PBGA wire bonding development

In a PBGA package, the existence of a glass transition temperature of 170/spl sim/215/spl deg/C for PCB substrate puts an upper ceiling to the usable wire bond temperature. The low thermal conductivity of PCB substrate and the need for a thicker material make fine pad pitch wire bonding even more difficult to do. To compensate for the limitation in thermal energy, high frequency thermo-sonic bonding was proposed and successfully demonstrated for fine pad pitch wire bonding. Of the four major bonding parameters investigated, bond force appeared to be the most important control factor for ball size and ball shear force optimization. By using ball size, ball shear force, and ball shear stress, respectively as objective functions, a minimum ball size of Xs=2.6 mil, Ys=2.7 mil, a maximum ball shear force of 41.9 g, and a maximum ball shear stress of 5.6 g/mil/sup 2/ were predicted. Tradeoffs may be necessary for a given bonding application.