Fixtures
Custom Test Fixture Machining: PCB and Functional Test
The machined half of a test fixture: probe plates, board nests and insulating details, made to your drilled-hole data.
A test fixture holds a board or an assembly in one repeatable position while probes, connectors or a functional test make contact. The machined half of it is what is quoted here: probe and guide plates drilled to your hole data, board nests located on tooling holes, standoffs and insulating details in G10/FR4 or Delrin, and an aluminum or steel base. Send the hole data and the plate print; a person quotes in 24-48 hours, standard lead time 4-6 weeks.
Updated September 2026
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Commercial work only. We don’t quote firearms, DoD, ITAR, or EAR-controlled parts.
What is quoted here, and what is not
A complete test system is a mix of mechanics, wiring, probes and software. This page covers the mechanics: the machined plates, nests, standoffs, guides and insulating details, made to your print and your hole data, inspected and shipped as parts. The test electronics, the probe wiring, the harness and the program are not part of the quote and no part of this page claims them. Plenty of buyers already have the electrical side settled and need the machined stack made to a drawing.
That is the usual split when a contract builder or a test engineer has a fixture design in hand: the probe plate, the guide plate and the board nest are ordinary precision machining jobs with unusually tight hole position, and the rest of the build happens where the wiring lives. If you need a wired fixture instead, this is not that offer, and the quote will say so rather than stretch.
Hole position is the whole job
On a probe plate the only interesting number is where the holes are. Spring probe receptacles have to line up with pads on a board that were themselves placed to a fabrication tolerance, and error stacks fast across a large plate. So the drilling data, not a dimensioned sketch, is what a probe plate is quoted from: the hole table or the drill file, the hole sizes, the plate datum the coordinates are referenced to, and the position tolerance you need held.
Guide plates add a second constraint. A probe passes through the guide plate and lands on the board, so the two plates have to agree with each other as well as with the board, and they are usually ordered as a matched pair and dowelled together. Say on the print that they are a matched set, and give the dowel scheme and the stack height, and both are quoted and inspected together rather than separately.
Locating the board: tooling holes, not the outline
Boards are routed to an outline tolerance that is looser than the pad positions on them, so a nest that locates a board by its edges locates it to the worst number on the board. The tooling holes are the better datum. A board nest usually locates on two of them, a round pin in one and a second locator in the other that the print names to stop the board turning, and supports the board elsewhere without constraining it. Give the tooling hole positions and diameters from the same origin as the pad data.
Support matters as much as location. A populated board flexes under probe force, and a board that bows mid-test gives intermittent contact that looks like a failed unit. Support pads under the probed area, placed to miss components, are part of the nest print, and so is the component keep-out on the underside. Mark tall components and connectors on the print so pockets are cut for them.
Materials: G10/FR4, Delrin and metal, each for a reason
G10 and FR4 are glass-reinforced epoxy laminates, and they are on test fixtures for their electrical properties as much as their stiffness. Piedmont Plastics’ G10/FR-4 page (piedmontplastics.com/products/g10-fr-4) puts dielectric strength at up to 500 volts per mil and flexural strength around 70,000 PSI, with low moisture absorption, and Wikipedia’s G-10 entry (en.wikipedia.org/wiki/G-10_(material)) covers the laminate construction. That combination is why probe and guide plates are usually G10 rather than plastic or metal.
Delrin goes where an insulating detail needs to machine cleanly and hold size, and where a contact face must not mark a board or a housing. Aluminum and steel carry the base, the frame and anything bolted down hard. Machining glass-reinforced laminate is abrasive work and dusty, which shows up in the quote; it is quoted per job like any other material and there is no minimum. G10 and phenolic fixture details covers the laminate in full.
Who orders these: contract builders and test engineers
On an electronics contract line, tooling is tied to a part number the same way it is at a molder, so each new assembly brings its own: a nest, often a wave or selective solder pallet, usually a test plate stack, sometimes a conformal coat mask that keeps connectors, test points and grounding locations clear of the coating. A revision that moves the tooling holes or adds a tall component invalidates what you had. That produces steady repeat orders rather than one-time purchases, and duplicate sets when a second line comes up, which are worth quoting together, so every stack is quoted and inspected against the same print as a matched set.
Material selection on an EMS line carries one constraint most fixture work does not: static. Where a fixture handles a bare board or an unprotected assembly, ordinary acetal and UHMW are insulators, and static-dissipative grades are bought as such. Put the requirement on the print by grade or by surface resistivity rather than as the word ESD, and the quote follows what the print names. Masking fixtures covers the coat-mask case, where the masking boundary and how far it may move belong on the print as a number.
What to send for a machined test fixture quote
The useful package is: the plate prints in PDF, the models in STEP, the hole data as a table or drill file with sizes and the datum they reference, the position tolerance you need, the board outline and tooling hole data if a nest is in scope, plate materials and thicknesses, the dowel and stack scheme if plates are a matched set, and any component keep-outs. Any file type is accepted and the quote lists what is missing.
If the design is still moving, say what is fixed and what is not. A plate quoted from a revision that then changes its hole table is a remake, and knowing which parts of the stack are settled lets the quote say what can be started and what should wait. Vendor setup takes a day: W-9, NDA, net terms available.
Inspection, quantity and lead time
Every plate is inspected against its print before it ships, and plates ordered as a matched pair are inspected together. What cannot be inspected as drawn is flagged in the quote rather than shipped unchecked.
One fixture is a normal order and there is no minimum; a second set for another line is quoted alongside the first. Standard lead time is 4-6 weeks with the quote back in 24-48 hours, and extended is 6-8 weeks when timing is flexible. Rush 1-2 weeks applies to machined parts with no secondary operations. Heat treat, grinding, EDM and finishing add time, and the quote gives the real date. Buyers who also need the enclosure or the chassis around the fixture will find those on enclosures and housings.
Questions
Before you send a job.
01 Do you design and wire test fixtures?
Not the wiring, probes, harness or program. What is quoted here is the machined half: probe and guide plates, board nests, standoffs and insulating details, made to your print and hole data. No drawing yet? Fixture design is quoted as its own line. Send the part, the features to locate and check, and how it’s loaded.
02 What data do you need for a probe plate?
The hole table or drill file with hole sizes, the plate datum the coordinates reference, the position tolerance you need held, the plate material and thickness, and the outline. A dimensioned sketch is not enough for a plate with hundreds of holes. If probe and guide plates are a matched pair, say so and give the dowel scheme and stack height.
03 Why locate a board on tooling holes instead of its edges?
Because the routed outline carries a looser tolerance than the pad positions, so locating on the edge locates to the worst number on the board. Two tooling holes, a round pin in one and a second locator in the other that stops the board turning, tie the nest to the same origin the pad data uses. Give the tooling hole positions and diameters referenced to that origin.
04 Should the plates be G10/FR4 or something else?
G10/FR4 is the usual choice for probe and guide plates: dielectric strength up to 500 volts per mil, flexural strength around 70,000 PSI and low moisture absorption. Delrin suits insulating details that must machine cleanly and hold size, and aluminum or steel carries the base and frame. The print names the material and the quote follows it.
05 Can you make a nest that supports a populated board?
Yes. Support pads under the probed area keep the board from bowing under probe force, which is what causes intermittent contact that reads as a failed unit. Mark tall components, connectors and underside keep-outs on the print so pockets are cut to clear them and the pads land where there is nothing in the way.
06 Can you make wave solder pallets and conformal coat masks?
Yes, machined to your print. Pallets are usually G10 or FR4, which hold size through repeated thermal cycles; coat masks are a machined shield or plug that keeps connectors, test points and grounding locations clear of the coating. Give the board outline and tooling hole data, the masked areas, the masking boundary with how far it may move, and the finished thickness if a stack height matters.
07 How do I specify a static-dissipative fixture material?
By grade or by surface resistivity on the print rather than by writing ESD. Ordinary acetal and UHMW are insulators; static-dissipative grades are bought as such and cost more. Put the requirement on the print where a fixture handles a bare board or an unprotected assembly and the quote follows what it names.
08 How long does a machined test fixture take?
Standard lead time is 4-6 weeks and the quote comes back in 24-48 hours. A single Delrin nest sits toward the front of the standard window; a matched G10 probe and guide pair with a tight hole position sits toward the back. Extended is 6-8 weeks when timing is flexible. Lead time starts at order approval. Put your need date in the part description and the quote answers it.
Related
Where to go next.
Custom machined fixtures
The hub: every fixture family, quoted from your print.
View →G10 and phenolic fixture details
Insulating laminate, and what it is good for.
View →Electronics enclosure parts
Panels, plates and housings for electronics builds.
View →Get a quote
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