Custom test fixtures are easiest to quote when the mechanical, electrical, and workflow constraints are known before the first drawing is released. A fixture is not only a holder for the device under test. It defines how the operator loads the DUT, how contacts are made, how measurement paths are protected, how safety states are enforced, and how repeatability is preserved after hundreds or thousands of cycles.
Start with the DUT and contact map
The first scoping package should include the DUT outline drawing, 3D model if available, connector locations, keep-out zones, pad pitch, board thickness, expected tolerances, and any surfaces that cannot be scratched or loaded. If the fixture touches spring-pin pads, coaxial launches, high-current terminals, optical ports, or fragile semiconductor packages, each contact needs a clear purpose and a target lifetime.
For board-level fixtures, identify whether the fixture contacts pads, connectors, test points, edge fingers, pogo pins, coaxial ports, or a combination of these. For semiconductor and RF fixtures, define the required alignment precision, probe type, shielding needs, calibration reference, and whether the DUT must remain visible under a microscope or camera.
Define the measurement path
The electrical and RF path should be scoped with the same care as the mechanical clamp. RF fixtures should state the frequency range, connector type, cable length, required shielding, calibration plane, allowed cable movement, and whether repeatable phase or insertion loss is important. A fixture that is fine at low frequency can become the main uncertainty source at microwave or mmWave frequencies if launch geometry, cable strain, or shielding is not controlled.
Power fixtures need voltage, current, peak power, insulation requirements, thermal limits, safe-discharge behavior, and interlock expectations. If the DUT can store energy, the fixture should define what happens after a failed test, emergency stop, door opening, or communication loss. For high-current contacts, also define allowable temperature rise, contact replacement method, and how operators will recognize wear.
Scope the operator workflow
Production fixtures should be designed around the operator’s real sequence: scan barcode, load DUT, close fixture, confirm seating, run test, display pass/fail, unlock, remove DUT, and store records. The quotation request should state target loading time, expected daily volume, shift pattern, cycle count, access for cleaning, and spare-part strategy. If the station must support several product variants, include recipe selection rules and any interchangeable nests, adapters, or keyed inserts.
This is where many fixture projects drift. The mechanical design may look finished, but the operator workflow may still be unclear. If serial-number capture, label printing, MES upload, or exception handling is required, those items should be scoped before the fixture is machined.
Add safety and acceptance criteria
A fixture used in RF, high voltage, high current, or automated motion should have explicit safety states. Define guard doors, presence sensors, emergency stop response, discharge delay, grounding points, shield connection, and who can reset a fault. If the fixture integrates into an automated test system, document the software hooks: open/closed state, DUT present, fixture locked, interlock healthy, test running, and safe to unload.
Acceptance should include more than one successful measurement. A useful fixture acceptance plan includes repeated load/unload cycles, contact resistance checks where relevant, RF path verification or calibration data, safety-state tests, operator prompts, report output, and replacement-part documentation. For critical fixtures, include a known-good DUT and a known-fail case so the station proves both pass and fail behavior.
Fixture acceptance matrix
A custom fixture should be accepted as a measurement interface, not as a finished machined part. The evidence must show that the DUT is seated consistently, contacts are controlled, the measurement path is stable, and unsafe states are blocked.
| Acceptance item | Evidence to capture | Reject or rework if |
|---|---|---|
| DUT seating and contact map | DUT drawing revision, nest drawing, contact list, keep-out review, seating check, and repeated load/unload result | Contacts land near pad edges, seating depends on operator feel, or the fixture cannot tolerate DUT drawing variation |
| Electrical/RF path verification | Contact resistance, insulation, RF insertion/return loss, calibration plane, shielding check, and cable strain review | The fixture passes one measurement but changes when the lid closes, cable moves, or the DUT is reloaded |
| Safety-state behavior | Door/lock sensors, emergency stop, discharge delay, high-voltage or high-current interlocks, and reset authority | The station can start before lock confirmation, or a failed test leaves stored energy without a defined safe state |
| Operator workflow | Barcode or ID capture, prompts, pass/fail display, unload permission, exception flow, and target cycle time | Operators can skip required steps, select the wrong recipe, or unload before the system is safe |
| Maintainability | Contact replacement method, spare parts, cleaning access, wear indicators, service interval, and documentation package | Wear items are hidden, replacement changes alignment, or the station has no path-health check after service |
Fixture failure modes to challenge
The fixture review should deliberately look for the failures that do not appear in a clean CAD render: side-loaded coax connectors, spring pins outside their working travel, inconsistent DUT seating, cable strain during clamp closure, shield leakage after repeated opening, high-current heating at contact points, and software that starts a test before the fixture is locked. These are not cosmetic concerns; they become measurement drift, operator frustration, and false pass/fail decisions.
Quantify the fixture where the risk lives. A scoping package should name the measurement bandwidth in Hz, MHz, or GHz; voltage and current limits in V and A; target cycle life in cycles; expected daily DUT count; contact replacement interval; and any report-retention requirement in days or months. For RF fixtures, add connector family, calibration plane, shielded-enclosure requirement, cable bend radius in mm, and a before/after load-unload comparison. For power fixtures, add discharge delay in seconds, interlock state count, maximum stored energy if known, and the reset authority after a fault.
Use example values only to force the review to become concrete: a 40 GHz RF fixture should identify the connector family and calibration plane; a 60 V / 10 A power fixture should document contact heating and insulation; a production nest targeting 5000 cycles should state the cleaning and contact-replacement trigger; a fixture with a 5-second discharge delay should prove the safe-unload state; and a report-driven station should preserve at least 10 fields that tie the result to DUT ID, fixture revision, operator, limits, instrument IDs, and software version. Replace those example numbers with the actual project limits before quotation.
For XGY test fixtures, the product-line boundary is broad enough to include spring-pin nests, coaxial launches, RF shielded enclosures, high-voltage interlocks, sensors, barcode workflow, and automation hooks. The quotation should therefore state which risks the fixture itself must control and which risks belong to the rack, software, or operator procedure. That split is what lets the fixture become a repeatable measurement interface rather than a custom mechanical part with unclear responsibility.
Reject a fixture acceptance result when it proves only the happy path. A credible handover includes repeated loading, one known-good DUT, one known-fail or forced-limit case, one safety input, one operator error path, and one report export. If the fixture cannot show those cases, the project is still in prototype territory.
Engineering FAQ
What drawings are needed before a custom fixture can be quoted accurately?
A useful package includes the DUT outline, connector or pad locations, keep-out zones, board thickness, tolerance stack, surfaces that cannot be marked, and the expected contact map. For RF, high-current, optical, or semiconductor devices, include the signal path and any alignment or force limits, not only the mechanical envelope.
How should fixture lifetime be specified?
Specify expected cycles per day, shift pattern, target service interval, contact replacement method, spare parts, and cleaning access. A fixture used for ten lab samples can be designed differently from one that must survive repeated production loading, barcode workflow, and operator variation.
What makes an RF fixture different from a low-frequency fixture?
An RF fixture must control launch geometry, shielding, cable movement, calibration plane, connector torque, and path repeatability. A mechanical clamp that holds the DUT securely can still be a poor RF fixture if the cable bends during closure or the calibration plane moves between calibration and measurement.
What should fixture acceptance include?
Acceptance should include repeated load/unload cycles, contact or path verification, safety-state checks, operator prompts, report output, and known-good or known-fail DUT behavior. One successful measurement is not enough to prove a fixture is ready for production use.
Fixture quote package
Before requesting a fixture quote, prepare the DUT drawings, contact map, measurement sequence, frequency or voltage/current limits, fixture cycle-life target, operator workflow, safety requirements, software/reporting requirements, and any calibration or traceability needs. If the fixture is part of a larger rack, include the instrument list and signal path diagram as well.
XGY Tek can scope custom fixtures as standalone hardware or as part of automated test systems. A defensible quotation request describes the measurement and acceptance workflow, not only the shape of the product. That gives engineering a practical basis for choosing spring pins, coaxial launches, high-voltage contacts, shielding, sensors, interlocks, and software integration points that match the real test process.