Selection of silane coupling agents for improved adhesion of polyurethane-based coatings filled with silicone rubber nanoparticles
Silane coupling agents have the ability to form a durable bond between organic and inorganic materials. The main goal of this paper is to investigate the effect of silane coupling agents on the adhesion behavior of polyurethane (PU) and polyurethane acrylate (PUA) on the tin solder pads. Adhesion behavior of PU and
PUA coatings filled with silicone rubber (SR), which makes these coatings more ductile and tougher, was also investigated. It was found that an isocyanate-based silane coupling agent provided excellent adhesion for PU and PU+SR based conformal coatings and an acrylic-based silane coupling agent for PUA and PUA+SR coatings on the tin surface. This was due to the reaction bond formation between the silane coupling agent and the coating. Hence, the selection of silane coupling agents with organofunctional group similar to the coating material is crucial to improve the adhesion properties of the coating.
Increased usage of pure tin (Sn) or Sn-rich alloy in Pb-free electronics results in putting more risk for the spontaneous growth of tin-whiskers. These whiskers can be mitigated by applying a conformal coating over the metal surface. Of all the material properties, adhesion strength of the conformal coating over the tin surface is crucial in mitigating the growth of tin whiskers. But the adhesion between dissimilar materials such as conformal coating (organic) and tin (inorganic) is often challenging.