Introducing the characteristics of metal whiskers and suppression techniques in tin alloy coatings
The document explains the nature of whiskers, which are microscopic crystal filaments that grow spontaneously from metal surfaces like Tin, Silver, and Zinc. It identifies internal compressive stresses as the primary cause of this growth and discusses how factors such as co-deposited impurities, atomic defects, and thermal stress contribute to the problem. The text highlights the industry's shift from Lead-bearing alloys to pure Tin plating due to environmental regulations, necessitating new strategies to prevent whisker formation.
| Maximum whisker length for risk-free coating | 50um |
|---|---|
| Post-bake temperature | 150°C |
| Post-bake duration | 1 hour |
Whisker growth is mainly due to internal compressive stresses near the metal surface that reach a critical level.
Internal stress can be reduced by applying a 1-hour 150°C bake within 24 hours of plating.