Do you need to work with your fabricator every time you start a design? Maybe not. Do you need to work with your fabricator early in the design process for flex and rigid-flex? Yes, I think so, especially if flex and rigid-flex designs are new to you. If you are well-experienced in flex and rigid-flex and have worked closely with your fabricator to understand their materials, preferences, and processes, you probably don’t need to reach out every time, although it’s a good practice when working with anything new, and working out the best stack up based on common materials is very beneficial.
So when do you need to work with your fabricator early in the design, every single time? When you are working with high reliability, avionics, or space applications that need to perform over an extended life in harsh environments. This market has stringent requirements which are difficult for rigid constructions and these requirements increase in complexity when you move to rigid-flex construction.
As a part of our continuing blog series intended to help fabricators communicate with designers on issues they believe are most critical, I reached out to Paul Cooke, Director of Field Applications Engineering and Technical Sales for FTG Circuits. Paul has more than 30 years of experience in printed board (PWB) design and manufacturing. He has held senior positions in operations, quality, process engineering, and field application engineering at some of the top North American PCB manufacturers. Paul has served on a number of IPC technical committees to develop industry standards, and recently received an award for contributions to IPC-9121, “Troubleshooting for Printed Circuit Boards.” His current position is solely focused on working with designers in the avionics and space industry to design and develop products that need to have extended life and long-term reliability in harsh environments, and he has graciously shared his expertise in response to these questions.
What do you wish every designer knew about flex, and why?
I wish more designers could spend more time learning how printed circuit boards are actually fabricated. This is more important today, especially with the design complexity increasing year to year. This is even more important with rigid-flex constructions because of the differences in fabrication compared to rigid PCBs. Today we are seeing designs upwards of 32 layers and 10 to 12 lamination cycles.
What is your best advice to someone just starting with flex and rigid-flex?
Talk to a good board shop and one that has a field application engineer who can steer your designs early in the process to make them successful, reliable, high yielding and cost effective. Talk to the board shop prior to starting the design to get advice on materials, stacks, layer counts, form factors, etc.
What is the key difference in the fabrication process when working with flex materials as compared to rigid materials?
Flex is a much different process than rigid and there are a few different methods to achieve the same goal. Talk to a few different fabricators and get them to present their fabrication process so that your engineers can learn how to manufacture the rigid-flex, which definitely helps with the design process. As a quick list, key things to understand and remember are rules for bend radius, rules for copper weight, stiffeners, surface finishes, aspect ratio, thermal management, controlled impedance (rigid to flex transition), line and space, via sizes and clearance, Class 2 vs. Class 3 etc.
In terms of flex and rigid-flex fabrication, what makes your company unique in the market and why is this important?
Today, fabricators need to be able to fabricate any and all constructions. Because we are focused only on products requiring high reliability, Class 3/DS, Aerospace, Military and Space markets, we understand the individual requirements of the customer. Long term reliability is our primary objective when working with customers and designers. We are seeing more products in these industries reducing in size and increasing in complexity with more rigid-flex requirements. This adds additional challenges for the designer who is forced to utilize a wide range of materials, including hybrid constructions. With our expertise in this market segment, we can help these designers achieve this successfully.
Wrapping up, what is the key take-away you want designers to learn from this short discussion?
Talk to the fabricator and visit a facility, remember they have probably dealt with issues and have solutions for things that you are yet to face.
Finally, I want to thank Paul Cooke for participating and answering these questions and giving insight into some of the bigger issues that flex and rigid-flex PCB fabricators deal with. Next, I want to encourage you to please reach out to us or post a comment suggesting questions that you would like to see answered in future blog posts!
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