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Signal Integrity and High Speed Digital High Speed PCB Design Informational

How does the launch connector affect the signal integrity of a high speed PCB test coupon?

How does the launch connector affect the signal integrity of a high speed PCB test coupon? The launch connector is the transition from the test instrument (VNA) to the PCB trace, and its quality determines the accuracy of the PCB channel measurement: (1) Why the launch matters: the launch connector + pad structure creates an impedance discontinuity at the start and end of the trace. Any reflection from the launch contaminates the S-parameter measurement of the trace itself. If the launch loss is significant: it adds to the measured trace loss, making the trace appear lossier than it actually is. De-embedding (mathematically removing the launch) is required for accurate trace characterization. (2) Common launch types: SMA/2.92 mm edge launch: the connector is soldered to a pad at the PCB edge. Quality: S11 = -15 to -25 dB at 20 GHz (depending on the pad design). Frequency: SMA to 18 GHz, 2.92 mm to 40 GHz, 2.4 mm to 50 GHz. The most common launch for PCB test coupons. GSSG probes: high-frequency probes (FormFactor, GGB) that make contact with pads on the PCB surface. Quality: S11 < -20 dB to 40+ GHz (better than SMA edge launch). Cost: $5,000-15,000 per probe + probe station. Used for precision measurements and high-frequency (> 40 GHz) PCB characterization. Solder-down connectors (press-fit): permanently mounted on the PCB. Better impedance match than edge launch (the connector is designed for the specific PCB stackup). Used in production but not ideal for test coupons (not reusable). (3) De-embedding: to extract the true PCB trace performance: measure the complete channel (launch + trace + launch). Measure or simulate the launch S-parameters separately. Subtract the launch S-parameters from the total measurement (de-embedding). Methods: 2x-thru de-embedding (measure a thru coupon with the same launches and no trace; the launch is automatically removed). AFR (Automatic Fixture Removal, built into many VNA firmware). 3D simulation of the launch structure (predict the launch S-parameters). (4) Best practices for test coupon launches: follow the connector manufacturer reference design (pad dimensions, anti-pad, ground via placement). Use multiple ground vias close to the connector signal pad (within 10-15 mil). Taper the trace from the connector pad width to the trace width over 50-100 mil (gradual impedance transition). Always de-embed the launches when reporting trace loss.
Category: Signal Integrity and High Speed Digital
Updated: April 2026
Product Tie-In: PCB Materials, Connectors, Test Equipment

PCB Test Coupon Launch

The launch connector is often the limiting factor in high-frequency PCB measurement accuracy, and a poor launch can make a good trace appear bad.

  • Performance verification: confirm specifications against the application requirements before finalizing the design
  • Environmental factors: temperature range, humidity, and vibration affect long-term reliability and parameter drift
  • Cost vs. performance: evaluate whether the application demands premium components or standard commercial grades
Common Questions

Frequently Asked Questions

How far can I trust my edge launch measurement?

A well-designed SMA edge launch: reliable to 15-18 GHz. 2.92 mm (K connector) edge launch: reliable to 35-40 GHz. 2.4 mm edge launch: reliable to 45-50 GHz. Beyond these limits: the launch becomes too lossy and reflective for useful measurement. For higher frequencies: use GSSG probes or waveguide-to-microstrip transitions.

How many test coupons should I include on a PCB panel?

Minimum: one coupon per impedance class (single-ended 50 ohm, differential 100 ohm) per signal layer. Recommended: 3-5 coupons per Class/layer (allows statistical analysis). Include: a thru coupon (for de-embedding), a long trace (6-12 inches for loss measurement), and a short trace (1-2 inches as a reference). Place coupons at the panel edge and center (to check uniformity across the panel).

What is the cost of a GSSG probe measurement?

Probe station + probes: $50,000-200,000 (one-time purchase). Per-measurement cost: minimal (probes are reusable). For labs that do not own probes: outsource to a PCB characterization service (e.g., Wild River Technology, Isola). Cost: $500-2,000 per board measured. The probe measurement provides the highest accuracy and is the reference for validating edge launch measurement quality.

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Glossary

Related Terms

Noise Figure → LNA → Noise Floor → S-Parameters → Insertion Loss → Return Loss →
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