FR4 · ENIG Finish · 1oz Copper
Copper traces on green epoxy. The trace is a wire drawn with light and acid. The via is a hole with a metallic soul. The pad is a landing zone for a component that weighs less than thought.
A modern PCB is a sandwich. Layer 1: the top copper layer, where most components sit. Layer 2: the ground plane — a solid sheet of copper at 0V that gives signals a return path and provides electromagnetic shielding.
Layer 3: the power plane — VCC, the supply voltage, distributed everywhere it needs to go without routing individual traces. Layer 4: the bottom copper layer, for routing signals that couldn't fit on top.
Between every copper layer: a prepreg layer of fibreglass and epoxy resin — FR4, the material of the modern world. The stack is compressed under heat and pressure until it becomes a single rigid laminate.
A CPU, RAM, flash memory, ADC, timers, and communication peripherals — all in one package 7mm × 7mm. It costs £1.20 in quantity. It is more powerful than a 1985 mainframe. We put them in lightbulbs.
Copper-clad board. A photoresist layer. UV light through a film negative — the circuit pattern. The exposed resist hardens. The unexposed resist washes away. Then acid: ferric chloride, eating the bare copper, leaving only the circuit. The trace emerges from destruction.
Paste: solder mixed with flux in the consistency of toothpaste, applied through a stencil by a squeegee. Components placed by machine at 20,000 placements per hour. Then the oven: 183°C, the solder flows and freezes. The circuit is born in a controlled melt.