We design electronic equipment that ends up in a fairly dirty environment (i.e. lots of dust bunnies, dirt, debris, etc...), and I was wondering if there were any detrimental affects of having no clean residue on our boards. I don't think it would cause any major problems, but just wanted to see if anyone had any cause for concern.
One person mentioned to me that the residue may attract dust and debris onto the PCBA. Has anyone had experience with this happening?
I would be far more concerned about the flux residue intentionally left on the board than the �dust bunnies� sticking to the flux. In �perfect� no-clean applications, flux residue, although present, is nearly invisible and marginally conductive. In less than perfect no-clean applications, you may have a more visible and more conductive residue (and a sticky finish that attracts dust). This could present a major issue. Besides dust, you also need to be concerned about other environmental attacks on the flux residue such as heat and humidity. This could increase the flux�s conductivity and residual corrosiveness, leading to board failures. You either need very good process control (flux delivery, profile, cleanliness testing, etc) or you can eliminate any flux-caused reliability issues by cleaning the board.
I assume you talk about wave soldering. No-clean fluxes are widely used since 1987 or earlier and after all these years they have proven to be reliable. If you clean the board or not the dust bunnies etc. will still reach the board surface. If you use a rosin/resin no-clean flux you will have a sticky board surface which will accumulate and hold a lot more dust then when you use a rosin/resin free (no-residue) flux. The solids in these fluxes evaporate when exposed to the conduction heat of the wave. In case you would have residues because of lack of heat the residues would a least not be sticky. The only sure solution to protect a board from a harsh environment is conformal coating.