Measurement of high-frequency dielectric stability in paper substrates with homogeneity mapping

Paper is attracting renewed interest as a sustainable substrate for high-frequency electronics, yet comparative, reliability-aware dielectric data remain scarce. We report a systematic assessment of seven commercial paper-based substrates—coated papers (Novatech, Terraprint, Astralux), fiberboards (Cupforma 184/214), and aramid papers (Nomex 410, SynTherm® YT510 60/250 µm), plus an eco board (EraCup)—combining split-cylinder resonator measurements near 10 GHz with highly accelerated stress tests (4000 thermal-shock cycles from −40°C to 125°C and 1920 h at 85°C/85% RH), and spatial homogeneity mapping before/after stress. Measurements were repeated at fixed locations (100-cycle / 48-h intervals) with an uncertainty of ±1% for εᵣ' and ±1×10⁻⁴ for tanδ. Aramid papers showed the tightest stability windows (εᵣ' ≈ 2.91–3.02; tanδ ≈ 0.012–0.020) under both stresses, consistent with their low hygroscopicity and thermally robust meta-aramid network. EraCup maintained an ultra-low εᵣ' ≈ 1.05–1.07 with low loss and minimal drift. Coated papers exhibited early-stage relaxation (tanδ drop) and moderate εᵣ' drift, while Cupforma displayed abrupt state changes (step-ups in εᵣ' and tanδ) consistent with possible barrier or interfacial degradation. Homogeneity maps quantified that aramids and EraCup remain spatially uniform, whereas Cupforma develops pronounced gradients after stress. These results translate into practical design guidance for sustainable GHz-range applications: aramids for precision/narrowband circuits, EraCup for low-εᵣ eco-designs, coated papers only with conditioning/encapsulation, and Cupforma avoided for tight-tolerance GHz-range applications unless fully sealed.