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

Print


Suggested Items

Chapter 2 Excerpt from the Book ‘Thermal Management: A Fabricator's Perspective’

12/21/2020 | Anaya Vardya, American Standard Circuits
Insulated metal PCBs (IMPCB) or metal-clad PCBs (MCPCB) are a thermal management design that utilizes a layer of solid metal to dissipate the heat generated by the various components on the PCBs. When metal is attached to a PCB, the bonding material can either be thermally conductive but electrically isolative (IMPCBs or MCPCBs), or in the case of RF/microwave circuits, the bonding material may be both electrically and thermally conductive. The reason that RF designers usually have the bonding material thermally and electrically conductive is that they are using this not only as a heat sink but also as part of the ground layer. The design considerations are quite different for these different applications.

Happy Holden: ECWC15 Virtual Event a Success

12/15/2020 | Happy Holden, I-Connect007
This is the first Electronic Circuits World Convention that I have not attended in person since 1978. To refresh your memory, these are held every three years on a rotating basis. The HKPCA hosted this year’s conference and they kept up the fine tradition of collecting outstanding keynotes, nearly 60 technical presentations and myriad poster papers. HKPCA was also kind enough to provide English slides and translations. It is still possible to sign up and view the presentations. I have listened to 20 of the presentations, and hope to attend even more in the coming days as they are all worth watching.

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

12/04/2020 | Andy Shaughnessy, Design007 Magazine
Around the holidays, we often see a slowdown in PCB design and manufacturing news. But this holiday season, there’s been no rest for the newsmakers in our industry! In the last week, our daily and weekly newsletters have been chock-full of breaking news and up-to-the-minute technical information that readers like you rely upon every day.



Copyright © 2021 I-Connect007. All rights reserved.