Operation and Maintenance Manual Model 7AF Wafer Grinder
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In software version 6.05 this was given an additional meaning. The integer
part still gives the minimum vacuum. The fractional part, limited to two
digits, tells how many seconds to tolerate vacuum below the minimum.
Vacuum may build slowly when first turned on, or there may be momentary
fluctuation. Use this timer to avoid unnecessary error messages. If the timer
is not set it will default to 4.1 seconds.
Example 1: 10.08 allows vacuum below 10 inches for up to 8 sec.
Example 2: 10 allows vacuum below 10 inches for up to 4.1 sec.
Number: 91 Value: 2.0 Label: RT Chuck Min Vac “hg
Minimum allowed right chuck vacuum and timer. See variable 90.
Number: 92 Value: 8.0 Label: SPIN Min Vac “hg
Minimum allowed spin station vacuum, in inches of mercury. (The chem.
symbol for mercury is Hg.)
Number: 93 Value: 10.0 Label: Robot Min Vac “hg
This value is not used in the software, and this variable may be assigned a
new meaning in the future.
Number: 94 Value: 10.0 Label: Prealigner Min Vac “hg
This value is not used in the software, and this variable may be assigned a
new meaning in the future.
Number: 95 Value: 0.0 Label: Dress Probe Avg Revs
See the next description. Variable 95 refers to dress, including in-situ dress,
while variable 96 refers to grinding wafers.
Number: 96 Value: 0.0 Label: Grind Probe Avg Revs
The 7AF averages the probe readings during the grind cycle and displays the
average near the lower left corner of the screen. The value zero provides the
instantaneous reading. A non-zero value, including a number with a
fractional part, will present the average after that many revolutions of the
work chuck.
It is very important to note that probe readings will be delayed by the time it
takes to do an average. If average revolutions is set to 1.0 at 20 rpm, each
probe reading will take 3 seconds! In this example, probe readings will be
more stable, but the target trip point that advances to the next step of the
grind recipe will be delayed for 0 to 3 seconds. This can lead to uncertain
target trip points. The lower the feed rate in the recipe, the less effect this
will have. That is an important consideration in selecting the number of
averaging revolutions to use.
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