Mechanism of electromigration in Au/Al wirebond and its effects

Abstract

This paper presents findings evidencing that electromigration(EM) imparts significant influence on the kinetics of contact failure of Au wire bonded to an Al pad. Contact resistance between Au wire and Al pad at moderately accelerated test conditions (T=150-175degC; j=5times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) revealed that the failure rate depends highly on the direction of electron flow across the contact: electron flow from Au to Al resulted in far faster failure rate than the opposite direction. Microscopic inspection of the contact interface indicated that the wirebond contact failure is related to the growth of Au-Al intermetallic compounds (IMC). EM was found to influence the failure kinetics because it accelerates or decelerates the growth rate of the IMC.