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Browse Prior Art Database

Closed Loop Laser Control System

IP.com Disclosure Number: IPCOM000048562D
Original Publication Date: 1982-Feb-01
Included in the Prior Art Database: 2005-Feb-08
Document File: 3 page(s) / 50K

Publishing Venue

IBM

Related People

Klauser, HE: AUTHOR

Abstract

A major concern in laser drilling of blind via holes in printed circuit boards is the lack of a control system which permits the adjustment of the laser parameters to the specific conditions of the hole being drilled. These conditions are given by the composition of the dielectric to be drilled (ratio of epoxy to glass fibers), the thickness of the dielectric, and the position and condition of both dot etch copper and buried via pad. A related concern is the lack of an instrument to measure individual laser pulses, specifically those pulses which are used to drill a given hole. Critical laser drilling parameters are pulse power, pulse duration, number of pulses, and pulse repetition rate.

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Closed Loop Laser Control System

A major concern in laser drilling of blind via holes in printed circuit boards is the lack of a control system which permits the adjustment of the laser parameters to the specific conditions of the hole being drilled. These conditions are given by the composition of the dielectric to be drilled (ratio of epoxy to glass fibers), the thickness of the dielectric, and the position and condition of both dot etch copper and buried via pad. A related concern is the lack of an instrument to measure individual laser pulses, specifically those pulses which are used to drill a given hole. Critical laser drilling parameters are pulse power, pulse duration, number of pulses, and pulse repetition rate.

A control system is proposed which is based on the availability of two types of information being collected continually on-line during laser drilling of circuit board composites. The one type of information, called signal a, characterizes the laser pulse delivered to the drilling site. The pulse is characterized with respect to peak pulse power, pulse width, and pulse energy. Such information can be collected with a fast sensor for infrared radiation such as, for example, a pyroelectric detector or a metal film detector. The laser beam used to drill holes can be sampled by reflecting a fixed fraction of the incoming beam with a beamsplitter and directing this sample beam onto a sensor for measurement, as shown.

The second type of information, called signal b, comes from the laser drilling action itself. It may be an optical signal or an acoustic signal or a combination of them. Optical and acoustic signals generated during laser drilling have been picked up with suitable sensors, such as microphones, piezoelectric and pyroelectric sensors. Also, piezoceramics which have both piezoelectric and pyroelectric properties pick up both optical and acoustic signals. As the drilling of the hole progresses, the intensity of these signals changes. These signals can be used to monitor the drilling process....