JP2007242891A - Heat radiator plate of copper or copper-contained alloy, and its joining method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of joining a DBA substrate and a heat radiating member by brazing or by soldering, and also a heat radiator plate manufactured by the joining method. <P>SOLUTION: A Cu plate or a Cu-contained alloy is joined to a foil or a particle-like Sn-based alloy by inserting the foil or the particle-like Sn-based alloy between the Cu or the Cu-contained alloy, and heating the alloys at a temperature not lower than the melting point of the Sn-based alloy. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a heat radiating plate (so-called heat sink material) used for quickly dissipating heat generated from a heating element such as a semiconductor element mounted on an electronic device, and a joining method thereof. The present invention relates to a heat sink that can be used for a module having a large calorific value, such as a power semiconductor module, and a joining method thereof.

  When an electronic device equipped with an electronic component such as a semiconductor element is operated, the electronic component generates heat as the electronic circuit is energized. If the electronic device has a high output, the amount of heat generated during operation increases. If the temperature rises too much due to heat generation, the characteristics of the semiconductor element change and the operation of the electronic device becomes unstable. Further, when exposed to an excessively high temperature after being used for a long period of time, a bonding material (for example, solder) or an insulating material (for example, synthetic resin) of an electronic component is altered, causing a failure of the electronic device. Therefore, it is necessary to quickly dissipate heat generated from the electronic components. Therefore, various techniques for dissipating heat through a heat sink have been studied.

The heat sink does not impair the thermal properties of each component, such as combining components with low thermal expansion such as W, Mo and ceramics and components with high thermal conductivity such as Al and Cu and not alloying each other. A material having a complexed structure is used.
For example, Patent Document 1 discloses a heat sink using a metal-metal composite material such as W-Cu or Mo-Cu. In this patent document 1, while using expensive W and Mo, a technique of using a relatively inexpensive Cr and applying a Cr—Cu material whose thermal expansion coefficient is adjusted by heat treatment to the heat sink is also examined. ing.

Patent Document 2 discloses a heat dissipation plate using a ceramic-metal composite material such as SiC-Al, Cu ₂ O—Cu.
When using these heatsinks, electronic parts are brazed or soldered on one side of the heatsink, and the heat dissipation member for efficiently dissipating the heat of the electronic parts on the other side of the heatsink Join. For example, the thermal expansion coefficient of a substrate (so-called DBA substrate) obtained by directly bonding an Al electrode to AlN used as a substrate for an electronic component (ie, a semiconductor element) is 5 to 7 × 10 ⁻⁶ K ⁻¹ . The thermal expansion coefficient of the W-Cu based composite material used as a heat sink is 6-9 × 10 ⁻⁶ K ⁻¹ , and the thermal expansion coefficient of the Mo—Cu based composite material is 7-14 × 10 ⁻⁶ K ⁻¹ . Yes, all have a coefficient of thermal expansion that is not significantly different.

However, the thermal expansion coefficient of pure Al, Al alloy, pure Cu, and Cu alloy used as a general-purpose heat dissipation member is 16 to 24 × 10 ⁻⁶ K ⁻¹ , Is significantly different. Therefore, when the DBA substrate is joined to one surface of the heat sink by brazing or soldering, and the heat dissipation member is similarly joined to the other surface of the heat sink, the heat sink and the DBA substrate Although a problem caused by thermal strain does not occur on the joint surface, problems such as peeling due to thermal strain occur on the joint surface between the heat sink and the heat dissipation member.

Therefore, the conventional W-Cu, metals such as Mo-Cu - metallic and composite _{materials, SiC-Al, Cu- 2 O} -Cu or the like of the ceramic - the heat radiating plate using a metal-based composite material Al (thermal expansion 23.5 × 10 ^-6 K ^-1 ), Cu (thermal expansion coefficient 17.6 × 10 ^-6 K ^-1 ), or alloy heat-dissipating members with alloying elements added to them by brazing or soldering If attempted, problems such as the occurrence of warpage during bonding and the occurrence of cracks on the bonding surface due to thermal cycles accompanying the rise and fall of temperature during use will occur, and heat cannot be dissipated stably. Therefore, conventional heat sinks are often mechanically joined by screws or the like. In the case of screwing, there is a problem that micro voids are generated on the joint surface and heat dissipation becomes insufficient, so measures such as filling with grease with good thermal conductivity are adopted, Sufficient heat dissipation characteristics are not obtained.

As a measure to solve the problem caused by thermal distortion caused by the difference in thermal expansion coefficient, the thermal expansion coefficient of the two opposing surfaces of the heat sink is adjusted by impregnating the powder compact with molten metal, A technique for studying a value close to the coefficient of thermal expansion of a member (DBA substrate or heat dissipating member) to be joined to the surface has been studied. By joining the thermal expansion coefficient of the heat radiating plate to the thermal expansion coefficient of the mating material to be joined in this way, joining that requires heating during joining such as brazing or soldering between the DBA substrate and the heat dissipation member. It becomes possible to join by the method. As a result, it is possible to efficiently transmit heat generated from the electronic component to the heat dissipating member, which not only prevents an increase in temperature accompanying an increase in output of the electronic component, but also greatly improves thermal shock resistance. However, there remains a problem that the yield of the molten metal impregnated in the powder compact is low and economically disadvantageous.
Japanese Patent Publication No. 5-38457 JP 2002-212651 A

  In order to solve the above-described problems, the present invention is to provide a technique for efficiently joining two or more kinds of Cu or Cu-containing alloys having different thermal expansion coefficients at low cost. It aims at providing the joining method for manufacturing the heat sink which can join a heat-dissipating member by brazing or soldering, and the heat sink manufactured by the joining method.

As a thermal characteristic of the heat sink, a surface to which an electronic component that generates heat, such as a semiconductor, is bonded has a low coefficient of thermal expansion like a conventional heat sink. On the other hand, it is desirable to use a material close to the thermal expansion coefficient of Cu or Al for the joint surface with a heat dissipation member typified by a cooler having cooling fins.
A clad material using hot rolling is known as a material that changes the characteristics of the upper and lower surfaces of the heat sink. For example, in the case of a clad material in which a W plate and a Cu plate are combined, the difference in coefficient of thermal expansion is large, so that warpage occurs due to the difference in coefficient of thermal expansion between the two after cooling at a high temperature. Therefore, it is difficult to stably manufacture an electronic component using a clad material.

  On the other hand, in the present invention, an Sn-based alloy is sandwiched between two or three or more Cu or Cu-containing alloys having different thermal expansion coefficients, and these are heated above the liquidus temperature of the Sn-based alloy. Promotes the reaction between Cu and Sn, and joins Cu or Cu-containing alloys. Therefore, since the temperature at which the bonding is performed is lower than that of the conventional cladding material, it is possible to suppress the occurrence of thermal distortion due to the difference in thermal expansion coefficient between the materials to be bonded. Furthermore, the Sn-based alloy that exists between the materials to be joined undergoes creep deformation even near room temperature, so that the generated thermal strain can be absorbed. As a result, the heat radiating plate manufactured by applying the joining method of the present invention exhibits excellent characteristics that thermal distortion can be greatly reduced.

Specifically, there is little warping that occurs when materials having different coefficients of thermal expansion are joined, and a flat surface can be obtained by performing simple flat surface correction in the cold. In addition, when used as a heat sink, it exhibits extremely excellent thermal shock resistance.
Since a process such as rolling is necessary to manufacture the clad material, it is suitable for mass production of the same clad material, but is not suitable for mass production of various products.

On the other hand, in the present invention, the combination of alloys and the thickness of each layer can be selected and manufactured, so that an optimal heat sink can be designed without waste in the manufacture of each module. In other words, the present invention is suitable not only for mass production of the same variety but also for small production of many types.
That is, according to the present invention, in a joining method of Cu or Cu-containing alloys having different coefficients of thermal expansion, a foil or a granular Sn-based alloy is sandwiched between Cu or Cu-containing alloys and heated to a temperature equal to or higher than the melting point of the Sn-based alloy. Is a joining method for joining Cu or a Cu-containing alloy.

  Moreover, this invention is a heat sink obtained by joining Cu or Cu containing alloy with the above-mentioned joining method.

  According to the present invention, the DBA substrate and the heat dissipating member can be joined by brazing or soldering, and the heat sink can be manufactured at low cost and with high efficiency.

First, Cu and a Cu-containing alloy to which the present invention is applied will be described.
The Cu-containing alloy having a low coefficient of thermal expansion to which the present invention is applied preferably has a coefficient of thermal expansion of ⁶ to 13 × 10 ⁻⁶ K ⁻¹ . The Cu-containing alloy is preferably a Cu-W alloy, a Cu-Mo alloy, a Cu-Cr alloy, or the like. However, if the Cu content is less than 10% by volume, sufficient thermal conductivity cannot be obtained. Therefore, the Cu content is preferably 10% by volume or more.

On the other hand, the high thermal expansion coefficient Cu or Cu-containing alloy preferably has a thermal expansion coefficient in the range of 15 to 25 × 10 ⁻⁶ K ⁻¹ . The Cu-containing alloy is preferably a Cu-Cr alloy, a Cu-Zn alloy, a Cu-Sn alloy, or the like. However, pure Cu with high thermal conductivity is most suitable.
Next, an Sn-based alloy used for joining Cu or Cu-containing alloys will be described.
The components of the Sn-based alloy used in the present invention are not particularly limited. That is, a general solder alloy can be used in addition to pure Sn. However, since the regulations regarding the use of Pb are becoming stricter, solder alloys that do not contain Pb, such as Sn-Ag alloys, Sn-Cu alloys, Sn-Ag-Cu alloys, Sn-Zn alloys, are preferable. .

However, in the present invention, a foil-like or granular Sn-based alloy is used. This is because the Sn-based alloy is uniformly and easily dissolved at the stage of heating and melting described later.
When a foil-like Sn-based alloy is used, if the thickness exceeds 0.25 mm, it is disadvantageous in terms of thermal shock resistance and economy. Therefore, the thickness of the foil-like Sn-based alloy is preferably 0.25 mm or less.
When using a granular Sn-based alloy, if its diameter exceeds 0.5 mm, it is disadvantageous in terms of thermal shock resistance and economy. Therefore, the diameter of the granular Sn-based alloy is preferably 0.5 mm or less. Further, a paste (for example, a solder paste) may be used so that the granular Sn-based alloy is stably fixed on the joint surface.

Next, the joining method of the present invention will be described.
In the joining method of the present invention, an Sn-based alloy is sandwiched between Cu or a Cu-containing alloy and heated to the melting point or higher of the Sn-based alloy. The upper limit of this heating temperature is the lower of (a) and (b) below.
(a) Boiling point of Sn-based alloy
(b) Melting point of Cu or Cu-containing alloy However, if the heating temperature exceeds the melting point of Sn-based alloy + 100 ° C, Sn and Cu react to produce an intermetallic compound with low ductility and thermal conductivity. The characteristics of the will deteriorate. Therefore, the heating temperature is preferably the melting point of the Sn-based alloy + 100 ° C. or less.

By heating in this way, only the Sn-based alloy is melted, and then Cu or the Cu-containing alloy is joined by being cooled.
By the way, the thermal expansion coefficient of a Cr-Cu alloy can be adjusted by heat treatment. For example, heat treatment can be performed at 550 ° C. to reduce the coefficient of thermal expansion of the Cr—Cu alloy. Therefore, if it joins by heating to 550 degreeC, joining of a Cr-Cu type alloy and adjustment of a thermal expansion coefficient can be achieved simultaneously.

In addition, if the time of heating and holding above the melting point of the Sn-based alloy is less than 5 seconds, sufficient bonding strength cannot be obtained. On the other hand, if the holding time exceeds 1 hour, Sn and Cu react to produce an intermetallic compound having low ductility and thermal conductivity, so the characteristics as a heat sink deteriorate. Therefore, the holding time is preferably in the range of 5 seconds to 1 hour.
The atmosphere for heating is preferably an inert gas atmosphere, a reducing gas atmosphere, or a vacuum atmosphere. Heating may be performed while keeping the inside of the heating furnace in these atmospheres, or heating may be performed after sealing in a sealed container kept in these atmospheres. Further, heating may be performed while spraying an inert gas or a reducing gas (so-called purge).

The Cu or Cu-containing alloy bonding method of the present invention may be performed alone or in combination with bonding to a DBA substrate or bonding to a heat dissipation member.
In addition, the heat sinks joined by applying the joining method of the present invention can be used with two or more kinds of Cu or Cu-containing alloys being joined, but if necessary, performance against corrosion or electrolytic corrosion. It is also possible to use Ni plating or the like on the surface in order to improve the resistance or to solder the DBA substrate or aluminum plate.

FIG. 1 is a cross-sectional view schematically showing an example of a heat sink manufactured by applying the present invention. As shown in FIG. 1, the heat radiating plate 1 has a configuration in which a Cu-containing alloy 1a having a low thermal expansion coefficient and Cu or a Cu-containing alloy 1b having a high thermal expansion coefficient are joined via an Sn-based alloy 1c.
As shown in FIG. 2, the heat sink 1 used for the use in which the prevention of the warp caused by the difference in the thermal expansion coefficient is strictly required is composed of two Cu-containing alloys 1a having a low thermal expansion coefficient or Cu or Cu having a high thermal expansion coefficient. A configuration may be adopted in which the alloy is sandwiched between the contained alloys 1b and joined via the Sn-based alloy 1c.

  The thickness of the heat sink 1 (that is, the thickness of the Cu-containing alloy 1a having a low coefficient of thermal expansion, the thickness of the Cu or Cu-containing alloy 1b having a high coefficient of thermal expansion, the thickness of the Sn-based alloy 1c) is appropriately determined as necessary. Can be adjusted. Therefore, the coefficient of thermal expansion of the heat sink 1 can be arbitrarily adjusted.

[Example 1]
Cr powder was filled into a mold and further sintered in a hydrogen atmosphere to produce a sintered body (50 mm × 50 mm × 2 mm) with a porosity of 50% by volume. A Cu plate was placed on the sintered body, heated to 1200 ° C. in a vacuum to dissolve Cu, and impregnated in the sintered body. The Cr—Cu composite metal material obtained in this way is heat treated (550 ° C., 1 hour) and adjusted so that the thermal expansion coefficient becomes an average of 11 × 10 ⁻⁶ K ^{−1 in} the range of room temperature to 200 ° C. did. Next, it was processed to a thickness of 1.5 mm with a milling machine.

In addition, a 50 mm × 50 mm × 1.5 mm pure Cu plate was cut out from the pure Cu piece using a milling machine.
A pure Sn foil (thickness 0.05 mm) was sandwiched between the Cr—Cu composite metal material thus produced and a pure Cu plate (thermal expansion coefficient 17.6 × 10 ⁻⁶ K ⁻¹ ), and hydrogen gas was further purged. Heat treatment was performed in the furnace (heating temperature: 232 ° C. or higher holding time of 30 minutes and maximum temperature reached 250 ° C.), and a Cr—Cu composite metal material and a pure Cu plate were joined to produce a heat sink. Thereafter, electrolytic Ni plating was applied to form a 5 μm thick Ni plating layer on the surface of the heat sink.

  FIG. 3 is a cross-sectional view schematically showing an electronic component cooling body manufactured using this heat radiating plate. As shown in FIG. 3, the DBA substrate 2 is soldered to the low thermal expansion Cu-containing alloy 1a (that is, Cr—Cu composite metal material) side of the heat radiating plate 1, and the high thermal expansion Cu or Cu-containing alloy 1b ( That is, the heat dissipating member 3 was soldered to the side of the pure Cu plate. Further, the semiconductor element 4 was soldered to the DBA substrate 2. For the heat dissipating member 3, an Al alloy plate having cooling fins was used. This is the electronic component cooling body of Invention Example 1.

Further, as Invention Example 2, a Cu-Mo alloy (thermal expansion coefficient 10 × 10 ⁻⁶ K ⁻¹ ) produced by the same method as that of Invention Example 1 was used as a Cu-containing alloy 1a having a low thermal expansion coefficient, and a pure Cu plate (thermal An electronic component cooling body was produced in the same manner as the invention example, using the heat sink 1 produced as Cu or Cu-containing alloy 1b having an expansion coefficient of 17.6 × 10 ⁻⁶ K ⁻¹ ).
On the other hand, as Comparative Example 1, a similar electronic component cooling body was manufactured using the above-described Cu-Mo alloy having a thickness of 3 mm as a heat sink.

  Thermal shock tests of the electronic component cooling bodies of Invention Examples 1 and 2 and Comparative Example 1 were performed. The thermal shock test was carried out using a WINTEC LT20 type (manufactured by Enomoto Kasei) liquid tank type thermal shock tester with the set temperatures being −40 ° C. and 120 ° C. and holding times in each tank being 5 minutes. In this way, repeated thermal shocks were applied, and an ultrasonic flaw detection test of each electronic component cooling body was conducted to investigate the relationship between the number of thermal shocks applied (hereinafter referred to as a cycle) and the occurrence of cracks and peeling.

As a result, in the electronic component cooling body of Comparative Example 1, cracks occurred on the joint surface between the heat sink 1 and the heat dissipating member 3 in 1000 cycles.
On the other hand, in the electronic component cooling bodies of Invention Examples 1 and 2, no peeling or cracking was observed even after 3000 cycles were completed.
[Example 2]
Cr powder was filled into a mold and further sintered in a hydrogen atmosphere to produce a sintered body (50 mm × 50 mm × 2 mm) with a porosity of 50% by volume. A Cu plate was placed on the sintered body, heated to 1200 ° C. in a vacuum to dissolve Cu, and impregnated in the sintered body. The Cr—Cu composite metal material obtained in this way is heat treated (550 ° C., 1 hour) and adjusted so that the thermal expansion coefficient becomes an average of 11 × 10 ⁻⁶ K ^{−1 in} the range of room temperature to 200 ° C. did. Next, it was processed to a thickness of 1.5 mm with a milling machine.

In addition, a 50 mm × 50 mm × 1.5 mm pure Cu plate was cut out from the pure Cu piece using a milling machine.
A furnace in which granular Sn (diameter: 0.1 mm) is sandwiched between the Cr—Cu composite metal material thus produced and a pure Cu plate (thermal expansion coefficient 17.6 × 10 ⁻⁶ K ⁻¹ ) and further purged with hydrogen gas Heat treatment (heating temperature: holding time at 232 ° C. or higher is 30 minutes and maximum temperature reached 250 ° C.) was performed, and a Cr—Cu composite metal material and a pure Cu plate were joined to produce a heat sink.

Further, the heat sink 1 (thickness 3 mm) was cold-rolled to a thickness of 1.5 mm, and then punched to a size of 50 mm × 50 mm. Thereafter, electrolytic Ni plating was applied to form a 5 μm thick Ni plating layer on the surface of the heat sink.
The DBA substrate 2 is soldered to the low thermal expansion coefficient Cu-containing alloy 1a (that is, Cr—Cu composite metal material) side of the heat radiating plate 1, and the high thermal expansion coefficient Cu or Cu-containing alloy 1b (that is, pure Cu plate) The heat dissipation member 3 was soldered to the side. Further, the semiconductor element 4 was soldered to the DBA substrate 2. For the heat dissipating member 3, an Al alloy plate having cooling fins was used. This is the electronic component cooling body of Invention Example 3.

On the other hand, as Comparative Example 2, a pure Cu plate (thermal expansion coefficient: 17.6 × 10 ⁻⁶ K ⁻¹ ) having a thickness of 1.5 mm and a thickness of 50 mm × 50 mm was used as the heat radiating plate 1, and the electronic component cooling body as in Invention Example 3. Was made.
Furthermore, as Comparative Example 3, an electronic component cooling body as in Invention Example 3, using a Cu—Mo alloy (thermal expansion coefficient 10 × 10 ⁻⁶ K ⁻¹ ) of 1.5 mm in thickness and 50 mm × 50 mm as the heat sink 1. Was made.
Thermal shock tests were performed on the electronic component cooling bodies of Invention Example 3 and Comparative Examples 2 and 3. The thermal shock test was performed by using a WINTEC LT20 type (manufactured by Enomoto Kasei) liquid tank type thermal shock tester, with the set temperatures being −40 ° C. and 120 ° C., and holding times in each tank being 5 minutes. In this way, repeated thermal shocks were applied, and an ultrasonic flaw detection test of each electronic component cooling body was conducted to investigate the relationship between the number of thermal shocks applied (hereinafter referred to as a cycle) and the occurrence of cracks and peeling.

As a result, in the electronic component cooling body of Comparative Example 2, the bonding surface between the heat sink 1 and the DBA substrate 2 was peeled off in 1000 cycles. In the electronic component cooling body of Comparative Example 3, cracks occurred on the joint surface between the heat radiating plate 1 and the heat dissipating member 3 in 1000 cycles.
On the other hand, in the electronic component cooling body of Invention Example 3, no peeling or cracking was observed even after 3000 cycles were completed.

It is sectional drawing which shows typically the example of the manufactured heat sink to which this invention is applied. It is sectional drawing which shows typically the other example of the manufactured heat sink which applied this invention. It is sectional drawing which shows typically the electronic component cooling body produced using the heat sink by this invention.

Explanation of symbols

1 Heat sink
1a Cu-containing alloy with low thermal expansion coefficient
1b High thermal expansion coefficient Cu or Cu-containing alloy
1c Sn-based alloy 2 DBA substrate 3 Heat dissipation member 4 Semiconductor element
5a Solder
5b Solder
5c solder

Claims (2)

  In the joining method of Cu or Cu-containing alloy having different thermal expansion coefficients, the Cu or Cu-containing alloy is sandwiched between Cu or Cu-containing alloy and heated to a temperature equal to or higher than the melting point of the Sn-based alloy. Alternatively, a Cu or Cu-containing alloy joining method characterized by joining a Cu-containing alloy. A heat radiating plate obtained by joining two or more kinds of Cu or Cu-containing alloys by the joining method according to claim 1.

Images