Printed Circuit Boards (PCBs) are not rushed off to the market after production. Instead, they are subjected to a series of tests to confirm the performance. One of such testing methods is called the functional testing.
In this article, we break down the concepts of this testing procedure, the processes involved, some of the potential challenges and why it is better than the other testing processes.
What is Functional Testing?
From the name, you can deduce that it is a dedicated testing process used to determine whether a circuit board is operational or functional.
The PCB functional testing, put simply, is a type of test used to examine the Printed Circuit Board (PCB) just to be sure it is operating as expected.
With this test, it is easier to discover some of the loopholes that could negatively impact the board’s performance – and suggest how best to resolve these challenges too.
The PCB functional testing method is also known by other names, including FCT testing and Functional Testing.
Usually, this testing process is used as the last leg of the circuit board design process, in the sense that it is the last thing done to the PCB before it is shipped for use.
Tools Needed for PCB Functional Testing
To make the most out of this testing procedure, you want to use the right tools. Here is a list of some of the common tools used for testing the functional operation of a circuit board:
- Connective interface
- Central Processing Unit (CPU) and;
Benefits of Putting a Circuit Board to Functional Testing
Besides checking the overall operation of the board, a couple other reasons suggest why the PCB functional tests are recommended.
Here are some of the benefits of towing this path:
1. Overall Board Assessment
It is pertinent to mention that the FCT testing is not limited to the circuit board components. Instead, it covers the overall performance of the board – a great way to be sure of the actual performance.
2. PCB Issue Detection
The primary aim of this testing procedure is to find out some of the issues or lagging performance factors that could make the PCB unable to reach the full potential.
In light of this, there are three (3) core issues that are commonly detected. These are:
The voltage of the overall circuit board might be inaccurate or not up to the exact rating. When this happens, you can be sure that the board wouldn’t meet up to the power requirements.
It is important to mention that certain factors could be responsible for the inaccuracy of the voltage or current outputs in the PCB. Factors like a missing component/part and the inappropriate placements of components could be responsible for the voltage inaccuracy.
Just like the voltage is required for the PCB to function fully, power supply is also required for the same purpose. So, when the power supply is limited or below the expected input, it creates a functional challenge for the circuit board.
By using the PCB functional testing method, you can find out whether the circuit board has power issues.
Potential causes for power integrity problems in a PCB include:
- PDN rippling
- Excessive jittering and;
- Low frequency noise
Perhaps one of the core attributes of the functional testing method is to test for the transmission of signals in the Printed Circuit Boards (PCBs).
Signal distortion issues are commonly caused by inappropriate wiring and often result in potential issues for the signal skews in buses and on various nets.
Getting Started with PCB Functional Testing
The simplest way to start testing the functional performance of a PCB is to make a list. Although the testing usually covers the entire board, it wouldn’t hurt to make a list of the important parts to test first.
PCB Functional Testing Methods
Now that you have made a list of the components/parts to test, let us look at some of the options you have.
Below are the popular testing methods you can to get the most out of FCT testing on your PCB.
Load Testing Method
This is a broad category of the PCB functional testing procedure that evaluates the capabilities of the PCB to withstand the “load” it carries. The load in this case refers to the likes of operating frequency and temperature.
The test is used to check the board’s ability to withstand both the pressures and potential changes in the operating frequency, temperature and current capacity.
That way, it is easier to figure out if the circuit board would be overly burdened when these changes become imminent.
Put simply, the FCT testing with X-Ray inspection is done to check the “inner workings of a circuit board.”
To be successful at this, either the 2D or 3D images are used to show every layer inside the PCB. The focus is usually on getting a view of how these components (including the layers) work inside the PCB.
Also called voltage meter testing, it is a type of PCB functional testing used to evaluate the performance of the voltage.
The focus is on whether the voltage is functioning accurately and if it is not, what are the factors impeding the performance?
This is another type of FCT testing that checks the inner workings of the PCB. However, it is a bit different than the X-Ray Inspection (automated X-ray inspection), because it helps in identifying some problems, such as thermo-mechanical problems, opens, shorts, defective components and solder reflow.
Note: it is better to use the micro-sectioning analysis for completed boards ready to be shipped. Using it for the Device Under Test (DUT) might not be a brilliant idea, considering that the analysis often exposes the components of such boards to destructive mechanisms, such as abrasion.
Using the PCB functional testing method is a nice way to test the board’s capabilities, find out issues on time and have them fixed before shipping.
You want to make the most out of this by hiring the services of a PCB manufacturer that has the capabilities to offer an extensive functional testing of the board before shipping.