Rick,

Concerning your problems with lpi exposure/develop:

1.  If you have some type of thermal profiler, you should check to see how
long the panels are actually at temperature and if you are actually reaching
188 deg F.  The tack dry time you are baking for is longer than most tack dry
cycles and the temperature should be high enough. It would be good to know if
you are using a tunnel oven or box oven.

2.  You may want to check the cooling system on your exposure unit. Some
units are adjustable like the Colight 1330 c.  You may be able to lower the
running temperature on the glass to avoid the  white hazing on the artwork.

3. If you have a way to check your deposit thickness you may want to ensure
that you are not putting down too much ink in the screening process.  You
should normally be putting down 1.2 - 1.6 wet mils of soldermask unless you
have very high plating or other special needs. Normally the thickness is
determined by your screen mesh (typical 94 - 110), screening pressure and
speed.

4. I would imagine you are screening the ink.  If this is the case, there are
some tricks to keeping the mask out of the holes in the first place that you
may not be aware of.  This is by far the best method of avoiding this
problem.  Because there is a variety of screening technologies out there
(double sided automatic, hand screen, single sided screeen press .....) you
might want to give me a call at the following number for further details .

Van Miller
Electra Polymers and Chemicals America
(612) 874 1983

Good Luck

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