AVR-Chat

Hi Tony,

On Tue, Jun 14, 2005 at 12:28:22PM -0000, arhodes19044 wrote:

> I still have not found a good reference on the technique of drag
> soldering?  I t seems as if the technique is to make a blob of
> solder and drag it across all the pads on one side of the chip.  I
> guess the solder mask prevents bridging?  I would have thought that
> all the pins would just get shorted together in one big glom of
> solder....

What I've found works best is to use a flux pen like this from Digikey:

  http://www.digikey.com/scripts/DkSearch/dksus.dll?PName?Name=KE1808-ND

It looks kind've like a highlighter.  First position the part and
while holding it in place, wet the leads on one side with the flux pen
and with a hot iron, tack the part in place - there will be enough
solder on the PCB to do this without adding any at this point.  Then
use the pen to wet all the leads.  With the part tacked down and all
the pins wetted with flux, use some 0.015" solder and lay it across
the pins, then drag the hot soldering iron across the solder and the
pins.  Control the amount of solder by pulling the solder away a
little as you drag the iron.  As long as you don't completely go
overboard on the solder, just enough will be applied to all the pins
and you won't have any bridges.  If you do find you have a bridge, it
will usually be on the last few pins.  With your soldering iron,
"comb" the tip on the pins dragging the solder toward the pin tips.
If there is a nearby via, you can dump the solder into the via,
clearing the bridge.  Otherwise, try adding a little flux if necessary
and redistribute the extra solder among the other pins by dragging
back in the other direction.

It's really very easy and takes only a little bit of practice before
you are an expert.  I just use a pretty standard 4x magnifying visor
which is plenty for me.

Don't forget to wash the board other wise the flux might react with
the copper or components.  I use water soluble flux and solder with
water soluble flux core which makes clean up with hot water and a
small brush easy.  Rinse in deionized water and air dry.

-Brian
-- 
Brian Dean
http://www.bdmicro.com/