PCB Design Child’s Play—The Paper Doll Approach

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PCB Design Child’s Play—The Paper Doll Approach

The most common method deployed by design teams to ensure that a rigid-flex PCB design will fit in an enclosure is the “paper doll” model of the PCB. These models, created from paper, are cut into what’s hoped to be an exact shape of the PCB in concept. This method has its roots in traditional PCB applications, but recently gained widespread use with the need to model flexible circuitry. Most PCB fabricators still promote this approach.
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Figure 1 shows an example of a cardboard paper doll being used to model the mechanical fit of a stepper-motor controller. To create this model, the designer first made a 1:1 printout of the 2D PCB outline, then cut it into its final shape. To more accurately model the assembly and provide a more precise feel to the model, the designer glued a piece of cardboard to the paper model to approximate the thickness of the rigid parts of the PCB.

1. To make this paper doll a rigid-flex PCB for a stepper-motor controller, the designer printed a 1:1 copy and then cut out the final shape.

While effective at modeling an approximate shape of a rigid-flex PCB, the paper doll approach has a number of inefficiencies and problems in application, including:

• Imprecise thickness: The paper doll isn’t the same thickness as the rigid and flexible sections of the PCB. Therefore, it becomes very difficult to simulate the bending of the paper model because it will bend in its final application. This makes it incredibly challenging to get a clear idea about the fatigue or natural folding properties of the design.

• No 3D models: The paper doll doesn’t include all of the 3D component models that will appear in the final design. One must wonder how the presence of these models will change how the model folds, and whether a 3D model might interfere with the clearance required for the rigid-flex sections to fold properly.

• Costly 3D printing: To determine a correct board fit with an enclosure, it might be necessary to print the enclosure with a 3D printer. Depending on the complexity of a design, this can become a costly option to implement—it adds a layer of unnecessary expenses to a project that could have been simulated entirely in software.Intelligent hardware

Despite its widespread use, the application of paper doll models to simulate the real-world application of a rigid-flex PCB design is both imprecise and impractical. Designers who rely on this method to ensure a correct PCB fit with the mechanical enclosure risk the potential of design revisions and expensive prototype adjustments during the fabrication process. So, are more sensible and efficient approaches available to designers?


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