Page 16 - Wire Bonding in Microelectronics

Introduction to

Third Edition

he new material in this book was introduced because of new
technical areas. (Examples are fine-pitch bonding, Cu wire
Tbonding, as well as different pad metallurgies.) Also, many
practical questions have been posed to the author by phone calls,
plant visits, e-mails, and during many short courses taught for the
University of Arizona, ISHM (IMAPS), SMI, IEEE, and other organi-
zations. Material has been included/updated to answer the most fre-
quently asked of these questions.
In 1970, wire bonds caused a large proportion—sometimes as
high as one-third of all semiconductor-device field-failures. However,
the number of recognized failure mechanisms at that time was quite
limited. Typically, they were cited as “purple plague,” underbonding,
overbonding, and nonspecified contamination-induced corrosion.
Currently (2009), dozens of chemical, metallurgical, and mechanical
failure mechanisms have been identified. Part of these new
mechanisms were discovered because of greatly improved analytical
methods and equipment (e.g., Auger and SIMS analysis), part because
of the many trillions of bonds made (and millions to billions failed),
and part because of the changing technology (e.g., new metallurgies,
plastic encapsulation). A study of recent Au and Al wire bond failure
papers indicates that the discovery of new failure mechanisms has
slowed, although the rediscovery of old ones, or variations of them,
has continued. Thus, it was felt that it is appropriate to review the
known failure modes and mechanisms of wire bonds, categorize
them, and where possible, explain and/or give solutions to them.
(New bond metallurgies are still fertile fields of investigation.)
Since failures are generally revealed by testing, the bond pull and
shear tests are still described, but updated(!) such as for fine pitch, new
mold compounds, etc. The book also discusses mechanical, metallurgical,
chemical, and miscellaneous failure mechanisms. Some of these overlap
and were placed in the most appropriate sections.

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