On the study of loop profiles in improving the sweep stiffness of wire bond

The deflection of gold wire bonds during the encapsulation of IC packaging can seriously cause wire crossover and shorting. Up to now, there is no (standard) algorithm has been proposed to decide the better bond looping system for optimal adjusting the parameters of wire bonder to obtain lower deflection of wire bond. The wire sweep experiment is developed to define the sweep stiffness of wire bond in the related studies. The sweep stiffness of wire bond is defined to be the index of sweep resistance to drag force during the transfer molding process. Higher sweep stiffness of wire bond possesses lower wire sweep and thereby higher yield rate of IC packaging. The sweep stiffness of three bond modes, Q-loop, S-loop and M-loop bonds is studied in this paper. The results show the Q-loop bond has the highest sweep stiffness values than those of the S-loop and M-loop bonds for fixed bond spans and bond heights. The sweep stiffness of S-loop and M-loop bonds, mostly used for longer connections or crossing another chip in multichip module/3-dimensional packages has found to be affected significantly by their kinking numbers within a bond. The experimental results points out that the M-loop bond has better sweep resistance than the S-loop bond does. The increment in the sweep stiffness could be up to 13-75% depend on the bond span and bond height used.