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Design rules
The Design for Test Analysis step runs an automated set of checks against your test point selection, guide pins, and board geometry. Each check reports pass, warning, or fail:
- Fail (critical) — a problem that prevents manufacturing a reliable fixture. Resolve it before ordering.
- Warning — the fixture can be built, but addressing the issue improves reliability or reduces cost.
- Pass — no action needed.
Threshold rules
These checks compare each test point against minimum and recommended values. A value below the recommended threshold raises a warning; below the minimum raises a critical issue.
| Rule | Recommended | Minimum | What it catches |
|---|---|---|---|
| Pad diameter | ≥ 0.8 mm | 0.6 mm | Pads too small to be reliably probed — applies to every test point's pad diameter, SMD or through-hole (hole size itself is not checked) |
| Test point to test point clearance | ≥ 1.9 mm | 0.99 mm | Probes too close together for receptacle spacing (same side only) |
| Guide pin to guide pin edge clearance | ≥ 1.5 mm | 1.0 mm | Guide pin holes too close to each other |
| Guide pin to test point clearance | ≥ 2.54 mm + pin radius | 1.9 mm + pin radius | Test points too close to a guide pin to probe safely |
These are the default thresholds. Test point distances are measured center to center. Guide-pin-to-guide-pin clearance is measured edge to edge (center distance minus both hole radii), and the guide-pin-to-test-point thresholds add the guide pin hole radius to the base values above — for a default 2.0 mm guide pin hole, the effective center-to-center thresholds are 3.54 mm (recommended) and 2.9 mm (minimum). All distances are rounded to two decimal places, matching what the UI displays.
Configuration checks
| Check | Result |
|---|---|
| Has test points | Fails if no test points are selected |
| Locating configured | Fails unless you use cradle locating or select at least 2 guide pins |
| Guide pins not collinear | Warns when 3+ guide pins sit on one line — the board may rotate |
| Probe side selected | Fails if no primary probe side is chosen |
Geometry checks
| Check | Result |
|---|---|
| Board fits cartridge | Checks your board outline against available cartridge sizes (either orientation) |
| Single-sided probing | Warns when test points are on both sides — requires a dual-sided fixture |
| Test point edge clearance | Warns when test points are within 3 mm of the board edge |
| Guide pin edge clearance | Warns when guide pins are within 3 mm of the board edge |
| Net coverage | Warns when selected test points cover less than 95% of nets |
Mechanical checks
| Check | Result |
|---|---|
| Has pressure pins | For boards larger than 25 cm²: warns when no pressure pins are placed (FixturFab will distribute a suggested set during fixture design) |
| Pressure pin distribution | Warns when pins are unevenly placed — center of pressure more than 25% off the board center, or more than one empty board quadrant |
| Pressure pin to test point clearance | Fails when a pressure pin lands within 2 mm of a test point |
| Total probe force | Informational — estimates 1–2 N per probe so you can size hold-down requirements |
| Force balance | Warns when the probe force center is more than 25% off the board center — may cause uneven contact |
If you have questions about a specific result, reach out at hello@fixturfab.com or use the chat inside Studio.