Abstract
Wetting of Cu and Sn-Cu intermetallics (IMCs) by molten Sn is the basic process for soldering, and it was studied by using the sessile drop method under high vacuum in this work. The IMCs substrates with a thin Au coating have better wettability than Sn/Cu system for all experimental temperatures. The oxide film on the surface of the metallic substrate is the key factor for wetting. Using the thin passivation Au film can be a method to enhance the wettability and control the thickness of the IMC layer. The precipitation reaction of IMC may be a driving force for spreading. However, when the substrate is without the effect of the oxide film, the precipitation of the IMC layer would never be a driving force for spreading due to the good intrinsic wettability of Sn/Cu. When the substrate is covered by a thin oxide film, the reaction of Sn with Cu2O (both of Sn/Cu system and Sn/IMCs system) can be a driving force for spreading.
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