Publications Details
An evaluation of prototype surface mount circuit boards assembled with three non-lead bearing solders
Prototype circuit board test vehicles wee assembled with three candidate lead-free solders: 96.5Sn-3.5Ag (wt %), 58Bi-42Sn, and 91.84Sn-3.33 Ag 83Bi., using a forced-convection/infrared furnace and RMA flux based pastes. Wettability of circuit board features and packages was best with Sn-Ag-Bi alloy followed in order by Bi-Sn and Sn-Ag solders. The Sn-Ag-Bi solder had a greater propensity for void formation in the joints. The reliability assessment was based upon solder joint microstructure and the shear strength of selected leadless packages. Solder joint damage was of a greater extent after thermal shock exposures rather than thermal cycling. The Sn-Ag-Bi alloy on the largest package appeared most susceptible to thermal shock. Test vehicle performance clearly demonstrated that, with the non-lead solders, local thermal expansion mismatch can be as detrimental to joint integrity as the traditional global mismatch damage.