JP2002093968A - Module structure - Google Patents

Abstract

(57) [Summary] [Problem] It is difficult to generate cracks in the solder under the semiconductor element and cracks in the ceramic substrate for a long period of time.
Moreover, an inexpensive module structure having excellent heat dissipation properties is provided. A module structure having a circuit for mounting an electronic component on one main surface of a ceramic substrate and a ceramic circuit substrate provided with a heat sink on the other main surface is joined to a cooling unit. A module structure, wherein the radiator plate is made of a metal containing aluminum as a main component, and the radiator plate and the cooling unit are joined by an aluminum brazing material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a module structure formed by joining a ceramic circuit board to a cooling unit,
Particularly, the present invention relates to a module structure suitable for a power module for power supply use.

[0002]

2. Description of the Related Art In power modules such as IGBT and IPM, aluminum oxide (Al
₂ O ₃ ), silicon nitride (Si ₃ N ₄ ), aluminum nitride (A
1N) and a circuit board made of a ceramic substrate such as copper (Cu) or aluminum (Al) are soldered to a heat sink (also called a heat sink) made of a metal such as aluminum, and then a resin case or the like is attached to obtain a power module. Have been.

On the other hand, in automotive applications such as electric vehicles including electric railway vehicles and hybrid cars, power modules are required to have higher reliability. It is known that factors that impair the reliability of the power module include cracks in the ceramic substrate used and cracks in the solder used to join the ceramic substrate and the heat sink.

[0004] Cracks generated in the ceramic substrate cause insulation failure, and cracks generated in the solder between the ceramic substrate and the heat radiating plate deteriorate heat radiation, resulting in inoperability of the semiconductor element. Since this directly leads to shortening of the life of the power module, there is a demand for a module which is highly reliable for a long period of time while preventing the above problems from occurring.

[0005] In view of the above circumstances, in order to prevent cracks generated in a ceramic substrate, aluminum (Al) having excellent stress relaxation properties is used as a circuit metal, and solder used between a ceramic substrate and a heat sink is used. In order to reduce the generated thermal stress, it has been proposed to use a composite material such as Al-SiC or Mo-Cu having a thermal expansion coefficient close to that of a ceramic substrate as a heat sink.

A module obtained by combining a ceramic substrate and a heat sink made of a composite material has high reliability and is suitable for electric railway vehicles and hybrid cars, but the cooling performance of such a structure is low. It is not expensive enough, and has the major disadvantage of being more expensive.

In terms of cooling performance, in the conventional module, the heat radiating plate and the cooling unit are fixed via heat radiating grease, and the ceramic substrate and the heat radiating plate are joined by solder. It is considered the main cause. Solder and heat radiation grease have extremely low thermal conductivity compared to ceramic substrates and heat radiation plates, and are bottlenecks in the overall cooling performance of the module structure.

If the cooling performance is high, the size and weight of the module can be reduced. However, for example, in a vehicle-mounted application, a compact module is expected to have a great advantage of securing an installation space and reducing the weight. Further improvement of the cooling performance of the structure is desired.

[0009] In terms of cost, a major drawback is that the module body is expensive. The main reason for this is that composite materials such as Al-SiC have to rely on a special production method, which has hindered the expansion of applications of high reliability modules. There is an aspiration to develop a power module with low cost and high reliability.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has greatly improved the cooling performance of the entire module structure.
It is an object of the present invention to provide a module structure that has a reliability equal to or higher than that of a case where a heat sink made of a SiC composite material is used, and that can reduce the cost.

[0011] In order to eliminate the solder between the ceramic substrate and the cooling unit, the ceramic substrate and the heat sink are joined by a high-temperature brazing material. When these are joined by a high-temperature brazing material, the following problems exist.

That is, since the ceramic substrate and the heat radiating plate are directly joined by using the high-temperature brazing material, the thermal stress generated in the substrate and the heat radiating plate is increased as compared with the case of the conventional module structure. Cracks easily occur on the ceramic substrate.

In order to solve this problem, a structure in which a ceramic substrate and a cooling unit are soldered has been proposed (Japanese Patent Laid-Open No.
However, as long as the solder is used as a bonding material between the ceramic substrate and the metal, cracks in the solder and cracks in the ceramic substrate occur even after 3000 heat cycles required for a hybrid car application. There is no way to gain the credibility of not doing it. Further, if a solder having a large thermal resistance is used, a module structure having a sufficient cooling performance cannot be obtained. Further, as described above, if cracks occur in the solder, the heat dissipation of heat generated from electronic components and circuits such as semiconductor elements in the module is deteriorated, which is not practically preferable.

[0014]

Means for Solving the Problems The present inventor has studied diligently in view of the above circumstances, and evaluated the structure of the module structure, its reliability and heat radiation characteristics, so that a module structure having a specific structure can be obtained. It was found that cracks in the solder under the semiconductor element and cracks in the ceramic substrate were unlikely to occur over a long period of time, and that they were excellent in heat dissipation, leading to the present invention. By eliminating the heat radiation grease and solder that exist between the cooling unit and the board, the ceramic board is directly joined to a cooling unit such as an aluminum alloy. The choice of materials achieves both high cooling performance and high reliability while realizing low cost.

That is, according to the present invention, a ceramic circuit board having a circuit for mounting electronic components on one main surface of a ceramic substrate and a heat sink provided on the other main surface is joined to a cooling unit. A module structure, wherein the heat sink is made of a metal containing aluminum as a main component,
Moreover, the module structure is characterized in that the radiator plate and the cooling unit are joined with an aluminum brazing material.

Further, the present invention is the above-mentioned module structure, characterized in that at least a surface of the circuit of the ceramic circuit board in contact with the ceramic substrate is made of a metal containing aluminum as a main component. The above-described module structure, wherein the brazing material contains magnesium and copper and / or zinc, and more preferably, the ceramic substrate is silicon nitride or aluminum nitride. It is a module structure.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION As a result of the inventor's intensive experiment, the module structure is a module structure formed by joining a ceramic circuit board to a metal cooling unit by brazing and having a specific laminated structure. Sometimes, cracks in the solder under the semiconductor element for a long time, and cracks in the ceramic substrate are unlikely to occur, and the knowledge that a power module with excellent heat dissipation and long-term reliability can be obtained, This has led to the present invention.

The module structure according to the present invention is characterized in that a ceramic circuit board having a circuit for mounting electronic components on one main surface and having a heat sink on another main surface is joined to a cooling unit. Wherein the radiator plate is made of a metal containing aluminum as a main component, and the radiator plate and the cooling unit are joined with an aluminum brazing material. By adopting the configuration, there is a feature that a power module having excellent heat dissipation and reliability can be obtained over a long period of time.

In the present invention, in a circuit for mounting an electronic component provided on a ceramic circuit board, it is preferable that at least a surface of the circuit in contact with the ceramic substrate is made of a metal containing aluminum as a main component. When such a configuration is employed, the durability of the module structure against repeated heating and cooling under actual use is further improved, and a power module with excellent heat dissipation and reliability over a longer period can be obtained. There are advantages.

Regarding the ceramic circuit board used in the present invention, any ceramic board may be used as long as it satisfies the required properties such as electrical insulation properties, high thermal conductivity and high mechanical strength. Aluminum nitride (AlN) having high thermal conductivity or silicon nitride (Si) having both high strength and relatively high thermal conductivity
₃ N ₄ ) is more preferred.

As for the circuit provided on the ceramic substrate, at least the surface in contact with the ceramic substrate is preferably made of a metal containing aluminum as a main component, as described above. Any conductive metal may be used. However, copper and aluminum and their alloys are preferably used because they are inexpensive and have high thermal conductivity and excellent electrical conductivity. In particular, copper and aluminum and their alloys are preferably used, and have high electrical conductivity and high plastic deformability against stress generation. Therefore, high-purity copper or aluminum is more preferably selected.

As the metal used for the cooling unit, aluminum or copper, which is relatively inexpensive and has high thermal conductivity, or an alloy containing these as a main component is preferably used. Further, a structure partially using the above metal or alloy may be used. Further, a Ni layer may be provided in advance on the surface of the cooling unit by an operation such as plating for the purpose of improving durability or facilitating joining with other components.

As a method for obtaining the module structure of the present invention, the method exemplified below is preferable since the module structure of the present invention can be obtained stably at a high yield. It is not limited to the obtained module structure.

A ceramic substrate having a circuit provided on one main surface is prepared in advance, and a metal heat radiating plate is arranged via a brazing material on the main surface of the ceramic substrate on which the circuit is not provided. By heating and joining a part of the brazing material so as to melt, a ceramic circuit board having a circuit on one main surface side and a heat sink on the other main surface side is produced.

Electronic parts such as semiconductor elements are mounted on the circuit of the ceramic circuit board, and operations such as wire bonding are performed to complete the circuit. In the case where the electronic components are mounted by soldering, a plating process may be performed on a desired portion in advance at an appropriate stage of the manufacturing process, if necessary.

When the circuit is joined to the ceramic substrate, when the heat radiating plate is joined to the ceramic substrate, or when the heat radiating plate is joined to the metal radiating fins, magnesium is used as a brazing material for joining the two. An aluminum alloy containing at least one element selected from the group consisting of copper, germanium, and silicon has excellent adhesion between the two,
This is preferable because a module structure excellent in heat dissipation and reliability can be obtained over a long period of time.

In particular, when the surface of the circuit on the ceramic substrate side is made of aluminum, or when the surface of the radiating plate or the metal radiating fin is made of a metal containing aluminum as a main component, JIS 2017 When aluminum alloy or JIS designation 7075 aluminum alloy is used, at the time of joining operation, these aluminum alloys are easily integrated with aluminum or aluminum alloy on the circuit surface, heat sink or heat sink fin surface,
Bonding with more excellent adhesion can be achieved, which is more preferable.

[0028]

[Example 1] As a ceramic substrate, 35
A silicon nitride substrate having a size of mm × 35 mm × 0.635 mm, a thermal conductivity by a laser flash method of 70 W / mK, and an average value of three-point bending strength of 560 MPa was prepared. Also, an aluminum plate having a size of 32 mm × 32 mm × 0.4 mm and a purity of 99.9% was prepared.

The JIS designation 2 is formed on both the front and back surfaces of the silicon nitride substrate.
Through 017 aluminum alloy foil (20 μm thickness)
The aluminum plates were stacked and pressed in a direction perpendicular to the main surface, and the aluminum plate and the silicon nitride substrate were joined while heating in vacuum at 630 ° C. for 20 minutes.

A circuit was formed by screen-printing an etching resist at a desired position on the surface of the aluminum plate and performing an etching process, thereby producing a ceramic circuit board.

On the other hand, a cooling unit made of an aluminum alloy having a size of 140 mm × 80 mm × 20 mm was prepared.
This cooling unit is provided with a water supply passage inside,
By flowing water, the heat transmitted to the unit body is exhausted.

A 20 μm-thick JIS 2017 aluminum alloy foil is sandwiched between the cooling unit and the ceramic circuit board.
Heating was performed at 5 ° C. for 5 minutes, and the module and the cooling unit were joined to produce a module structure (see FIG. 1).

With respect to the module structure, cooling performance and reliability were evaluated by the following methods. Table 1 shows the results.

<Cooling Performance Test> A cooling performance as a module was examined by mounting a heater on a circuit of a ceramic substrate and measuring the temperature of the heater with a thermocouple. The measurement was performed with the heater output during the test fixed at 100 W and the temperature of the cooling water in the water cooling unit fixed at 60 ° C.

<Reliability Test> A semiconductor element having a size of 13 mm × 13 mm × 1 mm is soldered to a circuit on a ceramic circuit board with high-temperature solder, and the temperature is reduced to −40 ° C. × 30 minutes, and then to 125 ° C. × 30 minutes. A heat cycle test was performed with this being one time, and after 500, 1000, and 3000 times, the bonding state between the solder portion under the semiconductor element, the ceramic substrate, and the water-cooled unit was determined to be SAT (ultrasonic image flaw detection). Device).

[0036]

[Table 1]

Example 2 In Example 1, after obtaining the ceramic circuit board, the entire ceramic circuit board was Ni-plated by an electroless method, and JIS designation 7075 was used for joining the ceramic circuit board and the cooling unit. A module structure was produced by the same operation as in Example 1 except that the temperature during the joining operation was set to 580 ° C. using an aluminum alloy foil, and the same evaluation as in Example 1 was performed. Table 1 shows the results.

Example 3 A silicon nitride substrate used in Example 1, an oxygen-free copper plate of 32 mm × 32 mm × 0.4 mm and a 99.9% pure aluminum plate were prepared as metal plates. Also, a mixed powder of Ag, Cu and Ti (A
g: Cu: Ti = 90: 10: 5% by mass), a PMMA binder and an appropriate amount of terpineol were prepared.

The brazing material was applied to the surface of the silicon nitride substrate by screen printing. Then, the copper plates were stacked, and the copper plate and the silicon nitride substrate were joined while heating under vacuum at 850 ° C. × 20 minutes.

A circuit was formed by screen-printing an etching resist at a desired position on the surface of the copper plate and performing an etching process. Next, the aluminum plate is laid on the surface of the silicon nitride substrate opposite to the surface to which the copper plate is bonded via a JIS designation 2017 aluminum alloy foil (thickness: 20 μm), and the pressure in the direction perpendicular to the main surface is Was loaded with a graphite jig. Then, in that state, 630 ° C. × 20 mi in vacuum
The aluminum plate and the silicon nitride substrate were joined while being heated under the condition of n, to obtain a ceramic circuit board having a circuit made of copper on one side and a radiator plate made of aluminum on the other side.

Next, the same aluminum alloy cooling unit as that used in Example 1 was prepared. Then, a thickness 2 is formed on the side of the aluminum radiator plate of the ceramic circuit board.
A 0 μm JIS 2017 aluminum alloy foil was placed, and the aluminum alloy foil was placed on the cooling unit such that the aluminum alloy foil was in contact with the cooling unit. The whole of the cooling unit, the aluminum alloy foil, and the ceramic circuit board laminated was pressed using a graphite jig. Then, the module was heated at 630 ° C. for 5 minutes in a nitrogen atmosphere to join the ceramic circuit board and the cooling unit, thereby producing a module structure. This module structure was evaluated in the same manner as in Example 1. Table 1 shows the results.

Comparative Example 1 As a ceramic substrate, 3
An aluminum nitride substrate having a size of 5 mm × 35 mm × 0.635 mm, a thermal conductivity of 170 W / mK by a laser flash method and an average value of three-point bending strength of 360 MPa was prepared, and the same operation as in Example 3 was performed. A ceramic circuit board was obtained. Furthermore, Ni-P plating was performed on the entire ceramic circuit board by an electroless method.

N having a size of 60 mm × 80 mm × 3 mm
A heat sink made of i-plated oxygen-free copper was prepared and soldered to a ceramic substrate with eutectic solder.

An aluminum alloy cooling unit having a size of 140 mm × 80 mm × 20 mm was prepared. Then, a thickness of 25 μm is formed on each surface of the heat sink and the cooling unit to which the ceramic circuit board is soldered.
Each of them was coated with a high thermal conductive silicone grease and screwed (see FIG. 2), and the same evaluation as in Example 1 was performed. The results are shown in Table 1.

Comparative Example 2 The aluminum nitride substrate of Comparative Example 1 and a metal plate for a circuit of 32 mm × 32 mm ×
An aluminum plate having a purity of 0.4 mm and a purity of 99.9% was prepared.

On the front and back surfaces of the aluminum nitride substrate,
The aluminum plates were stacked via a JIS designation 2017 aluminum alloy foil (thickness: 20 μm), and a pressure was applied in a direction perpendicular to the main surface. And 630 ° C in vacuum x
The aluminum nitride substrate and the aluminum plate were joined while heating for 20 minutes.

A circuit was formed by screen-printing an etching resist at a desired position on the surface of the aluminum plate and performing an etching process to produce a ceramic circuit board. Further, the ceramic circuit board was plated with Ni.

N having a size of 60 mm × 80 mm × 3 mm
A heat sink made of an i-plated Al-SiC composite material was prepared and soldered to a surface of the aluminum nitride substrate where no circuit was formed by eutectic solder.

An aluminum alloy cooling unit having a size of 140 mm × 80 mm × 20 mm was prepared. Then, high heat conductive silicone grease having a thickness of 25 μm is applied to surfaces of the heat sink and the cooling unit to which the ceramic circuit board is soldered, respectively, in contact with each other,
A screw was prepared (see FIG. 3). This module structure was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

[0050]

According to the module structure of the present invention, cracks due to solder under the semiconductor element and cracks in the ceramic substrate are unlikely to occur while using inexpensive metal as a heat radiating material. It has excellent characteristics of heat dissipation and reliability, and is very useful in industry.

[Brief description of the drawings]

FIG. 1 is a sectional view of a module structure according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of a module structure according to Comparative Example 1.

FIG. 3 is a sectional view of a module structure according to Comparative Example 2.

[Explanation of symbols]

 Reference Signs List 1 circuit 2 ceramic substrate 3 heat sink 4 brazing material 5 cooling unit 6 solder 7 grease

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4E351 AA07 DD10 DD21 GG04 5E322 AA11 AB02 AB09 EA10 FA06 5E338 AA02 AA18 BB71 EE01 EE02 EE28 EE33 5F036 AA01 BB01 BB08 BC06 BD03 BD13

Claims (4)

[Claims] 1. A module comprising a circuit for mounting electronic components on one main surface of a ceramic substrate, and a ceramic circuit substrate provided with a heat sink on the other main surface, joined to a cooling unit. A module structure, wherein the radiator plate is made of a metal containing aluminum as a main component, and the radiator plate and the cooling unit are joined by an aluminum brazing material. 2. The module structure according to claim 1, wherein at least a surface of the circuit of the ceramic circuit board in contact with the ceramic substrate is made of a metal containing aluminum as a main component. 3. The module structure according to claim 1, wherein the aluminum brazing material contains magnesium, copper, and / or zinc. 4. The module structure according to claim 1, wherein the ceramic substrate is silicon nitride or aluminum nitride.