What’s important to know when you need a flexible circuit, rigid flex, flexible heater, membrane switch, or other specialty interconnect.

Rob Spiegel

April 1, 2024

6 Min Read
How to build a better flexible circuit
Flexible Circuit Technologies

At a Glance

  • Want to build a better specialty interconnect?
  • What you need to know about the flexible circuit, rigid flex, flexible heater, or membrane switch.

When it’s time for a specialty interconnect, users need to know how they can get a circuit or circuit assembly that will perform in challenging applications.

Trends including miniaturization, connectivity, wearables, and mobility often drive product developers to specialty interconnects over standard rigid PCBs that are unable to meet challenging requirements.

The most important aspect that will lead to a better built specialty interconnect is the design phase. We caught up with Carey Burkett, vice president of Flexible Circuit Technologies, to get a clear idea of what it takes to build a flexible circuit, rigid flex, or flexible heater.

How does design expertise impact your ability to get to a solution that is built better?

Carey Burkett: Most often the customer is seeking a custom solution that will perform within their defined application.  There are many considerations when in the design phase including materials to use, stack ups, how the circuit must perform Is it a dynamic application that will flex many times over the life of product use, or is it a one-time bend for insertion? Is it a critical assembly that is at the heart of the overall device?

In order to build a better specialty interconnect, it starts with design. It is recommended that you partner with an organization that offers highly experienced application engineers with expertise in designing specialty interconnects.

Those with many years of experience, those who have addressed thousands of designs and associated projects, will bring valuable expertise to get you to a cost-effective, reliable solution, and they can do so faster than those with limited experience.

How does an experienced application engineer help to get to the most cost-effective solution that will perform in a challenging application?

Carey Burkett: Beyond having years of experience in design, one must also be familiar with the materials, material properties, what can and cannot be accomplished with these materials, and must understand IPC rules. You need to know where you can push and pull against those rules to accomplish a design that will perform.

The application engineer must ask questions to attain information related to your application including:

  • How is the circuit to be utilized?

  • What mechanical challenges are involved?

  • What electrical challenges exist?

  • What environmental challenges may exist?

  • How is the circuit or assembly going to be installed or used? 

These factors and more must be weighed when designing a circuit/assembly that is aimed at meeting the challenges of the application.

Features and characteristics of your desired circuit related to trace, space, via structures, and more, all weigh into the design and costs. When engaging a highly experienced specialty interconnect application engineer, they will work to meet your requirements, while also pushing the rules or perhaps relaxing some of the features, if needed, that will allow for the circuit to be built successfully at high yields.

Trends have led to rapid growth related to needs for specialty interconnects. Unfortunately, there is a limited supply of design expertise that can help guide customers to better solutions. Some great questions to ask may include:

  • Who is helping me design my flexible circuit?

  • Is it a flexible circuit expert or a standard rigid board design engineer who is now designing flex?

Design experience matters with these types of interconnects.   

How will expert guidance provide you with additional savings?

Carey Burkett: When engaging a highly experienced flexible circuit designer, they will review your requirements, the application, and will find ways to get to a reliable, cost-effective design.  Can layers be eliminated? Can we push the rules in one area of the circuit while relaxing the rules in other areas leading to improved yields? Can we deploy design ideas that we have used in the past that will help to get your circuit to perform in a challenging application? Expertise is extremely valuable in getting to a solution that will perform. It is not uncommon for a design expert to pull 10% to 20% or more in costs out of a customer’s initial design. Also, savings attained in the design phase often outweigh the savings associated with differences in piece price savings that one can attain when comparing production pricing between suppliers.

Another area of consideration is the number of potential revisions needed during prototyping, prior to pinning down the solution that will go to production. Utilizing highly skilled application engineers will help most often reduce the number of revisions – saving valuable product development life cycle time and associated costs.

Expertise also can be critical during prototyping when customers run into issues where the circuit or assembly is not performing as desired. Perhaps inserting the circuit in an improper manner is causing damage, or there is mechanical forces that are leading to issues causing a short or open or something else that is impacting the performance of the circuit. The customer is working to identify the issue but may not be having success. This again is where expertise can be extremely valuable.

For example, a customer was having issues with a challenging smaller flex assembly with tight features. For over 2 weeks they were attempting to identify the problem and utilized their in-house experienced engineers - including some who had flex expertise. The customer had the circuit placed under a scope and one of the top flex engineers in the USA came into the room, looked through the scope and in less than 30 seconds stated, “Well, here is the problem….” The customer and other engineers in the room were amazed that one with years of expertise could identify the issue almost immediately, unfortunately, they had lost 2 valuable weeks.

In another case, a customer chose to work with a low-cost Asia-based supplier, given their initial quote had attractive piece pricing related to production. At the same time, the low-cost supplier did not offer experienced design expertise. The customer application involved a wearable solution that would deal with significant mechanical challenges given its intended use. The flexible circuit would also need to be over molded adding complexity given the challenges involved in over molding a flexible circuit.

Unfortunately, after attaining the prototypes from the low-cost provider, the circuits were not performing at all, because they could not handle the mechanical challenges and associated bend cycle requirements. They also were running into major issues when they attempted to over-mold the flex assembly.

As the customer addressed their concerns with their chosen low-cost provider, the recommended solutions actually took the customer in the wrong direction, making matters even worse.

At this point the customer had no choice but to seek out a supplier that offered true expertise to get guidance to resolve their issues. The design expert advised them on how to resolve the issues with the flexible circuit, so that they could meet their bend cycle requirements and helped them to understand key points related to attaining success when over molding.

The result of this project?  The customer had significant lost opportunity costs, given it took them an additional year to get to product launch, further they had significant development costs due to multiple revisions, prior to getting proper guidance.

While the customer thought it was a great deal from the low-cost supplier, in the end it really added significantly MORE expense and development time.

But hey, they sure did get a great piece price from that low-cost supplier.

Bottom Line – to get to a better built specialty interconnect – it starts with design where utilizing true experts will guide you to cost-effective solutions that will perform. Also, true experts can help you along with way to resolve issues or challenges that often arise during product developmental efforts.

By working with a supplier that brings superior expertise while also providing you with competitive pricing, you can avoid costly pitfalls while attaining the greatest overall value – resulting in… a better built specialty interconnect.

About the Author(s)

Rob Spiegel

Rob Spiegel serves as a senior editor for Design News. He started with Design News in 2002 as a freelancer and hired on full-time in 2011. He covers automation, manufacturing, 3D printing, robotics, AI, and more.

Prior to Design News, he worked as a senior editor for Electronic News and Ecommerce Business. He has contributed to a wide range of industrial technology publications, including Automation World, Supply Chain Management Review, and Logistics Management. He is the author of six books.

Before covering technology, Rob spent 10 years as publisher and owner of Chile Pepper Magazine, a national consumer food publication.

As well as writing for Design News, Rob also participates in IME shows, webinars, and ebooks.

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