Product Focus: Flying Prober

A Flying Prober is an automatic testing system for electronic printed circuit boards (PCB) or assemblies which uses a measurement method similar to an in-circuit tester. However, it utilises a small number of both fixed and movable probes for contacting instead of a bed of nail fixture. The power supply nets are usually contacted using the fixed pins. All the other circuit nodes are contacted in sequence via pins that can be moved in an x/y direction (contact fingers).

Depending upon the model, a Flying Probe Tester is fitted with between 1 and 20 contact fingers (usually 4) which make contact with the printed circuit board from above and/or below and scan each circuit node in succession. Because the circuit nodes are contacted sequentially, the test times are significantly longer than is the case with in-circuit testers with a of nails fixture. If the Flying Prober is fitted with several contact fingers, it is possible to either take 4-wire measurements (for greater measuring accuracy), or several circuit nodes can be contacted at the same time (for a faster test rate). As a rule, Flying Probers can be reliably used for contacting contact surfaces with a diameter of less than 100 μm, whereby around 40 contacting operations per second are possible depending upon the travel path.

Since a test adapter is not needed for contacting, this eliminates the costs of the test fixture itself and the need to wait until it is completed. For the main part, programs can be generated automatically based on CAD data or manually via a learning process. For this reason, Flying Probers are primarily suited for testing prototypes or small series boards.

Flying Probe Testers usually perform analogue measurements of resistance, capacity and inductance, whereby the test assembly is not supplied with operating voltage. This allows the operator to check the correct mounting, and in some cases the functionality, of not only most discret components but also of integrated circuits.

The systems can be partially extended to include other test methods such as boundary scans, optical inspection (AOI), functional tests or thermal inspections to achieve a higher fault coverage. Some systems also support reverse engineering, which means they can even be used if no CAD data is available for the test assembly. The test program is then generated practically automatically.

In principle, Flying Probe Testers are available for three different fields of application: for testing electronic printed circuit boards as well as for testing and repairing electronic assemblies. The testers differ in their features and capabilities.

Printed circuit board test: To be able to run continuity and isolation tests, these Flying Probers usually operate with a voltage in excess of 100 volts. They are also fitted with around 20 movable probes for highly parallel testing with a high throughput.

Assembly test: These systems normally work with 4 movable probes, frequently on both sides of the assembly. In the main the probes are slightly angled so that they can also access the contact surfaces between high components. High fault coverage is also significant here, which means that the systems can be optionally supplemented with other test methods.

Repair test: These systems usually operate with just one scan head and one or two probes. An impedance analysis is used to detect faults on the assembly, with the measurement readings being compared against those for a flawless assembly. If any divergences are found, it can be assumed that there is a fault in the respective circuit node. The test throughput here is not so significant, with ease of use and a low purchase price being the key factors.