Unfortunately, the CFC's produced by using solvents were found to be damaging the atmosphere, so the majority of manufacturers migrated to "no clean" fluxes. Then, RoHS compliant Lead Free soldering was upon us. The industry has conceded that the combination of different solders, fluxes and soldering methods can result in a higher flux residue using RoHS materials. So now the debate is rife again.
Do we or don't we clean! The short answer is that there is no "one fix suits all" solution. This is because it is dependent upon many factors. Firstly the number of processes the board requires for assembly will effect its susceptibility. A board that is SMT only, uses one type of paste and is reflowed only should not be any different to similar board assembled using a no clean leaded process. However, an assembly which requires a combination of reflow, wave and hand soldering, may well have a higher concentration of flux residue than its non RoHS counterpart.
So why not clean all boards? Firstly there is inevitably a cost associated with cleaning. Secondly, there can be environmental issues with the waste and finally many advocate that cleaning can be detrimental to product performance/reliability. So in conclusion, if the assembly is housed in some way, most have decided not to clean whereas if the PCB assembly is supplied as a product in its own right aesthetics often prevail.
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