On 9/2/05, Rick Thompson <Revcon24@comcast.net> wrote:
> The best way I've found is to use Kester no-clean solder paste.  You must 
> first overlook the hefty price tag of $42 for 35 gm syringe at Digikey. 
> It's well worth it and that syringe will go a long way, and it keeps rather
> 
> well if stored tip down in the fridge.
> 
> For rework what I do is soak up any residual solder from the pads using 
> solder wick (after the old part is removed) so that the new part can lay 
> completely flat.  Then I put just a little dab of solder paste on the tip of
> 
> a sharp wooden toothpick.  It doesn't take much at all.  Under my desktop 
> magnifying glass I gently paint a little dab of the paste onto the pads.  It
> 
> takes 2 hands, one to hold the toothpick and the other to keep the other 
> hand steady.  Then I place the device onto the pads with a long-snooted pair
> 
> of tweasers (medical ones are the best).  Again, the second hand is 
> necessary for steading.  If the device gets a little cocked on the pads, I 
> just nudge it over with the tip of the toothpick.  After the part is set in
> 
> place, I touch the pad with the tip of my iron.  I only get the iron close 
> to the pin.  If I touch the pin, the device will move out of position.
> 
> For soldering an entire board, I do mostly the same thing.  Only to dispense
> 
> the solder paste, I put a little in the bottom of a 5-cc syringe with a 
> 21-ga. hypodermic needle.  I ususally take a sharpening stone & flatten the
> 
> tip of the needle just a bit.  Then I go around & apply paste to every pad 
> on the board.  I then come back & lay down all the devices.  Then it all 
> goes into the toaster oven per other posts.
> 
> Works fantastic for me.  I routinely solder SOT-23 devices with no hassle. 
> I'm just starting a layout using an 18F6390 TQFP that has 64 pins at .5mm 
> pitch.  For sure that will be a challenge, 


Hi, nice to see optimistic person.

I've tested an inteligent methode for 0.5mm pitch: use a profile for
your solder iron so you solder more than one pin once. The best
results works for 4-5 pins once. The amount of solder used is
essential. Also the PCB metalisation quality. I'm using an ordinary
0.5mm Sn60-Pb-40 2% flux, it's the only one I've found. However there
is the same in 0.3mm diameter, better for such work.

cheers,
Vasile

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