Evaluation of soldering and reliability performance of NiPdAu finished PPF with Pb-free solder alloy 95.5Sn4.0Ag0.5Cu

In this study, SO14 (14 pin small-outline package), TSSOP20 (thin shrink small-outline package) and TSSOP56 are taken as carriers to study the soldering and reliability performance of preplated NiPdAu finished components (PPF). The Pd layer is 0.5mu-inch thick and after preconditioning, the components are assembled on test boards with SAC Pb-free solder alloy (Sn4.0Ag0.5Cu). Preconditioning is aimed to simulate storage. Evaluation is done using wetting balance test, visual inspection of the solder fillet geometry, lead pull test, thermal cycling test, mechanical vibration and bump tests, and corrosion test. Components with traditional SnPb finish and components with a thicker Pd layer of 1.0mu-inch are used as reference. Results of the evaluation show that the overall performance of the PPF components with a 0.5mu-inch Pd layer is good. The major differences, if any, are found in the wetting of the side of the leads. Dry aging and combined steam aging/dry aging are more critical for the wetting than no aging and than steam aging. The wetting for finer pitch components as TSSOP56 tends to be more critical than for components with larger pitch as TSSOP20 and SO14. The PPF components with 0.5 mu-in thick Pd layer turn out to have similar lead pull strength as the reference components with SnPb finish. The durability of the assembled components with NiPdAu PPF is good; all assemblies withstand the vibration test, the bump test and 3000 T-cycles between -20 and +100degC. After exposure to a mixed gas environment, creep corrosion is observed for all the components with the NiPdAu PPF finish. The amount of corrosion products formed, however, is not enough to cause a decrease in insulation resistance between adjacent leads