Predicting the Reliability of Packaging-On Package-On- Package (POPOP) Interconnections Based on Accelerated Aging Experiments and Computational Modeling
Authors: P. T. Vianco, Ph.D., J.A. Rejent, J.M Grazier, A.C. Kilgo, B.M. McKenzie, and M.K. Neilsen Company: Sandia National Laboratories Date Published: 9/25/2016
Abstract: Package-on-package (PoP) and package-on-package-onpackage (PoPoP) technologies are being considered to reduce the size, weight, and power (SWaP) of military, space, and satellite electronics. The long-term reliability of PoPoP solder joints was assessed under thermal mechanical fatigue (TMF). The study included accelerated aging using the two-parameter (2P) Weibull probability distribution (characteristic lifetime, η, and slope, Β). Backwards compatible, test vehicles (bottom solder joints (SnPb paste/SAC305 solder balls) exhibited excellent TMF performance (η = 2600 ±200 cycles; Β = 7.6 ±3.5) as did the middle (η = 2500 ±300 cycles; Β = 6.6 ±3.4) and top joints (η = 2600 ±200 cycles; Β = 8.7 ±4.0). The 100% SAC305 test vehicle showed comparable &eta values: bottom joints, 2200 ±200 cycles; middle joints, 2600 ±500 cycles; and top joints, 2400 ±200 cycles. Underfill in the bottom gap improved the η of the SnPb/SAC305 interconnections but reduced that of the 100% SAC305 solder joints. When underfilled, the 100% SAC305 joints exhibited two failure modes: a “low η” mode that showed only TMF cracks and a “high η“ mode that had both TMF and tensile cracks. The computational model predicted that PoPoP warpage was not significantly changed by underfill placed in the bottom gap. Initial quantitative predictions of Nf were less than satisfactory, requiring further development of the model for the latter be a suitable design tool.