Bond pad surface quality for reliable wire bonding
The impact of fluoride and AlOx contaminants on the quality of wire bonding (Au to Al welding) has been measured. No or minor impact of these contaminants has been found with a standard ball shear test. Despite an accelerated lifetime test, the shear strength remains above the required specification limits. Intermetallic coverage, the percentage of the interface between the bond ball and the bond pad where welding resulted in intermetallic diffusion, gives a better picture of the quality decay, but this method is too elaborate for production control and specification limits are unclear.
wire bonding contamination ball shear test intermetallic coverage aluminum bond pad gold wire