Video Router PCB Design Guide: Specs, Impedance Rules, and Troubleshooting

High-performance video distribution relies heavily on the physical layer integrity of the Video Router PCB. Whether designing for 12G-SDI broadcast matrices or HDMI 2.1 switching, the printed circuit board is not just a carrier; it is an active component in the signal chain. A Video Router PCB must manage precise impedance control, minimize insertion loss, and handle the thermal density of large crosspoint switches. This guide provides the technical specifications, implementation steps, and troubleshooting protocols required to manufacture reliable video routing hardware.

Quick Answer (30 seconds)

Designing a Video Router PCB requires strict adherence to signal integrity rules to prevent jitter and data loss.

Impedance Control: Maintain 75Ω single-ended impedance for SDI traces and 100Ω differential impedance for HDMI/DisplayPort. Tolerance must be within ±5% (or ±7% for lower tiers).
Material Selection: For 12G-SDI or higher, standard FR4 is often insufficient due to dielectric loss. Use low-loss materials like Panasonic Megtron 6 or Rogers RO4350B.
Layer Stackup: Use a symmetrical stackup with ground planes adjacent to every high-speed signal layer to provide a clear return path and shield against crosstalk.
Connector Launch: The BNC or HDMI connector footprint is the most common failure point. Optimize the anti-pad size and void the ground plane under the signal pad to match impedance.
Via Management: Back-drill all high-speed signal vias to remove stubs, which act as antennas and cause signal reflection at high frequencies.

When Video Router PCB applies (and when it doesn’t)

Understanding the specific use case ensures you do not over-engineer a simple board or under-spec a critical system.

When to use a specialized Video Router PCB design:

Broadcast Matrices: Large-scale switching (e.g., 128x128) using 3G-SDI, 6G-SDI, or 12G-SDI standards where return loss is critical.
Live Event Processors: Equipment requiring near-zero latency switching between multiple camera feeds and projector outputs.
Medical Imaging: High-resolution, uncompressed video distribution where signal artifacts cannot be tolerated.
Surveillance Hubs: Systems aggregating dozens of feeds where crosstalk between channels must be minimized.
Hybrid Systems: Designs integrating a Video Matrix PCB with an Audio Router PCB on the same substrate.

When standard PCB practices suffice (specialized Video Router rules may not apply):

Low-Bandwidth Analog: Legacy composite video (CVBS) operating at low frequencies does not require ultra-low-loss materials.
Short Point-to-Point Links: If the trace length is less than 1 inch (25mm), transmission line effects are negligible.
Compressed IP Streams: If the video is already packetized (Ethernet), standard high-speed digital design rules apply, rather than specific video RF rules.
Low-Resolution Signage: Static displays where minor jitter or signal degradation is imperceptible to the viewer.

Rules & specifications

To ensure signal integrity on a Video Router PCB, specific physical parameters must be met. The following table outlines critical design rules.

Rule	Recommended Value/Range	Why it matters	How to verify	If ignored
Trace Impedance (SDI)	75Ω ±5%	Matches BNC/cabling impedance to prevent reflections.	TDR (Time Domain Reflectometry) simulation.	High Return Loss; signal drops out.
Trace Impedance (HDMI)	100Ω Diff ±10%	Standard for TMDS/FRL signaling.	Impedance calculator during stackup design.	Data errors; "sparkles" on screen.
Trace Width	> 6 mil (0.15mm)	Wider traces reduce skin effect losses at high frequencies.	Gerber viewer measurement.	Increased insertion loss; reduced cable reach.
Pair Length Matching	< 5 mil (0.127mm)	Prevents intra-pair skew (timing mismatch between P/N).	CAD Design Rule Check (DRC).	Mode conversion; EMI radiation.
Ground Reference	Unbroken Plane	Provides return current path; defines impedance.	Visual inspection of internal layers.	Impedance discontinuity; massive crosstalk.
Via Stub Length	< 10 mil (0.25mm)	Stubs act as resonant filters, attenuating specific frequencies.	Back-drill depth chart.	Signal notches at high frequencies (e.g., 6GHz).
Dielectric Constant (Dk)	3.0 - 3.7 (Stable)	Lower Dk allows wider traces for the same impedance; stability ensures consistency.	Material datasheet review.	Impedance varies across the board.
Loss Tangent (Df)	< 0.004	Minimizes signal attenuation over long trace runs.	Select High-Speed Laminate.	Signal too weak at the receiver; requires re-clocking.
Connector Anti-pad	Optimized per stackup	Controls capacitance at the connector launch point.	3D Electromagnetic Field Solver.	huge reflection at the input/output port.
Crosstalk Spacing	> 3W (3x trace width)	Prevents signal coupling between adjacent video channels.	DRC settings.	Ghosting or interference between channels.

Implementation steps

Once the specifications are defined, the manufacturing process for a Video Router PCB follows a strict sequence to preserve signal integrity.

Stackup Definition & Material Selection
- Action: Choose a material like Megtron 6 or Isola Tachyon. Define layer counts to ensure every signal layer has an adjacent ground reference.
- Parameter: Core thickness determined by desired trace width for 75Ω.
- Check: Use an Impedance Calculator to validate trace widths before routing.
Component Placement (Signal Flow)
- Action: Place BNC/HDMI connectors on the edge. Place equalizers (EQ) and cable drivers (CD) as close to connectors as possible.
- Parameter: Distance < 10mm ideally.
- Check: Ensure linear signal flow to avoid U-turns or meanders.
BGA Fanout & Breakout
- Action: Route signals out of the central crosspoint switch or FPGA.
- Parameter: Use "dog-bone" or via-in-pad (VIPPO) if pitch is tight (< 0.8mm).
- Check: Verify that fanout vias do not cut off the ground return path for inner signals.
Critical Routing (High-Speed)
- Action: Route video signals first. Avoid changing layers. If layer change is necessary, use ground transfer vias next to the signal via.
- Parameter: Bend angle = curved or 2 x 45°, never 90°.
- Check: Run length matching DRC.
Power Integrity & Plane Splits
- Action: Create power islands for different voltage rails (1.2V, 1.8V, 3.3V).
- Parameter: Keep power planes away from high-speed signal gaps.
- Check: Ensure no high-speed trace crosses a split in the reference plane.
Back-Drill Specification
- Action: Identify vias carrying signals > 3Gbps. Mark them for back-drilling.
- Parameter: Remaining stub < 8-10 mil.
- Check: Verify drill files clearly indicate which vias are back-drilled.
DFM & Solder Mask
- Action: Open solder mask on high-speed traces if required (rare) or ensure uniform coverage.
- Parameter: Solder mask Dk affects impedance (usually lowers it by 2-3 ohms).
- Check: Review DFM Guidelines to ensure manufacturability of tight tolerances.
Final Fabrication Data Generation
- Action: Export ODB++ or Gerbers.
- Parameter: Include impedance table in the fabrication drawing.
- Check: Confirm material notes specify "Do Not Substitute" without approval.

Failure modes & troubleshooting

Even with robust design, issues can arise during testing. Here is how to troubleshoot a failing Video Router PCB.

Symptom: High Return Loss (Signal Reflection)
- Cause: Impedance mismatch at the BNC connector or via.
- Check: Use TDR to locate the exact distance of the discontinuity.
- Fix: Adjust the anti-pad size on the connector footprint in the next revision.
- Prevention: Simulate connector launches using 3D field solvers.
Symptom: Bit Errors ("Sparkles")
- Cause: Inter-symbol interference (ISI) or excessive jitter.
- Check: Analyze the Eye Diagram. Look for a closed eye vertically or horizontally.
- Fix: Tune the Equalizer (EQ) settings on the receiver chip.
- Prevention: Use lower-loss materials to preserve high-frequency harmonics.
Symptom: Channel-to-Channel Crosstalk
- Cause: Traces routed too closely or shared return paths.
- Check: Inject signal on Channel A, measure output on Channel B (should be noise floor).
- Fix: Cannot fix on board; requires re-spin with increased spacing or ground stitching.
- Prevention: Follow the 3W rule (spacing = 3x trace width).
Symptom: Video Dropouts (Black Screen)
- Cause: Signal amplitude below receiver threshold or PLL unlock.
- Check: Measure signal amplitude at the receiver input.
- Fix: Increase drive strength on the transmitter; check for cold solder joints on BNCs.
- Prevention: Verify maximum trace length calculations against material loss budget.
Symptom: EMI/EMC Failure
- Cause: Return path discontinuity or unshielded connectors.
- Check: Near-field probe scanning over the PCB edges.
- Fix: Add shielding cans; improve chassis grounding.
- Prevention: Stitch ground vias around the board perimeter (Faraday cage).
Symptom: Overheating Crosspoint Switch
- Cause: Inadequate thermal dissipation for the FPGA/ASIC.
- Check: Thermal camera imaging during full-load operation.
- Fix: Add heatsink or fan; improve airflow.
- Prevention: Use thermal vias under the BGA connected to internal ground planes.

Design decisions

Troubleshooting often reveals that the root cause lies in early architectural decisions. When planning a Video Router PCB, the integration of related subsystems influences the layout strategy.

Integration with Audio: Many systems are hybrid. An Audio Router PCB section may handle AES/EBU or Dante streams. While audio frequencies are lower, digital audio clocks are sensitive to the high-frequency noise generated by video circuits. Isolate the video matrix ground from the analog audio ground, connecting them at a single "star" point near the power supply to prevent ground loops.

Video Processing Blocks: If the board includes a Video Processor PCB section (e.g., scalers, color correctors), the memory interface (DDR4/DDR5) becomes a critical noise source. Place the processor and its memory far from the sensitive analog inputs of the video router matrix.

Modular vs. Monolithic: For large matrices (e.g., 64x64), a modular approach using a backplane and daughter cards is common. This turns the backplane into a massive Video Matrix PCB that is essentially all routing. In this case, connector density and mechanical alignment become the primary challenges alongside signal integrity.

FAQ

Q: What is the difference between designing for 3G-SDI and 12G-SDI? A: 3G-SDI (3 Gbps) can often be routed on standard FR4 with careful design. 12G-SDI (12 Gbps) almost always requires high-speed materials (like Megtron 6) and back-drilling to prevent signal loss and jitter.

Q: Can I use standard FR4 for a Video Router PCB? A: Only for low speeds (SD-SDI, HD-SDI) or very short traces. For 4K/8K video, the dielectric loss of FR4 is too high, causing the signal to degrade before reaching the receiver.

Q: Why is 75Ω impedance used for video instead of 50Ω? A: 75Ω offers lower attenuation (signal loss) over long cable runs compared to 50Ω, which is optimized for power handling. Video distribution prioritizes signal voltage preservation.

Q: How do I handle BGA breakouts for large video crosspoint switches? A: Use a "dog-bone" fanout for standard pitch. For fine pitch, use Via-in-Pad Plated Over (VIPPO). Ensure that the breakout routing does not perforate the ground plane so badly that it breaks the return path.

Q: What is the impact of fiber weave effect on video signals? A: At high data rates, the glass weave in the PCB material can cause skew if one leg of a differential pair runs over glass and the other over resin. Use "spread glass" materials or route traces at a slight angle (zigzag) to mitigate this.

Q: Do I need blind and buried vias? A: For high-density Video Matrix PCB designs, blind/buried vias help route signals without consuming space on all layers, but they increase manufacturing cost significantly. Through-hole with back-drilling is a cost-effective alternative.

Q: How does a Video Converter PCB differ from a Router? A: A Video Converter PCB focuses on changing formats (e.g., HDMI to SDI) and usually has fewer I/O ports but more processing logic. A Router focuses on switching many inputs to many outputs with minimal processing.

Q: What is the lead time for a high-speed Video Router PCB? A: Standard lead time is 8-12 days. If special materials (Rogers/Megtron) are not in stock, add 1-2 weeks. Check with APTPCB (APTPCB PCB Factory) for current stock status.

Q: How do I verify the impedance of the manufactured board? A: Request an Impedance Control Report or Coupon Test Report from the manufacturer. This uses a test coupon on the panel margin to verify the stackup meets the TDR requirements.

Q: What surface finish is best for video PCBs? A: ENIG (Electroless Nickel Immersion Gold) is preferred. It provides a flat surface for fine-pitch BGAs and does not oxidize like OSP, ensuring reliable high-frequency connections.

Glossary (key terms)

Term	Definition
SDI (Serial Digital Interface)	A standard for transmitting uncompressed digital video over coaxial cable (75Ω).
Return Loss	The ratio of reflected signal to incident signal; a measure of impedance matching quality.
Insertion Loss	The loss of signal power as it travels through the PCB trace and components.
Jitter	The deviation of a signal pulse from its ideal timing location; causes bit errors.
Eye Diagram	An oscilloscope display that overlays multiple bits to visualize signal quality and margins.
Crosspoint Switch	The central IC in a router that connects any input to any output.
Re-clocker	A circuit that recovers the clock from the video signal to remove jitter before re-transmitting.
Differential Impedance	The impedance between two conductors in a pair (e.g., 100Ω for HDMI).
Skew	The time difference between the arrival of two signals (e.g., Positive and Negative legs of a pair).
TDR (Time Domain Reflectometry)	A measurement technique used to determine the impedance profile of a trace.
Back-drilling	The process of drilling out the unused portion of a plated through-hole (via stub) to improve signal integrity.
EQ (Equalizer)	A circuit that boosts high frequencies to compensate for PCB and cable losses.

Conclusion

Designing a Video Router PCB is a balance of material science, precise geometry, and rigorous testing. From selecting the right low-loss laminate to back-drilling vias for 12G-SDI compliance, every decision impacts the final video quality. Ignoring these rules leads to black screens and signal artifacts that are costly to debug.

For engineers ready to move from prototype to production, APTPCB offers the specialized manufacturing capabilities required for high-speed video hardware. Whether you need controlled impedance verification or access to advanced materials like Megtron 6, we ensure your design performs as intended.

Request a DFM Review and Quote