Effect of Transient Thermal Profiles in Wave Soldering Processes on Connector Performance

Developing lead free connector products involves at least two distinct steps: removing the lead from the product and ensuring the product has sufficient thermal stability. Lead is most commonly found in terminal finishes and has been removed from most thermoplastic materials used in connectors. Ensuring sufficient thermal stability requires knowledge of the thermal excursions involved in soldering and how these excursions translate into product performance metrics. For reflow soldering, we know the maximum soldering temperatures will increase by 20 to 30 C. The magnitude of this change is not large, however, the temperature value, 260 C, exceeds the melt point of many engineering thermoplastics. Since the cost of these plastics typically scales with melt temperature, an increase in thermal requirements can mean a significant cost increase. In this paper we strive to understand the fundamental response of the plastics to the transient thermal excursions involved in wave soldering. FEM simulations demonstrate the thermal gradients that exist during these processes. These results can be used to understand the heat transfer and then to engineer the products to ensure reliability. Wave solder process simulation shows that the pin to plastic interface resides at a temperature very near to that of the solder. Connector terminals, made from copper based alloys, often have very high thermal diffusivities, increasing heat flow from the solder pot into the plastic. FEM results are compared to experimental results from lab and production manufactured testing of solderable interconnects. A test method for evaluating plastic performance in wave solder applications is proposed