Low-temperature lead-free solder alloy

Abstract

The invention discloses a low-temperature lead-free solder alloy, containing larger than or equal to 30% of and smaller than or equal to 60% of Bi, larger than 0.001% of Si and smaller than or equal to 0.02% of Si, as well as microalloy elements (alterant), rare earth elements, antioxidant elements and the balance of Sn and inevitable impurities. The large crystal grains of a Bi phase in a traditional Sn-Bi alloy system and the problem of reliability of brittle rupture of a welding joint is caused by that Bi is segregated at a Cu/Cu3Sn interface to form a brittle Bi layer in a long-term service process of the traditional Sn-Bi alloy system are effectively improved, and the mechanical impact and falling resistance of the traditional Sn-Bi system alloy can be greatly improved.

Description

Technical field: [0001] The invention relates to the technical field of electronic soldering, in particular to soldering using lead-free tin alloys, in particular to a low-melting-point Sn-Bi-Si lead-free solder alloy. Background technique: [0002] Since electronic assembly became lead-free, Sn / Cu-based and Sn / Ag / Cu-based lead-free solder alloys are commonly used for wave soldering and reflow soldering processes. For example, in the wave soldering process, SnCu0.7, SnCu0.7-Ni, SnCu0.7-Si, SnAg0.3Cu0.7 (SAC0307) are commonly used, while in the reflow soldering process, SnAg3.0Cu0.5 (SAC305 ), SnAg3.8Cu0.7 (SAC387), SnAg1.0Cu0.5 (SAC105), SnAg0.3Cu0.7 (SAC0307), etc. Although the above lead-free alloys avoid the use of Pb in traditional Sn / Pb solder alloys, which effectively protect the environment and human health, they have the following problems: ①The melting point of this type of lead-free alloy is in the range of 217-227°C, which is higher than that of traditional solde...

AI Technical Summary

Problems solved by technology

Although the above lead-free alloys avoid the use of Pb in traditional Sn / Pb solder alloys, which effectively protect the environment and human health, they have the following problems: ①The melting point of this type of lead-free alloy is in the range of 217-227°C, which is higher than that of traditional solder alloys. The melting point of Sn63Pb37 is 35-45°C. Therefore, in electronic assembly, the wave furnace or reflow furnace needs to be set at a higher temperature, which increases the energy consumption of electronic assembly.

According to statistics, after the electronic assembly is converted from the traditional Sn / Pb to the lead-free process, the comprehensive energy consumption has increased by 25-30%.

②The increase of electronic assembly temperature increases the adverse effect of temperature on the performance of electronic components due to overheating and assembly quality

Its melting point ranges from 85 to 100°C, but it contains about 50% In, and the cost is extremely high, and the alloy contains Zn that is easily corroded and oxidized, which is also greatly limited in the application of solder paste

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