Page 153 - Wire Bonding in Microelectronics

CHAPTER 5

Gold-Aluminum

Intermetallic

Compounds and

Other Metallic

Interface Reactions

in Wire Bonding

5.1 Gold-Aluminum Intermetallic Compound Formation
and Classical Wire-Bond Failures

5.1.1 Introduction
Gold-aluminum intermetallic compound formation and associated
Kirkendall voids have resulted in more documented wire-bond fail-
ures than any other problem over the years. There have been hun-
dreds of papers on this subject, and this chapter can only present an
overview of them. Modern packaging and device environments do
not (or need not) involve the high temperatures (≥ 300°C) that pro-
duced most of the classical failures. The compounds are typically
referred to as “purple plague (the Al-rich phase).” This term comes
from the characteristic color of the AuAl intermetallic compound
2
that often occurs around the perimeter of an Au bond on an Al pad.
(Such colored intermetallic compounds are quite commonly found in
metallurgy, and, as an example, Au and In also form a purple-colored
intermetallic compound.) Most present day Au-Al related failures are

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