All About Flex: High-Temperature Performance Flexible Circuits


Reading time ( words)

Markets requiring thermal exposure at elevated temperatures include down-hole oil drilling, semiconductor processing, medical diagnostics and a multitude of military/aerospace requirements. But a limitation of flexible circuitry has been performance at extremely high temperatures. For purposes of this discussion, the definition of “extremely high” is temperatures that exceed 150–200°C on a continuous basis or 288°C on an intermittent basis[1]. The flexible circuit industry has made inroads improving this product feature with recent developments and significantly improved high-temperature performance, which is being accomplished with new material constructions requiring some unique fabrication processing.  

The adhesive system used to bond the various layers in a flexible circuit is normally considered the weakest link when parts are exposed to high temperature or a harsh chemical environment. This weakness has driven adoption of adhesiveless base laminate technology (the word “laminate” remains an industry term but is a bit misguiding when describing adhesiveless structures as they are not generally produced with a laminating process). Multiple methods for creating an adhesiveless base laminate substrates have become common (copper sputtering, vacuum deposition, cast polyimide) and provide improved performance in both extreme thermal and chemical environments.

But the most frequently used “top side” flexible circuit insulation is generally another layer of polyimide film commonly called coverlay or coverfilm. This layer of film is coated with an uncured adhesive and positioned onto the etched circuitry pattern and then permanently fastened during a temperature/pressure lamination cycle in a platen press. Consequently, an adhesive has been reintroduced into the circuit composite, despite removing the adhesive in the base substrate. Another top side dielectric used in the world of flexible printed circuits is a photo-imaged soldermask, but this material often becomes brittle at elevated temperatures, and can fracture or flake off when bent or folded.

Share




Suggested Items

PCB Technologies’ InPack to Focus on Miniaturization, Packaging

05/16/2022 | Andy Shaughnessy, Design007 Magazine
I recently spoke with PCB Technologies’ Jeff De Serrano, Yaniv Maydar, and Alon Menache about their new venture, InPack. They explain their plans to focus on advanced packaging, miniaturization, and other high-end technology, with much faster time to market, and they offer a view of the global market as well.

EIPC Technical Snapshot: Supporting Autonomous Driving

05/12/2022 | Pete Starkey, I-Connect007
EIPC’s 17th Technical Snapshot webinar on May 4 focused on developments in automotive electronics, particularly on advances in the technologies required to support the evolution of autonomous driving. The team brought together two expert speakers to present their detailed views on topics encompassed within “CASE,” the acronym that appears to be taking over the automotive industry.

Catching up with EISO Enterprises’ President Gary Chien

04/19/2022 | Dan Beaulieu, D.B. Management Group
While there are many Chinese companies now selling in the United States, I wanted to find one in Taiwan that is penetrating the U.S. market. I was delighted to come across EISO Enterprise Co. Ltd., a printed circuit board fabricator located in Taiwan. I know that the American companies are usually looking for PCB global partners in countries other than China, which made my conversation with Gary (Jung Kun) Chien all the more interesting, especially when he shared his thoughts on the U.S-China trade wars.



Copyright © 2022 I-Connect007. All rights reserved.