JP3529085B2 - Circuit board with heat sink - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power module electronic circuit component, and more particularly to a circuit board with a heat sink suitable for an intelligent power module.

In recent years, with the high performance of industrial equipment such as robots and motors, the transition of high power and high efficiency inverters and other high power modules has progressed, and the heat generated from semiconductor elements has also continued to increase. . In order to efficiently dissipate this heat, various methods have been taken in high power module circuit boards. Recently, ceramic substrates with good heat conduction have become available, so after joining a metal plate such as a copper plate on the substrate to form a circuit, the semiconductor is mounted as it is or after plating or other treatment. A heat-dissipating copper plate is joined to the opposite surface of the ceramics substrate, and a copper base plate having a thickness of about several mm is soldered to the heat-dissipating copper plate and then screwed to a heat sink such as aluminum or copper. .

However, when such a circuit board with a heat sink is used in a high temperature environment, cracks may occur in the ceramic substrate without being subjected to a mechanical shock from the outside. The reason is that the heat expansion coefficient of the heat sink of aluminum, copper or the like is 16 to 23 × 10 ⁻⁶ / ° C., and that of the ceramic substrate of aluminum nitride or the like is 4 to 7 ×.
This is because it is different from about 10 ⁻⁶ / ° C., so that thermal stress remains on the ceramic substrate when subjected to a heat cycle.

Therefore, it has been proposed to use a heat sink having a structure in which a silicon carbide sintered body is impregnated with aluminum, which has a good thermal conductivity and a thermal expansion coefficient close to that of a ceramic substrate (Japanese Patent Laid-Open No. 9-157773). Gazette)
Since this product has poor workability such as cutting, there was a problem in productivity of the circuit board. In addition, when soldering the copper base plate or screwing the heat sink, it is necessary to pay close attention not to pinch foreign matter, which is also one of the reasons that productivity is not improved.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a circuit board with a heat sink, which is highly reliable against heat cycles and has high productivity.

[0006]

That is, according to the present invention, a ceramic substrate is provided with a circuit on one surface and a heat radiating plate on the opposite surface, and the heat radiating plate of the circuit substrate is provided with or without a base plate. A heat sink mounted circuit board with a heat sink, characterized in that the material of the heat sink is silica-alumina fiber reinforced aluminum or aluminum alloy, and in particular, the heat sink and the heat dissipation plate of the circuit board. Alternatively, the base plate and the base plate are joined together via a joining layer in which an alloy layer containing an Al component and a Ni component is present.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail below. The material of the ceramic substrate used in the present invention is as follows.
Although silicon nitride, aluminum nitride, alumina, etc. are used, aluminum nitride is suitable for power modules.
Particularly, thermal conductivity of 120 W / mK or more, bending strength of 35 kg
/ Mm ² or more, volume resistivity in air at 150 ° C 1 ×
An aluminum nitride sintered body having a resistivity of 10 ¹³ Ω · cm or more is suitable, and its manufacturing method is described in detail in the examples of Japanese Patent Application No. 9-121995.

Regarding the material of the circuit, the heat dissipation plate and the base plate, copper or copper alloy is most suitable in consideration of electric conductivity and heat conductivity. Aluminum or aluminum alloys are used when durability against thermal stress is emphasized. Furthermore, a copper-third metal-aluminum clad foil can also be used, which provides both the electrical conductivity of copper and the durability of aluminum. Specific examples of the third metal in the clad foil include nickel, titanium,
Examples include chromium and zirconium.

The metal used for the circuit, the heat dissipation plate and the base plate may have a surface plated with nickel. Especially as described later, the heat sink and the base plate,
When joining the heat sink and the heat sink to the joining layer
An alloy layer containing Ni and Ni components, or copper-
When forming a circuit or heat sink having a nickel-aluminum clad structure on a ceramic substrate, it is preferable that either one or both of the metals be nickel-plated. The thickness of nickel plating is 3-20μ
It is about m.

The thickness of the circuit is preferably 0.1 to 0.5 mm. If the thickness is too thin, the current capacity becomes small and the circuit capability is limited, and if the thickness is too thick, the ceramic substrate is subject to large thermal stress due to the difference in thermal expansion, and the durability of the circuit substrate deteriorates.

The thickness of the heat sink is preferably 0.1 to 1.0 mm. If the thickness is too thin, the cushioning effect between the circuit board and the base plate or heat sink will decrease,
On the other hand, if the thickness is too large, a great amount of thermal stress will be applied to the ceramic substrate, and the durability of the circuit substrate will deteriorate.

Further, the thickness of the base plate is preferably 5 mm or less. If the thickness is too thin, the thermal shock to the heat cycle cannot be alleviated, and the metal component of the brazing material diffuses into the heat dissipation plate to change the heat conduction characteristics. Also, if the thickness is too thick, it becomes heavy and difficult to handle. Such a base plate is not always necessary in the present invention, and the heat sink can be directly joined to the heat dissipation plate of the circuit board. By attaching the heat sink to the heat dissipation plate via the base plate, there is an advantage that the thermal shock to the heat cycle can be remarkably alleviated and the durability is further improved.

As a method of forming a circuit and a heat dissipation plate on a ceramics substrate (manufacturing a circuit board having no heat sink), a method of etching a bonded body of a ceramics substrate and a metal plate, a circuit punched from the metal plate or It can be performed by a method of joining the pattern of the heat sink to the ceramic substrate.

The metal plates or patterns can be joined by a brazing method using a brazing material containing an active metal component, a joining method using an organic adhesive, a DBC method, or the like. For the power module, the ceramic substrate is an aluminum nitride substrate, and copper is suitable for the metal. In that case, a brazing method using a brazing material containing an active metal component is used.

The metal component of the brazing material containing the active metal component is
It contains silver and copper as main components, and an active metal as a sub-component in order to ensure wettability with the ceramic substrate during melting. Specific examples of the active metal component are titanium, zirconium, hafnium, niobium, tantalum, vanadium and their compounds. As a ratio of these, silver 70 to 100
Parts (weight parts, the same applies hereinafter), total amount of copper 30 to 0 parts 100
3 to 35 parts of active metal per part.

When a metal plate or pattern made of aluminum or its alloy is bonded to a ceramic substrate, the brazing filler metal contains Al and Si as main components, and copper is used to ensure wettability with the ceramic substrate during melting. And an active metal as an accessory component. These ratios are aluminum 70-
Total amount of 95 parts, 30 to 5 parts of silicon and 1 to 5 parts of copper 1
The active metal is 1 to 35 parts per 100 parts.

The metal component of the brazing material is usually prepared by adding an organic solvent and, if necessary, an organic binder to the metal component and mixing them with a roll, a kneader, a universal mixer, a ladle mixer or the like to prepare a paste for use. To be done. As the organic solvent, methyl cellosolve, terpineol, isophorone, toluene, etc., and as the organic binder, ethyl cellulose, methyl cellulose, polymethacrylate, etc. are used.

The material of the heat sink used in the present invention is aluminum or aluminum alloy reinforced with silica-alumina fiber.

The silica-alumina fiber preferably has an alumina content of 60% by weight or more, particularly 80% by weight or more, an average fiber diameter of 1 to 10 μm, and an average fiber length of 0.5 mm or more. The coefficient of thermal expansion of the formed aluminum or aluminum alloy is close to that of the ceramic substrate. On the other hand, as aluminum or an aluminum alloy, in addition to aluminum, an alloy of aluminum and silicon or the like is used.
A (JIS standard) is most suitable.

The ratio of silica-alumina fiber to aluminum or aluminum alloy is 2: 1.
It is preferable to contain 0 to 40% by volume, especially about 30% by volume. Such a fiber-reinforced aluminum or aluminum alloy is a preform made of silica-alumina fiber and having a molding density of 0.5 to 2.3 g / cm ³ . Can be molded and impregnated with aluminum or an aluminum alloy, to produce the same. If the molding density of the preform is less than 0.5 g / cm ³ , the thermal expansion coefficient of the heat sink will be large, and if it exceeds 2.3 g / cm ³ , the thermal conductivity will decrease.

In order to impregnate a silica-alumina fiber preform with aluminum or an aluminum alloy, the preform is preheated to a temperature of about 200 to 600 ° C.
It is preferable to carry out at a pressure of 00 to 700 kgf / cm ² . If the preheating temperature is less than 200 ° C, the temperature difference with the molten metal is large, and the impregnation speed decreases and the impregnation varies.
On the other hand, if it exceeds 600 ° C, the cooling rate becomes small and the productivity is lowered. On the other hand, if the impregnation pressure is less than 300 kgf / cm ² , the impregnation rate will decrease and the impregnation will vary.
If it exceeds 0 kgf / cm ² , the preform is compacted.

After impregnating with aluminum or aluminum alloy and cooling, the member is cut out in the direction parallel to the fiber length. The obtained member has high thermal conductivity, a thermal expansion coefficient close to that of ceramics, and excellent machinability, and is suitable for the heat sink material of the circuit board of the present invention. To attach this member to the heat sink of the circuit board as a heat sink of the circuit board of the present invention with or without the base plate, the surface parallel to the silica-alumina fiber length is bonded to the heat sink or the base plate. To do.

The heat sink has a larger area than the heat radiating plate or the base plate, and a flat plate shape, a rectangular parallelepiped shape or a fin shape is used.

When the heat sink is attached to the heat dissipation plate of the circuit board, it is carried out through a joining layer in which an alloy layer containing an Al component and a Ni component is present. When the heat sink is attached to the base plate, this joining layer is used. In addition to the method of interposing, a physical means such as screwing can be used.

In order to fabricate the circuit board with the heat sink of the present invention by integrating the circuit board, the base plate and the heat sink, or the circuit board and the heat sink, a method of joining each of them and any two or more of them. A method of joining members in advance and joining them, or a method of joining all the members or a part of the members at the same time as the production of the circuit board by utilizing a heat source at the time of producing the circuit board is adopted.

One of the features of the present invention is that, in joining these members, a heat sink and a heat sink of a circuit board, or a heat sink and a base plate, and an alloy layer containing an Al component and a Ni component are present. That is, they are joined through layers. As a result, the circuit board with a heat sink has higher reliability than the conventional soldering method using Pb-Sn eutectic solder.

In order to join with such a joining layer interposed, either or both of the heat dissipation plate (the base plate when the base plate is interposed) and the heat sink are nickel-plated, and they are arranged in direct contact with each other. It can be performed by heat treatment. Heat treatment is 1 × 10 ^-4 Torr
It is desirable that the heating furnace is carried out under a vacuum of a certain degree, and the heating furnace such as an infrared heating furnace can rapidly raise the temperature and can perform delicate temperature control. The heating raises the temperature to near the eutectic point of aluminum and nickel, slightly melts the interface between aluminum and nickel, and then cools at a rate of 1 ° C./minute or more. Specifically, the temperature is 620 to 630 ° C., and the value is 3-1.
Hold for 0 minutes and cool at a rate of 1 ° C./minute or more.

[0028]

EXAMPLES The present invention will be described in more detail below with reference to examples.

Preparation of Heat Sink A preform made of silica-alumina fiber shown in Table 1 was preheated at 500 ° C. and immersed in an aluminum alloy (AC3A) melted at 750 ° C. Impregnation pressure is 500 kgf
/ Cm ² and the impregnation rate was 12.5 mm / sec. After cooling, the member was taken out and used as a heat sink material, and its thermal conductivity, thermal expansion coefficient by the laser flash method, and machinability by a milling machine were evaluated. The machinability was rated as ◯ when it was comparable to the machining speed during machining of the aluminum alloy (AC3A). The results are shown in Table 1.

[0030]

[Table 1]

Manufacture of Ceramic Substrate 96 parts of aluminum nitride powder and 4 parts of yttria powder were premixed in a ball mill for 30 minutes, 1 part of oleic acid was added and further mixed for 30 minutes. To this mixture, 8 parts of methyl cellulose was added and mixed for 1 minute with a high-speed mixer, then a mixed solution of 3 parts of glycerin and 12 parts of water was added while stirring the mixer, and mixed for 2 minutes to obtain a granulated product. The granulated product was kneaded with a roll and then charged into an extrusion molding machine while performing vacuum deaeration, and extruded into a green sheet shape. Next, this is punched into a size of 58 mm × 45 mm × 0.635 mm, dried at 80 ° C. for 20 minutes, and then in air at 500 ° C.
After removing the binder by heating for 1 hour in a reducing atmosphere,
Pressureless sintering was performed under the condition of holding at 1900 ° C. for 1 hour to manufacture an aluminum nitride substrate. The thermal conductivity of the obtained aluminum nitride substrate was 130 W / mK, the bending strength was 37 kg / mm ² , and the volume resistivity in air at 150 ° C. was 1 × 10 ¹⁴ Ω · cm.

Preparation of circuit board A Silver powder 75 parts, copper powder 25 parts, zirconium powder 15
Part, 15 parts of terpineol, and 1 part of a solid solution of a toluene solution of polyisobutyl methacrylate as an organic binder were added and kneaded to prepare a brazing paste. This brazing paste was applied to both sides of the aluminum nitride substrate manufactured above. The coating amount (after drying) at that time is 6 to 8
It was set to mg / cm ² .

Next, a copper plate (thickness: 0.3 mm) is placed in contact with the brazing material paste application surface, and the degree of vacuum is 1 × 10 ^-5.
A joined body was manufactured by heating at a temperature of 900 ° C. for 30 minutes under a high vacuum of Torr or less and then cooling at a temperature decrease rate of 2 ° C./minute.

After applying a UV curing type etching resist on the copper plate of this bonded body by screen printing,
Etching is performed using a cupric chloride solution to dissolve and remove unnecessary portions of the copper plate, and the etching resist is peeled off with a 5% caustic soda solution to form a copper circuit pattern on one side and a solid copper pattern on the other side. (57 mm x 44 m
m, corner R2 mm) was formed. Between the copper circuit patterns, there is a residual unnecessary brazing material or a reaction product of the active metal component and the aluminum nitride substrate.
It was removed by immersing it in a 10% ammonium fluoride solution for 10 minutes. Then, nickel plating (thickness 5 μm) was applied to produce a circuit board A.

Preparation of Circuit Board B To 100 parts of a mixed powder consisting of 86 parts of aluminum powder, 10 parts of silicon powder, 4 parts of copper powder and 15 parts of titanium hydride powder, 15 parts of terpineol and a toluene solution of polyisobutyl methacrylate are added, A brazing material paste was prepared by kneading and applied to both surfaces of the aluminum nitride substrate manufactured above. Application amount at that time (after drying)
Was 3.0 mg / cm ² .

Next, an aluminum plate (purity 99.5%, thickness 0.5 mm) is placed in contact with the brazing material paste application surface, and the temperature is set to 6 at a high vacuum of a vacuum degree of 1 × 10 ^-5 Torr or less.
After heating at 40 ° C. for 30 minutes, it was cooled at a temperature decrease rate of 2 ° C./minute to manufacture a joined body.

Next, a UV-curing type etching resist is applied on the aluminum plate of this joined body by screen printing, and then an etching treatment is carried out using a cupric chloride solution so that a space between the aluminum plate unnecessary portion and the aluminum circuit is obtained. The existing unnecessary brazing material is dissolved and removed, and the etching resist is peeled off with a 5% caustic soda solution to form a circuit board B having an aluminum circuit on one side and a solid aluminum pattern (57 mm x 44 mm, corner R2 mm) on the other side. It was made.

Manufacturing of Circuit Board C Both surfaces of the bonded body (bonded body in which aluminum plates are bonded to both sides of an aluminum nitride substrate) manufactured in the manufacturing process of the circuit board B were nickel-plated (thickness: 5 μm). A copper plate having a thickness of 0.3 mm is placed in contact with the infrared heating type bonding furnace, and a high vacuum with a vacuum degree of 0.1 Torr or less is used.
Bonding was performed under the conditions of 30 ° C. × 5 minutes. The obtained joined body is etched in the same manner as in the production of the circuit board B, and a circuit made of aluminum-nickel-copper clad foil is formed on one surface of the aluminum nitride substrate and a heat dissipation plate made of a clad foil having the same structure is formed on the other surface. A circuit board C having

Joining of Base Plate The base plate was joined to the heat dissipation plate of the circuit board by a to c shown in Table 2.

[0040]

[Table 2]

Attachment of Heat Sink According to Table 3 to 3, the heat sink was attached to the heat dissipation plate of the circuit board with or without the base plate.

[0042]

[Table 3]

Examples 1 to 9 Comparative Example 1 A circuit board with a heat sink was manufactured by various combinations shown in Table 4 for manufacturing the circuit board, joining the base plate and attaching the heat sink.

A heat cycle (thermal shock) test was performed on the obtained circuit board with a heat sink. The heat cycle test was carried out in the air at −40 ° C. for 30 minutes, then left at 25 ° C. for 10 minutes, further held at 125 ° C. for 30 minutes, and then left at 25 ° C. for 10 minutes as one cycle. The first number of heat cycles in which at least one of the copper plates peeled off or had defects such as breakage at the interface with the heat sink was measured. The results are shown in Table 4.

With respect to the circuit boards obtained in Examples 1 to 9, the composition of the bonding layer formed between the heat sink of the circuit board or the base copper plate and the heat sink was measured by EPMA (electron beam microanalyzer). As a result, in all the bonding layers, the alloy layer containing Al-Ni-Cu was 3 μm.
, Al-Ni-Si containing alloy layer is about 5 μm, A
An alloy layer made of l-Ni was contained in a thickness of about 8 μm.

[0046]

[Table 4]

[0047]

According to the present invention, it is possible to provide a circuit board with a heat sink, which is suitable as an electronic circuit component for a power module and is excellent in heat dissipation and heat cycle resistance, thereby improving the productivity of the power module. .

─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-4-363052 (JP, A) JP-A-11-269575 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C22C 49/00-49/14 H01L 23/373

Claims (2)

(57) [Claims] 1. A heat sink is attached to a heat sink of a circuit board having a circuit on one side of a ceramic substrate and a heat sink on the opposite side, with or without a base plate, A circuit board with a heat sink, characterized in that the material of the heat sink is silica-alumina fiber reinforced aluminum or aluminum alloy. 2. The heat sink and the heat radiating plate or the base plate of the circuit board are joined via a joining layer having an alloy layer containing an Al component and a Ni component. 1. A circuit board with a heat sink according to 1.