Reliability of Fine Pitch Sn–3.8Ag–0.7Cu Flip Chip Solder Joints With Different Connection Pads on PCB

Abstract

The reliability of fine pitch Sn–3.8Ag–0.7Cu flip chip solder joints with three different pads, i.e., bare pads, pads with solder masks, and pads with microvia, on printed circuit boards (PCBs) was studied through thermal cycling. After assembly, (Au,Ni)Sn4 intermetallics (IMCs) formed both in the bulk solder and at the interfaces due to the immersion-Au finish on the PCB side. The (Au,Ni)Sn4 IMCs formed in the solder joints on the pads with microvia were more abundant than those formed in the solder joints on the pads without microvia. The results showed that the solder joints on the pads with a microvia had poor reliability due to the insufficient solder volume and the formation of large amounts of (Au,Ni)Sn4 IMCs. The main crack initiation position was the corner of solder joint at the chip side. For the pads with microvia, the main location of failure was at the (Au,Ni)Sn4/solder interface on the chip side, and for the solder joints on bare pads and pads with solder mask, the possible failure location was in the bulk solder.