Printed Circuit Board

When you unscrew a phone or a television, you usually see a flat green plate. On it sit small black blocks, silvery dots and fine lines. This plate is called a printed circuit board. It has two jobs: it holds all the components mechanically in place. And it connects the components electrically, so current can flow from one to the next. Instead of many individual wires, there are hair-thin copper traces that are fixed firmly onto the board for this purpose. In English it is called a Printed Circuit Board, or PCB for short.

Why no device works without a board

Before the printed circuit board, electronic circuits were wired by hand. Every connection was a single wire, every solder joint was manual work. That was slow, expensive and error-prone. A device with a thousand connections would practically not have been buildable that way. The printed circuit board turns this wiring into a printing process: you design the pattern once on a computer and can then produce it identically millions of times over.

That is the reason electronics have become so cheap. A modern chip can be as powerful as it likes — without a board that connects it to power supply, memory and connectors, it is useless. This is especially true for AI data centers. A graphics card is, at its core, a compute chip on a very elaborate printed circuit board.

That is also why the manufacturing of printed circuit boards is economically and politically sensitive. A very large share of global production takes place in East Asia, especially in China, Taiwan and South Korea. When these supply chains falter, factories for cars and computers grind to a halt — even if the chips themselves would be available.

Copper traces, layers and holes

The base is a rigid plate made of resin and glass-fiber fabric. This material does not conduct electricity, so it is an insulator. On top of it lies a thin layer of copper, usually only a few hundredths of a millimeter thick. The circuit pattern is worked out of this layer: everything that is meant to become a conductor is protected, and the rest is etched away with a chemical. What remains are the fine traces you see on a board.

For complex devices, one layer is not enough, because the traces would otherwise cross each other. That is why several such copper layers are pressed together on top of one another, separated by insulating layers. A phone board often has eight to twelve layers. Connections between the layers are created by tiny drilled holes plated with copper on the inside, called vias.

Finally, the components are placed on top and soldered in place. This is done by pick-and-place machines, which position several components per second. Afterwards the board passes through an oven, in which solder paste melts and connects all the contacts at once. A common misconception, by the way, is that green is the color of the material itself. Green is only the protective coating that keeps the copper from rusting; it also comes in blue, red or black.

From the washing machine to the server rack

Printed circuit boards are found in practically everything that needs electricity and can do more than just light up: in washing machines, headphones, car keys, e-bikes and game consoles. Anyone who builds things themselves encounters them in hobbyist boards like Arduino or Raspberry Pi. There, the components are deliberately large and labeled, so that you can trace the circuit.

In business news, the term usually appears as part of the supply chain. When shortages in electronics are discussed, it is often not just about chips, but also about boards and their assembly. Contract manufacturers like Foxconn build them for many well-known brands that do not own a factory themselves.

The printed circuit board should be distinguished from the chip. The chip is a single component made of silicon with billions of microscopically small switches. The printed circuit board is the level above it: visible, millimeters thick and recognizable to the naked eye. Both are necessary, but they are manufactured in completely different factories.