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Hi Tracy,
Thanks for the comments. Here is some
additional information on the design.
Here is a photo of the printer I designed and
made. It has basically two major components, the squeegee holder and
bed of 1/2" x 6" x 9" aluminum slab with T tracks mounted on each
side. The squeegee holder shown toward the rear rides the
tracks mounted along the side of the bed. This has a
1 1/2" tube as a handle at the rear. It also permits you to
adjust the pressure on the tracks making it easier or harder to pull
it.
While this can all be done free-handed, I
felt that finding and maintaining a constant pressure of squeegee
against the stencil and board would result in a more consistent solder lay-down
pattern.
The Squeegee is a standard 3/8" thick polyurethane
squeegee used in the graphics art industry $12.00 compared to the same thing
sold to the SMD community for from $50- 250.
I use a clear plastic stencil cost $24.00 vice the
cheapest metal stencil ($145). You would probably want to use a metal
stencil for runs above 25 or so. But, if you use polyurethane on the
plastic stencil, it should last a fairly long time.
The big metal tube on the back is the handle you
grab to pull it along on the rails along the side. The springs of course
apply the consistent pressure and can be varied until you find the magic
combination.
The board is captured by a cut-out in a 0.060
acrylic sheet. The board sets just a hair below the top of the
sheet and provides for "snap back" or "stand-off". Meaning the
stencil is not actually resting on the board, but a hair above it. So when
the squeegee passes over the holes in the stencil, it presses it down to contact
the board, and deposits the solder paste in the cut-out of the stencil onto
the board pad underneath - the stencil then "pops" back after the
squeegee passes giving you a clean separation (hopefully) and a nice solder
paste deposit. The real test will be a SMD socket of 30 pins with 0.25mm
separation
The 3/8" squeegee is held by a 3/8" aluminum
channel trim piece on its top (where the springs push down) and between two 1/8"
x 1" strips front and back. Just pull the squeegee runner off its rails
and you can slip the squeegee out or clean it, etc.
It takes about 30-60 seconds to untape the
stencil on one end, lift it up, pull the pasted PC board out and stick a
new board in and tape it down again.
I planned on doing my first board for real
today, but when I was doing a dummy run, I found that one of the SMD
diodes did not fit its pad - I ordered the wrong diode size.
Hopefully the correct size will be here middle on next
week.
This contraption rides on a strip of MSD
impregnated nylon in rails along each side. The side mount holding up the
handle and squeegee is attached to these strips and ride inside the "T" slot
rails mounted along each side of a 1/2" slab of aluminum. The T rails,
acrylic sheet and MSD nylon are from McMaster - the rest was from local
hardware store.
Only machining I did was squaring up the sides of
the 1/2" slab after cutting it out. The rest can be done with a band saw
and drill press.
Also solder paste has come a long ways, it will now
last six months without refrigeration and up to a year with it.
Naturally keeping it cool prolongs its useful life.
So that's it in a nut shell, will let you know how
it works. Oh, yes, my Reflow Oven cost $38.99 at Wal-Mart and has a temp
increase profile that almost perfectly matches the solder I have.
So much fun when its fun
Ed
----- Original Message -----
Sent: Friday, February 16, 2007 11:56
AM
Subject: [FlyRotary] Re: Rusty's Rv-8 For
Sale!
Hi Ed,
I'll be very interested in that soldering experiment. Just the kind
of 'real world solution' I have come to expect of you ! :-) I farm that
job out to PC board contractors and it is one of the biggest expenses in
building my stuff.
Tracy (Back from brother's divorce court hell)
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