Just started using VOC free no clean in a fully inerted wave. Have problem with one assembly with solder balling. This assembly is single sided mixed and solder mask is UV cured wet film. Other assemblies we build are L.P.I. solder mask and do exhibit solder balling. Flux manufactuer applications people cannot help. Have tried everything from drastic profile changes to trying different flux brands. Can anyone offer suggestions?
Re: VOC Free No Clean Solder Balling| 23 June, 2000
Sounds like the mask to me. Had a similar situation a couple years ago. The mask wasn't fully cured, so it absorbed water that the preheaters couldn't dry out. When it outgassed at the wave, it caused a lot of micro turbulence that broke the surface tension of the solder and created a zillion little solder balls. My wave wasn't fully inerted, so I also had the pleasure of microdross clinging to the mask and shorting test points.
One way to check to see if the mask is fully cured is to take a swab of methylene chloride (if you can get it in your facility) and rub it across the mask. If it comes up green, the mask isn't fully cured.
The same thing will work with IPA if the mask is really bad. If it's just marginal, you'll need the methylene chloride.
Doesn't offer a solution, but a potential root cause.