It is very normal for school-age children to find any means possible to avoid taking a test. But “testing” is so much more than simply being able to solve specific equations on a mid-term. To be tested implies that someone or something has been found worthy and capable of performing a task. No one would want to board an airplane if the crew had not passed their flight tests, and the same is true of a circuit board that hadn’t passed its tests.
There are many different tests and inspections that a circuit board will go through during manufacturing. Some of these tests are designed to catch specific problems or conditions, while others are more general. All testing culminates with the final functional test to ensure that the board is ready to operate. This article will examine these different tests and explore the benefits of PCB functional testing methods.
What is PCB Functional Testing?
PCB manufacturing has many different checks and balances folded into both the fabrication and assembly processes. Starting with inspections, circuit boards are carefully examined for problems such as metal to metal shorts and that the correct components are installed in their expected locations. PCB testing will then be used to check for metal traces that don’t connect as intended or component leads that aren’t soldered firmly to the board. The functional test then takes these examinations to the next level by ensuring that the board operates as it should.
The PCB functional test is designed to simulate the board’s operating behavior based on the specifications for which it’s developed. If the circuit board is not operating as expected, then technicians will use a more detailed process to trace any faults found by the functional test down to the component level for correction. This level of testing aims to evaluate the board’s functionality, determining if it has been fabricated and assembled according to the design specifications and intentions.
The functional test does its job by sending different signals and currents through the board through various connection methods to simulate its operating behavior. It will detect both digital and analog problems, including signal distortions, timing issues, and incorrect current levels. Functional testing is conducted through cable connections and test points designed into the board and uses specific software developed for its circuitry to find and report problems. Next, we’ll look at some different ways that function testing is carried out on a printed circuit board assembly.
The Benefits of PCB Functional Testing Methods
Before a circuit board gets to the functional testing stage of its manufacturing, there are many other tests and inspections that it will go. These include:
- Manual inspections: Inspections are used to verify different aspects of the circuit board manufacturing processes. Some of these inspections use microscopes or close-up videos for detailed examinations.
- Automated Optical Inspection (AOI): These inspection systems use different video capabilities to compare images of the board to known “golden” images. They are used to check for shorts between metal, spacing violations, drilled hole breakout, solder paste application, finished solder connections, and the location and orientation of components on the board.
- X-ray: For circuit boards with complex and dense component placement, X-ray inspection systems are used to examine components such as BGA’s for solder defects.
Here are some of the systems that can do some or all of the functional testing of a circuit board:
- Flying Probe: This system maneuvers between two and six probes around the board to contact tiny metal pads called test points built into the design. Primarily this machine is used to detect improper solder connections, but it can include some limited functional testing. However, with only six probes available at any one time, the range of testing is severely restricted.
- In-Circuit Test (ICT): The ICT system accesses the same onboard test points as the flying probe test. The difference is that the ICT system uses a test fixture with probes arranged to contact each test point simultaneously. The resulting coverage of test points not only allows the ICT system to work very fast, but it can also run sophisticated functional tests making it ideal for production builds of circuit boards. On the other hand, the ICT fixture is time-consuming and expensive to develop or modify, and therefore is generally not used for prototypes or low-volume production.
- CableScan: This testing system relies on connectors instead of test points to connect to the board and is a good fit for backplanes or other interface boards. CableScan will check every pin to each other through its connections, searching for assembly problems such as improper solder connections. Simultaneously, it will run functional test signals through the same connections.
Functional testing is an integral part of producing high-quality circuit boards by verifying the PCB as operational before it is shipped to the customer. Here is where the abilities of your local PCB contract manufacturer are essential to the success of your circuit board build.
Effective Functional Testing with Your PCB Contract Manufacturer
PCB CMs typically have a staff of experienced test engineers that will help their customers define the test strategy of the circuit board being built. Expect the following from a contract manufacturer when it comes to testing a board:
- A full suite of test systems that can handle any level of functional testing that a design needs.
- Standard ICT or flying probe testing systems to verify the assembly of the circuit board.
- Experienced test engineers will help develop the test strategy for a design.
- CM’s can develop or modify the testing hardware and software that designs will require.
Functional testing is constantly growing with each new part available for PCB design. Additionally, new test systems with improved features and capabilities are advancing test engineering. At VSE, we have the test experience and skills that you need for your design. Our test engineers will work with you to ensure that all of your specifications are met in the test strategy for your circuit board.
