Abstract: This work chose Sn-3.0Ag-0.5Cu lead-free solder as experimental material, by adding different contents of Bi (0.1wt%, 0.5wt%,1.0wt%) into it. Through aging at different time, investigation was performed on the effect of Bi addition on the interface reaction of solder joints and microstructure evolution of intermetallic compounds. The results showed that the scallop-like Cu6Sn5 was formed at the interface of solder/Cu after soldering, a Cu3Sn layer appeared between the Cu6Sn5 layer and the substrate after the aging treatment. Ag3Sn particles were observed in the bulk solder and on the surface of Cu6Sn5 layer, and the number of Ag3Sn particles increased with the aging time. After five days of aging, it was found that the Kirkendall void was formed within the Cu3Sn layer and at the Cu3Sn/Cu interface. Cracks were formed between the solder and Cu6Sn5 IMC layer in most samples due to the residual stress resulted from different thermal expansion coefficients of solder and Cu6Sn5 IMC. In the process of isothermal aging, the thickness of interfacial IMC layer increased linearly with the square root of aging time. The experimental results indicated that the addition of a small amounts of Bi elements would inhibit IMC layer growth comparing to the sample without Bi elements. When the content of Bi was 1.0%, its inhibitory effect was the most obvious. While the content of Bi was 0.5%, the inhibitory effect was the worst. The average diameter of the Cu6Sn5 grains increased linear with the cubic root of the aging time.
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2018, Vol. 32 
