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58 DESIGN007 MAGAZINE I MARCH 2022 ment of tabs in some cases for edge plating. For a single edge requiring plating, tabs may not be required for stability. Development of Tabs for Transporting the Panels e drawing on the le in Figure 2 shows how perforated tabs are implemented for a circuit that is manufactured in a multiple-up array. e requirement is that the tabs being used to hold the board in the array will be broken off aer the assembly operation (also called singulation). Figure 2 (right) shows a solid tab that is placed at the plated rout pro- cess. In both cases the internal and external layer artwork around the tabs must be void of metal. is will prevent the metal from being exposed in the singulation process. When a solid tab is used, the tab is removed at the final fabrication stage using a router (the same router that removes standard parts from the carrier panels). Removal of the tab will leave a small protrusion along the edge of the part. Also detailed are the minimum require- ments for the dimensions of the tabs. Place- ment of the tabs is based on assembly require- ments and materials being used to construct the circuits. Less dimensionally stable materi- als, typically non-reinforced materials, as well as thin (<0.060") and thicker panels (>0.200"), will require additional tabs for stability in pro- cessing. Conservatively, the tabs are placed every two inches along the plated edges. For non-FR-4 materials this is more the rule. Design Rules for Plated Edges It is required that the plating not only encap- sulate the edge of the panel, but that the plating also wrap around to the surface of the panel. is is shown in Figure 3, and the minimum distance the plating is required to wrap around to the surface is 0.015". e wrap-around is required for internal processing and adhesion of the plating to the edge. Also detailed is the minimum distance a feature can be placed to the wrap around plating (0.010") as well as the distance required for an adjacent routed fea- ture (0.100"). It is typical that the plating be continuous along the entire edge of the circuit, but inter- ruptions in the plating can be designed with two methods. By placing a tab at the interrup- tion, and subsequently removing it, the tab prevents the plating (Figure 4a). Alternatively, the plating interruptions can be removed at the final routing stages. e subsequent removal of the plating will leave a small tab or an inden- tation into the circuit (Figure 4b). e inden- Figure 2: A solid tab that is placed at the plated rout process. In both cases the internal and external layer artwork around the tabs must be void of metal.