SAC-series lead-free Sn-Cu soldering paste as well as preparation method and use method of SAC-series lead-free Sn-Cu soldering paste

Abstract

The invention relates to the field of lead-free soldering paste, in particular to SAC lead-free Sn-Cu soldering paste and a preparing method and using method.The SAC lead-free Sn-Cu soldering paste at least comprises the following raw materials of, by weight, 50-80 parts of micron-sized SAC305 alloy powder, 8-40 parts of micron-sized spherical copper powder, 1 part of nano-sized nickel powder and 11-13 parts of flux paste. High-strength, reliable high-temperature stability and low-void-rate packaging connection can be achieved, the advantage of no pressure is achieved, and the risk that electronic components are damaged in the pressure process is effectively reduced.

Description

Technical Field

[0001] The present invention relates to the field of lead-free solder paste, and specifically to a SAC-based lead-free Sn-Cu solder paste, its preparation method and usage method. Background Art

[0002] With the rapid development of industries such as the Internet of Things, 5G communication, and new energy, compared with traditional power devices, high-power devices such as SiC (silicon carbide) and GaN (gallium nitride), which have higher conversion efficiency, greater output power, and better thermal fatigue resistance, are increasingly widely used. The temperature of high-power devices during operation is much higher than the melting point of traditional SAC305 solder paste. Under such high-temperature working conditions, not only the high-temperature resistance performance of electronic devices themselves needs to be considered, but also the high-temperature performance of the solder connecting the electronic devices needs to be considered. Therefore, considering cost factors, it is urgent to develop a SAC-based lead-free solder paste (tin-silver-copper lead-free solder paste) based on tin-silver-copper solder, which has high strength, high reliability, and excellent high-temperature service performance.

[0003] For the currently mainstream connecting material tin-silver-copper (SAC305), the strengthening of solder joints after welding mainly depends on the intermetallic compound Ag 3 Sn and Cu 6 Sn 5 phases. It can be seen that the melting points of these two phases are about 480°C and 500°C respectively, and both can exhibit high stability in high-temperature environments. However, the silver and copper contents in the tin-silver-copper (SAC305) alloy are relatively low, and not enough intermetallic compound phases can be formed. In addition, the price cost of Ag is relatively high, which is not conducive to large-scale commercial applications. Chinese Patent (publication number CN108526747A) discloses a cerium dioxide nanoparticle-reinforced tin-silver-copper composite solder paste and its preparation method, which mainly enhances tin-silver-copper by introducing cerium dioxide nanoparticles into the solder paste system. However, the size effect of nanoparticles may cause bridging or void soldering in ultra-fine pitch solder joints (such as 5G chip packaging), and the dispersion stability of nanoparticles needs to be controlled, resulting in problems such as complex process and increased cost, and it is not suitable for large-scale industrial promotion and application. Summary of the Invention

[0004] In order to solve the above problems, the present invention provides a SAC-based lead-free Sn-Cu solder paste. By optimizing the addition of micro-nano copper powder in the tin-silver-copper solder paste system, it can achieve high-strength, reliable high-temperature stability, and low void rate packaging connections, and has the advantage of no pressure, effectively reducing the risk of damage to electronic components in the pressure process.

[0005] On the one hand, the present invention provides a SAC-based lead-free Sn-Cu solder paste, which, by weight, at least includes the following raw materials: 50-80 parts of micron-sized SAC305 alloy powder, 8-40 parts of micron-sized spherical copper powder, 1 part of nano-sized nickel powder, and 11-13 parts of solder paste.

[0006] In one embodiment, the particle size of the micron-sized SAC305 alloy powder is 5 - 45 μm.

[0007] In one embodiment, the particle size of the micron-sized SAC305 alloy powder is 20 - 38 μm, the product name is Sn96.5Ag3.0Cu0.5 tin powder, the product specification is T4, and it is sourced from Suzhou Younuo Electronic Materials Technology Co., Ltd.

[0008] In one embodiment, the particle size of the micron-sized spherical copper powder is < 7 μm.

[0009] In one embodiment, the particle size of the micron-sized spherical copper powder is 1 - 5 μm.

[0010] In one embodiment, the particle size of the micron-sized spherical copper powder is 1 μm.

[0011] In one embodiment, the particle size of the nano-sized nickel powder is 10 - 200 nm.

[0012] In one embodiment, the particle size of the nano-sized nickel powder is 20 - 100 nm.

[0013] In one embodiment, the particle size of the nano-sized nickel powder is 50 nm.

[0014] In one embodiment, the trade name of the soldering paste is B07 halogen-free soldering paste, and it is sourced from Suzhou Younuo Electronic Materials Technology Co., Ltd.

[0015] In the present invention, by using an alloy powder including micron-sized SAC305 alloy powder, micron-sized spherical copper powder, and nano-sized nickel powder, during the welding process of the provided soldering paste, the low-melting-point SAC-based alloy solder melts to form a liquid phase to wrap the high-melting-point copper powder particles. As the welding progresses, high temperature causes a reaction between Cu and Sn to form high-melting-point intermetallic compounds Cu 6 Sn5, Cu 3 Sn (IMC phase) is distributed in the weld seam, thereby achieving "low-temperature connection and high-temperature service" of electronic devices. Further, by controlling the particle size of the micron-sized spherical copper powder to be 1 - 5 μm, the uniformity of the distribution of the alloy powder in the tin powder is ensured, and more IMC phases with suitable sizes and uniform distributions are obtained, resulting in good welding effects. However, if the particle size of the micron-sized spherical copper powder is too high, the formed IMC phases are larger in size and unevenly distributed, and the brittle and hard IMC phases are likely to cause non-uniform mechanical properties of the solder joints, and the state of the well-stirred soldering paste cannot meet the printing conditions. Further, by controlling the addition amount of the micron-sized spherical copper powder in the control system, as many IMC phases with a reticular structure as possible are obtained while avoiding solder joint voids to ensure the overall morphology of the solder joints.

[0016] On the other hand, the present invention provides a method for preparing a SAC-based lead-free Sn-Cu solder paste, which at least includes the following steps: micron-sized spherical copper powder is acidified and then stirred and blended with micron-sized SAC305 alloy powder and nano-sized nickel powder to obtain alloy powder; the alloy powder is stirred and mixed with pre-stirred solder paste to obtain the SAC-based lead-free Sn-Cu solder paste.

[0017] In one embodiment, the step of acidification treatment includes: putting micron-sized spherical copper powder into formic acid for 10 - 20 min, washing with alcohol and drying.

[0018] In one embodiment, the pre-stirred solder paste is obtained by the following method: putting the solder paste into a stirring container, stirring at 40 - 60 rpm / min under normal pressure for 5 - 8 min, keeping the rotation speed unchanged, and stirring at a vacuum pressure of -0.07 to -0.09 MPa for 5 - 8 min to obtain the pre-stirred solder paste.

[0019] In one embodiment, the step of stirring and mixing includes: adding the alloy powder into the pre-stirred solder paste, stirring at 30 - 40 rpm / min under normal pressure for 20 - 40 min, keeping the rotation speed unchanged, and stirring at a vacuum pressure of -0.07 to -0.09 MPa for 20 - 40 min to obtain the SAC-based lead-free Sn-Cu solder paste.

[0020] The method for preparing the SAC-based lead-free Sn-Cu solder paste provided by the present invention is simple, easy to control, greatly reduces the difficulty and cost of industrial production, and has high practical value.

[0021] In one embodiment, the using method of the SAC-based lead-free Sn-Cu solder paste includes the following steps:

[0022] (1) Put the upper and lower copper frames into absolute ethanol for ultrasonic cleaning, take them out and dry them to obtain the cleaned copper frames; dot the SAC-based lead-free Sn-Cu solder paste on the surface of the cleaned lower copper frame, and then place the dried upper copper frame on the solder paste for positioning and assembling into a Cu / Sn-Cu / Cu sandwich structure solder sheet;

[0023] (2) Place the Cu / Sn-Cu / Cu sandwich structure solder sheet on a vacuum heating table, the welding temperature curve follows the SAC305 reflow soldering temperature curve, control the peak heating temperature to be 235℃ - 270℃, the peak temperature time to be 60 - 90 s, fill inert gas throughout the heating process, the overall reflow time to be 5 - 10 min, after welding, cool with the furnace to 90 - 110℃ and then air-cool to 20 - 30℃.

[0024] Beneficial effects

[0025] 1. The present invention provides a lead-free Sn-Cu solder paste of the SAC system. By optimizing the addition of micro-nano copper powder in the tin-silver-copper solder paste system, it can achieve high-strength, reliable high-temperature stability, and low void rate for encapsulation connection. It has the advantage of no pressure, effectively reducing the risk of damage to electronic components in the pressure process.

[0026] 2. The present invention uses an alloy powder including micron-sized SAC305 alloy powder, micron-sized spherical copper powder, and nano-sized nickel powder. During the soldering process of the provided solder paste, the low-melting-point SAC-based alloy solder melts to form a liquid phase that wraps the high-melting-point copper powder particles. As the soldering progresses, high temperature causes a reaction between Cu and Sn to form a high-melting-point intermetallic compound Cu 6 Sn5、Cu 3 Sn (IMC phase) is distributed in the weld seam, thus realizing the "low-temperature connection and high-temperature service" of electronic devices.

[0027] 3. The present invention controls the particle size of the micron-sized spherical copper powder to be 1 - 5 μm, ensuring the uniform distribution of the alloy powder in the tin powder, obtaining more IMC phases with suitable and uniform sizes, and achieving good soldering effects.

[0028] 4. The present invention controls the addition amount of the micron-sized spherical copper powder in the system, obtaining as many IMC phases with a reticular structure as possible while avoiding solder joint voids and ensuring the overall morphology of the solder joints.

[0029] 5. The preparation method of the lead-free Sn-Cu solder paste of the SAC system provided by the present invention is simple and easy to control, greatly reducing the difficulty and cost of industrial production, and having high practical value. Description of the Drawings

[0030] Figure 1-11 They are respectively the microstructural morphology characterization diagrams after slicing and embedding the soldered copper frame solder joints obtained in Examples 1 - 11. Detailed Embodiments

[0031] Examples 1 - 11

[0032] On the one hand, Examples 1 - 11 of the present invention provide a lead-free Sn-Cu solder paste of the SAC system. By weight, the formula is shown in Table 1.

[0033] Table 1

[0034]

[0035] On the other hand, Embodiments 1-11 of the present invention provide a method for preparing a SAC-based lead-free Sn-Cu solder paste, comprising the following steps: micron-sized spherical copper powder is acidified and then stirred and blended with micron-sized SAC305 alloy powder and nano-sized nickel powder to obtain alloy powder; the alloy powder is stirred and mixed with pre-stirred solder paste to obtain the SAC-based lead-free Sn-Cu solder paste.

[0036] The step of acidification treatment includes: putting micron-sized spherical copper powder into formic acid for 15 minutes, washing with alcohol and drying.

[0037] The pre-stirred solder paste is obtained by the following method: putting the solder paste into a stirring container, stirring at 50 rpm / min under normal pressure for 6 minutes, keeping the rotation speed unchanged, and stirring at a vacuum pressure of -0.08 MPa for 6 minutes to obtain the pre-stirred solder paste.

[0038] The step of stirring and mixing includes: adding the alloy powder into the pre-stirred solder paste, stirring at 35 rpm / min under normal pressure for 30 minutes, keeping the rotation speed unchanged, and stirring at a vacuum pressure of -0.08 MPa for 30 minutes to obtain the SAC-based lead-free Sn-Cu solder paste.

[0039] The usage method of the SAC-based lead-free Sn-Cu solder paste includes the following steps:

[0040] (1) Put the upper and lower copper frames (thickness 0.5 mm) into absolute ethanol for ultrasonic cleaning, take them out and dry them to obtain the cleaned copper frames; apply the SAC-based lead-free Sn-Cu solder paste on the surface of the cleaned lower copper frame, and then place the dried upper copper frame on the solder paste for positioning and assembling into a Cu / Sn-Cu / Cu sandwich structure solder sheet;

[0041] (2) Place the Cu / Sn-Cu / Cu sandwich structure solder sheet on a vacuum heating table, the welding temperature curve follows the SAC305 reflow soldering temperature curve, control the peak heating temperature to be 250 °C, the peak temperature time to be 90 s, fill inert gas throughout the heating process, the overall reflow time to be 8 minutes, after welding, cool with the furnace to 100 °C and then air-cool to 25 °C to obtain the welded copper frame solder sheet.

[0042] Performance testing

[0043] 1. After the welded copper frame solder sheets obtained in Embodiments 1-11 are subjected to slicing and embedding treatment, the microstructure morphology is characterized, and the results are shown in Figure 1-11 , Figure 1-11 The analysis results are shown in Table 2.

[0044] Table 2

[0045]

[0046]

Claims

1. A SAC-based lead-free Sn-Cu solder paste, characterized in that: By weight, it includes at least the following raw materials: 50-80 parts of micron-grade SAC305 alloy powder, 8-40 parts of micron-grade spherical copper powder, 1 part of nano-grade nickel powder and 11-13 parts of solder paste.

2. The SAC lead-free Sn-Cu solder paste according to claim 1, characterized in that: The particle size of the micron-sized spherical copper powder is less than 7 μm.

3. The SAC lead-free Sn-Cu solder paste according to claim 2, characterized in that: The particle size of the micron-sized spherical copper powder is 1-5 μm.

4. The SAC lead-free Sn-Cu solder paste according to claim 1, characterized in that: The particle size of the nano-grade nickel powder is 10-200 nm.

5. The SAC lead-free Sn-Cu solder paste according to claim 4, characterized in that: The particle size of the nano-grade nickel powder is 20-100 nm.

6. A method for preparing the SAC lead-free Sn-Cu solder paste according to any one of claims 1 to 5, characterized in that: At least the following steps are included: The micron-sized spherical copper powder is acidified and then mixed with the micron-sized SAC305 alloy powder and nano-sized nickel powder to obtain alloy powder; the alloy powder is mixed with the pre-mixed solder paste to obtain the SAC series lead-free Sn-Cu solder paste.

7. The method for preparing the SAC lead-free Sn-Cu solder paste according to claim 6, characterized in that: The acid treatment step comprises: placing the micron-sized spherical copper powder in formic acid for 10-20 minutes, washing with alcohol, and drying.

8. The method for preparing the SAC lead-free Sn-Cu solder paste according to claim 6, characterized in that: The pre-mixed solder paste is obtained by the following method: putting the solder paste into a stirring container, stirring at 40-60 rpm / min at normal pressure for 5-8 minutes, keeping the speed constant, stirring at a vacuum pressure of -0.07 to -0.09 MPa for 5-8 minutes to obtain the pre-mixed solder paste.

9. The method for preparing the SAC lead-free Sn-Cu solder paste according to claim 6, characterized in that: The stirring and mixing step comprises: adding alloy powder into pre-stirred solder paste, stirring at 30-40 rpm / min at normal pressure for 20-40 min, keeping the speed constant, stirring at a vacuum pressure of -0.07 to -0.09 MPa for 20-40 min to obtain SAC series lead-free Sn-Cu solder paste.

10. A method for using the SAC lead-free Sn-Cu solder paste according to any one of claims 1 to 5, characterized in that: At least the following steps are included: (1) placing the upper and lower copper frames in anhydrous ethanol for ultrasonic cleaning, taking them out and drying them to obtain a cleaned copper frame; applying SAC lead-free Sn-Cu solder paste on the surface of the cleaned lower copper frame, and then placing the dried upper copper frame on the solder paste to position and assemble them into a Cu / Sn-Cu / Cu sandwich structure welding piece; (2) The Cu / Sn-Cu / Cu sandwich structure solder piece is placed on a vacuum heating table. The welding temperature curve follows the SAC305 reflow soldering temperature curve. The peak heating temperature is controlled to be 235°C to 270°C, the peak temperature time is 60 to 90s, and the inert gas is filled throughout the heating process. The overall reflow time is 5 to 10 minutes. After the welding is completed, the solder piece is cooled to 90-110°C in the furnace and then cooled to 20-30°C in air.

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