisoimides and BT resins, and resins based on thermoplastic resins such as polyetherimides and polyimides. It can be obtained by blending a high thermal conductive insulating powder such as aluminum, boron nitride, beryllia, alumina, silica, magnesia, diamond and / or a metal powder such as silver, copper or aluminum. The compounding amount of the high thermal conductive insulating powder and / or the metal powder is preferably 70% by weight or more. Furthermore, a coupling agent such as vinyltriethoxysilane and a viscosity modifier such as long-chain polyaminoamide can be present in these adhesives.

The thickness of the adhesive layer is preferably as thin as possible in terms of thermal conductivity. However, since the above-mentioned powder is filled in the adhesive in order to impart high thermal conductivity, if the thickness is too thin, the coatability deteriorates. Therefore, in consideration of both, it is desirable that the adhesive thickness is 10 to 40 μm. If the thickness of the adhesive layer exceeds 40 μm, the thermal conductivity of the adhesive will be 2
Even if it is W / mK or more, the heat generated in the power semiconductor chip cannot be efficiently conducted, and the characteristics of the ceramic plate having good thermal conductivity cannot be sufficiently exhibited.

Even with the adhesive having the above characteristics, it is necessary to consider the insulating property in addition to the thermal conductivity for bonding the metal foil circuit on the main surface to the ceramic plate. This is because in the case of a conductive adhesive, the insulation between the circuits cannot be obtained unless the adhesive is applied in a circuit pattern on a ceramic plate such as an aluminum nitride plate.

On the other hand, it is not always necessary that the backside metal foil circuit and the ceramic plate are bonded to each other by insulating, and a conductive adhesive may be used. This is because the back surface metal foil circuit is used for joining with the metal plate by soldering, but the insulating property between the metal foil circuit on the main surface and the metal plate can be secured by the ceramic plate.

As the material of the ceramic plate used in the present invention, ceramics which are not metallized such as aluminum nitride, beryllia, boron nitride, silicon nitride, alumina and glass are used. Among them, aluminum nitride is preferable from the viewpoint of thermal conductivity and safety, and in particular, aluminum nitride whose surface is mechanically polished or whose surface layer is subjected to an oxidation treatment to improve the adhesiveness is preferable. Higher thermal conductivity and mechanical strength of the ceramic plate are preferable, and particularly thermal conductivity is an important factor that influences the heat dissipation characteristics of the power semiconductor chip mounting substrate. If the thickness of the ceramic plate is thin, the thermal conductivity will be good, but the withstand voltage will be poor, so it is 0.2 to 1.0 m.
It is good to set m. The ceramic plate is bonded to a partial surface or the entire surface of the metal plate.

On the other hand, for the metal plate used in the present invention, in order to serve as a heat radiation and support plate for the power module, it is an important condition that the metal plate be capable of being bonded by thermal conductivity and strength and further by soldering. Examples of these metal plates include aluminum and its alloy plated with nickel, copper and its alloy plated with nickel, and iron plated with nickel. Among them, from the viewpoint of lightness and adhesiveness, aluminum-nickel-plated one or an alloy thereof is preferably nickel-plated, and from the viewpoint of thermal conductivity, copper-nickel-plated one and its alloy are preferable. Nickel plated is preferable. The thickness of the metal plate is preferably 0.5 to 5 mm, and is 3 to 5 mm from the viewpoint of strength in a power module for high power. Hybrid IC with smaller power
For an igniter or the like, it may be 2 mm or less.

The metal foil circuit of the main surface used in the present invention is
It is possible to ultrasonically connect with a thick aluminum wire and to pass a large current. For example, a two-layer foil made of aluminum / thick copper and a three-layer foil made of aluminum / thick copper / aluminum are formed on a thick copper circuit formed by selective etching (Japanese Patent Laid-Open No. 61-284991, etc.). A circuit having an ultrasonic connection pad of aluminum or a circuit formed by nickel plating of thick copper. Here, the thick copper is preferably a copper foil or a copper plate having a thickness of 70 to 1500 μm, and particularly 200 to 1
Those having a thickness of 000 μm are preferable.

The metal foil circuit on the back surface used in the present invention can be joined to a metal plate by soldering, and is made of copper foil, nickel-plated copper foil, aluminum / copper clad foil, nickel / copper clad foil, or the like. Good. The thickness of the back surface metal foil circuit is preferably close to the thickness of the main surface metal foil circuit so that the ceramic substrate after bonding does not warp.

In the circuit board of the present invention, the circuit board may be further adhered to the entire surface or a partial surface of the metal foil circuit adhered to the ceramic plate with an adhesive to form a multilayer board. There is no particular limitation as to the circuit board used for multilayering,
A flexible substrate, a glass epoxy substrate, a low temperature baking glass substrate, an alumina substrate, or the like can be used.

[0020]

In the circuit board of the present invention, when the ceramic plate used is, for example, an aluminum nitride plate, the difference in the coefficient of thermal expansion from the silicone semiconductor is small, and the thermal conductivity is 5 to 10 times that of the alumina substrate. Therefore, the heat spreader required for mounting the power semiconductor chip on the insulating aluminum substrate becomes unnecessary. Further, the circuit board according to the present invention is joined by soldering onto the metal plate which plays a role of a supporting plate at the time of assembling the power module. This process is the same as that at the time of assembling the power module by the conventional thick copper foil clad ceramic substrate. Therefore, there is no need to change the process.

Further, in the circuit board of the present invention, a ceramic board on which a power semiconductor chip can be easily mounted and a control board (for example, an alumina board with resistance printing or a multi-layer glass epoxy board) for controlling the power semiconductor chip are provided. Since they can be assembled on the same metal plate by bonding or soldering, the so-called intelligent power module currently attracting attention can be easily manufactured.

[0022]

EXAMPLES The present invention will be described more specifically with reference to Examples and Comparative Examples.

Example 1 A mounted circuit board for a power module shown in FIG. 1 was produced. On the upper and lower surfaces of the aluminum nitride plate (thickness: 0.635 mm, thermal conductivity: 135 W / mK) 16, a high thermal conductivity organic adhesive having a thermal conductivity of 2.0 W / mK mainly made of alumina powder and epoxy resin (thickness: 20 μm) ) 10 is applied and the upper surface is plated with Ni of 4 μm in thickness, which is 300 μm
The metal foil circuit 3 made of the copper plate of
The metal foil circuits 4 made of i-plated copper plate having a thickness of 250 μm were arranged and bonded together. Adhesion was performed under conditions of a temperature of 150 ° C. and 10 hours.

Then, this circuit board was bonded to a thick aluminum plate (thickness 3 mm) 15 plated with Ni of 4 μm with solder 5 to obtain a power module circuit board. Then, after washing with an organic solvent and drying, a 5 mm square power semiconductor (power transistor) chip 7 was bonded onto the metal foil circuit 3 with solder 5. Further made of aluminum (300
(μm diameter) Bonding wire 6 was used to obtain a circuit board on which the power module shown in FIG. 1 was mounted. Then, after the circuit board was screwed on a water-cooled aluminum heat sink through a heat-dissipating grease, the power transistor 7 was energized and the thermal resistance was measured by a normal ΔVBE method to find that it was 0.81 ° C / W. It was

Example 2 A circuit board on which the power module shown in FIG. 2 was mounted was produced. In Example 1, instead of the Ni-plated main surface metal foil circuit 3, 20 μm aluminum / 300
A circuit was used in which aluminum and copper were selectively etched from a three-layer foil made of μm thick copper / 20 μm aluminum to expose the aluminum foil circuit 18 and the thick copper circuit 19. Therefore, in this structure, the connection from the power semiconductor chip 7 by the bonding wire 6 is made to the aluminum foil circuit 18. Further, unlike the first embodiment, aluminum nitride powder and epoxy resin are used as the high thermal conductive organic adhesive 10 for adhering the aluminum foil circuit 18 and the Ni-plated rear surface metal foil circuit 4 and the aluminum nitride plate 16. Main thermal conductivity 4.2W
A high thermal conductive organic adhesive (thickness 20 μm) of / mK was used. The thermal resistance measured in the same manner as in Example 1 is 0.78.
C / W.

Example 3 A mounted circuit board for a power module shown in FIG. 3 was produced. In Example 1, the aluminum nitride plate 16 and the thick film circuit 1 are provided on the thick aluminum plate 15 plated with Ni.
The difference is that the alumina plate 17 with 3 is bonded, and both plates are connected by soldering of the metal fitting 12 for connection. The power semiconductor chip 7 is mounted on the aluminum nitride plate 16, and a signal for driving the power semiconductor chip 7 is transmitted from the alumina plate 17 side. Also, thick aluminum plate 1
For bonding the 5 and the alumina plate 17, a silicone-based adhesive (thickness 150 μm) 21 mainly composed of silica powder and silicone resin and having a thermal conductivity of 0.5 W / mK is used because the calorific value is small. The thermal resistance measured in the same manner as in Example 1 was 0.81 ° C./W.

Example 4 A mounted circuit board for a power module shown in FIG. 4 was produced. Instead of the alumina plate 17 of Example 3, a glass epoxy plate 11 with a multilayer circuit having a copper foil circuit 14 with gold plating as the uppermost layer is used. Power semiconductor chip 7
Is mounted on an alumina plate 17 having a thickness of 0.3 mm, and a signal for driving it is transmitted from the glass epoxy plate 11 via the bonding wire 6. The thermal resistance measured in the same manner as in Example 1 was 0.83 ° C./W.

Comparative Example 1 Assuming that alumina DBC is actually used, a metal foil circuit 3 made of thick copper with Ni plating on the front side is used.
However, the ceramic plate (thickness 0.635 mm made of alumina) 2 having the back surface circuit 4 joined to the back side is soldered to the thick copper plate 15 having a thickness of 4 mm, which is plated with Ni, for the power module shown in FIG. A mounted circuit board was produced. The thermal resistance measured in the same manner as in Example 1 was 0.86 ° C./W.

COMPARATIVE EXAMPLE 2 The heat generated from the power semiconductor chip 7 is the solder 5, the thick copper circuit 19 having a thickness of 300 μ, and the epoxy high thermal conductive organic adhesive (heat conductivity 2 W / mK) 10 having a thickness of 160 μm.
A power circuit mounted circuit board having a structure (FIG. 6) that is transmitted to the thick aluminum plate 20 via each of the above was produced. The thermal resistance measured in the same manner as in Example 1 is 0.89 ° C.
Was / W.

[0030]

According to the present invention, in a power module or the like, the power semiconductor chip can be easily mounted without impairing the heat dissipation and the withstand voltage reliability, and the power semiconductor chip and the control component can be installed in the same module. There is an advantage that can be implemented. Therefore, the present invention can be conveniently applied to intelligent power modules and the like, which are currently receiving attention.

[Brief description of drawings]

FIG. 1 is a front view when a power semiconductor chip is mounted on a circuit board of an actual example of the present invention.

FIG. 2 is a front view when a power semiconductor chip is mounted on a circuit board according to one practical example of the present invention.

FIG. 3 is a front view when a power semiconductor chip is mounted on a circuit board according to one practical example of the present invention.

FIG. 4 is a front view when a power semiconductor chip is mounted on a circuit board according to one practical example of the present invention.

FIG. 5 is a front view of a conventional thick copper foil-clad ceramic substrate mounted for a power module.

FIG. 6 is a front view of a conventional mounting base for a power module using an insulating aluminum substrate at the time of mounting.

[Explanation of symbols]

 1: Ni-plated thick copper plate 2: Ceramic plate 3: Ni-plated main surface metal foil circuit 4: Ni-plated back metal foil circuit 5: Solder 6: Bonding wire 7: Power semiconductor Chip 8: Mounting hole 9: Heat spreader 10: High thermal conductive organic adhesive 11: Glass epoxy plate with multi-layer circuit 12: Connection metal fitting 13: Thick film circuit 14: Copper foil circuit with gold plating 15: Ni plating Thick aluminum plate 16: Aluminum nitride plate 17: Alumina plate 18: Aluminum circuit 19: Thick copper circuit 20: Thick aluminum plate 21: Silicone adhesive

Claims (2)

[Claims] 1. A circuit board, wherein metal foil circuits are adhered to both sides of a ceramic plate by a high thermal conductive organic adhesive. 2. A circuit according to claim 1, wherein a circuit board made of a ceramic plate having metal foil circuits adhered to both sides thereof and a partial surface or the whole surface of the metal plate are joined by solder. substrate.