Flexible PCB Test: The Ultimate Guide

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Oakley Mae

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A flexible PCB test is critical to circuit board manufacturing.

Generally, the process ensures that you design boards free of errors and top-level performance.

Surprisingly, few designers understand what actual circuit board testing involves. 

The process involves complex methods like in-circuit testing, engineering inspection, flying probe testing, and functional testing.

And that is not all; these processes require some special equipment. 

We have you covered if you’re stranded on carrying out flexible PCB tests.

Keep reading to understand the flexible testing methods, benefits of PCB tests, and flexible PCB faults. Let’s get started. 

Table of Contents

What’s Flexible PCB Testing?

Testing a circuit board

(Testing a circuit board)

Flexible PCB testing involves inspecting circuit boards to determine whether or not they’re in the best working conditions.

Generally, we use PCB testing systems whose main purpose is fault isolation and identification.

You determine the failure modes with fault identification, while fault isolation guarantees a reliable final assembly. 

Fortunately, there are several testing methods to help you test a flexible PCB and including:

Flexible PCB Testing Methods

As highlighted above, we have several PCB testing methods, each serving a unique purpose.

We’ll go through each option below: 

In-circuit Testing

This automated testing method inspects each circuit on the flexible PCB.

It guarantees that circuit components are within the right specifications and are without human error.

Moreover, this test can correct the circuit orientation and identify short circuits and other faults. 

One common in-circuit testing type is the peel test, which determines the strength you need to peel a lamination from your circuit board.

Also, we have a solder float test, which determines the penetration of solder to the PCB surface.

Therefore, it improves the chance of developing stronger solder joints.

Additional in-circuit testing options include: 

  • Surface mount simulation
  • Wetting balance analysis
  • Solderability

Flying Probe Testing

A multipurpose flying probe system

(A multipurpose flying probe system)

With this testing method, you apply electrical test power and signal to probe locations.

You can determine whether your board has a fault depending on how much deviation the result is from the expected value.

Surprisingly, this method is more precise and accurate than the in-circuit test, and you can use it to test more than 90% of the boards. 

And since you’ll have multiple probes in your circuit board at different places, you can manage multiple tests simultaneously.

Therefore, we recommend this testing method for high-volume production and prototypes.

Generally, you’ll find this method cheaper than in-circuit testing.

Automated Optical Inspection (AOI)

A vision instrument inspecting a PCB

(A vision instrument inspecting a PCB)

This approach employs different microscopes and cameras to capture flexible circuit board images.

Afterward, the software will compare these captured images to a predefined schematic to detect differences. 

The good thing with AOI is that it can detect excess solder, solder gap, and over and under etching.

Moreover, you can use it to detect component defects like incorrect values, improper alignment, and missing components.

However, we noted that the approach is sometimes imperfect and might fail all parts. 

Functional Testing

The purpose of a functional test is to inspect a board’s physical components.

Also, it goes further to test the component signals and the connectors linking the components.

Surprisingly, the test works perfectly for both digital and analog signals. 

With functional testing, you’re guaranteed to determine sub-component fit and usage.

Therefore, ensuring the end product performs the intended purpose becomes easier.

Inspection by Humans

This is a manual testing approach, and we consider it the least effective.

The process takes advantage of human labor to check and identify faults.

To succeed, the inspecting team should exercise high visual judgment and insight. 

In most cases, the process produces inconsistent results, and the inspectors might experience fatigue.

Also, they might miss important information, thus affecting the final results.

Furthermore, with this method’s high downtime and cost, we recommend automated testing methods. 

GM/LTS

GM/LTS testing involves different processes and tests to identify and remove internal CCA failures.

Also, it involves discrete analog lines, multiplexors, and interface tests.

The advantage of this is it isolates and identifies faults with high-level accuracy. 

Burn-in

With burn-in testing, you push maximum power levels through your flexible circuit board for 48-168 hours.

The process is very intensive; you might refer to it as the infant mortality method.

What this means is that it removes premature failures from your circuit board. 

Surprisingly, to manage burn-in tests, you must expose your board to high-stress situations, temperature extremes, and high voltages. 

Benefits of A Flexible PCB Test

Flexible circuit board tests help identify errors and problems during development and usage.

Therefore, designers and engineers can use the finding to correct errors before they escalate into serious problems. 

For example, in the case of a short circuit, ignoring the testing process might result in a PCB blowing up upon connecting to a power supply.

Fortunately, identifying problems during testing is quick and saves you costs.

What are you waiting for?

Load testing software and put your PCB into action.   

What Do You Test In A Flexible PCB?

(Automated industrial robotic electronic production)

Generally, a circuit board test evaluates the circuit board products, processes, and raw materials. Below are things to test on a circuit board: 

  • Material test: This involves combining the flexible endurance tester and enduring snap tester to evaluate your board’s flexibility. 
  • Thickness measurement: You can use an X-ray thickness tester to evaluate whether the circuit board thickness is up to standard. 
  • Electrical performance is the most common thing tested on a circuit board. It involves testing the performance of components and doing some continuity tests. Therefore, you can know whether the current will flow flawlessly through the board. 
  • Also, testing solder will determine the conductive quality of your circuit board. Furthermore, it determines how well you attach components to the board, and we recommend a wetting balance tester to evaluate this quality. 
  • Wire bonding involves checking the connection quality between components and the circuit board. Consequently, you can use an automatic wire bonding or tensile testing instrument. 
  • Environmental test: Finally, you should test whether the circuit board will withstand different environmental conditions to protect the circuit board component and the users. The best approach is to use a thermal shock tester to implement temperature cycling. Moreover, employ the temperature and humidity chamber for temperature and humidity cycling. 

FAQ

What is the design for testing?

Designing for testing, also known as design for testability, involves employing IC design technologies to incorporate testability features on a circuit board.

Therefore, the features make it easy to create and employ manufacturing tests.

Also, it validates that the circuit board has no defects and is ready to perform its functions. 

In most cases, you do the tests using test programs that function with automatic test equipment.

Is circuit board testing simple?

Never expect circuit board testing to be easy, especially regarding critical things like short circuits.

However, it’s still something you can learn to perfection.

Also, you can optimize your circuit board for future testing with signal and voltage test pads and add LEDs as communication, I/O, and powerful visual indicators. 

What’s the cost of in-circuit PCB testing?

In-circuit PCB testing costs about $20,000 and could range between $10,000 to $15,000.

However, the actual cost depends on the following:

  • The PCB volume
  • The circuit board size
  • PCB complexity
  • Time is taken to test the PCB

Conclusion

Flexible PCB testing is an important part of the assembly process as it guarantees an error-free circuit board.

With proper testing, you can identify problems in the circuit board and make adjustments to restore normal performance. 

Therefore, you can adopt common testing methods like in-circuit, flying probe, and functional testing.

And nothing stops you from inspecting manually or considering burn-in and GM/LTS.

Surprisingly, board testing improves performance and reduces production costs.