JP2006068765A - Joint and joining method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a joint and a joining method capable of providing a reliable joint in which physical damages such as cracks and breakage at joining parts attributable to the temperature change of the joint less occur. <P>SOLUTION: In this joint, a joining layer 3 between a first joining material 1 and a second joining material 2 has a metal particle containing layer 6 which includes a plurality of metal particles 9, tin or tin alloy 10 present between the plurality of metal particles 9, and a film 11, and is present on the first joining material 1 side, a tin-containing layer 5 which uses tin or tin alloy containing ≥50 wt.% tin, and is present on the second joining material side, and first and second joining boundary layers 7, 8. Stresses generated in the joined portion can be mitigated thereby. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention is particularly suitable for joining electronic device components, and relates to a joined body of the same or different materials and a joining method thereof.

  Solder bonding as a bonding technique using an object and a material having a melting point lower than that of the object has been used for a long time. Even in the bonding of electronic devices, semiconductor elements such as microprocessors, memories, resistors, and capacitors, Widely used for joining electronic components and mounting boards. Solder bonding is characterized by not only fixing a component to a substrate but also having electric bonding by adding a conductive metal to the solder.

  Today, with the rapid spread of personal devices such as personal computers and mobile phones, the selection of bonding materials and bonding methods in the mounting technology of electronic components has become increasingly important.

  Conventionally, the most frequently used solder has been a tin / lead eutectic solder. This tin-lead eutectic solder is extremely suitable for practical use. However, the lead contained in tin-lead eutectic solder has become known to be harmful to the human body. Development is urgently needed.

  Under such circumstances, the bonding materials currently used in, for example, power devices among semiconductor devices are mainly low melting point solder having a melting point of about 183 ° C. (Pb—Sn eutectic solder) and melting point. A high melting point solder (Pb-5Sn solder) having a temperature of about 300 ° C. is used.

  Of these, low melting point solder is a joint that is sandwiched between a heat sink that is mainly processed from copper or copper alloy, which is provided to efficiently dissipate heat from the power device, and the ceramic substrate on which the semiconductor element is mounted. It is used as a material and has a function of fixing the ceramic substrate on the heat sink after heating and melting.

  However, even with such a heat sink, a power device such as a power transistor or the like generates a large amount of heat due to a high voltage, high current load, and the temperature rise / fall is repeated by the operation / stop of the device / apparatus. In addition, a heating process exceeding 200 ° C. must be performed when manufacturing the device.

On the other hand, the ceramic substrate on which the semiconductor element of the power device is directly mounted uses aluminum or silicon oxide or nitride to maintain the strength of the entire device, and the linear expansion coefficient differs greatly from the heat sink side. A close difference occurs (for example, AlN is 4 × 10 ⁻⁶ / K, while Cu is 17.7 × 10 ⁻⁶ / K).

  For this reason, when the temperature of the device is repeatedly raised and lowered, or in the heating process during device manufacture, thermal stress occurs due to the difference in the coefficient of linear expansion of the material, causing distortion at the part joint in the device / equipment. Produce. Further, when the temperature rises severely, the bonding material constituting the bonded portion is melted. When physical damage such as cracks and fractures occurs in the joint due to strain and melting caused by such temperature change, there is a problem that the performance of the device deteriorates.

  Conventionally used Sn—Pb eutectic solder has excellent ductility characteristics from room temperature to 125 ° C., the solder is heated and melted, the heat sink and the ceramic plate are joined, and then the heat sink and the ceramic plate are bonded in the cooling process. Therefore, even if there is a large difference in shrinkage, the deformability can follow, so even if there is a change in temperature due to subsequent use of the device, there is little cracking at the joint and it is a bonding material suitable for ensuring the reliability of power semiconductor devices. It was. However, as described above, in a situation where lead-free solder is required, a bonding material in place of Sn—Pb eutectic solder is required.

  Sn-3Ag-0.5Cu composition, Sn-3Ag-1Bi-3In composition, Sn-3Ag-1Bi composition, or Zn base as shown in Non-Patent Document 1 as an alternative solder for mounting electronic components on printed wiring boards Although alloys and the like have been proposed, the tensile strength of these solders is higher than that of Pb-Sn eutectic solder, but the elongation at break tends to be low. As the bonding material to be used, the deformability is small, and there is a risk that cracks may occur in the bonded portion and the reliability of the power device cannot be ensured.

“Conditions to prevent chip cracking when die-attached with Zn-Al-based lead-free solder” Sumitomo Metal Mining Co., Ltd. Electronic Business Division Technical Center Toshikazu Shimizu, Haruo Ishikawa 6th Symposium on “Microjoining and Assembly in Electronics ”February 3-4,2000, Yokohama

  The present invention provides a bonded body capable of providing a highly reliable bonded body with little occurrence of physical damage such as cracks and fractures in a bonded portion caused by a temperature change of the bonded body, and a bonding method. Is intended to provide.

The present invention comprises a first material to be bonded, at least a surface to be bonded is a metal material,
A second bonded material having at least a bonded surface made of a metal material and having a thermal expansion coefficient equal to or higher than that of the first bonded material;
A bonding layer for bonding the first bonded material and the second bonded material;
The bonding layer is
A plurality of metal particles made of a metal material having a melting point of 300 ° C. or higher and capable of forming a eutectic composition or a solid solution with tin, a tin alloy existing between the metal particles and a tin alloy containing 50% by weight or more, and A metal particle-containing layer present between the tin or the tin alloy and the metal particles, and comprising a compound or solid solution coating containing tin and the metal particle constituent elements, and present on the first bonded material side;
A tin-containing layer present on the second bonded material side using tin or a tin alloy containing 50 wt% or more of tin;
A first bonding interface layer including tin and the first bonded material constituting element, interposed between the first bonded material and the metal particle-containing layer;
A second bonding interface layer containing tin and a second bonded material constituent element, interposed between the second bonded material and the tin-containing layer;
It is a joined body characterized by comprising.

  The present invention also provides a plurality of metal particles made of a metal material having a melting point of 300 ° C. or higher and capable of forming a eutectic composition or a solid solution with tin at least on the surface of the first material to be bonded whose surface to be bonded is a metal material. A metal particle layer containing, a tin-containing layer using a tin alloy containing 50 wt% or more of tin or tin on the surface of the metal particle layer, at least a surface to be bonded is a metal material, and thermal expansion of the first material to be bonded The first bonded material, the metal particle layer, the tin-containing layer, and the second bonded material are stacked so that a second bonded material having a thermal expansion coefficient equal to or greater than the rate is disposed to form a laminate. And a step of heating the laminated body to join the first material to be joined and the second material to be joined.

  The metal particles are preferably particles having irregularities on the surface.

  According to the joined body according to the present invention, there is little occurrence of physical damage such as cracks and fractures caused by temperature changes of the joined body without using a joining material containing a high concentration of lead, which is reliable. A high bonded body can be provided.

  First, the joined body according to the present embodiment will be described.

  FIG. 1 is a schematic cross-sectional view of a joined body according to this embodiment. In this bonded body 4, the first bonding material 1 is bonded to the second bonding material 2 via the bonding layer 3.

  The first material to be bonded 1 and the second material to be bonded 2 have metal materials on at least the surfaces to be bonded, and even those made only of metal materials are metallized surfaces of base materials such as ceramics with metal materials. There may be. The metal material may be a single metal element or an alloy containing a plurality of metal elements.

  The base materials of the first material to be joined and the second material to be joined may be the same material or different materials, but the present invention is particularly effective when the coefficients of thermal expansion are different.

  About the case where it is a material with a high thermal expansion coefficient of the 2nd to-be-joined material 2 compared with a 1st to-be-joined material, the joining layer 3 which joins the 1st to-be-joined material 1 and the 2nd to-be-joined material 2 which both consist of a metal. The cross-sectional microstructure will be described.

  FIG. 2 is a schematic cross-sectional view showing an example of the bonding layer 3 of the bonded body 4 in FIG. As shown in FIG. 2, the bonding layer 3 exists between the first and second bonded materials 1 and 2 of the bonded body 4 and bonds the first and second bonded materials 1 and 2. The bonding layer 3 includes a tin-containing layer 5 present on the second bonded material 2 side, a metal particle-containing layer 6 present on the first bonded material 1 side, a second bonded material 2 and a tin-containing layer 5. And a first bonding interface layer 8 interposed between the first material to be bonded 1 and the metal particle-containing layer 6.

  The tin-containing layer 5 is a layer composed of tin or a tin alloy containing 50 wt% or more of tin.

  The metal particle-containing layer 6 includes a plurality of metal particles 9, a tin alloy 10 containing 50% by weight or more of tin or tin existing between the plurality of metal particles 9, a tin or tin alloy 10, and metal particles 9. And a coating 11 interposed between the two.

  The second bonding interface layer 7 is a layer composed of a compound or a solid solution at least between tin and a constituent element of the second bonded material 2.

  The first bonding interface layer 8 is a layer formed of at least a compound or solid solution between tin and the constituent elements of the first bonded material 1.

  The metal particles 9 are particles using a metal material that has a melting point of 300 ° C. or higher and is a metal or alloy that can form a eutectic composition or a solid solution with tin. The coating 11 is a coating composed of a compound or solid solution between the constituent elements of the metal particles 9 and tin or the tin alloy 10. Further, between the plurality of metal particles 9, tin or a tin alloy containing 50 wt% or more of tin exists.

  As described above, the bonding layer 3 includes the tin-containing layer 5 and the metal particle-containing layer 6, both of which are integrated by including a tin base material having excellent wettability with a metal. Further, at the interfaces between the metal particle-containing layer 6 and the first material to be bonded 1, the second material to be bonded 2 and the tin-containing layer 5, bonding interface layers 8 and 7 are formed, respectively, thereby achieving bonding. Further, the metal particles 9 of the metal particle-containing layer 6 are joined to the tin base material tin or tin alloy 10 by forming a coating 11 around the metal particles 9.

  In the bonding layer 3 as described above, the metal particle-containing layer 6 including the metal particles 9 having a high melting point is present on the side of the first bonded body 1 having a low coefficient of thermal expansion, and the second object having a high coefficient of thermal expansion. The tin-containing layer 6 is present on the bonding material 2 side.

  With such a structure, when the joined body 4 is placed under a high temperature condition, the presence of the metal particle-containing layer 6 containing metal particles having a high melting point causes the first bonded material 1 side of the joining layer 3 to be relatively While the hardness is maintained, the second material to be bonded 2 side is in a state of low hardness due to the presence of the tin-containing layer 5, and each physical property becomes a shape close to that of the material to be bonded. Therefore, the stress generated between the first material to be bonded 1 and the second material to be bonded 2 in the bonding layer 3 can be relaxed.

  In addition, since the plurality of metal particles 9 take such a structure that the composition is dispersed in a gradient composition in the bonding layer 3, a difference in expansion coefficient is generated stepwise from the metal particle-containing layer to the tin-containing layer. The stress generated at the joint between the first and second materials to be joined can be efficiently relaxed by the effect of the gradient material. For example, when a first material to be bonded using ceramics as a base material and a second material to be bonded made of only a metal material are used, the expansion rate is gradually increased in the bonding layer 3 as it approaches the second material to be bonded side. Since it can approach the 2nd to-be-joined material, it becomes possible to acquire joining reliability.

  Furthermore, with this structure, heat transfer can be efficiently performed between the materials to be joined.

  In the joined body of FIG. 1, the first material to be joined 1 and the second material to be joined 2 are made of a metal material, or at least a material in which a metal material is metallized on the surface of the surface to be joined is used. Specific examples include a member made of metal such as copper, germanium, molybdenum, platinum, palladium, vanadium, titanium, zirconium, a member made of an alloy such as SUS stainless steel, a member made of a composite metal material of these metals or alloys, Alternatively, ceramics or polymer material parts in which these metals or alloys are metallized at least on the surfaces to be joined, and metal materials, ceramics or polymer materials in which these metals or alloys are at least metallized on the surfaces to be joined And composite materials.

  Moreover, the material which has a thermal expansion coefficient more than a 1st to-be-joined material is used for a 2nd to-be-joined material. Alternatively, a material having a coefficient of thermal expansion higher than that of the base material of the first material to be joined is used as the base material of the second material to be joined.

  Next, the bonding layer 3 of the bonded body shown in FIG. 1 will be described.

  The content of the metal particles 9 is desirably in the range of 20 to 60 vol% of the entire bonding layer 3. This is because if the amount of the metal particles 9 is too large, the contact between the particles is narrow and the contact between the particles is increased. However, if the amount is too small, the effect of the gradient material cannot be obtained.

  The metal particle-containing layer 6 is a layer containing usually 40% by volume or more of metal particles 9. The content of the metal particles 9 in this layer is preferably in the range of 50% by volume or more and 74% by volume or less in order to enhance the reaction between the particle surface and tin or an alloy containing 50% by weight or more of tin. Moreover, since it becomes difficult to arrange a metal particle uniformly when it exceeds 74 volume%, it is unpreferable.

The thickness of the metal particle-containing layer 6 is desirably in the range of 20% to 60% of the entire bonding layer thickness. This is because the deformability of the bonding layer can be increased within this range.
The plurality of metal particles 9 are desirably particles having an average particle diameter of 100 μm or more and 800 μm or less. The shape of the metal particles is not particularly limited, such as a spherical shape, a lump shape, a polyhedron, and a combination of these shapes, but it is preferable that the surface has irregularities to increase the bonding strength.

  The metal particles 9 are made of a metal material having a melting point of 300 ° C. or higher and capable of forming a eutectic composition or a solid solution with tin. A metal having a melting point of 300 ° C. or more and capable of forming a eutectic composition or a solid solution with tin or an alloy using a metal that forms a eutectic composition or a solid solution with tin is suitable. 2 Metal particles made of metal such as germanium, molybdenum, platinum, palladium, vanadium, titanium, zirconium, etc. having a smaller linear expansion coefficient than copper as the material to be joined, metal particles made of an alloy in which these metals are combined with zinc, and The metal particle which made zinc adhere to these metals is mentioned. In addition, zinc-containing particles containing zinc form a zinc-rich intermetallic compound film at the interface contacting with copper when tin alone or an alloy containing 50 wt% or more of tin is melted, and this phase increases the bonding strength. It is desirable because it has a function.

  The tin alloy 10 containing 50 wt% or more of tin or tin existing between the plurality of metal particles 9 is desirably the same material as the tin alloy used for the tin-containing layer 5 in order to obtain good bonding characteristics. . Specific examples of the tin alloy 10 include an alloy made of tin and copper containing 1% by weight to less than 10% by weight, an alloy made of tin and silver containing 4% by weight to less than 10% by weight, and made of tin and zinc. An alloy containing 1 to 12% by weight of zinc can be used.

  The coating 11 interposed between the tin or tin alloy 10 and the metal particles 9 is an intermetallic compound or solid solution containing constituent elements of the particles and the surrounding tin or tin alloy. This contributes to bonding with the metal particles 9. This composition varies depending on the composition of the tin or tin alloy 10 and the composition of the metal particles 9, but contains a germanium layer in which tin is slightly dissolved, molybdenum and tin in an atomic ratio of about 1: 2 or about 3: 1. Alloy layer, alloy layer containing platinum and tin in an atomic ratio of about 1: 4 or about 1: 2, alloy layer containing palladium and tin in an atomic ratio of 1: 1 to 1: 4, about molybdenum and tin An alloy layer containing an atomic ratio of 1: 2 or about 3: 1, an alloy layer containing palladium and tin in an atomic ratio of 1: 1 to 1: 4, an atomic ratio of vanadium and tin of about 2: 3 An alloy layer comprising titanium and tin in an atomic ratio of about 6: 5 or about 5: 3, an alloy layer comprising zirconium and tin in an atomic ratio of about 1: 2 or about 4: 1, or Zirconium layer containing 7.3 wt% or less of tin, alloy layer containing silver and tin in an atomic ratio of about 3: 1 Tin layer comprising zinc 0.6% by weight or less can be given as specific examples.

For example, in the metal particle-containing layer 6, when the first and second bonded materials 1 and 2 are both copper, the metal particles 9 are palladium particles, and the tin or tin-containing alloys 5 and 10 are tin, An intermetallic compound such as Pd ₃ Sn or PdSn ₄ is formed as the coating 11 formed at the bonding interface between the metal particles 9 and the tin-containing alloy 10.

  The thickness of the coating 11 is preferably in the range of 1 μm to 10 μm.

  The tin-containing layer 5 is a layer composed of tin or a tin alloy containing 50 wt% or more of tin, and the content of materials other than tin is preferably 20 wt% or less, and more preferably 10 wt% or less. In this layer, the content of the metal particles 9 is a layer that is not more than the content of the metal particles 9 in the metal particle-containing layer 6.

  The thickness of the tin-containing layer 5 is desirably in the range of 10 μm to 200 μm. This is because the deformability of the joint can be maintained within this range.

  Specific examples of the tin alloy include an alloy composed of tin and germanium containing 0.2% by weight of germanium, an alloy composed of tin and silver containing 4% by weight to less than 10% by weight, and an alloy composed of tin and aluminum containing 2 aluminum. An alloy containing 0.4% by weight is included.

The second bonding interface layer 7 is a layer composed of at least an intermetallic compound or a solid solution between tin and a constituent element of the second bonded material 2, and has a thickness in the range of 1 μm to 20 μm. Is desirable. This is because within this range, the bonding between the second bonding interface layer 7 and the second bonded material can be maintained. Specific examples of the second bonding interface layer 7 include Cu ₃ Sn, Cu ₅ Sn, Cu ₆ Sn _{5 and the} like.

The first bonding interface layer 8 is a layer composed of at least an intermetallic compound or a solid solution between tin and the constituent elements of the first bonded material 1, and the thickness thereof is in the range of 1 μm to 20 μm. Is desirable. This is because within this range, the bonding between the first bonding interface layer 8 and the first material to be bonded can be favorably maintained. Specific examples of the first bonding interface layer 8 include a reaction layer in which an alloy phase such as Cu ₃ Sn, Cu ₅ Sn, Cu ₆ Sn ₅ or the like is composed of a single layer or a plurality of layers, or these single layers / multilayers A composite reaction layer in which compounds such as Ag ₃ Sn and PdSn ₄ are mixed is used.

  In the joined body of the present embodiment, the content of lead contained in the joining layer including the tin alloy 10 containing 50 wt% or more of tin or tin existing between the plurality of metal particles 9 and the lead-containing layer 5 is 0. It is desirable to set it to 1 wt% or less.

  The joined body according to the present embodiment may be obtained by any method, for example, by the joining method according to the invention.

  FIG. 3 is a schematic cross-sectional view for explaining an embodiment of the joining method.

  First, a tin-containing layer 12 using a tin alloy containing 50% by weight or more of tin processed into a sheet shape on the surface of the second material to be joined 2, and the surface of the tin-containing layer 12 has a melting point of 300 ° C. or higher and tin And a metal particle layer 13 containing a plurality of metal particles 14 made of a metal material capable of forming a eutectic, a second material to be bonded 2, and a tin-containing material so that the first material to be bonded 1 is disposed on the surface of the metal particle layer 13 A laminated body of the layer 12, the metal particle layer 13, and the first bonded material 1 is formed. In FIG. 3, the layers are illustrated separately for the sake of convenience, but in actuality, the layers are stacked so as to be in contact with each other.

  Next, the first bonded material 1 and the second bonded material 2 are bonded by pressurizing the stacked body in the stacking direction (the arrow direction in the figure) or without applying pressure.

  The heating is preferably performed in such a direction that the sheet material is heated as the first step and the metal particles are arranged in the upper layer portion of the sheet material. At this time, it is desirably in the range of 210 to 255 ° C. in an atmosphere maintained at an oxygen concentration of 0 ppm (substantially 1 to 5 ppm which can be regarded as almost oxygen-free below the detection limit of oxygen concentration) and 1000 ppm or less. Preferably it heats in the range temperature range of 210-235 degreeC.

  In heating, the temperature rise condition is appropriately adjusted so that the time during which the joint is in the range of 210 to 235 ° C. is within 0.5 to 5 minutes.

  When the base material of the material to be joined is ceramic, it is desirable that the metal on the surface is metalized with a metal material that is difficult to oxidize. In this case, the bonding material can be directly heated and melted on the surface of the member.

  When the material to be joined or metallized metal material has an oxide formed on the surface, such as copper, hydrogen vapor, alcohol vapor such as methanol vapor, ethanol vapor, and propanol vapor, acid vapor such as formic acid and acetic acid, ammonia It is desirable to reduce the amount of oxygen on the surface of the member by reduction using a reducing gas such as hydrogen.

  When the joined body is a semiconductor device having a heat sink, reflow heating is performed as a second step after heat joining of the sheet material. In reflow heating, in a non-oxidizing atmosphere such as nitrogen gas, argon gas, or the oxygen concentration is 0 ppm or more and 1000 ppm. By performing in the following low oxygen atmosphere, the reliability of the joint surface is increased.

  In this manufacturing method, the tin-containing layer 12 desirably has a thickness in the range of 10 μm to 1000 μm. The tin-containing layer 12 is a layer composed of tin or a tin alloy containing 50 wt% or more of tin, and the content of other materials is preferably 20 wt% or less. The thickness of the tin-containing layer 12 is desirably in the range of 10 μm to 1000 μm. This is because the melting during the reflow heating is completed within a few minutes if it is within this range. This tin-containing layer 12 is preferably formed in advance by plating, vapor deposition, paste reflow, or heating using an alloy sheet material before forming the metal particle layer 13. This is because it becomes easy to secure the tin-containing layer with a certain thickness or more in order to impart deformability to the joint portion of the joined body obtained by the present embodiment.

  Specific examples of the tin alloy include an alloy composed of tin and germanium containing 0.2% by weight of germanium, an alloy composed of tin and zinc and containing 4% by weight to less than 11% by weight, and an alloy composed of tin and aluminum containing 2 aluminum. Examples include alloys containing up to .4% by weight.

  In recent years, the formation of alloy films by reflow heating has attracted attention. For this reason, these alloys are made into a powder having a particle size of 20 to 50 μm, and the obtained powder is dissolved in isopropyl alcohol at a ratio of 1: 4 to 1: 9, and then 0.1% by weight of bromine. The tin-containing layer 12 can be obtained by applying onto the second material to be bonded 2 as a paste obtained by kneading with a flux to which a system activator is added, and reflow heating for 1 to 3 minutes.

  In this manufacturing method, the metal particle layer 13 is a layer formed by aggregating a plurality of metal particles 14. The metal particles 14 are preferably particles having an average particle diameter in the range of 100 μm or more and 800 μm μm or less because the particles are not melted instantaneously.

  The shape of the metal particles 14 may be a spherical shape, a lump shape, a donut-shaped ring, a washer, a cylindrical pellet, or the like. Although the surface form of the metal particles is not particularly limited, it is desirable that the surface has irregularities because the amount of intermetallic compound coating produced can be increased and the bonding strength can be increased.

  The metal particles 14 are made of a metal or alloy having a melting point of 300 ° C. or higher and capable of forming a eutectic or solid solution with tin. An alloy using a metal having a melting point of 300 ° C. or more and capable of forming a eutectic or solid solution with tin or a metal forming a solid solution with tin is suitable. As a specific example, as a general-purpose second bonded material Metal particles made of metals such as germanium, molybdenum, platinum, palladium, vanadium, titanium, zirconium, etc., which have a smaller linear expansion coefficient than copper, metal particles made of alloys of these metals with silver or zinc, or these metals Examples include metal particles to which silver or zinc is attached.

  Furthermore, when the sheet material contains an easily oxidizable element such as aluminum or zinc, the depth is obtained by intermittently irradiating the particle surface with a beam having a high energy density such as a focused ion beam, a laser beam, or an electron beam. It is desirable to increase the surface area by providing irregularities with a particle size of 2 μm to 1/5 or less of the particle size. At this time, if the depth is less than 2 μm, the effect of increasing the surface area is diminished. Furthermore, the irradiation interval is preferably in the range of 5 μm to 1/5 of the diameter of the particle. If the width is smaller than this range, vacancies are likely to occur at the time of joining, and if it is larger than this range, the surface area increases. No effect. At this time, a focused ion beam using gallium ions can be easily obtained together with irradiation with a clear image of channeling contrast. Therefore, it is preferable that the particle surface can be processed while controlling the depth.

  In addition, zinc particles or zinc-containing particles containing zinc have a zinc-rich intermetallic compound film formed at the interface that contacts copper when tin alone or an alloy containing 50 wt% or more of tin is melted. Has the function of increasing strength. Examples of the composition of the zinc-containing particles include 30% by weight of zinc and the remaining copper, 35% by weight of zinc and the remaining copper, 30% by weight of zinc, 1% by weight of nickel and the remaining copper.

  When a metal containing zinc is used, the temperature rises and oxidizes due to heating, which easily affects wettability and strength. Therefore, the preparation of metal particles containing zinc, especially the melting / mixing process, prevents oxidation using a non-oxidizing atmosphere such as nitrogen or argon so that the amount of oxygen contained in the resulting solder material is 100 ppm (weight ratio) or less. However, it is preferable to carry out.

  In order to reduce oxygen contained in tin and zinc used as raw materials, there is a method in which phosphorus, magnesium, etc. having a low melting point and easily reacting with oxygen are added as oxygen scavengers to these molten raw materials. As a result, the oxygen scavenger and oxygen in the molten raw material combine to float on the surface of the molten raw material as slag and can be easily removed. The amount of the oxygen scavenger used is preferably about 0.01 to 0.1% by weight of the raw material. When the raw material deoxygenated by such a method is used, bonding particles whose oxygen content is reduced to 30 ppm or less can be prepared.

  The metal particles 14 consist of a flux in which rosin is dissolved in isopropyl alcohol in a ratio of 1: 4 to 1: 9, and then 0.1% by weight of a bromine-based activator is added, 9% by weight of tin and zinc, and the balance It is kneaded with tin alloy powder (particle size 20-40 μm) to prepare a paste. Note that the flux may be prepared by blending various substances as necessary to efficiently express the chemical action and the physical action. The obtained paste is applied on the tin-containing layer 12 in a thickness range of 200 to 800 μm, and the first material to be bonded 1 is placed thereon and reflow-heated. Further, when zinc or zinc-containing particles are used, the process temperature can be relatively lowered, and a heating temperature of 210 ° C. to 235 ° C. is appropriate.

  The metal particle layer 13 is obtained by heating using a paste obtained by kneading the metal particles 14 together with tin-containing alloy particles and a flux, and 9% by weight of zinc processed into a sheet having a thickness of 200 to 800 μm and the balance. Metal particles 14 are embedded in the tin alloy by pressurization, and rosin is added to isopropyl alcohol in a ratio of 1: 4 to 1: 9 between the sheet in which the metal particles 14 are embedded and the first bonded material 1. It can also be obtained by reflow heating 210 ° C. to 255 ° C. after dropping a flux to which 0.1 wt% bromine-based activator has been dissolved. The thickness of the metal particle layer 13 is desirably 250 μm or more and 900 μm or less.

  The joined body and joining method of this embodiment are highly versatile materials that do not contain lead, and can join parts using equipment and equipment used in the current product assembly manufacturing process. Therefore, it can be used as an alternative to the conventional tin-lead solder, and is suitable for junction formation in electrical equipment with increased temperature, power semiconductor devices, and apparatuses using the same.

  For example, power semiconductor devices use transistors, thyristors, GTO thyristors, diodes, MOSFETs, and the like as power elements, and junctions and devices in devices such as power modules such as power transistor modules and power ICs are incorporated. It can be used for forming a junction in an apparatus.

  The joined body and joining method of the present embodiment can sufficiently cope with fine solder joining, and can cope with solder joining of thin metal members having a narrow interval of 500 μm or less. Depending on the material of the member to be joined, a metal precoat may be applied to the member in advance by plating, pressure bonding, or the like, and the precoat composition and precoat method can be appropriately selected. At this time, instead of the sheet material, a linear 300 to 800 μm alloy wire can be appropriately cut and used on the bonding surface as the bonding material to be used. For example, a plating layer such as nickel / gold flash plating or tin plating or a metal layer formed by applying and heating a paste containing tungsten particles or titanium particles is applied to the side of the power semiconductor device that contacts the solder material. By attaching, the bonding strength of the electrode portion having a width of 1 mm or less can be increased.

  FIG. 4 is a cross-sectional view showing an example of a power semiconductor device to which the joined body according to this embodiment can be applied. This device has a structure in which a heat sink 21 made of copper, a metal circuit board 23, a ceramic board 24, a metal circuit board 25, and a semiconductor pellet 28 are laminated. The heat sink 21 and the metal circuit board 23 are joined by soldering and there is a joining layer 22. The metal circuit board 25 and the semiconductor pellet 28 are also joined by using a solder resist 26 to suppress a short circuit due to solder overflow, and there is a solder joint layer 27. The bonding layer and bonding method of the present embodiment can be applied to the formation of the solder bonding layer 22 and the solder layer 27, but it is particularly preferable that the bonding layer and the bonding method be applied to the solder layer 22 in which a conventional low-temperature solder is used.

  Examples will be described below.

(Examples 1-30 and Comparative Examples 1-3)
In a nitrogen atmosphere with an oxygen concentration of 100 ppm or less, tin with a purity of 99.98%, silver with a purity of 99.98%, nickel with a purity of 99.98%, germanium, platinum, vanadium, palladium, titanium, zirconium, purity 99.99 Metal particles and sheet materials for joining were prepared so as to have the combinations of Examples 1 to 30 and Comparative Examples 1 to 3 in Table 1 using% zinc and aluminum. As for the metal particles, the particles obtained by the atomization method were stored in a container not contaminated with other metals or halogens by nitrogen sealing. Further, when combined with a sheet material containing aluminum, the effects of oxidation are likely to be manifested. Therefore, the focused ion beam using gallium ions on the surface of the metal particles used in Example 14, Example 15, and Example 16 is used in two or more locations. The unevenness was provided at a pitch of 20 to 50 μm until reaching 20% or more of the particle surface, and then stored in a container not contaminated with other metals or halogens by nitrogen sealing.

Next, the sheet material was placed on a copper plate as a heat sink (dimensions: 40 mm × 75 mm × 3 mmt) as a second material to be joined, and heated at a surface temperature of 255 to 265 ° C. Before heating, a flux of isopropyl alcohol containing 12% by weight of rosin as a solvent and 0.1% by weight of a bromine-based activator was dropped onto the heat sink to a rate of 0.01 cc / cm ² and tin alloy was added. Made the layer easier to form.

  Next, the obtained metal particles were kneaded with a flux in which 25% by weight of rosin was dissolved in isopropyl alcohol and 0.1% by weight of a bromine-based activator was added to prepare a paste. Moreover, about Example 1, Example 4, Example 11, Examples 17-19, Example 22, and Examples 25-30, the alloy powder (particle diameter 20 ~) which consists of tin, zinc 9weight%, and remainder tin. 40 μm) and kneaded together to prepare a paste. In any of the examples, the paste obtained in the examples was applied on the tin-containing layer in a thickness range of 200 to 800 μm, and further the first coated layer made of ceramic whose surface to be joined was metallized with a metal layer. The bonding material was placed and reflow heated. The reflow heating at this time was controlled by the peak temperature, and the reflow peak temperature in the range of 225 to 255 ° C. shown in the table was heated for a maximum of 1 minute to integrate the joining materials to obtain a joined body.

When the cross section of the bonding layer of the obtained bonded body of Example 1 was analyzed by SEM-EDX, as shown in FIG. 2, 600 μm existing between the first and second bonded materials 1 and 2 of the bonded body 4. The bonding layer 3 having a thickness of 5 μm on the second bonded material 2 side includes a tin-containing layer 5 having a composition of 99.9% by weight or more, and a coating 11 on the first bonded material 1 side. The composition interposed between the metal particle-containing layer 6 in which metal particles 9 consisting of 30% by weight of zinc having a particle size of 500 μm and the remainder of copper are dispersed, and the second material to be joined 2 and the tin-containing layer 5 is Cu. ₅ Sn ₆ , composition Cu ₅ Zn _{8 having a} thickness of 2 μm, which is interposed between the bonding interface layer 7 (intermetallic compound layer) having a thickness of 5 μm and the first material to be bonded 1 and the metal particle-containing layer 6. There was a bonding interface layer 8 (intermetallic compound layer). Around the metal particles 9, there was an intermetallic compound coating 11 having a thickness of 3 μm in which the compositions Cu ₅ Sn ₆ and Cu ₅ Zn ₈ were mixed.

  Further, in any of the examples, a bonding interface layer 7 made of an intermetallic compound or a solid solution layer between the second bonded material 2 and the tin-containing layer 5, the first bonded material 1 and the metal particle containing Between the layer 6, there was a bonding interface layer 8 made of an intermetallic compound or a solid solution layer. In addition, a coating 11 made of an intermetallic compound or a solid solution containing an element containing tin and a metal compound metal particle was present around the metal particle 9.

Investigating the occurrence of warping of the joined body of each example, A judgment within 30% compared to the current tin-lead eutectic solder, B judgment of 30-70%, 70% or more, or Table 1 shows the results of evaluating the occurrence of cracks as C determination.

Sectional drawing which shows one Embodiment of a conjugate | zygote. Sectional drawing which shows an example of the joining layer of a conjugate | zygote. The cross-sectional schematic for demonstrating one Embodiment of the joining method. Sectional drawing which shows an example of a power semiconductor device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... 1st to-be-joined material 2 ... 2nd to-be-joined material 3 ... Joining layer 4 ... Joined body 5 ... Tin containing layer 6 ... Metal particle containing layer 7 ... 1st 2 bonding interface layer 8 ... first bonding interface layer 9 ... metal particles 10 ... tin or tin alloy 11 ... coating 12 ... tin-containing layer 13 ... metal particle layer 14 ..Metal particles 21 ... heat sink 22 ... bonding layer 23 ... metal circuit board 24 ... ceramic board 25 ... metal circuit board 26 ... solder resist 27 ... solder layer 28 ...・ Semiconductor pellets

Claims (3)

A first material to be bonded, at least a surface to be bonded is a metal material;
A second bonded material having at least a bonded surface made of a metal material and having a thermal expansion coefficient equal to or higher than that of the first bonded material;
A bonding layer for bonding the first bonded material and the second bonded material;
The bonding layer is
A plurality of metal particles made of a metal material having a melting point of 300 ° C. or higher and capable of forming a eutectic composition or a solid solution with tin, a tin alloy existing between the metal particles and a tin alloy containing 50% by weight or more, and A metal particle-containing layer present between the tin or the tin alloy and the metal particles, and comprising a compound or solid solution coating containing tin and the metal particle constituent elements, and present on the first bonded material side;
A tin-containing layer present on the second bonded material side using tin or a tin alloy containing 50 wt% or more of tin;
A first bonding interface layer including tin and the first bonded material constituting element, interposed between the first bonded material and the metal particle-containing layer;
A second bonding interface layer containing tin and a second bonded material constituent element, interposed between the second bonded material and the tin-containing layer;
A joined body comprising:   A metal particle layer containing a plurality of metal particles made of a metal material having a melting point of 300 ° C. or higher and capable of forming a eutectic composition or a solid solution with tin on the surface of the first material to be bonded, at least the surface to be bonded is a metal material; A tin-containing layer using tin or a tin alloy containing 50 wt% or more of tin on the surface of the metal particle layer, at least a bonded surface is a metal material, and has a thermal expansion coefficient equal to or higher than the thermal expansion coefficient of the first bonded material. Laminating the first material to be joined, the metal particle layer, the tin-containing layer, and the second material to be joined to form a laminate, and the lamination. And a step of heating the body to join the first material to be joined and the second material to be joined.   The bonding method according to claim 2, wherein the metal particles are particles having irregularities on the surface.

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