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Functional Testing of PCB Assembly and PCBA FCT Costs

functional test
pcbonline PCBONLINE Team Fri, Apr 09, 2021

functional test for PCB assembly

Functional testing (FCT) can identify if PCB assemblies are working correctly before they are distributed.

Is It Necessary to Conduct Functional Testing for PCB Assembly?

Imagine this:

A PCB assembler doesn't process the functional test on your boards. When you get them, suddenly, an error occurs, and your device has to be returned to the PCB assemblers to check and troubleshoot the error.

But this is a tough task, as AOI testing can locate only the assembly's surface issues, and even a specific crew of assemblers can hardly locate the error within the PCB in such a circumstance.

Both you and the manufacturer are unhappy, as no one knows if the problem is with the assembler, the components, or the circuit designers. Things go into a dilemma.

This is unfortunate, and what's worse, it happens in the PCB industry.

So, I would say yes, conducting the functional test is necessary, which makes sure the assembly quality is to the highest degree.

What is Functional Testing for PCB Assembly

A functional test (FCT) happens after the assembly and before the thermal aging test. It stimulates the working condition to check the PCBA's functionality performance.

This is how PCBONLINE processes a functional test:

  • First, our senior test engineers use LabView to do the test programming.
  • Then, a test technician connects the PCB assembly to the PCBA tester, opens the test program, and powers the PCBA. (our testing system is configured in Visual Basic)
  • Next, the technician operates the PCBA tester to take the signals from the PCB chips and routes the test points.

In this way, the voltage value, signals, and other important parameters are loaded on an oscilloscope. The oscilloscope is connected to a computer, whose screen displays OK if the PCBA is good, or otherwise, displays NG (not good) so that our technician can verify the signal integrity and know if voltages run properly.

All test process data are recorded. If the computer says OK, the PCB assembly goes to the next procedure, which is IC programming or thermal aging test. If the computer says NG, our engineers debug them, and all PCBA tests start again.

Usually, we advise customers whose PCB's area is larger than 3 square meters to conduct the functional testing. It reveals any open connections, defective components, solder shorts, and anything that isn't okay with the PCB. Through it, PCBA manufacturers make sure the assembly quality is of extreme precision.

What is the Cost of Functional Testing for PCB Assembly

Generally, if you ask a PCB assembler to process functional testings before delivery, you need to pay additional costs. At different PCB assembly houses, the functional testing prices differ. The cost of functional testing ranges from $0.1 to $1 per piece of PCB assembly.


Very few manufacturers perform overall FCT to verify the PCB's full functionality, but PCBONLINE does. If your order amount is over $5,000, we provide free functional testing. Plus, free complete PCBA samples.

PCBONLINE is a one-stop PCB manufacturer that can provide free functional testing. We offer advanced PCB, PCB assembly, box builds, and design. We accept large volumes, small-batch, and prototypes.

The functional test is not the only free test at PCBONLINE, here are other free tests and services: a design for excellence, one-to-one engineering support, Gerber and BOM check before PCBA manufacturing, and the first article inspection (FAI) for PCBA. Plus, you can enjoy $100 off coupons for online purchases once you register on our website.

Benefits of Performing FCT for Your PCB Assembly

You can get these benefits from FTC:

  • The FCT saves money for the customer to buy equipment to find issues or ask a testing company to do so, which is much more expensive.
  • It eliminates the necessity for performing systems tests.
  • It includes most of the PCB's sections such as resistance, voltage, communication protocols, and anything that could cause issues with the PCB.
  • It is also the stage where manufacturers can add additional serializing factors, such as serial numbers and calibrating factors.

During the FTC, the whole operational environment inside the PCB is cleansed of any errors. Responses are monitored at specifically chosen points to ensure the product's functionality and guarantee it won't malfunction. This is quite important for the average customer who might not be able to troubleshoot the issue by themselves.

Besides FCT, There Are Other Different PCB Testings

These different testings for a PCB can be:

  • Micro-sectioning analysis
  • PCB contamination test
  • X-ray inspection
  • PCB solderability test
  • Peel test
  • Solder float test
  • Time-domain reflectometer test, or TDR
  • Four-terminal sensing

Here you can take a look at the details for some of them:

PCB X-Ray Inspection Service

The PCB X-ray inspection, also known as AXI, mainly involves 3D digital images that specifically show every single layer of the PCB board. The procedure allows the examiner to take a look at the workings of the entire board, no matter how small they could be.

X-ray inspection is usually conducted for lead-free assembly and BGA assembly. The main advantages of the X-ray inspection are the possibility of an  Inside View without damage and the chance to troubleshoot Complex PCBs.

Micro-Sectioning Analysis

The specific chore the micro-sectioning analysis does is to take a 2D sample that will expose the inner workings of the PCB. The components that the test will identify: are shorts, opens, solder reflow, thermo-mechanical problems, and defective components.

Micro-sectioning can be truly destructive for a device that is under the test. But the components that aren't working correctly can be removed from the PCB, placed into a curing epoxy, entirely exposed by any means of abrasion, and then compared with the functioning component. With a closer look, via micro-sectioning analysis, an experienced technician will be able to spot: the failure of solder joints, the thickness of the plate, and the intermittent thickness of any metallic layer throughout the PCB.

PCB Contamination Test

A PCB can be contained in more ways than we are willing to admit, such as flux residue, human byproducts, handling, and reaction products.

Essential results of the contamination tests can show the significant activity of Corrosion, Degradation, and Metalization. Each non-tested product could significantly interfere with the customer's usage of the PCB and can lead to unwanted issues.

Bottom Line

Now you have a good understanding of the PCBA functional testing. If something stops the whole PCB from working, it can be quite a painful experience for the customer. The FCT simulates the operating environment of the circuit board and helps you prevent any errors you might struggle with in the future.


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