Advanced analysis on board trace reliability of WLCSP under drop impact

An adaptive Cu trace fatigue model based on average cross-section strain

“…As a result, the investigation headed away from a fracture mechanics (FMs) approach, and more toward a continuum damage mechanics (CDMs) approach. Mattila et al [29] and Syed et al [11] have offered similar studies, but with less depth, and using existing fatigue models.…”

“…Studies show that redesigned Cu traces can indeed survive repetitive mechanical loading and that the failure site shifts elsewhere [9,11,13].…”

“…This generally results in stiffer, more robust solder interconnects. Consequently, the mechanically weakest point in the chain becomes the traces on the PWA [7][8][9][10][11][12].…”

“…When assessing the mechanical durability of electronic assemblies, the dominant failure site is generally believed to be in the solder interconnect [11]. However, in many package styles, such as ball grid arrays (BGAs), land grid arrays (LGAs), micro-lead frame (MLFs) and quad flat no-lead (QFNs), the Cu trace emanating from the solder pad may be the weakest failure site, particularly if the solder joint is copper-defined rather than mask-defined, and if there is a sudden neck in the copper trace with sharp re-entrant corners where the copper trace emanates from the solder pad [10,12].…”

“…However, in many package styles, such as ball grid arrays (BGAs), land grid arrays (LGAs), micro-lead frame (MLFs) and quad flat no-lead (QFNs), the Cu trace emanating from the solder pad may be the weakest failure site, particularly if the solder joint is copper-defined rather than mask-defined, and if there is a sudden neck in the copper trace with sharp re-entrant corners where the copper trace emanates from the solder pad [10,12]. This is particularly true in situations with cyclic mechanical loading, such as cyclic quasi-static bending, vibration and repetitive drop/shock [7][8][9][10][11][12].…”