Reliability Of Lead-free Solder Under Cyclic Bending

Abstract

To characterize particular compositions of lead free solder, four point cyclic bending test was conducted to study the affects of accelerated stress testing on the package to board interconnects. Nine CTBGA packages with 0.5 mm ball pitch and 12 x 12 mm package size were reflowed on 8 layered PWB's using solder balls with lead free composition alloys and different PWB copper pad finishes. The boards were subjected to test conditions based on proposed standards by JEDEC. Strain gages were mounted at different locations on the test boards as well as on bare boards in order to observe the difference caused in the board strain use this information for simulation purposes. Failure analysis results have been presented as part of the work on the characterization of the various compositions of lead free alloys. This work reports and explains some of the observations found from the results of this test.