Solder-metal mesh composite and its manufacturing method

Abstract

Provided is a solder-metal mesh composite material characterized in that a metal mesh that exhibits high thermal conductivity is contained within a lead-free solder layer formed from a Sn-Cu-Ni-based lead-free solder, the proportion of pores in a cross section in the thickness direction is 15% or less, and the Sn-Cu-Ni-based lead-free solder either contains 0.1-2 wt% of Cu and 0.002-1 wt% of Ni, with the remainder being Sn, or contains 0.1-2 wt% of Cu, 0.002-1 wt% of Ni and 0.001-1 wt% of Ge, with the remainder being Sn. This solder-metal mesh composite material is a member that exhibits heat resistance, excellent thermal conductivity and high bonding reliability. In cases where the solder-metal mesh composite material is used as a solder bonding material at a bonding section of an electronic device or a heat-dissipating material, because the number of pores in a soldered body is low, it is possible to efficiently transfer heat generated by an electronic component and form a bonding section having superior thermal conductivity and high bonding reliability.

Description

[Technical Field]

[0001] The present invention relates to a solder-metal mesh composite and a method for manufacturing the same, particularly to a solder-metal mesh composite that is suitable for use in joining electronic components in electronic circuits exposed to high temperatures, and a method for manufacturing the same, and also to a soldered joint formed using the solder-metal mesh composite. [Background technology]

[0002] In recent years, semiconductor elements (power devices) used in power converters such as inverters and converters in electric vehicles, hybrid vehicles, air conditioners, and various general-purpose motors have been attracting attention as devices used to effectively utilize energy. The more power loss during power conversion and the higher the operating voltage of the power device, the higher its performance. Furthermore, there is a demand for power devices to operate at high temperatures due to demands for miniaturization of cooling mechanisms in systems. Therefore, in power devices that require the above-mentioned performance, the solder that joins the electronic components together must also be able to withstand high-temperature operation under high-voltage loads. However, it is widely known that the strength of the joints between electronic components deteriorates when the electronic components are exposed to high temperatures or temperature changes.

[0003] Therefore, as one method to solve the above problems, a composite material has been developed in which a thin metallic Cu and Ni mesh is embedded in the solder joint of SAC305 (composed of "tin (Sn), silver (Ag), and copper (Cu)" and expressed as Sn-3.0Ag-0.5Cu, an alloy of 3.0 wt% silver, 0.5 wt% copper, and the remainder tin) (Non-Patent Document 1). However, with metal prices currently fluctuating and rising, this is also affecting the metals used in solder alloys, with the price of silver having a particularly large impact. Therefore, solders such as the SAC305 solder mentioned above, which contain 3.0% silver by weight, are not desirable from a cost perspective. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Adrian Lis et al., Materials and Design 160 (2018) 475-485 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a solder-metal mesh composite material that is heat-resistant, has excellent thermal conductivity, and has high bonding reliability, a method for manufacturing the same, and a soldered joint formed using such a solder-metal mesh composite material. [Means for solving the problem]

[0006] The present inventors have been conducting intensive research to solve the above-mentioned problems, and have discovered that by incorporating a metal mesh with high thermal conductivity into a lead-free solder layer made of a specific Sn-Cu-Ni-based lead-free solder, it is possible to achieve heat resistance and excellent thermal conductivity, and since the solder has excellent fluidity and progress when pressure is applied during the manufacturing process, it is easy to adjust the thickness to the desired level, and moreover, the occurrence of voids that affect the heat resistance and thermal conductivity in the soldered joint after joining is reduced, thereby completing the present invention.

[0007] That is, the gist of the present invention is (1) A solder-metal mesh composite material, characterized in that a lead-free solder layer formed from a Sn-Cu-Ni-based lead-free solder contains a metal mesh having high thermal conductivity, the ratio of voids in a cross section in the thickness direction being 15% or less, and the Sn-Cu-Ni-based lead-free solder contains 0.1 to 2 wt% Cu, 0.002 to 1 wt% Ni, the balance being Sn, or 0.1 to 2 wt% Cu, 0.002 to 1 wt% Ni, 0.001 to 1 wt% Ge, the balance being Sn; (2) The solder-metal mesh composite according to (1), wherein the metal mesh is a copper mesh. (3) A soldered joint formed using the solder-metal mesh composite material according to (1) or (2). (4) A method for producing a solder-metal mesh composite, comprising: a step of coating a surface of a metal mesh having high thermal conductivity with a Sn-Cu-Ni based lead-free solder to obtain a solder-coated metal mesh; a step of placing the solder-coated metal mesh between Sn-Cu-Ni lead-free solder sheets, and then heating the metal mesh to a temperature equal to or higher than the melting point of the Sn-Cu-Ni lead-free solder while applying pressure to melt the lead-free solder sheets; Cooling the molten solder until it solidifies and recovering the solder-metal mesh composite. Including, a method for producing a solder-metal mesh composite material, characterized in that the Sn-Cu-Ni based lead-free solder contains 0.1 to 2 wt% Cu, 0.002 to 1 wt% Ni, and the balance being Sn, or 0.1 to 2 wt% Cu, 0.002 to 1 wt% Ni, and 0.001 to 1 wt% Ge, and the balance being Sn; (5) The manufacturing method according to (4), wherein the metal mesh is a copper mesh. (6) The manufacturing method according to (4) or (5), in which a Sn-Cu-Ni based lead-free solder sheet, the solder-coated metal mesh, and a Sn-Cu-Ni based lead-free solder sheet are placed between a heat-resistant plate A and a heat-resistant plate B in this order, and then heat is applied from the heat-resistant plate B side while pressure is applied from the heat-resistant plate A side. Regarding. [Effects of the Invention]

[0008] The solder-metal mesh composite of the present invention is a heat-resistant component with excellent thermal conductivity and high joint reliability. Furthermore, because there are few voids in the solder joint, when it is used as a solder joint material in the joints of electronic devices or heat dissipation materials, it is possible to efficiently transfer the heat generated by the electronic components, and to form joints with even better thermal conductivity and high joint reliability. Therefore, the solder-metal mesh composite of the present invention can be suitably used as a bonding material for electronic components or a bonding material for heat dissipation materials such as heat sink materials in semiconductor elements (power devices) used in power converters such as inverters and converters in electric vehicles, hybrid vehicles, air conditioners, and various general-purpose motors. [Brief explanation of the drawings]

[0009] [Figure 1] 1 shows a schematic diagram of a cross section in the thickness direction of a solder-metal mesh composite material 1 of the present invention. In the solder-metal mesh composite material 1, a metal mesh 3 having high thermal conductivity is enclosed in a composite layer 2, which is a lead-free solder layer formed from a Sn-Cu-Ni-based lead-free solder. The composite layer 2 is mainly composed of a lead-free solder 4 and the metal mesh 3. [Figure 2] A schematic diagram of an example of the solder-metal mesh composite of the present invention is shown. Figure 2(a) shows the stacked state of each component before pressing and heating. The Sn-Cu-Ni lead-free solder sheet 6, solder-coated metal mesh 5, and Sn-Cu-Ni lead-free solder sheet 6 are placed between heat-resistant plate A7 and heat-resistant plate B8 in this order, and then placed on heating device 9. Figure 2(b) shows the state after the components are stacked on heating device 9 as shown in Figure 2(a). While applying pressure from above to heat-resistant plate A7, heating device 9 is heated to the desired temperature. This heats heat-resistant plate B8 to a temperature above the melting point of the Sn-Cu-Ni lead-free solder, melting the lead-free solder sheet 6 and integrating it with the solder-coated metal mesh 5. [Figure 3]This shows an image of the thickness direction cross section of the solder-metal mesh composite material 1 obtained in Example 1, observed with a digital microscope. In the solder-metal mesh composite material 1, a copper mesh 3 is enclosed in a composite layer 2 formed from a Sn-Cn-Ni-based lead-free solder. Although voids 11 are observed in the composite layer 2, the proportion of voids in the thickness direction cross section is 1% or less. [Figure 4] 1 shows an image of a cross section in the thickness direction of the solder-metal mesh composite obtained in Comparative Example 2A, observed with a digital microscope. [Figure 5] This shows the image after binarization of the image in Figure 4. The proportion of voids in the cross section of the composite layer in the thickness direction was 15.1%. DETAILED DESCRIPTION OF THE INVENTION

[0010] As shown in Figure 1, the solder-metal mesh composite 1 of the present invention is characterized in that a metal mesh 3 having high thermal conductivity is contained in a composite layer 2 formed from a Sn-Cu-Ni-based lead-free solder, the proportion of voids in the thickness direction cross section is 15% or less, and the Sn-Cu-Ni-based lead-free solder contains 0.1 to 2 wt% Cu, 0.002 to 1 wt% Ni, the balance being Sn, or 0.1 to 2 wt% Cu, 0.002 to 1 wt% Ni, 0.001 to 1 wt% Ge, the balance being Sn.

[0011] In the solder-metal mesh composite material 1 of the present invention, the composite layer 2 formed from Sn-Cu-Ni based lead-free solder is basically composed of Sn-Cu-Ni based lead-free solder 4 and the enclosed metal mesh 3. Furthermore, as will be described later, during production, heating may be performed to cause a reaction between the lead-free solder 4 and the metal mesh 3, resulting in an intermetallic compound at the interface between the lead-free solder 4 and the metal mesh 3 (not shown).

[0012] The thickness of the composite layer 2 is not particularly limited as long as it provides the effects of the present invention.

[0013] Examples of the Sn-Cu-Ni based lead-free solder (hereinafter also referred to as lead-free solder) include lead-free solder containing 0.1 to 2 wt % Cu, 0.002 to 1 wt % Ni, and the balance being Sn, or lead-free solder containing 0.1 to 2 wt % Cu, 0.002 to 1 wt % Ni, and 0.001 to 1 wt % Ge, and the balance being Sn. In the solder-metal mesh composite material of the present invention, by using the lead-free solder, a joining member with significantly fewer voids and excellent thermal conductivity can be obtained, as will be described later. The lead-free solder may also contain elements such as Bi, In, Sb, P, Ga, Co, Mn, Mo, Ti, Al, and Au. The content of these elements is not particularly limited as long as it does not significantly alter the thermal conductivity of the lead-free solder.

[0014] In the present invention, the high thermal conductivity of the metal mesh means that the metal mesh has a thermal conductivity higher than that of the lead-free solder. Examples of materials for the metal mesh having high thermal conductivity include metals that have higher thermal conductivity than the lead-free solder and have higher melting points than the lead-free solder, such as relatively inexpensive copper, copper-based alloys, tin-based alloys, etc. Among these, copper (Cu) is preferred because Sn-Cu-Ni-based lead-free solder has good wettability to the metal mesh and the strength of the solder-metal mesh composite of the present invention is high. Furthermore, the shape of the metal mesh is not particularly limited as long as it has the effects of the present invention, and a wire diameter that makes it easy to control the process of incorporating it into Sn-Cu-Ni-based lead-free solder and improves the strength of the solder-metal mesh composite of the present invention is preferred. The wire diameter is not particularly limited as long as the effects of the present invention are achieved, but for example, the wire diameter is preferably 500 μm or less, more preferably 100 μm or less.Furthermore, the cross-sectional shape of the wires of the metal mesh is preferably circular or elliptical. Furthermore, the opening size of the metal mesh is not particularly limited as long as it has the effect of the present invention, and any opening size can be used as long as it has good wettability with Sn-Cu-Ni-based lead-free solder and does not cause the mesh to break during the manufacturing process of the solder-metal mesh composite of the present invention or cause problems when the mesh is incorporated into the lead-free solder. Furthermore, the solder-metal mesh composite material, in which the lead-free solder of the present invention contains a metal mesh with high thermal conductivity, can be processed to a predetermined size by rolling so as not to break the metal mesh. The size of the metal mesh is not particularly limited as long as it is suitable for mounting on an electronic device.

[0015] In the solder-metal mesh composite 1 of the present invention, the percentage of voids in the thickness direction (L) cross section refers to the void area (excluding the area of ​​the copper wire) that occupies the entire area of ​​the solder-metal mesh composite 1 within the intersection section of the knitted wire 1, which is the repeating unit of the metal mesh. The detection of voids in the solder-metal mesh composite 1 can be carried out using an X-ray fluoroscopy device that observes a fluoroscopic image of the solder-metal mesh composite 1 from vertically above or below. If necessary, an X-ray CT device may also be used. Next, the thickness cross section containing the detected voids is observed with a digital microscope, and the proportion of voids in the thickness cross section can be measured from the obtained image in accordance with IEC 61191-6:2010, an international standard established by the International Electrotechnical Commission (IEC).

[0016] In the solder-metal mesh composite 1 of the present invention, the proportion of voids in the thickness direction (L) cross section is 15% or less, and from the viewpoint of excellent thermal conductivity and bonding reliability, 10% or less is preferable, and 5% or less is more preferable. For example, as in Comparative Example 2A described below, even SAC305, a typical lead-free solder composition with a proven track record, contains 15.1% voids. In comparison, the solder-metal mesh composite 1 of the present invention in Example 1 has a low proportion of voids in the solder joint, as described above. Therefore, when used as a solder joint material in the joints of electronic devices, it is possible to efficiently transfer heat generated by electronic components, and to form joints with better thermal conductivity and higher joint reliability. When a soldered joint is formed using a solder-metal mesh composite material with a low proportion of voids as in Example 1, it becomes possible to suppress the occurrence of voids in the resulting joint.

[0017] The method for producing the solder-metal mesh composite material of the present invention having the above-described structure (hereinafter also referred to as the method of the present invention) is as follows: A step (first step) of coating the surface of a metal mesh having high thermal conductivity with Sn-Cu-Ni-based lead-free solder to obtain a solder-coated metal mesh; a step (second step) of placing the solder-coated metal mesh between Sn-Cu-Ni lead-free solder sheets, and then heating the metal mesh to a temperature equal to or higher than the melting point of the Sn-Cu-Ni lead-free solder while applying pressure to melt the lead-free solder sheets; A process of cooling the molten solder until it solidifies and recovering the solder-metal mesh composite material (third process) The method includes the steps of:

[0018] In the first step, the surface of a metal mesh having high thermal conductivity is coated with Sn-Cu-Ni based lead-free solder to obtain a solder-coated metal mesh. By coating the surface of the highly thermally conductive metal mesh with Sn-Cu-Ni lead-free solder in the first step, the lead-free solder sheet melted in the second step and the solder coating on the metal mesh can be easily blended together, resulting in a homogeneous solder. As a result, the occurrence of voids in the composite layer can be reduced, and the solder-metal mesh composite can be efficiently produced while significantly reducing the proportion of voids in the composite layer 2. In particular, the Sn-Cu-Ni lead-free solder has excellent fluidity when molten, allowing it to efficiently coat the openings of the metal mesh quickly.

[0019] Methods for coating the surface of a metal mesh having high thermal conductivity with the lead-free solder include, but are not limited to, a method in which the metal mesh is immersed in molten lead-free solder (dip method), a method in which molten lead-free solder is poured onto the surface of the metal mesh, and a method in which the metal mesh is sandwiched between solder sheets on both sides and then the solder sheets are melted. The lead-free solder is used in a molten state by being heated above its melting point during the coating process.

[0020] The coating state is not particularly limited as long as the gaps between the meshes of the metal mesh are filled with the lead-free solder.

[0021] Furthermore, by previously applying flux to the surface of the metal mesh before coating with the lead-free solder, the lead-free solder can be coated with a good finish. The method for applying the flux includes, but is not limited to, a method of immersing the metal mesh in the flux (dipping method) and a method of applying the flux to the surface of the metal mesh.

[0022] The flux has a basic composition consisting of an activator and a solvent, and the activator may be one selected from malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, maleic acid, citric acid, tartaric acid, and benzoic acid. The content is not particularly limited as long as the effects of the present invention are achieved, but is preferably 4.55 mmol / g to 45.5 mmol / g per 100 g of flux.

[0023] The solvent used in the flux is not particularly limited as long as it achieves the effects of the present invention, but examples include alcohols such as ethanol, isopropanol, and isobutanol; glycol ethers such as butyl carbitol and hexyl carbitol; glycols such as ethylene glycol and diethylene glycol; esters such as ethyl propionate and butyl benzoate; hydrocarbons such as n-hexane and dodecane; terpene derivatives such as 1,8-terpine monoacetate and 1,8-terpine diacetate; and isobornylcyclohexanol. The content of the solvent can be set as desired within a range that satisfies the effects of the activator and the application and stability of the flux.

[0024] After the coating, the metal mesh is cooled to obtain a solder-coated metal mesh. The cooling temperature is not particularly limited as long as it is equal to or lower than the melting point of the lead-free solder.

[0025] In the second step, the solder-coated metal mesh is placed between Sn-Cu-Ni-based lead-free solder sheets (hereinafter also referred to as lead-free solder sheets), and then heated to a temperature above the melting point of the lead-free solder while applying pressure to melt the lead-free solder sheets. In the second step, the solder-coated metal mesh is sandwiched between two lead-free solder sheets, and then pressurized and heated, causing the lead-free solder coated on the metal mesh and the lead-free solder sheet to melt and become one. Furthermore, because the metal mesh is pre-coated with lead-free solder, the lead-free solder sheet melts and blends easily with the lead-free solder coated on the metal mesh, achieving homogeneity and the advantage that voids are less likely to form even when integrated. Furthermore, when the lead-free solder composition contains 0.1 to 2 weight percent Cu, 0.002 to 1 weight percent Ni, and 0.001 to 1 weight percent Ge, with the remainder being Sn, the solder has excellent fluidity when melted, so that when the metal mesh is dipped into molten solder, the solder flows smoothly into the openings of the metal mesh, has good wettability with the metal mesh, suppresses the inclusion of voids, and enables the metal mesh to be coated uniformly.Furthermore, when the pressurized heating is performed after melting, the excellent fluidity has the advantage of making it less likely for voids to occur in the solder.

[0026] The size of the lead-free solder sheet is not particularly limited as long as it is the same size as the electronic components to be joined, such as semiconductor elements, or heat dissipation materials, such as heat sink materials. The thickness of the lead-free solder sheet is not particularly limited as long as it can be adjusted appropriately depending on the application of the solder-metal mesh composite.

[0027] The second step may be performed, for example, by applying pressure and heat as shown in Figures 2(a) and 2(b). Specifically, as shown in Figure 2(a), a Sn-Cu-Ni lead-free solder sheet 6, the solder-coated metal mesh 5, and another Sn-Cu-Ni lead-free solder sheet 6 are stacked in this order between a heat-resistant plate A7 and a heat-resistant plate B8.

[0028] The heat-resistant plate A7 may be a sheet of a size and thickness that allows easy application of pressure to the solder-coated metal mesh 5, lead-free solder sheet 6, etc., and there are no particular limitations on the thickness and size. Furthermore, the size of the heat-resistant plate A7 may be made larger than the solder-coated metal mesh 5, and spacers 10 may be provided around the solder-coated metal mesh 5. The material of the heat-resistant plate A7 and the spacer is preferably one that has excellent heat resistance, is easy to process, and is inexpensive, and examples thereof include ceramics such as alumina and zirconia, as well as aluminum, steel, and stainless steel, but there is no particular limitation.

[0029] Next, as shown in FIG. 2(b), the heat-resistant plate A7 is pressed from the outside while the heat-resistant plate B8 is heated from the outside. The means for applying pressure is not particularly limited as long as it is a method that applies a uniform load to the metal mesh having high thermal conductivity and the lead-free solder sheet, and examples include hydraulic or air pressing, and application of pressure by placing a weight on top. The degree of pressure is not particularly limited as long as it is sufficient to ensure a thickness that will produce the effects unique to the solder-metal mesh composite of the present invention, and may be set arbitrarily to achieve a target that is suitable for the object to be joined.

[0030] The heat-resistant plate B8 may be a sheet of a size and thickness that allows easy heating of the laminate of the solder-coated metal mesh 5 and lead-free solder sheet 6 between it and the heat-resistant plate A7, and there are no particular limitations on the thickness or size.

[0031] The heat-resistant plate B8 can be heated, for example, by connecting a heating device 9 to the lower surface of the heat-resistant plate B8 or by heating the entire heat-resistant plate B8 in a high-temperature bath. The heating temperature may be any temperature equal to or higher than the melting point of the lead-free solder that constitutes the lead-free solder sheet 6. In addition, the upper limit of the heating temperature is preferably adjusted to within a temperature range of the melting point of the lead-free solder + 50°C, from the viewpoints of preventing quality deterioration such as oxidation of the lead-free solder and economic efficiency. For example, when the lead-free solder contains 0.1 to 2 wt % Cu, 0.002 to 1 wt % Ni, 0.001 to 1 wt % Ge, and the remainder Sn, the heating temperature can be adjusted to approximately 227 to 350°C to efficiently melt the lead-free solder sheet 6 that sandwiches the solder-coated metal mesh 5 from above and below. Also, when the Sn-Cu-Ni based lead-free solder contains 0.1 to 2 wt % Cu and 0.002 to 1 wt % Ni, and the remainder Sn, the heating temperature can be adjusted to approximately 227 to 350°C.

[0032] In the third step, the solder melted in the second step is cooled until it solidifies, and the solder-metal mesh composite is collected.

[0033] The method of cooling the molten lead-free solder sheet or the like until the solder solidifies includes a method of cooling while maintaining the pressurized state in the second step. The cooling temperature may be any temperature below the temperature at which the lead-free solder solidifies, but from the viewpoint of efficient cooling, it is preferable to cool at a lower temperature.

[0034] As described above, after the molten solder has cooled to solidify, the pressurized state is released and the solder-metal mesh composite is recovered.

[0035] If the molten solder has solidified and leaked from the end of the solder-metal mesh composite, the leaked portion may be cut off or the solder-metal mesh composite may be molded into the desired shape. To achieve a more uniform thickness of the solder-metal mesh composite, the surface of the solder-metal mesh composite may be polished or flattened using a three-roll mill or press. Furthermore, the solder-metal mesh composite may be rolled to a predetermined size to prevent breakage of the metal mesh.

[0036] The solder-metal mesh composite of the present invention can be used, like conventional solder, as a bonding material for electronic components or a bonding material for heat dissipation materials such as heat sink materials.

[0037] A soldered joint according to the embodiment is formed using the solder-metal mesh composite, and includes a predetermined substrate and a joint formed by the solder-metal mesh composite joined to the substrate. The substrate is not particularly limited as long as it is for electronic components used in semiconductor elements (power devices).The substrate may also be a heat dissipation material such as a heat sink material, and is not particularly limited. The solder-metal mesh composite can be bonded in a conventional manner, for example, by a reflow method. The heating temperature may be adjusted appropriately depending on the heat resistance of the substrate and the melting temperature of the solder alloy used in the solder-metal mesh composite material. In order to prevent the formation of voids in the bonded body, a process such as decompression may be carried out during bonding.

[0038] The solder joint formed in this manner has heat resistance at the joint and excellent thermal conductivity, resulting in high joint reliability. Therefore, even if the joint is heated by heat generated by electronic components in a high-voltage load environment, distortion stress is unlikely to occur inside the joint and the joint can withstand the stress. Therefore, the solder-metal mesh composite of the present invention can be suitably used as a bonding material for electronic components, for example, in semiconductor elements (power devices) used in power converters such as inverters and converters in electric vehicles, hybrid vehicles, air conditioners, and various general-purpose motors. It is also suitable for joining heat-dissipating materials such as heat sink materials, for which heat dissipation characteristics are an important factor, and applications are expected. [Example]

[0039] Example 1 A commercially available copper mesh (wire diameter approximately 50 μm, mesh size 75 μm, length 6 cm, width 6 cm) was immersed in a container containing flux (NS-334 low-residue no-clean flux manufactured by Nippon Superior Co., Ltd.). The copper mesh was removed from the container, excess flux was removed, and then the mesh was immersed in a container containing SN100C (a lead-free solder with a composition of Sn-0.7Cu0.05Ni+Ge manufactured by Nippon Superior Co., Ltd.) that had been heated to 260°C and melted to perform lead-free solder coating.The mesh was then removed from the container, and excess SN100C was removed to obtain a solder-coated copper mesh. Next, as shown in Figure 2(a), the obtained solder-coated copper mesh 5 was sandwiched between two SN100C sheets 6 of the same size to create a laminate, which was then sandwiched between alumina plate A7 (2.5 cm long, 7.5 cm wide, 0.6 mm thick) and alumina plate B8 (5 cm long, 5 cm wide, 500 μm thick) from the outside of the SN100C sheet 6, and placed on a heating device 9 with the alumina plate B8 side facing up. Spacers 10 having a thickness of 120 μm were provided on both ends of the alumina plate A7. Next, as shown in Figure 2(b), a pressure of 0.5 atm was applied from above the alumina plate 7 using a pressure device, while the temperature of the heating device 9 was adjusted to 227°C. After confirming that the SN100C sheet 6 melted and that the molten SN100C had leaked from the laminate to the outside of the alumina plate 7, heating was stopped. Next, the mixture was cooled using a local fan, and after it was confirmed that the leaked SN100C had solidified, the pressure was released to obtain a solder-metal mesh composite in which copper mesh was embedded in the lead-free solder layer of SN100C.

[0040] (Test Example 1) In the solder-metal mesh composite obtained in Example 1, the proportion of voids in the thickness direction cross section was measured using an X-ray fluoroscopy device to observe a fluoroscopic image of the solder-metal mesh composite 1 from vertically above or vertically below in accordance with IEC61191-6:2010 (not shown). Next, an image of the cross section in the thickness direction observed with a digital microscope is shown in Figure 3. The proportion of pores 11 in the cross section in the thickness direction was measured in accordance with IEC61191-6:2010 based on the image shown in FIG. 3, and was found to be 1%. Therefore, the solder-metal mesh composite obtained in Example 1 is a component with high strength and excellent thermal conductivity because it contains copper mesh, and furthermore, since there are significantly fewer voids in the solder joint, it is found to have higher heat resistance, better thermal conductivity, and high joint reliability even in high-voltage load environments, and to be able to withstand high-temperature operation. Therefore, it can be seen that the solder-metal mesh composite obtained in Example 1 can be suitably used as a bonding material for electronic components and heat dissipation materials such as heat sink materials in semiconductor elements (power devices) used in power converters such as inverters and converters in electric vehicles, hybrid vehicles, air conditioners, and various general-purpose motors.

[0041] (Test Example 2) Sample 1 was prepared in the same manner as in Example 1, except that the metal mesh was not used (Comparative Example 1). For each sample (n=4) of Example 1 and Comparative Example 1, the density, specific heat, and thermal diffusivity were measured according to the following procedure, and then the thermal conductivity was calculated.

[0042] <Density measurement> According to Archimedes' method, each sample of Example 1 and Comparative Example 1 was submerged in water in a container with the same inner diameter as the sample, and the sample volume was measured from the change in the liquid level before and after adding the sample, and calculated from the sample weight.

[0043] <Specific heat measurement> Using a differential scanning calorimeter DSC3500 (manufactured by NETZSCH), the specific heat of each sample of Example 1 and Comparative Example 1 was measured by the DSC method under an argon atmosphere at room temperature using sapphire as a reference material.

[0044] <Measurement of thermal diffusivity> The thermal diffusivity of each sample of Example 1 and Comparative Example 1, which had been subjected to blackening treatment using the aerosol dry graphite film-forming lubricant DGF (manufactured by Nippon Senpaku Tool Co., Ltd.), was measured in air at room temperature using a laser flash analyzer LFA457 (manufactured by NETZSCH).

[0045] <Thermal conductivity> For each sample of Example 1 and Comparative Example 1, the thermal conductivity was calculated from the density, specific heat, and thermal diffusivity obtained as described above according to the following formula. Thermal conductivity (W / (m K)) = Thermal diffusivity (m 2 / s)×density(Kg / m 3 ) × specific heat (J / (Kg K))

[0046] The above results are shown in Table 1.

[0047] [Table 1]

[0048] The results shown in Table 1 show that the solder-metal mesh composite obtained in Example 1 has a significantly increased thermal conductivity of approximately three times that of Sample 1 in Comparative Example 1 due to the inclusion of metal mesh.

[0049] (Test Example 3) Sample 2A (Comparative Example 2A) was produced in the same manner as in Example 1, except that the solder was changed to SAC305 (composition: Sn-3Ag-0.5Cu composition) instead of SN100C. Similarly, Sample 3A (Comparative Example 3A) was produced in the same manner as in Example 1, except that the solder was changed from SN100C to Sn-5Sb. Furthermore, Samples 2B and 3B were prepared in the same manner as Comparative Examples 2A and 3A, except that no metal mesh was used (Comparative Examples 2B and 3B). Next, the thermal conductivity of each of the samples (n=4) of Comparative Examples 2A, 2B, 3A, and 3B was measured in the same manner as in Test Example 2. The results are shown in Table 1. In addition, Table 1 shows the calculated ratio of the thermal conductivity of a sample with a metal mesh to the thermal conductivity of a sample without a metal mesh when the solder alloy is the same.

[0050] From the results shown in Table 1, the thermal conductivity of the solder-metal mesh composite material obtained in Example 1 was the highest compared to Comparative Examples 2A and 3A. Furthermore, the thermal conductivity of the solder-metal mesh composite obtained in Example 1 tended to be higher than that of the solder-metal mesh composite without the mesh. In particular, when the thermal conductivity ratio of the solder-metal mesh composite obtained in Example 1 was taken as 100, it was higher than that of SAC305 (96.5), a typical lead-free solder composition with a proven track record, and Sn-5Sb (89.7), which has a high melting point.

[0051] Furthermore, for Comparative Example 2A, as in Test Example 1, the proportion of voids in the thickness direction cross section was measured using an X-ray fluoroscopy device to observe a fluoroscopic image of the solder-metal mesh composite 1 from vertically above or vertically below in accordance with IEC61191-6:2010. Next, an image of the cross section in the thickness direction observed with a digital microscope is shown in Figure 4. The proportion of voids in the thickness direction cross section was measured (FIG. 5) by binarizing the image shown in FIG. 4 in accordance with IEC 61191-6:2010, and was found to be 15.1%. This indicates that the voids in the solder joint of Comparative Example 2A were significantly larger. The voids remaining in the state of Comparative Example 2A may impair the thermal conductivity of the solder joint, preventing the power device from fully performing its functions, and may also impair the joint reliability required for electronic components.

[0052] Therefore, a solder-metal mesh composite using a Sn-Cu-Ni based lead-free solder containing 0.1 to 2 wt % Cu, 0.002 to 1 wt % Ni, 0.001 to 1 wt % Ge, with the remainder being Sn, is a bonding material with higher heat resistance and better thermal conductivity, and higher bonding reliability, even when the components heat up in a high-voltage load environment, and can therefore be suitably used as a bonding material for electronic components of semiconductor elements (power devices) used in power converters such as inverters and converters in electric vehicles, hybrid vehicles, air conditioners, and various general-purpose motors, as well as a bonding material for heat dissipation materials such as heat sinks.

[0053] In addition, a solder-metal mesh composite was prepared using a Sn-Cu-Ni based lead-free solder containing 0.1 to 2 wt. % Cu, 0.002 to 1 wt. % Ni, and the remainder being Sn, and measurements were carried out in the same manner as in Test Examples 1 and 2. As with the solder-metal mesh composite obtained in Example 1, all of the results showed significantly fewer voids and higher thermal conductivity. Therefore, the lead-free solder in the solder-metal mesh composite of the present invention, in which the solder alloy contains 0.1 to 2 wt % Cu, 0.002 to 1 wt % Ni, and the remainder Sn, is a bonding material with higher heat resistance and better thermal conductivity, and higher bonding reliability, even when the components heat up in a high-voltage load environment, and can therefore be suitably used as a bonding material for electronic components of semiconductor elements (power devices) used in power converters such as inverters and converters in electric vehicles, hybrid vehicles, air conditioners, and various general-purpose motors, or as a bonding material for heat dissipation materials such as heat sink materials. [Explanation of symbols]

[0054] 1. Solder-metal mesh composite 2 Composite layer formed by Sn-Cu-Ni lead-free solder 3. Metal mesh with high thermal conductivity 4 Sn-Cu-Ni lead-free solder 5 Solder-coated metal mesh 6 Sn-Cu-Ni lead-free solder sheet 7 Heat-resistant plate A 8 Heat-resistant plate B 9 Heating device 10 spacers 11 Vacancies

Claims

1. A lead-free solder layer formed by heating and melting a Sn-Cu-Ni lead-free solder, followed by cooling and solidifying, includes a metal mesh having a higher thermal conductivity than the Sn-Cu-Ni lead-free solder, The ratio of pores in the thickness direction cross section is 5% or less, The solder-metal mesh composite material is characterized in that the Sn-Cu-Ni based lead-free solder contains 0.1 to 2 wt % Cu, 0.002 to 1 wt % Ni, and the balance being Sn, or contains 0.1 to 2 wt % Cu, 0.002 to 1 wt % Ni, and 0.001 to 1 wt % Ge, and the balance being Sn.

2. The solder-metal mesh composite of claim 1 , wherein the metal mesh is a copper mesh.

3. A soldered joint formed using the solder-metal mesh composite material according to claim 1 or 2.

4. 1. A method for manufacturing a solder-metal mesh composite, comprising: a step of coating a surface of a metal mesh having a higher thermal conductivity than the Sn—Cu—Ni-based lead-free solder with the Sn—Cu—Ni-based lead-free solder to obtain a solder-coated metal mesh; a step of placing the solder-coated metal mesh between Sn—Cu—Ni-based lead-free solder sheets, and then heating the metal mesh to a temperature equal to or higher than the melting point of the Sn—Cu—Ni-based lead-free solder while applying pressure to melt the lead-free solder sheets; cooling the molten solder until it solidifies and recovering the solder-metal mesh composite. Including, The Sn-Cu-Ni based lead-free solder contains 0.1 to 2 wt % of Cu, 0.002 to 1 wt % of Ni, and the balance being Sn, or contains 0.1 to 2 wt % of Cu, 0.002 to 1 wt % of Ni, and 0.001 to 1 wt % of Ge, and the balance being Sn; A method for producing a solder-metal mesh composite, characterized in that the proportion of voids in a cross section of the solder-metal mesh composite in the thickness direction is 5% or less.

5. The method of claim 4 , wherein the metal mesh is a copper mesh.

6. 6. The manufacturing method according to claim 4 or 5, wherein a Sn—Cu—Ni-based lead-free solder sheet, the solder-coated metal mesh, and a Sn—Cu—Ni-based lead-free solder sheet are arranged between a heat-resistant plate A and a heat-resistant plate B in this order, and then heat is applied from the heat-resistant plate B side while pressure is applied from the heat-resistant plate A side.

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