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
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