Development and Validation of Tin-Whisker Growth Model and Accelerated Testing

Reliabilities of lead-free soldered assemblies and surface finishes are different from heritage tin-lead eutectic alloys when used in high-performance or long-lived military and aerospace applications. Single crystal, beta-tin whiskers have erupted spontaneously from surfaces of lead-free soldered and tin-plated circuits, causing electrical short circuits and component failures. The proposed work will involve systematic investigations of whisker growth in electronic materials to identify initiating and propagating mechanisms, quantitatively linked to physical stress state, temperature and crystallographic and impurity factors. The work will result in determinations of the effects of each of these factors, and development of a unifying growth model to account for them. The model will be validated against tin and other metals used in electronics that are prone to sprout electrically conductive single crystals. Using this model, TRI will develop a protocol to accelerate representative conditions that excite whisker growth mechanisms. A global solution to whisker growth in electronics will be forthcoming upon availability of this demonstrated growth model. TRI will rely on its metallurgical and materials experience to identify the most robust and least expensive solutions possible. We will develop and qualify an inexpensive tin whisker mitigation technique capable of rapid application using standard manufacturing practices.