Pre‐tinning and Flux Considerations on the Reliability of Solder Surfaces Available to Purchase

The kinetics of wetting were studied on several different prepared surfaces of copper (Cu) to simulate the microstructure observed in pre‐tinned Cu‐clad printed circuit boards. The results illustrate the effectiveness of pre‐tinning in maintaining the solderability of Cu surfaces. Pre‐tinning with Pb‐rich solder (95Pb‐5Sn) is particularly effective since solderability is preserved even after a relatively long ageing treatment. On the other hand, pre‐tinning with eutectic solder risks the loss of solderability during ageing or baking due to surface exposure of an ε‐phase intermetallic with poor wetting properties. The results also confirm the presence of carbon in pre‐tinned specimens due to the use of flux. The effect of carbon on solderability is not yet known.