Pb phase coarsening in eutectic Pb/Sn flip chip solder joints under electric current stressing

Experimental research on the Pb phase coarsening of eutectic Pb/Sn flip chip solder joint under current stressing is reported. Phase growth is observed under different current densities and temperatures. Higher current density leads to faster grain coarsening. Based on the test results, a grain coarsening equation including the influence of current density is proposed, dⁿ - d₀ⁿ = Kj^mt. The current density exponent m is found to be 3, and phase growth exponent n is 5.5. Within our test temperature range, electric current seems to have a greater influence on Pb phase growth of the solder joint than temperature or thermomigration caused by the temperature gradient due to Joule heating during current stressing.