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18 DESIGN007 MAGAZINE I AUGUST 2022 Sidebar by Happy Holden Note: For this issue, Happy Holden provided a range of options for designers who are seeking to conserve materials in their next design. He also offered an example of the relative cost index, or RCI, that he developed at HP exclusively for PCB design. With this RCI, designers can figure out the relative cost of a new design compared to an eight- layer through-hole board. • Consider making the board thinner; eliminate prepregs • Design to HDI for smaller board or fewer layers (Figure 1 and Reference 1) • Design inner layers with 1 to 2 mil smaller traces/spaces • Swing vias for BGA breakout can reduce layer count • Nesting and rotation on panels Happy's Design Tips for Material Conservation • Using HDI "skip vias" to eliminate a build-up layer Consider using new technologies: • VeCS can reduce layer count (Figure 2 and Reference 2) • Additive creates more routing per layer and smaller boards • Switch HDI layers to RCF (RCC) • Power mesh can yield fewer layers (Reference 3) • Landless vias on the surface can mean higher routings (Figure 3 and Reference 4) • Smaller panel peripheral border • Different panel sizes for higher utilization • Add-on 0.062" gold fingers as components • Board replacement for X-outs and repanelization (Reference 5) • Inkjet solder mask just on traces/pads Figure 1: Replacement chart for through-hole to HDI with Relative Cost Index. Note: RCI = the relative cost compared to an eight-layer through-hole board (RCI=1.0). DEN = total wiring in inches per square inch (diagonals of equivalent density).

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