A joint between an insulative sidewall of a medical electrical lead subassembly and an underlying fluoropolymer layer includes an interfacial layer. A first section of the interfacial layer is bonded to the fluoropolymer layer and is formed by a thermoplastic fluoropolymer； a second section of the interfacial layer extends adjacent the first section and is bonded to the insulative sidewall. The insulative sidewall, of the subassembly, and the second section, of the interfacial layer, are each formed from a material that is not a fluoropolymer. A recess is formed in the first section of the interfacial layer and the second section of the interfacial layer extends within the recess.
