FR-4
What Is FR-4?
FR-4 (Flame Retardant 4) is the most common base material used in printed circuit board manufacturing. It consists of woven fiberglass cloth impregnated with an epoxy resin binder, forming a rigid, flame-retardant laminate with good electrical insulation properties. FR-4 has been the industry-standard PCB substrate for decades due to its favorable combination of mechanical strength, thermal stability, moisture resistance, and affordability. The vast majority of consumer electronics, industrial controls, and computing hardware use FR-4-based circuit boards.
Key electrical properties of FR-4 include a dielectric constant (Dk) of approximately 4.2 to 4.5 at 1 GHz and a dissipation factor (Df) of around 0.02. While adequate for many applications, these properties become limiting at very high frequencies where signal loss through the substrate becomes significant. For designs operating at multi-gigabit data rates or above 10 GHz, engineers often select low-loss materials like Megtron 6, Rogers, or Isola laminate systems that offer lower Dk and Df values at the expense of higher material cost.
Material Selection in Physics-Driven Layout
The choice of PCB material directly affects impedance calculations, signal loss budgets, and layer stackup design. Physics-driven AI layout tools can incorporate material properties into their generation algorithms, ensuring that trace geometries and stackup configurations are optimized for the specific laminate being used. When engineers want to evaluate whether a design can be implemented on standard FR-4 or requires a higher-performance substrate, AI-generated layout candidates across different material options provide concrete data for that decision — replacing rough estimates with actual routed results.






