Degradation of bondcontacts in chip-on-board microelectronic assemblies

The degradation of bondcontacts in Chip-on-Board assemblies under thermic and corrosive stresses were investigated. Degree for quantity of degradation was the changing of the electrical resistance of the bondcontacts. Connections between the silicon die and the substrate (printed circuit board) were manufactured using the well-known ultrasonic bonding process. The PCB's were plated with functional surfaces of Ni and Au by electrolytic or electroless/immersion methods. The deposition method and the thickness of the gold surface have an important influence in the degradation of bondcontacts under thermic and corrosive stresses. The results show that compared to electroless/immersion gold surfaces wire bonds on thick electrolytic deposited gold surfaces (greater than or equal to 1.5 mu m) tend much faster to degradation.