Abstract

The present invention is directed to an improved system for inspection of microelectronic assemblies, including chips and interconnection elements such as wires, ball bonds, and wedge bonds contained therein. This system includes a high speed illumination subsystem, a dual magneification video camera sensor subsystem, a commercial machine vision system supported by a video display and printer, a three dimensional transport stage for moving the microcircuit under inspection, and a computer controller for operational control under unique software of all of the above system elements. The illumination subsystem includes formation of multiple light rings starting with light generated by a tungsten lamp, collimation by a condenser lens, then passage through a liquid crystal light valve having a plurality of circular active transmission areas. A projector lens receives both rings of light and projects the larger ring on an ellipsoidal reflector which redirects the light onto the microcircuit at a large off-verical axis angle which has been found to provide optimal contrast for rounded bodies such a wires and ball bonds. The projector lens also focuses the more narrow beam of light on a torroidal Fresnel lens mounted above the microcircuit, and which also redirects the beam at a smaller off-vertical axis angle which has been found provide optimal contrast for wedge shaped bonds. By alternating the light transmission through each of these rings at high speed, defective reflective signatures of interconnect wires, ball bonds, bond wedges and microcircuit chips can be captured by the an objective lens and mirror reflected to the light responsive camera system.