Photo-Exposure Radiometry

June 2001

Bob Angelo, President , Gigahertz-Optik, Inc.

Photoresist exposure systems used in the manufacture of printed circuit boards are designed to deliver optimum levels of ultraviolet and/or visible optical radiation to flood the target zone in order to polymerize a photocureable chemical or resist.

Radiometry, the measurement of optical radiation, is used to monitor and control the photo-exposure process to ensure that good product is manufactured consistently. Many exposure systems use a built-in metering system, but very often a third party radiometer is employed for verification. As a valuable field service tool, the external radiometer can be easily serviced and recalibrated without interrupting operations. New lamps and delivery systems can be evaluated since the meter can easily go to any measurement zone. Further to this, the photosensor spectral response can be altered as needed to key on certain wavelengths or bandpasses. Also, since the sensor is not fixed in position, profiling of the exposure plane is easily accomplished.