Solder-metal mesh composite and method for manufacturing the same

Abstract

A solder-metal mesh composite material characterized by a lead-free solder layer formed by a Sn-Cu-Ni lead-free solder, wherein a metal mesh having high thermal conductivity is included, and the ratio of vacancies in the cross-section in the thickness direction is 15% or less, and wherein the Sn-Cu-Ni lead-free solder comprises 0.1 to 2 wt% Cu and 0.002 to 1 wt% Ni with the remainder being Sn, or comprises 0.1 to 2 wt% Cu, 0.002 to 1 wt% Ni and 0.001 to 1 wt% Ge with the remainder being Sn. The solder-metal mesh composite of the present invention is a material with high bonding reliability that has heat resistance and excellent thermal conductivity, and also has few pores in the solder joint, so when used as a solder joint material in the joint of an electronic device or heat dissipation material, it is possible to efficiently transfer heat emitted by electronic components and form a joint with better thermal conductivity and high bonding reliability.

Description

Technology Field

[0001] The present invention relates to a solder-metal mesh composite and a method for manufacturing the same. In particular, the invention relates to a solder-metal mesh composite suitable for joining electronic components in electronic circuits exposed to high temperatures and a method for manufacturing the same. Furthermore, the invention relates to a solder joint formed using the solder-metal mesh composite. Background Technology

[0002] Recently, semiconductor devices (power devices) used in power converters, such as inverters and converters, for devices used for the efficient utilization of energy, such as electric vehicles, hybrid vehicles, air conditioners, and various general-purpose motors, are attracting attention.

[0003] Regarding the aforementioned power devices, components that exhibit low power loss during power conversion and can be used in high-voltage load environments are considered to have high performance. Furthermore, high-temperature operation of power devices is also required due to demands such as the miniaturization of system cooling mechanisms.

[0004] Therefore, in power devices requiring such performance as described above, solder, which serves as a bonding material between electronic components, is also required to withstand high-temperature operation in a high-voltage load environment. However, it is widely known that when electronic components reach a high temperature or are exposed to temperature changes, the bonding strength of the electronic components deteriorates.

[0005] Therefore, as one method to solve the above problem, a composite material containing a thin metal Cu and Ni mesh within a solder joint of SAC305 (composed of tin (Sn), silver (Ag), and copper (Cu), expressed as Sn-3.0Ag-0.5Cu, with 3.0 wt% silver and 0.5 wt% copper and the remainder being tin alloy) has been developed (Non-patent Literature 1).

[0006] However, as metal prices are fluctuating and skyrocketing, they are affecting the metals used in solder alloys, and since the impact of silver prices is particularly significant, solder containing as much as 3.0 weight% silver, such as the SAC305 solder mentioned above, is not desirable from a cost perspective. Prior art literature

[0007] Non-patent literature 1 Adrian Lis et al., Materials and Design 160(2018) 475-485 The problem to be solved

[0008] The objective of the present invention is to provide a solder-metal mesh composite with high joining reliability, excellent heat resistance and thermal conductivity, and a method for manufacturing the same. In addition, the invention is to provide a solder joint formed using such a solder-metal mesh composite. means of solving the problem

[0009] The inventors of the present invention, while conducting careful research to solve the above problem, discovered that by including a metal mesh having high thermal conductivity in a lead-free solder layer made of a specific Sn-Cu-Ni-based lead-free solder, the solder has heat resistance and excellent thermal conductivity, and also has excellent fluidity and progression of the solder during the manufacturing process and pressure, making it easy to adjust to a desired thickness and reducing the occurrence of voids affecting heat resistance and thermal conductivity in the solder joint after bonding, and thus completed the present invention.

[0010] In other words, the gist of the present invention is,

[0011] (1) A lead-free solder layer formed by Sn-Cu-Ni lead-free solder, wherein a metal mesh having high thermal conductivity is included, and the ratio of vacancies in the cross-section in the thickness direction is 15% or less, and wherein the Sn-Cu-Ni lead-free solder comprises 0.1 to 2 wt% Cu and 0.002 to 1 wt% Ni with the remainder being Sn, or comprises 0.1 to 2 wt% Cu, 0.002 to 1 wt% Ni and 0.001 to 1 wt% Ge with the remainder being Sn.

[0012] (2) The solder-metal mesh composite material described in (1) above, wherein the metal mesh is a copper mesh,

[0013] (3) A solder joint formed using the solder-metal mesh composite material described in (1) or (2) above,

[0014] (4) A method for manufacturing a solder-metal mesh composite,

[0015] A process of obtaining a solder-coated metal mesh by coating a Sn-Cu-Ni-based lead-free solder on the surface of a metal mesh having high thermal conductivity,

[0016] A process of placing the above solder-coated metal mesh between Sn-Cu-Ni lead-free solder sheets, and subsequently heating the above lead-free solder sheets to a temperature above the melting point of the Sn-Cu-Ni lead-free solder while applying pressure to melt the above lead-free solder sheets.

[0017] A process of cooling the molten solder until it solidifies and recovering the solder-metal mesh composite

[0018] Including,

[0019] A method for manufacturing a solder-metal mesh composite, characterized in that the above Sn-Cu-Ni lead-free solder comprises 0.1 to 2 wt% Cu and 0.002 to 1 wt% Ni with the remainder being Sn, or comprises 0.1 to 2 wt% Cu, 0.002 to 1 wt% Ni and 0.001 to 1 wt% Ge with the remainder being Sn.

[0020] (5) The manufacturing method described in (4) above, wherein the metal mesh is a copper mesh,

[0021] (6) A Sn-Cu-Ni lead-free solder sheet, the solder-coated metal mesh, and the Sn-Cu-Ni lead-free solder sheet are arranged in that order between heat-resistant plate A and heat-resistant plate B, and then heat is applied from the heat-resistant plate A side while heating from the heat-resistant plate B side. This is the manufacturing method described in (4) or (5).

[0022] It is about. Effects of the invention

[0023] The solder-metal mesh composite of the present invention is a material that has heat resistance, excellent thermal conductivity, and high bonding reliability. In addition, because there are few pores in the solder joint, when used as a solder joint material in the joint of an electronic device or a heat dissipation material, it is possible to efficiently transfer heat generated by electronic components, thereby forming a joint with better thermal conductivity and high bonding reliability.

[0024] Therefore, it can be seen that the solder-metal mesh composite of the present invention can be suitably used as a bonding material for electronic components or heat sink materials, etc., in semiconductor devices (power devices) used in power converters such as inverters or converters for electric vehicles, hybrid vehicles, air conditioners, etc., or various general-purpose motors. Brief explanation of the drawing

[0025] FIG. 1 shows a schematic cross-sectional view in the thickness direction of the solder-metal mesh composite (1) of the present invention. In the solder-metal mesh composite (1), a metal mesh (3) having high thermal conductivity is included in a composite layer (2), which is a lead-free solder layer formed by Sn-Cu-Ni lead-free solder. The composite layer (2) is mainly composed of lead-free solder (4) and metal mesh (3). FIG. 2 shows a schematic diagram of an example of the solder-metal mesh composite of the present invention. FIG. 2(a) shows the stacked state of each member before pressing and heating each member, and shows the state in which a Sn-Cu-Ni lead-free solder sheet (6), a solder-coated metal mesh (5), and a Sn-Cu-Ni lead-free solder sheet (6) are arranged in order between a heat-resistant plate A (7) and a heat-resistant plate B (8), and then mounted on a heating device (9). FIG. 2(b) shows a state in which, after loading each member onto the heating device (9) as in FIG. 2(a), the heating device (9) is heated to a desired temperature while applying pressure from the upper direction of the heat-resistant plate A (7), thereby heating the heat-resistant plate B (8) to a temperature above the melting point of the Sn-Cu-Ni-based lead-free solder, and melting the lead-free solder sheet (6) to be integrated with the solder-coated metal mesh (5). FIG. 3 shows an image of a cross-section in the thickness direction of a solder-metal mesh composite (1) obtained in Example 1, observed with a digital microscope. The solder-metal mesh composite (1) shows a state in which a copper mesh (3) is included in a composite layer (2) formed by Sn-Cn-Ni lead-free solder. In addition, pores (11) are visible in the composite layer (2), but the proportion of pores in the cross-section in the thickness direction was 1% or less. FIG. 4 shows an image of a cross-section in the thickness direction of a solder-metal mesh composite obtained in Comparative Example 2A, observed with a digital microscope. Figure 5 shows the processed image of Figure 4 when the image is binarized. The proportion of voids in the cross-section in the thickness direction of the composite layer was 15.1%. Specific details for implementing the invention

[0026] The solder-metal mesh composite material (1) of the present invention is characterized in that, as shown in FIG. 1, a metal mesh (3) having high thermal conductivity is included in a composite layer (2) formed by Sn-Cu-Ni-based lead-free solder, and the ratio of vacancies in the cross-section in the thickness direction is 15% or less, and the Sn-Cu-Ni-based lead-free solder comprises 0.1 to 2 weight% of Cu and 0.002 to 1 weight% of Ni with the remainder being Sn, or comprises 0.1 to 2 weight% of Cu, 0.002 to 1 weight% of Ni and 0.001 to 1 weight% of Ge with the remainder being Sn.

[0027] In the solder-metal mesh composite material (1) of the present invention, the composite layer (2) formed by Sn-Cu-Ni lead-free solder is basically composed of Sn-Cu-Ni lead-free solder (4) and the embedded metal mesh (3). In addition, as described below, during manufacturing, an intermetallic compound generated by the reaction of the lead-free solder (4) and the metal mesh (3) by heating may be generated at the interface between the lead-free solder (4) and the metal mesh (3) (not shown in the drawing).

[0028] There is no particular limitation on the thickness of the above composite layer (2) in the range having the effect of the present invention.

[0029] Examples of the above 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% of Cu and 0.002 to 1 wt% of Ni with the remainder being Sn, or lead-free solder containing 0.1 to 2 wt% of Cu, 0.002 to 1 wt% of Ni and 0.001 to 1 wt% of Ge with the remainder being Sn.

[0030] In the solder-metal mesh composite of the present invention, by using the lead-free solder, a bonding member with significantly fewer voids and excellent thermal conductivity is obtained as described below.

[0031] It is also possible to use the above-mentioned lead-free solder to which elements such as Bi, In, Sb, P, Ga, Co, Mn, Mo, Ti, Al, and Au have been added. The content of these elements should be an amount that does not significantly alter the thermal conductivity of the above-mentioned lead-free solder, and there are no particular limitations.

[0032] In the present invention, the high thermal conductivity of the metal mesh refers to having a higher thermal conductivity than the lead-free solder.

[0033] As the material for the metal mesh having the above high thermal conductivity, examples include metals with a higher melting point than lead-free solder, such as copper, alloys with copper as the main component, and alloys with tin as the main component, which have higher thermal conductivity characteristics than lead-free solder and are relatively inexpensive. Among these, Sn-Cu-Ni-based lead-free solder has good wettability to the metal mesh, and copper (Cu) is preferred from the perspective of high strength of the solder-metal mesh composite of the present invention.

[0034] In addition, regarding the shape of the metal mesh, there are no particular limitations in the range of effects of the present invention, and a wire diameter that is easy to manage when incorporating into Sn-Cu-Ni lead-free solder and improves the strength of the solder-metal mesh composite of the present invention is preferred.

[0035] Furthermore, regarding the above wire diameter, there is no particular limitation in the range having the effect of the present invention, but for example, the wire diameter is preferably 500 μm or less, and more preferably 100 μm or less. In addition, the cross-sectional shape of the above metal mesh wire is preferably circular or elliptical.

[0036] In addition, regarding the aperture of the metal mesh, there are no particular limitations in the range having the effects of the present invention, and any aperture that has good wettability of Sn-Cu-Ni lead-free solder and does not cause the mesh to break or fail to be incorporated into the lead-free solder during the manufacturing process of the solder-metal mesh composite of the present invention is acceptable.

[0037] In addition, the solder-metal mesh composite material, which includes a metal mesh having high thermal conductivity in the lead-free solder of the present invention, can be processed into a predetermined size by rolling the metal mesh so that the metal mesh does not break.

[0038] In addition, regarding the size of the metal mesh, it should be a size suitable for installation in electronic devices, and there are no specific limitations.

[0039] In the solder-metal mesh composite material (1) of the present invention, the ratio of the voids in the cross-section in the thickness direction (L) refers to the void area that occupies the entire area of ​​the solder-metal mesh composite material (1) within the intersection section of the woven line 1, which is the repeating unit of the metal mesh (except for the area portion of the copper wire).

[0040] For detecting voids in the above solder-metal mesh composite (1), an X-ray imaging device that observes a projection image from the vertically upward or vertically downward direction of the solder-metal mesh composite (1) may be used. Additionally, an X-ray CT device may be used as needed. Furthermore, from the image obtained by observing the cross-section in the thickness direction containing the detected voids with a digital microscope, the ratio of the voids in the cross-section in the thickness direction may be measured in accordance with IEC 61191-62010, an international standard established by the International Electrotechnical Commission (IEC).

[0041] As for the solder-metal mesh composite material (1) of the present invention, the ratio of vacancies in the cross-section in the thickness direction (L) is 15% or less, and from the perspective of excellent thermal conductivity and bonding reliability, it is preferable that the ratio be 10% or less, and more preferable that the ratio be 5% or less.

[0042] For example, compared to SAC305, which has a long track record as a representative composition of lead-free solder as described in Comparative Example 2A below and contains 15.1% of voids, the solder-metal mesh composite material (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 joint of an electronic device, it is possible to efficiently transfer heat generated by electronic components, thereby forming a joint with superior thermal conductivity and high joint reliability.

[0043] In addition, as in Example 1, when a solder joint is formed using a solder-metal mesh composite with a low proportion of voids, it becomes possible to suppress the occurrence of voids in the resulting joint.

[0044] A method for manufacturing a solder-metal mesh composite of the present invention having the above-described structure (hereinafter also referred to as the method of the present invention) comprises:

[0045] A process of obtaining a solder-coated metal mesh by coating a Sn-Cu-Ni-based lead-free solder on the surface of a metal mesh having high thermal conductivity (first process),

[0046] A process (second process) of placing the above solder-coated metal mesh between Sn-Cu-Ni-based lead-free solder sheets, and subsequently heating to a temperature above the melting point of the Sn-Cu-Ni-based lead-free solder while applying pressure to melt the lead-free solder sheets,

[0047] A process (3rd process) of cooling the molten solder until it solidifies and recovering the solder-metal mesh composite

[0048] Methods of inclusion can be cited.

[0049] In the first process above, a lead-free Sn-Cu-Ni based solder is coated on the surface of a metal mesh having high thermal conductivity to obtain a solder-coated metal mesh.

[0050] As in the first process above, by coating the surface of a metal mesh having high thermal conductivity with Sn-Cu-Ni-based lead-free solder, the lead-free solder sheet melted in the second process and the solder coating of the metal mesh become more compatible, thereby promoting homogenization. As a result, a reduction in voids occurring in the composite layer can be expected, and as a result, the solder-metal mesh composite can be efficiently manufactured while significantly reducing the ratio of voids in the composite layer (2). In particular, since the Sn-Cu-Ni-based lead-free solder has excellent fluidity when melted, it can efficiently and quickly coat the aperture portion of the metal mesh.

[0051] Methods for coating the lead-free solder on the surface of a metal mesh having high thermal conductivity include immersing the metal mesh in molten lead-free solder (dip method), flowing molten lead-free solder onto the surface of the metal mesh, and holding the metal mesh in a solder sheet from both sides and then melting the solder sheet, but are not particularly limited.

[0052] The above lead-free solder is used in a molten state by heating it above its melting point during the coating process.

[0053] In addition, regarding the coating state, it is preferable that the gaps between the mesh of the metal mesh be filled with the lead-free solder, and there are no particular limitations on the thickness of the coating.

[0054] In addition, the coating of the lead-free solder can be properly finished by applying flux to the surface of the metal mesh in advance before coating the lead-free solder.

[0055] Methods for attaching the above flux include immersing the metal mesh in the flux (dipping method) or applying the flux to the surface of the metal mesh, but are not particularly limited.

[0056] The above flux may be one in which the basic composition consists of an activator and a solvent, and the activator contains one selected from malonic acid, succinic acid, glutaric acid, adipic acid, souveric acid, azelaic acid, sebacic acid, maleic acid, citric acid, tartaric acid, and benzoic acid, and the content thereof is not particularly limited in the range having the effect of the present invention, but is preferably 4.55 mmol / g to 45.5 mmol / g per 100g of flux.

[0057] The solvent used in the above flux is not particularly limited in the range having the effect of the present invention, but may include alcohols such as ethanol, isopropanol, and isobutanol; glycol ethers such as butylcarbitol and hexylcarbitol; 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-terpene monoacetate and 1,8-terpene diacetate; isobornylcyclohexanol, etc., and the content thereof can be arbitrarily set within a range that satisfies the effect of the activator and the coating properties or stability of the flux.

[0058] A solder-coated metal mesh is obtained by cooling after the above coating. The cooling temperature may be lower than the melting point of the lead-free solder, and is not particularly limited.

[0059] In the second process above, 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, while applying pressure, the lead-free solder sheets are melted by heating to a temperature above the melting point of the lead-free solder.

[0060] In the second process above, the solder-coated metal mesh is clamped between two lead-free solder sheets, and subsequently, by applying pressure and heating, the lead-free solder coated on the metal mesh and the lead-free solder sheets are melted and integrated. In addition, since the metal mesh is pre-coated with lead-free solder, the lead-free solder sheets melt and become familiar with the lead-free solder coated on the metal mesh, thereby promoting homogenization and having the advantage that it is difficult for voids to enter even when integrated.

[0061] In addition, when the above lead-free solder composition contains 0.1 to 2 wt% Cu, 0.002 to 1 wt% Ni, and 0.001 to 1 wt% Ge and the remainder is Sn, the fluidity during melting is excellent, so when the metal mesh is dipped into the molten solder, the solder flows smoothly between the apertures of the metal mesh, so the wettability with the metal mesh is good and the incorporation of voids can be suppressed, allowing the metal mesh to be coated uniformly, and in addition, when the above pressurized heating is performed after melting, there is an advantage that it is difficult for voids to occur in the solder due to the excellent fluidity.

[0062] The size of the above lead-free solder sheet may be the same as that of electronic components such as semiconductor devices or heat dissipation materials such as heat sinks to be joined, and is not particularly limited. In addition, the thickness of the above lead-free solder sheet may be appropriately adjusted to correspond to the application target of the solder-metal mesh composite material, and is not particularly limited.

[0063] As a method for the second process above, for example, a method of pressurized heating as shown in FIG. 2(a) and 2(b) can be used. Specifically, as shown in FIG. 2(a), first, a Sn-Cu-Ni lead-free solder sheet (6), the solder-coated metal mesh (5), and the Sn-Cu-Ni lead-free solder sheet (6) are stacked and arranged in that order between a heat-resistant plate A (7) and a heat-resistant plate B (8).

[0064] The heat-resistant plate A (7) above may be a sheet of size and thickness that is easy to press against the solder-coated metal mesh (5), lead-free solder sheet (6), etc., and there are no particular limitations on the thickness and size.

[0065] In addition, the size of the heat-resistant plate A (7) may be made larger than the solder-coated metal mesh (5), and a spacer (10) may be installed around the solder-coated metal mesh (5).

[0066] The material of the above heat-resistant plate A (7) and spacer is preferably inexpensive, easy to process, and has excellent heat resistance. Examples include aluminum, steel, stainless steel, etc., in addition to ceramics such as alumina or zirconia, but there are no specific limitations.

[0067] As shown in FIG. 2(b), heat is applied from the outside of the heat-resistant plate B (8) while applying pressure from the outside of the heat-resistant plate A (7).

[0068] As for the above-mentioned means of applying pressure, there are no particular limitations as long as a uniform load is applied to a metal mesh having high thermal conductivity and a lead-free solder sheet, and methods such as applying force by pressing with hydraulic pressure or air, or by loading a heavy weight may be used.

[0069] The degree of pressure mentioned above is such that it can secure a thickness that has a characteristic effect on the solder-metal mesh composite of the present invention, and there are no particular limitations; it may be arbitrarily set to a target suitable for the bonding target.

[0070] The heat-resistant plate B (8) is positioned between the heat-resistant plate A (7), and the laminate of the solder-coated metal mesh (5) and the lead-free solder sheet (6) may be a sheet of a size and thickness that is easy to heat, and there are no specific limitations on the thickness and size.

[0071] As a means of heating the heat-resistant plate B (8), examples include connecting a heating device (9) to the lower surface of the heat-resistant plate B (8) or heating the entire heat-resistant plate B (8) with a high-temperature tank.

[0072] The above heating temperature should be a temperature above the melting point of the lead-free solder constituting the lead-free solder sheet (6). In addition, regarding the upper limit of the heating temperature, it is desirable to adjust it within the temperature range of the melting point of the lead-free solder + 50°C from the perspective of quality deterioration such as oxidation of the lead-free solder and economic efficiency.

[0073] For example, when the composition of the above lead-free solder comprises 0.1 to 2 weight% Cu, 0.002 to 1 weight% Ni, and 0.001 to 1 weight% Ge, and the remainder is Sn, the heating temperature can be preferably adjusted to around 227 to 350°C to efficiently melt the lead-free solder sheet (6) that is clamping the solder-coated metal mesh (5) from the upper and lower directions. In addition, when the above Sn-Cu-Ni-based lead-free solder comprises 0.1 to 2 weight% Cu and 0.002 to 1 weight% Ni, and the remainder is Sn, it is preferable to adjust the heating temperature to around 227 to 350°C.

[0074] In the third process above, the solder-metal mesh composite is recovered after cooling the molten solder from the second process until it solidifies.

[0075] As a method for cooling the solder, such as the molten lead-free solder sheet, until it solidifies, a method of cooling while maintaining a pressurized state in the second process may be used. Regarding the cooling temperature, it is preferable that it be lower than the temperature at which the lead-free solder solidifies, but from the perspective of efficient cooling, it is desirable to cool at a lower temperature.

[0076] As described above, after cooling until the molten solder solidifies, the above-mentioned pressure is released to recover the solder-metal mesh composite.

[0077] In addition, if molten solder leaks out at the end of the solder-metal mesh composite and solidifies, the leaked portion may be cut off or the solder-metal mesh composite may be formed into a desired shape. In addition, to make the thickness of the solder-metal mesh composite more uniform, the surface of the solder-metal mesh composite may be polished, for example, or the surface may be flattened using three rolls or a press machine. In addition, the solder-metal mesh composite may be processed to a predetermined size by rolling so that the metal mesh does not break.

[0078] The solder-metal mesh composite of the present invention can be used as a heat dissipation material bonding material, such as an electronic component bonding material or a heat sink material, just like conventional solder.

[0079] The solder joint according to the embodiment is formed using the solder-metal mesh composite material. The solder joint includes a predetermined substrate and a joint formed by the solder-metal mesh composite material bonded to the substrate.

[0080] The above material may be for electronic components used in semiconductor devices (power devices), and is not particularly limited. Additionally, the above material may be a heat dissipation material such as a heat sink, and is not particularly limited.

[0081] The joining method using the above solder-metal mesh composite can be performed using a conventional method, for example, a reflow method.

[0082] In addition, the heating temperature should be appropriately adjusted in correspondence with the heat resistance of the substrate or the melting temperature of the solder alloy used in the solder-metal mesh composite.

[0083] In addition, from the perspective of suppressing the occurrence of voids in the bonded body, treatment such as depressurization may be applied during bonding.

[0084] In the solder joint formed in this way, the joint has heat resistance, excellent thermal conductivity, and high joint reliability. Therefore, even when the joint is heated by heat generated by electronic components in a high-voltage load environment, for example, it is difficult for deformation stress to occur inside the joint, and it can withstand stress.

[0085] Therefore, the solder-metal mesh composite of the present invention can be suitably used as an electronic component bonding material in semiconductor devices (power devices) used in power converters such as inverters or converters for electric vehicles, hybrid vehicles, air conditioners, and various general-purpose motors.

[0086] In addition, it is also desirable for bonding heat dissipation materials, such as heat sinks, where heat dissipation characteristics are an important factor, so applications can be expected.

[0087] Examples

[0088] (Example 1)

[0089] A commercially available copper mesh (wire diameter approximately 50 µm, aperture 75 µm, length 6 cm, width 6 cm) was immersed in a container containing flux (low residue type no-clean flux NS-334 from Speria, Japan).

[0090] The copper mesh was removed from the container to remove excess flux, and subsequently, heated to 260°C and immersed in a container containing molten SN100C (a lead-free solder with a composition of Sn- 0.7Cu 0.05Ni+Ge, manufactured by Speria Co., Ltd. of Japan) to apply a lead-free solder coating, and the copper mesh was removed from the container to remove excess SN100C to obtain a solder-coated copper mesh.

[0091] Next, as shown in FIG. 2(a), the obtained solder-coated copper mesh (5) was clamped between two SN100C sheets (6) of the same size to produce a laminate, and then clamped between an alumina plate A (7) (length 2.5 cm, width 7.5 cm, thickness 0.6 mm) and an alumina plate B (8) (length 5 cm, width 5 cm, thickness 500 μm) from the outside of the SN100C sheets (6), and placed on a heating device (9) from the alumina plate B (8) side.

[0092] In addition, spacers (10) with a thickness of 120 μm were installed at both ends of the alumina plate A (7).

[0093] As shown in FIG. 2(b), the temperature of the heating device (9) was adjusted to 227°C while applying a load of 0.5 atm using a pressurizing device from the upper direction of the alumina plate (7), and the heating was stopped after confirming that the SN100C sheet (6) melted and the molten SN100C leaked out of the alumina plate (7).

[0094] The above was cooled using a local blower, and after confirming that the leaked SN100C had solidified, the above pressurized state was released to obtain a solder-metal mesh composite material containing copper mesh in the lead-free solder layer of SN100C.

[0095] (Test Example 1)

[0096] In the solder-metal mesh composite obtained in Example 1, the ratio of voids in the cross-section in the thickness direction was measured using an X-ray imaging device that observes a projection image from the vertically upward or vertically downward direction of the solder-metal mesh composite (1) in accordance with IEC 61191-62010 (not shown in the drawing).

[0097] Continuing, an image of the cross-section in the thickness direction observed with a digital microscope is shown in Fig. 3.

[0098] The proportion of the void (11) in the cross-section in the thickness direction above was 1% as measured in accordance with IEC 61191-62010 based on the image shown in FIG. 3.

[0099] Therefore, it can be seen that the solder-metal mesh composite obtained in Example 1 is a material with high strength and excellent thermal conductivity because it contains copper mesh, and also has significantly fewer voids in the solder joint, so it exhibits high bonding reliability with better heat resistance and better thermal conductivity, even in high-voltage load environments, and can withstand high-temperature operation.

[0100] Therefore, it can be seen that the solder-metal mesh composite obtained in Example 1 can be suitably used as a heat dissipation material bonding material, such as an electronic component bonding material or a heat sink material, in semiconductor devices (power devices) used in power converters such as inverters or converters for electric vehicles, hybrid vehicles, air conditioners, and various general-purpose motors.

[0101] (Test Example 2)

[0102] Sample 1 was prepared in the same condition as in Example 1, except that a metal mesh was not used (Comparative Example 1).

[0103] 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.

[0104] Density Measurement

[0105] According to the Archimedes method, each sample of Example 1 and Comparative Example 1 was immersed in water inside a container with the same inner diameter as the sample, and the sample volume was measured from the change in liquid level before and after the sample was introduced and calculated from the sample weight.

[0106] Specific heat measurement

[0107] The specific heat of each sample of Example 1 and Comparative Example 1 was measured by the DSC method using a differential scanning calorimeter DSC3500 (manufactured by NETZSCH) and sapphire as the reference material under room temperature conditions in an argon atmosphere.

[0108] Measurement of Thermal Diffusivity

[0109] The thermal diffusivity of each sample of Example 1 and Comparative Example 1, which was blackened using the aerosol dry graphite film-forming lubricant DGF (manufactured by Nippon Marine Tools Co., Ltd.), was measured at room temperature in the atmosphere using a Laser Flash Analyzer LFA457 (manufactured by NETZSCH).

[0110] Thermal conductivity

[0111] For each sample of Example 1 and Comparative Example 1, the thermal conductivity was calculated according to the following formula from the density, specific heat, and thermal diffusivity obtained as described above.

[0112] Thermal conductivity (W / (m·K)) = Thermal diffusivity (m 2 / s) × Density (Kg / m³) 3 )×Specific heat(J / (Kg·K))

[0113] The above results are shown in Table 1.

[0114]

[0115] From the results shown in Table 1, it can be seen that the solder-metal mesh composite obtained in Example 1 has a significantly increased thermal conductivity of about 3 times by including a metal mesh compared to Sample 1 of Comparative Example 1.

[0116] (Test Example 3)

[0117] Sample 2A was prepared in the same condition as Example 1, except that the solder was changed from SN100C to SAC305 (composition: Sn-3Ag-0.5Cu composition) (Comparative Example 2A).

[0118] Likewise, Sample 3A was prepared in the same condition as Example 1, except that the solder was changed from SN100C to Sn-5Sb (Comparative Example 3A).

[0119] In addition, Sample 2B and Sample 3B were prepared in the same condition as Comparative Example 2A and Comparative Example 3A, except that a metal mesh was not used (Comparative Example 2B and Comparative Example 3B).

[0120] Next, the thermal conductivity of each sample (n=4) of Comparative Examples 2A, 2B, 3A, and 3B was measured in the same condition as Test Example 2.

[0121] The results are shown in Table 1.

[0122] In addition, Table 1 shows the 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 soldering alloy is the same.

[0123] From the results shown in Table 1, the thermal conductivity of the solder-metal mesh composite obtained in Example 1 was the highest compared to Comparative Examples 2A and 3A.

[0124] In addition, compared to the thermal conductivity without a mesh, the thermal conductivity with a mesh tended to improve, but among them, when the ratio of the thermal conductivity of the solder-metal mesh composite obtained in Example 1 was set to 100, it was higher than SAC305 (96.5), which has a long track record as a representative composition of lead-free solder, and Sn-5Sb (89.7), which has a high melting temperature.

[0125] In addition, for Comparative Example 2A, the ratio of voids in the thickness direction cross-section as in Test Example 1 above was measured using an X-ray imaging device that observes a projection image from the vertically upward or vertically downward direction of the solder-metal mesh composite material (1) in accordance with IEC 61191-62010.

[0126] Figure 4 shows an image of the cross-section in the thickness direction observed with a digital microscope.

[0127] The proportion of voids in the cross-section in the thickness direction shown above is 15.1% as a result of measuring with binary processing in accordance with IEC 61191-62010 based on the image shown in FIG. 4 (Fig. 5), and it can be seen that the voids in the solder joint of Comparative Example 2A are significantly large. It is thought that the voids remaining in the state of Comparative Example 2A impede thermal conductivity in the solder joint, become a factor that prevents the power device from fully exhibiting performance, and also become a factor that impairs the bonding reliability required for electronic components.

[0128] Therefore, it can be seen that a solder-metal mesh composite using a Sn-Cu-Ni lead-free solder containing 0.1 to 2 wt% Cu, 0.002 to 1 wt% Ni, and 0.001 to 1 wt% Ge with the remainder being Sn is a bonding material with better heat resistance, superior thermal conductivity, and high bonding reliability, even when the component generates heat in a high-voltage load environment, for example. Thus, it is suitable for use as a bonding material for electronic components of semiconductor devices (power devices) used in power converters such as inverters or converters for electric vehicles, hybrid vehicles, air conditioners, and various general-purpose motors, or as a bonding material for heat dissipation materials such as heat sinks.

[0129] In addition, a solder-metal mesh composite was prepared using a lead-free solder of the Sn-Cu-Ni type containing 0.1 to 2 wt% Cu and 0.002 to 1 wt% Ni, with the remainder being Sn, and each measurement was taken under the same conditions as Test Examples 1 and 2. In both cases, just like the solder-metal mesh composite obtained in Example 1, the results showed significantly fewer pores and a higher thermal conductivity.

[0130] Therefore, it can be seen that the lead-free solder in the solder-metal mesh composite of the present invention, in which the solder alloy contains 0.1 to 2 weight% of Cu and 0.002 to 1 weight% of Ni and the remainder is Sn, is a bonding material with better heat resistance, superior thermal conductivity, and high bonding reliability, even when the component generates heat in a high-voltage load environment, for example. Thus, it can be suitablely used as a bonding material for electronic components of semiconductor devices (power devices) used in power converters such as inverters or converters for electric vehicles, hybrid vehicles, air conditioners, and various general-purpose motors, or as a bonding material for heat dissipation materials such as heat sinks. Explanation of the symbols

[0131] 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 sheets 7 Heat-resistant plate A 8 Heat-resistant plate B 9 Heating device 10 spacers 11 public

Claims

Claim 1 A lead-free solder layer formed by Sn-Cu-Ni lead-free solder contains a metal mesh having high thermal conductivity, and the ratio of vacancies in the thickness direction cross-section 5％ A solder-metal mesh composite material characterized by the following, wherein the Sn-Cu-Ni lead-free solder comprises 0.1 to 2 wt% Cu and 0.002 to 1 wt% Ni with the remainder being Sn, or comprises 0.1 to 2 wt% Cu, 0.002 to 1 wt% Ni and 0.001 to 1 wt% Ge with the remainder being Sn. as , A solder-metal mesh composite material obtained by coating the surface of the metal mesh with the Sn-Cu-Ni-based lead-free solder, placing the solder-coated metal mesh between sheets made of the Sn-Cu-Ni-based lead-free solder, and melting and cooling the sheets made of the Sn-Cu-Ni-based lead-free solder. Claim 2 A solder-metal mesh composite according to claim 1, wherein the metal mesh is a copper mesh. Claim 3 A solder joint formed using the solder-metal mesh composite of claim 1 or 2. Claim 4 A method for manufacturing a solder-metal mesh composite comprises: a process of obtaining a solder-coated metal mesh by coating a Sn-Cu-Ni-based lead-free solder on the surface of a metal mesh having high thermal conductivity; a process of placing the solder-coated metal mesh between Sn-Cu-Ni-based lead-free solder sheets and subsequently heating the lead-free solder sheets to a temperature above the melting point of the Sn-Cu-Ni-based lead-free solder while applying pressure to melt the lead-free solder sheets; a process of cooling until the molten solder solidifies and recovering the solder-metal mesh composite, wherein the Sn-Cu-Ni-based lead-free solder comprises 0.1 to 2 wt% Cu and 0.002 to 1 wt% Ni with the remainder being Sn, or comprises 0.1 to 2 wt% Cu, 0.002 to 1 wt% Ni, and 0.001 to 1 wt% Ge. A method for manufacturing a solder-metal mesh composite material characterized by the remainder being Sn. Claim 5 A method for manufacturing a solder-metal mesh composite in which the metal mesh is a copper mesh, as described in claim 4. Claim 6 A method for manufacturing a solder-metal mesh composite according to claim 4 or 5, wherein a Sn-Cu-Ni lead-free solder sheet, the solder-coated metal mesh, and a Sn-Cu-Ni lead-free solder sheet are arranged in that order between a heat-resistant plate A and a heat-resistant plate B, and subsequently, heat is applied from the heat-resistant plate B side while applying pressure.

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