I purchased a stencil cleaner from ECD(yes, the same people who make the
M.O.L.E.) We use a noclean solder paste, but isopropyl alcohol is required
to wash the stencils. All the stencil cleaners that I looked at could use
IPA, but because they had electric motors, they required a fire
supressionsion system, at a considerable cost. Many used heated solutions,
and I had some of the same questions you have raised, espcially about the
bonding to the frames/stencil.
The ECD system uses air motors, no electricity is required, thus no fire
supression system(the system is grounded). It has been working well for
two years. We use it to clean misprints and stencils. This is a spray
system, with the IPA at room temperature. We have used it on fine
pitch(20mil) aperatures. I have heard that ECD is selling their stencil
cleaning system to Austin American. Good luck
E. Holton
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-------------
Original Text
From: C=US/A=INTERNET/DDA=ID/TechNet-request(a)ipc.ipc.org, on 1/16/97 3:21
PM:
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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