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Gravitational sag of edge-supported glass master can be eliminated by using an air pressure differential across the master to enable closer undistorted proximity exposure during circuitization processing.
English (United States)
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Elimination of Sag During Exposure of Glass Masters
Gravitational sag of edge-supported glass master can be eliminated by using
an air pressure differential across the master to enable closer undistorted
proximity exposure during circuitization processing.
In Fig. 1, glass master 1, a phototool for exposing sensitized workpiece 2,
serves as the bottom member of an evacuated chamber, formed with a top sheet
3 of quartz or fused silica glass and air-tight sidewalls 4. Evacuation occurs
through duct 5 to produce a negative pressure sufficient to counterpart any sag in
the glass master 1. Particulate contamination falling on the top glass 3 will not
print defects because of the long distance to the workpiece surface.
An alternative arrangement is shown in Fig. 2 in which an illumination source
6 and sensitized workpiece 2 are within different controlled pressure
compartments separated by glass master 1. An air-tight chamber 7 is divided
into two compartments 7a and 7b by glass master 1 joined at its edges by seals
8 to the vertical chamber walls. Chamber 7a is supplied with filtered cooling air
through duct 9 and some of the cooling air is diverted to pump 10 that supplies
air through duct 11 to chamber 7b at a pressure higher by approximately one-half
inch of water. Each compartment has restrictive vents to maintain the desired
difference in air pressure and flatten glass master 1.