Operation and Maintenance Manual Model 7AF Wafer Grinder
6
When the coarse wheel is referenced over the left work chuck, the actual
measurement is used in the software instead of this default. During grinding,
as the wheel is worn away, the actual measurement is adjusted by the amount
of wheel wear, so it continues to tell the left chuck reference position relative
to the (now thinner) grind wheel.
However, that actual value is NOT saved into the machine variables, and this
default value will be used again when the 7AF is reset.
A negative number means “down” and the letter u resembles the Greek letter
mu which is the symbol for microns.
Number: 22 Value: -8000.0 Label: Right Coarse Z ref u
This is similar to the preceding value, but is calculated for the right work
chuck.
Number: 23 Value: -7700.0 Label: Left Coarse Z hover u
This value is not used in the software, and this variable may be assigned a
new meaning in the future.
However, there are concepts of up height and hover height that need to be
explained.
The bridge travels when the grind wheels have been raised to their up height.
During the grind cycle, that is calculated to be a distance far enough above
the wafers to avoid any crashing, but close enough to the wafers to avoid
much time loss due to raising and lowering the grind wheels. Outside the
grind cycle, the up height is taken to be the home position of the grind wheel
Z-axis.
The hover height is calculated to be not so far away as the up height. The
only time the wheel is lowered to the hover height is during Machine
Maintenance, when the “H” button is pressed.
Comparing these heights with the actual grind wheel Z position tells if the
wheel is “up” or “down.”
Number: 24 Value: -3728.0 Label: Right Coarse Z hover u
This value is not used in the software, and this variable may be assigned a
new meaning in the future.
Number: 25 Value: 2000.0 Label: Coarse Wear Lim microns
When this much material has been worn away from the coarse wheel, a
warning is issued.
Number: 26 Value: 0.0 Label: Coarse Max Whl/Wafer
When this much material has been worn away from the coarse wheel during
the grinding of a single wafer, a warning is issued. The value zero in variable
26 means “do not test coarse wheel wear per wafer.”
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