Observations of microstructural coarsening in micro flip-chip solder joints

Coarsening of solder microstructures dramatically affects fatigue lifetimes . This paper presents a study of microstructural evolution due to thermal c ycling and aging of small solder joints. The lead-tin solder joints in this study have a height of 55 +/-5 mum and a tin content of 65-70 wt.%, with a degenerate eutectic microstructure. The joint microstructure coarsens more rapidly during aging at 160 degreesC than cycling from 0-160 degreesC. No coarsened bands are observed. The cycling data scales with standard coarsen ing equations, while the aging data fits to an enhanced trend. The joints e xperiencing 2.8% strain during cycling fail by 1000 cycles.