Brazing powder and paste composition containing the same

Abstract

To provide a brazing filler metal which is low in material cost and enables satisfactory brazing between a ceramic member and a metal member.SOLUTION: A brazing filler metal powder according to the present invention includes a powder mixture of 80.0 to 99.7% by mass of a Cu-Sn alloy powder and 0.3 to 20.0% by mass of at least one active metal component powder, wherein the Cu-Sn alloy powder contains 18.0 to 37.0% by mass of Sn, with the balance being Cu and inevitable impurities. A paste composition containing 75.0 mass% to 92.0 mass% of the wax powder and 8.0 mass% to 25.0 mass% of an organic varnish is suitable for joining a ceramic member and a metal member. The active metal component powder may be a powder containing at least one selected from Ti, Zr, Hf, and Nb as a main component.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a brazing powder suitable for joining ceramic members to metal members, and a paste composition containing the brazing powder. [Background technology]

[0002] In recent years, power modules such as IGBTs (Insulated Gate Bipolar Transistors) have become increasingly important due to the increasing performance of industrial equipment such as robots and motors, as well as the development of power-saving technologies. While power modules are capable of handling high voltages and currents (i.e., high power and high output), the increase in heat generated by semiconductor elements has become an issue. For this reason, ceramic substrates (such as Si3N4 (silicon nitride), AlN (aluminum nitride), and Al2O3 (aluminum oxide)) with excellent heat resistance and insulation properties are used for the substrates mounted in power modules. Power module substrates in which copper foil is bonded to both sides of this ceramic substrate have traditionally been widely used.

[0003] The main methods used to bond ceramic substrates and copper foils in power module substrates are direct copper bonding (DCB), which bonds ceramics and copper by directly reacting them, and active metal brazing (AMB), which uses a brazing filler metal containing active metal components. However, the DCB method has the problem of requiring a relatively high bonding temperature and resulting in poor bonding strength, so the AMB method is increasingly being used for bonding.

[0004] In the AMB method, a brazing filler metal containing an active metal component added to BAg-8 specified in JIS Z 3261:1998 "Silver Brazing Filler Metal" is commonly used. In addition, new Ag-Cu alloy brazing filler metals have also been proposed, such as those described in the following Patent Documents 1 to 3. While brazing filler metals containing Ag as a primary component are known to be effective for joining ceramic and metal members, the inclusion of Ag in the brazing filler metal inevitably results in high costs.

[0005] In order to reduce the cost of brazing filler metals, for example, a Cu-Ti-Sn-Ni brazing filler metal that does not contain Ag has been disclosed, as described in Patent Document 4. However, the brazing filler metal in Patent Document 4 contains 10 mass% or more of Ti, an active metal component, as an alloy. To powder such a brazing filler metal alloy, for example, by atomization, it is essential to take measures to control the melting atmosphere in the raw metal melting process so that the oxygen partial pressure is low. However, powders produced in processes that take such measures to control the melting atmosphere are expensive.

[0006] In addition, Cu alloy-based brazing filler metals have been proposed as Ag-free brazing filler metals as described in Patent Documents 5 to 7. However, the Cu-Sn alloy-based brazing filler metals described in Patent Documents 5 and 6 contain a relatively large amount of Sn as a main component, which widens the melting temperature range of the brazing filler metal, resulting in problems such as melt separation and making proper brazing difficult. The Cu-P-Sn-Ni alloy-based brazing filler metal described in Patent Document 7 has a narrow melting temperature range, but contains a large amount of P, which restricts the need to appropriately control the joint interface structure.

[0007] As described above, the general-purpose brazing filler metals that have been used up to now and the brazing filler metals described in Patent Documents 1 to 7 have the above-mentioned problems, and at present, no brazing filler metal for ceramic-metal bonding has been proposed that is inexpensive, has an appropriate melting temperature, and has properties that allow easy bonding. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2023-6077 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-130686 [Patent Document 3] Patent No. 6100501 [Patent Document 4] Patent No. 3095187 [Patent Document 5] Japanese Patent Publication No. 2022-27647 [Patent Document 6] WO2014 / 084242 publication [Patent Document 7] Patent No. 6819299 Summary of the Invention [Problem to be solved by the invention]

[0009] Brazing applied to power module substrates requires a brazing filler metal that does not contain expensive Ag, can be produced inexpensively, and has excellent material properties. The present invention aims to solve the above-mentioned problems in the prior art, reduce the cost of brazing filler metals, and provide a brazing filler metal that has an excellent melting temperature range and brazeability. [Means for solving the problem]

[0010] As a result of extensive research to achieve the above object, the inventors have found that by mixing a Cu-Sn alloy powder having a predetermined Cu / Sn ratio with an active metal component powder in a specific ratio, a brazing powder can be obtained that can be produced inexpensively and that can properly braze ceramic members and metal members, and have completed the present invention.

[0011] The brazing powder of the present invention comprises: A mixed powder of 80.0 to 99.7 mass% of Cu-Sn alloy powder and 0.3 to 20.0 mass% of at least one active metal component powder, The Cu—Sn alloy powder is characterized in that it contains 18.0 to 37.0 mass % of Sn, with the remainder being Cu and unavoidable impurities.

[0012] The active ingredient powder is preferably a powder containing at least one selected from Ti, Zr, Hf and Nb as a main component.

[0013] The present invention also relates to a paste composition for brazing, characterized in that the paste composition contains 75.0 to 92.0 mass % of the brazing powder and 8.0 to 25.0 mass % of an organic varnish. [Effects of the Invention]

[0014] The brazing powder and paste composition containing the brazing powder of the present invention are effective in joining ceramic members and metal members, and can be produced at low cost. DETAILED DESCRIPTION OF THE INVENTION

[0015] The brazing powder of the present invention contains a binary alloy (Cu-Sn alloy) powder of Cu and Sn. Because the Cu-Sn alloy does not contain Ag or active metal components (Ti, Zr, Hf, and / or Nb), it can be produced inexpensively, reducing the cost of brazing materials for ceramic-metal bonding. Here, Cu and Sn are used as a Cu-Sn alloy rather than as a mixed powder of the respective pure metal powders because alloying narrows the melting temperature range. The liquidus and solidus temperatures of a Cu-Sn alloy vary depending on the component ratio, and the melting temperature range can be narrowed by appropriately controlling the component ratio. On the other hand, in the case of a mixed powder of pure Cu powder and pure Sn powder, the melting point difference (melting temperature range) between the Cu and Sn constituting the mixed powder does not change even if the mixing ratio is changed, so the melting temperature range cannot be narrowed. Therefore, in the present invention, it is essential to alloy Cu and Sn.

[0016] The Cu-Sn alloy powder contains 18.0 to 37.0 mass% Sn, with the remainder being Cu and inevitable impurities. Here, inevitable impurities refer to impurities that are not intentionally added but are inevitably mixed in during the manufacturing process of each raw material. Such impurities include Al, C, Mg, S, O, N, V, etc., and the total amount of these is usually 0.3 mass% or less, which is not enough to affect the effects of the present invention.

[0017] The Cu-Sn alloy powder of the present invention can be obtained by adjusting and blending Cu and Sn to a predetermined composition, completely melting them in a crucible of a melting furnace, and then powdering the molten alloy by gas atomization, water atomization, or melt-pulverization.

[0018] In particular, Cu-Sn alloy powder produced by the atomization method can be adjusted to a particle size suitable for the intended application method, and then a predetermined amount of active metal component powder can be mixed to obtain brazing powder suitable for joining ceramic and metal components.

[0019] The brazing powder of the present invention contains, in addition to the Cu-Sn alloy powder, a powder containing an active metal component (Ti, Zr, Hf, and / or Nb) as a main component in order to improve wettability with ceramics.

[0020] The active metal component powder contains at least one selected from Ti, Zr, Hf, and Nb as a main component. The brazing powder of the present invention may contain one or more active metal component powders. For example, it may contain one or more active metal component powders whose main component is only one selected from Ti, Zr, Hf, or Nb. Alternatively, the brazing powder of the present invention may contain an active metal component powder containing two or more selected from Ti, Zr, Hf, and Nb. In this specification, "containing as a main component" means that the active metal component powder contains the active metal component (Ti, Zr, Hf, and / or Nb) in an amount of 80 mass% or more, preferably 90 mass% or more.

[0021] The active metal component powder may contain a hydride of an active metal component (Ti, Zr, Hf, Nb). It is preferable to use a hydride due to its excellent activity in the brazing process, and titanium hydride (TiH2) powder is particularly preferable. A preferred example of the active metal component powder is a powder consisting of any one component selected from the group consisting of Ti, Zr, Hf, Nb, and their hydrides, with a purity of 90% or more, preferably 95% or more, more preferably 97% or more, 98% or more, or 99% or more. Such powders are commercially available.

[0022] The brazing powder of the present invention can be produced by blending and mixing the Cu-Sn alloy powder and the active metal component powder so that the total mass (100 mass%) of the brazing powder is 80.0 to 99.7 mass% and 0.3 to 20.0 mass%, respectively.

[0023] Furthermore, when the brazing powder (a mixed powder of Cu-Sn alloy powder and active metal component powder) is made into a paste and brazed, the brazing powder is blended so that it accounts for 75.0 to 92.0 mass% and the organic varnish is blended so that it accounts for 8.0 to 25.0 mass% of the total mass (100 mass%) of the paste composition, and good brazing properties can be obtained by using the paste composition obtained by mixing them.

[0024] In order to develop a brazing filler metal having an appropriate melting temperature range and excellent material strength, the inventors set the following target values ​​(1) and (2) when examining the composition of a Cu-Sn alloy, and set the following target value (3) when examining the brazing properties of a paste composition containing the brazing powder of the present invention. (target value) (1) Melting temperature range (difference between liquidus and solidus temperatures) → 100°C or less (2) Material strength [transverse rupture strength] → 200N / mm 2 End (3) Brazeability (brazed state) → No cracks, peeling, or voids in the brazed area

[0025] The melting temperature range in (1) is defined as the value obtained by subtracting the solidus temperature from the liquidus temperature of the Cu-Sn alloy. When brazing using a Cu-Sn alloy, if the melting temperature range is too large, a melt separation phenomenon occurs during brazing, leading to defects such as excessive wetting. Therefore, we investigated the Cu-Sn ratio with the goal of achieving a melting temperature range of 100°C or less, as a characteristic that enables proper brazing.

[0026] Regarding the material strength of (2), if the transverse rupture strength of the Cu-Sn alloy is low, the necessary strength will not be exhibited after brazing. 2With the above as the goal, the Cu-Sn ratio was investigated.

[0027] Regarding (3), brazing performance was evaluated using the paste composition described below, and the blending ratio of the paste composition was examined with the goal of preventing cracks, peeling, and voids from occurring in the brazed joint.

[0028] A paste composition containing a Cu-Sn alloy that satisfies the above target values ​​(1) and (2) and satisfies the target value (3) can be produced relatively inexpensively and has an appropriate melting temperature range and material strength as a brazing material.

[0029] The reasons for limiting the ranges of each component in the present invention as described above will be explained below.

[0030] Sn is an element that undergoes a peritectic reaction with Cu, and an increase in the Sn content decreases the melting temperature (liquidus temperature and solidus temperature). In Cu-Sn alloy powder, if the Sn content is less than 18.0 mass%, the decrease in the liquidus temperature is small and the melting temperature range exceeds 100°C, which is not preferable. Furthermore, if the Sn content exceeds 37.0 mass%, the η phase (Cu6Sn5) will be formed in the metal structure, resulting in a significant decrease in transverse rupture strength. For this reason, the Sn content is set to 18.0 to 37.0 mass%. Note that a narrower melting temperature range is better, and in order to keep the melting temperature range within 50°C, the Sn content is more preferably 22.0 mass% or more. In addition, from the viewpoint of bonding strength, a higher transverse rupture strength is better, and a transverse rupture strength of 400 N / mm 2 To achieve a transverse rupture strength of 700 N / mm or more, the Sn content is preferably 33.0 mass% or less. 2 To achieve this or more, the Sn content is more preferably 28.0 mass % or less. That is, the amount of Sn in the Cu—Sn alloy powder is more preferably 22.0 to 33.0 mass %, particularly preferably 22.0 to 28.0 mass %.

[0031] The active metal component improves the wettability with the ceramics and forms a bonding layer (reaction layer). However, if the amount added is too small, the reaction layer may not be formed sufficiently, resulting in an insufficient bond. Conversely, if the amount added is too large, the amount of reaction layer formed may be excessive, reducing the bond strength and the risk of an insufficient bond. Heat dissipation also tends to be reduced. Therefore, the active metal component powder content in the brazing powder is set to 0.3 to 20.0 mass%. Note that a small amount of active metal component reduces the amount of reaction at the ceramic interface, resulting in a decrease in bond strength. Therefore, the active metal component powder content is preferably 0.5 mass% or more, more preferably 1.0 mass% or more, and particularly preferably 2.0 mass% or more. That is, the ratio of the active metal component powder to the total mass of the brazing powder is more preferably 0.5 to 20.0 mass%, particularly preferably 1.0 to 20.0 mass%, and even more preferably 2.0 to 20.0 mass%. The active metal component is preferably used in the form of a hydride, which has a low decomposition temperature, and titanium hydride or zirconium hydride is preferred. Furthermore, since the hydride forms a compound, mainly with Sn, after decomposition, which leads to a decrease in bonding strength, the amount of hydride added is preferably 15.0 mass% or less, and more preferably 10.0 mass% or less. That is, when the active metal component is in the form of a hydride, the ratio of the active metal component powder to the total mass of the brazing powder is more preferably 0.5 to 15.0 mass%, particularly preferably 1.0 to 15.0 mass%, and even more preferably 2.0 to 10.0 mass%.

[0032] The brazing powder of the present invention can be produced by mixing Cu-Sn alloy powder and active metal component powder using a mixer such as a V-type mixer. Adding the active metal component powder to the Cu-Sn alloy powder and mixing it allows the active metal component to be added inexpensively. In contrast, alloying the active metal component with Cu and Sn requires, for example, controlling the melting atmosphere to a low oxygen partial pressure during the raw metal melting process using the atomization method, which increases costs. The Cu-Sn alloy powder and active metal component powder can be mixed using a double-cone mixer or a rocking mixer, in addition to a V-type mixer. Furthermore, the brazing powder of the present invention can be obtained in small quantities by placing the powder in a container such as a polyvinyl chloride bottle and shaking the container to mix.

[0033] The paste composition (brazing filler paste) of the present invention can be obtained by mixing the brazing powder of the present invention with an organic varnish in a predetermined ratio. The mixing ratio of the organic varnish in the paste composition is set to 8.0 to 25.0 mass% because if it is less than 8.0 mass%, a uniform coating cannot be formed during the paste application work, making it impossible to obtain a stable brazing thickness and resulting in poor dimensional accuracy of the joint, and if it exceeds 25.0 mass%, dimensional change during brazing becomes large, making it impossible to braze a uniform thickness and resulting in uneven joint strength.

[0034] The organic varnish used in the present invention can be a natural or synthetic resin dissolved in an organic solvent. Examples of such resins include cellulose-based resins (carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, etc.), polyvinyl butyral (alkyl acetalized polyvinyl alcohol), and acrylic resins (polyacrylic esters, sodium polyacrylate, polyacrylonitrile, etc.). Examples of such organic solvents include carbitol-based solvents (ethyl carbitol, butyl carbitol, hexyl carbitol, etc.), cellosolve-based solvents (methyl cellosolve, ethyl cellosolve, butyl cellosolve, hexyl cellosolve, etc.), and alcohol-based solvents (ethanol, methanol, isopropyl alcohol, etc.). The resin-to-solvent ratio in the organic varnish is preferably 30 to 85% by mass of the resin component and 15 to 70% by mass of the solvent component, more preferably 50 to 80% by mass of the resin component and 20 to 50% by mass of the solvent component.

[0035] The method of applying the brazing powder of the present invention to the joint can be freely selected from a variety of methods, including mixing the brazing powder with an organic varnish to form a paste and applying it, sprinkling (spraying) the organic varnish and brazing powder separately on the joint surface, or processing the brazing powder into a sheet or foil shape and applying it.

[0036] The paste composition of the present invention is suitable as a brazing filler metal for joining metal members and ceramic members, but can also be used to join ceramic members (which may be the same type of ceramic members or different types of ceramic members). [Example]

[0037] The Cu-Sn alloys of the present invention (Examples 1 to 5) and comparative Cu-Sn alloys (Comparative Examples 1 to 5) shown in Table 1 were prepared, and the melting temperature range and transverse rupture strength were measured and evaluated by the methods described below.

[0038] (1) Melting temperature range measurement: 100 g of ingot containing each alloy composition was heated to approximately 1200°C in an argon gas stream in an electric furnace. The molten metal was then cast into a graphite mold to obtain an ingot. The resulting ingot was then machined to a size of 3 mm x 3 mm x 3 mm or less to prepare a test specimen. The melting temperature range (liquidus and solidus temperatures) of the test specimen was measured by differential thermal analysis (TG-DTA). TG-DTA was performed in a nitrogen atmosphere at a heating rate of 20°C / min, and the melting temperature was determined from the peak position of the resulting heating curve.

[0039] (2) Transverse rupture strength measurement: The base metal was melted in the same manner as in (1) above, and the molten metal was cast into a quartz glass tube, which was then machined to a size of approximately φ5 x 35 mm to prepare a test piece. Next, the test piece was placed on a transverse rupture strength test jig (three-point support, distance between supports 25.4 mm (jig described in JIS Z 2511:2006 "Metal powder - Method for measuring the strength of green compacts by transverse rupture test")), and a load was applied using a universal testing machine to measure the load at which it broke. The transverse rupture strength (N / mm) of the alloy was determined from the test piece shape and the breaking load. 2 ) was calculated.

[0040] The results are shown in Table 1. TIFF2026011656000001.tif93170

[0041] In Table 1, Examples 1 to 5 are Cu-Sn alloys of the present invention, and all of them have a melting temperature range of 100°C or less. 2 These values ​​show that the Cu-Sn alloys of the examples are also excellent in terms of material strength. Among them, examples 2 and 3 are Cu-Sn alloys having compositions that fall within the particularly preferred range of Sn content, 22.0 mass % to 28.0 mass %, and have a melting temperature range of 50°C or less and a transverse rupture strength of 700 N / mm 2 I am more than satisfied.

[0042] On the other hand, Comparative Examples 1 to 3 in Table 1 do not meet the target values ​​for the melting temperature range or transverse rupture strength. Specifically, Comparative Example 1 has an Sn content below 18.0 mass %, and the melting temperature range exceeds 100°C. Comparative Examples 2 and 3 have an Sn content above 37.0 mass %, and the transverse rupture strength is 200 N / mm 2 The melting temperature range of Comparative Example 3, which has an excessively high Sn content, is below 100°C. Comparative Example 3 is also a preceding brazing filler metal described in JP 2022-27647 A (Patent Document 5). Comparative Example 4 is a preceding brazing filler metal described in WO 2014 / 084242 (Patent Document 6), and has a melting temperature range exceeding 100°C. Comparative Example 5 is a preceding brazing filler metal described in Japanese Patent No. 6819299 (Patent Document 7), and since it satisfied the melting temperature range and transverse rupture strength defined as the target properties of the present invention, a brazeability evaluation was also carried out (see Comparative Example G in Table 2).

[0043] Brazing paste compositions shown in Table 2 were prepared and their brazing properties were evaluated according to the following evaluation method. (3) Brazeability Evaluation: A Cu-Sn alloy powder having the composition shown in Table 2 was mixed with an active metal component powder in the ratio shown in Table 2 to prepare a brazing powder. This brazing powder was then kneaded with an organic varnish in the ratio shown in Table 2 to form a paste, and approximately 0.3 g of the brazing paste was applied between a metal plate (a Cu plate measuring 10 mm × 10 mm × 3 mm thick) and a ceramic plate (a silicon nitride plate measuring 10 mm × 10 mm × 1 mm thick). The Cu-Sn alloy powder used here was produced by atomization and had a particle size adjusted to under 350 mesh. The active metal component powder was titanium hydride (TiH2) or zirconium hydride (ZrH2) powder (both with a purity of 99.5% or higher) with a particle size adjusted to under 150 mesh. The organic varnish used was prepared by mixing 68% by mass of alkyl acetalized polyvinyl alcohol as a resin and 32% by mass of butyl carbitol as a solvent. The paste-coated sample was dried at 120°C for 30 minutes, then heated at 850°C for 30 minutes, and then heated for 10 minutes. -2 ~10 -1Brazing heat treatment (hereinafter referred to as brazing) was carried out in a vacuum of 100 Pa. After brazing, the brazed portion was visually inspected for defects (cracks, peeling, voids), and samples without defects were rated as "good," while samples with defects were rated as "poor."

[0044] The results are shown in Table 2. [Table 2]

[0045] Examples a to g in Table 2 are paste compositions containing the brazing powder of the present invention, and as is clear from the brazing property evaluation results, no cracking, peeling, etc. occurred after brazing in any of them, indicating that the brazing property was good.

[0046] On the other hand, Comparative Examples A to F shown in Table 2 are brazing filler metals that do not correspond to the brazing powder or paste composition of the present invention, and were evaluated as "poor" in brazing properties. Specifically, Comparative Examples A and B had active metal component powder mixing ratios below 0.3 mass%, while Comparative Examples C and D had active metal component powder mixing ratios above 20.0 mass%. Neither of these satisfy the brazing powder composition of the present invention. When brazing was performed using these brazing powders, cracks and peeling occurred in the brazed portion. Comparative Example E contained the brazing powder of the present invention, but the organic varnish mixing ratio was below 8.0 mass%, which prevented the paste from being uniformly applied during the paste application process, resulting in the generation of large voids in the brazed portion. Comparative Example F contained the brazing powder of the present invention, but the organic varnish mixing ratio was above 25.0 mass%, resulting in large dimensional change after brazing, resulting in the generation of large voids in the brazed portion. In Comparative Example G, a brazeability evaluation was performed using a paste containing the Cu-Sn alloy of Comparative Example 5 shown in Table 1 (the prior brazing filler metal described in Japanese Patent Publication No. 6819299), and peeling occurred after brazing. The Cu-Sn alloy of Comparative Example 5 satisfied the target properties of the brazing filler metal alloy (melting temperature range and transverse rupture strength) (see Table 1). However, when a brazing filler metal paste containing this Cu-Sn alloy mixed with an active metal component powder and an organic varnish was used to join ceramic and metal members, direct brazing was difficult, and it became necessary to appropriately control the joint interface structure. This is thought to be because the high P content inhibited the wettability-enhancing effect of the active metal component powder.

[0047] The brazing filler powders of the above examples can be used regardless of the particle size, and can even be applied to coarse particle sizes such as under 80 mesh. Furthermore, it has been confirmed that the brazing filler powders of the above examples and paste compositions containing them exhibit good brazing properties when joining ceramic members other than silicon nitride (aluminum nitride, aluminum oxide, etc.) to metal members (copper or copper alloys), and can also be used to join ceramic members of the same type or to join ceramic members of different types. [Industrial Applicability]

[0048] As described above, the brazing filler powder of the present invention can be produced by mixing a Cu-Sn alloy powder and an active metal component powder, thereby reducing material costs. Furthermore, a paste containing the brazing filler powder and an organic varnish in a predetermined ratio is suitable for joining ceramic members and metal members, and has good brazing properties, so it can be used as a joining brazing filler metal for power module substrates.

Claims

1. A brazing powder comprising a mixed powder of 80.0 to 99.7 mass% Cu—Sn alloy powder and 0.3 to 20.0 mass% at least one active metal component powder, The Cu—Sn alloy powder contains 18.0 to 37.0 mass % of Sn, with the remainder being Cu and unavoidable impurities.

2. 2. The brazing powder according to claim 1, wherein the active metal component powder is a powder containing at least one selected from the group consisting of Ti, Zr, Hf and Nb as a main component.

3. A paste composition comprising 75.0 to 92.0% by mass of the brazing powder according to claim 1 or 2 and 8.0 to 25.0% by mass of an organic varnish.

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