What is an Exchangeable Test Fixture Cartridge?

Most FixturFab Test Fixture bases support exchangeable cartridges that can be easily interchanged, facilitating the testing of various PCBAs with a single fixture base. This is particularly useful in Test Systems where the fixture base typically holds a set of integrated Automated Test Equipment.

A fixture base that supports modular cartridges can reduce both the price and lead time when a test fixture or test system needs to be updated because of alterations to the Device Under Test (DUT) or transitioning to the production test fixture version when the circuit board is ready for mass production.

Production Test Fixture Cartridges

FixturFab uses Ingun as our primary supplier for Production Test Fixture materials because they are architected for modularity. Their test fixture cartridges comprise a probe plate, pressure plate, and moving plate and are designed to be easily interchanged in each test fixture base. Each plate is made from firm materials to withstand the wear from mass-production, particularly the probe plate, which is FR4, a type of fiberglass known for its strength, durability, and electrical insulation properties.

ingun-test-fixture-base-and-cartridge
A Test Fixture Base and its Cartridge.

Mechanical components like pogo pins, test probe receptacles, guide pins, and pressure pins are added to the cartridge plates to interface with the DUT, making it a custom test fixture. Test Point Carrier Boards (TPCB) can also be added to the bottom of each probe plate.

test-fixture-cartridge-and-test-point-carrier-board-render
A render of a Cartridge with a TPCB below the Probe Plate.

Electrical connectivity can be designed to be modular through a system of specialized connectors that break contact when the cartridge is removed, providing a truly plug-and-play fixture implementation.

ingun-test-fixture-kit-and-components
Ingun Modular Cartridges and Components.

Ingun Test Fixture Cartridge Types

Each test fixture base size (MA260 / MA2111 / MA2112 / MA2113 / MA2114) supports three primary types of cartridges.

  • Standard cartridges, for most applications.
  • ESD protection cartridges, for particularly sensitive DUTs or automated test equipment.
  • RF-shielded cartridges, for protection from radio frequency interference.
ingun-exchangeable-test-fixture-kit-ma2112
Standard Cartridge for Ingun MA2112 Test Fixture Bases.
ingun-esd-exchangeable-test-fixture-kit-ma2112
ESD Cartridge for Ingun MA2112 Test Fixture Bases.
ingun-rfd-exchangeable-test-fixture-kit-ma2112
RF Cartridge for Ingun MA2112 Test Fixture Bases.

Development Test Fixtures

The DEV260 Pro Development Test Fixture supports exchangeable probe plates and pressure plates with the simple removal of four corner fasteners. FixturFab can replace both plates within a short lead time (1-2 days!) after the customer has submitted new design files for an updated DUT.

dev260-pro-development-test-fixture-exchangeable-plates
DEV260 Pro Exchangeable Cartridge Plates.

Standard Development Test Fixtures do not support exchangeable plates, as the entire fixture is inexpensive to make from scratch to accommodate design updates.

FixturFab Test Fixture Cartridge Types

The DEV260 Pro supports two types of probe plates.

  • A single-layer MDF probe plate is used for most applications.
  • A TPCB probe plate stack up for when the customer wants to route test point signals directly to feed-throughs on the back of the test fixture.
DEV260 Pro MDF Cartridge - ISO
A DEV260 Pro MDF Probe Plate.
DEV260 Pro TPCB Cartridge - ISO
A DEV260 Pro TPCB Probe Plate.
DEV260 Pro MDF Cartridge - Detail
A DEV260 Pro MDF Probe Plate, highlighting Pogo Pin Receptacles on the bottom side.
DEV260 Pro TPCB Cartridge - Detail
A DEV260 Pro TPCB Probe Plate stack up, highlighting the standoff and bottom-layer TPCB Probe Plate with Pogo Pin Receptacles going through both.

FixturFab Test Point Carrier Board (TPCB) Probe Plates

Similar to how FixturFab automates 80% of the design for Bed of Nails Test Fixtures, we’re also developing the automation to design “Auto” TPCBs. When a test point’s signal only needs to be routed to a pin on a connector, we can leverage KiCad’s Python plugins and auto-routing libraries to eliminate many hours of custom electrical engineering design time.

Besides eliminating the need for individual test point wiring (avoiding rat nests of wires found in traditional test systems!) and reducing labor costs, having the ability to integrate other test system features directly into the test point signal interface adds many possibilities. Future posts will dive into the various applications that FixturFab has planned.

Conclusion

Exchangeable test fixture cartridges represent a significant advancement in the efficiency and adaptability of circuit board testing by offering a versatile and cost-effective solution for varying testing requirements. The inclusion of different cartridge types, such as standard, ESD protection, and RF-shielded, further enhances their applicability across a diverse range of testing scenarios.

This modularity not only simplifies the testing process but also significantly reduces the time and expense associated with adapting test fixtures to new PCB designs, making them an invaluable asset in the fast-paced world of electronic manufacturing and development.

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