INVESTIGATION OF THE FORWARD AND BACKWARD COMPATIBILITY OF SOLDER ALLOYS WITH COMPONENT FINISHES FOR HASL AND OSP PCB FINISH

摘要

The primary objective of the investigation presented in this paper is to qualify the reliability of mixed electronic assemblies. The experiment investigates both backward and forward compatibility using design of experiments approach. Forward compatibility (FC) refers to the compatibility of lead-free solder paste with lead-containing component finish. On the other hand, backward compatibility (BC) refers to the compatibility of Eutectic Sn-Pb solder with lead-free component finish. The experimental design used a full factorial approach to comprehensively compare across the levels of main factorspaste alloy, component termination finish or solder bumps and board surface finish. The experimentation used a test vehicle that contained an area array component (BGA169) and chip components (0603 resistors). HASL and OSP (type: Enthone-604) surface finishes were used on the test vehicles to represent Sn-Pb and lead-free alternatives respectively. The assembled test vehicles were paneled into two sections – one containing resistors for isothermal aging and another containing BGA and resistors for thermal shock. The isothermal aging and thermal shock tests were conducted as per IPC/JEDEC standards. The resistors were sheared in the ‘as-soldered’ condition, at various isothermal aging intervals and thermal shock cycles. In order to simulate an intermetallic failure in isothermal aging, a reduced shear height (20μm) was used. The response variable in case of the resistors was the shear force. The reliability of the BGA during thermal shock testing was quantified using ‘number of cycles to failure’.