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JUNE 2019 I PCB007 MAGAZINE 37 ed through-holes both mechanically support- ing and electrically connecting with the flex layers. This particular design required heavier copper for shielding and was in danger of not being flexible enough for the end application. To solve that problem, a loose-leaf construc- tion was used. In this case, the layers were split into two sections. Figure 7 is also a rigid-flex design, having circuitry included in the rigid areas. This sam- ple gives one of my favorite views of the pow- er of loose-leaf construction. This design did not have heavy copper but did have 10 flexible layers that if all bonded together, would nev- er allow for the flexibility required in end use. Something that isn't shown well in the photo is the use of crosshatch shielding in the flexi- ble layers, which is also added to the flexibility of each of these layers. Figure 8 displays a common rigid-flex con- struction with two rigid areas connected by flexible layers. I wanted to include this for two reasons. First, it's simplicity. This type of de- sign is one that many start with when they first move into rigid-flex. The concept is simple, and this is one of the lowest cost forms of rigid-flex design. The second thing I wanted to point out with this image is the use of strain relief with a simple bead of epoxy where the flex and rigid layers meet. This prevents damage to the flex in that critical area. Figure 9 is another example of a rigid-flex construction and demonstrates how the flex- Figure 6. Figure 8. Figure 9. Figure 7.

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