At the end of the PCB production process we electrically test every multilayer PCB against the original board data.  Using a flying probe tester we check each net to ensure that it is complete (no open circuits) and does not short to any other net.

The flying probe testers in our quality control department are easy to set up as they don’t need a test fixture but testing every net is slow.  A faster test method is the Acceler8.  This uses 4000 tiny probes like a brush.  It builds an electronic map of the PCB from a pre-tested good board.  Then it compares each board to be tested with its map.  This cuts test times by 90%.

For double sided boards electrical test is an option.