Re: [uCsimm] RTL Port, actually RTAI.

From: Donald J Dionne (jdionne@ns1.rt-control.com)
Date: Fri Jan 07 2000 - 18:05:34 EST


> If you are dealing with the 0.050" pitch leads, then just a 10 watt iron and some
> fine solder will do the trick, use plenty of flux (the flux will help you when
> "wiping" out solder bridges). A friend of mine has a rather novel approch to these
> parts, first he solders them to the board (without regard to solder bridges), then
> he uses solder wick to pick up the exess and removes any bridges!

This is the best way if you don't have a hot air tool. It works just fine
with parts of _any_ pitch (including the TQFP100 parts used on the uCsimm).

>
> If you are dealing with the 0.020" pitch leads, then the only real way to do these

Even with a hot air tool, unless you can put down _exactly_ the right amount
of solder paste, you will likely get a bride or two until you've got enough
practice.

Flux and solder wick is the key, and perhaps a little china glue. Use the
china glue, which is a thin liquid, to stick the part to the board. There
are professional adhesives but china glue works just fine. Position the
part and leave it set for a half hour or so. Then carefully (with a big
magnifying glass or better still a 30 power microscope) apply some liquid
flux to the pins (lots) and solder them. Use the corner of the end of the
finest braid solder wick (put flux on it too, honest!) and heating the wick
not the pins with the iron. Touch the solder wick to the excess solder and
it will suck it away from bridgeing the pins. If you've got a really big
mess just apply solder wick to the top of the flat part of the pins, but
carefully inspect after since that has sometimes left me with pins unconnected.

> parts is with the right equipment. I looked a number of manufacturers, had two of
> them demo their stuff, and finally purchased an outfit from Zephyrtronics

Look at the air tool from Edsyn as well. You can get the replacement air tool
handle without the base station for about $350 and use a fish tank pump and
valve.

> ('http://www.zeph.com'). Look at
> 'http://www.openhardware.net/Users/TomW/MPUPicture.html' to see what I just put
> together last night. It took about 2.5 hours to put this board together, once I got
> the technique of "pasting" the parts onto the board (I destroyed one board while in
> the learning process, "hot air leveling" is not an ideal finish for a PCB and this
> will be the last time I use a PCB house that uses that process)!

They all use that process. Your only other option is immersion gold which
costs big money. For hand assy, hot air leveling is a pain in the ...
Use solder wick to take everything you can off the pads first (don't apply
too much heat) and then clean with alcohol before assembling.

Jeff.

>
> When looking at the Zeph system, keep in mind that you need both the Air Bath (I got
> the cheaper model, 7 CFM for $299), and the Air Pencil. If you intend on hacking
> hardware in the future, I think that you may want to consider investing in this type
> of equipment?
>
> Regards,
>
> TomW
>
>
>
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>

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