Propensity for Fatigue Failure of the FCBGA UF-Substrate Interface After Prolonged Storage

Abstract Electronics in automotive applications may be exposed the thermal excursions owing to environmental temperature changes and power-on/off cycling. Temperatures may range from −40C to +200C depending on the location of electronics in the automotive underhood. Flip-chip Ball-Grid Arrays (FCBGAs) are finding applications for advanced driver assistance systems on the automotive platform. Failure of the chip-underfill interface or the substrate-underfill interface is often the precursor for the failure of the flip-chip solder joints. Depending on the power output of the FCBGA package — the top of the chip may have a thermal-interface material to form a low thermal-resistance connection to the lid of the package. Interface reliability under monotonic and repetitive loads after long durations of storage are thus needed for the assessment of the thermo-mechanical reliability of the FCBGA architecture in the automotive underhood environments. In this study UF-Substrate interface reliability has been investigated as a function of Paris’ Constants developed from the samples subjected to 4-point bend fatigue loading. The samples were tested till catastrophic failures, and the critical stress intensity factor (ΔK) was correlated with cycles to failure (da/dN). The slope and the intercept parameters were studied as a function of 4 months’ aging time and 2 temperatures (100°C and 150°C). The evolution of these constants shows the effect of sustained high-temperature operation on the fatigue reliability of 4 underfill interfaces. Several cycles to failure were measured to rank the underfills for future applications in field-deployed electronics.