Laser generation of conductor patterns

Abstract

A laser pattern generation system has been developed to define gold conductor patterns on ceramic substrates. Such patterns are used as interconnection circuitry for silicon integrated circuits. The system consists of a mechanical positioning device for the substrates, a numerical control system, and an Nd:YAG laser to evaporate the gold selectively to form the desired pattern. Rotational motion is used to position the substrates in order to achieve high pattern generation rates. The positioning system uses a drum around whose periphery are mounted the substrates. Associated with each substrate is a code plate, which chops an auxiliary laser beam to provide timing signals to the control system. The substrates are rotated at constant speed past a lens assembly, which is advanced by one address unit in the orthogonal direction after each revolution to produce a sequential scan of the substrates. The laser acoustooptic Q switch is operated in synchronism with the timing pulses from the moving code plate, and patterns are written by use of an extracavity acousto-optic lead molybdate deflector synchronized to the Q switch. The energy source is a krypton-pumped Nd:YAG laser. In order to machine at a rate of 17 s/cm2of substrate the laser is Q switched at 25 kHz. Laser mode control and stability were found to be decisive parameters to obtain uniform patterns. Output in the TEM 00 mode was found to be necessary. Suitable patterns may be made with a 4.9-W TEM 00 output. The system has a 14-μm resolution. Test patterns that demonstrate the feasibility of laser pattern generation at economical rates are shown.