JP2003282770A - Circuit board with metal base plate and module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly reliable circuit board with a metal base plate and a mobile. <P>SOLUTION: The circuit board with a metal base plate has a circuit made of aluminum having hardness of ≤250 MPa on one surface of a ceramic substrate and a heat sink made of aluminum or an aluminum alloy having hardness of 300-460 MPa on the other surface of the substrate. In addition, a metal base plate made of copper, a copper alloy, aluminum, or an aluminum alloy is bonded to the heat sink through a soldering layer having a solder void rate of <10% and a maximum solder void diameter of <1 mm. The circuit, heat sink and/or metal base plate are coated with a plated-nickel film. The module uses the circuit board. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a circuit board with a metal base plate and a module.

[0002]

2. Description of the Related Art Conventionally, in a semiconductor device used for a power module or the like, Cu, Al, an alloy containing these metals, etc. are formed on the front and back surfaces of a ceramic substrate such as alumina, beryllia, silicon nitride, aluminum nitride, etc. A circuit board is used in which the circuit and the heat sink are formed. A feature of such a circuit board is that it is possible to stably obtain a higher insulation than a composite board of a resin board and a metal board or a resin board.

The advantage of using Al or Al alloy as the material for the circuit and the heat sink is that Cu or Cu alloy is superior to Cu or Cu alloy.
Alternatively, Cu alloys cannot avoid long-term reliability because the generation of thermal stress due to the difference in thermal expansion from the ceramics substrate or solder is unavoidable, whereas Al or Al alloys have poor thermal conductivity. Although it is slightly inferior in electric conductivity to Cu or Cu alloy, it is easily plastically deformed even when subjected to thermal stress, so that stress is relaxed and reliability is dramatically improved.

[0004]

However, the plastic deformation of Al and Al alloys (hereinafter, both are also referred to as "Al, etc.") is caused by the magnitude of thermal stress and the portion of Al, etc. which is subjected to thermal stress. Depends significantly on. In particular, if plastic deformation concentrates on a part of the circuit or the heat sink, the amount of plastic deformation of the solder may be exceeded, and solder cracks may occur. In order to avoid this, high hardness Al or the like may be used, but the stress relaxation effect is reduced. Therefore, the present problem in the field is to achieve the trade-off of suppressing solder cracks as much as possible while sufficiently maintaining the stress relaxation effect on the ceramic plate.

In order to solve this problem and ensure high reliability of the module, as represented by Al / SiC,
It has been proposed to use a base plate having a thermal expansion coefficient similar to that of a ceramic substrate instead of the metal base plate. However, while such a base plate is highly reliable, it has a lower thermal conductivity than a metal base plate,
It is expensive and can only be used for special purposes.

In view of the above, an object of the present invention is to provide a high reliability module using an inexpensive metal base plate. An object of the present invention is that the occurrence of solder cracks differs between the case where a semiconductor element is soldered to a circuit and the case where a metal base plate is soldered to a heat dissipation plate.
Focusing on the influence of hardness such as Al, there are many materials such as Al to select the material and thickness to design the hardness suitable for the circuit and the heat sink, and Ni plating with excellent solder wettability. This can be achieved by applying a film, preferably by specifying the mounting position on the circuit surface of the semiconductor element, and reducing the solder void that is the starting point of the solder crack.

[0007]

[Means for Solving the Problems] That is, the present invention is as follows. (Claim 1) A hardness of 250 on one surface of the ceramic substrate.
Al circuit below MPa, hardness 300-on the opposite side
It has a heat sink made of Al or Al alloy of 460 MPa, and further, a metal base plate made of Cu, Cu alloy, Al or Al alloy is used for the heat sink, and the solder void ratio is 10% or less and the maximum solder void diameter (diameter). A circuit board with a metal base plate, wherein the circuit board, the heat dissipation plate and / or the metal base plate are bonded with a solder bonding layer of 1 mm or less, and a Ni plating film is applied to the circuit, the heat dissipation plate and / or the metal base plate. (Claim 2) The solder void ratio of the solder bonding layer portion located immediately below the circuit portion on which the semiconductor element is mounted is 5% or less, and the maximum solder void diameter (diameter) is 0.5 mm or less. The circuit board with a metal base plate according to claim 1. (Claim 3) The Ni-plated film has a thickness of 8 μm or less, and has the crystallinity and the degree of oxidation defined in the present invention. The circuit with a metal base plate according to claim 1 or 2, substrate. (Definition) Crystallinity of Ni plating film: X-ray crystal diffraction (CuKα2θ)
The full width at half maximum of the Ni (111) plane is 0.8 or less. Oxidation degree of Ni plating film: X-ray photoelectron spectroscopy (ESCA)
The peak area ratio of Ni-O to Ni-metal is 0.6 or less. (Claim 4) A module using the circuit board with a metal base plate according to any one of claims 1, 2 and 3.

[0008]

The present invention will be described in more detail below.

The circuit board of the present invention is characterized by optimizing the difference in hardness of Al and the like between the circuit and the heat radiating plate to adjust the plastic deformation when a heat history is applied, and the Ni plating film excellent in solder wettability is formed of Al or the like. The solder voids, which are the starting points of solder cracks, can be reduced by suitably applying it to the mounting surface of the semiconductor element on the circuit surface, and both the solder cracks and the ceramics board cracks of the circuit board having a circuit such as Al can be drastically reduced. That's what I did. The circuit board of the present invention is formed by forming an Al circuit on the front surface of a ceramic substrate and a heat sink such as Al on the back surface, and
It can be manufactured by applying a plating film and then soldering the semiconductor element and the metal base plate.

Conventionally, in order to improve the reliability of the circuit board, the voids in the ceramic sintered body are reduced (Japanese Patent Laid-Open No. 7-097265), and the voids at the bonding interface between the ceramic substrate and the metal plate are reduced ( Japanese Patent Laid-Open No. 11-0
No. 26640). Although these improved the reliability of the ceramic substrate itself,
The reliability of a module using a circuit board having an equal circuit was not sufficient.

In order to enhance the reliability of the module, how efficiently the heat generated from the semiconductor element (Si chip or the like) is released to the outside of the system. 2. Description of the Related Art In recent years, along with the miniaturization of electronic devices such as semiconductor devices, semiconductor elements themselves have been highly integrated and output, and the amount of heat generated during operation has also increased. A general module structure is one in which a metal base plate is soldered to the heat dissipation plate of the circuit board, and a semiconductor element is soldered to the circuit.In such a structure, a solder joint layer having a large thermal resistance is used. Reliability is essential. Therefore, how to suppress the occurrence of cracks in the solder joint layer having a large thermal resistance and how to reduce the solder voids that are the starting points of the solder cracks are important factors for improving the reliability of the module. Will be an important point. The method of reducing voids in a ceramics sintered body having a high heat conductivity and reducing voids at the joint interface has reached the limit.

The first requirement that the circuit board of the present invention must have is the definition of Vickers hardness of Al or the like. That is, for a heat sink having a large soldering area and the occurrence of solder cracks being a controlling factor of the defect, Al having a slightly higher hardness and a Vickers hardness of 300 to 460 MPa is selected, and the ceramic substrate is affected by the circuit pattern. It is necessary to select Al or the like having a low hardness and a Vickers hardness of 250 MPa or less for a circuit in which the occurrence of cracks is dominant.

Since soft Al or the like is easily plastically deformed, thermal stress is relieved even when the circuit board is subjected to thermal history, and cracks are less likely to occur on the ceramic substrate, but the plastic deformation amount is less than that of solder. If it exceeds, the solder will be broken and solder cracks will easily occur. Conversely, hard Al or the like easily causes cracks in the ceramic substrate, but suppresses solder cracks.

In the circuit board for the module, since the metal base plate is soldered on almost the entire surface of the heat dissipation plate, thermal stress on the solder joint layer is large and solder cracks are likely to occur and progress. On the other hand, the circuit surface is a relatively small soldering area because only semiconductor elements are attached, and the soldering area is usually about 1/10 to 1/3 of the circuit area. Further, since the thermal stress on the ceramic substrate is concentrated on the end portion of the circuit pattern, the pattern shape cannot be ignored. It does not cause much problems on the heat dissipation surface of a so-called "solid pattern" without a pattern, but on the circuit surface, it occurs at the edge part along the pattern, and "horizontal cracks" that proceed inside the pattern deteriorate heat dissipation. Cause

From the above, in the circuit board of the present invention, the Vickers hardness of the circuit such as Al is set to 250 MPa or less to suppress cracks generated in the ceramic substrate,
Vickers hardness of heat sink such as Al is 300-460MPa
As a result, the generation of solder cracks is suppressed.

The Vickers hardness of the circuit such as Al is 250MP
If it exceeds a, the plastic deformation due to thermal stress becomes non-uniform,
There is a possibility that the partial deformation becomes large and plating or the peeling of the bonding wire may occur. The smaller the hardness is, the more preferable it is, but if it is too soft, it is easily scratched. Therefore, the hardness is preferably 180 to 220 MPa. On the other hand, if the Vickers hardness of the heat dissipation plate is more than 460 MPa, it becomes difficult to plastically deform and cracks easily occur in both the ceramic substrate and the solder bonding layer. Further, when the pressure is less than 300 MPa, the plastic deformation becomes easy, and therefore, when it is subjected to repeated heat history, large deformation occurs, and solder cracks easily occur.
Particularly preferable Vickers hardness of the heat sink is 350 to 430.
It is MPa.

The Vickers hardness is a method in which a fine indenter is driven to apply a weight to read the hardness, and is widely used as a method for measuring the hardness of metals and ceramics. Since the value may be slightly different depending on the measurement condition, in the present invention, the condition is a weight of 9.8 N and a holding time of 15 seconds.

The hardness in the present invention is the hardness of the circuit and the heat sink, not the hardness of Al before joining. Since Al or the like is usually bonded to a ceramic substrate by heating it to 500 to 640 ° C. using a bonding material, the microstructure is changed by heat treatment, and the bonding material diffuses to lower the purity of Al or the like. . Further, although heat treatment is also performed after joining, the characteristics of Al and the like change. For these reasons, it is meaningless to strictly define the hardness of Al or the like before joining.

The hardness of Al or the like can be adjusted by selecting a material, heat treatment conditions, or both. As for the material, the purity is selected in consideration that Al and the like after joining become softer in a higher purity product. Those commercially available as pure Al usually have a quite wide range of 99.0 to 99.999%, and a large difference occurs in hardness. That is, 99.5%
It is difficult to set the Vickers hardness of the following Al to 250 MPa or less after joining, and it is difficult to set the Al of 99.9% or more to 300 MPa or more after joining. Therefore,
In the present invention, it is preferable to select a high-purity Al material for the Al circuit and an Al alloy or a relatively low-purity Al for the heat dissipation plate. An example of the Al alloy is AA
Symbols such as 3003 and other Al-Mn alloys, 50
52 and other Al-Mg alloys.

Next, a method of adjusting the heat treatment conditions will be described. When manufacturing the circuit board of the present invention, the joining temperature between Al or the like and the ceramic substrate is the annealing temperature of Al of 30.
Since it becomes higher than 0 to 350 ° C., the cooling condition after joining becomes important. The hardness decreases when the cooling is slowly performed at 2 ° C./min or less in the temperature range higher than the annealing temperature, and the hardness increases when the cooling is performed faster at 5 ° C./min or more.

The second requirement that the circuit board of the present invention must have is that the solder void ratio of the solder joint layer between the heat sink and the metal base is 10% or less and the maximum solder void diameter (diameter) is 1 mm or less. That is. In order to efficiently dissipate the heat generated in the semiconductor element to the outside of the system, the solder voids in the solder joint layer having a large thermal resistance have a great influence, so the solder void ratio must be 10% or less. If the solder void ratio is more than 10%, the thermal resistance increases,
Module function deteriorates. As a result, heat is accumulated in the semiconductor element, a large thermal stress is applied, and the semiconductor element itself is damaged.

On the other hand, the present inventors have found that the solder voids in the solder joint layer are the starting points of the solder cracks, and that the larger the diameter of the solder voids, the more easily the solder cracks occur. The solder joint layer between the heat dissipation plate of the circuit board and the metal base plate undergoes a large strain due to the difference in thermal expansion between the ceramics board and the metal base plate when heat is applied. This strain is accumulated in the solder joint layer, and when it exceeds the limit, a solder crack occurs. The solder cracks lead to an increase in thermal resistance, which deteriorates the module function. The strain applied to the solder joint layer at the time of heat load is further increased at the solder void, and becomes a starting point of the solder crack. Therefore, in the present invention, the maximum solder void diameter (diameter) must be 1 mm or less.

In particular, thermal stress is further increased at a portion of the solder bonding layer between the heat dissipation plate of the circuit board and the metal base plate, which is located immediately below the semiconductor element, so that the solder void ratio is 5 at that portion. %, The maximum solder void diameter (diameter) is preferably 0.5 mm or less. The solder void ratio and the maximum solder void diameter (diameter) can be measured using a soft X-ray flaw detector and an image analyzer.

In order to reduce the solder void ratio and the maximum solder void diameter in the solder joint layer between the heat dissipation plate of the circuit board and the metal base plate, the solder wettability of the surface to be soldered is increased. For that purpose, a Ni plating film is applied to the circuit, the heat dissipation plate and / or the metal base plate. Even if the metal base plate is not limited to Al or the like and is made of a Cu material, it is preferable that a Ni plating film is applied in order to prevent deterioration of reliability due to oxidation and reaction with solder.

The Ni plating film applied in the present invention has a thickness of 8 μm.
m or less, especially 3 to 7 μm, the “crystallinity” defined as the half-value width of the Ni (111) plane in the X-ray crystal diffraction (CuKα2θ) of the Ni plating film is 0.8 or less, and X-ray photoelectron spectroscopy The "oxidation degree" defined as the peak area ratio of Ni-O (Ni-O / Ni-metal) to Ni-metal in (ESCA) is preferably 0.6 or less. The heat dissipation characteristics of the module assembled using such a circuit board become much better.

To manufacture the circuit board of the present invention, a circuit,
The heat radiation plate and the metal base plate always go through the soldering process. For soldering, there are a method of reflowing in the air or nitrogen using a flux and a method of reflowing in a hydrogen atmosphere without using a flux, but either method can be adopted in the present invention. As solder, S
n-Pb type solder, Sn-Ag type, Sn-Ag-Cu
A Pb-free solder such as a system, Sn-Zn-Bi system, or Sn-Ag-Cu-Bi system is used.

On the other hand, there are an electroplating method and an electroless plating method for applying the Ni plating film, but any of them can be adopted in the present invention. The electroplating method has a good reactivity between the Ni component of the plating film and the Sn component of the solder, but it has a feature that the handling is complicated and thus the cost is high and it cannot be applied to a fine pattern. On the other hand, the electroless plating method has an advantage that it can be applied to fine patterns and is inexpensive, but the reactivity between the Ni component and the Sn component is not always sufficient.

Therefore, in the present invention, in order to enhance the reactivity between the Ni component of the plating film and the Sn component of the solder, the crystallinity of the Ni plating film is 0.8 or less and the degree of oxidation is 0.6 or less. It is preferable. Such a Ni plating film can be applied as follows.

The surface of the circuit to which the Ni plating film is applied, the heat radiating plate and / or the metal base plate is preferably smoothed by grinding, physical polishing, chemical polishing or the like, and the surface roughness is Ra ≦ 0. It is preferably 2 μm. The surface roughness may be measured by contact method or non-contact method, but Al
It is desirable to use a non-contact type surface roughness meter such as a laser type for measuring soft metals such as.

In the present invention, the electroless Ni-P plating film having a thickness of 1 to 5 μm, preferably 3.5 to 4.5 μm is applied, and then the total film thickness is 8 μm or less.
A preferable example is to perform B plating. Instead of such two-step electroless Ni plating, one-step electroless Ni-B plating may be used, but it takes time. The electroless Ni-P plating can be performed by a general method, and there is no adverse effect even if the deposition rate is increased as much as possible. On the other hand, the deposition rate of electroless Ni-B plating is 0.
It is preferably 7 to 3 μm / hr. Further, it is desirable to prepare the electroless Ni-B plating solution so that the B concentration in the Ni plating film is at most 0.1%.

The portion formed by the electroless Ni-B plating film is 1 μm.
When it is less than m, the crystallinity of the Ni plating film is insufficient and the degree of oxidation is increased, and the reactivity with the Sn component of the solder cannot be increased to a target level. Further, even if the portion formed by electroless Ni—B plating exceeds 5 μm, the effect of reducing the degree of oxidation does not increase. On the other hand, if the total film thickness is more than 8 μm, the crystallinity of the Ni plating film is disturbed and the stress of the Ni plating film is increased, so that the reliability of the circuit board is not further improved. Further, if the deposition rate is less than 0.7 μm / hr, the productivity is poor, and impurities may be taken into the Ni plating film, and if it exceeds 3 μm / hr, the Ni plating film quality becomes non-uniform and high crystallinity occurs. It becomes difficult to obtain a Ni-plated film having good properties.

A further low degree of oxidation of the Ni plating film is realized,
In order to enhance the reactivity with the Sn component of the solder, electroless Ni
-It is desirable to perform sufficient cleaning and drying after the B plating. It is preferable that the washing is performed with a surface treatment agent containing an unsaturated fatty acid such as oleic acid after washing with water. The surface treatment agent is preferably one that imparts water repellency to the Ni plating film or one that can remove oxides of the Ni plating film by etching.
The former has, for example, the product name "Suffthru" manufactured by Okuno Chemical Industries Co., Ltd., and the latter has, for example, a 5% sulfuric acid aqueous solution.
Desirably, the drying is performed after substituting with an alcohol solvent.

The ceramic substrate used in the present invention is
A silicon nitride substrate or an aluminum nitride substrate having a thermal conductivity of 70 W / mK or more is preferably used for a module.

In order to form an Al circuit and a heat sink such as Al on the ceramic substrate, these patterns are joined, the plates such as Al are joined and then etched, or both of them are used together. In either case, it is necessary to bond the ceramic substrate to the circuit and the heat sink. Although there is a method of joining which does not use a joining material such as the molten metal method, it is preferable to use an Al—Cu—Mg alloy foil for joining in the present invention. The bonding material is not limited to this, but Al-Si type, Al-Ge type, or M
A system in which g is added can also be used.

The thickness of the bonding material is 10 to 5 depending on the type.
It is about 0 μm. If the thickness is less than 10 μm, joining becomes difficult, and if it exceeds 50 μm, the alloy component diffuses into Al or the like to increase the number of hard portions, which causes a decrease in reliability when subjected to heat history. The preferable thickness of the bonding material is 1
It is 5 to 35 μm. The bonding material is the ceramic substrate side,
It may be arranged on either side of Al or the like.

In the present invention, a plate such as Al, a pattern, or both are arranged on both sides of the ceramic substrate with the above alloy foil interposed therebetween, and the plate is arranged in the direction perpendicular to the ceramic substrate.
It is preferable to apply a pressure of 98 to 9.8 MPa. The pressurization can be performed by placing a weight on the laminate or mechanically sandwiching it with a jig or the like.

In the conventional manufacture of a circuit board, a weight is placed and pressure is applied at the time of joining a metal plate and a ceramics substrate, but even if the pressure is high, at most 9.
It is about 8 kPa. With such a pressure, the plate made of Al or the like can follow only the relatively gentle warpage and undulation of the ceramic substrate. On the other hand, 0.98-
When a high pressure of 9.8 MPa is applied, sufficient bonding can be stably obtained, and plastic deformation of Al or the like occurs relatively uniformly, so that it becomes easy to manufacture a highly reliable circuit board. Preferred pressurization is 1.47-7.84MP
a.

The obtained bonded body is then etched if necessary. Etching is not necessary when joining the circuit or heat sink pattern. The thickness of the circuit is not particularly limited and is generally 0.3 to 0.5 mm. The thickness of the heat sink is 0.1 to 0.5 mm.

[0039]

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

Examples 1 to 8 Comparative Examples 1 to 6 Commercially available aluminum nitride substrates and silicon nitride substrates were prepared. Each of them has a size of 20 × 20 × 0.635 mm, and the thermal conductivity by the laser flash method is 175 W / mK for the aluminum nitride substrate and 72 for the silicon nitride substrate.
W / mK, 3 point bending strength, aluminum nitride substrate is 4
20MPa, silicon nitride substrate is 780MPa.

An Al plate and a bonding material were stacked on the front and back surfaces of the ceramic substrate, a carbon plate was pressed against the ceramic substrate, and pressed against the ceramic substrate in a direction perpendicular to the surface. The joining was performed under pressure in a nitrogen atmosphere at a temperature of 550 to 635 ° C.

An etching resist was screen-printed on the obtained bonded body, which was then etched with a ferric chloride solution, and then the resist was peeled off. As a result, a square (corner R is 2 mm) pattern was formed on the circuit surface and the heat dissipation surface in the central portion of the ceramic substrate (creeping distance 1 mm).

Then, in Examples 1 to 4 and Comparative Examples 1 to 6, an electroless Ni-P plating film (plating solution: trade name "Top Nicolon" manufactured by Okuno Chemical Industries Co., Ltd.) was used to obtain an average thickness of 6 μm.
After that, it was replaced with isopropyl alcohol and air blow dried. The thickness of the plating film was measured using a fluorescent X-ray plating thickness measuring device (“XA-1050” manufactured by Fisher Co.).

In addition, in Examples 5 to 8, the above electroless Ni-P plating film was applied to a thickness of 3 to 4 μm, and then an electroless Ni-B plating film (plating solution: product name "BEL801" manufactured by Uemura Kogyo Co., Ltd.). ) Was applied so that the total average thickness was 6 μm. The deposition rate of electroless Ni-B plating is 1.0 to
The temperature of the plating solution was adjusted to be 1.2 μm / hr. After that, the surface of the Ni plating film was subjected to surface treatment using a commercially available etching solution (trade name "ET-140" manufactured by World Metal Co., Ltd.) for the purpose of removing oxides, followed by replacement with isopropyl alcohol and air blow drying. It was

With respect to the obtained circuit board, the crystallinity and oxidation degree of the Ni plating film, and the Vickers hardness of the circuit and the heat sink were measured as follows. The results are shown in Table 1.

(1) Ni measured by a crystalline X-ray crystal diffraction (CuKα2θ) device ("Geiger Flex RAD-IIX" manufactured by Rigaku Denki Co., Ltd.) of Ni plating film
The full width at half maximum of the peak of the (111) plane was determined. (2) Degree of oxidation of Ni plating film Peak of Ni-O (Ni-O / Ni-metal) with respect to Ni-metal measured by X-ray photoelectron spectroscopy (ESCA) measuring device ("ESCA-1000" manufactured by Shimadzu Corporation) The area ratio was calculated. (3) Vickers hardness The cross section of the circuit board was cut out, and the Vickers hardness was measured at a depth of 100 μm from the surface of each of the circuit and the heat sink. The measurement was performed under the conditions of a weight of 9.8 N and a holding time of 15 seconds.

On the other hand, with respect to the circuit board manufactured under the same conditions as above, solder pieces (Pb / Sn = 90/10, size 10 × 10 × 0.1) having flux applied to the circuit surface thereof.
mm) and Si chip (10 × 10 × 0.4 mm)
Was placed. In a hydrogen atmosphere, this was heated up to a temperature of 150 ° C at a rate of 17 ° C / min, and then 2.4 ° C / min.
After raising the temperature at a rate of 3 to raise the temperature to 350 ° C., it was rapidly heated at room temperature under the condition of natural cooling for soldering. During the period from the melting of the solder to the temperature of 350 ° C., the circuit board was vibrated so that the solder voids would come off.
Then, the solder void ratio and the solder void diameter immediately below the soldered Si chip were measured using a soft X-ray flaw detector (“PRO-TEST100” manufactured by Softex) and an image analyzer. The results are shown in Table 1.

Next, regarding the circuit boards manufactured by the steps of Examples 1 to 4 and Comparative Examples 1 to 3 in which the Si chips were soldered to the circuit as described above, the heat dissipation plate of Table 1 was used.
The metal base plate (40 × 40 × 4 mm) shown in 1 was soldered. For soldering, solder pieces with flux applied (Pb / Sn = 50/50, size 20 × 20 × 0.3 m)
m) was placed on a metal base plate, the heat dissipation plate surface of the circuit board was placed on the metal base plate, and then heated in a hydrogen atmosphere until the temperature reached 220 ° C. At this time, the circuit board was vibrated so that the solder voids were removed. Then soft X
The solder void ratio and the solder void diameter were measured using a wire flaw detector. The results are shown in Table 1.

On the other hand, the circuit boards manufactured through the steps of Examples 5 to 8 and Comparative Examples 4 to 6 and having the Si chip soldered to the circuit as described above were soldered without using flux. Other than the above, the metal base plate was soldered to the heat dissipation plate in the same manner as above.

Using these circuit boards, an Al heat sink was attached to a metal base plate to assemble a simple module, and the power supply amount to the Si chip was 145 W and the Al heat sink temperature was 65 ° C., and the heat between the Si chip and the Al heat sink was set. The resistance was measured and used as the initial value.

After that, a heat cycle test of the circuit board was subsequently performed. Heat cycle test is -40 ° C x 30
Minutes → room temperature × 10 minutes → 125 ° C. × 30 minutes → room temperature × 10 minutes as 1000 cycles and 2000 cycles, and then the thermal resistance between the Si chip and the Al heat sink was measured in the same manner as above. The increase rate of thermal resistance with respect to the initial value was calculated. The results are shown in Table 1.

Further, after 2000 times of the heat cycle test, the circuit board was heated to 400 ° C. on a hot plate to remove the solder joint layer, the circuit and the heat dissipation plate, and it was examined whether or not cracks were generated on the ceramic substrate. The results are shown in Table 1.

[0053]

[Table 1]

As is clear from Table 1, all the circuit boards (Examples) of the present invention were subjected to the heat cycle test 2000.
Even after the rotation, the rate of increase in thermal resistance was small and the reliability was high. On the other hand, in the comparative example, any one of the Vickers hardness, the solder void rate, and the solder void diameter was outside the range of the present invention, so that the increase rate of the thermal resistance after the heat cycle test was large.

[0055]

According to the present invention, a circuit board with a metal base plate and a module with high reliability are provided.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Nobuyuki Yoshino             1 Shinkaimachi, Omuta City, Fukuoka Prefecture             Ceremony company Omuta factory

Claims (4)

[Claims] 1. A hardness of 25 on one surface of a ceramic substrate.
Al circuit below 0 MPa, hardness 300 on the opposite side
Having a heat sink made of Al or Al alloy of ~ 460 MPa,
Further, a metal base plate made of Cu, Cu alloy, Al or Al alloy is bonded to the heat dissipation plate via a solder bonding layer having a solder void ratio of 10% or less and a maximum solder void diameter (diameter) of 1 mm or less, A circuit board with a metal base plate, characterized in that a Ni plating film is applied to a circuit, a heat sink and / or a metal base plate. 2. The solder void ratio of the solder bonding layer portion located immediately below the circuit portion on which the semiconductor element is mounted is 5% or less, and the maximum solder void diameter (diameter) is 0.5 mm or less. The circuit board with a metal base plate according to claim 1. 3. The circuit with metal base plate according to claim 1, wherein the Ni plating film has a thickness of 8 μm or less and has the crystallinity and the degree of oxidation defined in the present invention. substrate. (Definition) Crystallinity of Ni plating film: X-ray crystal diffraction (CuKα2θ)
The full width at half maximum of the Ni (111) plane is 0.8 or less. Oxidation degree of Ni plating film: X-ray photoelectron spectroscopy (ESCA)
The peak area ratio of Ni-O to Ni-metal is 0.6 or less. 4. A module using the circuit board with a metal base plate according to claim 1, claim 2, or claim 3.