Investigate the Performance of SnCuNi (SCN) Alloy for Wave Soldering

摘要

The solderability of SnAgCu (SAC305) and SnCuNi (SCN) alloys for DIP components on thick PCB (2.3 mm) with OSP and LF-HASL surface finishes were studied. Force rework was also applied after DIP process by using SCN and SAC305 solder alloys. In addition, the SCN solder properties, including copper dissolution, mixed alloys, solder joint corrosion, and corrosion property to soldering tank were tested. The solder joints of SCN exhibited slightly lower appearance defect rate than that of SAC305 solder joints at 270?°C with dwell time of 8 sec. SAC305 alloy showed slightly lower defect rate with respect to insufficient PTH hole fill than SCN. Copper dissolution did not occur at PTH knee area after DIP and rework by using SCN alloy. The solder joints reworked with SCN alloy exhibited thicker IMC thickness compared to that with SAC305. From copper dissolution test, SCN showed much lower dissolution rate due to the formation of (Cu, Ni)6Sn5 IMC. There was no segregation or apparent alloy boundary when SAC305 mixed with SCN in the solder joint. Solder joint did not appear surface corrosion after exposed at room environment even with excessive flux residue during experimentation. As for the corrosion resistance of the solder tank, SS316L and Ti alloy were not found to corrode after being in contact with SCN solder for 650 hrs at 300?°C. Test vehicles with DIMM socket, electrolyte capacitor, and headers were subjected to temperature cycling and thermal shock tests.