We use spray under immersion (Alpha SC1080, cold proces) which works
very good for 20 mil pitch, both for stencils and for misprints. Wave
pallets also no problem, for adhesives the cold solvent isn't aggresive
enough.  
A problem with ultrasonic cleaning could be that not all customers allow
this technique for populated boards (like misprints of double sided
reflow boards, or boards with adhesive on them).


Hanif, Nasir wrote:
> 
> I am currently in the process of evaluating SMT stencil washing equipment at
> our facility here.  I am looking at ultrasonic technology versus coventional
> spray systems.  What I would like from you all are any pros & cons, that
> might come with a particular technology.  For example, I have heard that the
> stencils should not be exposed to temperatures higher than 110 degrees F.
>  The theory behind this being that, the stencil is made up of three
> different materials:
> 1.  The outer frame usually constructed of  Aluminum frame
> 2.  The screen portion that bonds the outer frame with the metal foil
> 3.  The metal foil that has the apertures, stainless steel
> 
> And so, when a stencil is subjected to these higher temperatures of >140 F
> in a conventional spray system(hot water), the materials with different
> thermal coefficients of thermal expansion, expand and contract at different
> rates.  And in doing so, can cause irreversible stretch in the metal foil.
>  In the case of fine pitch applications this could translate into
> significant off alignment with the land pads on the board during printing.
>  What I would like to know is if this holds true? And if so, is there any
> research findings available that I could look into that would provide me
> with the answers, or any experience with such findings. Also with certain
> wash chemistry, the adhesive that bonds the foil and the screen and the
> outer frame tends to loosen up.
> 
> Another question would be, the effectiveness of cleaning fine pitch
> apertures,  20mils & below with one or the other system? Also, how about
> cleaning other materials such as misprinted boards, boards with adhesive,
> wave pallets, etc.
> 
> Would appreciate your effort in answering the above questions
> 
> Thanks
> 
> Nasir
> [log in to unmask]
> 
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