Richard wrote:

I am also working in evaluation of VOI for our process. The directive came
from up stairs and my first reaction was, what for? We are pretty simple
when it comes to SM: .031"pitch, one QFP per assy. And we are not having
problems with the paste printing process (that we know of!!)

I have identified the January article, but have not read it yet.

Got any ideas on how to quantify the 'non-effectiveness' of measuring paste
height? I know when I go back with the prices, that alone will cause a few
palpitations! I don't want to just say it is too expensive for our use. And
in our case, Yes, the paste height has been identified as a reliability
issue, but not by anyone who knows if it really is or not.

Richard Hamilton
Clemar Mfg. / Rain Bird
[log in to unmask]

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Richard:

I've been trying to implement SPC for our stencil printing process by plotting
solder paste thickness.  SPC says that I have a process that's out of control,
but the finished product has no solder paste (volume) related defects.  I've
found that the thickness can vary depending on the temp/humidity, age of paste,
time the paste has been on the stencil, etc.  I think that the paste
"stretches" at varying amounts when the stencil is lifted, thus giving
erroneous thickness readings, but yet a consistent amount of paste.  You would
have to weigh the board prior to and after printing to determine consistent
solder paste mass, something I'd rather not do.

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