Volpiano (Italy)

March 27, 2025

ICT Bed-of-Nails vs. Flying Probe: A Comparison of PCB Assembly Testing Methods

Understanding how In-Circuit Testing is Done on PCBAs

In-circuit testing is used extensively in high-volume production environments to identify defects in Printed Circuit Board Assemblies. To ensure that their PCBAs conform to quality standards and function correctly, manufacturers utilize automatic test equipment for in-circuit testing that apply electrical signals to the electronic boards and assess the responses, ensuring that parameters including resistance, capacitance, voltage, and current are within specified limits. 

Flying Probe Testers operate using movable electrical probes that rapidly move to designated points to conduct tests. In contrast, Bed-of-Nails Testers, also known as In-Circuit Testers (ICT), utilize a fixed matrix of spring-loaded pins arranged to contact specific test points. 

Determining the most suitable automatic test equipment can be quite challenging due to the multitude of factors to consider.

When to Use Bed-of-Nails Testers or Flying Probe Testers? 

Bed-of-Nails Testers and Flying Probe Testers are automatic test equipment used for in-circuit testing. Although they both detect defects thus ensuring the quality and functionality of printed circuit board assemblies, they differ significantly in their approach and application suitability. 

When selecting between these two options for in-circuit testing, some key factors should be taken into account:

• Production volume. Bed-of-Nails Testers utilize a fixed test fixture with multiple test points corresponding to the design of the PCBA under test. This setup facilitates the simultaneous testing of multiple boards, thereby providing a cost-effective option for extensive production runs. Flying Probe Testers, on the other hand, involve the use of multiple test probes that move independently and in sequence from one test point to another across the PCBA surface. The absence of test fixtures, thus the cheaper initial setup costs, make flying probe testers particularly suitable in production scenarios characterized by smaller production runs.
• Stability of the Product. The requirement of in-circuit testing can emerge in any point of product development, manufacturing or during prototyping. For mature products with very few revisions expected, where production is at a steady volume year over year, the investment in a Bed-of-Nails Tester is proven to be beneficial as the long-term savings are considerable. On the other hand, Flying Probe Testers can easily adapt to any frequent changes in PCBA without needing for new test fixtures, enabling faster testing turnaround. 
• Complexity of the PCBA Design. Technological progress has brought new challenges to in-circuit testing, such as the presence of multilayers, components on both sides, higher frequencies, and miniaturization. This means highly populated PCBAs, reduced accessibility for testing, and increased interconnections. When high complexity leads to the impossibility to embed test pads in the PCBA layout, Flying Probe Testers have the capability to probe various test points with extreme precision even when no actual test pads exist, as well as hitting small targets in highly populated PCBAs that might be inaccessible to the fixed test pins.

Which Method is Better for Testing PCBAs: Bed-of-Nails Testers or Flying Probe Testers? 

While the factors outlined can assist PCBAs manufacturers in selecting between Bed-of-Nails Testers and Flying Probe Testers, it is not always feasible to categorize all production requirements and scenarios strictly into one of these options. 

In some cases, an optimal solution may not be present, thus employing a combined test strategy could be crucial to capitalize on the advantages of each testing method. 

For instance, a PCBA testing workload cycle might see the test program split between Flying Probe Tester and Bed-of-Nails Tester. The Flying Probe test station executes testing on all components non-accessible by the Bed-of-Nails fixture. It also executes the net test to detect 100% short circuits and wrong-value I/Os and additional test techniques such as LED Color & Intensity test, board planarity test and optical test. Later the PCBA goes into the Bed-of-Nails test station, where in-circuit testing on all accessible nets are executed including power on & power off, flashing, and functional test.

However, given the critical nature of time and cost efficiency in PCBAs manufacturing, there is an escalating demand for optimizing production processes and adopting automatic test equipment that combines the advantages of both methods, ensuring flexibility, accuracy, and high throughput. 

In this context, SPEA emerges as a leader in in-circuit testing with its Bed-of-Nails Testers and Flying Probe Testers that address a broad spectrum of application demands for today’s electronic boards with a wide range of testing tools and adaptable configurations.

SPEA enhances precision by utilizing advanced technologies, such as linear encoders with sub-micron accuracy and high-performance position meters in Flying Probe Testers. In Bed-of-Nails Testers, the direct pin connections ensure optimal signal integrity for best accuracy. 

To maximize throughput and minimize testing time, SPEA Flying Probe Testers utilize ultra-fast motion technology and bouble sided probing. Bed-of-Nails Testers offer a multi-core architecture to deliver different test techniques concurrently and a dual-site test area that enables parallel testing for improved productivity.

Through the implementation of SPEA technology, PCBAs manufacturers can effectively meet diverse production requirements without sacrificing the advantages offered by either of the two test equipment.

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