Brazing powder and paste composition containing same

Abstract

Provided is a brazing filler metal which is inexpensive in terms of material cost, and which enables good brazing between ceramic members and metal members.　This brazing powder is characterized by comprising a mixed powder 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 type of active metal component powder, wherein the Cu-Sn alloy powder contains 18.0 to 37.0 % by mass of Sn, with the remainder being Cu and unavoidable impurities. A paste composition containing 75.0 to 92.0 % by mass of the brazing powder and 8.0 to 25.0 % by mass of an organic varnish is suitable for joining ceramic members and metal members. The active metal component powder may be a powder having at least one element selected from Ti, Zr, Hf, and Nb as a main component.

Description

Brazing powder and paste composition containing same

[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.

[0002] In recent years, with the advancement of high performance industrial equipment such as robots and motors and the development of power-saving technologies, power modules such as IGBTs (Insulated Gate Bipolar Transistors) have become increasingly important. While power modules are capable of handling high voltages and large 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 (Si ３ N ４ (silicon nitride), AlN (aluminum nitride), Al ２ O ３ (aluminum oxide, etc.) has been used. Power module substrates in which copper foil is bonded to both sides of this ceramic substrate have 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 an active metal component. However, the DCB method has the drawback of requiring a relatively high bonding temperature and resulting in poor bonding strength, so the AMB method is increasingly being used.

[0004] In the AMB method, a brazing filler metal in which an active metal component is added to BAg-8 specified in JIS Z 3261:1998 "Silver Brazing Filler Metal" is generally used. In addition, new Ag-Cu alloy brazing filler metals have also been proposed, for example, as described in Patent Documents 1 to 3 listed below. 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, Patent Document 4 discloses a Cu-Ti-Sn-Ni brazing filler metal that does not contain Ag. However, the brazing filler metal of 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 material 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 problematic in that they 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.

[0008] Japanese Patent Publication No. 2023-6077 Japanese Patent Publication No. 2017-130686 Japanese Patent Publication No. 6100501 Japanese Patent Publication No. 3095187 Japanese Patent Publication No. 2022-27647 WO2014 / 084242 Japanese Patent Publication No. 6819299

[0009] For brazing applied to power module substrates, there is a need for a brazing filler metal that does not contain expensive Ag, can be produced inexpensively, and has excellent material properties. An object of the present invention is to solve the above-mentioned problems in the prior art, reduce the cost of the brazing filler metal, and provide a brazing filler metal that has an excellent melting temperature range and brazeability.

[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 is 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, characterized in that the Cu-Sn alloy powder contains 18.0 to 37.0 mass% 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.

[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.

[0015] The brazing filler 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 filler metals 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 Cu-Sn alloys 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 when the mixing ratio is changed, making it impossible to narrow the melting temperature range. Therefore, in the present invention, alloying Cu and Sn is essential.

[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 are 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 impurities 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, by adjusting the particle size of Cu-Sn alloy powder produced by the atomization method to a particle size suitable for the intended application method and then mixing it with a predetermined amount of active metal component powder, a brazing powder suitable for joining ceramic members and metal members can be obtained.

[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 containing only one selected from Ti, Zr, Hf, or Nb as a main component. 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 hydrides of active metal components (Ti, Zr, Hf, Nb). It is preferable to use hydrides because they have excellent activity in the brazing process. Titanium hydride (TiH ２ A preferred example of the active metal component powder is a powder of any one component selected from the group consisting of Ti, Zr, Hf, Nb, and hydrides thereof, having 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 filler powder (a mixed powder of Cu-Sn alloy powder and active metal component powder) is made into a paste and brazed, the brazing filler powder is blended in an amount of 75.0 to 92.0 mass% and the organic varnish is blended in an amount of 8.0 to 25.0 mass% relative to 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 filler powder of the present invention. (Target Values) (1) Melting temperature range (difference between liquidus temperature and solidus temperature) → 100°C or less (2) Material strength (transverse rupture strength) → 200 N / mm ２ (3) Brazeability (brazing condition) → 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 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. ２ With the above as the goal, the ratio of Cu—Sn was investigated.

[0027] Regarding (3), the brazing property 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 portion.

[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 filler metal.

[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 reduces 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. On the other hand, if the Sn content exceeds 37.0 mass%, the η phase (Cu ６ Sn ５ ) are formed, resulting in a significant decrease in the bending strength. For this reason, the Sn content is set to 18.0 to 37.0 mass%. The narrower the melting temperature range, the 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, the higher the bending strength, the better, and a bending 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 the above, the Sn content is more preferably 28.0 mass % or less. That is, the Sn content in the Cu—Sn alloy powder is more preferably 22.0 to 33.0 mass %, and particularly preferably 22.0 to 28.0 mass %.

[0031] The active metal component improves the wettability with the ceramic and forms a bonding layer (reaction layer). However, if the amount added is too small, the reaction layer may not be formed sufficiently, and a good bond may not be obtained. Conversely, if the amount added is too large, the amount of reaction layer formed may be excessive, which may reduce the bond strength and prevent a good bond from being obtained. Heat dissipation also tends to decrease. Therefore, the mixing ratio of the active metal component powder in the brazing powder is set to 0.3 to 20.0 mass%. Note that if the amount added is small, the amount of reaction at the ceramic interface decreases, resulting in a decrease in bond strength. Therefore, the mixing ratio of the active metal component powder 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 having a low decomposition temperature, with titanium hydride or zirconium hydride being preferred. Furthermore, since the hydride forms a compound, mainly with Sn, after decomposition, which leads to a decrease in joining 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 a Cu—Sn alloy powder and an 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 them allows for inexpensive addition of the active metal component. 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. Mixing the Cu—Sn alloy powder and the active metal component powder can be performed using a double-cone mixer or a rocking mixer, in addition to a V-type mixer. Furthermore, in the case of small amounts, the brazing powder of the present invention can be obtained 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%, it is not possible to form a uniform coating film during the paste application work, making it impossible to obtain a stable brazing thickness, resulting in poor dimensional accuracy of the joint, and, if it exceeds 25.0 mass%, dimensional change during brazing becomes so large that brazing of a uniform thickness is not possible, 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 weight of the resin component and 15 to 70% by weight of the solvent component, more preferably 50 to 80% by weight of the resin component and 20 to 50% by weight 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 a metal member and a ceramic member, but can also be used to join ceramic members (which may be the same type of ceramic member or different types of ceramic members).

[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 ranges and transverse rupture strengths were measured and evaluated by the methods described below.

[0038] (1) Melting temperature range measurement: 100 g of ingot having the composition of each alloy was heated to approximately 1200°C in an argon gas flow using an electric furnace and melted. The molten metal was cast into a graphite mold to obtain an ingot. The resulting ingot was then processed to a size of 3 mm x 3 mm x 3 mm or less to prepare a test specimen. The melting temperature range (liquidus temperature and solidus temperature) 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 read from the peak position of the obtained 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 × 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 the alloy broke. The transverse rupture strength (N / mm ２ ) was calculated.

[0040] The results are shown in Table 1.

[0041] In Table 1, Examples 1 to 5 are Cu—Sn alloys according to 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 ２The melting temperature range of Comparative Example 3, which has an excessively high Sn content, is also below 100°C. Comparative Example 3 is also the preceding brazing filler metal described in JP 2022-27647 A (Patent Document 5). Comparative Example 4 is the 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 the 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 according to the following evaluation method, and brazing properties were evaluated. (3) Brazing property evaluation: A Cu-Sn alloy powder having the composition shown in Table 2 and an active metal component powder were mixed in the ratio shown in Table 2 to prepare brazing powders. These brazing powders were 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 x 10 mm x 3 mm in thickness) and a ceramic plate (a silicon nitride plate measuring 10 mm x 10 mm x 1 mm in thickness). The Cu-Sn alloy powder used here was prepared by atomization, and its particle size was adjusted to under 350 mesh. The active metal component powder was titanium hydride (TiH ２ ) powder or zirconium hydride (ZrH ２ ) powder (all with a purity of 99.5% or more), 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 －１ Brazing 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 evaluated as "good," while samples with defects were evaluated as "poor."

[0044] The results are shown in 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, or the like occurred after brazing in any of them, and it can be seen that the brazing property is 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 performance. 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 which satisfied 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 brazing 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. Although 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), 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 members 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 powders of the above examples can be used regardless of the powder particle size, and can even be applied to coarse particle sizes such as under 80 mesh. Furthermore, it has been confirmed that the brazing 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.

[0048] As described above in detail, 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, wherein the Cu-Sn alloy powder contains 18.0 to 37.0 mass% Sn, with the remainder being Cu and unavoidable impurities.

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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