JP2020189307A - Joining sheet and method of manufacturing joining body - Google Patents

Abstract

To provide a joining sheet that can achieve compatibility of heat conductivity and joinability during brazing.SOLUTION: The present invention is a joining sheet having a metallic layer (30), a first layer (31) composed of a first brazing material formed on a first surface of the first layer, and a second layer (32) composed of a second brazing material formed on a second surface of the metallic layer. The metallic layer is composed of high heat conductive metal having a higher melting point than that of the first brazing material and the second brazing material and having a heat conductivity of 300 W/mk or higher. A thickness of the metallic layer is more than 50% relative to the thickness of the whole joining sheet. At least the first brazing material contains 1-10 mass% of an active metallic element in total. When joining, for example, a graphite plate (first layer side) and a copper plate (second layer side) using this joining sheet, high heat conductivity can be secured in their joining parts without causing peeling or warping.SELECTED DRAWING: Figure 1

Description

The present invention relates to a joining sheet or the like used for brazing.

Brazing is one of the methods for joining members. Brazing is common to soldering in that it is joined using a filler material that melts at a temperature lower than the melting point of the members to be joined. However, brazing is distinguished from soldering in which the melting point (liquidus temperature) of the filler metal (brazing material) is 450 ° C. or higher and the melting point is less than 450 ° C.

By the way, in order to perform brazing properly, it is necessary to ensure the wettability of the molten brazing material with respect to the surface to be joined. When the member to be joined (appropriately referred to as "member to be joined") is made of a carbon-based material (graphite or the like) or ceramics having a small surface energy, a brazing material containing an active metal element (to ensure wettability) ( Active metal wax) is used. A description related to this is found in, for example, the following patent documents.

Japanese Unexamined Patent Publication No. 64-87059

Patent Document 1 proposes a brazing material in which a massive active metal is embedded only in the surface layer portion in order to optimize the amount of active metal according to the material of the member to be joined and prevent the activity of the active metal from decreasing.

However, it has been found that when a high thermal conductive member (graphite or the like) is brazed using a brazing material as in Patent Document 1, the thermal conductivity of the bonded body is significantly reduced. It is considered that this is because the active metal element dissolves or precipitates in the bonding layer to increase the thermal resistance of the bonding layer.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a joint sheet or the like capable of ensuring high thermal conductivity of a joint portion formed by brazing.

As a result of diligent research to solve this problem, the present inventor has succeeded in ensuring high thermal conductivity of the joint portion by using a bonding sheet in which a high thermal conductive metal layer and a brazing material are combined. By developing this result, the present invention described below has been completed.

《Joint sheet》
(1) In the present invention, a first layer composed of a metal layer, a first brazing material formed on the first surface of the metal layer, and a second brazing material formed on the second surface of the metal layer. A bonding sheet comprising a second layer composed of, wherein the metal layer has a higher melting point than the first brazing material and the second brazing material and a thermal conductivity of 300 W / m · K or more. It is composed of a conductive metal, and the thickness of the metal layer is 50% or more with respect to the thickness of the entire bonded sheet, and the first brazing material is the sum of active metal elements with respect to the entire first brazing material. It is a bonding sheet containing 1 to 10% by mass.

(2) In the bonded sheet of the present invention, first, the first brazing material constituting the first layer contains an active metal. Therefore, brazing of carbon-based materials, ceramics, etc. is possible at least on the first layer side.

Next, most of the bonded sheet of the present invention is occupied by a metal layer having a higher melting point and higher thermal conductivity than each brazing material. Most of this metal layer remains even after brazing (heating). Therefore, the thermal conductivity of the joint portion is almost dominated by the thermal conductivity of the remaining metal layer, and the joint portion formed after brazing exhibits high thermal conductivity. In other words, the active metal element contained in the first layer is retained in a thin bonding layer near the interface of the surface to be bonded. Therefore, when viewed as a whole, the increase in thermal resistance due to the active metal element is suppressed, and high thermal conductivity is ensured.

By the way, the high thermal conductive metal constituting the metal layer usually has a low Young's modulus (high ductility). Further, the metal layer remaining after brazing has a sufficient thickness. Therefore, the metal layer can relieve the residual stress acting on the joint portion after brazing, the thermal stress generated by the use of the joint body, and the like. Therefore, when the bonding sheet of the present invention is used, it is expected that the bonding failure can be suppressed and the durability (reliability) of the bonded body can be improved. Such stress relaxation properties due to the metal layer are particularly effective when brazing dissimilar members having a large difference in coefficient of thermal expansion (CTE (Coefficient of Thermal Expansion)) and where residual stress or thermal stress is likely to act. It becomes.

<< Manufacturing method of joint >>
The present invention can also be grasped as a method of joining members (a method of manufacturing a joined body) using the above-mentioned joining sheet. For example, the present invention is a method for manufacturing a joined body in which a first member and a second member are joined, wherein the first member (first layer side) and the second member (first layer side) sandwiching the above-mentioned joining sheet are provided. A method for producing a bonded body including a brazing step of heating the second layer side) at a temperature lower than the melting point of the metal layer and at a temperature higher than the temperature at which the first brazing material and the second brazing material are melted may be used. Since the first brazing material contains an active metal element, for example, a first member whose surface to be bonded is made of a carbon-based material (graphite or the like) or ceramics can be bonded to the first layer side of the bonding sheet.

《Joint body》
The present invention can also be grasped as the bonded body. For example, the present invention is a joint body including a first member, a second member that can be joined to the first member, and a joint portion that joins the first member and the second member. Has a metal layer, a first bonding layer for brazing the metal layer and the first member, and a second bonding layer for brazing the metal layer and the second member. It is composed of the first joint layer and a high thermal conductive metal having a higher melting point than the second joint layer and a thermal conductivity of 300 W / m · K or more, and the thickness of the metal layer is the thickness of the entire joint. On the other hand, the first bonding layer may be a bonded body containing 1 to 10% by mass of active metal elements in total with respect to the entire first bonding layer.

The first member bonded by the first bonding layer containing an active metal element has, for example, a surface to be bonded made of a carbon-based material (graphite or the like) or ceramics. When the second bonding layer does not contain an active metal element, the second member bonded by the second bonding layer has, for example, a surface to be bonded made of metal. When the second bonding layer contains an active metal element, the second member bonded by the second bonding layer has, like the first member, a surface to be bonded made of, for example, a carbon-based material or ceramics.

《Others》
(1) In the present specification, the names of the first or the second are used for convenience of explanation. Then, at least the "first" side is the side to be joined by a brazing material containing an active metal element (appropriately referred to as "active metal brazing"). The "second" side may have the same configuration as the "first" side, or may have a different configuration.

(2) Unless otherwise specified, "x to y" in the present specification includes a lower limit value x and an upper limit value y. Any numerical value included in the various numerical values or numerical ranges described in the present specification may be newly established in a range such as "ab" as a new lower limit value or upper limit value. Further, unless otherwise specified, "x to y μm" in the present specification means x μm to y μm. The same applies to other unit systems.

It is sectional drawing which shows typically the joining process using the joining sheet.

One or more components arbitrarily selected from the present specification may be added to the components of the present invention. The contents described in the present specification may apply not only to the bonded sheet and the bonded body of the present invention, but also to the manufacturing method thereof. A component related to "method" can also be a component related to "thing".

《Joint sheet》
The joining sheet has a metal layer serving as a core material, and first and second layers which are brazing material layers formed on the respective surfaces thereof. These will be described in detail below.

(1) Metal layer The metal layer is made of a highly thermally conductive metal having a melting point higher than the temperature at the time of brazing (bonding temperature) and having a thermal conductivity of 300 W / m · K or more and further 350 W / m · K or more. It should be. The highly thermally conductive metal is, for example, either gold, silver or copper. These may be pure metals. The pure metal (pure silver, etc.) referred to in the present specification is a metal having a purity (mass ratio) of 98% or more, further 99% or more.

By the way, gold has a melting point: 1064 ° C., a thermal conductivity: 319 W / m · K, and a Young's modulus: 78 GPa. Silver has a melting point: 962 ° C., a thermal conductivity: 428 W / m · K, and a Young's modulus: 83 GPa. Copper has a melting point of 1085 ° C., a thermal conductivity of 408 W / m · K, and a Young's modulus of 130 GPa. In particular, (pure) silver has a very high thermal conductivity, is soft (low Young's modulus, high ductility), and is excellent in thermal conductivity and stress relaxation.

The thickness of the metal layer is preferably 50% or more, 70% or more, and further 85% or more with respect to the thickness of the entire bonded sheet. By increasing the thickness ratio of the metal layer to the entire joint sheet (or the entire joint portion), the brazing material layer (joint layer) becomes relatively thin, and the thermal conductivity of the joint portion increases. Further, as the metal layer becomes thicker, the stress relaxation property due to the metal layer also increases, but the thermal conductivity of the joint portion decreases accordingly. Therefore, the thickness of the metal layer may be, for example, 10 to 500 μm, 30 to 400 μm, or even 50 to 300 μm.

When the metal layer is formed from the metal foil, the bonded sheet can be efficiently manufactured. The metal foil is, for example, either gold foil, silver foil or copper foil. Since gold, silver or copper has excellent malleability, a metal foil having a desired thickness can be obtained.

(2) Wax layer (first layer, second layer)
The type (composition), thickness, etc. of the brazing material can be selected according to the member to be joined. Therefore, the first layer and the second layer may be the same or different in material and form (thickness, etc.).

The brazing material includes silver brazing, gold brazing, copper brazing, brass brazing, aluminum brazing, nickel brazing and the like. It is selected according to the material of the member to be joined. By using a eutectic alloy system for any of the brazing materials, the melting point (brazing temperature) can be lowered.

Silver wax is used for joining carbon-based materials (graphite, etc.), ceramics, etc., as well as for joining many metal materials, and has good thermal conductivity. Silver wax is usually composed of a silver alloy containing Cu (mainly an Ag-Cu eutectic alloy) in addition to Ag, which is the main component (remaining portion). The silver wax may contain one or more of Zn, Sn, and Ni. It is preferable that the entire brazing material of each layer is 100% by mass, for example, Cu: 20 to 35% by mass, Zn: 0 to 20% by mass, Sn: 0 to 10% by mass, and Ni: 0 to 5% by mass. When any one or more of Zn, Sn and Ni are contained, the lower limit value may be 1% by mass.

When joining members made of aluminum or its alloys, aluminum brazing may be used. Aluminum wax is made of an aluminum alloy, and is usually made of an aluminum alloy containing Si (mainly an Al—Si eutectic alloy) in addition to Al which is the main component (remaining part). Aluminum wax contains, for example, Si: 5 to 20% by mass, with the total amount being 100% by mass. The aluminum wax may further contain one or more of either Mg or Bi.

According to the active metal method, brazing of members made of carbon-based materials, ceramics, etc. is efficient because the pretreatment required for the metallizing method can be omitted. The brazing material used in the active metal method may contain, for example, 1 to 10% by mass and further 3 to 8% by mass of active metal elements in total, in addition to the composition range described above. If the amount of active metal element is too small, the wettability becomes insufficient and bonding becomes difficult. When the amount of active metal element is excessive, the thermal resistance of the bonding layer increases.

The active metal element is, for example, Ti, Zr, Hf, Ta and the like. In particular, the active metal element may contain at least one of Ti and Zr.

The thickness of the first layer and the second layer may be, for example, 1 to 50 μm and further 2 to 10 μm. If the thickness is too small, the formation of the reaction layer required to secure the bonding strength becomes insufficient. If the thickness becomes excessive, the thermal conductivity of the bonding layer decreases.

When the type or composition of the brazing material is different between the first layer and the second layer, the melting point difference between the two materials is, for example, ± 20 ° C. or ± 10 ° C. in order to perform brazing stably and efficiently. It would be nice to have it.

(3) Manufacturing Method The bonded sheet is obtained by laminating a first layer and a second layer (each layer is also simply referred to as a "wax layer") on each surface of a metal layer. Laminating methods include mechanical laminating methods such as rolling, physical deposition methods such as sputtering, and chemical deposition methods such as plating. For example, a bonded sheet (raw fabric) can be obtained by superimposing a high thermal conductive metal foil as a metal layer and a brazing material (alloy) foil as a brazing material layer and hot rolling or clading or the like.

A brazing material layer may be formed by depositing a brazing material (alloy) on a high thermal conductive metal foil by sputtering, vacuum deposition, or the like. The brazing material layer can also be formed by applying (screen printing) a paste composed of fine particles of the brazing material on the metal foil, for example.

<< Member to be joined >>
There may be various members and combinations thereof that are brazed and joined by the joining sheet. The bonding sheet of the present invention may be used for bonding high thermal conductive members. Examples of high thermal conductive members include sheet materials and plate materials made of carbon-based materials. The carbon-based material is, for example, graphite, diamond, carbon nanotube, or the like. These thermal conductivitys are very high, for example, 500-5500 W / m · K. For a sheet material or plate material made of graphite, the ab surface having a high thermal conductivity (the surface perpendicular to the c-axis of graphite) may be the surface to be joined.

A specific example of the high thermal conductive member is, for example, a heat radiating member (including a heat sink, a heat spreader, a cooling plate, a housing, etc.) of a semiconductor device (module).

The members to be joined may be of the same type or different materials. When dissimilar members having a large difference in coefficient of thermal expansion are joined by the joining sheet of the present invention, a joined body in which not only thermal conductivity but also stress relaxation property is ensured can be obtained.

The present invention will be described in more detail while showing an example of joining members using a joining sheet.

"Overview"
FIG. 1 shows a manufacturing process of a bonded body M in which the first member 1 and the second member 2 are brazed using the bonding sheet 3.

The bonding sheet 3 has a metal layer 30 made of a core material (metal foil), a first layer 31 made of a first brazing material laminated on the first surface thereof, and a second layer 31 laminated on the second surface thereof. It has a second layer 32 made of a brazing material. When the first member 1 and the second member 2 sandwiching the joining sheet 3 are heated (brazing step), the first member 1 and the second member 2 become a joined body M joined by the joining portion 4.

The joint portion 4 is composed of a metal layer 40, a first joint layer 41, and a second joint layer 42. The metal layer 40 is formed by reacting the metal layer 30 with the first layer 31 and the second layer 32 by heating during brazing. Similarly, the first bonding layer 41 is formed by reacting the first layer 31 with the bonded surface of the first member 1 and the metal layer 30. The second bonding layer 42 is formed by reacting the second layer 32 with the bonded surface of the second member 2 and the metal layer 30. A thin reaction layer (not shown) is formed at each interface. Further, since the metal layer 30 is made of a metal having a melting point higher than that of the first brazing material and the second brazing material, the metal layer 30 remains as the metal layer 40 almost as it is even after brazing except for the reaction layer.

"Concrete example"
[Sample 1]
(1) Silver alloy as a brazing material (Ag-27% Cu-5% Ti / unit: mass%, the same applies hereinafter) on both sides of a silver foil (purity: 99.98%, thickness: 20 μm) as a core material. Was laminated by the high frequency magnetron sputtering method. The thickness of the brazing filler metal layer was 3 μm. The laminated sheet thus obtained was formed (cut) into a 10 mm square to obtain a bonded sheet.

The joint sheet was sandwiched between two graphite a face plates (10 mm □ × t1 mm / manufactured by Thermographics Co., Ltd.), which are members to be joined. At this time, 30 MPa was applied between the surfaces to be joined. They were heated in a vacuum atmosphere (less than 5 Pa) for 30 minutes using a discharge plasma sintering apparatus. The set temperature on the device was 700 ° C. However, when measured with a thermocouple inserted in the portion corresponding to the joint portion in advance, the sample temperature was about 830 ° C. In this way, a bonded body in which two graphite plates were brazed was obtained.

(2) When the joint was observed with an ultrasonic microscope, no defect was confirmed in the joint. In addition, no warpage was observed in the joint visually. The average thermal conductivity of the joint measured by the laser flash method was 270 W / m · K. The "average" here means the average of the thermal conductivity obtained at five different measurement positions in the same junction (the same applies hereinafter).

[Sample 2]
(1) A bonding sheet was produced in which one of the brazing material layers (second layer) of the bonding sheet of Sample 1 was made of another silver alloy (Ag-28% Cu). Using this bonded sheet, the graphite a face plate (first member) and the oxygen-free copper plate (JIS C1020 / second member) described above were brazed. At this time, the second layer (Ag-28% Cu) of the bonding sheet was made to face the oxygen-free copper plate. Others were brazed under the same conditions as sample 1. In this way, a bonded body in which a graphite plate and a copper plate were brazed was obtained.

(2) When the joint was observed with an ultrasonic microscope, no defect was confirmed in the joint. In addition, no warpage was observed in the joint visually. The average thermal conductivity of the joint measured by the laser flash method was 280 W / m · K.

[Sample C1]
(1) The bonding sheet of Sample 1 was replaced with a commercially available active metal brazing foil (Ag-28% Cu-2% Ti-5% Sn / 10 mm □ × t0.1 mm / manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.). Others were brazed under the same conditions as sample 1. In this way, a bonded body in which two graphite plates were brazed was obtained.

(2) When the joint was observed with an ultrasonic microscope, no defect was confirmed in the joint. In addition, no warpage was observed in the joint visually. The average thermal conductivity of the joint measured by the laser flash method was 110 W / m · K.

[Sample C2]
(1) The bonding sheet of Sample 2 was replaced with the above-mentioned active metal brazing material foil (Ag-28% Cu-2% Ti-5% Sn), and a graphite plate and a copper plate were brazed under the same conditions as Sample 1. .. In this way, a bonded body in which a graphite plate and a copper plate were brazed was obtained.

(2) When the joint was observed with an ultrasonic microscope, no defect was confirmed in the joint. However, the joint was warped. The average thermal conductivity of the joint measured by the laser flash method was 90 W / m · K.

《Evaluation》
As is clear from the results of Sample 1 and Sample 2, when a bonding sheet having a thick metal layer (thickness ratio: about 77%) made of a highly thermally conductive metal is used, bonding defects can be caused between members of the same type or members of different types. It was found that brazing can be performed without causing warpage. It was also found that the joint has low thermal resistance and high thermal conductivity is ensured.

As is clear from the results of Sample C1 and Sample C2, it was found that the thermal conductivity of the joint portion was significantly reduced when the conventional brazing material foil was used. It was also found that brazing of dissimilar members causes poor joining such as warpage.

From the above, it was confirmed that by using the bonding sheet of the present invention, brazing capable of achieving both bondability and thermal conductivity at a high level is possible.

M Joined body 1 First member 2 Second member 3 Joined sheet 30 Metal layer 31 First layer 32 Second layer

Claims (9)

With a metal layer
A first layer made of a first brazing material formed on the first surface of the metal layer, and
A second layer made of a second brazing material formed on the second surface of the metal layer, and
It is a joining sheet provided with
The metal layer is made of a high thermal conductive metal having a melting point higher than that of the first brazing material and the second brazing material and having a thermal conductivity of 300 W / m · K or more.
The thickness of the metal layer is 50% or more with respect to the thickness of the entire bonded sheet.
The first brazing material is a bonding sheet containing 1 to 10% by mass of active metal elements in total with respect to the entire first brazing material. The bonding sheet according to claim 1, wherein the high thermal conductive metal is either gold, silver or copper. The joining sheet according to claim 1 or 2, wherein the first brazing material is made of silver brazing. The bonding sheet according to any one of claims 1 to 3, wherein the active metal element contains at least one of Ti and Zr. The bonding sheet according to any one of claims 1 to 4, wherein the metal layer has a thickness of 10 to 500 μm. The bonding sheet according to any one of claims 1 to 5, wherein the first layer and the second layer have a thickness of 1 to 50 μm. The bonding sheet according to any one of claims 1 to 6, wherein the first layer is used for brazing a surface to be bonded made of graphite. A method for manufacturing a joined body in which a first member and a second member are joined.
The first brazing material and the second brazing material are melted at a temperature lower than the melting point of the metal layer in the first member and the second member sandwiched by the joining sheet according to any one of claims 1 to 6. A method for manufacturing a bonded body including a brazing step of heating above a temperature. The first layer of the joining sheet faces the surface to be joined of the first member.
The method for manufacturing a bonded body according to claim 8, wherein the surface to be bonded of the first member is made of graphite.

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