Excerpts from my project at Cummins India Limited (Subsidiary of Cummins Inc.)

4.2   Hardware testing:

Initially, Bare Board Testing (BBT) of PCB was performed before mounting any components on it. This test is necessary for a newly itched PCB to decide the quality and working possibility of its circuit at an earlier stage.

I.   Purpose of hardware testing:

         hardware testing would detect fault in PCB due to the factors mentioned below:

·    Under itching

·    Careless drilling (if done manually)

·    Shifting of layout film during itching process

·    Mistakes done during film making

·    Tracks shorted with each other

·    Tracks are open (no connection)

·    VCC - GND are short

·    Pad short with GND plane

·    Track is missing

II.   Procedure: In procedure, continuity of each track is tested with reference to actual circuit diagram.

1.         Check for VCC -GND short in the circuit with multi-meter probe.

2.         Consider a reference device, an IC which is having maximum number of connections, then check all connection from that IC i.e. check each tracks continuity from that IC.

3.         While checking each pad, also check all nearest surrounding pads to verify continuity.

4.         Make a log of each track tested by marking in the circuit diagram.

5.         Also make a table for track short and track open.

6.         Repeat this until all ICs are done.

Connect the open track by wire and open the track and pad shorts, by scrubbing it with sharp razor, as per the table maintained. Image below illustrates a typical bare board testing setup.

Photo: Bare board testing setup