There are three main reasons cause LISM under develop. They are:
1. Over track dry
2. Over exposure
3. Under develop

If you use a batch oven for track dry, I suggest you  check the temp.
distribution and air
circulation of your oven. Printed panels should be racked 1 cm (min.)
space. It will provide
a better air circulation. Reduce the temp. by 2 deg C if you still have
the problem.

Your exposure energy seems a bit too high for me. I usually set the
stepwedge solid 8-10
on copper.

You should also check the developing condition.

Spray pressure    > 2.0 bar
Soln. temp.          30-35 deg C
Developing time   > 1 min. (breakpoint ~10%)
Soda ash             0.8-1.2 %
Rinse pressure     > 1.0 bar
Rinse time            > 30 sec.
Rinse temp.         > 20 deg C

Mixed LISM should be used within 24 hrs and Printed panels should be
exposed/developed
within 24 hrs.

I hope the above information can help. Good Luck!

Best Regards,

Chan Chi Man

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