Issue link: https://resources.pcb.cadence.com/i/1541046
36. Designing for Effective Test Point Access and Coverage How To Implement 1. Identify key signals and nets for access: f List all power rails, ground, reset, oscillator/clock lines, and communication buses needing test or debug access. f Include analog inputs/outputs, voltage references, and any "must-measure" signals for board validation or compliance testing. 2. Select appropriate test point styles: f Use dedicated test point components (small pads with solder mask openings), test hooks, or through-hole loops for standard probes. f For high-density boards, use "flying probe" compatible pads or accessible via-in-pad where needed. 3. Position test points for maximum accessibility: f Place test points on the board's top side when possible and away from tall components or mechanical obstacles. f Maintain a minimum clearance (≥1.5 mm or 60 mil) around each point for probe access; more if hand probing is expected. f For an automated test (In Circuit Test (ICT) or bed-of-nails), position test points on a grid matching the fixture's pinout. 4. Label and document each test point clearly: f Assign test point reference designators (TP1, TP2, etc.) and clearly indicate their associated nets in both schematic and silkscreen. f Include a test point legend in the assembly and test documentation, with location, function, and reference signal. 5. Avoid introducing stubs or signal degradation: f For high-speed or sensitive signals, design test points at endpoints (not mid-trace) or use high-impedance probe pads. f Minimize trace length and avoid branching from the main signal path; use series damping resistors if required. 6. Plan for programming and field updates: f Include dedicated test/programming headers or pads for firmware, boundary scan (JTAG), or configuration interfaces. f For secure designs, place programming pads in unpopulated or "hidden" areas if field updates are not intended. 7. Verify access and usability: f Use a 3D viewer to check for physical probe access. f Confirm automated test fixture compatibility and coverage with your Contract Manufacturer or test team before layout sign-off. Common Pitfalls, Their Impact, and How to Avoid Them Common Pitfall How to Avoid it Forgetting required signals Omitting key nets can make debugging or rework nearly impos- sible – Maintain a checklist of critical nets for test and debug. Placing test points under tall or crowded parts Limits access and increases risk of damage during probing – Plan component placement and use 3D visualization to confirm probe access. Creating signal stubs or loading sensitive lines Degrades signal integrity or intro- duces test-time failures – Use series damping resistors if necessary. Inadequate labeling or documentation Makes finding or identifying test points time-consuming and error- prone – Clearly label all test points in silkscreen and include test point legend in documentation.