Low-Frequency Dielectric Tests of PLA/Flax Sustainable and Degradable PCB Substrates

To pursue a move towards sustainability in electronics manufacturing, recently we presented a biodegradable printed circuit board (PCB) alternative substrate, where polylactic-acid (PLA) and flax-textile reinforcement forms a composite with flame retardancy. The novel PLA/Flax substrate is capable of being a core material for double-sided PCB designs. This paper investigates into the lowfrequency ($1 \mathrm{~Hz}-500 \mathrm{kHz}$) dielectric capabilities of the substrates with Omicron Dirana dielectric spectrometer and Wayne-Kerr 6430A impedance analyzer. For the experimental, two generations of one-sided substrates were measured, where the top side was covered with $35 \mu \mathrm{~m}$ Cu layer with PLA foil and polypropylene (PP) foil (A and B groups consequentially) serving as bonding layer between the composite and the Cu. It was found that The PLA/Flax substrates have high permittivity values at low frequencies, while at high frequencies, the permittivity is lower than that of the most commonly used FR4. Moreover, the additional PP layer caused a further increase in the relative permittivity. The tan $\delta$ of PLA/PLA samples was higher over the investigated frequency range. This high value of relative permittivity and dielectric loss at low frequency is connected to interfacial polarization originated from the structure of PLA/Flax samples. A local peak of $\tan \delta$ was observed at 500 Hz on PLA/Flax samples indicating the presence of orientation polarization.