Ken Bloomquist correctly identified the dewetting problem he was having with conformal coating and found a workable solution.
   
  Sometimes solder masks contain chemicals (surfactants, plasticizers.....) that can cause dewetting. These chemicals are usually trapped in the solder mask when it's cured. Sometimes the mask will be cured on the surface but not completely cured beneath the surface. If holes were drilled in an incompletely cured solder mask these dewetting chemicals could migrate out. I occasionally heard that one batch of solder mask was a dewetting disaster but the ones before and after coated with no problem.
   
  Someone suggested baking out boards washed in an aqueous cleaner. This is a particularly good idea when water can hide in nooks and crannies (beneath flat packs, etc.). Occasionally customers would call me who were have dewetting problems near plastic components. Heat from a lengthy bake would drive mold release agents back to the surface of the plastic. So while a bake is desirable a lengthy bake (particularly at a high temperature) is not.
   
  I never liked aqueous cleaners but we are stuck with them. 
   
  I frequently heard another solution will I will not mention so as not to give anyone bad ideas.
  Kudos to Ken for hitting on a good solution.
   
  One word of caution - isopropyl alcohol will soften some acrylic conformal coatings and can cause those coatings (if recently coated) to rub off. It may also temporarily cloud that coating. The cloudiness will frequently disappear on it's own or can be baked out. Should you find that problem a mixture a water and iPA is frequently good for removing contamination.
   
  Ed Mines

 
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