Issue link: https://iconnect007.uberflip.com/i/1500943
70 DESIGN007 MAGAZINE I JUNE 2023 width transitions, or traces non-perpendicular to the bend axis in a bend area. Also, I-beaming where traces are coincident on adjacent flex- ible layers. 2. Delamination Pads or vias in bend areas with improper pad shapes or coverlay exposures. When it is required to have vias or other pads in bend areas, special care must be taken when design- ing the coverlay to reduce delamination poten- tial. Oen in these conditions, the coverlay overlaps the pad area to prevent delamination. In other designs, pads are adorned with tabs to extend under the coverlay. 3. Tearing e absence of tear stops on slits or inside corners. Copper segments, arcs, circles, or other shapes are added to prevent tear around slits or inside corners. 4. Squeeze out Epoxy leakage onto adjacent copper or other layer surfaces. In order to prevent epoxy squeeze out, a perimeter air gap or fence must be present around adjacent layer content. For example, a larger annular ring may be required on the epoxy layer than its corresponding cov- erlay annular ring. is prevents epoxy from squeezing out onto adjacent copper or traces. 5. Button plating Absence of exposures in coverlay for vias. e most common method of plating vias in a bend area is button plating. is requires vias to be plated have an exposure on their adjacent coverlay. Absence of an exposure on the cover- lay would prevent plating. 6. Orphaned conductors Conductors located outside, or off of, their respective layers. As mentioned previously, absence of individual layer profiles in PCB CAD systems may ultimately lead to orphaned conductors. Analysis against a board outline rather than a layer's profile is a common cause of this error condition. It puts the onus on a designer to visually inspect layer content for this condition. 7. Coverlay dams Dams of coverlay between pads rather than ganged exposure. Coverlay is not installed in the same way as liquid photoimageable solder mask. It is a die cut film that does not support thin solder dams between adjacent pads. 8. Layer against layer Inter-layer dependencies unique to flex and rigid-flex. Many layers in flex and rigid-flex designs are inter-dependent. For example, a RF or shield layer over a conductive layer requires coverlay exposures, contact points between copper, and RF layers to be properly aligned. 9. Area management e creation and management of stackup zones, bend areas and other regions. Proper analysis requires well defined regions of stackup, bend, flex, rigid and other areas. It is impossible to analyze bend area constraints without precisely defined bend areas. 10. Stackup management e creation and management of multiple stackups. Almost all rigid-flex designs have multiple stackup areas. To fully analyze a design, the DFM analysis must support the presence of more than one stackup and their related zones of the PCB. Creation and assign- ment of stackups to zones is required when the data does not provide adequate content for analysis. 11. Intelligent data passing e ability to pass analyzed data to fabri- cators in intelligent file formats. Aer a full DFM analysis, the design should be passed via intelligent file formats to minimize guesswork