Rigid-Flex PCB Right the First Time--Without Paper Dolls


Reading time ( words)

The biggest problem with designing rigid-flex hybrid PCBs is making sure everything will fold in the right way, while maintaining good flex-circuit stability and lifespan. The next big problem to solve is the conveyance of the design to a fabricator who will clearly understand the design intent and therefore produce exactly what the designer/engineer intended.

Rigid-flex circuit boards require additional cutting and lamination stages, and more exotic materials in manufacturing; therefore, the cost of re-spins and failures are substantially higher than traditional rigid boards. To reduce the risk and costs associated with rigid-flex design and prototyping, it is desirable to model the flexible parts of the circuit in 3D CAD to ensure correct form and fit. In addition, it is necessary to provide absolutely clear documentation for manufacturing to the fabrication and assembly houses.

The traditional attempt most design teams use to mitigate these risks is to create a “paper doll” of the PCB, by printing out a 1:1 representation of the board and then folding it up to fit a sample enclosure. This presents a number of issues: 

  1. The paper doll does not also model the 3D thickness of the rigid and flex sections
  2. The paper doll does not include 3D models of the electronic components mounted on the PCB
  3. A physical sample of the final enclosure is needed, which may not yet be available
  4. If the mechanical enclosure is custom designed, a costly 3D print will be required for testing. This adds much time and expense to the project. As cool as 3D printers are, it's not a sensible use for them if the modeling can be done entirely in software.

This paper discusses practical steps in two approaches to solve these problems, contrasting against the traditional paper doll approach above.

In the first scenario, a 3D MCAD model of the PCB assembly can be created in the MCAD package where a sheet metal model can be generated for the PCB substrate model. This sheet metal model can be bent into shape in the MCAD software to fit the final enclosure and check for clearance violations. This is not the best approach, but it is better than paper dolls.

In the second scenario, a significant part of the enclosure or mechanical assembly model is brought from the MCAD package into the PCB design software, where the rigid-flex board outline can be designed specifically to fit with it. Rigid-flex layer stack sections can be defined and then flexible circuit areas have bending lines added. In the PCB design tool's 3D mode, the folds are then implemented to reveal where potential clearance violations and interference occurs. The PCB design can then be interactively modified to resolve the problems and check right away—without having to build any further mock-ups or translate design databases from one tool to another. 

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

Share

Print


Suggested Items

Real Time with… IPC APEX EXPO: Siemens’ Supply Chain Solutions

01/17/2022 | Nolan Johnson, I-Connect007
Nolan Johnson speaks with Oren Manor of Siemens Digital Industries Software about the company’s booth at IPC APEX EXPO, which will highlight a DSI platform meant to help designers find and use components in their designs during these tough supply chain challenges. If you can’t make it to IPC APEX EXPO, don’t worry. We’ll be bringing you interviews with the engineers, managers and technologists who are making a difference in our industry.

A High-Voltage PCB Design Primer

01/12/2022 | Zachariah Peterson, NWES
Of all the different boards a designer can create, a high voltage PCB design can be complicated and requires strict attention to safety. If not laid out correctly these boards can be safety hazards or can fail to function on first power up, leaving a designer with wasted time and effort. In the best case, the board will function reliably for a long period of time thanks to correct layout practices. High-voltage PCB design can be as complex as any high-speed digital design. Boards for high-voltage systems can be space constrained and they carry important safety requirements. They also need to be highly reliable to ensure they will have a long life when run at high voltage and current.

High-Voltage PCB Design: Beating Separation Anxiety

01/11/2022 | I-Connect007 Editorial Team
In recent surveys, PCB designers named high voltage among the issues causing problems in their designs. That led us to speak with Zuken USA’s Andy Buja, Wilmer Companioni, and Sanu Warrier about the challenges PCB designers and design engineers must confront when working with high-voltage designs. In this conversation, we discuss everything from the nuts and bolts of high-voltage design, such as the need to separate components of a high-voltage board, to the compliance problems companies like Tesla face when installing EV chargers around the world in countries with varying regulations.



Copyright © 2022 I-Connect007. All rights reserved.