Fabrication of a thin, flexible chip package using liquid crystal polymers

Abstract

Thin, flexible packaging of integrated circuits (ICs) is essential for next-generation implantable devices, where extreme miniaturisation must be achieved without compromising reliability. This work presents a fabrication process for ultrathin chip packages based on liquid crystal polymer (LCP), selected for its biocompatibility, chemical stability, and barrier properties. Dies thinned to 30 𝜇 m were embedded into laser-skived cavities within a high- and low-temperature LCP stack using vacuum lamination. Electrical access was achieved using a hybrid picosecond-laser and reactive ion etching (RIE) via process, followed by metallisation and fan-out patterning. The approach was validated using PTCE daisy-chain structures and MSP430 microcontrollers. Across 11.704 vias, all were electrically functional with negligible resistance contribution. Of 16 encapsulated MSP430 devices, 62.5% remained programmable. Assembly on flexible substrates yielded high pad-level connectivity (96.8% PTCE, 99.1% MSP430) and 75% functional yield. Full LCP encapsulation was demonstrated as a proof of concept, confirming the feasibility of this scalable ultrathin packaging approach.