Effect of Solder Paste Alloy and Volume on Solder Voiding

Lead-free solder alloys have been extensively utilized and examined since the early 2000s, owing to the harmful effects of lead on the environment and health. However, it is argued that lead-free solder joints are more susceptible to solder voids, lowering their reliability. Solder voids are cavities or holes that indicate a lack of solder alloy in some areas of the solder joint and may include air, flux, and cured resins. This study explored the impact of solder paste alloys, solder paste volume, and surface finishes on the number and size of solder voids after reflow. The test vehicle of this study consists of a chip array ball grid array (CABGA208) and 2512 surface mount resistors (SMR) components assembled with three solder paste alloys (SAC305, SAC-3.0 Bi, and SAC-3.2 Bi-3.0 Sb). On the boards, three different paste volume ratios (0.1, 0.3, and 0.5) were printed with two surface finishes, including electroless nickel immersion gold (ENIG) and organic solderability preservative (OSP). Mountains9 software was used to capture and analyze X-ray images of CABGA208 components to evaluate solder voiding. The results demonstrated that the size of the voids increased proportionately to the paste/sphere volume ratio. Among solder paste alloys, SAC-3.2 Bi-3.0 Sb exhibited the highest voiding, whereas SAC305 and SAC-3.0 Bi had the best size characteristics. Furthermore, in most combinations, OSP revealed larger voids than ENIG.