In terms of increasing the thickness of your solder mask deposit on top of
circuits using a DP-10 type machine, may I offer the following suggestions:

1. Use a coarser mesh. Down to about 83 strands/inch is about as low as you
will want to go.

2. Use a softer durometer squeegee. About 60 is as low as you would want to
go.

3. Increase your print speed. You can go to about 6-8 inches/sec and should
not experience skipping.

4. Increase your squeegee angle to 32-35 degrees.

5. Change from the normal flood/print/print mode to the
flood/print/flood/print mode. This will deposit more mask.

I've found that the best way to monitor the amount of mask you are applying
(analgous to your coverage over circuits) is by using wet weight. This is
fairly easy to do and basically only requires a scale and a little extra
work. It works like this:

1. Measure the image area of your screens (in inches).

2. Determine the square footage of your image area. This is done by (length
times width times 2) divided by 144.

3. Weigh the dry panel

4. Apply mask and weigh the wet panel

5. Determine the wet weight of solder mask by subtracting the dry panel
weight from the wet panel weight.

6. Determine the wet weight of mask per square foot by dividing the wet
weight of mask by the square footage of the image area.

7. With a DP-10 type of machine, you usually want 5.0 to 7.0 grams/square
foot. For your coverage requirements you will want to be closer to the 7.0
grams/square foot.

Please keep in mind that putting more mask on the panels is also going to put
more mask in the holes. Therefore, you may have to increase your drying
parameters to completely dry the mask and you may have to bump up your
development to completely clear all the holes (higher develop temp or slower
conveyor speed.

Good luck and don't hesitate to contact me if I can be of further assistance.

Larry Fisher
Dexter Electronic Materials
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