A Test Point Carrier Board (TPCB) is a custom PCB designed to route test probes to any connector, circuitry, or instrumentation needed to implement a test. TPCBs simplify fixture wiring by consolidating signal routing on a manufactured board rather than individual wires.
Design Process#
The typical TPCB design workflow:
- Download design assets specific to your fixture type (outlines, mounting holes)
- Create schematic defining signal routing from test points to connectors
- Initial layout with probe footprints positioned to match DUT test points
- Submit for review — FixturFab validates mechanical fit (STEP files + gerbers)
- Route signals — Manual routing recommended for differential and sensitive signals
- Final fit confirmation — Verify alignment with fixture and DUT
- PCB fabrication — Order boards from your preferred manufacturer
- Assembly — Populate connectors and any active components
- Integration and QA — FixturFab integrates TPCB into fixture
Development vs. Production TPCBs#
Development TPCBs#
Use through-hole receptacle footprints:
- Footprints: R50-TH, R75-TH, R100-TH
- Receptacles solder into plated through-holes
- Simpler assembly, suitable for low volumes
- Manual wire connections where needed
Production TPCBs#
Employ SMD pads compatible with wireless receptacles:
- Footprint: R-WL (wireless)
- Receptacles interface via spring-loaded pins
- No soldering of receptacles required
- Sub-probe plate mounted with standoffs accommodates spring pin working stroke
Production fixtures use a sub-probe plate that positions the TPCB at the correct height for spring-loaded receptacle engagement.
Design Guidelines#
Test Point Placement#
- Position test points on the TPCB bottom side (facing the DUT)
- Place components on the TPCB top side (facing away from DUT)
- If probing the DUT's top surface, mirror the test point positions
Alignment Features#
- Include 2-3mm NPTH (Non-Plated Through Holes) in opposite corners
- Alignment holes prevent incorrect TPCB orientation during assembly
- Match hole positions to fixture mounting points
Receptacle Footprint Selection#
| Footprint | Type | Application |
|---|---|---|
| R50-TH | Through-hole, 50 mil | High-density development |
| R75-TH | Through-hole, 75 mil | Standard development |
| R100-TH | Through-hole, 100 mil | Wide-pitch development |
| R-WL | Wireless SMD | Production fixtures |
Signal Routing#
- Use manual routing for differential pairs
- Keep sensitive analog signals away from digital traces
- Provide adequate ground plane for signal integrity
- Consider controlled impedance for high-speed signals
Available Resources#
FixturFab provides DXF and PDF board outlines via Google Drive for:
- Development fixture (Dev, Dev XL)
- Dev Pro fixture (Dev Pro, Dev Pro XL)
- Ingun fixture models (MA11, MA12, MA13, etc.)
Contact FixturFab for access to current design resource packages.
Review Checklist#
Before fabrication, verify:
- Board outline matches fixture mounting area
- Mounting holes align with fixture
- Test point positions match DUT (mirrored correctly)
- Receptacle footprints appropriate for fixture type
- Connector placement accessible after fixture assembly
- Signal routing meets electrical requirements
Related Documentation#
- Selecting Probes — Probe selection for TPCB integration
- Receptacles Guide — Receptacle specifications
- DUT Presence Detection — Presence switch integration on TPCBs