Method and apparatus for electrical and optical inspection and testing

Abstract

This application describes a novel method and apparatus for the electrical and mechanical inspection and testing of unpopulated electronic printed circuit boards, ceramic substrates and other items which have conductive pathways formed thereon, interconnecting conductive pads and other conducting surfaces. Examination and testing is accomplished by placing a printed circuit board or other item to be tested within a sealed chamber which contains a gaseous atmosphere capable of cathode luminescence such as argon, neon and the like. The sealed chamber includes a transparent panel or partition which allows viewing of the printed circuit board or other item under test and preferably is electrically conductive. One terminal of a source of excitation electric potential is connected to the transparent conductive panel and the other terminal is applied to one of the metallic runs or paths on the surface of the sample item to be tested. The electric field produced between the metallic run or path on the sample item and the transparent panel or window in the sealed chamber causes the gas immediately adjacent to the run to emit light or other electromagnetic radiation in accordance with the well-known 'cathode luminescence' phenomenon. The light or other emissions thus produced forms a pattern which matches in size and shape the conductive pathway or run on the sample item which has been electrically excited. The observed pattern is then compared to a known or desired pattern to determine whether it meets a preset standard.