Hi Dennis,
> i get paste stencils for about $320 USD, so that seems in
> line w/ what you are all saying
Yep.
> they usually take about 1 day turn since i am near silicon valley
> actually my assembler gets them but i pay for them
I haven't been able to get them in less then about 3 days, most
suppliers are interstate, and a few are coming from china now.
> the trouble is they sure prove to be a disincentive to what i
> feel to be the worthy goal of 'continuous improvement'
>
> if we build 100 pcs of board before a rev spin we are doing well so i
> guess $3.20 a board for a stencil is not too bad but when we do 5
> different protos and then spin all the revs to the inevitable
> rev 'B' it sure adds up to a lot of trashed stencils and money
>
> seems like there ought to be a better way
Agree, I have been thinking about it for a while. Inkjet style
device is what is needed.
> the only thing i have come up with is putting 2-4 different
> boards on a 15" x 15" with about 1" between, this can save a bunch,
> especially on protos
Yes, I do the same often.
> camtastic (2000!) makes it pretty easy
>
> darren, not sure what you mean it 'takes a while to burn that
> w/ manual paste placement'
As in the labour cost to paste the boards, V the cost of the
stencil, which still takes a lot of time to paste a few boards
and then clean up.
> are you saying you can do a lot of bds for $320 ?
> yes, maybe 2- 5 bds depending on the features
Well it still take time to setup the stencil, screen the
boards and clean up. Then what do you do with the old
stencils ..
> what do you use ?
I have one of these
http://www.apsgold.com/p_place.html
The MPP21.
and for an oven..
http://www.apsgold.com/reflow.htm
> a manual time/pressure dot dispenser like EFD?
> i have one of those and it is gathering dust now (actually we
> sometimes use it for gluing things but not bd parts)
I run it on full manual, much faster then setting the time for
each size pad. You get very fast at it.
> for protos i gave up on that and just hand solder with the good old
> metcal and a big jug of flux with a teensy needle tip on the end, it
> does a better job i think - no solder balls
I use a metcal style iron, hakko in fact to do the fine pitch
stuff, too much trouble to paste, place reflow and then rework
the fine pitch. Paste placement is just not controlled well enough.
> either way both methods take a LONG time to build one or three boards
Yes, it is very time consuming.
> i realize that w/ QFNs and BGAs a stencil is a must so i use
> those only if they are a must do
I haven't done much BGA stuff in house yet, but I will have to
address that soon.
> in fact after switching over to 0603s i am now switching back
> to 0805s due to low volumes and the greater ease of
> troubleshooting and mods
0603 can be small, but after doing some 0402 stuff, they don't
seem so bad. I remember 20 years back when 1206 seemed to be
small. :|
> back to SIPAD...
> it appears that somewhere along the process, unless i have been
> misinformed, they make a stencil and do what the assembler
> would do just at a different point in time
> still, it does allow storage and therefore time shifting of
> that process
To me I can't see much gain.
Regards,
Darren Moore
> ds
>
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