Evaluation of Directional Properties of SAC305 Solder Joints Using the Nanoindentation Technique

Abstract

Solder joints provide mechanical support, and electrical and thermal interconnection among various packaging levels in microelectronics assemblies. Reliability of electronic packages and expected functionality of these interconnections predominantly depend on the micromechanical properties of the solder joints. Therefore, material characterization of reflowed area array solder joints is essential for predicting the deformation behavior and reliability of electronic components. The dimensions of solder joints are typically in the sub-millimeter range. Hence, size effects must be taken into account when evaluating constitutive properties of lead- free solder joints. However, it is difficult to evaluate constitutive behavior by using traditional uniaxial tests for material samples that are so small. Thus, instrumented indentation or nanoindentation techniques have proven to be convenient in investigating mechanical properties such as elastic moduli and hardness of different materials.In this study, samples of solder joints were collected from ball grid array packages. The samples were then cross- sectioned and prepared for electron back-scattered diffraction (EBSD) experiments to record the orientations of the various single and multiple-grained solder balls. After characterization of the joint orientations, nanoindentation experiments were performed on individual grains with various material orientations to obtain the elastic moduli along different directions. Using the recorded experimental modulus data, calculations were performed to evaluate the elastic compliance and stiffness matrices, which incorporate the directional material properties.