The Effect of Isothermal Aging on the Intermetallic Growth between SN100C Lead-Free Solders and ENIG Surface Finish

Abstract

The selection of substrate material depends on solder joint requirements and will influence intermetallic compound (IMC) layer formation and reliability of the solder joints. Besides, using different solder materials can also affect the microstructure of IMCs formed during soldering and isothermal ageing process. This study investigated the effect of the IMC formation and microstructure evolution during reflow soldering and isothermal ageing using SN100C lead-free solders and ENIG surface finish. The characterization of the IMC formed during both reflow soldering and isothermal ageing in terms of the type, morphology, and thickness is then analyzed by using the Optical Microscope (OM), Scanning Electron Microscope (SEM) and Energy Dispersive X-ray (EDX). The result reveals that there are two IMC formed at an interface between SN100C and ENIG which are (Cu, Ni)₆Sn₅ and (Ni, Cu)₃Sn₄ where (Ni, Cu)₃Sn₄ grows beneath (Cu, Ni)₆Sn₅. The thickness of the IMC formation in the SN100C/ENIG solder joint is also directly proportional to the ageing duration, indicating that the longer the time of the IMC exposed to high temperature affects the thickness of the IMC.