Definition

Isola FR408 and FR408HR are high-Tg laminates with lower Dk/Df than standard high-Tg FR-4, bridging the gap between commodity FR-4 and premium low-loss materials. FR408 offers Dk 3.66, Df 0.012, Tg 180°C, and Td 360°C. FR408HR improves further to Dk 3.65, Df 0.0095, and Tg 190°C. Both provide T260 exceeding 60 minutes for robust lead-free processing. The lower Dk (vs. 4.0+ for standard high-Tg) means narrower traces for 50Ω impedance, potentially saving a layer. Choose FR408/FR408HR for 10 Gbps designs where Megtron would be overkill but standard FR-4 causes marginal eye diagrams. Cost positions between standard high-Tg and Megtron 4.