WLCSP and BGA Reworkable Underfill Evaluation and ReliabilityAuthors: Fei Xie, Ph.D., Han Wu, Daniel F. Baldwin, Ph.D., Swapan Bhattacharya, Ph.D., Kelley Hodge, Qing Ji, Ph.D., and Ben Bo
Company: Engent, Inc. and H. B. Fuller
Date Published: 9/27/2015 Conference: SMTA International
This paper continues our recent published work. Prior work presented the reworkable underfill evaluation process and several criteria were investigated which included underfill flow rate, flux compatibility, reworkability, solder extrusion, material properties such as viscosity, Tg, modulus and cure time. This paper conducts a deeper and wider study on the underfill/flux compatibility issues. It investigates the flux compatibility between four most popular commercial solder pastes and over six popular commercial CSP and BGA underfills. Two most compatible solder pastes were then selected to assemble the WLCSP and BGA rigid and flex circuits. Ten reworkable underfills from various venders were applied to the devices on these boards. The thermal cycle, temperature humidity aging, autoclave, and drop reliability tests were performed. The underfill and solder paste combination with the best performance for both rigid and flex boards were selected and applied to the production process.
Reworkable underfill, Underfill, Reworkability, Flux Compatibility, WLCSP, BGA
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