Comparison of Copper Erosion at Plated Through-Hole Knees in Motherboards Using SAC305 and an SnCuNiGe Alternative Alloy for Wave Soldering and Mini-pot Rework

摘要

Copper erosion from plated through holes (PTH) barrels in printed circuit boards (PCB) during both wave soldering and mini-pot rework can increase the risk of PTH reliability failures during field use. Alternative Alloys are being touted as one solution to reducing copper erosion. This study will compare the copper erosion resulting from use of one alternative alloy in wave soldering and mini-pot rework with the currently used SAC305 solder alloy. The PTH knee thickness will be measured on as-received boards, after wave soldering and after one 45 second cycle of mini-pot rework, and compared with the minimum PTH thickness necessary to meet product reliability requirements. The board test vehicle for this study has a thickness of 93 mils (2.362 mm) and its design is similar to a mid-size server board. The SnCuNiGe alternative alloy was chosen from the results of the previous investigation that compared 5 different alloys for the magnitude and variation in copper erosion from PTH knees when subjected to a mini-pot rework cycle, without prior wave soldering. While the mean value of the copper erosion data sets from all 5 alloys did not show any technically significant difference, a particular alloy exhibited significantly lower variation in copper erosion data at the PTH knees. A comparison of this alloy with the SAC305 alloy for PTH knee copper erosion under actual wave solder and mini-pot rework process conditions was required.