High speed illumination system for microelectronics inspection

Abstract

This invention is a high speed illumination apparatus and technique which highlights bond wires, ball bonds, bond wedges and microcircuit chips separately against a similar substrate background for manual or high speed automatic inspection of microelectronics assemblies. Preferred angles of illumination are provided which reflect off the different specular surfaces of the bond wires, wire bonds, and bond wedges, providing improved background contrast. Light projected on the flat surfaces of microchip bodies tends to be absorbed, producing a negative contrast shadow if the other elements are illuminated in parallel. Formation of the multiple light rings starts 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 the large off-verical axis angle. 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 the smaller off vertical axis angle. By alternating the light transmission through each of these rings at high speed, reflective signatures of interconnect wires, ball bonds, bond wedges and microcircuit chips can be captured by the an objective lens and mirror reflected to light responsive cameras. When displayed, the resulting unique signatures are easily distinguishable.