Abstract
We did study for development of new solder composition to cover the positive reliability of SAC305 Thermal shock and SAC120S5N drop shock reliability. General Sn-Ag-Cu solder composition have limitation of stable material property in thermal affecting condition because solder hardness is changed by microstructure with Ag <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn particle distribution which is precipitation hardening mechanism [1]. Therefore, we did test the new solder composition with minimum precipitation hardening of solder material. The material hardness of new solder composition is controlled by substitutional hardening mechanism with Bi element in Tin base solder composition. High contents of Bi in Sn-0.065Ni make the high brittle property compare to non-Bi solder composition. However, we find that optimum Bi contents in SNC (Sn-0.065Ni-0.7Cu) composition as below 2wt%. The 3wt% Bi solder also has reasonable ductile property at fractured area after tensile test. However, brittle fracture was observed when Bi content is over 3wt% due to Bi segregation by excessive Bi element. In tensile test result, Bi contents is optimized with 1.5 to 2.0 wt% to overcome the higher TC than SAC305 and higher drop reliability than SAC1205N solder composition. Even 3wt% Bi in Sn-0.065Ni-0.7Cu solder has lower elongation property than SAC305, it shows higher drop shock reliability than SAC305 solder composition because Ni additive make stable interfacial IMC layer around 40 times at 1,500G drop shock condition. Optimized Bi content solder composition shown higher drop than SAC1205N about 2 times on Cu OSP pad or Ni/Au pad finish. And also, Thermal shock reliability of optimized Bi contents solder shown higher than SAC305 solder composition about 2 times on Cu OSP or Ni/Au pad finish. Therefore, just one solder composition as optimized Bi in Sn-0.065Ni-0.7Cu can be replace of all lead-free solder composition because it shown satisfaction of drop and thermal shock reliability.
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