Anatomy of an Electronics Test Jig

What is an Electronics Test Jig?

Also known as a test fixture or test rig, a test jig is a specialized tool designed to verify the functionality of electronic components or assemblies. It serves as a platform for conducting various tests, including functional testing, in-circuit testing, boundary scan testing, and more. The primary goal is to ensure that devices meet specified performance criteria before they are shipped to customers and assist with manufacturing steps such as calibration and programming.

In other words, it’s a giant, purpose-built connector going from your test equipment setup (test engine) to the device under test (DUT), with a bunch of features to make it easy to use.

The Components of a Test Jig:

In general a test jig has the following sections.

1. Cassette:: The physical connection point between the test jig and the DUT. It includes the cradle, plus connectors, sockets and/or pogo pins that establish electrical contact between the DUT and the test engine.

• Probes and Test Pins: These components allow access to specific nodes or signals on the DUT for testing purposes. They enable precise measurement and monitoring of characteristics such as voltage, current, timing, and signal integrity.
• Cradle: Provides structural support and accurate location for probes, support pins, and other hardware embedded in it. It is highly customizable and generally consist of multiple layers to accomplish it’s various functions. See Cradle & Layers for more.
• Cover: Pressure plate holding the pressure pins. The pins are distributed to evenly compress the DUT into the cradle without letting it tip or slide around.
• Support Plate & Brackets: These connect the cassette to the test chassis. If you need to change chassis (e.g. to make room for a bulkier test engine), only the support plate and pressure plate need to be replaced.
• Probe Board: Houses the test probes and provides the necessary electrical connections between the DUT and the test engine. Using PCB instead of individually-soldered wires improves signal integrity, and also makes the jig less fragile and much easier to repair and replicate.

2. Test Chassis: The physical structure of the test jig, including the fixture housing and support structures. It holds the cassette, cover, and actuator, and usually has space inside for smaller parts of the test engine, such as USB test instruments, DC/DC converters, and so on. It may incorporate shielding to minimize electromagnetic interference (EMI) and ensure accurate measurements.

   • Actuator: What opens and closes the cover. Common actuators are vacuum fixtures, linear clamps, and hinged lids. Our standard one is an over-center lever clamp.
   • Test Engine Crate: An enclosure housing the connections from the cassette to the test engine. This makes it easy to integrate the test engine and share it between different jigs. It also serves to strain-relieve and route cabling for improved reliability.

3. Test Engine

   • Instrumentation and Measurement Devices: Test jigs often integrate instrumentation such as oscilloscopes, multimeters, and signal generators to perform electrical measurements and stimulus-response tests.
   • Control and Data Acquisition System: The control and data acquisition system acts as the brain of the test jig, coordinating test sequences, acquiring measurement data, and analyzing results. It may include microcontrollers, programmable logic controllers (PLCs), or dedicated test equipment interfaces. Simple USB-attached test gear is often cheap enough that you can have one set per chassis. Examples are 25-MHz-class logic analyzers, small DAQ bricks, DC-DC converters, USB hubs and isolators, and single-board computers.
   • Signal Sources: These include pulsers, arbitrary waveform generators (AWGs or ‘arbs’), and non-electrical sources such as LEDs or speakers.

4. External Stimulus & Measurement: Some test jigs may incorporate actuators or mechanical components to simulate real-world conditions or perform physical tests. These may include pneumatic cylinders, servo motors, or relays for applying pressure, actuating switches, or engaging connectors. These components are controlled by the test engine but are not part of it as they are typically not trivially removable from the jig.

5. Controller Software:

   • Interfaces with the control and data acquisition system to manage test sequences, monitor measurements, store the data, and analyze results. It should provide a user-friendly interface for operators to interact with the test jig and configure testing parameters. (Note this does not mean it requires a fancy UX/UI. Pass/fail lights and/or a command line tool with a simple interface is fine.)