Reliability of CSP/lead free solder joints with different surface finishes and reflow profiles

Abstract

The reliability of chip scale package (CSP) using lead free solder process was studied in this paper. The impact of reflow process, peak reflow temperature ranging from Tm+5'C to Tm+40"C (Tmmelting temperature of the lead free) and the dwell time ranging from 30 to 90s were investigaged. Two commonly used PCB surface finishes were employed organic solderability preservative (OSP) and electronic nickel immersion gold (ENIG). The test vehicle covers various CSPs including rigid interpose, laminate interpose and land grid array. From the results of thermal cycling test, it is learnt that all CSPs tested are qualified for consumer products application but only CSP24 and CSP308 can meet the requirement of telecomm applications. Compared to ENIG, OSP is more reliable as PCB surface finish in both thermal cycling and thermal shock tests. The reliability is affected not only by the peak temperature but also by the dwell time. The optimum setting would be different when using ENIG or OSP finishes.