Package Design Characterization Influencing Substrate Metal Crack in BGA Package

Nearly every aspect of the automotive industry is undergoing a transformation. At its core, mechanical parts of the vehicle are being replaced by sophisticated electronic systems and complex software environments. With the automotive megatrends of autonomy, electrification, vehicle intelligence, and connectivity-enhanced driving, the value of the semiconductor content in an automobile is expected to more than triple in 10 years. Conventional vehicles may contain an average of $330 value of semiconductor content while hybrid electric vehicles can contain up to $1,000 and 3,500 semiconductors [1]. Requirements for semiconductor devices are becoming more stringent. For an example, a high performance automotive application device found in electric vehicle charging stations can be specified for 20 years of service life instead of the standard 15 years. Because of its function, the mission profile defines much longer duration at higher temperatures. Meeting such a mission profile entails passing higher cycles of component level temperature cycling (-55°C to 150°C), which can be beyond the robust requirement (2000cycles) of AEC Grade 1. Wire bonded Mold Array Process Ball Grid Array (MAPBGA) packages have been used in many automotive processor applications such as powertrain, chassis, infotainment, networking, safety and control, and body electronics. Increasing processor complexity drives large die sizes, higher functionality density and subsequently substrate design complexity. Packages with large die to package ratio and higher density substrate designs were evaluated against more stringent temperature cycling reliability. The MAPBGA parts subjected to temperature cycling condition -55°C to 150°C passed 1000 cycles but failed after 1500 temperature cycles. Failure analysis found cracks in the substrate top metal trace crossing the die edge. Additional delayering of the package from the bottom up showed cracks in the top soldermask and the die attach above the cracked top metal trace. Cross-sectioning of packages after successive temperature cycling found further crack propagation into the substrate core region. This finding suggests that the crack initiated in the die attach then propagated to the substrate soldermask, metal trace and core dielectric causing opens failure. A series of studies and thermo-mechanical simulations were launched to study substrate trace cracks at the die edge in relation to (1) die to package ratio; (2) die attach bond line thickness (BLT), (3) die attach dispensing quality, (4) die attach material types, and (5) substrate trace width. The 14x14mm MAPBGA packages with different die to package ratios ranging from 15% to 30% were studied. Packages were submitted to temperature cycling (-55°C to 150°C) and tested. Package cross sectioning and substrate de-layering were performed to characterize the die attach quality and crack propagation through temperature cycling durations. This paper will present the results from thermo-mechanical simulations and empirical data collection.