Hi Ed,

I think a good many shops do ask to remove dams on 19 mil pitch components
but are not always obliged.  My experience is that with most LPI's you should
be able to produce dams down to 4 mils with little difficulty.  With some
masks you can safely build 3 mil dams (Ciba 65 or 52).

Factors that need to be controlled with dams this small are:
  -  Wet weight (thickness)
  -  Tack dry
  -  Image clarity (and all that entails)
  -  Developing

One problem a shop can get into is when they neglect to ask the customer if
removal of dams is OK.  Some shops have adopted the position that, like
non-functional pads, they will automatically remove the dams.  Clearly not
good practice.

Mark Mazzoli

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