Root Cause and Reliability Predictions of Failed Multilayer Ceramic Capacitors

SUMMARY & CONCLUSIONSThe reliability of larger size ceramic capacitors is usually discussed in the context of cracking propensity and its subsequent effects upon failure modes such as silver migration. Consequently, recommendations for preventing capacitor cracking often constrain temperature ramp rates during surface mount, minimize hand rework, and limit board depaneling stresses. Facing recent infant mortality failures involving 1210 ceramic capacitors mounted on boards about 2.6 in. (66 mm) by 0.8 in. (20 mm), we reproduced these by dropping the boards from different heights or dropping steel balls upon the capacitors directly and then subjecting the boards to elevated temperature, relative humidity, and bias. This definitively identified the role of internal defects such as cracks in instigating the field failures. Subsequent drop tests using packages outfitted with accelerometers enabled deriving a shock profile for predictions of drop probabilities. The correlation between these predictions and our failure incidences points possibly to incidental drops as a factor in the failures. Using this postulated root cause as guidance, we eliminated this capacitor in future board iterations and also instituted a burn-in to contain existing inventory. Although not necessarily substantiation of this root cause, the declining field failure rate seen for this failure mode is consistent with our hypothesis and also represents a positive reliability trend.