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

Print


Suggested Items

Interconnect Reliability Correlation With System Design and Transportation Stress

08/12/2019 | Dr. Paul Wang, Vincent Weng, and Dr. Kim Sang Chim, Mitac International Inc.
Interconnect reliability is very critical to ensure product performance at predefined shipping conditions and user environments. Plating thickness of the compliant pin and the damping mechanism of electronic system design are key success factors for this purpose. This paper discusses design variables—such as pin hard gold plating thickness, motherboard locking mechanism, and damping structure design—to ensure interconnect reliability.

A Guide to High-reliability PCBs from Design to Specification

07/24/2019 | Jeff Beauchamp, NCAB Group
Creating reliable PCBs is an outcome of considering all aspects that can affect reliability as early as possible in the design process. The further down the design process, the more expensive and risky it can be to fix. As they say, everything starts with the design. Because a good board design improves the reliability of the end product and lessens the risk of failure.

How Changing Cleaning Technologies Affect Reliability

07/22/2019 | Andy Shaughnessy, I-Connect007
At the recent IPC High-Reliability Forum and Microvia Summit, Andy Shaughnessy spoke with Michael Konrad, founder and president of Aqueous Technologies and a speaker and panelist at the event in Baltimore, Maryland. They discussed Konrad’s presentation and the recent proliferation of cleaning, from solely high-reliability products to Class 1 consumer products.



Copyright © 2019 I-Connect007. All rights reserved.