We have occasionally used dryfilm to tent both sides of a via hole prior
to applying LPI mask.  Other than the added expense and additional steps,
it works quite well and is cosmetically good.  We have not observed any
degradation or adhesion loss after multiple thermal stresses.  Since the
dryfilm is applied over high pressure areas you don't need to utilize a
vacuum  system when applying the film. If you have this equipment
available, it does result in a slightly lower profile "bump" over the vis
because the dryfilm is deformed into the hole.  Be sure to use the .0015
film to avoid assembly issues with stencil interference during
solderpaste application in high density component areas.

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