EFFECT OF COOLING RATE ON INTERFACIAL FATIGUE-CRACK GROWTH IN SN-PB SOLDER JOINTS

The effect of the cooling rate after the reflow on the behavior of fat igue crack growth along Cu/Sn-Pb interfaces was examined in solder joi nts. Flexural peel specimens made from eutectic Sn-Pb solder alloy and Cu were cooled down from reflowing to room temperature using furnace cooling, air cooling, and water quenching. Kinetics of fatigue crack g rowth along the solder/Cu interface were measured from the flexural pe el specimens as a function of strain energy release rate. The effect o f tooling rate was found to depend on the level of strain energy relea se rate. Increasing the cooling rate from furnace cooling to water-que nching enhanced the fatigue crack growth resistance by up to more than 50% at tow strain energy release rates, but reduced the fatigue crack growth resistance by up to 100% at high strain energy release rates. The enhanced fatigue crack growth resistance at the low strain energy release rates is shown to result from roughening of the interface with increasing cooling rate, while the reduction in the fatigue crack gro wth resistance at very high strain energy release rates followed the c hange in crack growth mechanisms from cohesive to interfacial.