The Art of Bending and Forming PCBs


Reading time ( words)

Flexible circuits are designed to be bendable, but bending rigid PCBs is a little unusual. However, many applications that do not use flex circuit technology will also require bending and forming the circuit. Some of these applications use high-frequency circuit materials to create a circuit in a form that enables improved antenna functionality. Another application involves wrapping a circuit around a structure, which sometimes functions as an antenna as well.

Bending and forming a circuit with dynamic flexing action will require understanding a few basic principles, regardless of the circuit material used. Of course, the circuit material used can make a huge difference in the success of forming circuits without causing conductor or material fracturing. As a general statement with a few exceptions, a circuit material used for bending, forming and flexing cannot have woven glass reinforcement. Because of this, typical FR-4 materials with woven glass are not recommended. Several materials used in high-frequency rigid board applications do not have glass reinforcement and have been used successfully for bending, forming and flexing.

LCP circuit materials are quite suitable for applications where bending, forming and flexing is necessary, and they offer very good high-frequency electrical performance as well. These materials are made as relatively thin laminates, typically less than 5 mils. This thinness aids in the successful bending of the circuits.

However, another set of high-frequency materials has been on the market for many years and used in forming applications: PTFE-based laminates, without glass reinforcement. These materials typically use fillers with the PTFE substrate to help lower the high CTE of PTFE, and this does not detract from the material’s bending capabilities.

The basic idea of bending circuits is based on mechanical beam composite theory. As an example, a simple double-sided circuit will be used to demonstrate the concepts. This circuit will be considered a microstrip transmission line with a signal conductor on the top conductor layer and ground plane on the bottom as shown in Figure 1.

The beam composite concept considers the cross-sectional area of a circuit that is made from different layers of materials. One property critical to understanding bending is modulus; in this case, modulus is the measurement of how stiff the circuit is. A high modulus is stiff, and low modulus is soft. When bending a circuit, softer material will generate less stress within the circuit and when there is less stress, the different layers are less likely to fracture.

Bend radius is another very important issue. A simple way to think about this: If it is necessary to bend a metal sheet that is 1/8” thick without fracturing the metal, then having a large bend radius will be advantageous and, of course, a small, tight bend radius is more likely to cause metal fracturing. The small bend radius causes more internal stress on the metal and is prone to fracturing.

To read this entire article, which appeared in the June 2015 issue of The PCB Design Magazine, click here.

Share




Suggested Items

A Definitive Review of New Expert Guide to High-Performance Materials

04/13/2022 | Happy Holden, I-Connect007
I am always surprised when a colleague produces a statement about PCB laminates that seems incorrect or out of date. This need not happen today as the specialists at Isola have written an excellent book about high performance materials, now available for download from I-Connect007. Author Michael Gay, a 25-year veteran of laminate manufacturing, meticulously guides readers through the most pertinent questions regarding rigid laminates. This is essential information for everyone, including the experts, because the materials and applications for laminates in printed circuits are constantly changing.

New Book From Isola Highlights Importance of Material Selection

01/14/2022 | I-Connect007 Editorial Team
In "The Printed Circuit Designer’s Guide to... High Performance Materials," the latest release from I-007eBooks, readers will learn how to overcome challenges associated with choosing the right material for their specific application. Author Michael Gay of Isola provides a clearer picture of what to know when determining which material is the most desirable for which products. PCB materials and DFM expert Mark Thompson says, “I love this book, particularly the sections on the effects of the glass weave, the history of laminate, and the difference between Dk and effective Dk."

Living in a Material World: High-Speed Design Strategies

01/13/2022 | I-Connect007 Editorial Team
Any discussion about high-speed PCB design techniques would be incomplete without considering the properties and requirements of the materials. Your material selection drives much of your design strategy when you’re operating at 28 gigabits per second or faster. We recently spoke with high-speed design expert Lee Ritchey of Speeding Edge, and electronic materials veteran Tarun Amla of Avishtech and Thintronics, about the relationship between advanced PCB materials and high-speed design techniques. They discuss the challenges facing designers and engineers working with materials at speeds that were considered unreachable not long ago, and what designers need to know about material selection as board speeds continue rising toward the stratosphere.



Copyright © 2022 I-Connect007. All rights reserved.