The growing problem of electronic waste poses an environmental challenge due to petroleum-based materials and toxic metals. Recycling e-waste is complex and costly due to numerous components requiring separation. Using bio-based, biodegradable materials for printed circuit board (PCB) substrates simplifies PCB component separation and improves environmental impact [1]. Hornified cellulose fibrils are promising PCB substrates due to their mechanical properties, thermal stability, processability, and biodegradability [2]. Combining cellulose fibrils and lignin as lignocellulose nanofibrils (LCNF) further enhances material properties. LCNF are obtained from a lignin-rich pulp [3] by disintegration in a friction mill as an aqueous suspension. A dewatering process (Δp = up to 1500kN, ΔT = up to 120°C) transforms the LCNF into a rigid PCB substrate. The flexural strength of LCNF substrates is approx. 133 MPa with a flexural modulus of approx. 11 GPa (0%RH and 23°C). Humidity (50%RH, 85%RH) leads to a reduction in the strength of LCNF substrates due to the plasticizing property of water. However, the dimensions of the substrates are maintained. As the temperature rises to 100°C, the LCNF substrate initially loses weight due to moisture evaporation and complete decomposition of LCNF takes place at 258°C under N2. The thermal conductivity of the LCNF substrate of max. 0.302W/mK is comparable to that of epoxy glass fibre reinforced substrates (0.343W/mK). The electrical resistivity of the LCNF substrates is determined as ρ(0%RH) = 23.9×10³Ωcm and decreases under the influence of moisture. Finally, the LCNF substrate was integrated into a complete PCB with electronic components for a wired computer mouse. The circuit layout was produced using an inkjet printing process. The device housing was 3D printed using PLA/wood filament [4]. The functionality of the computer mouse demonstrates the readiness of LCNF substrates and points the way to sustainable eco-electronics.