Mechanical Strength of Aged Solder Joints: Impact of Plasma Treatment

Abstract

The reliability of solder joints, crucial for electronic assemblies, is influenced by factors including intermetallic compound (IMC) growth during aging and surface properties. This study investigated the impact of atmospheric plasma pre-treatment on the shear strength and IMC formation of aged (thermal aging and thermal shock) SAC305 solder joints on various PCB finishes (Cu, ImT, HASL, ENIG). Shear testing revealed that plasma treatment had a limited effect on mechanical strength under the applied test conditions. Fracture mode analysis indicated that failures predominantly occurred at the component’s lead metallization, suggesting that component quality was the limiting factor, masking potential effects of the plasma treatment applied to the PCB pads. Thermal shock aging was observed to be more detrimental to joint strength than thermal aging, particularly affecting the component-level integrity. IMC analysis showed expected growth with thermal aging. Plasma treatment had negligible impact on IMC thickness for ENIG finish, while an unexpected trend of reduced IMC thickness was observed for HASL finish, warranting further investigation. The study highlights the critical role of component robustness in reliability testing and suggests its potential to overshadow the influence of PCB surface treatments.