SOLDER JOINT RELIABILITY OF DIFFERENT EGAs REWORKED USING LOW MELTING POINT LEAD FREE ALLOYS

摘要

BGA packages with SAC (Sn-Ag-Cu) 385 balls were assembled on Printed Circuit Board (PCB) test vehicles using no clean SAC 385 paste. These components were then reworked using a new low temperature lead-free rework process.In this process, a solder alloy with a melting range lower than that of SAC solder was used. The lower process temperature introduces less risk of heat damage to both the reworked and adjacent components and well as to the board (cratering and board warpage).The microstructure of the resulting mixed solder joints when SAC 385 balls were assembled using low melt paste was examined "as assembled" as well as after "accelerated thermal cycling" (ATC) using optical and scanning electron microscopy methods.ATC study was performed in a temperature range of 0-100°C following IPC-9701 specification [1] to 6000 cycles. Previous work had reported thermal fatigue reliability results up to 2500 cycles [2].Ddifferent surface finishes including Immersion Silver (ImmAg) and Electroless Nickel/Immersion Gold (ENIG) were used on these assembly test vehicles. The low melt rework process was performed on 0.093" and 0.125" thick boards and was done in nitrogen atmosphere.It has been observed that independent of component type, thermal fatigue life of SAC BGA components reworked using Lower melting point alloys may be comparable or slightly better than that of the components reworked using conventional SAC 385.