When creating a prototype problems may occur with the design, i.e. not everything works as expected. Then to redesign and order new pcb's just to discover "next" fault will be a very costly thing to do.

In order to keep the costs down, the solution will be to patch the first prototypes. For example by soldering new wires or replacing components, in order to verify the electrical functions as much as possible before next CAD.

The image below illustrates an advanced patch where we have stacked some memory components on each other and soldered quite a lot of new wires.

An example of an advanced patch work