Early detection for Cu wire bonding corrosion using accelerated Autoclave reliability test

Rapid change of technologies, coupled with increase in demand of quality and reliability, development speed is the top challenge to have market win for semiconductor industries. As semiconductor is moving towards copper wire bonding, failure associated with reliability is critical. While reliability results take time to wait for the cycles to complete in order to have next decision or improvement. In this paper, the study is initiated due to corrosion failure in Autoclave 96hours. Corrosion associated with copper wire bonding is considered one of the challenges to solve in term of reliability risk which happened at very low ppm rate. The focus on this paper is on early detection for corrosion associate with Cu wire on Aluminum pad. Therefore, establishment of early detection method in detecting/checking corrosion would significantly shorten the development cycle as complete package with normal Autoclave 96hours reliability stress. The development of Autoclave test on non-encapsulation samples was developed based on assumption that mould compound is not the source of chlorine contamination to aluminum metallization corrosion. Without mould compound encapsulation, corrosion rate between copper wire and Aluminum bondpad in moisture environment would expect to be accelerated. This hypothesis is then proven in the experiment of non-encapsulation stripes with Autoclave 1 hours, 2hours, 4hours and 6hours. The study shows that Autoclave 1hour is not enough to provoke the corrosion whereas Autoclave 2hours onwards is found to be corresponding and tally with moulded AC96 hours result where we observed similar corrosion signs — corrosion with crack mechanism and exposed metal stack. From the EDX mapping analysis on the corroded pad, presence of Cl on the bondpad is still persistence as similar observation on Autoclave 96 hours corroded pad. By means of the failure replication in Autoclave 2hours test is successful and the failure mechanism was successfully demonstrated. With the findings in hypothesis study, the Autoclave 2hours was used as the stress test to investigate the corrosion and the failure rate from each category actually tally with the final finding in DOE and it shows significant reduction in corrosion rate during Autoclave short duration test for the dominant corrosion influencing factor. In the final of the experiment, a proper full DOE leg was run with the highly dominant contributor of corrosion and the encapsulation units was send for Autoclave 96 hours as per standard JEDEC requirement, the results show positive with no sign of corrosion, the root cause was then nailed. As a conclusion, result of Autoclave 2hours on non-encapsulation stripes are compatible with conventional Autoclave 96 hours in revealing a sign of corrosion in this case study and it is proven to be a reliable result. This newly developed method not only save the reliability cycle time compared to the conventional Autoclave 96 hours, it also save in term of the product assembly from processing in End of Line which normally easily takes up to 7 days. If all round up together this new method actually save the overall cycle time of minimum 30 days however in actual only need 2 days to get the DOE results after Autoclave 2hours implementation.