Hello Steve,
My first question is:
Where is most of the rework required/ scrap coming from on the boards?
Once you have answered that question, you can see where the process needs
more control. A lot of companies monitor tons of stuff, but for get to look
at the big picture. Start by making a "Pareto analysis" of previously
observed defects and then strike at the biggest targets, the processes that
these defects are coming from. You can then move on down the list of
defects.
Alain Savard, B.Sc.
Chemical Process Analyst
CAE Electronics Ltd.
e-mail: [log in to unmask]
-----Original Message-----
Hi All,
I'd like to ask any input or opinions on how to implement a SPC program that
will really be meaningful. I don't want to waste time and effort on
something
if all it's going to produce is "window dressing"...
Our business is very high-mix/low volume stuff. From boards that are very
straight forward, standard 50-mil pitch stuff, to those that have every part
on the board (SOIC's, CQFP's) cut and formed, pre-tinned, and then placed
and
reflowed. A big run for us is 100-boards, most of the time it's 50 and
under.
I guess what I'm saying is that there are TONS of variables with a lot of
the
products we build here.
We do a lot of hi-rel stuff here, very custom, almost hand built boards. We
also hand place a lot of components here...for example the resistors on a
lot
of the boards come to us in little 2" X 2" matrix trays that can't be
machine
placed. Any design problems that cause defects on the boards most of the
time
won't be corrected because the document trail that has be completed is so
daunting that our customers tell us to not ask for changes because it won't
happen, and our time is best spent figuring out a way how to deal with it.
So what I'm wondering in a situation like this, what good is SPC going to
do?
I think the time spent trying to correctly identify all the variables and
gather meaningful data would be better spent in training and working with
our
operators to learn all the little nuances with the product we build so we
can
deal with them. What was proposed to me for example in screen printing, was
to create a simple attribute chart for example;
1. Is the paste coverage complete? Yes/No
2. Is it registered on the pads? Yes/No
3. Is the paste smeared? Yes/No
or such simple attributes such as that, and then plot them on a chart. To me
it'll be a waste of time. We don't have anything to quantify any
measurements...no paste height measuring equipment, or X/Y measuring
equipment, everything will be done by the ol' Mark-I / MOD-I eyeball with
all
it's subjectivity...but I am still being asked
to establish an SPC program in SMT.
Am I fighting this too much? Or is there some means that will be worthwhile
to make this happen? Oh yeah, it's gotta be cheap (next to nothing) too...
Thanks in advance!
-Steve Gregory-
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