joint

Abstract

A sintered bonding material containing metal nanoparticles is used to create a bonded body that can be bonded without pressure even when the bonding area is large, suppresses void generation, and improves productivity. [Solution] The jointed body 1 is formed by joining a heat spreader 2 as a first member and a semiconductor element 5 as a second member via a brush structure 3 and a sintered bonding layer 3. The brush structure 4 is formed on the semiconductor element 5 and is composed of a plurality of columnar metal wires 41. The sintered bonding layer 3 is positioned away from a part of the semiconductor element 5 different from the brush structure 4 and is bonded to the tip side of the brush structure 4. In a plane perpendicular to the extension direction D1 of the metal wires 41, the porosity is defined as the area ratio occupied by the gaps between the metal wires 41, and the brush structure 4 has a porosity of 15% to 85%.

Description

Technical Field

[0001] The present disclosure relates to a bonded body using a metal wire and a sintered material.

Background Art

[0002] Conventionally, a bonded body in which two members are sintered and bonded using metal nanoparticles having high thermal conductivity is known. Since organic substances and moisture often adhere to the surface of the metal nanoparticles in the sintered bonding material, these deposits can be released as gas during the sintering bonding process. When the gas generated in the sintering bonding process remains at the joint, voids, that is, gaps are formed, so that the bonded body has reduced bonding strength and reliability. In particular, when the bonding area is large, voids are likely to be generated in the center of the bonding portion. Further, although sintering bonding is performed while applying pressure, when pressure is applied, the members to be bonded may crack or the productivity may decrease. Therefore, in recent years, bonding without pressure has been desired.

[0003] As a bonded body that is sintered and bonded without pressure using a sintered bonding material containing metal nanoparticles, for example, the one described in Patent Document 1 has been proposed. This bonded body is manufactured through a volatilization step of applying a paste of a sintered bonding material to a first member, placing a second member on the paste, and then volatilizing the volatile components contained in the paste, and a sintering step of bonding these members without pressure by heating.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The joint described in Patent Document 1 uses a sintered joining material containing metal nanoparticles, and is joined without pressure even when the joining area is large, and the generation of voids is suppressed because it undergoes a volatilization process. However, this joint needs to be joined by two stages: the volatilization process and the subsequent sintering process by heating, and there is room for improvement in terms of productivity.

[0006] In view of the above, this disclosure aims to provide a bonded body that uses a sintered bonding material containing metal nanoparticles, can be bonded without pressure even when the bonding area is large, and has a structure that achieves both suppression of void generation and improvement of productivity. [Means for solving the problem]

[0007] According to one aspect of this disclosure, the joint is The first member (2) and A second member (5) having a brush structure (4) composed of multiple metal wires (41) extending in a columnar shape, The first member and the brush structure are joined together, and the second member comprises a sintered bonding layer (3) which is positioned away from the part of the second member that is different from the brush structure, The direction in which multiple metal wires are extended is defined as the extension direction (D1), and the void ratio is defined as the area ratio occupied by the gaps between the multiple metal wires in the brush structure in a plane perpendicular to the extension direction. The void ratio of the brush structure is 15% to 85%.

[0008] This joint comprises a first member and a second member having a brush structure, with a sintered bonding layer, positioned away from the portion of the second member different from the brush structure, being bonded to the brush structure. The brush structure is composed of multiple columnar metal wires, and the void ratio, defined as the area ratio occupied by the gaps between the metal wires in a plane perpendicular to the extension direction of the metal wires, is 15% to 85%. Because this joint has a structure in which a brush structure with a void ratio of 15% to 85% is arranged on a sintered bonding layer, gases generated from the material of the sintered bonding layer during the sintering process can be released to the outside through the voids in the brush structure. Therefore, even when sintering is performed without pressure and the area of ​​the joint is large, this joint does not require a volatilization process to release gases generated from the material of the sintered bonding layer, thus achieving both improved productivity and suppression of void generation.

[0009] The reference numerals in parentheses attached to each component indicate an example of the correspondence between that component and the specific components described in the embodiments described later. [Brief explanation of the drawing]

[0010] [Figure 1] This is a cross-sectional view showing a joint according to an embodiment. [Figure 2] Figure 1 is an explanatory diagram of the joining process for the joined body. [Figure 3] This corresponds to the cross-sectional view between III-III in Figure 2, and is an explanatory diagram regarding the void ratio of the brush structure. [Figure 4] This is an explanatory diagram illustrating the suppression of void formation in a joined body according to an embodiment. [Figure 5] This is an explanatory diagram of the joint and void formation in the comparative example. [Figure 6] This figure shows the results of scanning electron microscopy (SEM) observation of a semiconductor device with a brush structure formed on it. [Figure 7] This figure shows the assembled bodies and evaluation results of the examples and comparative examples. [Modes for carrying out the invention]

[0011] The embodiments of this disclosure will be described below with reference to the drawings. In the following embodiments, parts that are the same or equivalent to each other will be denoted by the same reference numerals.

[0012] (Embodiment) The assembled body 1 according to the embodiment will be described below.

[0013] [Basic configuration] The bonded body 1, as shown in Figure 1 for example, has a structure in which a heat spreader 2 as a first member and a semiconductor element 5 as a second member are joined via a sintered bonding layer 3 and a brush structure 4. The bonded body 1 constitutes a semiconductor device in which, for example, the semiconductor element 5 is a power semiconductor and the heat generated when the semiconductor element 5 is driven is diffused to the heat spreader 2 via the brush structure 4 and the sintered bonding layer 3.

[0014] The heat spreader 2 is part of a lead frame made of a conductive material such as copper (Cu) or iron (Fe) or an alloy thereof, and is formed by press punching or the like. The heat spreader 2 is a heat dissipation member that releases heat from the semiconductor element 5 to the outside during operation. One surface 2a of the heat spreader 2 is joined to the brush structure 4 formed on the semiconductor element 5 by a sintered bonding layer 3. The term "heat spreader" here refers to a member with a configuration that can efficiently dissipate heat, and may be not only the lead frame described above, but also, for example, an insulating heat dissipation substrate with metal layers such as copper formed on both sides of a ceramic substrate, or other known heat dissipation members.

[0015] The sintered bonding layer 3 is obtained, for example, by heating a sintered bonding material having metal nanoparticles at a temperature below the melting point and sintering it. As the metal nanoparticles, for example, copper, silver (Ag), or other metal materials having a higher thermal conductivity than solder or a combination thereof are used. Having a higher thermal conductivity than solder means, for example, having a thermal conductivity higher than 35 W / mK of a general lead-rich solder (Pb-5Sn). For example, other metal nanoparticles include, but are not limited to, gold (Au), nickel (Ni), etc. The metal nanoparticles are, for example, metal particles having a particle size on the order of nanometers, such as several tens of nm or more and several hundreds of nm or less.

[0016] As shown in, for example, FIG. 2, the sintered bonding layer 3 is obtained by applying the above-described sintered bonding material 30 to one surface 2a of the heat spreader 2, placing the semiconductor element 5 having the brush structure portion 4 thereon, and sintering it by heating without applying pressure. The sintered bonding layer 3 is bonded to the heat spreader 2 and the brush structure portion 4, but is not directly bonded to the semiconductor element 5. That is, the sintered bonding layer 3 is arranged away from a portion of the semiconductor element 5 different from the brush structure portion 4 and is bonded to the tip side of the brush structure portion 4. The sintered bonding layer 3 has, for example, a thickness t in the extending direction D1 of the metal wire 41 described later of 10 μm or more and 500 μm or less.

[0017] The brush structure portion 4 is composed of a plurality of columnar metal wires 41 extending on one surface 5a of the semiconductor element 5. The brush structure portion 4 serves as a heat transfer path for transferring the heat of the semiconductor element 5 to the heat spreader 2, with the tip sides of the plurality of metal wires 41 being bonded to the sintered bonding layer 3.

[0018] The plurality of metal wires 41 are, for example, made of other metal materials with a higher thermal conductivity than copper, silver or solder and are electrically plating - capable, and are columnar wire bodies extending in a substantially straight line by electroplating. "Substantially straight line" means not only a state formed in a straight line along the normal direction to one surface 5a of the semiconductor element 5, but also a state that is not in a straight line along the normal direction due to inevitable factors in the process, but is slightly inclined and can be regarded as substantially straight. In other words, taking the direction along which the metal wires 41 extend as the extension direction D1, the angle formed by the plurality of metal wires 41 and the one surface 5a is perpendicular or substantially perpendicular. Since the plurality of metal wires 41 are joined to the sintered joint layer 3 without pressure, they remain substantially straight after joining.

[0019] The plurality of metal wires 41 are formed, for example, by forming a seed layer (not shown) on one surface 5a of the semiconductor element 5 and a patterned resist layer partially covering the seed layer, and then performing electroplating and growing from the exposed portion of the seed layer from the resist layer. The above - mentioned resist layer (not shown) is removed after electroplating. The plurality of metal wires 41, for example, taking the length in the extension direction D1 as the height h, the height h is set to be 5 μm or more and 500 μm or less.

[0020] Here, for example, as shown in FIG. 3, a plane perpendicular to the extension direction D1 of the metal wire 41 is defined as an "orthogonal plane", and in the orthogonal plane, the gap between the metal wires 41 is defined as a "gap portion 42". As shown in FIG. 4, for example, the gap portion 42 serves as a gas flow path for discharging the gas generated from the sintered joint material 30 to the outside in the sintering process using the sintered joint material 30, and plays a role in suppressing the generation of voids in the sintered joint layer 3.

[0021] Furthermore, the area ratio occupied by voids 42 within the brush structure 4 is defined as the "porosity," and the brush structure 4 is specified to have a porosity of 15% to 85%. If the porosity of the brush structure 4 is less than 15%, the gas generated from the sintered bonding layer 3 has difficulty escaping to the outside, making it difficult to suppress void generation in the sintered bonding layer 3. For example, as in the comparative example bond 100 in Figure 5, when the heat spreader 2 and the semiconductor element 5 are bonded using only the sintered bonding layer 110 without pressure, the gas generated from the sintered bonding material cannot escape to the outside, and voids V are generated in the sintered bonding layer 110. If the porosity of the brush structure 4 is less than 15%, the same phenomenon as bonding using only the sintered bonding layer 110, i.e., a porosity of 0%, occurs. On the other hand, if the porosity of the brush structure 4 exceeds 85%, the heat dissipation path from the semiconductor element 5 to the heat spreader 2 decreases, and the thermal conductivity decreases. In other words, the bonded body 1 has a structure in which the porosity of the brush structure 4 is in the range of 15% to 85%, which allows for both ensuring thermal conductivity between the heat spreader 2 and the semiconductor element 5, and suppressing voids in the sintered bonding layer 3.

[0022] The porosity is defined as the area ratio of the void portion 42 when the outermost outline of the brush structure 4 is considered as a rectangle in an orthogonal plane, as shown by the dashed line in Figure 3, and the area of ​​this rectangle is set to 100%. Furthermore, since the bonding between the heat spreader 2 and the semiconductor element 5 is performed without pressure, the porosity of the brush structure 4 is approximately the same before and after bonding with the sintered bonding layer 3.

[0023] The semiconductor element 5 is, for example, a plate-like structure with one surface 5a, and is mainly composed of semiconductor materials such as Si (silicon), SiC (silicon carbide), GaN (gallium nitride), GaO (gallium oxide), and diamond. The semiconductor element 5 is, for example, a power semiconductor element such as an IGBT or a power MOSFET, and is manufactured by a known semiconductor process. IGBT and MOSFET are abbreviations for Insulated Gate Bipolar Transistor and Metal Oxide Semiconductor Field Effect Transistor, respectively. As shown in Figure 6, for example, the semiconductor element 5 has multiple metal wires 41 with lengths on the order of micrometers formed on one surface 5a. Figure 6 shows the result of observing a cross-section of the semiconductor element 5 with a scanning electron microscope before bonding to the heat spreader 2.

[0024] The above describes the basic structure of assembly 1.

[0025] In this specification, the case in which the bonded body 1 is applied to a semiconductor device with a single-sided heat dissipation structure is described as a representative example, but it is not limited to this. For example, the bonded body 1 may be a semiconductor device with a double-sided heat dissipation structure in which a heat dissipation member is bonded to the opposite side of the semiconductor element 5. Also, for example, the bonded body 1 may have a structure in which the heat dissipation member is the first member and the heating element is the second member, with a brush structure portion 4 formed on one of these members and a sintered bonding layer 3 arranged on the other, and the sintered bonding layer 3 and the tip side of the brush structure portion 4 are bonded together. For example, the bonded body 1 may be applied to configurations other than semiconductor devices, such as an electronic device in which the heating element is an electronic component other than a semiconductor element, and the components other than the bonding structure of the sintered bonding layer 3 and the brush structure portion 4 may be changed as appropriate.

[0026] [Examples] Next, we will describe the results of simulation evaluations of the presence or absence of voids in the sintered bonding layer 3 and the thermal conductivity for several configurations of bonding structures having a sintered bonding layer 3 and a brush structure 4 between the heat spreader 2 and the semiconductor element 5, as well as comparative examples.

[0027] The simulation evaluation can be performed using, for example, known numerical analysis software such as the finite element method, or a multilayer heat conduction calculation model. The simulation evaluation results shown in Figure 7 were performed under the premise that the junction between the copper heat spreader 2 and the SiC semiconductor element 5 is performed without pressure, and by changing various settings of the structure and material conditions of the junction. Furthermore, the simulation evaluation in Figure 7 was obtained by calculation using a theoretical formula for a parallel planar multilayer model.

[0028] Furthermore, regarding the presence or absence of voids among the evaluation items shown in Figure 7, a "○" was used if no voids were found in the sintered bonding layer 3 in the simulation results, and a "×" was used if voids were found. Also, regarding the thermal conductivity among the evaluation items shown in Figure 7, the entire configuration between the heat spreader 2 and the semiconductor element 5 was considered the bonding area, and a "○" was used if the thermal conductivity of the bonding area was 60 W / mK or higher in the simulation results, and a "×" was used if it was less than 60 W / mK.

[0029] Comparative Examples 1 and 2 and Examples 1 to 5 have a sintered bonding layer 3 and a brush structure 4 as the joint, and the constituent material of these is copper. Examples 6 and 7 differ from Examples 1 to 5 in that the constituent material of the sintered bonding layer 3 is silver.

[0030] In Example 1, after bonding, the height of the metal wire 41 was 5 μm, the porosity of the brush structure 4 was 70%, and the thickness of the sintered bonding layer 3 was 10 μm. In Example 1, there was no void formation in the sintered bonding layer 3, and the overall thermal conductivity of the sintered bonding layer 3 and the brush structure 4 was good at 60 W / mK or higher.

[0031] In Example 2, after joining, the height of the metal wire 41 was 500 μm, the porosity of the brush structure 4 was 70%, and the thickness of the sintered bonding layer 3 was 10 μm. Similar to Example 1, in Example 2, void generation was suppressed, and the thermal conductivity of the joint was also ensured.

[0032] In Example 3, after joining, the height of the metal wire 41 was 5 μm, the porosity of the brush structure 4 was 70%, and the thickness of the sintered bonding layer 3 was 500 μm. Similar to Example 1, in Example 3, void generation was suppressed, and the thermal conductivity of the joint was also ensured.

[0033] In Example 4, after joining, the height of the metal wire 41 was 500 μm, the porosity of the brush structure 4 was 85%, and the thickness of the sintered bonding layer 3 was 500 μm. Similar to Example 1, in Example 4, void generation was suppressed, and the thermal conductivity of the joint was also ensured.

[0034] In Example 5, after joining, the height of the metal wire 41 was 500 μm, the porosity of the brush structure 4 was 15%, and the thickness of the sintered bonding layer 3 was 500 μm. Similar to Example 1, in Example 5, void generation was suppressed, and the thermal conductivity of the joint was also ensured.

[0035] The above evaluation results suggest that void suppression in the sintered bonding layer 3 is possible when the sintered bonding layer 3 and the metal wire 41 are made of copper, the porosity is between 15% and 85%, the thickness of the sintered bonding layer 3 is between 10 μm and 500 μm, and the height of the metal wire 41 is between 5 μm and 500 μm. In this case, it is also possible to ensure thermal conductivity between the heat spreader 2 and the semiconductor element 5, thus achieving both void suppression in the sintered bonding layer 3 and ensuring heat dissipation of the semiconductor element 5.

[0036] In Example 6, after joining, the height of the metal wire 41 was 500 μm, the porosity of the brush structure 4 was 85%, and the thickness of the sintered bonding layer 3 was 500 μm, with silver used as the sintered bonding layer 3. Similar to Example 1, void generation was suppressed in Example 6, and the thermal conductivity of the joint was also ensured.

[0037] In Example 7, after joining, the height of the metal wire 41 was 500 μm, the porosity of the brush structure 4 was 15%, and the thickness of the sintered bonding layer 3 was 500 μm, with silver used as the sintered bonding layer 3. Similar to Example 1, void generation was suppressed in Example 7, and the thermal conductivity of the joint was also ensured.

[0038] The evaluation results for Examples 6 and 7 indicate that when the sintered bonding layer 3 is made of silver, the height of the metal wire 41 and the thickness of the sintered bonding layer 3 are 500 μm, and the porosity is between 15% and 85%, it is possible to achieve both void suppression and ensure thermal conductivity at the joint. Furthermore, considering the evaluation results for Examples 1 to 5, it is considered that even when the sintered bonding layer 3 is made of silver, it is possible to achieve both void suppression and ensure thermal conductivity at the joint if the height of the metal wire 41 is 5 μm or more and the thickness of the sintered bonding layer 3 is 10 μm or more.

[0039] On the other hand, in Comparative Example 1, after joining, the height of the metal wire 41 and the thickness of the sintered bonding layer 3 were 500 μm, and the porosity of the brush structure 4 was 10%. In Comparative Example 1, although the thermal conductivity of the joint was good, voids were formed in the sintered bonding layer 3. Based on these results, it is thought that when the porosity of the brush structure 4 is at least 10% or less, the flow path for gas generated from the sintered bonding material decreases, and voids are generated because the gas cannot escape to the outside.

[0040] Comparative Example 2 had the following conditions after joining: the height of the metal wire 41 and the thickness of the sintered joining layer 3 were 500 μm, and the porosity of the brush structure 4 was 90%. In Comparative Example 2, although void generation in the sintered joining layer 3 was suppressed, the thermal conductivity of the joint was less than 60 K / mK. Based on these results, it is considered that when the porosity of the brush structure 4 is at least 90%, gas generated from the sintered joining material can be released to the outside, but the reduction in the number of metal wires 41 makes it impossible to ensure sufficient thermal conductivity at the joint.

[0041] Comparative Example 3 lacks a sintered bonding layer 3 and a brush structure 4, and the heat spreader 2 and semiconductor element 5 are bonded using solder. Although no voids were generated in Comparative Example 3, the thermal conductivity was less than 60 K / mK, failing to achieve both void suppression and sufficient thermal conductivity at the joint.

[0042] Based on the above evaluation results, it is considered that in order to achieve both void suppression and ensure thermal conductivity of the joint in the joined body 1 having a sintered bonding layer 3 and a brush structure 4, the void ratio of the brush structure 4 must be at least 15% to 85%. Furthermore, it is preferable that the thickness of the sintered bonding layer 3 of the joined body 1 is 10 μm to 500 μm, and the length of the metal wire 41 is 5 μm to 500 μm. In addition, it is preferable that the sintered bonding layer 3 and the metal wire 41 of the joined body 1 are composed of copper or silver, but it is considered that it is possible to achieve both void suppression and ensure thermal conductivity of the joint even if a metal material with higher thermal conductivity than solder is used.

[0043] According to this embodiment, the joint 1 comprises a heat spreader 2 as a first member, a semiconductor element 5 as a second member having a brush structure 4, and a sintered bonding layer 3 positioned away from the part of the second member that is different from the brush structure 4. The sintered bonding layer 3 is bonded to the brush structure 4. The brush structure 4 is composed of a plurality of columnar metal wires 41, with a void ratio of 15% to 85%. Since the joint 1 has a brush structure 4 with a void ratio of 15% to 85% on the sintered bonding layer 3, gas generated from the material of the sintered bonding layer 3 during the sintering process can be released to the outside through the voids 42 of the brush structure 4. Therefore, even when sintering is performed without pressure and the area of ​​the bonded portion is large, a volatilization process to release gas generated from the material of the sintered bonding layer 3 to the outside is unnecessary, resulting in a joint 1 structure that can achieve both improved productivity and suppression of void generation. The joint 1 also has the following features.

[0044] (1) The jointed body 1 has a height equal to the length along the extension direction D1 of the brush structure 4, and the height of the multiple metal wires 41 is 500 μm or less. Although it is thought that the void suppression effect can be obtained even if the height of the metal wires 41 exceeds 500 μm, from the viewpoint of improving productivity and reducing manufacturing costs, the height is preferably 500 μm or less.

[0045] (2) The joined body 1 has a thickness of 500 μm or less along the extension direction D1 of the sintered bonding layer 3.

[0046] (3) The joint 1 is composed of multiple metal wires 41 made of copper, silver, or a metal material with a higher thermal conductivity than solder.

[0047] (4) The bonded body 1 has a sintered bonding layer 3 made of copper, silver, or a metal material with a higher thermal conductivity than solder.

[0048] (Other embodiments) This disclosure is described in accordance with the embodiments, but it is understood that this disclosure is not limited to such embodiments or structures. This disclosure also includes various modifications and variations within the equivalence range. In addition, various combinations and forms, as well as other combinations and forms including one, more, or less of those elements, fall within the scope and concept of this disclosure.

[0049] It goes without saying that, in each of the above embodiments, the elements constituting the embodiment are not necessarily essential unless explicitly stated to be particularly essential or unless they are clearly considered essential in principle. Furthermore, in each of the above embodiments, when numerical values ​​such as the number, numerical values, quantities, or ranges of the components of the embodiment are mentioned, the embodiment is not limited to those specific numbers unless explicitly stated to be particularly essential or unless it is clearly limited to a specific number in principle. Furthermore, in each of the above embodiments, when the shape, positional relationship, etc., of the components are mentioned, the embodiment is not limited to those shapes, positional relationships, etc., unless explicitly stated or unless it is clearly limited to a specific shape, positional relationship, etc., in principle.

[0050] (Perspective of this disclosure) The above disclosure can be understood from the following perspectives, for example. [First point of view] A joint, The first member (2) and A second member (5) having a brush structure (4) composed of multiple metal wires (41) extending in a columnar shape, The first member and the brush structure are joined together, and the sintered bonding layer (3) is positioned away from the portion of the second member that is different from the brush structure, The extension direction (D1) is defined as the direction in which the plurality of metal wires are extended, and the void ratio is defined as the area ratio occupied by the gaps between the plurality of metal wires in the brush structure in a plane perpendicular to the extension direction, wherein the brush structure has a void ratio of 15% or more and 85% or less. [Second perspective] The joint according to the first aspect, wherein the brush structure is such that the height of the plurality of metal wires is 500 μm or less, with the length along the extension direction being the height. [Third perspective] The bonded body according to the first or second aspect, wherein the sintered bonded layer has a thickness of 500 μm or less along the extension direction. [Fourth perspective] The joint according to any one of the first to third aspects, wherein the plurality of metal wires are composed of copper, silver, or a metallic material having a higher thermal conductivity than solder. [Fifth perspective] The bonded body according to any one of the first to fourth aspects, wherein the sintered bonding layer is composed of copper, silver, or a metallic material with a higher thermal conductivity than solder. [Explanation of Symbols]

[0051] 2. Heat spreader (first component) 3. Sintered bonding layer 4. Brush structure 41 Metal wire 5. Semiconductor element (second component) D1 Extension direction of metal wire

Claims

1. A joint, The first member (2) and A second member (5) having a brush structure (4) composed of multiple metal wires (41) extending in a columnar shape, The first member and the brush structure are joined together, and the sintered bonding layer (3) is positioned away from the portion of the second member that is different from the brush structure, The direction in which the plurality of metal wires extend is defined as the extension direction (D1), and in a plane perpendicular to the extension direction, the area ratio occupied by the gaps between the plurality of metal wires in the brush structure is defined as the void ratio, wherein the brush structure has a void ratio of 15% or more and 85% or less.

2. The joint according to claim 1, wherein the brush structure has a height equal to the length along the extension direction, and the height of the plurality of metal wires is 500 μm or less.

3. The bonded body according to claim 2, wherein the sintered bonding layer has a thickness of 500 μm or less along the extension direction.

4. The joint according to claim 3, wherein the plurality of metal wires are made of copper, silver, or a metal material with a higher thermal conductivity than solder.

5. The bonded body according to claim 4, wherein the sintered bonding layer is composed of copper, silver, or a metallic material with a higher thermal conductivity than solder.

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