Thermomechanical Fatigue Performance of Lead-Free Chip Scale Package Assemblies with Fast Cure and Reworkable Capillary Flow Underfills

Abstract

In this paper, we present the results of temperature cycling test for full and partial capillary flow underfilled lead-free chip scale packages (CSPs), the tests were carried out on the basis of JEDEC standard. Two kinds of representative fast cure and reworkable underfill materials are used in this study, and CSPs without underfills were also tested for comparison. The test results show that the two underfill materials reduce the thermomechanical fatigue performance of CSP assemblies. The underfill with high T g and storage modulus yielded better performance; indeed, the coefficient of thermal expansion (CTE) is also very critical to the thermomechanical fatigue performance, but its effects is not so obvious in this study owing to the similar CTEs of the underfills used. In addition, the negative effect of a partial underfill pattern is smaller than that of a full underfill pattern. Failure analysis shows that the dominant failure mode observed is solder cracking near the package and/or printed circuit board pads.

Evaluation of thermal fatigue crack propagation in underfill resin materials for electronic packages

“…However, the studies on thermal fatigue that have focused on fatigue crack propagation in underfill resins are very limited 10–12 . Furthermore, in thermal cycle tests on IC packages, it is difficult to determine where and when the crack initiated and how it propagated in underfill resins because the disconnection of solder joints was usually measured electrically 13,14 . Therefore, it is important to clarify the thermal fatigue crack growth characteristics of underfill resins to understand the failure mechanism and design reliable IC packages.…”

Analysis of edge and corner bonded PSvfBGA reliability under thermal cycling conditions by experimental and finite element methods

“…The improvement does not seem to be as much as full capillary flow underfill but it is enough to help the package pass mechanical requirements [12][13][14][15]. However, depending on the selection of materials the thermal fatigue life may easily end up worse than that without an adhesive [15][16][17]. This is true for lead-free soldered assemblies compared to eutectic SnPb soldered assemblies.…”

Polymeric reinforcement approaches and materials selection to improve board-level drop reliability of SnAgCu soldered area array packages

“…The polymeric reinforcement approaches include full capillary flow underfill (FCFU), partial capillary flow underfill (PCFU), edge bond adhesive (EBA), and corner bond adhesive (CBA) [4][5][6][7][8][9][10][11][12][13]. Although no-flow underfill, epoxy flux, and preform underfilm technologies are available in the marketplace, high volume manufacturing (HVM) of these approaches has not been adopted due to their shortcomings [14][15][16][17].…”