Low-temperature welding method for welding copper and aluminum special materials through non-Zn tin-based welding flux

Abstract

The low-temperature welding method comprises the steps that firstly, abrasive paper is adopted for polishing the surfaces of a copper substrate and an aluminum substrate, then a welding clamp is adopted for fixing the aluminum substrate, then an interconnection interface of the aluminum substrate is filled with proper Sn0. 3Ag0. 7Cu alloy powder, the aluminum substrate is placed on a constant-temperature table to be heated after being covered with the copper substrate, and the copper substrate and the aluminum substrate are welded at the same time. And simultaneously applying ultrasound and pressure to the copper substrate and the aluminum substrate, and continuously keeping the temperature and the pressure after the ultrasound is stopped until the experiment is finished. The prepared connector is free of zinc element, the copper-aluminum connector with the (Sn) + Al2Cu + AlCu ternary eutectic is formed and has good plasticity and toughness, the welding method is easy to operate, the welding temperature is low, the welding time is short, the production cost is reduced, and the production efficiency and the product reliability are greatly improved.

Description

Technical Field

[0001] The present application belongs to the technical field of electronic packaging interconnection, and in particular relates to a low-temperature welding method for welding copper and aluminum dissimilar materials with non-Zn tin-based solder. Background Art

[0002] Based on the "replacing copper with aluminum" strategy proposed in the industry, the demand for copper / aluminum interconnection in the field of electronic packaging has become increasingly urgent in recent years. However, due to the large differences in the physical properties of copper and aluminum, as well as the dense oxide film on the surface of aluminum, the weldability of copper / aluminum welding is poor. Brazing technology not only has the characteristics of high efficiency, small welding stress and deformation, but also the connection temperature is lower than that of the parent material. Therefore, brazing is one of the commonly used technologies for copper / aluminum dissimilar material interconnection in the packaging field. The commonly used Zn-Al and Al-Si brazing fillers for brazing copper / aluminum belong to the categories of medium and high temperature brazing, respectively. The higher welding temperature limits its application in the field of electronic packaging. In order to ensure that the life of heat-sensitive electronic components is not damaged or even directly fails during the packaging process, the research and development of copper-aluminum dissimilar material low-temperature interconnection materials and technologies has become a hot issue of common concern in the industry and academia.

[0003] The patent (CN102642099A) applied by Dalian University of Technology discloses a Sn-Zn-based lead-free solder alloy for copper-aluminum soft soldering. The solder has good wettability on both copper and aluminum, and forms a copper-aluminum interconnection joint of good quality after low-temperature reflow soldering. In the solder and welding method for low-temperature interconnection of copper and aluminum dissimilar materials disclosed in the patent (CN114434039) applied by Chongqing University of Technology, a pure Sn strip or Sn alloy strip is used as an intermediate welding carrier, a Zn layer is pressed on the surface, and ultrasonic vibration is used to break the oxide film on the surface of the parent material to promote the metallurgical reaction between the Zn layer and the parent material to achieve low-temperature interconnection of copper and aluminum dissimilar materials. The connection materials used in the above patent documents all contain Zn, which reduces the oxidation resistance and corrosion resistance of the solder, seriously affecting the mechanical properties and service life of the copper-aluminum welding joint. Summary of the invention

[0004] In view of this, the present application provides a low-temperature welding method for welding copper and aluminum dissimilar materials with non-Zn tin-based solder, which solves the problem that the tin-based solder selected in the existing copper-aluminum low-temperature interconnection technology contains zinc elements, which makes the joints easy to oxidize and corrode, and the low-melting-point tin residue causes poor high-temperature performance. The joints prepared by the welding method do not contain zinc elements, the welding method is simple to operate, the welding temperature is low, and the welding time is short, which not only reduces the production cost, but also greatly improves the production efficiency and product reliability.

[0005] The specific technical solution provided by the present invention is:

[0006] First, the surfaces of the copper substrate and the aluminum substrate were polished with sandpaper, and then the aluminum substrate was fixed with a welding fixture. Then, appropriate Sn0.3Ag0.7Cu alloy powder was filled on the interconnection interface of the aluminum substrate. After the copper substrate was covered, it was placed on a constant temperature table for heating. At the same time, ultrasound and pressure were applied to the copper substrate and the aluminum substrate. After the ultrasound stopped, the temperature and pressure were kept constant until the end of the experiment.

[0007] Preferably, the ultrasonic generators are longitudinal ultrasonic generators with an ultrasonic frequency of 20kHz. The No. 1 ultrasonic wave acts on the copper substrate with a power of 600-800W, specifically 600W, 700W, and 800W; the No. 2 ultrasonic wave acts on the aluminum substrate with a power of 300-500W, specifically 300W, 400W, and 500W;

[0008] Preferably, the horizontal spacing distance between the No. 1 ultrasonic generator and the No. 2 ultrasonic generator is 5 to 40 cm, and specifically 5 cm, 12 cm, 18 cm, and 40 cm can be selected;

[0009] Preferably, the temperature of the constant temperature stage is 220-260°C, and specifically 220°C, 240°C, and 260°C can be selected;

[0010] Preferably, the dual ultrasound is turned on simultaneously, and the ultrasound time is 5 to 9 seconds, and specifically 5 seconds, 7 seconds, and 9 seconds can be selected;

[0011] Preferably, the auxiliary pressure provided by ultrasonic generator No. 1 is 8 MPa, and the entire welding time is 5 min;

[0012] Preferably, in the low-temperature welding method for welding copper and aluminum dissimilar materials with non-Zn tin-based solder, the SnAgCu alloy powder comprises the following components in mass percentage: 0.3±0.02wt.% Ag, 0.7±0.2wt.% Cu, and the rest Sn.

[0013] Beneficial technical effects:

[0014] (1) The present invention provides a low-temperature welding method for welding copper and aluminum dissimilar materials with non-Zn tin-based solder, in which pure SnAgCu alloy powder is used as solder to weld copper and aluminum dissimilar materials. The solder does not contain Zn elements that react with Al, and the corrosion resistance and oxidation resistance of the joint are enhanced.

[0015] (2) The present invention provides a low-temperature welding method for welding copper and aluminum dissimilar materials with non-Zn tin-based solder, forming a copper-aluminum joint structure of (Sn)+Al2Cu+AlCu ternary eutectic, and the joint has good plasticity and toughness.

[0016] (3) The present invention provides a low-temperature welding method for copper-aluminum dissimilar materials using non-Zn tin-based solder. The method adopts dual ultrasonic assisted welding technology, which can flexibly adjust the horizontal spacing between two ultrasonic generating devices to form a resonance effect at the copper-aluminum joint to enhance the ultrasonic effect, reduce the welding temperature, and enhance the metallurgical behavior of the weld, and is suitable for the interconnection of copper-aluminum dissimilar materials of different sizes. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the assembly of the double ultrasonic assisted welding process;

[0018] Figure 2 The weld structure of the joint in Example 1;

[0019] Figure 3 The weld structure of the joint in Example 2;

[0020] Figure 4 The weld structure of the joint in Example 3;

[0021] Figure 5 The weld structure of the joint in Example 4;

[0022] In the attached picture:

[0023] 1. Ultrasonic vibrator No. 2; 2. 1060 aluminum; 3. Ultrasonic vibrator No. 1; 4. T2 copper; 5. Sn0.3Ag0.7Cu alloy solder powder; 6. Fixture; 7. Constant temperature table; DETAILED DESCRIPTION

[0024] In order to enable professionals in the technical field to better understand the solutions of the present invention, the technical solutions in the implementation cases of the present invention will be clearly and detailed described below with reference to the accompanying drawings.

[0025] The present invention discloses a low-temperature welding method for welding copper and aluminum dissimilar materials with a non-Zn tin-based solder, comprising the following steps:

[0026] First, the surfaces of the copper substrate and the aluminum substrate are polished with sandpaper, and then the aluminum substrate is fixed with a welding fixture. Then, appropriate Sn0.3Ag0.7Cu alloy powder is filled on the interconnection interface of the aluminum substrate, and the copper substrate is covered and placed on a constant temperature table for heating. At the same time, ultrasound is applied to the copper substrate and the aluminum substrate, and finally the temperature is kept for a period of time until the welding is completed.

[0027] The ultrasonic generating devices are all longitudinal ultrasonic generators with an ultrasonic frequency of 20kHz. The No. 1 ultrasonic wave acts on the copper substrate with a power of 600-800W, specifically 600W, 700W, and 800W can be selected; the No. 2 ultrasonic wave acts on the aluminum substrate with a power of 300-500W, specifically 300W, 400W, and 500W can be selected; the ultrasonic horizontal interval distance is 5-40cm, specifically 5cm, 12cm, 18cm, and 40cm can be selected; the temperature of the constant temperature table is 220-260℃, specifically 220℃, 240℃, and 260℃ can be selected; the ultrasonic time is 5-9s, specifically 5s, 7s, and 9s can be selected; the dual ultrasonic auxiliary pressure is 8MPa, and the entire welding time is 5min.

[0028] Implementation Case 1

[0029] In the implementation of a specific case, the non-Zn tin-based solder used is Sn0.3Ag0.7Cu alloy powder, which includes the following components in mass percentage: Ag is 0.3±0.02wt.%, Cu is 0.7±0.2wt.%, and the rest is Sn.

[0030] During the implementation of the specific case, the temperature of the constant temperature table was 260°C;

[0031] In the implementation of the specific case, the power of ultrasonic wave No. 1 is 600W, the auxiliary pressure provided by ultrasonic wave No. 1 is 8MPa, and the power of ultrasonic wave No. 2 is 500W;

[0032] In the implementation of the specific case, the horizontal distance between ultrasonic generator No. 1 and ultrasonic generator No. 2 is 5 cm;

[0033] In the implementation of the specific case, the dual ultrasonic loading time was 7s and the welding time was 5min.

[0034] In the implementation process of specific cases, dual ultrasonic assistance is used to enhance the effect of ultrasonic waves. The local high temperature and high pressure generated by ultrasonic waves are used to accelerate the dissolution of Al and Cu atoms in the base material into the SnAgCu alloy solder, increase the concentration of Al and Cu atoms in the solder, and promote the formation of interface compounds.

[0035] In the implementation of a specific case, the solder is completely liquid during welding, a continuous Cu6Sn5 is formed on the copper side interface of the joint, and a (Sn)+Al2Cu+AlCu ternary eutectic is formed on the aluminum side interface and the center. The joint has the highest shear strength, which can reach 30.6MPa.

[0036] Implementation Case 2

[0037] In the implementation of a specific case, the non-Zn tin-based solder used is Sn0.3Ag0.7Cu alloy powder, which includes the following components in mass percentage: Ag is 0.3±0.02wt.%, Cu is 0.7±0.2wt.%, and the rest is Sn.

[0038] During the implementation of the specific case, the temperature of the constant temperature table was 220°C;

[0039] In the implementation of the specific case, the power of ultrasonic wave No. 1 is 700W, the auxiliary pressure provided by ultrasonic wave No. 1 is 8MPa, and the power of ultrasonic wave No. 2 is 400W;

[0040] In the implementation of the specific case, the horizontal distance between ultrasonic generator No. 1 and ultrasonic generator No. 2 is 12 cm;

[0041] In the implementation of the specific case, the dual ultrasonic loading time was 9s and the welding time was 5min.

[0042] In the implementation of specific cases, a longer ultrasonic loading time was selected, and the local temperature rise effect formed in the joint was more obvious, which further increased the dissolution rate of the base material into the liquid solder and promoted the formation of eutectic structure. However, too long ultrasonic time will cause deformation or even cracking of the base material.

[0043] In the specific case implementation process, the ultrasonic time was selected as 9s, the alloy particles in the joint melted, and a white solidification zone was formed after cooling. A continuous Cu6Sn5 was formed on the copper side interface, and a discontinuous (Sn)+Al2Cu+AlCu ternary eutectic was formed on the aluminum side interface. The shear strength of the joint reached more than 18.9MPa.

[0044] Implementation Case 3

[0045] In the implementation of a specific case, the non-Zn tin-based solder used is Sn0.3Ag0.7Cu alloy powder, which includes the following components in mass percentage: Ag is 0.3±0.02wt.%, Cu is 0.7±0.2wt.%, and the rest is Sn.

[0046] During the implementation of the specific case, the temperature of the constant temperature table was 240°C;

[0047] In the implementation of the specific case, the power of ultrasonic wave No. 1 is 800W, the auxiliary pressure provided by ultrasonic wave No. 1 is 8MPa, and the power of ultrasonic wave No. 2 is 300W;

[0048] In the implementation of the specific case, the horizontal distance between ultrasonic generator No. 1 and ultrasonic generator No. 2 is 18 cm;

[0049] In the implementation of the specific case, the ultrasonic loading time was 5s and the welding time was 5min.

[0050] In the implementation of a specific case, the alloy solder is in liquid state during welding. The cavitation effect and acoustic streaming effect of ultrasound are used to wash and break the oxide film on the surface of the base material, which is beneficial for the dissolution of Cu and Al atoms in the base material into the liquid solder, and at the same time promotes the formation of interface compounds and Al-Sn-Cu ternary eutectic structure.

[0051] In the implementation of a specific case, the No. 1 ultrasonic wave acts on the upper side of the joint, and the ultrasonic effect is more significant. The use of high-power No. 1 ultrasonic wave has more advantages. A continuous Cu6Sn5 is formed at the copper side interface of the joint, and a continuous Al-Sn-Cu ternary eutectic is formed at the aluminum side interface. The center of the weld is mainly composed of Al-Sn-Cu ternary eutectic, and the joint strength can reach 29.3MPa. However, excessive No. 1 ultrasonic power will cause deformation of the base material.

[0052] Implementation Case 4

[0053] In the implementation of a specific case, the non-Zn tin-based solder used is Sn0.3Ag0.7Cu alloy powder, which includes the following components in mass percentage: Ag is 0.3±0.02wt.%, Cu is 0.7±0.2wt.%, and the rest is Sn.

[0054] During the implementation of the specific case, the temperature of the constant temperature table was 240°C;

[0055] In the implementation of the specific case, the power of ultrasonic wave No. 1 is 500W, the auxiliary pressure provided by ultrasonic wave No. 1 is 8MPa, and the power of ultrasonic wave No. 2 is 500W;

[0056] In the implementation of the specific case, the horizontal distance between ultrasonic generator No. 1 and ultrasonic generator No. 2 is 40 cm;

[0057] In the implementation of the specific case, the ultrasonic loading time was 9s and the welding time was 5min.

[0058] In the implementation of a specific case, the alloy solder is in liquid state during welding. The cavitation effect and acoustic streaming effect of ultrasound are used to wash and break the oxide film on the surface of the base material, which is beneficial for the dissolution of Cu and Al atoms in the base material into the liquid solder. At the same time, it promotes the formation of interface compounds and Al-Sn-Cu ternary eutectic structure, and the joint strength can reach 28.5MPa.

[0059] Finally, it should be noted that the above implementation cases are only used to illustrate the technical solution of the present application, rather than to limit the technical solution. Although the applicant has described the present application in detail with reference to the preferred implementation cases, ordinary technicians in the field should understand that modifications or equivalent replacements of the technical solution of the present application should be included in the scope of the claims of the present application as long as they do not deviate from the purpose and scope of the technical solution.

Claims

1. A low temperature welding method for welding copper and aluminum dissimilar materials with non-Zn tin-based solder, characterized in that: First, the surfaces of the copper substrate and the aluminum substrate were polished with sandpaper, and then the aluminum substrate was fixed with a welding fixture. Then, appropriate Sn0.3Ag0.7Cu alloy powder was filled on the interconnection interface of the aluminum substrate. After the copper substrate was covered, it was placed on a constant temperature table for heating. At the same time, ultrasound and pressure were applied to the copper substrate and the aluminum substrate. After the ultrasound stopped, the temperature and pressure were kept constant until the end of the experiment.

2. A low temperature welding method for welding copper and aluminum dissimilar materials with non-Zn tin-based solder as claimed in claim 1, characterized in that: The ultrasonic waves acting on the substrate are all longitudinal ultrasonic waves, the ultrasonic frequency is 20kHz, the ultrasonic power acting on the copper substrate is 600-800W, the ultrasonic power acting on the aluminum substrate is 300-500W, the ultrasonic loading time is 5-9s, the ultrasonic auxiliary pressure is 8MPa, the dual ultrasonic distance is 5cm-40cm, the constant temperature table temperature is 220-260℃, and the entire welding time is 5min.

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