The Effect of Surface Finish on the Reliability of PB-Free Solder Joints in Chip Scale Packages

ABSTRACT Organic Surface Protectant (OSP), Immersion Silver (IAg), and Electroless Nickel Immersion Gold (ENIG or Ni/Au) surface finishes were tested to determine the effect on reliability of lead-free solder joints in 12mm chip scale packages. Each surface finish was subjected to three tests: A four-point 1 mm bend test at a deflection rate of two cycles per second, a cyclic drop test reaching 1500 g's at .5MS, and a thermal shock test cycling from -55° to 125°C in 30 minute intervals. Both the IAg and the OSP surface finishes did not perform as well as the Ni/Au finish for both the bend and the drop test. The dye-and-pry revealed similar failure modes between the IAg and OSP finish. Both finishes saw packages with trace failures and delamination to the underside of the copper pad. Neither case was prevalent in the Ni/Au finish. It is possible that the delamination on these two surface finishes could be the result of a chemical attack process that occurred when the vendor originally put down the surface finish. As a result, the integrity of the copper was compromised and resulted in the deterioration of the pad and trace.