The low cost way to build prototypes. Each donut is separated from its neighbours by about a 0.5mm gap. This effectively isolates each pad but also makes it easy to bridge solder across to make interconnections. Each board also has `fingers' on opposite ends with a 3.6mm edge pitch. These can be used to connect to and from the board or to a card edge connector. Finally the non- solder side of the board has an alpha- numeric grid printed on it to assist in component identification board layout.