Test Coupons Flex PCBs: All You Need To Know


Oakley Mae

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So what are test coupons flex PCBs, and what are their primary functions?

We use these printed boards to test the quality of the printed wiring board (PWBs) wiring process.

Generally, we fabricate on the same panel holding the printed wiring boards, specifically on the edges. 

For your information, PWBs are simply boards with insulating materials and designed with conductive layers on the surface.

We use them to offer electrical connections and mechanical support.

Therefore, a test coupon flex PCB is handy to ensure that PWBs function effectively and are up to the required quality. 

Today’s piece looks into flex PCB test coupons, including their location, advantages, and limitations. Let’s get rolling!

Table of Contents

What Are Flex PCB Test Coupons

Flex PCB test coupons have become common in the electronics industry since they evaluate and test the reliability and quality of flexible PCBs.

They’re also circuit boards and undergo the same fabrication process and materials as flexible circuit boards.

Moreover, they reproduce the same mechanical and electrical properties as flexible PCBs. 

Generally, you can use test coupons to test different circuit board performance aspects, including mechanic strength, signal integrity, and electrical connectivity.

As a result, it becomes easier to identify errors in your flexible board before they escalate into major irreparable issues. 

Test Coupons Location

Different circuit board elements

(Different circuit board elements)

You’ll find flex PCB test coupons at the flex PCB corners or panel edges. But you might be wondering why this location would matter.

It allows manufacturers and engineers to handle the process and material employed in the circuit board in a standardized and controlled manner.

Moreover, the location guarantees that you identify any errors relating to material quality and the fabrication process before they escalate further.

Also, you can locate test coupons over your PCB surface to give it a more accurate electrical property representation.

However, this approach affects the signal traces, thus interfering with the board’s performance.

Generally, it would be best to locate the test coupons in strategic positions that don’t damage your board.

Sometimes, this could mean more time and money, but we guarantee everything is worth it. 

Flex PCB Impedance Coupon

Beautiful flex PCBs

(Beautiful flex PCBs)

Most flexible circuit boards have controlled impedance to guarantee signal integrity during transmission.

Therefore, there is a need for an impedance coupon to evaluate and test the circuit board’s impedance characteristics. 

Surprisingly, impedance coupons emulate the actual PCB’s mechanical and electrical properties.

It has an impedance track line and vias linked to the impedance trace.

The vias or holes allow the conduction of signals and power to the internal layers containing impedance traces.

Therefore, you test the track impedance value by having the impedance testing machine’s probes through the vias/holes

Designing Test Coupons and What You Can Test

Engineers working on a project

(Engineers working on a project)

To design a test coupon, you create a replica of the circuit board you intend to test.

And the test coupon should mirror the mechanical and electrical properties of the real flex PCB.

However, in most cases, the test coupon is smaller but with the accuracy to determine the reliability and quality of the circuit board. 

The industry has many test coupons to test countless PCB performance features, including solderability, peel strength, conductivity, thermal shock, and surface finish. 

Advantages of Using Flex PCB Test Coupons

There are several reasons why you should embrace flex circuit board test coupons, and we’ll highlight them below: 

Standardization: First, flex PCB test coupons are standardized to mirror the very circuit boards they’re meant to test.

They have the same mechanical and electrical properties as the actual board.

Therefore, we guarantee you’ll consistently test your board’s reliability, quality, and effectiveness. 

Cost-effective: We expect circuit board test coupons to be smaller than the board you place them on.

This means that you’ll spend less to design them compared to what you’ll spend on the circuit board.

Moreover, these products ensure you don’t experience PCB issues; detecting and correcting becomes easy if you do. 

Time-saving: With test coupons, you don’t have to wait until the end of the fabrication process to identify errors.

Interestingly, it allows you to test for errors and circuit board quality in the manufacturing process, not at the end.

For example, if an error arises at the earliest fabrication stage, you deal with it at that point and not at the end.

This approach accelerates the fabrication process, thus saving time. 

Reliable: If you’re worried about accuracy, we guarantee that flex PCB test coupons offer a reliable way of testing the quality and performance of flexible PCBs. 

Quality control: Finally, the set industrial quality standards and what the customer expects.

Flex PCB test coupons provide the essential quality control tools to ensure your board meets your expectation and the set quality standards. 

Test Coupons Limitations

An electronic manufacturing factory

(An electronic manufacturing factory)

Despite the above benefits, we still have some test coupon limitations worth your attention:

Limited scope: Although flexible PCB test coupons provide information relating to quality and performance, they won’t cover some complex issues.

Therefore, you must acquire complex testing capabilities for such complex tasks. 

Single-use: Flex PCB test coupons are designed to offer tests for single-use, meaning that you can’t use them to get ongoing information about a manufacturing process.

You’ll have to use multiple test coupons to get such information, which is more expensive. 

Size constraints: Almost every flex circuit board test coupon is smaller than the circuit board they work on.

Therefore, it becomes difficult to replicate the mechanical and electrical properties of the actual circuit board with accuracy and precision. 

Limited accessibility: Generally, we locate test coupons at the PCB corners and panel edges.

And sometimes, you can place them on the surface, although it affects trace performance.

Therefore, the limited test coupon location makes accessing and testing some areas challenging. 

Expensive: Although test coupons are less costly than the actual circuit board, they still represent an added cost to the manufacturing process.

Unfortunately, you’ll have to invest in complex and expensive equipment and materials. 


Why use test coupons?

You cannot do away with flex PCB test coupons if you want to design quality and highly efficient circuit boards quickly.

First, test coupons come in handy when testing and evaluating the reliability and quality of the PCB manufacturing process.

In short, they offer a controlled and standardized approach to testing the process and materials, meeting customer expectations, and limiting production errors. 

What are the PCB test coupons types?

The market is full of flex PCB test coupon types for testing almost every performance aspect of the circuit board.

Whether you’re considering evaluating solderability or conductivity, there is a test coupon for you.

We will highlight all the common options below: 

  • Solderability test coupons
  • Surface finish test coupons
  • Thermal shock test coupons
  • Conductivity coupons
  • Microsection coupons
  • Peel-strength coupons

Can you reuse flex PCB test coupons?

A flex circuit board test coupon is meant for single use; thus, reuse isn’t advisable.

Since it mirrors an actual circuit board’s mechanical and electrical properties, it’s also prone to tear and wear.

Therefore, reuse will mean compromising the accuracy and integrity of the tests. 

Final Remarks

Whether you like it, you must include a PCB test coupon on your circuit board to achieve high-performance and error-free products.

Many manufacturers appreciate its importance after encountering errors at the end of the manufacturing process, only to realize such errors could have been avoided at the initial stages.

This sad situation ends up consuming a lot of time in error correction.

Therefore, use a test coupon all the time to evaluate the mechanical and electrical properties of your PCB as you develop it.