Thermal cycle reliability of solder joints to alternate plating finishes

Abstract

Studies immersion gold over electroless nickel, immersion gold over electroless palladium, immersion gold over electroless palladium over electroless nickel, immersion gold over immersion silver and immersion silver. In the palladium finishes, two palladium thicknesses were evaluated: 10‐12μin. and 18‐20μin. Multiple plating chemistry suppliers provided plated test vehicles. HASL and OSP test vehicles were included as control samples. In total, 14 finishes were evaluated in the test matrix. The test vehicle was a daisy chain of zero ohm 1,206 chip resistors that could be monitored individually. Test vehicles were assembled using 63Sn/37Pb eutectic solder paste on an automated assembly line. The thermal cycle range was ‐40°C to 125°C with 30‐minute transition times and 15 minutes at each extreme in a single chamber air system. For each test matrix cell, 120 zero ohm resistors (40 from three boards) were continuously monitored for electrical failure (>100ohms). In addition, resistors were sheared from test vehicles and the shear force at failure was recorded. A decrease in shear force did occur with thermal cycling due to crack initiation and growth in the solder joints. Solder joint cracks have also been examined.