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44 DESIGN007 MAGAZINE I MARCH 2024 Core-to-core alignment can also be a chal- lenge with thinner cores since heavy copper PCBs are more prone to registration issues that manifest in exposed copper in the winding cut- outs as well as at the edge of the board. Most fabricators use fixed pins to align pre-punched cores to match these pin locations. Heavy cop- per on thin cores faces the dual threat of han- dling difficulty and a thin dielectric around the punch that oen results in tearing, which, in turn, produces alignment issues. Design Solution e most cost-effective method is to create greater allowances for layer-to-layer registra- tion. Fabrication Solution Hope remains if these design considerations cannot be met. Fabricators can enhance align- ment by using either an indexed pin setup or auto-alignment lamination machines, which do not require the use of pins. in core mate- rials require varying degrees of scale factors to account for material shrinkage during lamina- tion. Both copper weight and circuit pattern affect shrinkage so experienced fabricators counter this through data collection. X-ray drills equipped with high-resolution cameras measure each layer and collect material shrink- age data to optimize future production runs. Aer collecting the data, the X-ray drills fresh tooling holes that optimize for layer-to-layer alignment, shi, and rotation to ensure drilled components and via holes are within capture pads. Design issue: Feature-to-feature spacing too small Manufacturing pitfall: Over-etching (anti-puddling) Small features and spaces (within acceptable limits) are a burden to be borne by the fabrica- tor alone. e focus would need to be on the actual etching process whereby circuit features are created. In this process, etching chemistry is sprayed from above and below the panel dur- ing this horizontal process. While the chemis- try sprayed from beneath the panel falls away because of gravity, the chemistry sprayed from above remains on the PCB in the form of a pud- dle, obstructing the surface and absorbing the force of the ensuing spray. Since etching is as much a function of physically hitting the cop- per as it is a chemical reaction, the etch rate of the top side is thereby reduced. As a result, the operator must reduce line speed to properly etch the top side which, in turn, over-etches the bottom. It goes without saying that etching heavy copper features will only exacerbate this predicament. Table 5: Common design resolutions. Figure 5: Material shrinkage.