PCB Functional Testing – Meaning, Benefit, and Testing Methods

In the field of electronic products, quality is paramount. PCB functional testing is meant to ensure that. During the test, assembled boards are placed in a specially designed fixture or enclosure, and its electrical operating environment simulated. The results of this test are then use to decide if the board can leave the factory or not.

This article will help you grasp the meaning of the PCBA functional test and why it’s such an important step when manufacturing printed circuit boards. Read on to learn more, including how it differs from the popular ICT (or in circuit test).

What is Functional PCB Testing?

Functional PCB testing is the process where assembled circuit boards are checked for functionality, usually by testing them in their specific operating conditions.

This normally involves sending electrical signals and different power levels to the board, taking measurements, and using the results to identify problems.

The PCB functional test is a complex procedure that comes last in its manufacturing process. This is when the board has been populated with components and passed through several other tests.

PCBAs that fail the functional test cannot proceed to the market as products, or for use in their specified devices and systems.

As such, the customer is assured of a high quality PCB that will not fail in its usage environment, whether immediately or sooner than expected.

Why We Do Functional Testing of PCB

The functional test is done to decide if an assembled, printed circuit board can leave the factory or not. In other words, it’s the final test-to-market.

During its manufacturing stages, a PCB undergoes many different tests, from in circuit test to boundary scan and visual inspection. The functional test crowns it all.

That’s because, whereas other tests check components and traces for manufacturing or assembly defects, this test checks for performance errors. When done at the end of fabrication and assembly steps PCB functional testing offers these benefits.

• The entire PCBA is checked for functionality and not only single electronic components or parts of the board. This provides for a more reliable testing procedure.
• A functional test can help avert the damage that a failed PCB could bring.
• When undertaken by the manufacturer, it saves the customer huge costs, seeing that custom fixtures and testing programs are needed.
• Functional testing of PCB boards can help guide on the kinds of changes required to improve quality during both fabrication and assembly steps.

PCB Functional Tester

To carry out the functional test, a specific type of equipment is used. This is called a functional tester. The typical tester is composed of these different components: the enclosure or test fixture, the PCB interface, connectors, a processing unit, and monitors.

An example PCB functional tester is seen above. It holds the board being tested and contains the interface that connects to the board being tested. The connectors, on the other hand, pass the required signals to and from the tester.

The results of the test are relayed to a monitor or monitors, from where testing experts can use them to confirm if the board is good or bad. The following requirements apply when using a functional testing machine.

• Because circuit boards are different in terms of design and application, a custom program is usually needed to perform a functional test.
• This software is usually written to fit the particular PCB’s testing parameters.
• A custom testing fixture, too, is constructed based on the specific device to be tested.
• Like the program, a PCB functional test fixture contains custom features that suit the specific board’s structure.

PCB Functional Testing Methods

The specific PCB functional testing method is based on the required results and testing equipment. It can be a hot mock-up where the board is simply checked for functionality by powering it up, or it can be a more complex procedure where a series of checks are done.

This includes the specific power or signal inputs to simulate an electrical condition and the desired outcome of the testing procedure.

The entire procedure requires a testing program to be written. This program is specific to the PCB, seeing that each has its required operational specifications. Generally, a PCBA functional test involved checking it for the following.

• Power issues
• Signal integrity problems
• Voltage or current correctness
• Malfunctions that shorts or opens may cause

Boards that pass the test are fit for use in their particular applications. Problems, if any, are corrected and improvements made. That way, only quality circuit boards are shipped to the customer or client.

In Circuit Test vs. Functional Test

Functional testing in PCB production is often confused with the in circuit test. But while the two tests share some similarities, a few differences distinguish one from the other. These are highlighted below:

• First, the in-circuit test is performed as part of the circuit board’s manufacturing process and steps.
• It checks the board components using what’s commonly referred to as a bed of nails, where an array of spring-loaded pins makes contact with the board at specific points.
• In contrast, a PCB functional test checks the operation of the entire board.
• During the test, the tester interfaces with the board at designated points, sending electrical signals to it to simulate its application condition.

Given the complexity of today’s PCBAs, the in-circuit method alone cannot provide the required test results, which is the board’s functionality. So manufacturers adopt the more effective functional test as the last step to verify the correct operation of assembled boards.

Conclusion

PCB functional testing, when used on assembled circuit boards or PCBAs, provides the final say on their functionality. It confirms if the board will work as it should or not, and is the last step before finished boards are sent to customers. Coupled with other tests, functional testing ensures electronic products that are not only high quality and reliable, but also durable.