Comprehensive Study of Long-Term Reliability of Copper Bonding Wires at Harsh Automotive Conditions

Copper (Cu) has been by far the most widely used bonding wire material in the consumer electronics sector for several years now. However, gold (Au) bonding wires still dominate in many automotive applications. But even in this field, there have been efforts for years to benefit from the significant cost advantage of copper compared to gold. There are now various Cu wire materials in the market, which are now increasingly advancing into applications with challenging conditions and high reliability requirements. The present study, which was conducted in a three-party project, investigates the suitability of copper wire materials to meet the reliability aspects following the AEC-Q006 requirements. As part of a bonding wire evaluation, two palladium-coated copper (APC) wires were considered - a conventional APC wire and the EX1R wire optimized for harsh application conditions.In short, the results of the investigation are summarized as follows.•bHAST and AC testing: both wire types showed similar results, and the pull/shear tests and interface analysis revealed no significant degradation of bond quality in both wire types.•TCT: both wire types maintained sufficiently high pull/shear strength after the tests. However, the interface analysis revealed an unknown voiding effect inside the remaining Al pad metallization. The voiding effect seems to worsen as the number of thermal cycling increases and slightly differ between wire types.•HTSL 150/175°C: the tests yielded the most significant differences between wire types, with EX1R wire showing clearly higher robustness against high temperature aging. Comparing the test conditions (150°C-4,000hrs vs. 175°C2,000hrs), the test at 175°C gave a more drastic progress of interface corrosion and a more decrease in pull/shear strength after the tests.In the paper, each test results will be summarized, but a more in-depth analysis will be given to the high-temperature storage life tests at 150°C and 175°C, where the most significant differences between the two types of wire occurred. Overall, the results show the importance of the knowledge for the material reliability upfront a device qualification process (robustness validation) and give further guidance for material selection.