Voiding Mechanisms in SMT

Abstract

The mechanisms for void formation are investigated for applications involving solder paste in surface mount technology. Generally, voids are caused by the outgassing of entrapped flux in the sandwiched solder during reflow. The voiding is dictated mainly by the solderability of metallisation, and increases with decreasing solderability of metallisation, decreasing flux activity, increasing metal load of powder, and increasing coverage area under the lead of the joint. Decrease in the solder powder particle size has only a slightly negative effect on voiding. The data indicate that voiding is also a function of the timing between the coalescing of solder powder and the elimination of immobile metallisation oxide. The sooner the paste coalescence occurs, the worse the voiding will be. Increase in voiding is usually accompanied by an increasing fraction of large voids, suggesting that factors causing voiding will have an even greater impact on the joint reliability than shown by the total‐ void‐volume analysis results. Preliminary data suggest that certain predry treatment and flux solvent with higher boiling point appear to cause increased voiding.

Citation

Hance, W.B. and Lee, N.C. (1993), "Voiding Mechanisms in SMT", Soldering & Surface Mount Technology, Vol. 5 No. 1, pp. 16-21. https://doi.org/10.1108/eb037810