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18 DESIGN007 MAGAZINE I NOVEMBER 2025 When early computer ECAD tools arrived in the 1980s, engineers carried those classic terms into the digital world. "Let's flood the ground" meant "fill that area with copper." That's how our linguistic confusion began. Those first PCB CAD programs—Protel, PADS, OrCAD, and others—were miracles compared to Mylar and tape, but we still had to find a way to automate that same "fill with copper" process. So, software engineers borrowed a concept from computer graph- ics called "flood fill," which is the same algorithm behind the "paint bucket" tool in art programs. Click inside a shape, and the computer automatically fills it with color (or in this case, copper). Thus, the term "flood" became part of the PCB vocabulary. Designers would select an area and run the "flood" command to fill it, but when they moved a trace or pad, they would have to re-flood the whole thing. Many late nights were spent watch- ing copper slowly refill the screen like an incoming tide. It was tedious but magical when your board slowly came alive in glowing copper zones, and if you had your colors set up correctly, it made it look like Walt Disney had thrown up on your screen. However, nothing stands still in PCB design, which was the case with ECAD tools. They replaced that static "flood" with something more innova- tive—the polygon pour, which allowed the drawing of boundaries (as a polygon) and assignment of a specific net. Then, the software automatically filled it with copper, adhering to clearance and thermal rules. If you had to move a component or reroute a trace, the pour could automatically adjust to accom- modate the changes. Suddenly, copper was intel- ligent. This was the difference between filling a bucket manually and installing an automatic sprin- kler system. It was the same water but with more intelligent control. However, the old terminology remained. Design- ers still said "flood" when they meant "pour." Some even used both: "Re-flood that polygon pour." Yes, it was confusing; however, it was accepted, and everyone knew what it meant. While polygons ruled the outer layers, another idea was taking shape inside the board: planes— solid sheets of copper dedicated to a single pur- pose—either grounding or power. Instead of draw- ing copper, you define a plane in the layer stack. Planes act like copper highways. They have low resistance, low noise, and excel at dissipating heat. They make circuits more sta- ble, signals cleaner, and layouts easier to live with. Why this isn't clear depends on who you are speaking to: The veteran PCB designer who used old tools still says "flood" even though they're using "dynamic pours." Begin- ners see large copper areas and assume they're planes. The ECAD documentation doesn't help—casually calling a polygon a "ground plane." And the ECAD tools blur the line by having a polygon pour on internal layers or split planes on signal layers. I have a method for resolving this issue, espe- cially for new PCB designers when they encoun- ter different terms being used. The planes are the ocean—broad, deep, and stable. Polygon pours are ponds you dig yourself—flexible and local. Flooding is just filling them with water. The confusion surrounding these terms is nostal- gic. It reminds us how far PCB design has come: from X-ACTO knives and tape to dynamic polygons. Some may still say "flood the board" because it connects us to those designers who once literally cut copper with razor blades. It's a small way of keeping the craft's history alive. So, the next time you click "repour all" and watch the copper shimmer into place, take a moment to appreciate it. That single click repre- sents decades of evolution, countless innovations, and a thousand cups of coffee. DESIGN007 John Watson is a professor at Palomar College, San Marcos, California. To read past columns, click here. E L E M E N TA RY, M R . WATS O N