Sn-Ag-Bi-Cu 系無鉛はんだの引け巣と合金組成

概要

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Correlation between composition and shrinkage cavity of Sn-Ag-Bi-Cu lead-free solder alloys was investigated. Incidence of surface cracks on solder fillets, caused by shrinkage cavity, was significantly influenced by Ag content of solder alloys (1.0-2.5wt%) ; for solder fillets with less than 2.0wt% of Ag content, surface cracks decreased in accordance with a reduction in Ag content. On the other hand, incidence of surface cracks was independent of Bi content of solder alloys (0-4.0wt%). Compositional mapping analysis with EDX revealed that less Ag_3Sn phases were formed for solder fillets with less Ag content, suggesting that the formation of the Ag_3Sn/Sn eutectic network band triggers the formation of surface cracks, i.e., shrinkage cavity. Wettability of solder alloys with various Ag contents was also investigated. It was clarified that a decrease in Ag content leaded to degradation of solder wettability, indicating an increase in liquidus temperature of solder.
2002-09-01