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48 FLEX007 MAGAZINE I APRIL 2019 that is 8,000 pieces of core material that must be removed. Again, pouch removal is done at the end of manufacturing just before electrical test where, often, a buyer won't understand why their parts are taking so long to complete. Pouches also leave an edge along the rigid- to-flex transition area that is exposed glass fab- ric. It is customary to bead these edges—espe- cially with high-reliability applications—to protect the flexible arm from coming into con- tact with the glass fabric edge and to protect it from abrasion (Figure 5). The beading material is usually epoxy-based but is soft, similar to silicone. The beading material is also placed by hand, resulting in longer lead times. In the previous example, each flex arm will have two beads placed by hand for a total of 16,000 beads, which can take time to process as well. One other issue with pouched constructions that needs to be accommodated is dimension- ing of the rigid-to-flex transition area—the line of which is defined by no-flow prepreg. The Figure 4: Rigid-flex board with pouch construction. Figure 5: Strain-relief beads applied to the edge of rigid areas to protect flex.

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