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Advanjet HV-2000C Jet Controller Setup and Operation
Page 39 of 60
Appendix 1: First Drop Compensation
Appendix 1-1:
Background
Many viscous fluids are thixotropic and their viscosity decreases with motion. This is
often referred to as shear thinning. When dispensing a thixotropic fluid, the very first
drop ejected is often smaller than subsequent drops if the jet has been idle for some
time.
Traditional
ly, operators dispense a few ―wasted drops‖ in a blank area of the substrate
to get the dispensing material into a shear-thinning condition. Although this technique is
a good idea because it gets rid of the first drop problem altogether, it wastes time and
fluid. The Advanjet HV-2000C has a better solution.
Appendix 1-2:
Calculating First Drop Compensation
To compensate for small first drops, the HV-2000C offers two jetting parameters:
and
+
. The first drop compensation process is based on the following:
T
+
= First Drop Compensation
T
++
= Extended Drop Compensation
Elapse Time = Idle time of the jet since the last dispense
Extended Timeout = Time entered in the Recipes Menu/Adjust Refill Time
for fi
rst drop ―msec after YY seconds‖
If Elapse Time < Extended Timeout, then Refill Time = T
+
If Elapse Time > Extended Timeout, then Refill Time = T
++
Examples: For a time-cure material, the fluid could be slightly thickening if it sits idle for
a long time, especially if the fluid is being actively heated. Suppose Extended Timeout is
set at 20 seconds. The first drop refill time will equal (T*), where the value of T*
depends on how long the jet has been idle.
If Elapse Time < 20 sec (Extended Timeout), then T* = T
+
If Elapse Time
≥
20 sec (Extended Timeout), then T* = T
++
Lines: For the first drop of all the lines, Refill Time = T
++
. Subsequent drops will
have a Refill Time without any compensation if multiple drops are specified.
Individual Drops: For individual drops, Refill Time = T
+
. When dispensing
individual drops with an Elapse Time of less than 20 seconds, the compensation is
always applied.