Investigation of charge induced bond pad corrosion

Several post wafer saw Al bond pad corrosion events were found with the defect size much larger than that of the conventional Al pad Al₂Cu theta-phase galvanic corrosion. The large corrosion defect size has great of concern on degrading the wirebond interconnect reliability. To understand the cause of large size corrosion defect and find the possible solution, the evaluation including splits from both wafer process, such as Al deposition temperature and thickness, and assembly process, such as saw DI water resistance/flow rate/pressure, with/without surfactant, de-taping process ESD control and post-saw wafer clean, were performed using simulated as well as real wafer saw process. The results showed, with 40 minute long wafer saw time, all other splits found pad corrosion defects. Only the split of the worse de-taping ESD control was found with large corrosion defect size by real wafer saw process. The corrosion was found strongly static charge dependent. With proper ESD control during wafer de-taping process or implementing surfactant during wafer saw process, the charge induced pad corrosion can be resolved.