CN105290418B - Plate the plating subsidiary formula method for the thick tin layers for attaching solderability thickness in a kind of micro-nano copper ball surface - Google Patents

Abstract

The present invention provides the plating subsidiary formula methods that a kind of micro-nano copper ball surface plating attaches the thick tin layers of solderability thickness, obtain surface plating with thick tin layers based on Cu@Sn nucleocapsid metal powders.Preset suppressed using the metal powder material is carried out welding and (250 DEG C) welding of low temperature can be realized, gained solder joint is amenable to (676 DEG C) military services of high temperature, and the stability for greatly improving welding spot reliability and weld seam can be widely applied to various high-temperature soldering fields.

Description

The invention discloses a method of coating the surface of micro-nano copper balls with a thick tin layer with solderability thickness. method

technical field

The invention belongs to the interdisciplinary technical field of material chemistry and material processing, and relates to a plating method for plating a thick tin layer with a solderable thickness on the surface of micro-nano copper balls.

Background technique

High temperature power devices are attracting increasing attention due to their great potential in automotive, downhole oil and gas industry, aircraft, space exploration, nuclear reaction environment, and radar. At present, the IGBT chips on the market generally use silicon as the raw material. However, due to the low parameters such as the bandgap width of the silicon material, the critical breakdown electric field strength, and the electron saturation rate, the development of this material is currently approaching the bottleneck. Silicon carbide (SiC) has better physical properties than silicon materials, and power devices made of SiC have the characteristics of small off-tail current and fast response. At the same time, power devices made of this material can withstand very high temperatures, and are especially suitable for applications in high-power, high-frequency and high-temperature environments. At present, silicon carbide chips have been put into commercial application in some fields, and are expected to completely replace silicon chips as the third-generation semiconductor. At present, the third generation of silicon carbide semiconductors is about to be widely used, but there are very few solders suitable for this kind of power device packaging that can withstand high temperature service conditions, and each has its own advantages and disadvantages. Therefore, it is urgent to develop A solder capable of high melting point and high reliability.

At present, the die-attaching process for high-temperature power devices mainly includes the use of improved alloy solder, nano-silver sintering method, and transient liquid phase bonding (Transient Liquid Phase bonding, TLP) process. Each of these processes has its own characteristics, but also has its own application limitations. Superalloy solders mainly include gold-based systems, lead-based systems, zinc-based systems, bismuth-based systems and silver-based systems. Among these candidate components, gold-based alloys such as Au–Sn (Tm=280°C) and Au–Ge (Tm=356°C) are relatively common high-temperature solders, but the eutectic structure of gold-based alloys is very hard, and at the same time Substrate materials that can match its thermal expansion coefficient are also very limited, and the high cost of gold-based solder also limits its large-scale mass production; although lead-based alloys have many advantages, due to the toxicity of lead, as the electronics industry leads to lead-free The promotion of chemicalization is obviously no longer applicable to the present; the wetting and spreading of zinc-based solder is not good, and because of its low plasticity, it is prone to hard and brittle phases; bismuth-based solder (such as Bi-Ag) on Cu substrates The wettability of solder is not high, the bonding strength is weak, and the plasticity is poor. At present, the substrates of most electronic products are Cu substrates, so this also limits the application of this solder. Moreover, the high-temperature alloy solder has a relatively high melting point, and it must be heated to the melting point of the solder when performing brazing interconnection, so a higher reflow soldering temperature during soldering will cause greater reliability damage to the device. The nano-silver sintering method is considered by the industry to be the most potential high-temperature lead-free solder replacement product. The sintered nano-silver has excellent thermal conductivity (240Wm ^-1 K ^-1 ) and electrical conductivity (4.1×10 ^-7 Sm ^-1 ) And the higher melting point (961°C), what is particularly attractive is the sintering temperature of nano-silver. At present, the nano-silver sintering technology at low temperature or even room temperature is realized in the industry, and the melting point of nano-silver after sintering returns to 961°C, which is It shows that if nano-silver is used for connection, only a lower reflow soldering temperature is required to sinter the nano-silver to each other, and the obtained sintered silver solder joint needs to be heated to a high temperature of 961°C to melt again, so the nano-silver has low-temperature sintered solder joints. The advantage of being able to withstand high temperatures; however, nano-silver sintering technology has some disadvantages at the same time. For example, the raw materials are relatively expensive so it is not suitable for mass production in enterprises; Large-scale applications require the overall replacement of equipment; when applying nano-silver for sintering and welding, pressure assistance (usually several MPa) is required, and even so, the sintered silver obtained due to the limitation of the sintering neck has microscopic pores, which is very easy to become The source of microcrack initiation and propagation, and the electromigration of silver at high temperature can have a negative impact on the reliability of the overall solder joint. Another feasible method is Transient Liquid Phase Sintering (TLPS) or Solid Liquid Interdiffusion (Solid Liquid Interdiffusion). Its welding principle is completely different from nano-silver sintering. In the TLP bonding process, at least two combinations are required. One element has a low melting point as the brazing material (such as tin), while the other has a higher melting point as the substrate of the device (such as copper), and the low melting point solder is placed between the two high melting point substrate materials to be connected. During low-temperature reflow, the solder with a low melting point melts and spreads at the interface with the high-melting point material, so that the entire tissue has no voids; during the subsequent reflow process, the two materials undergo interdiffusion motion at the interface and generate compounds (such as Cu ₆ Sn ₅ ), as the diffusion movement proceeds, the compound grows up and eventually consumes all the low-melting point materials to form a solder joint that is completely compounded at the weld. This compound usually has a relatively high melting point, so that the solder joints obtained by low-temperature soldering can withstand high temperatures. The advantage of this welding method is that the source of raw materials is wide and the cost is low, and it has high processing compatibility with the machines of the current enterprise production line; the disadvantage is that due to the limited diffusion rate of elements in the entire process, the formation and growth of compounds The speed is relatively slow, so it takes a long time to obtain the structure of the full compound solder joint. Therefore, the TLP process is currently only suitable for the welding of narrow welds. Due to the difference in thermal expansion coefficient, stress concentration problems will occur at the welds, and this problem is more prominent for narrower welds. The external compound is usually a hard and brittle phase. It greatly increases the possibility of solder joint cracking and failure during compound service. Although increasing the thickness of the weld seam can solve the problem of stress concentration, the reflow time or reflow temperature will also be increased. A longer reflow time or a higher reflow temperature will have an adverse effect on other devices on the substrate.

CN103753049A provides a method for preparing Cu@Sn core-shell structure metal powder, comprising: weighing Cu powder and making it completely dispersed in deionized water; weighing Sn and dissolving it in deionized water, the mass ratio of Sn to Cu is 1 :8 to 1:2, stir evenly to form a deionized aqueous solution; mix and stir at room temperature for 10 to 40 minutes to ensure complete reaction; use water or absolute ethanol to wash the reaction product repeatedly until the solution is clear and dry in the shade. The preferred solution is to weigh the dispersant PVP, uniformly mix the Cu powder and the dispersant at a mass ratio of 1:1, and then completely disperse it in deionized water. In this way, a core-shell structure with Sn-coated Cu particles is formed. During the welding process, the weld structure in which copper particles are dispersed in the intermetallic compound can be formed above the melting point of Sn. After formation, it can be formed in Cu ₆ Sn ₅ Service below the melting point. This scheme is based on the principle of displacement reaction. When the surface of copper particles is in contact with the plating solution, the addition of complexing agent thiourea lowers the electrode potential of copper, so that copper atoms can undergo a displacement reaction with tin ions in the plating solution to generate tin atoms. With copper ions free in the solution, the specific principle is as follows:

Thiourea can form a stable complex with Cu ²⁺ [Cu((NH ₂ ) ₂ CS) ₂ ] ²⁺ , which moves the electrode potential of Cu ²⁺ /Cu to negative value and replaces Sn ²⁺ . Its reaction equation can be written as:

Sn ²⁺ +Cu+2(NH ₂ ) ₂ CS＝Sn+[Cu((NH ₂ ) ₂ CS) ₂ ] ²⁺

The prerequisite for the replacement reaction to occur is that the two components to be replaced must be in contact with each other, and in this plating reaction, although copper atoms can indeed replace tin with the assistance of thiourea and completely cover the surface of the copper ball A core-shell structure is formed, but once a dense tin atomic layer is formed on the copper surface to completely cover the copper ball, the copper ball cannot continue to contact with the plating solution, and the replacement reaction cannot continue, which fundamentally blocks the continued growth of the plating layer. Thick possibility.

Therefore, although the method described in CN103753049A can be used to obtain Cu@Sn core-shell metal powder, the tin-shell part of the plating cannot reach a specific thickness so that the coating has the best solderability. Generally, the industry believes that the tin coating is > 4 μm In order to make the coating have good solderability, that is, for a single Cu@Sn core-shell structure metal particle, when the tin coating on the surface of the copper particle is larger than 2 μm, the internal copper core can achieve excellent soldering connection through the external tin shell.

CN104117782A, on the basis of CN103753049A, through the addition of stabilizers, reducing agents, antioxidants and other drugs, the reaction principle of tin plating is upgraded from displacement reaction to self-catalysis reaction, tin atoms are reduced in the solution and deposited on the solid-liquid At the interface, after a certain period of plating, a tin layer with a certain thickness can be obtained on the surface of the copper core. This method does not use a dispersant, and further produces a new type of prefabricated high-temperature solder by pressing the obtained core-shell structure metal powder, and the application of the prefabricated sheet for pad welding, thereby forming a method of high-temperature welds . This structure can realize the brazing connection to the pad under the short-time reflow process at 250°C, and after the solder joint is formed, it can be stably served at 676°C, achieving the purpose of low-temperature connection and high-temperature service. However, at present, the performance of Cu@Sn core-shell metal powder is well reflected in the process of pressing into pre-chips, but when the metal powder is prepared into solder paste, the porosity of the weld seam obtained after welding with paste is significantly higher. The connection strength is relatively low, and the popularization and application of this core-shell metal powder and solder paste needs to be broken through in subsequent research.

Based on the problems existing in various brazing methods and brazing materials in the field of high-temperature connection in the prior art, the present invention innovatively proposes a method for preparing metal powder with a core-shell structure, and applies this metal powder to high-temperature applications for the first time. In the field of connection, it satisfactorily solves the problems commonly faced by the industry.

Contents of the invention

In order to solve the deficiencies in the above-mentioned prior art, the present invention provides a plating method for coating the surface of micro-nano copper balls with a thick tin layer with a solderable thickness, so as to prepare micro-nano-scale Cu@Sn core-shell structure metals. Powder, and the application of this low-temperature transient liquid phase-connected LT-TLPS (Low Time-Transient Liquid Phase Soldering) metal powder in the field of high-temperature solder.

A method for plating a thick tin layer with solderability thickness on the surface of a micro-nano copper ball, comprising:

(1) Weigh the complexing agent, reducing agent, stabilizer, antioxidant and appropriate amount of methanesulfonic acid and ethylene glycol, add ultra-pure deionized water, heat to 80 ° C and apply stirring until the solution is completely dissolved to obtain a solution A;

It is preferable to weigh the complexing agent, reducing agent, stabilizer, antioxidant and appropriate amount of methanesulfonic acid and ethylene glycol, add ultra-pure deionized water, the concentration of the complexing agent is 1.2-1.5mol/L, and the concentration of the reducing agent is 0.75 ～0.9mol/L, stabilizer concentration 0.002～0.0035mol/L, antioxidant concentration 0.003～0.004mol/L, methanesulfonic acid concentration 0.075～0.1mol/L, ethylene glycol concentration 10～15ml/L , heated to 80°C and applied stirring until the solution was completely dissolved to obtain solution A;

Through a large number of experimental studies, it is found that the temperature selection can only be achieved at 80°C, and the solubility of the solute below 80 degrees cannot meet the requirements to completely dissolve the various solutes weighed before. If the solute is not completely dissolved in the plating solution for subsequent plating Operation has two unavoidable disadvantages:

1. The solute is not completely dissolved, and some of the solute’s role in the plating solution cannot be fully displayed, such as insufficient reducing ability or poor stability of the plating solution.

2. The solute cannot be completely dissolved and the subsequent long-term high-speed plating is carried out at room temperature. If the solute cannot be completely dissolved in this step, the solute cannot be dissolved during the subsequent operation, so that the target metal powder is filtered and cleaned until the end. There are still a lot of solutes that cannot be completely dissolved in the first step, that is, inorganic salts, which are doped in the finally obtained and shell-structured metal powders, which cannot be separated, because core-shell structure metal powders are highly temperature-sensitive as new welding materials , if the prepared metal powder and inorganic salt are heated to 80°C again, although the inorganic salt will dissolve and the metal powder will be obtained by filtration, while the metal powder with Cu@Sn core-shell structure will undergo an irreversible phase transition at 80°C, and the tin The shell part is completely transformed into Cu-Sn compound due to the diffusion of copper atoms, and the metal powder loses its most basic value. Therefore, once the metal powder is made, it cannot be reheated in other steps unless it is in the reflow soldering step. , which is why it is necessary to ensure that the inorganic salt is fully dissolved during the early plating process. Although the temperature higher than 80°C can also dissolve the solute, the too high temperature makes the solution volatilize rapidly, which is not conducive to the stable control of the plating solution volume.

The complexing agent is preferably thiourea, the reducing agent is preferably sodium hypophosphite, the stabilizer is preferably ethylenediaminetetraacetic acid, and the antioxidant is preferably hydroquinone and ascorbic acid.

If the above components and corresponding contents are selected improperly, the main disadvantages are that the coating thickness is not enough, the coating coating result is not good, tin whiskers appear on the coating, and the surface oxidation is seriously unfavorable for the welding application of metal powder in the next step.

(2), weigh an appropriate amount of copper powder, clean and remove surface stains and oxide layers, and activate the surface of copper balls, then clean with deionized water and set aside;

Preferably, the copper powder is placed in a hydrochloric acid-ethanol solution with a volume ratio of 5% according to a mass ratio of 1:10, a surfactant is added and ultrasonic waves are applied to the copper powder, and then the copper powder is cleaned with deionized water for 4 times for later use. The surfactant is preferably polyethylene glycol, polyethylene glycol: ethanol mass ratio=1:100.

The particle size of the copper powder is preferably at the micro-nano level, from nano-copper powder to micro-copper powder below 50 microns, this formula can achieve relatively good plating results.

(3), take by weighing 1.8～2.5g stannous chloride and dissolve in 1ml hydrochloric acid, as solution B;

Described hydrochloric acid is selected as pure hydrochloric acid for use, because stannous chloride can be hydrolyzed, it is dissolved in hydrochloric acid solidly.

(4) Pour the solution B into the stirring solution A at 80°C, and adjust the temperature and pH of the plating solution to a suitable range after mixing evenly;

The suitable temperature for adjusting the plating solution after mixing the two solutions is preferably 20-35° C., and the suitable pH value is preferably 0.8-1.

Through a large number of experimental studies, it is found that if the temperature range is higher than the stated value, the core-shell structure metal powder is prone to phase change due to the high surface energy of the micro-nano particles during the plating process, and the tin is converted into a Cu-Sn compound and loses its solderability. If it is lower than the value, the reaction rate is greatly reduced, which greatly prolongs the time required for the plating reaction.

If the pH value is too high or too low, the tin plating effect will be poor, and the plating speed is the fastest in the pH range.

(5), the copper powder that step (2) is processed is poured in the mixed solution of A and B, increases stirring speed, and electromagnetic stirring and glass rod manual stirring are carried out alternately, guarantees reaction 3h;

The increased stirring rate after mixing of the two solutions is preferably 300 rpm.

(6), filtering the plating solution and cleaning the metal powder to obtain a Cu@Sn core-shell structure based bimetallic powder with a thick tin layer on the surface.

The heating and stirring refer to electromagnetic stirring in a water bath.

The micro- and nano-scale metal powder based on Cu@Sn core-shell structure refers to a core-shell structure in which copper cores of various sizes between 20nm and 50 μm are plated with a tin metal layer with a solderable thickness (>3 μm) .

The material conditions required by the method of the present invention are simple, the cost is low, and there are very broad prospects for practical promotion and application in enterprises. In addition, compared with other preparation methods of high melting point solder joints such as nanomaterial sintering, the materials prepared by this method are comparable to those in traditional industries when welding. The reflow soldering production line has better compatibility, which is very conducive to the preparation and promotion of applications on the basis of existing processing equipment.

More specific preparation method steps are described in detail as follows:

(1), Weigh sodium hypophosphite (0.86mol/l), thiourea (1.3mol/L), hydroquinone (0.0036mol/L), ethylenediaminetetraacetic acid (0.0028mol/L) dissolved in Add methanesulfonic acid (0.083mol/L) and ethylene glycol (15ml/L) to 50ml of deionized water and heat in a water bath to 80°C, apply electromagnetic stirring at a stirring speed of 100rpm, and wait until the solute is completely dissolved to obtain solution A.

(2), weigh 4g of copper powder, place it in 5% hydrochloric acid-ethanol solution for pickling, add surfactant polyethylene glycol (2g/L) at the same time and carry out ultrasonic cleaning to copper powder to remove surface stains and oxide layer At the same time, activate the surface of the copper ball, and finally wash the copper powder with deionized water 4 times for later use;

(3), take by weighing 2g stannous chloride and be dissolved in 1mL pure hydrochloric acid, as solution B;

(4) Pour 80°C solution B into the stirring solution A, adjust the temperature of the mixed solution to 30°C, and adjust the pH of the plating solution to be between 0.8-1 by adding ammonia water and hydrochloric acid, during the whole process The solution has been in a state of stirring at 100rpm;

(5) Pour the copper powder pickled and surface-treated in the previous second step into the mixed solution of A and B at 30°C, and increase the electromagnetic stirring rate to 300rpm; but the electromagnetic stirring must be interspersed with manual glass rods Stir to ensure that the state of the particles in the plating solution is uniform, and switch to the manual glass rod for 5 minutes every 20 minutes of electromagnetic stirring, and reciprocate to ensure that the reaction time is 3 hours;

(6), filtering the plating solution and cleaning the metal powder to obtain a Cu@Sn core-shell structure based bimetallic powder with a thick tin layer on the surface.

One object of the present invention is to provide a pre-set sheet of high-temperature fiber material, which is prepared by the following preparation method steps: (7), Cu@Sn core-shell structure bimetallic powder is pressed under 30Mpa pressure to form a pre-set sheet piece.

Low-temperature (250° C.) welding can be realized by using the pressed pre-sheet of high-temperature fiber material for welding, and the obtained solder joints can withstand high temperature (676° C.).

The inventors have found through a large number of experimental studies that the formula and test method of the present invention can achieve a pure tin layer with solderability thickness on the surface of copper balls for copper balls in the size range of 20nm to 50 μm. The core-shell structure metal powder pressed preset sheet can greatly shorten the time required for the complete IMC of the weld seam when welding, so that it can be realized in a short time and low temperature

Compared with the prior art, the present invention has the advantages of:

1. The melting point of traditional solder is low, which is difficult to meet the requirements of higher temperature devices. However, the most promising nano-silver sintering method in the industry has the inevitable silver migration problem, which will greatly reduce the reliability of solder joints, and the nano-silver The high cost is not suitable for large-scale production of enterprises. The raw material of the Cu@Sn core-shell metal powder prepared by the present invention is copper powder, the cost of medicines required in the plating process is also very low, and the processing technology is simple. Point can withstand the advantages of high temperature service.

2. The nano-silver sintering process is quite different from the traditional process, and cannot be compatible with the existing production line of the enterprise. If large-scale production requires a new production line. However, the welding materials provided by this solution, which are compressed by Cu@Sn core-shell metal powder, are well compatible with the reflow soldering process of traditional solders. Enterprises can realize it without making too many changes on the existing production line, which is easier. Promote apps.

3. Since the copper particles are evenly distributed in the weld, the time required for the consumption of residual tin inside the weld is greatly shortened, which greatly reduces the possibility of heat damage to the device due to prolonged reflow.

4. Copper has excellent electrical and thermal conductivity. Compared with traditional tin-based solder, copper particles mixed in the weld can greatly improve the electrical and thermal conductivity of the weld.

5. The traditional weld structure is sandwiched between two solder pads, and the atomic diffusion can only occur at the cross section, so the time for the weld to be completely compounded depends on the thickness of the weld, and it is made of Cu@Sn core-shell metal powder. The time for complete compounding of the solder formed by the pre-chip depends on the thickness of the tin-plated layer on the surface of the copper ball, so it is possible to completely IMC the thicker solder in a short time. The thick weld seam can significantly alleviate the stress concentration problem caused by the different thermal expansion coefficients of different materials at the weld seam, thereby greatly improving the reliability of the solder joints.

Description of drawings

Figure 1 is a cross-sectional view of a Cu@Sn core-shell metal particle cut by FIB.

Figure 2 shows the high-melting point interconnection solder joints prepared by using Cu@Sn core-shell metal powder under low temperature and short-term conditions. In the figure: 0201 is the copper substrate; 0202 is the preset sheet made by pressing Cu@Sn core-shell metal powder .

Figure 3 is an enlarged view of the prefabricated sheet structure prepared by Cu@Sn core-shell metal powder, in which: 0301 is the copper core, and 0302 is the part of the tin shell plated on the surface of the copper core before reflow, which is converted into Cu with a high melting point after reflow ₃ Sn compounds.

Fig. 4 is a schematic diagram of the 30-micron particle size core-shell structure particles obtained in an embodiment of the present invention and a schematic diagram of the weld structure. Among them, the schematic diagram of the particles 4 (a), the schematic diagram of the weld structure 4 (b), and 4 (c) are 4 (a) ) is a schematic diagram at another size, and 4(d) is a partial enlarged view of 4(c).

Fig. 5 is a schematic diagram of core-shell structure particles with a particle size of 1 micron and a weld structure obtained by an embodiment of the present invention. Among them, the schematic diagram of the particles 5 (a), the schematic diagram of the weld structure 5 (b), and 5 (c) are 5 (a) ) Schematic diagram after welding.

Detailed ways

The implementation of the present invention will be described below through specific examples and accompanying drawings, but not limited thereto.

Implementation example 1, with reference to Figures 1, 2 and 3:

Based on the above considerations, through a large number of experimental attempts and data analysis, we invented the plating method for plating the surface of micro-nano copper balls with a solderable thick tin layer. The purpose of plating a thick tin layer on the surface of the copper ball.

The method specifically includes the following steps (using 50ml of plating solution to tinplate 4g of copper powder with a particle size of 30 μm and finally making it into a high-temperature-resistant solder joint as an example):

(1), weigh 3.7g of sodium hypophosphite, 5g of thiourea, 0.02g of hydroquinone, 0.04g of ethylenediaminetetraacetic acid, dissolve in 50ml of deionized water and apply stirring at a stirring rate of 100rpm, add methanesulfonic acid 0.4g, 0.7ml of ethylene glycol, put the solution in a water bath and heat to 80°C until the solute is completely dissolved to obtain solution A.

(2) Weigh 4g of copper powder with a particle size of 30 μm, place it in 5% hydrochloric acid-ethanol solution and apply ultrasonic pickling, the purpose is to remove the stain and oxide layer on the surface of copper powder, and add 0.1g polyethylene glycol at the same time Activate the surface of the copper powder, and finally wash the copper powder with deionized water 4 times for later use.

(3), take by weighing 2g stannous chloride and be dissolved in 1ml pure hydrochloric acid, as solution B;

(4) Pour the 80°C solution B into the stirring solution A, adjust the temperature of the mixed solution to 30°C, and adjust the pH of the plating solution to be between 0.8-1 by adding ammonia water and hydrochloric acid. The solution has been in a state of stirring at 100rpm;

(5) Pour the copper powder pickled and surface-treated in the previous second step into the mixed solution of A and B at 30°C, and increase the electromagnetic stirring rate to 300rpm; but the electromagnetic stirring must be interspersed with manual glass rods Stir to ensure that the state of the particles in the plating solution is uniform, and switch to the manual glass rod for 5 minutes every 20 minutes of electromagnetic stirring, and reciprocate to ensure that the reaction time is 3 hours;

(6) Filtrating the plating solution and cleaning the metal powder to obtain a Cu@Sn dual metal core-shell structure with a particle size of 30 μm and a thick tin layer on the surface.

(7) Press the Cu@Sn core-shell metal powder into a preset sheet under a pressure of 30Mpa, and use the pressed preset sheet for welding to achieve low temperature (250°C) welding, and the obtained solder joints can withstand high temperature (676°C) the goal of.

The obtained core-shell structure particles and weld structure are shown in Figure 4(a)-4(d):

It has been verified by a large number of experiments that the resistivity of this weld is 6.50μΩ·cm, and its electrical conductivity is far superior to that of traditional tin-based solder (11.5μΩ·cm) and the copper-tin compound made by traditional TLP process. The pure IMC solder joints (Cu ₆ Sn ₅ : 16.5 μΩ·cm; Cu ₃ Sn: 8.9 μΩ·cm) are in the same order (2.5-10 μΩ·cm) as the welds after nano-silver sintering.

At the same time, due to the doping of copper particles in this new type of weld, its thermal conductivity is as high as 154.26W/m K, and its thermal conductivity is also much better than that of tin-based solder (63.2W/m K) and pure IMC solder joints ( Cu ₆ Sn ₅ : 34.1 W/m·K; Cu ₃ Sn: 70.4 W/m·K).

In addition, when the weld is sheared at a high temperature of 0.1mm/min at 400°C, the average shear strength reaches 29MPa, which is enough to meet the reliability service of the device under any harsh conditions.

Implementation example 2,

In order to verify that this formula has an excellent coating effect on thick tin layers with solderability for copper powders of various particle sizes, we specially selected copper powders with a particle size of 1 μm for tin plating, and finally tinned the copper powder with a particle size of 1 The micron Cu@Sn core-shell copper powder is prepared into a pre-chip for actual welding to obtain solder joints that can withstand high temperature service.

The method specifically includes the following steps (using 100ml of plating solution to tinplate 8g of copper powder with a particle size of 1 μm and finally making it into a high-temperature-resistant solder joint as an example):

(1), Weigh 7.4g of sodium hypophosphite, 10g of thiourea, 0.04g of hydroquinone, 0.08g of ethylenediaminetetraacetic acid, dissolve in 100ml of deionized water and apply stirring at a stirring rate of 100rpm, add methanesulfonic acid 0.8g, 1.4ml ethylene glycol, put the solution in a water bath and heat to 80°C until the solute is completely dissolved to obtain solution A.

(2), Weigh 8g of copper powder with a particle size of 1 μm, place it in 5% hydrochloric acid-ethanol solution and apply ultrasonic pickling, the purpose is to remove the stains and oxide layer on the surface of the copper powder, and add 0.2g polyethylene glycol at the same time Activate the surface of the copper powder, and finally wash the copper powder with deionized water 4 times for later use.

(3), take by weighing 4g stannous chloride and be dissolved in 2ml pure hydrochloric acid, as solution B;

(4) Pour the 80°C solution B into the stirring solution A, adjust the temperature of the mixed solution to 30°C, and adjust the pH of the plating solution to be between 0.8-1 by adding ammonia water and hydrochloric acid. The solution has been in a state of stirring at 100rpm;

(5) Pour the copper powder pickled and surface-treated in the previous second step into the mixed solution of A and B at 30°C, and increase the electromagnetic stirring rate to 300rpm; but the electromagnetic stirring must be interspersed with manual glass rods Stir to ensure that the state of the particles in the plating solution is uniform, and switch to the manual glass rod for 5 minutes every 20 minutes of electromagnetic stirring, and reciprocate to ensure that the reaction time is 3 hours;

(6) Filtrating the plating solution and cleaning the metal powder to obtain a Cu@Sn dual metal core-shell structure with a particle size of 1 μm and a thick tin layer on the surface.

(7) Press the Cu@Sn core-shell metal powder into a preset sheet under a pressure of 30Mpa, and use the pressed preset sheet for welding to achieve low temperature (250°C) welding, and the obtained solder joints can withstand high temperature (676°C) the goal of.

The resulting core-shell structure particles and weld structure are shown in Figure 5(a)-5(c):

The weld seam still has excellent electrical and thermal conductivity and reflow soldering can be realized at low temperature, and the obtained solder joints can withstand high temperature.

Comparative Example 1

High-temperature solder prepared by CN104117782A method

The effect comparison found that the main difference is mainly reflected in Figure 4.b. The new plating process can achieve a thicker coating and better meet the welding requirements, so that the final prefabricated sheet has better electrical and thermal conductivity and mechanical connection performance. superior.

Comparative Example 2

High-temperature solder prepared by CN103753049A method

The effect comparison shows that when the metal powder is prepared into solder paste, the porosity of the weld seam obtained after welding with the paste is obviously more, and the connection strength is relatively low.

Claims (4)

1. a kind of micronano copper ball surface is plated and has the plating method of the thick tin layer of weldability thickness, it is characterized in that, comprises: (1), take complexing agent, reducing agent, stabilizer, antioxidant and methanesulfonic acid and ethylene glycol, add ultra-pure deionized water, complexing agent is thiourea, and described reducing agent is sodium hypophosphite , the stabilizer is ethylenediaminetetraacetic acid, and the antioxidant is hydroquinone or ascorbic acid; after adding ultra-pure deionized water, hydroquinone: water mass ratio=0.006:1, ascorbic acid: water=0.008 : 1; the concentration of complexing agent is 1.2～1.5mol/L, the concentration of reducing agent is 0.75～0.9mol/L, the concentration of stabilizer is 0.002～0.0035mol/L, the concentration of methanesulfonic acid is 0.075～0.1mol/L, B The diol concentration is 10-15ml/L, heated to 80°C and stirred until the solution is completely dissolved to obtain solution A; (2), take by weighing an appropriate amount of copper powder, the particle size of the copper powder is micro-nano level, from nano-copper powder to micron copper powder below 50 microns; clean and remove surface stains and oxide layers, and activate the copper ball surface, and then Clean with deionized water, adopt copper powder to be placed in hydrochloric acid-ethanol solution according to mass ratio 1:10, described hydrochloric acid-ethanol solution is the hydrochloric acid-ethanol solution of volume ratio 5%, add surfactant and carry out to copper powder Apply ultrasound, then clean the copper powder with deionized water 4 times for use, the surfactant is polyethylene glycol, polyethylene glycol: ethanol mass ratio = 1:100, for use; (3), take appropriate amount of stannous chloride and be dissolved in hydrochloric acid, as solution B; (4) Pour solution B into solution A under stirring at 80°C, adjust the temperature of the plating solution to 28-35°C after mixing evenly, and adjust the pH value to 0.8-1, during which the solution has been in a stirring state ; (5), the copper powder that step (2) is processed is poured in the mixed solution of A and B, increases stirring speed, and electromagnetic stirring and glass rod manual stirring are carried out alternately, guarantees reaction 3h; (6), filtering the plating solution and cleaning the metal powder to obtain a Cu@Sn core-shell structure based bimetallic powder with a thick tin layer on the surface. 2. a kind of micronano copper ball surface plating according to claim 1 has the plating method of the thick tin layer of weldability thickness, it is characterized in that, in described step (3), take by weighing 1.8～2.5g chlorine Stannous and dissolved in 1ml of hydrochloric acid, as solution B. 3. a kind of micronano copper ball surface plating method according to claim 1 has the thick tin layer of solderability thickness, it is characterized in that, after the two kinds of solutions described in the described step (5) are mixed The increased stirring rate was 300 rpm. 4. a kind of micronano copper ball surface plating according to claim 1 has the plating method of the thick tin layer of weldability thickness, it is characterized in that, (1), Weigh 0.86mol/L of sodium hypophosphite, 1.3mol/L of thiourea, 0.0036mol/L of hydroquinone, and 0.0028mol/L of ethylenediaminetetraacetic acid, dissolve them in 50ml of deionized water, add methanesulfonate Acid 0.083mol/L, ethylene glycol 15ml/L, heated in a water bath to 80°C, applying electromagnetic stirring at a stirring speed of 100rpm, until the solute is completely dissolved to obtain solution A; (2), weigh 4g of copper powder, place it in 5% hydrochloric acid-ethanol solution for pickling, add surfactant polyethylene glycol 10g/L at the same time, and carry out ultrasonic cleaning to copper powder to remove surface stains and activate the oxide layer at the same time On the surface of the copper ball, wash the copper powder 4 times with deionized water for later use; (3), take by weighing 2g stannous chloride and be dissolved in 1mL pure hydrochloric acid, as solution B; (4) Pour 80°C solution B into the stirring solution A, adjust the temperature of the mixed solution to 30°C, and adjust the pH of the plating solution to be between 0.8-1 by adding ammonia water and hydrochloric acid, during the whole process The solution has been in a state of stirring at 100rpm; (5) Pour the copper powder pickled and surface-treated in the previous second step into the mixed solution of A and B at 30°C, and increase the electromagnetic stirring rate to 300rpm; but the electromagnetic stirring must be interspersed with manual glass rods Stir to ensure that the state of the particles in the plating solution is uniform, and switch to the manual glass rod for 5 minutes every 20 minutes of electromagnetic stirring, and reciprocate to ensure that the reaction time is 3 hours; (6), filtering the plating solution and cleaning the metal powder to obtain a Cu@Sn core-shell structure based bimetallic powder with a thick tin layer on the surface.