Driving force and mechanism for spontaneous metal whisker formation.
The room temperature spontaneous growth of low melting point metal whiskers, such as Sn, poses a serious reliability problem in the semiconducting industry; a problem that has become acute with the introduction of Pb-free technology. To date, this 50+ year old problem has resisted interpretation. Herein we show that the driving force is essentially a reaction between oxygen and the sprouting metal. The resulting volume expansion creates a compressive stress that pushes the whiskers up. The model proposed explains our observations on In and Sn whiskers and many past observations. The solution is in principle simple: diffusion of oxygen into the metal must be prevented or slowed down. This was demonstrated by coating the active surfaces with a polymer coating.
Barsoum
M W
MW
Department of Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania 19104, USA.
Hoffman
E N
EN
Doherty
R D
RD
Gupta
S
S
Zavaliangos
A
A