Operations and Maintenance Manual Mechanical Description
Version 1.2 - June 2004 4 - 5
LEFT/RIGHT WORK CHUCKS
Each work chuck spindle is an air bearing (see below) spindle mounted to one of the
side plates of the bed. The work chuck spindles are functionally and structurally very
similar to the coarse and fine (upper) spindles, with the exception that the upper
spindles are designed to rotate at faster speeds than the lower (work chuck) spindles.
Each work chuck assembly is bolted to its associated spindle; vacuum used for wafer
retention is routed through the ceramic chuck. The ceramic chuck is mounted to the
backing plate, and the unit is bolted to the mounting plate which attaches directly to
the air bearing and acts as a coupler to retain the work chuck. Note that the work
chuck spindles provide rotational motion only (no vertical or horizontal motion).
Lines for vacuum/air blowoff and D.I. water/backflush run through a hole in the center
of each work chuck spindle. Vacuum is used to retain the wafer during grinding, and
air is used for blowoff to aid in releasing the wafer. D.I. water, used during
conditioning, cleans the vacuum pores by blowing water through them, helping to
ensure good vacuum for the next wafer.
AIR BEARING SPINDLES
The four Westwind (Federal Mogul) air bearing spindles use clean dry air flowing
through close tolerance rotating surfaces to provide smooth, stiff rotational motion.
(A circular disk on a shaft hovers within a stabilizing plate which rides on air.) The
absence of metal to metal contact provides a high degree of stiffness and eliminates
friction, resulting in cooler operating temperatures and longer spinning. Due to the
close tolerances involved, the air used must be clean and dry to prevent clogging of the
air ports. For proper function of the spindles, consistent maintenance of the air system
must be performed.
The grind (upper) spindles each require 5.5 cubic feet per minute (CFM) at 70 PSI
clean dry air. The work (lower) spindles each require 3.3 CFM at 80 PSI. 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, 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 a part of the preventive
maintenance schedule.
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