Just Ask Tara Dunn: Maximum Number of Flex Layers?

Estimated reading time: 1 minute

First, we asked you to send in your questions for Happy Holden, Joe Fjelstad, John Mitchell, and others in our “Just Ask” series. Now, it’s Tara Dunn’s turn! Tara is the vice president of marketing and business development for Averatek. Tara discusses flexible circuits, rigid-flex, and rigid PCBs, as well as RF/microwave technology, microelectronics, and additive processes. She is also co-founder of Geek-a-Palooza and a show manager for the SMTA Additive Electronics TechXchange event. She has over 20 years of experience in the PCB industry. We hope you enjoy “Just Ask Tara.”

Q: What is the outside maximum number of flex layers that have been used in an actual product?

A: I could answer with a number based on just my personal experience and memory, but I think it is important to include some context along with that. The key issue with the number of layers in a flexible circuit is the ability for that flex to function in a reliable manner, over time, as intended, whether that be flex-to-install or in a dynamically flexing application.

“The flex that didn’t flex” is something we joke about, but it happens more often than one would think. I have seen three-layer flex circuits that were not flexible enough to be bend around the corner of the package, and I have seen 12-to-14-layer flex circuits that functioned beautifully in high-flexing environments. Key considerations to improve flexibility such as material selection, using unbonded layer construction and cross-hatch copper patterns vs. solid copper can have a significant impact on performance.

Involve your fabricator early in the design cycle; they have a lot of knowledge to draw from on how to best meet your overall flexing requirements.

To submit your questions for Tara, click here.

As a regular I-Connect007 contributor, Tara writes the column Flex Talk for FLEX007.