Molding wirebonded BGA (ball grid array) packages in an array format improves manufacturing efficiency over individually molded packages. Historically, larger packages (typically >21mm) were individually molded. However, recent advances in mold processing has enabled packages up to 27mm to be assembled in an array format. Consequently, the package outline changed such that the mold cap extended to the substrate edge, thereby altering the strain of the outer solderball rows, affecting the SJR (solder-joint reliability). This paper describes experimental and simulation work to study SJR of a 1.0mm pitch, 27mm body BGA package used in automotive under-the-hood applications. Both MAPBGA (molded array BGA) and TEPBGA (individually molded thermally enhanced BGA) packages were testing in TCoB (temperature cycle on board) in AATS (air-to-air thermal shock) between -40°C and +125°C. The target requirement was to pass 3000 cycles before the first failure. The solder-joint lifetime was observed to depend on the PCB (printed circuit board) pad diameter. Both MAPBGA and TEPBGA packages performed well and behaved similarly for larger diameter pads. However, for the smallest PCB pad, the MAPBGA failed prematurely. Failure analysis determined that the corner solder-joints were the culprits. Simulations confirmed the trend, demonstrating that for sufficiently small PCB pads, the failure location moves from the package side to the PCB side of the solder-joint with reduced lifetime.
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