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Drop impact performance of solder joints of IC packages becomes a great concern for handheld products, such as mobile phones and PDA. Failure modes of solder joints under drop impact depend on solder alloys, interfacial strength, intermetallic formulation, and etc. Submodeling technique is applied to model detailed structure of critical solder joint. The stress and strain concentration at different locations of solder joint correlate well with failure modes observed during testing. Eutectic solder joint is more susceptible to bulk solder failure while Sn-4Ag-0.5Cu is more susceptible to intermetallic compound (IMC) layer failure. Softness of Sn-37Pb reduces the stress in IMC while increases the plastic strains in bulk solder. Life prediction model is determined by solder joint failure mode and mechanism. Stress criteria is suitable for IMC interfacial brittle crack while plastic strain criteria should be applied for life prediction of bulk solder ductile failure.
Date of Conference: 30 Aug.-2 Sept. 2005