AbstractBismuth additions of 1% to 10% were made to the 96.5Sn-3.5Ag (wt.%) alloy in an effort to develop a Sn-Ag-Bi ternary composition. A DSC evaluation of the melting properties of the 91.84Sn-3.33Ag-4.83Bi composition suggested the appearance of metastable, short-range order in the atomic structure as a result of low temperature, thermal aging. More extensive solid-state aging studies on 91.84Sn-3.33Ag-4.83Bi/Cu couples resulted in the growth of an intermetallic compound layer at the solder/substrate interface comprised of Cu3Sn and the Cu6Sn5 sub-layers. The growth kinetics of the total layer thickness (x) as a function of solid-state aging time (t) and temperature (T) were represented by the following expression:
% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaacbaGaa8hEai% abgkHiTiaa-HhadaWgaaWcbaGaa83BaaqabaGccqGH9aqpcaWFbbqe% feKCPfgBaGqbdiaa+bcacaWF0bWaaWbaaSqabeaacaWFUbaaaOGaci% yzaiaacIhacaGGWbGaaiikaiabgkHiTmXvP5wqonvsaeHbfv3ySLgz% aGGbaiab9ffarjaac+cacaWFsbGaa8hvaiaacMcaaaa!4E15!
$$x - x_o = A t^n \exp ( - Q/RT)$$
where x0=0.57 × 10−6 m; A=6.22 × 10−3 m/sn; n=0.46±0.15; and Q=49±8 kJ/mol. TEM analysis of the 91.84Sn-3.33Ag-4.83Bi composition indicated that solid-solution and precipitation strengthening mechanisms were a likely consequence of the Bi additions. Contact angle measurements, Cu/solder/Cu solder joint shear strength tests, and microhardness evaluations were also performed on the Sn-Ag-Bi alloys; those results are reported in Part II.
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