Ball bond process optimization using in situ ball shear force

Increasing I/O count on chips requires that wire bonders improve their productivity and cost effectiveness in order to remain a viable chip packaging solution. Increasing I/O density has pushed bond pad pitches smaller and smaller. Currently, 45 μm pitch processes are being qualified for high volume production and 35 μm pitch pads are on the road map. These fine pitch ball bonding processes are more sensitive to process variation than the larger pitch processes of only a few years ago and require more precise process setups and high degree of quality control during production. A key quality measure for the ball bond process is the bonded ball´s shear strength. Standard shear test methods are time consuming and therefore costly. A new shear test method has been developed that is performed directly on the wirebonder by the bond head during wire bonding. This in situ test requires no operator intervention and is automatically applied to the current wire bonding recipe. It correlates well to the standard shear force test and can be used effectively to improve machine utilization by minimizing recipe optimization time. This paper discusses the benefits of using an optimization strategy tailored for the in situ test when optimizing the ball bond process.