Hi Mike - Here's my two cents worth, from an assemblers viewpoint: I've tried to spec the same thing in the years gone by, only to learn that the HASL process doesn't have the degree of control that many folks would like. After a number of attempts, we finally learned that the paramount charactaristics are SOLDERABILITY and UNIFORMITY. Specifying minimum thickness led our suppliers to be absolutely sure they had enough thickness to meet our minimums. This often gave us boards with tall solder crowns, which affected both past application and component placement. We also found substantial variations: on individual boards, from side to side; on the same side; from board to board; and from one production lot to the next. To make a long story short, we now spec solderability requirements and tell the supplier our preference on thickness, without it being mandatory. Regards - Kelly PS - we're still looking at the white tins by Omikron (Florida CirTech) and Dexter in hopes of getting that ultimate solderable board with flat pads!!!!