Suppression of Interdiffusion in Copper/Tin Thin Films

Copper/tin thin film couples are often used in microelectronics assembly as device backside coatings for die attach and also as circuit board coatings to maintain solderability. In this article, we report a temperature treatment that slows down the room temperature reaction of these two metals and therefore can extend the storage life of the devices significantly. It was found by x-ray diffraction that during an anneal at 473 K for 1 minute a thin layer of the Cu/Sn ε-phase is formed which introduces an additional interface to the system. The diffusion suppressing effect of this treatment was studied by focused ion beam microscopy.