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'[EE] Handling SMT components'
2006\02\25@084702 by Vic Fraenckel

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I have had some success at do-it-myself SMT board reflow soldering. For components like capacitors, resistors, LEDs etc, I have confined myself to the larger 1206 size. I have recently had some luck with using SOIC packages. I have a syringe of paste solder and some fairly small bore tips and can usually get the solder on the pads in a manner that gives acceptable results. I had to struggle to do the SOICs tho. I would also like to use a 44-pin TQFP in a future design.

I need to find a better way to place ths paste on the SOIC and TQFP pads and to place the component on the pads. I had a thought that it might be possible to glue the component on the board with a drop of some sort of adhesive. Aligning the device pads to the board pad is difficult and if someone has a suggestion, I would appreciate hearing it. In fact, I would like to hear any suggestions for using SMT components in home-brew projects. I have considered using a magnifing TV system to help me to better see what I am doing, but these are quite expensive. Anyone home-brew one of these? I would like to find one of those vacuum pickup devices (what is the official name?) to help position components. I am currently using twezzers.  Anyone home-brew one of these?  I am aware of Toaster Oven reflow devices. In fact, I use the Spark Fun idea of a Electric Fry Pan for my reflowing. I am happy with the results.

Any enlightenment will  be appreciated.

Vic

________________________________________________________

Victor Fraenckel - The Windman        
victorf ATSIGN windreader DOT com
KC2GUI                                                  

2006\02\25@120316 by Robert Young

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> I have had some success at do-it-myself SMT board reflow soldering. For
components like capacitors, resistors, LEDs etc, I have confined myself to
the larger 1206 size. I have recently had some luck with using SOIC
packages. I have a syringe of paste solder and some fairly small bore tips
and can usually get the solder on the pads in a manner that gives acceptable
results. I had to struggle to do the SOICs tho. I would also like to use a
44-pin TQFP in a future design.
>
> I need to find a better way to place ths paste on the SOIC and TQFP pads
and to place the component on the pads.

I regularly place passive parts 0603 by hand using fine pointed tweezers,
depending on the clearance around the part I use either straight tweezers or
ones with a "reflex" curve.  Keep the tweezer tips very clean so flux or
paste residue doesn't cause small parts to stick.

For ICs I use the same tweezers or a slightly larger pair with flat tips
that I have reground to be a touch narrower, just fit between pins on 50mil
pitch parts.  For very large parts (208 pin TQFP, etc) I use an inexpensive
vacuum system.

With reflow you can be a little bit off center but try to be less than 1/2
pad width off.

Support your whole forearm either by working further onto the bench or with
a pad of some kind.  You can also use your free hand as a cradle under the
wrist of your working hand.

For inspection and final adjustment before reflow I use a stereo microscope
on a dual rod boom stand.  Microscope has a good ring light and about 7cm
working room under lenses.

Don't drink lots of coffee or other caffinated beverages, try to work when
you are well rested and take frequent breaks to stretch and refocus your
eyes on distant targets.

Work at a comfortable angle and height and have GOOD indirect lighting and
an adjustable direct light source.  A good choice would be one of the
magnifying lamps with a nice daylight ring light installed.  Even just 3x
helps a lot  but try to keep your work centered in the viewing area, the
single lens units tend to distort heavily as you move from the center.

Hand placement will NEVER be faster than a good automated pick-and-place
machine but for hobby work or a very small prototype run it generally works
just fine.

Toaster ovens are "OK" if you control the heat, at the minimum consider
adding a thermocouple to a scrap piece of FR-4 near the center and monitor
the heat yourself.  The ovens can be automated relatively easily or for
about $3K you can buy units that will handle boards smaller than 8x10".
Ventilate well and watch your fingers!

Rob

2006\02\28@060956 by Alan B. Pearce

face picon face
>I need to find a better way to place ths paste
>on the SOIC and TQFP pads and to place the
>component on the pads.

have a look at how the Seattle Robotics group do it here.

http://www.seattlerobotics.org/encoder/200006/oven_art.htm

They do not worry about individual spots on pads, just a strip along the
pads. The solder then pulls back onto the pads as it wets the leads and
pads.

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