Improved strength of boron-doped Sn-1.0Ag-0.5Cu solder joints under aging conditions

The mechanical properties of new lead-free Sn–Ag–Cu solder alloys containing 0.05–0.1 wt.% boron were investigated under a range of isothermal aging and reflow conditions. The boron-doped solder joints showed higher ball pull strength than the baseline Sn-1.0Ag-0.5Cu solder joint under all isothermal aging and reflow conditions examined. In particular, the high-speed ball pull strength of the 0.05 wt.% B-doped solder joint was approximately 2.5 times greater than that of the baseline Sn-1.0Ag-0.5Cu solder joint aged at 150 °C for 200 h, which is attributed mainly to the reduced rate of grain growth in the intermetallic compound (IMC) layers of B-doped solder joints under aging conditions.

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► B-doped lead-free solder is a potential solution under harsh environments.
► Trace amount of B ranging from 0.05 to 0.1 wt.% is added.
► B-doped solder joints show good strength under thermal conditions.
► B addition causes grain size refinement in IMC layers.