Modern chips are not simple circuits. Your phone contains hundreds of millions of parts (even billions if it’s a very recent model), and they need to be connected just right. The wires connecting all this cannot be placed one at a time. That would take too long and be too error-prone.
Instead, the circuits are printed onto the circuit board using photolithography, which is a hi-tech use of stencils and lasers (and solvents and resins, but we won't get into that part!).
In your every day life, using a stencil means:
- choosing your paper;
- placing your stencil on top;
- spraying your paint on.
In photolithography, it looks more like:
- choosing and preparing your semiconductor and resin;
- placing your optical mask on it;
- shining your laser at it.
This “stencil” approach allows you to print the complex chip circuit in a repeatable way.