Interconnection reliability and interfacial structure between Au alloy bump and Al pad using ultrasonic bonding^*

* Presented at Mate 2004, February 2004.

Abstract

Flip chip technology with Au bumps on a substrace has been widely applied to electronic equipment such as smart phones. The purposes of this study are to examine the effect of Al pad thickness on the bondability of flip chip using ultrasonic bonding and to clarify interfacial structures between Au alloy bumps and Al pads by ultrasonic bonding compared before and after a thermal cycle test. Suitable Al thickness for excellent initial Au/Al bonding without chip cracking are 0.8 μm because a thin Al layer could not reduce stress to a chip under an Al pad during the ultrasonic bonding process. Intermetallic compounds between the Au alloy bump and chip after reflows consisted of five Au-Al layers, and a pure Al layer remained. On the other hand, after the temperature cycle test at 218/423 K, intermetallic compounds between the Au alloy bump and chip were changed into two kinds of Au-Al layers, so a pure Al layer did not exist. In addition, if thick intermetallic compound layers existed around the bonding region, bondability deteriorated easily by thermal stress due to a thermal cycle test, therefore the open failure rate was rising when the Au thickness was 1.2 μm.

Keywords:

• Flip-chip bonding
• ultrasonic bonding
• Au–Al
• interfacial microstructure
• temperature cycle test
• TEM

Notes

Selected from Quarterly Journal of the Japan Welding Society 2014 32(2) 57–63

* Presented at Mate 2004, February 2004.