Abstract:
Many trillions of gold/aluminum bonds have worked successfully. But there are still some failures, typically caused by impurities in one or both of the metals, exacerbated by incompletely formed bonds (too little force or too little time). Examples of such failures are presented for recently produced ASIC devices. One example is the use of plasma cleaners using silicon pump oil: this deposits SiO2 glass surfaces onto the bond pads, interfering with bonding). Another example is debris trapped in vias overcoated with aluminum: this debris diffuses through the aluminum and introduces a sheet of Kirkendall-like voids adjacent to the intermetallic layer, which dramatically lowers the strength of the bond.