Operation and Maintenance Manual Model 7AA Wafer Grinder
9 - 6 Version 1.2 - April 18, 1996
AIR BEARING SPINDLE
MAINTENANCE
As mentioned previously the wafer chuck and grind wheel spindles
are air bearings. These bearings use clean dry air flowing through
close tolerance rotating surfaces to provide exceptionally smooth,
stiff rotational motion. Due to the close tolerances and speeds
involved it is essential that good maintenance practices be observed
to maintain air bearing performance.
The grind spindle requires 5.5 cubic feet per minute (CFM) @ 70 PSI
clean dry air. The work spindle requires 3.3 CFM @ 80 PSI. As
mentioned previously a pair of air filters provides the required
filtration and isolation for the air supply for each spindle. A gauge on
the outlet of each filter pair indicates the supply pressure at each
spindle (assuming negligible pressure drop in the supply tubing).
If filter elements accumulate excessive contamination resulting in
insufficient supply pressure for either bearing the filter elements
should be replaced. Pressure switches are connected to each
spindle supply to provide added protection against spindle failure.
Each switch is adjusted to open when pressure falls below the
minimum requirement. However, it is still advisable to implement
filter inspection and replacement as part of a regular preventive
maintenance schedule.
In the event of air bearing spindle contamination it is sometimes
possible to restore the air bearing by flushing with isopropyl alcohol.
To flush the bearing first turn off the air by rotating the ball valve 90
degrees. Disconnect the spindle supply line at the outlet of the filter
pair and pour approximately 10 ounces of alcohol into the line.
Reconnect the line to the filter outlet and open the ball valve. Allow
approximately 30 seconds to purge the alcohol. After purging the
spindle should rotate freely if the contamination has been removed.
Repeat twice to assure thorough cleaning. If the spindle rotates
freely by hand and at normal operating speed then the cleaning may
be sufficient; if not then field irreparable damage may have occurred
in which case spindle replacement is required, (see Note 1, in the
“Facilities Requirements” section of the Installation chapter of this
manual).
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