Programmable interposers for connecting integrated circuits, methods for programming programmable interposers, and integrated circuit packaging are provided. The programmable interposers are electrically reconfigurable to allow custom system-in-package (SiP) operation and configuration, field configurability, and functional obfuscation for secure integrated circuits fabricated in non-trusted environments. The programmable interposer includes, in one implementation, an interposer substrate and a programmable metallization cell (PMC) switch. The PMC switch is formed on the interposer substrate and is coupled between a signal input and a signal output. The PMC switch is electrically configurable between a high resistance state and a low resistance state.