Reliability and process characterization of electroless Nickel-Gold/Solder flip chip interconnect technology

This paper describes the reliability evaluation of the electroless nickel-gold (Ni/Au) solder interconnect technology under development in the Motorola Advanced Interconnect Systems Laboratory. This work was conducted jointly with the Motorola Automotive Products Division. The test vehicle used for evaluation is a high-power functional device which is assembled in a flip chip format to an organic test substrate using an epoxy underencapsulant. The reliability study evaluated the interconnect technology using both generic and application-specific reliability tests. Generic package level testing included: liquid thermal shock [-55/+125°C], air temperature cycle [-55/+125°C], temperature humidity bias [85°C/85%/15 V], and high temperature bake [150°C]. The application-specific tests included: power temperature cycle [-40/+125°C], operational life [150°C], and air temperature cycle [-40/+150°C]. Analysis of reliability results and identification of failure mechanisms led to recommendations for process improvements. The Ni-Au/solder interconnect has not failed after 1000+ cycles/hours of reliability testing and has passed application-specific requirements for operational life. Failure modes for each reliability test have been identified and are being addressed. In all cases of continuity failure, there was no evidence of failure at the interface of the solder bump and Ni/Au bump, or between the Ni/Au bump and the Al bondpad. Diagnosis of electrical failures are not covered in this paper