Definition

FR-4 (Flame Retardant 4) is the most common PCB laminate material, consisting of woven fiberglass cloth impregnated with epoxy resin. Standard FR-4 has a glass transition temperature (Tg) of 130-140°C, dielectric constant (Dk) of 4.2-4.5, and dissipation factor (Df) of 0.02. High-Tg versions (170-180°C) are used for lead-free assembly. FR-4 is cost-effective but has limitations for high-frequency (>3 GHz) and high-reliability applications due to higher losses and moisture absorption.