Failure criteria of flip chip joints during accelerated testing

The criteria used to determine electrical failure was explored during accelerated testing of underfilled flip chip joints as a function of both different thermal cycling conditions and different sampling methods. The criteria was based on resistance measurements of daisy-chained solder joints monitored in situ and by endpointing. The sensitivity of the resistance criteria was found to depend strongly on test conditions and often could not be categorized into simple pass/fail groupings. Also, extremely small resistance changes were measured for joints with through-cracks generated by fatigue. Experimental error associated with fixing the cycles to failure was minimized by monitoring the absolute changes in resistance as a function of cycling time while simultaneously measuring the temperature dependence of resistance as the joints degrade. Failure times derived from interval part monitoring closely approximated in situ monitoring, but the resistance measurements for mild cycling conditions required a high degree of accuracy. Finally, a tunneling model is proposed to explain the resistance behavior of cracked joints.