What is the reason for the positive trapezoidal state of pcb wires?

Because the process of PCB plate making is formed by top-down corrosion. The longer the downward etching time of pcd plate, the greater the side etching amount. Due to the influence of side etching, the completed circuit becomes trapezoidal, so the cross section is trapezoidal. The principle document has been established for Pcb board design circuit steps. Design working environment, place components, wiring schematic diagram, establish network report, check electrical rules, compile and adjust, save files and report output.