Effect of Bonding Position between Cu Wire and Al pad in THB Reliability Test

Cu wire is widely used in IC packages in the automotive field, where high reliability is required. This report looks at failure cases and the countermeasures that were taken for moisture resistance reliability which need to be taken into consideration when designing Cu wire products. One of the failure cases is a well-known case where corrosion occurred in the THB (Temperature Humidity Bias) test. This case showed that corrosion occurred more frequently the closer to the chip’s corner at the wire bonding area. Corrosion always occurred at the chip’s center direction in the wire bonding pad. It is presumed that crevices were formed during the reflow, causing condensation to get into the crevices. Countermeasures were taken in the form of reducing reflow stress by increasing the distance between the chip corner and the bonding position. This case showed that it is essential to take measures in the package design stage in the automotive field, where high reliability is required.