Two printed circuit boards, c 1970s.
© Science Museum / Science & Society Picture Library
Printed circuit boards such as these are composed of an electronic circuit based on thin strips of a conductor on an insulating board. The foil is etched away to leave tracks that connect the components together. A layer of lacquer protects the board except where components are inserted. This allows the components to be fixed in place by skimming the entire board acros a bath of molten solder.