Content area
Full Text
(ProQuest: ... denotes non-US-ASCII text omitted.)
I.
INTRODUCTION
A tin whisker is a unidimensional material; a single-crystal wire of [beta]-Sn. Typical whiskers are about 1-5 micrometers in diameter, and tens of micrometers to several millimeters in length. These whiskers were first observed to grow spontaneously from tin plating. As a scientific phenomenon, tin whiskers were first observed about 60 years ago.1 Due to their high conductivity, tin whiskers can easily cause a short circuit in an electronic device, and so far there have been several catastrophic accidents due to whiskers.2 Therefore, both scientists and engineers in industry have been greatly interested in the phenomenon of tin whisker growth. During the past 60 years, many growth mechanisms, such as the dislocation model,3 the recrystallization model4 and an oxide-crack model5 have been proposed to explain the growth of whiskers from tin plating. However, until now, none of the explanations have been universally accepted. In particular, the mechanism of tin whisker growth, as a solid-solid whisker growth phenomenon, has been a topic of considerable interest ever since the phenomenon was first found in 1951.
In the past, the tin whisker phenomenon was mainly reported to occur in tin plating.1-5 But recently, whiskers were also observed on the surface of bulk tin-based solders doped with rare-earth elements (RE).6,7 It is interesting that, Jiang and Xian,6 and Chuang et al.,7 reported that whiskers only grew from Sn-RE intermetallic compounds (IMCs) in the solder, whereas no whiskers were found on the Sn matrix. To explain the phenomenon of spontaneous whisker growth from a bulk Sn-based solder, an oxidation reaction between Sn-RE IMC and oxygen in air was hypothesized.6,7 According to this explanation, the decomposition of the Sn-RE IMC by oxidation is the crucial step, by which nascent Sn atoms are released for the whisker growth.6 However, in recent research, it was observed that the whisker growth rate from a Sn-RE IMC was sometimes so widely variable that it appeared to be dependent upon the weather on the day when the experiments were carried out. This implies that traces of water vapor in the air could have a significant part in the process of...