Characterization of metal-polymer interaction forces by AFM for insert molding applications

Abstract

There is a growing interest in the overmolding of electronics with thermoplastics and the embedding of electronics in 3D printed parts. However long term device reliability requires good adhesion between the metallic surfaces of the electronic components and the overmolding polymer. In order to provide a guide to material selection, interaction forces between tin, a common electronics metallization and six commodity thermoplastics were studied. The force measurements were undertaken using atomic force microscopy (AFM) with probes functionalized with tin particles. The particles were attached to the probes by a novel method using a focused ion beam (FIB) instrument. Highly consistent cantilever deflections at pull-off were obtained, allowing the thermoplastics to be robustly ranked by strength of interaction with tin as: PC > PMMA > PBT > ABS > PS > PA 6. From consideration of possible contributions to the pull-off forces measured, it was concluded the data and the developed AFM tip functionalization technique are likely to be useful in materials selection for electronics overmolding with thermoplastics. The FIB functionalization technique may be useful in the wider context of investigations of other metal-polymer interaction forces, for example with alloys, where other methods of functionalization may be difficult to apply.