Welding materials, preparation methods and joint preparation methods for welding below 200°C and high-temperature applications

Abstract

A welding material, a preparation method thereof and a joint preparation method for welding below 200°C and high-temperature applications, which are composed of core-shell structure powders. The core material is a metal material with high thermal conductivity and electrical conductivity and high melting point, such as Cu, Ni, Ag, etc., and the shell material is a low-melting-point simple substance or eutectic alloy, such as Sn, SnBi alloy, SnBiAg alloy, etc. When the shell material is the low-melting-point simple substance Sn, through ultrasonic solid-phase diffusion welding or pressure sintering below the melting point of Sn (180-200°C), the complete transformation of the low-melting-point metal is realized, and a welding joint with high temperature resistance (~450°C) is generated; when the shell material is the low-temperature eutectic metal SnBi or SnBiAg, a high-temperature resistant joint is prepared by low-temperature transient liquid-phase diffusion welding (160-200°C). The double-sided tin plating of the core-shell structure preformed solder sheet solves the non-coplanarity problem of the composite solder sheet, and realizes the preparation of large-area, high-density and high-temperature resistant joints at a process temperature below 200°C. The solder paste prepared from the composite powder solves the welding problem of special-shaped parts, and the device has wide welding adaptability.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-temperature welding materials, and particularly relates to a welding material, a preparation method thereof, and a joint preparation method for welding below 200°C and high-temperature applications. It is used in cryogenic welding processes, and the welding form is sheet or paste. The product has a wide adaptability, and the prepared joint has high-temperature and high-reliability performance. Background Art

[0002] With the development of the electronics industry, the working environmental temperature of electronic components is getting higher and higher. There is a need to develop welding materials and technologies with higher heat resistance, higher reliability, and lower process temperatures to adapt to more severe service environments. In particular, the development of high-temperature welding materials and technologies for the third-generation wide-bandgap semiconductors SiC / GaN chips has increased the operating temperature of power electronic devices from 125°C of Si devices to 200°C. In addition, the demand for welding materials for cryogenic welding and high-temperature service in military fields such as aviation, aerospace, and ordnance is also extremely urgent. For example, the cryogenic repair of high-temperature blades of aeroengines; the welding of lead wires of stator windings of high-power density and complex-structured small-volume military motors all require stable welding at lower process temperatures, and the devices or joints can serve reliably in extremely high-temperature environments. Current "cryogenic welding and high-temperature application" welding materials and technologies include sintered nano-Ag, sintered nano-Cu, and transient liquid-phase diffusion welding technology. The sintered nano-Ag technology has a high material cost, a sintering temperature of 250°C, and there is an electromigration problem; while the sintered nano-Cu material is easy to oxidize, has a high storage cost, and requires a high-pressure process during welding; the transient liquid-phase diffusion welding material has a low cost, is close to the thermal expansion coefficient of the welding substrate, and is compatible with traditional welding material processes. Commonly used transient liquid-phase diffusion welding materials are Cu / Sn, Ag / Sn, Au / Sn, Ni / Sn, etc. The welding temperature is 250 - 280°C, the reaction time is long, and the joint is too thin, which is not conducive to stress conduction.

[0003] The transient liquid-phase diffusion welding technology of core-shell structure Cu@Sn, Ag@Sn and other welding materials has a large material contact area, shortened reaction time, unrestricted joint thickness, which is conducive to stress conduction and evacuation, but the reaction welding temperature is still greater than 250°C, making it difficult to meet the process welding requirements at lower temperatures. Summary of the Invention

[0004] Aiming at the above technical problems, the present invention discloses a welding material, a preparation method thereof, and a joint preparation method for welding below 200°C and high-temperature applications; the welding material is made into a core-shell structure composite solder sheet or solder paste with a welding temperature in the range of 160 - 220°C, and the joint prepared by using the principle of solid-phase diffusion or solid-liquid diffusion welding meets the application requirements of being resistant to high temperatures above 450°C, solving the problems of high welding temperature and poor adaptability of the solder sheet to devices in the traditional transient liquid-phase diffusion welding technology.

[0005] For this, the technical solution adopted by the present invention is as follows:

[0006] A welding material for welding below 200 °C and high-temperature applications. The welding material is a core-shell structure composite welding material, including a core layer and a shell layer coated outside the core layer; wherein the core layer material is Cu or Ag, and the shell layer material is elemental Sn, SnBi alloy or SnBiAg alloy.

[0007] A preparation method of a composite welding material for welding below 200 °C and high-temperature applications, which includes the following steps:

[0008] Prepare Cu@X (X = Sn, SnBi, SnBiAg, the same below), and the thickness of the Sn or Sn-based alloy layer is 1 - 2 μm;

[0009] For the prepared Cu@X, electroplate the Sn layer or Sn alloy layer with Cu particles of different particle sizes, and mix the Cu@X particles of different particle sizes (<15 μm, 15 - 25 μm, 25 - 50 μm) to make a mixed powder.

[0010] Furthermore, for the prepared Cu@X, electroplate the Sn layer or Sn alloy layer with Cu particles of different particle sizes, and press and form the Cu@X particles of different particle sizes (<15 μm, 15 - 25 μm, 25 - 50 μm) according to a ratio of 3:2:1 to prepare a Cu@X solder sheet.

[0011] Furthermore, for the prepared Cu@Sn particles, the electroplating solution used is stannous methylsulfonate electroplating solution, with a pH of 6 - 7, an electroplating temperature of 15 - 35 °C, and a chronopotentiometric electroplating mode with a constant current, and the current density is 30 A / dm 2 , and the electroplating time is 2 - 4 min;

[0012] Furthermore, for the prepared Cu@Sn-based eutectic alloy, the electroplating solution used is characterized by adding a benzoxazole sulfonic acid compound with good water solubility, and the mass concentration of the benzoxazole sulfonic acid compound in the electroplating solution is 1×10 －5 - 10 g / L, preferably 1×10 －4 - 5 g / L;

[0013] Furthermore, for the prepared Cu@Sn-based eutectic alloy, antioxidants such as hydroquinone, catechol, resorcinol, phloroglucinol, pyrogallol, α or β - naphthol are added to the electroplating solution to prevent Sn in the electroplating solution 2+ from being oxidized to Sn 4+ . The mass concentration of the antioxidant is 0.05 - 5 g / L, preferably 0.2 - 2 g / L;

[0014] Further, various additives such as brighteners, complexing agents, pH adjusters, conductivity aids, and surfactants can be added to the plating solution to improve the properties of the plating solution and the coating. The pH value of the plating solution is 1-8, and the temperature of the plating solution is 10-60 °C, preferably 15-35 °C.

[0015] Further, the Cu@X powder (x = Sn, SnBi, SnBiAg, etc.) prepared by the above electroplating method is added to the commercial soldering flux DL-405 in a ratio of 9:1, and ball-milled and mixed evenly to prepare a Cu@X lead-free solder paste.

[0016] The present invention also provides a method for preparing a welding material joint for welding below 200 °C and high-temperature applications, including the following steps: The Cu@X solder sheet prepared by the above method is subjected to secondary electroplating to coat a 1-2 μm Sn layer or Sn-based alloy layer on the surface of the preformed solder sheet. The preformed solder sheet with a Sn or Sn-based alloy coating on the surface is ultrasonically assisted welded at 170-200 °C. The former uses the principle of solid-liquid diffusion, and the latter uses the principle of solid-solid diffusion welding. After isothermal aging for 8-10 minutes, a dense and tough three-dimensional network joint is obtained, and the room temperature shear strength is not less than 80 MPa.

[0017] The present invention also provides a method for preparing a welding material joint for welding below 200 °C and high-temperature applications, including the following steps: The Cu@X solder paste prepared by the above method is printed on a Cu substrate in a layer of 80 μm solder paste by the secondary printing method, degummed at 120 °C for 90 minutes, and then another layer of 40 μm solder paste is printed. The Cu@Sn solder paste is heated to 150 °C at a heating rate of 70 °C / min, and then heated to 200 °C at a heating rate of 5 °C / min, and held for 10 minutes to obtain a dense three-dimensional network joint.

[0018] In the present invention, the "high temperature" in "high temperature resistance" refers to the maximum tolerated temperature of 450 °C.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] 1. The Cu@Sn preformed solder sheet of the present invention accelerates the solid-phase diffusion rate between the Cu core and the Sn shell material by using an ultrasonic-assisted welding method in the temperature range of 180-200 °C below the melting point of Sn. The Sn layer is completely transformed into the interfacial intermetallic compound IMCs within 2 minutes, forming a dense network structure joint of Cu@IMCs; compared with the transient liquid-phase diffusion welding technology (TLPS) of traditional core-shell structure solder sheets, not only the welding time is shortened, but more importantly, the welding process temperature is reduced, and the temperature resistance of the joint is still greater than 450 °C, meeting the special low-temperature welding temperature requirements of special devices such as optical modules and the reliable application requirements of high service temperature.

[0021] 2. The Cu@X (X = eutectic alloys such as SnBi, SnBiAg, etc.) preformed solder pads of the present invention are subjected to transient liquid phase diffusion welding at 170 - 200°C, which is 30 - 50°C above the melting point of the X alloy. The low-melting X alloy is completely transformed into IMCs within 20 minutes, forming a dense network joint of Cu@IMCs. Compared with the traditional Cu@Sn material TLPS technology, the shell material uses a Sn-based alloy with a lower melting point, the welding process temperature is lower, and the temperature resistance of the joint remains unchanged, meeting the special welding requirements at a lower temperature below 200°C.

[0022] 3. The Cu@X (X = Sn element, eutectic alloys such as SnBi, SnBiAg, etc.) preformed solder pads of the present invention are reinforced by surface plating of the shell material, solving the coplanarity problem existing during the welding of composite solder pads. The joint interface is dense, the shear strength is higher (not less than 20 MPa), and the thermal and electrical conductivity performance is better, meeting the high-temperature and high-reliability applications of power electronic devices.

[0023] 4. The Cu@X (X = Sn element, eutectic alloys such as SnBi, SnBiAg, etc.) solder paste of the present invention adopts the secondary printing method, and realizes dense welding through steps such as degumming, rapid heating, and slow pressure welding, meeting the requirements of lower-temperature welding, high-temperature resistance, and high-reliability applications for special-shaped parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Diagrams of Sn - Bi and Sn - Bi - Ag alloys; a) Phase diagram of SnBi alloy; b) Phase diagram of SnBiAg alloy;

[0025] Figure 2 Microscopic morphology diagrams of the welded joints of Cu@Sn preformed solder pads and solder paste with double-sided plated shell metal;

[0026] a) Microscopic morphology of the Cu@Sn solder paste joint; b) Microscopic morphology of the Cu@Sn solder pad;

[0027] Figure 3 Shear strength of Cu@Sn solid-phase diffusion welded joint and Cu@Sn-based alloy - TLPS welded joint;

[0028] Figure 4 Comparison diagrams of thermal resistance and resistance between the surface-reinforced preformed solder pad Cu@X joint and the traditional Cu@Sn TLPS joint. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] The following further details the preferred embodiments of the present invention.

[0030] Example 1

[0031] A welding material and a method for preparing a joint for welding below 200°C and high-temperature applications, the preparation steps are as follows:

[0032] Step 1, prepare Cu@X (X = Sn, Sn 58 Bi alloy or Sn 35 Bi 0.5 Ag alloy): Cu particles with different particle sizes (<15 μm, 15 - 25 μm, 25 μm < particle size ≤ 50 μm) are respectively plated with Sn, Sn 58 Bi alloy coating or Sn 35 Bi 0.5 Ag alloy coating.

[0033] Prepare the Sn coating for Cu particles with a particle size <15 μm to obtain small - particle - size core - shell structure Cu@Sn powder; prepare the Sn coating for Cu particles with a particle size of 15 - 25 μm to obtain medium - particle - size core - shell structure Cu@Sn powder; prepare the Sn coating for Cu particles with 25 μm < particle size ≤ 50 μm to obtain large - particle - size core - shell structure Cu@Sn powder.

[0034] Prepare the Sn 58 Bi alloy coating for Cu particles with a particle size <15 μm to obtain small - particle - size core - shell structure Cu@Sn 58 Bi powder; prepare the Sn 58 Bi alloy coating for Cu particles with a particle size of 15 - 25 μm to obtain medium - particle - size core - shell structure Cu@Sn 58 Bi powder; prepare the Sn 58 Bi alloy coating for Cu particles with 25 μm < particle size ≤ 50 μm to obtain large - particle - size core - shell structure Cu@Sn 58 Bi powder.

[0035] Prepare the Sn 35 Bi 0.5 Ag alloy coating for Cu particles with a particle size <15 μm to obtain small - particle - size core - shell structure Cu@Sn 35 Bi 0.5 Ag powder; prepare the Sn 35 Bi 0.5 Ag alloy coating for Cu particles with a particle size of 15 - 25 μm to obtain medium - particle - size core - shell structure Cu@Sn 35 Bi 0.5 Ag powder; prepare the Sn 35 Bi 0.5 Ag alloy coating for Cu particles with 25 μm < particle size ≤ 50 μm to obtain large - particle - size core - shell structure Cu@Sn 35 Bi 0.5 Ag powder.

[0036] For Cu particles of different particle sizes, the preparation methods of different coating materials are the same, but the coating thickness of Cu particles <15μm is 1-1 micron, the coating thickness of Cu particles with a particle size of 15-25μm (i.e., particle size) is 1-2μm, and the coating thickness of Cu particles with a particle size greater than 25μm and less than or equal to 50μm is 2-3μm; the Sn coating is prepared by electroplating, the electroplating solution used is stannous methanesulfonate electroplating solution, the pH is 6-7, the electroplating temperature is 15-35°C, a constant current chronopotentiometric electroplating mode is used, and the current density is 30A / dm 2 , electroplating time is 2 to 4 minutes; Sn 58 Bi alloy and Sn 35 Bi 0.5 Ag alloy coating was prepared by chemical plating method, Sn 58 The plating solution used in the preparation of Bi alloy plating layer is characterized by the addition of a benzoxazole sulfonic acid compound with good water solubility, and the mass concentration of the benzoxazole sulfonic acid compound in the plating solution is 1×10 －5 ~10g / L, preferably 1×10 －4 ~5g / L; Sn 35 Bi 0.5 In the preparation of Ag alloy plating, antioxidants such as hydroquinone, catechol, resorcinol, pyrogallol, pyrogallol, α or β-naphthol are added to the plating solution to prevent Sn in the plating solution from 2+ Oxidation to Sn 4+ The mass concentration of the antioxidant is 0.05-5g / L, preferably 0.2-2g / L; various additives such as brightener, complexing agent, pH adjuster, conductive additive and surfactant can also be added to the plating solution to improve the performance of the plating solution and the coating. The pH value of the plating solution is 1-8, and the plating solution temperature is 10-60°C, preferably 15-35°C.

[0037] Large-grained core-shell structure Cu@Sn powder, medium-grained core-shell structure Cu@Sn powder, and small-grained core-shell structure Cu@Sn powder are graded in a weight ratio of 1:2:3 to obtain composite powder; the composite powder is a welding material.

[0038] Large-grained core-shell structure Cu@Sn 58 Bi powder, medium-sized core-shell Cu@Sn 58 Bi powder, small-size core-shell structure Cu@Sn 58 The Bi powder was graded in a weight ratio of 1:2:3 to obtain the graded Cu@X (X = Sn 58 Bi) composite powder; the composite powder is welding material.

[0039] Large-grained core-shell structure Cu@Sn 35 Bi 0.5Ag powder, medium-grained core-shell structure Cu@Sn 35 Bi 0.5 Ag powder, small-grained core-shell structure Cu@Sn 35 Bi 0.5 The Ag powder is proportioned according to the weight ratio of 1:2:3 to obtain the particle size-graded Cu@X (X = Sn 35 Bi 0.5 Ag) composite powder; the composite powder is a welding material.

[0040] Step 2, respectively perform pressure forming treatment on the composite powder, forming pressure: 5 MPa, forming time 5 min, and perform surface Sn plating on the obtained preformed solder sheet to strengthen the surface coating, and the thickness of the Sn coating is 1 - 2 μm;

[0041] Step 3, for the Cu@Sn preformed solder sheet, surface reinforcement is carried out through a Sn layer with a double-sided Sn plating of 1 - 2 μm. An ultrasonic-assisted solid-state diffusion welding method is adopted, and an ultrasonic welding device is added in a conventional reflow welding furnace body to increase the diffusion rate between elements, thereby accelerating the solid-solid reaction rate of elements at the interface. Keep it at 200 °C for 2 min to completely convert the low-melting-point Sn into high-melting-point Cu 3 Sn, which coats the surface of the remaining Cu particles, to prepare a Cu@Cu 3 Sn joint; for Cu@Sn 58 Bi and Cu@Sn 35 Bi 0.5 Ag adopts ultrasonic-assisted transient liquid-phase diffusion welding and keeps it at 180 °C and 200 °C for 2 min respectively to completely convert the low-melting-point Sn into Cu 3 Sn, and completely convert the Ag element into Ag 3 Sn, and the Bi element is diffusely distributed at the joint interface; complete the preparation of Cu@Cu 3 Sn / Bi and Cu@Cu 3 Sn / Ag 3 Sn / Bi joints; The Sn-Bi and Sn-Bi-Ag alloy diagrams are as Figure 1 shown. a) When the weight content of the Bi element in the Sn-Bi alloy is 58 wt.%, Sn-Bi is a eutectic alloy with a unique melting point: 158 °C; b) When the weight content of Bi in Sn-Bi-Ag is 35 wt.% and the weight content of Ag is 0.5 wt.%, the melting point of the Sn 35 Bi 0.5 Ag eutectic alloy is 173 °C, and welding can be achieved at temperatures below 200 °C.

[0042] Step 4: Add Cu@X composite powder with a particle size distribution and Halys commercial flux with a weight ratio of 8:1. The flux grade is DL-405. After ball milling and mixing evenly, a solder paste is prepared. First, print a layer of solder paste with a thickness of 80 μm on the Cu substrate using the double printing method, degum at 120 °C for 90 min, and then print another layer of solder paste with a thickness of 40 μm.

[0043] Step 5: Cu@Sn and Cu@Sn 35 Bi 0.5 The Ag solder paste is heated to 150 °C at a heating rate of 70 °C / min, and then heated to 200 °C at a heating rate of 5 °C / min. The pressure is 0.5 MPa. After holding for 10 min, a dense three-dimensional network joint is obtained; Cu@Sn 58 The Bi solder paste is heated to 130 °C at a heating rate of 70 °C / min, and then heated to 170 °C at a heating rate of 5 °C / min. The pressure is 1 MPa. After holding for 10 min, a dense three-dimensional network joint is obtained.

[0044] The microscopic morphology of the joint prepared by welding the double-sided plated shell metal Cu@Sn preform b) obtained in Step 1 and the solder paste a) obtained in Step 4 is as Figure 2 shown. The shear strength of the Cu@Sn solid-phase diffusion welded joint and the Cu@Sn-based alloy-TLPS welded joint obtained in Step 5 was tested using a CONDOR150 push-pull force gauge, as Figure 3 shown. The shear strength of the Cu@X joint of the surface-reinforced preform obtained in Step 3 and the traditional Cu@Sn TLPS joint without surface-reinforced Sn plating is not less than 20 MPa, as Figure 3 shown; the thermal conductivity and resistance of the joint are as Figure 4 shown. The thermal conductivity and thermal diffusivity satisfy the following relationship: k = α·C p ·ρ. The thermal conductivity can be calculated by measuring the thermal conductivity α, heat capacity C p and density. The thermal diffusivity is measured using a laser thermal conductivity meter. The heat capacity is measured using the sapphire method in DSC. Take a sample with a mass similar to that of the sapphire standard sample, and measure the specific heat of the sample through the specific heat of the sapphire. The density of the sample is measured by the drainage method. The resistance is measured using the I-V curve.

[0045] Example 2

[0046] Step 1: Prepare Cu@X (X = Sn, Sn 58 Bi alloy or Sn 35 Bi 0.5 Ag alloy): Cu particles with different particle sizes (<15 μm, 15 - 25 μm, 25 μm < particle size ≤ 50 μm) are respectively plated with Sn or Sn 58 Bi / Sn 35 Bi0.5 Ag alloy coating.

[0047] The coating preparation method is the same as that of step 1 in Example 1.

[0048] Cu particles with a particle size < 15 μm are used to prepare the Sn coating to obtain small particle size core-shell structured Cu@Sn powder; Cu particles with a particle size of 15 - 25 μm are used to prepare the Sn coating to obtain medium particle size core-shell structured Cu@Sn powder; Cu particles with a particle size of 25 μm < particle size ≤ 50 μm are used to prepare the Sn coating to obtain large particle size core-shell structured Cu@Sn powder.

[0049] Cu particles with a particle size < 15 μm are used for Sn 58 preparation of the Bi alloy coating to obtain small particle size core-shell structured Cu@Sn 58 powder; Cu particles with a particle size of 15 - 25 μm are used for Sn 58 preparation of the Bi alloy coating to obtain medium particle size core-shell structured Cu@Sn 58 powder; Cu particles with a particle size of 25 μm < particle size ≤ 50 μm are used for Sn 58 preparation of the Bi alloy coating to obtain large particle size core-shell structured Cu@Sn 58 Bi powder.

[0050] Cu particles with a particle size < 15 μm are used for Sn 35 Bi 0.5 preparation of the Ag alloy coating to obtain small particle size core-shell structured Cu@Sn 35 Bi 0.5 Ag powder; Cu particles with a particle size of 15 - 25 μm are used for Sn 35 Bi 0.5 preparation of the Ag alloy coating to obtain medium particle size core-shell structured Cu@Sn 35 Bi 0.5 Ag powder; Cu particles with a particle size of 25 μm < particle size ≤ 50 μm are used for Sn 35 Bi 0.5 preparation of the Ag alloy coating to obtain large particle size core-shell structured Cu@Sn 35 Bi 0.5 Ag powder.

[0051] The coating thickness of Cu particles < 15 μm is ~1 μm, the coating thickness of Cu particles with a particle size of 15 - 25 μm is 1 - 2 μm, and the coating thickness of Cu particles with a particle size of 25 - 50 μm is 2 - 3 μm for the preparation of large particle size core-shell structured Cu@X powder, medium particle size core-shell structured Cu@X powder, and small particle size core-shell structured Cu@X powder (X = Sn, Sn 58 Bi alloy or Sn 35 Bi 0.5The (Ag alloy) is proportioned according to the weight ratio of 1:2:3 to obtain a composite powder; the composite powder is a welding material.

[0052] Step 2: The composite powder is subjected to pressure molding treatment. The molding pressure is 8 MPa, and the molding time is 5 min. The obtained preformed solder sheet is subjected to surface Sn plating treatment to strengthen the surface coating. The thickness of the Sn plating layer is 1.5 μm.

[0053] Step 3: For the Cu@Sn preformed solder sheet, an ultrasonic-assisted solid-phase diffusion welding method (the same as in Example 1) is used. This method adds ultrasonic technology to the conventional reflow welding to accelerate the solid-phase diffusion rate between Cu and Sn. Under the welding condition of holding at 190 °C for 2 min, the low-melting-point Sn is completely converted into high-melting-point Cu 3 Sn, forming a Cu@Cu 3 Sn three-dimensional network joint structure; for Cu@Sn 58 Bi and Cu@Sn 35 Bi 0.5 Ag are subjected to ultrasonic-assisted transient liquid-phase diffusion welding and held at 170 °C and 190 °C for 5 min respectively to completely convert the low-melting-point alloy into Cu 3 Sn or Ag 3 Sn, and the Bi element is concentrated in the interface region and is diffusely distributed in the joint after aging at 300 °C for 48 h, realizing the joints of Cu@Cu 3 Sn / Bi and Cu@Cu 3 Sn / Ag 3 Sn / Bi preparation;

[0054] Step 4: The Cu@X composite powder and the commercial soldering flux of Haris, with the brand number DL-405, are added according to the weight ratio of 9:1, and are ball-milled and mixed evenly to prepare a solder paste. The secondary printing method is used to first print a layer of solder paste with a thickness of 70 μm on the Cu substrate, degum at 120 °C for 90 min, and then print another layer of solder paste with a thickness of 50 μm.

[0055] Step 5: The Cu@Sn and Cu@Sn 35 Bi 0.5 Ag solder pastes are heated to 150 °C at a heating rate of 70 °C / min, and then heated to 190 °C at a heating rate of 5 °C / min, with a pressure of 0.5 MPa. After holding for 10 min, a dense three-dimensional network joint is obtained; Cu@Sn 58 Bi solder paste is heated to 140 °C at a heating rate of 70 °C / min, and then heated to 165 °C at a heating rate of 5 °C / min, with a pressure of 0.35 MPa. After holding for 8 min, a dense three-dimensional network joint is obtained.

[0056] Example 3

[0057] Step 1, prepare Cu@X (X = Sn, Sn 58 Bi alloy or Sn 35 Bi 0.5 Ag alloy): Cu particles with different particle sizes (<15 μm, 15 - 25 μm, greater than 25 μm and less than or equal to 50 μm) are respectively plated with Sn or Sn 58 Bi / Sn 35 Bi 0.5 Ag alloy plating.

[0058] The plating preparation method is the same as that of Step 1 in Example 1.

[0059] Cu particles with a particle size <15 μm are plated with Sn to obtain small - particle - size core - shell structured Cu@Sn powder; Cu particles with a particle size of 15 - 25 μm are plated with Sn to obtain medium - particle - size core - shell structured Cu@Sn powder; Cu particles with a particle size of 25 μm < particle size ≤50 μm are plated with Sn to obtain large - particle - size core - shell structured Cu@Sn powder.

[0060] Cu particles with a particle size <15 μm are plated with Sn 58 Bi alloy to obtain small - particle - size core - shell structured Cu@Sn 58 Bi powder; Cu particles with a particle size of 15 - 25 μm are plated with Sn 58 Bi alloy to obtain medium - particle - size core - shell structured Cu@Sn 58 Bi powder; Cu particles with a particle size of 25 μm < particle size ≤50 μm are plated with Sn 58 Bi alloy to obtain large - particle - size core - shell structured Cu@Sn 58 Bi powder.

[0061] Cu particles with a particle size <15 μm are plated with Sn 35 Bi 0.5 Ag alloy to obtain small - particle - size core - shell structured Cu@Sn 35 Bi 0.5 Ag powder; Cu particles with a particle size of 15 - 25 μm are plated with Sn 35 Bi 0.5 Ag alloy to obtain medium - particle - size core - shell structured Cu@Sn 35 Bi 0.5 Ag powder; Cu particles with a particle size of 25 μm < particle size ≤50 μm are plated with Sn 35 Bi 0.5 Ag alloy to obtain large - particle - size core - shell structured Cu@Sn 35 Bi 0.5 Ag powder.

[0062] The coating thickness of 15μm Cu particles is ~1μm, the coating thickness of Cu particles with a particle size of 15 - 25μm is 1 - 2μm, and the coating thickness of Cu particles with a particle size of 25 - 50μm is 2 - 3μm. The large-grained core-shell structured Cu@X powder, medium-grained core-shell structured Cu@X powder, and small-grained core-shell structured Cu@X powder are proportioned by weight in a ratio of 1:2:3 to obtain a composite powder; the composite powder is a welding material.

[0063] Step 2, perform pressure molding on the composite powder, molding pressure: 10MPa, molding time 5min, and perform surface Sn plating on the obtained preformed solder sheet to strengthen the surface coating, and the thickness of the Sn coating is 2.6μm;

[0064] Step 3, for the Cu@Sn preformed solder sheet, use an ultrasonic-assisted solid-state diffusion welding method. This welding method causes Cu and Sn to undergo a solid-solid diffusion reaction at 180°C to transform into high-melting-point Cu 3 Sn. The auxiliary ultrasonic technology accelerates the Cu / Sn solid-state reaction rate, enabling the joint to complete the Cu@Cu 3 Sn joint preparation in 3 minutes; for Cu@Sn 58 Bi and Cu@Sn 35 Bi 0.5 Ag, use ultrasonic-assisted transient liquid-phase diffusion welding (TLPS) to complete the joints Cu@Cu 3 Sn / Bi and Cu@Cu 3 Sn / Ag 3 Sn / Bi preparation at 180°C and 210°C for 4 minutes respectively. This ultrasonic-assisted TLPS technology adds ultrasonic technology on the basis of conventional transient liquid-phase diffusion welding, aiming to accelerate the interfacial reaction rate between elements and reduce the reaction time;

[0065] Step 4, add Halys commercial flux, grade DL-405, to the Cu@X composite powder in a weight ratio of 9:1, and prepare a solder paste by ball milling and mixing; use the double-printing method to first print a layer of solder paste with a thickness of 90μm on the Cu substrate, degum at 120°C for 90min, and then print another layer of solder paste with a thickness of 30μm;

[0066] Step 5, heat the Cu@Sn and Cu@Sn 35 Bi 0.5 Ag solder paste at a heating rate of 70°C / min to 140°C, and then at a heating rate of 5°C / min to 210°C, with a pressure of 0.3MPa. After holding for 10min, a dense three-dimensional network joint is obtained; Cu@Sn 58The Bi solder paste is heated to 140 °C at a heating rate of 70 °C / min and then heated to 170 °C at a heating rate of 5 °C / min under a pressure of 0.30 MPa. After holding for 6 min, a dense three-dimensional network joint is obtained.

[0067] Example 4

[0068] Step 1, prepare Cu@X (X = Sn, Sn 58 Bi alloy or Sn 35 Bi 0.5 Ag alloy): Cu particles with different particle sizes (<15 μm, 15 - 25 μm, greater than 25 μm and less than or equal to 50 μm) are respectively plated with Sn or Sn 58 Bi / Sn 35 Bi 0.5 Ag alloy plating is prepared.

[0069] The plating preparation method is the same as that of Step 1 in Example 1.

[0070] Cu particles with a particle size <15 μm are plated with Sn to obtain small particle size core-shell structured Cu@Sn powder; Cu particles with a particle size of 15 - 25 μm are plated with Sn to obtain medium particle size core-shell structured Cu@Sn powder; Cu particles with a particle size of 25 μm < particle size ≤ 50 μm are plated with Sn to obtain large particle size core-shell structured Cu@Sn powder.

[0071] Cu particles with a particle size <15 μm are plated with Sn 58 Bi alloy plating to obtain small particle size core-shell structured Cu@Sn 58 Bi powder; Cu particles with a particle size of 15 - 25 μm are plated with Sn 58 Bi alloy plating to obtain medium particle size core-shell structured Cu@Sn 58 Bi powder; Cu particles with a particle size of 25 μm < particle size ≤ 50 μm are plated with Sn 58 Bi alloy plating to obtain large particle size core-shell structured Cu@Sn 58 Bi powder.

[0072] Cu particles with a particle size <15 μm are plated with Sn 35 Bi 0.5 Ag alloy plating to obtain small particle size core-shell structured Cu@Sn 35 Bi 0.5 Ag powder; Cu particles with a particle size of 15 - 25 μm are plated with Sn 35 Bi 0.5 Ag alloy plating to obtain medium particle size core-shell structured Cu@Sn 35 Bi 0.5 Ag powder; Cu particles with a particle size of 25 μm < particle size ≤ 50 μm are plated with Sn35 Bi 0.5 Preparation of Bi-Ag alloy coating to obtain large-grained core-shell structure Cu@Sn 35 Bi 0.5 Ag powder.

[0073] The coating thickness of <15μm Cu particles is ~1μm, the coating thickness of Cu particles with a particle size of 15 - 25μm is 1 - 2μm, the coating thickness of Cu particles with a particle size of 25 - 50μm is 2 - 3μm. The large-grained core-shell structure Cu@X powder, medium-grained core-shell structure Cu@X powder, and small-grained core-shell structure Cu@X powder are proportioned by weight at 1:2:3 to obtain a composite powder; the composite powder is a welding material.

[0074] Step 2, perform pressure molding on the composite powder. The molding pressure is 8 MPa and the molding time is 6 min. For the obtained preformed solder sheet Perform surface Sn plating treatment to strengthen the surface coating. The thickness of the Sn plating layer is 1.3μm;

[0075] Step 3, for the Cu@Sn preformed solder sheet, use an ultrasonic-assisted solid-state diffusion welding method. This welding method causes Cu and Sn to undergo a solid-solid diffusion reaction at 160°C to transform into high-melting-point Cu 3 Sn. The auxiliary ultrasonic technology accelerates the Cu / Sn solid-state reaction rate, enabling the joint to complete the Cu@Cu 3 Sn joint Cu@Cu 3 Sn preparation; for Cu@Sn58Bi and Cu@Sn 35 Bi 0.5 Ag, use ultrasonic-assisted transient liquid-phase diffusion welding to complete the joints Cu@Cu 3 Sn / Bi and Cu@Cu 3 Sn / Ag 3 Sn / Bi preparation. This ultrasonic-assisted TLPS technology adds ultrasonic technology on the basis of conventional transient liquid-phase diffusion welding, aiming to accelerate the interfacial reaction rate between elements and reduce the reaction time;

[0076] Step 4, add the Cu@X composite powder and Halys commercial flux at a weight ratio of 8.5:1, with the brand number DL-405. After ball milling and mixing evenly, prepare a solder paste; use the double-printing method to first print a layer of solder paste with a thickness of 75μm on the Cu substrate, degum at 120°C for 90 min, and then print another layer of solder paste with a thickness of 60μm;

[0077] Step 5, Cu@Sn and Cu@Sn 35 Bi 0.5The Ag solder paste is heated to 155 °C at a heating rate of 70 °C / min, and then heated to 190 °C at a heating rate of 5 °C / min, with a pressure of 2 MPa. After holding for 5 min, a dense three-dimensional network joint is obtained; Cu@Sn 58 The Bi solder paste is heated to 110 °C at a heating rate of 70 °C / min, and then heated to 180 °C at a heating rate of 5 °C / min, with a pressure of 3 MPa. After holding for 5 min, a dense three-dimensional network joint is obtained.

[0078] The parts not elaborated in detail in the present invention belong to the well-known technologies of those skilled in the art. The above-described embodiments are only descriptions of the preferred embodiments of the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing a welded material joint for welding below 200°C and high-temperature applications, characterized in that, the welding material is a core-shell structured composite welding material, including a core layer and a shell layer coated outside the core layer; wherein the core layer material is Cu, and the shell layer material is SnBiAg alloy; the high temperature resistance means that the maximum tolerable temperature of the welding material is 450°C; the shell layer is a SnBiAg alloy coating; the SnBiAg alloy coating is prepared by electroplating, and the coating thickness is 1 - 2 μm; the welding material is prepared by the following steps: Electroplating a metal layer on Cu particles with a particle size < 15 μm to obtain Cu@X particles with the first particle size; electroplating a metal layer on Cu particles with a particle size of 15 - 25 μm to obtain Cu@X particles with the second particle size; electroplating a metal layer on Cu particles with a particle size greater than 25 and less than or equal to 50 μm to obtain Cu@X particles with the third particle size; the metal layer thickness in the Cu@X particles with the first particle size, the Cu@X particles with the second particle size, and the Cu@X particles with the third particle size is all 1 - 2 μm; mixing the Cu@X particles with the first particle size, the Cu@X particles with the second particle size, and the Cu@X particles with the third particle size to obtain the welding material; wherein, the metal is SnBiAg; the mixing weight ratio of the Cu@X particles with the first particle size, the Cu@X particles with the second particle size, and the Cu@X particles with the third particle size is 3:2:1; the method for preparing a welded material joint for welding below 200°C and high-temperature applications includes the following steps: pressure-forming the welding material into a preformed solder sheet, and coating a 1 - 2 μm thick Sn layer or Sn-based alloy layer on the surface of the preformed solder sheet by secondary electroplating. The preformed solder sheet with the Sn or Sn-based alloy coating on the surface is ultrasonically assisted welded at 170 - 200°C. The preformed solder sheet coated with Sn utilizes the solid-liquid diffusion principle, or the preformed solder sheet coated with Sn-based alloy utilizes the solid-solid diffusion welding principle, and a three-dimensional network joint is obtained after isothermal aging for 8 - 10 min. The room-temperature shear strength of the three-dimensional network joint is not less than 80 MPa; the Sn-based alloy layer is a SnBi alloy layer or a SnBiAg alloy layer.

2. According to the method described in claim 1, characterized in that, The welding material with a shell material of SnBiAg eutectic alloy, and the SnBiAg eutectic alloy is SnBi 35 Ag 0.5 eutectic alloy, and the SnBi 35 Ag 0.5 eutectic alloy has a melting point of 172 °C and a welding temperature of 200 °C, and transient liquid phase diffusion welding is used to achieve high-temperature connection.

3. According to the method described in claim 2, characterized in that, The prepared Cu@SnBiAg eutectic alloy particles, hydroquinone, catechol, resorcinol, phloroglucinol, pyrogallol, or α- or β-naphthol antioxidant is added to the plating solution to prevent Sn 2＋ from being oxidized to Sn 4＋ ; the mass concentration of the antioxidant is 0.05-5 g / L; One or more of a brightening agent, a complexing agent, a pH adjuster, a conductivity aid, and a surfactant are further added to the plating solution. The pH value of the plating solution is 1 - 8, and the plating solution temperature is 10 - 60°C.

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