PCB Selection in Automotive Millimeter-Wave Radar: High-Frequency Performance Optimization Tips for FPC/Rigid-Flex Boards
Date: 2025-08-26
Automotive millimeter-wave radar—critical for ADAS features like adaptive cruise control and collision avoidance—relies on PCBs to transmit high-frequency signals (76–81 GHz) with minimal loss. For tight spaces in radar modules, FPCs and rigid-flex boards are top choices—but their high-frequency performance needs careful tuning. Here are actionable optimization tips.
High-frequency signals fade fast in poor substrates. For FPCs, use polyimide with low dielectric loss (Df < 0.002 at 80 GHz)—like DuPont’s Kapton HN. It keeps signal attenuation low, even in the radar’s compact layout. Rigid-flex boards need matching rigid layers: choose FR-4 variants with ceramic fillers (e.g., Isola FR408HR) to align dielectric constants (Dk) between rigid and flexible parts, avoiding signal reflection.
Millimeter-wave signals are sensitive to noise. For FPCs, use microstrip lines with narrow trace widths (0.15–0.2 mm)—this reduces parasitic capacitance. Keep traces short: a 1mm longer trace can increase loss by 0.3 dB at 80 GHz. For rigid-flex boards, place high-frequency traces on flexible sections only when needed; rigid layers offer better stability for critical paths. Also, add ground planes close to signal traces (distance < 0.1mm) to shield against interference from nearby power lines.
Radar modules require 50Ω impedance for signal integrity. For FPCs, adjust trace width and substrate thickness: a 0.18mm trace on 0.125mm thick Kapton hits 50Ω. For rigid-flex boards, use laser drilling for vias (diameter < 0.3mm) to avoid impedance jumps—traditional drilling can widen holes, disrupting signal flow. Test impedance with a network analyzer post-production to catch deviations.
Real-World Win: Bosch’s latest radar modules use optimized rigid-flex boards. By pairing Kapton FPC layers with low-loss rigid substrates and 0.18mm microstrip lines, they cut signal loss by 20%—boosting radar detection range by 5 meters.
Poor PCB performance can make radar misdetect obstacles. With these tips, FPCs and rigid-flex boards deliver the reliability ADAS needs—while fitting in tight radar enclosures.
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