How Clean Must Bare Boards Be? Print E-mail User Rating: / 0
Written by Terry Munson    Thursday, 31 July 2008 19:00  The
fabrication process is a prime source of contaminants.  Process
Doctor Many ask why we need clean bare boards for a “cleaned
assembly” process. The answer is most cleaning systems are
designed to remove only the easy-to-get-to flux residues. But
take, for instance, underneath low-standoff areas, where it is
difficult to reach some flux residues. Why compound the issue of
high chloride levels from a HASL flux or high sulfate residues
from trapped etchant below these components as well?  To better
understand what contamination levels must be met, we should
understand where contamination resides and from where it comes.
Contamination on a bare board resides on and in the following
areas:  1. Metal surfaces (pads and plated holes) form thin
films of dry residue (including in hole and via barrels). The
smaller diameter the via, the more difficult the rinsing of
these etch residues. If the via i