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16 DESIGN007 MAGAZINE I NOVEMBER 2025 If there were a PCB Design Dic- tionary of Confusing Terms, the cover would feature four words that have baffled generations of engineers: polygons, pours, planes, and floods—or what I refer to as the four horsemen of cop- per confusion. They sound sim- ple, as if they belong in a geome- try textbook or a weather report, but in PCB design, they overlap, develop, and sound interchange- able until you realize they aren't. Ask 10 designers to explain the difference and you'll get 10 answers, three sighs, and at least one person saying, "It depends on the software." These four terms have been misused, rede- E L E M E N TA RY, M R . WATS O N by J ohn Watson, CID The Four Horsemen of Copper Confusion fined, and occasionally blamed for design errors that weren't their fault. Poor copper can't catch a break. Welcome to a very confus- ing concept in PCB design. These four terms, in fact, describe how copper is distributed on printed circuit boards. It's one of those topics where history, technology, and habit have become entan- gled like a poorly routed trace. To understand why they're con- fusing, we need to rewind to the early days of manual PCB design, when designers sat at light tables and hand-drew on transparent Mylar sheets, adding black adhe- sive tape to represent copper traces. Each roll of tape was a specific line width. You built your circuit one strip at a time, like cop- per origami, and went home with bits of black tape all over you and nicks in your fingers. If you have never hand-taped a PCB, I rec- ommend trying it, not just for the experience, but also to appreci- ate today's modern tools. When manual PCB designers wanted a large copper area for ground or power, they didn't draw it; they stuck down a solid sheet of black film. If they wanted a clear- ance, they carefully sliced away the film with a razor blade. Those larger areas of copper appeared to have been poured or flooded onto the sheet. The language stuck.