Conditions of producing full-strength joints in strip aluminium leadouts of microcircuits in ultrasonic welding

Analysis of possible areas of failure as determined by the geometry of weld components and of the completed weld, determines the optimum size of the welding tool point and the components when assembling leads to casing-free integrated microcircuits. Basic parameters used are the ratio of tool point diameter to the Al lead width ( delta ) and the ratio of Al lead thickness at the weld to the original thickness (K). These are used in calculating expressions for areas of likely fracture surfaces resulting from failure in testing. Graphs relate different fracture surfaces to values of delta and K. The effects of lead material hardening were determined by testing after various durations of ultrasound at contact forces of 35 and 50 cN. Hardening coefficients thus determined are plotted against K. Ratios of possible fracture surfaces to cross-section area are related to delta and K in series of curves. It is concluded that, to obtain full strength, the welding tool tip/leadout width ratio should be 0.37-0.4 for the external leadout and approx 1.2 for the internal leadout at K = 0.20-0.45. (Original in Russian). Graphs. 3 ref.--J.V.R.