Five Levels of Test Fixture Design for Electronic Circuits

Hello Reader,

Whether you're producing a handful of prototypes or scaling to millions of units, the design of your test fixture directly affects quality control, throughput, and production cost. For those using boundary scan, JTAG programming, or high-volume manufacturing techniques, having the right fixture strategy can make a significant impact.

Different production scales require very different testing systems; manual testing works nicely for a small number of prototype boards but would be far too time consuming to perform when thousands roll off a production line every day, but at the other extreme, the time and cost of setting up automated testing or customised jigs would be prohibitive for small scale production.

In this article, we’ll take a look at the five key levels of production scale, how this can affect the sort of testing systems that would be used and talk about the benefits and limitations of each type of fixture.

Level 1: Basic Test Jig (1-100 Units)

At the prototype stage or for small batches, flexibility is essential. Having a basic jig to hold the board steady might be enough, while you manually connect JTAG cables, USB cables, or multimeter probes. This sort of fixture is perfect for early validation or development testing using boundary scan tools when the design hasn’t been finalised yet.

✔️ Best for: Prototypes, pre-production, design validation
⚙️ Benefits: Low cost, adaptable, quick turnaround
⚠️ Limitations: Manual, slow, and operator-dependent

Level 2: Flying Probe System (10-1,000 Units)

Flying probe testers have a very high up-front cost, however if you or your board manufacturer have access to them, they offer excellent coverage for low-to-medium volume production without needing custom fixtures. Probes are moved automatically to contact test points based on software-driven test plans which can be easily updated. This is ideal for testing components not accessible by boundary scan, allowing you to perform open/short detection and in-system programming. This flexibility means low cost per board design, at the expense of the initial purchase price.

✔️ Best for: Low-medium volume or frequently changing designs
⚙️ Benefits: No fixture needed, flexible, good test coverage
⚠️ Limitations: Slower test times than fixed probes, not ideal for very high volumes, expensive machine

Level 3: Semi-Automated Bed-of-Nails Fixture
(1,000-50,000 Units)

With moderate batch sizes, a semi-automated fixture improves speed and repeatability. Bed-of-nails provides fixed access to many test points and JTAG headers simultaneously, reducing both handling and testing time. Pneumatic or mechanical press-downs provide reliable contact, and tests can be partially automated.

✔️ Best for: Medium-high volume production
⚙️ Benefits: More consistent results, less operator fatigue, ideal for fast in-situ programming
⚠️ Limitations: Higher upfront cost, not flexible for design changes

Level 4: Fully Automated In-Line System
(20,000+ Units)

For very high-volume production, testing needs to become an automated part of the assembly line. Fixtures are integrated with conveyors, robotic handlers, and factory MES systems. Boundary scan and JTAG programming are fully automated with minimal operator involvement.

✔️ Best for: Large-scale contract manufacturing
⚙️ Benefits: Maximum throughput, consistent quality, minimal labour
⚠️ Limitations: High initial investment, requires robust planning and maintenance

Level 5: No Fixture – Zero-Touch Testing
(1,000,000+ Units)

At the extreme end of production (think mobile phones, wearables, or IoT devices), yields are so consistently high that traditional testing is deemed unnecessary with device self-testing often being sufficient. In these cases, fixture-based testing may be eliminated entirely. Validation is performed at the process level through statistical analysis, design-for-test techniques, and upstream controls, ensuring that products meet specifications without the need for in-depth testing.

✔️ Best for: Ultra-high-volume products with mature, stable processes
⚙️ Benefits: No test time, reduced manufacturing cost, simplified logistics
⚠️ Limitations: Only viable with near-perfect yields and extensive process control

Smarter Testing with Boundary Scan and Scalable Fixtures

Boundary scan and XJTAG systems offer immense flexibility across the first four levels of physical testing, reducing fixture complexity, increasing test coverage and enabling faster development, as well as simplifying and speeding up in-system programming. In all cases, it can help with finding problems and fixing any boards which fail testing, allowing those boards to be returned to production as soon as possible. Whether you're testing 10 boards or 10 million, the right test strategy ensures quality and efficiency from day one.

Want to know how XJTAG can help decrease your time to market?

Speak to one of our team members for expert advice on how XJTAG tools can speed up your prototyping and ensure manufacturing reliability. Sign up for a five minute interactive workshop where you can create and test board faults yourself. Start a one month free trial. Have your first board’s project and test designed by us. All these options are available when you contact us at XJTAG.com.

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