Testing of interconnection circuitry using two modulated charged particle beams

Abstract

Apparatus and a method for non-contact electrical testing of printed circuit boards, solid state display devices, integrated circuits and other substrates with traces that connect together components of a circuit, using two modulated charged particle beams. The apparatus includes two sources of beams, electrodes to modulate the beams, optics to focus the beams and deflection coils to deflect the beams over a large area. The apparatus also has an enclosure around the optics and the deflection coils of magnetically soft material. A surrounding solenoid excitation coil creates an almost uniform axial magnetic field within the magnetic enclosure. A detection system for detecting the voltage contrast signals, including suitable signal processing system is also provided. The use of two beams simultaneously allows fast, direct measurement of impedance parameters. By selecting appropriate beam modulation frequencies, the sensitivity to a certain kind of defect can be selectively increased. The use of modulated beams and frequency filtering of the voltage contrast signals allows such measurement to be quantitative, more sensitive and more discriminating between various possible defects in the interconnection network then the prior art methods.