Process Optimization
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In this case, the second reverse movement also uses the above settings.
A second reverse movement is possible in principle, but it is also rather unusual for ball-wedge bonding.
8.2.2 Expert Loop
The Expert Loop has its own settings and it differs from the Standard Loop because, for example, the difference in
height between the first and second bond points is taken into account when calculating the loop height.
For this reason, Expert Loop usually has a loop height of 60-90%.
In contrast to the Standard Loop, Expert Loop offers the following additional options:
>>
Use Reverse 3
>>
U-Turn instead of Turn Height
>>
Use Loopheight Compensation
Use Reverse 3.
It is possible to program up to 3 reverse movements.
It is also possible to move the 2nd reverse movement in loop direction to bend the wire in the other direction. This
is mostly only of interest for ball bonding, e.g. to let the loop sag down and keep the loop height as low as possible.
U-Turn instead of Turn Height.
The U-Turn may only be used if the 1st bond point is higher than the 2nd bond point and is especially suitable for
applications where the height difference between the bond points is greater than the loop length.
The U-Turn offers the possibility to move behind the 2nd bond point and to prevent the bending of the wire at the
first bond point and also the lateral bending to a large extent by an arc-shaped movement.
You define with <UTurn> how far the wire should be passed and with <Loop-Point 1 & 2> at which height between
loop height and height of the second bond point the maximum pass position is reached or at which this pass position
is left again to return to the XY position of the second bond point.
These two heights together may not exceed 80% of the loop height.
Use Loopheight Compensation.
The Loopheight Compensation should make it possible to use one loop setting for different loop lengths.
Starting from a defined loop length, which you set ideally beforehand and use as a reference afterwards, a little (%) is
subtracted from the programmed loop height for longer loops and a little (%) is added to the programmed loop height
for shorter loops.
The value set at <Looplength Longer> is only fully effective when the loop length is doubled! Typical values here are
between 6-12%.
The value set at <Looplength Shorter> becomes fully effective at 1/3 of the loop length! Values between 25-45% are
common here.
Typically the <ref. looplength> is set to 1000-1500µm for thin wire. For thick wire, however, 3000 - 5000 is usually
used as the ref. looplength. But this depends mainly on the loop lengths used in the program.
IMPORTANT!
The <ref. looplength> should ideally be about half the maximum loop length in the bond program.