Solid-State Reaction in an Au Wire Connection with an AI-Cu Pad During Aging

摘要

In integrated-circuit packages,wire-bonding techniques are the preferred methods for making electrical connections between the chip and the lead frame.The influence of aging at 150deg C up to 3,000 hr on interfacial reactions of Au wire bonded with the Al-Cu pad was investigated herein.To observe various intermetallic compounds (IMCs) with field-emission scanning electron microscopy,polished samples were ion-milled through precision etching and coating techniques.Three IMCs,i.e.,(Al,Cu)Au_4,(Al,Cu)_3Au_8,and (Al,Cu)Au_2,were found between the Au wire and the Al-Cu pad in the as-assembled wire bond.After 168 hr of aging,Al_3(Au,Cu)_8 formed between (Al,Cu)_3Au_8 and (Al,Cu)Au_2 in the center of the wire bond.In fact,the Al-Cu pad,(Al,Cu)Au_2,and Al_3(Au,Cu)_8 IMCs were completely reacted after 500 hr of aging.(Al,Cu)_3Au_8 was thus transformed into (Al,Cu)Au_4.Near the edge of the wire bonds,(Al,Cu)Au_2 formed between the Al-Cu pad and (Al,Cu)_3Au_8 during 500 hr of aging.For aging longer than 1000 hr,Al_3(Au,Cu)_8 was detected between (Al,Cu)_3Au_8 and (Al,Cu)Au_2.It was noted that the Al_3(Au,Cu)_8 IMC gradually grew with aging.With the aid of microstructure evolution and quantitative analysis,the interfacial phase transformation between the Au wire and the Al-Cu pad could be probed.In addition,the growth kinetics of (Al,Cu)Au_4 and (Al,Cu)_3Au_8 in the center of wire bonds were also evaluated and discussed.