Reliability and ageing characteristics of polyamic acid and product polyimide films for advanced space systems

Polyamic acid resin, the polyimide film (PIF) precursor, is synthesized from diamino diphenyl ether and an aryl tetracarboxylic acid. When processed as a 10% solution in dimethylacetamide (DMAc), it is prone to self-condensation if not stored under controlled conditions. The first phase of this study examines the feasibility of using polyamic acid resin for up to 12 months to process space‑grade PI films. The resin was maintained at a controlled temperature of −10 °C, and its solid content and inherent viscosity were periodically monitored. Over 12 months, the inherent viscosity of the resin decreased by 13.6%, while the solid content remained unchanged. PI films were then produced via solution casting at regular intervals using aged polyamic acid resin. Mechanical, electrical, outgassing, and thermal stability evaluations revealed a 14% reduction in tensile strength and increased surface resistivity for films made from 12‑month‑aged resin. Although the outgassing properties declined, the thermal stability remained relatively stable. The second phase focused on the long‑term aging behavior of plain polyimide films (PPIF, 50 µm thickness) and copper‑clad PI films (CCPIFs) stored for 12 and 10 years, respectively. Aging led to a gradual reduction in tensile strength and elongation, alongside an increase in outgassing characteristics. This work provides rare and systematic long‑term aging data for polyamic acid resin and PI films, filling a significant literature gap. The results offer critical insights for improving storage protocols, predicting property degradation, and ensuring the durability and reliability of polyimide materials in extended or delayed aerospace missions.