Interfacial reactions between lead- free solders and electroless nickel/ immersion gold (ENIG) surface finish

Abstract

The growth of advanced electronics has brought human to new eras which allow human to fully utilize the innovation of technology in daily applications. As semiconductor industry develops rapidly, flip chip based electronic packaging faces new challenges for packaging design and performance to meet far more stringent requirements on package size, quality, performance and reliability. This research has been made to study the effect of nickel additions on the interfacial reactions between Sn-3.0Ag-0.5Cu lead-free solder and electroless nickel (boron)/ immersion gold (ENIG) surface finish. The effect of isothermal ageing treatment on solder joints after reflow soldering, at temperatures of 150°C and 175°C for 250, 500 and 1000 hours, is also investigated. Several material characterization techniques including optical, scanning electron microscopy, energy dispersive x- ray analysis and image analysis were applied to investigate the intermetallic in terms of morphology, composition, thickness and distribution. From the study, it was observed that the IMC growth is influenced by ageing temperature and ageing duration where the thickness of intermetallic compounds increases with ageing. The result also showed that solder with Ni addition formed thinner IMC after reflow and ageing up to 1000 hours. The EDX analysis shows that the IMC formation and growth in the solder joints led to the formation of several types of IMC with different morphologies and chemical composition.