Engineering Examples · Test, lab & inspection fixturing
Keeping 64 pins in contact under load
A bed-of-nails test fixture is only as good as its worst pin. We proved the pin plane stays flat under the full preload — so no pin throws a false open.
The result at a glance
Problem → built result
What we solved
A DUT/pogo fixture presses a circuit board onto an array of spring-loaded pins to test it. Each pin needs a minimum contact force to read a clean, low-resistance node. The catch: the pins all push back at once, and the summed spring force of a full field — here 96 N across 64 pins — tries to bow the plate they sit in.
What we built
Treat the plate as a flat plate under a distributed load, because that's what it is. Pick the material for the one property that matters — rigidity — and compute the plate's deflection under the full pin preload, then convert that deflection straight into the thing the customer cares about: how much each pin's contact force varies across the field.
How we proved it
The engineering behind the result.
Flatness is the spec, not strength
Under the 96 N preload the worst pin base sits 3.5 µm off the standoff tops the board rests on. Through the pin spring rate, that 3.5 µm is a 0.2% change in contact force — 49× inside a ±10% uniformity target, so every pin stays in its reliable-contact band.…
CF-Nylon and steel, each where it belongs
The plate is carbon-fibre-filled nylon, chosen for stiffness and dimensional stability — the whole job is not moving under load. The pins ride pressed-in steel receptacles that take the contact and the wear.…
Bracketed by hand-calc, balanced to zero
We solve two load cases and publish the worse. In the calibration case the plate is clamped at its edge band, the sag (3.4 µm) lands between two independent textbook plate-bending solutions for the free span — a clamped-edge plate (1.5 µm) and a simply-supported one (4.8 µm) — an…
Delivered result
Evidence a buyer can use.
A printed test fixture that ships sized to the customer's board, with the analysis proving the pin plane stays flat enough that no pin throws a false open — backed by an FEA that's bracketed by hand-calc and balanced to zero.…
Application notes
The stiffness model uses the solid plate — the Ø1.70 mm pin holes (~1.4% of area on a 10 mm pitch) and the perimeter bolt/dowel holes are non-structural for plate bending and omitted. Flatness scales with pin count and plate span; the configurator re-solves each layout and we add a center support or step the thickness for a very large fie…
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