Investigation of isothermal aged Sn-3Ag-0.5Cu/Sn58Bi-Co hybrid solder joints on ENIG and ENEPIG substrate with various mechanical performances

Abstract

The stability of solder joints is of utmost critical in electronic equipment. The integration of packaged devices in these systems often leads to the generation of heat, which might have a significant impact on how long the equipment lasts when exposed to high temperatures. It is imperative to perform an isothermal aging test on the solder joints in order to replicate the extended use of these joints. This research looked into how the mechanical characteristics and IMC growth of hybrid solder joints were affected by isothermal aging over 240 h, 480 h and 720 h. The reliability of solder joint under isothermal aging condition was improved by adding Pd coating and Co element. The results revealed that Pd coating over ENIG (Electroless Nickel Immersion Gold) pad reduced the growth rate of IMC in SAC305/SnBi hybrid solder joints during isothermal aging. ENIG solder joint strength dropped by 57.66% after 720 h of isothermal aging, and practically all fractures were IMC fractures. ENEPIG (Electroless Nickel Electroless Palladium Immersion Gold) shear strength lowered 31.01%, IMC fracture mode 20%, strong reliability at high temperature. IMC development was suppressed in SAC305/SnBi-Co hybrid solder joints by higher Co content. After 720 h isothermal aging, SAC305/SnBi-Co solder joints had better shear strength than non-Co joints. According to fracture morphology, SAC305/SnBi-Co hybrid solder joints reliability improves owing to the change of IMC morphology and grain refining.