Abstract
SAC305 solder alloy is one of the most widely used lead-free materials to fabricate solder joints in electronic packaging industries. Almost 97% weight percentage is β-Sn which is a highly directional material in terms of elastic modulus (E) and coefficient of thermal expansion (CTE). Since β-Sn is a crystalline material, deformation beyond the elastic limit is described by various atomic planes and directions, which are termed as slip systems together. Ten different slip families have been recognized in literatures for β-Sn body-centered tetragonal (BCT) crystals. When external load is applied on solder balls, plastic deformation is dictated by the movement of dislocations and direction of deformation is defined by slip properties.In this study, a physics-based crystal plasticity finite element (CPFE) model has been used to explain the mesoscale deformation behavior of solder joints that have dimensions in the sub-millimeter range. A crystal plasticity theory-based subroutine was implemented in ABAQUS finite element (FE) software to forecast the effects of β-Sn crystal orientations on overall deformation behavior of SAC305 BGA solder joints. Since the crystal c-axis is the strongest axis in terms of elastic modulus, a number of finite element models were developed and run with varying c-axis orientation in the x-y plane to assess the effects of various slip systems on the deformation patterns.
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