Assessment of 20 micron diameter wires for wire bond interconnect technology

In the domain of wire bonding technology, the size and pitch of bond pads and ball bonds are shrinking to accommodate the demand for higher I/Os and increased functionality per chip area. This trend serves as a catalyst for bonding wire manufacturers to continuously develop lower diameter bonding wires. One mil (25 mu m) diameter bonding wire, used widely in this interconnection technique, is now being replaced by 0.8 mil (20 pm) diameter bonding wire. In keeping with the need for higher operating speeds and higher temperatures for today's lCs, the reliability of ball bonds formed by small diameter wires is of concern and requires investigation. This study explores the effects of 0.8 mil (20 pm) diameter bonding wire on the wire bond ball joint reliability and compares these effects with 1.0 mil (25 pm) diameter bonding wire. The reliability of the ball bonds was assessed using mechanical tests (wire pull and ball shear) for units subjected to stress tests such as the unbiased highly accelerated stress test and high temperature storage tests. The results of this investigation reveal that both the wire diameters are able to sustain their integrity after moisture testing. But, the bond strength degrades after high temperature tests due to the Kirkendall voiding mechanism occurring between gold wire and the aluminum bond pad.