Homebrew PCBs

"The syringe should be as rigid as possible so the
post-drive flow is minimized.  I'd choose something
like a stainless tube and plunger.  The seal on the
plunger can simply be an o-ring."

I was thinking an el-cheapo syringe, very easily accessible, like those used
to refill printer ink.  The metal needle has a fine hole, and can be removed
for filling up (larger diameter hole).

Someone mentionned that the paste will run easily when warmed.  What about
filling up the syringe with paste in liquid form, turn it upside down and
store at a temperature where the paste turns to the right 'thickness'?  Time
for a small fridge for the lab?  Please say yes, I need it to cool the beer.


"post-drive dribble can be handled in the control code by backing off a tad
on the screw drive at the end of a dispensing run"

Good idea!


"I don't know how much a pick and place file will buy
here as the operation is going to be manual unless
component pickup is from an automated dispenser (eg:
tape and reel).  Even then commercial solutions include
machine vision to align the component on the vacuum head."

I was planning on using a 1/2 machine 1/2 man solution.  :)

I'd preload a 'cartridge' with the components so that the pick head only has
to lift the part, polarity for capacitors, pin #1 for ICs and such would be
done by hand.  The cartridge would basically be a thin rail tilted at an
angle so that the components slide down towards the pick spot.  Maybe a
small vibration at the far end to move parts down (small rotating cam?).

One note, I was only considering SMD components with this application.
Bending wire gets WAY too complicated.


"I'm just looking for something to pick up a 0603
capacitor out of a dish and give me an accurate means
to manually locate it on the board."

WAY too difficult for me, hence the idea of manually loading cartridges.


"There is some tolerance for placement inaccuracy in reflow soldering
as the surface tension of the solder paste upon
liquefaction will pull the component into alignment
with the pad.

Yeah, I'm counting on that.  :D


"I'm unsure how much usable resolution you may get
with USB cameras.  I'm also uncertain if standard
NTSC resolutions will be enough though I haven't yet experimented.
Low power microscope cameras are available which
render NTSC which is both encouraging and a possible
solution as well.  10x seems to be more than enough
for 0603 work and likely 0402 as well."

All things I'll have to test.  Putting a magnifying lense on the USB camera
was my first option (read el cheapo).  If the resolution is not acceptable,
then I'll see what is available at that time.  I have an old 8mm video
camera that chews tapes, I could jam the 'tape detector switch' and use
that.  I could even use the zoom feature by hotwiring the contacts.  The
more I think about it, the more I like this idea.  I'll have to check how
close I can focus.


"Try a jewelers loupe.  They are both inexpensive and
available in suitable magnification powers."

Yup, that's part of the el cheapo USB camera solution.


"The advantage of NTSC is also
that you don't need a PC to decompress the video and
can simply use a standard analog monitor."

I will have a PC dedicated to this task anyways.  It will run only Mach 2 so
the CPU is not bothered by other tasks.  I'm setting up another desktop for
all my other development software; QCAD, Visual BASIC, MPLAB IDE, PBP
Compiler, PIC serial programmer, etc.  Right now I'm doing all that on my
laptop, and that's not efficient use of a laptop.

Robert
:)


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