EFFECT OF SOLDER BUMP SIZE ON INTERFACIAL REACTIONS DURING SOLDERING BETWEEN PB-FREE SOLDER AND Cu AND Cu Ni/Pd/Au SURFACE FINISHES

Flip chip technology provides the ultimate in high I/O-density and count with superior electrical performance for interconnecting electronic components. Therefore, the study of the intermetallic compounds was conducted to investigate the effect of solder bumps sizes on several surface finishes which are copper and Electroless Nickel/Electroless Palladium/Immersion Gold (ENEPIG) which is widely used in electronics packaging as under-bump metallization (UBM) for flipchip application nowadays. In this research, field emission scanning electron microscopy (FE-SEM) analyses were conducted to analyze the morphology and composition of intermetallic compounds (IMCs) formed at the interface between the solder and UBM. The IMCs between Sn-Pb and lead- free solder with Cu surface finish during reflowing were mainly (Cu, Ni)6Sn5 dan Cu6Sn5. While the main IMCs formed between Sn-Pb and lead-free solder on ENEPIG surface finish are (Ni, Cu)3Sn4 and Ni3Sn4. The results from FESEM with energy dispersive x-ray (EDX) have revealed that isothermal aging at 150°C has caused the thickening and coarsening of IMCs as well as changing them into more spherical shape. The thickness of the intermetallic compounds in both finishes investigated ware found to be higher in solders with smaller bump size. From the experimental results, it also appears that the growth rate of IMCs is higher when soldering on copper compared to ENEPIG finish. Besides that, the results also showed that the thickness of intermetallic compounds was found to be proportional to isothermal aging duration.