Wettability of molten Sn-Bi-Cu solder on Cu substrate

摘要

The wetting behavior of a new Sn-Bi-Cu Pb-free solder on Cu substrate was investigated by sessile drop method under an Ar-H_2 flow in the temperature range from 493 K to 623 K. The contact angle curves tested at 548 K and 623 K are found to fit exponential rule very well. However, the contact angle curve tested under 493 K is not well consistent with exponential rule, for which the spreading course may be classified into three stages. Equilibrium contact angles between Sn-Bi-Cu solder and Cu substrate decrease monotonously with the increase in temperature, which are 28°, 24° and 18° at 493 K, 548 K and 623 K, respectively. The results show that 69.5Sn-30Bi-0.5Cu exhibits good wettability on Cu substrate. Intermetallics formed at the 69.5Sn-30Bi-0.5Cu/Cu interface are identified as Cu_6Sn_5 adjacent to the solder and Cu_3Sn adjacent to the Cu substrate, respectively. Formation of intermetallic seems to improve strong wetting of the substrate by the solder.