Study On The Metallurgical Behavior Of Bond Interface In Ultrasonic Wedge Bonding

Ultrasonic wire bonding is one of the most important techniques for die interconnection in microelectronic packaging. It is widely used in microwave devices, photoelectron devices and power devices packaging.It is a process of making wire and metallization join together by the application of ultrasonic energy through a resonating transducer tool combination while applying a clamping force. The wires are channels by which the electricity and heat are transported between internal circuit and exterior circuit, so the bonds burden their shock. For better understanding the realiability of the bonds, high temperature storage experiment was carried out to study the metallurgical behavior of the bond interface.The ultrasonic bonds, after bonding and aging, of Au wire bonded on the Al metallization pad were analyzed by Scanning Electronic Microscopy(SEM) with Energy Dispersive X-Ray Spectrometer(EDX). It is found that, there was evident diffusion of Au and Al, and Au5Al2 intermetallic compound (IMC) formed first after aging for 10 days at 200℃in atmosphere, and there was also some Au₂Al formed at the edge of the interface. After aging for 20 days, the IMC developed slightly, and also Kirkendall voids generated at the interface. After aging for 30 days, the IMC began to transform to other Au-Al IMCs, and it became Au₂Al IMC finally after aging for 40 days.Al+1%Si wires were also uesd to be bonded on two different kinds of Au/Ni/Cu pads. After aging for 30 days at 200℃and 250℃, the interface of the bonds on thin Au pads didn't change much, there was no evident diffusion between Al and Ni. But the interface of the bonds on thick Au pads changed much after aging for 10 days, and Au₂Al IMC formed. With increasing aging time, the voids generated in Al wires, and a part of Au₂Al IMC transformed to AuAl phase. Finally, the IMC became the compound of Au₂Al and AuAl₂.