Decreasing Bend Radius and Improving Reliability—Part I


Reading time ( words)

Application: Design guidelines to improve the flexibility and reliability of flexible circuits.

Many of the issues that arise when using a flex circuit come from a lack of knowledge about how to properly design one, especially when the circuit is required to bend. Many novices will design a circuit that calls for bending the flex in too tight of a bend radius, which can cause damage to the circuit and lower the reliability of the end product. This series of articles will focus on the seven key aspects to consider when designing for maximum durability and maximum “flexibility.” It is important to know that because flexibility is a relative term, this study will instead use the phrase "reducing bend radius." Here are two of the seven design strategies (please see Part II and Part III for more tips):

1. Reduce overall thickness:

IPC guidelines typically list minimum bend radius of 6X the circuit thickness for single-sided flex, 10X for double-sided flex, and 20X for multiple layer flex. The area of focus is the thickness where flexing or bending will occur, which should be only in a location with conductors and not plated through-holes. Thickness can best be reduced by:

A. Using thinner copper

B. Using adhesive-less base materials

C. Stagger conductors

D. Specifying button plating or pads only plating

Any flex circuit with plated through-holes will need to be either panel plated or button plated. Button plating is preferred because it only plates the vias and leaves the conductors un-plated and which does not increase the thickness.

2. Use only rolled annealed (RA) copper:

There are two common types of copper; rolled annealed (RA) and electro-deposited (ED) copper.

A. Rolled annealed copper is best for achieving a tighter bend radius.

B. It is also important for you to put on your drawings the direction of the grain in relation to where the tight bending will occur.

flex.jpg

Go to Part two of this article.

Share




Suggested Items

I-Connect007 Editor’s Choice: Five Must-Reads for the Week

10/28/2022 | Nolan Johnson, I-Connect007
Halloween is next Monday and parties will be taking place over the weekend, I’m sure. Here in the United States, at least, the “any-holiday-is-an-excuse-for-a-party” crowd has integrated Halloween, along with Valentine’s Day, St. Patrick’s Day, and Cinco de Mayo into wide-ranging opportunities for themed revelry. The news this week has been a bit crazy as well, though certainly not alcohol-fueled. There was a lot of important news and narrowing it down to just five was thought-provoking yet ultimately rewarding. Here then, are the five top pieces of news you shouldn’t miss this week.

PCB Technologies Sees Substrates as a Foundation

10/27/2022 | Nolan Johnson, I-Connect007
In this interview, PCB Technologies CEO Oved Shapira discusses the company's move into advanced packaging and heterogenous integration. Shapira explains how substrates and advanced packaging fit into the PCB fab and assembly ecosystem, and makes the argument that an all-inclusive fabrication and assembly supplier can be of great value to customers in product development and small scale production.

I-Connect007 Editor’s Choice: Five Must-Reads for the Week

10/21/2022 | Andy Shaughnessy, Design007 Magazine
Where did the year go? I can’t believe we’re planning our January and February issues now. It was 84 degrees most of last week in Atlanta, and now it’s 31. I guess I should take my Hawaiian shirts out of rotation! This week we have quite a variety of articles for you. It’s officially show time and the industry is back in business in a major way. We have some news coming out of last week’s advanced packaging event in Washington, D.C., and an article about navigating SMTA International, which opens on Halloween this year in Minneapolis. We have a great column on avoiding EMI with good routing strategies, and an article on electrically conductive inks. To top it off, I-Connect007 has published a new book, written by Matt Stevenson of Sunstone Circuits, that posits a new “design for”: Designing for Reality. If you’re a designer, isn’t designing for reality what it’s all about?



Copyright © 2022 I-Connect007 | IPC Publishing Group Inc. All rights reserved.