>
>
>
> Thanks, I do have a hot air rework station with interchangeable "tips" bu=
t
> never really used it yet, as the few times I tried it looked less
> productive
> than my Elsa iron station, with which I have had always very good results=
..
>
> One question: should I tin only the pads of the IC or also the pads of th=
e
> PCB? When I soldered the QFN I tinned both, but I had the feeling it was
> too
> much.
>
> Thanks,
> Mario
>
>
It all depends on how solderable the surface of the PCB is. If it is an
bare copper pads, or tin pads board, then it could probably do with a
tinning, and running over with solder wick so you have a fresh solder
coating (scrub with IPA on a swab afterwards to get rid of any burnt/dark
flux, and re-flux it with your flux of choice) . If its fresh HASL (as long
as its flat enough) or gold plated you can probably get away without
tinning/cleaning the pads, but with a proper temp setup on your iron you
wouldnt be hurting anything tinning and cleaning it with solder wick, imo.


And what you have on the IC should be "pillowed" some, but definitely not
starting to take a ball shape. With a hoof/gullwing tip  (
http://www.newark.com/productimages/nio/standard/4840843.jpg except the
flat/face of it has an indent you cant see thats filled with solder, just
to make sure we're on the same page), you can generally remove excess
solder from the IC if its a problem, just apply flux to the IC, tin the
iron with flux core solder to wash away any contaminates, wipe it on a
sponge to get off as much solder as you can and go around to equalize the
pads.   Take care to not overheat the IC for any of this,  you should be
able to move fairly quickly, just a few seconds to do a row of pads.

Since you have a hot air station, you can probably try tinning the PCB pads
and not the IC, and reflowing it all, Ive had less luck balancing the IC on
the solder bumps and reflowing, vs the bumps being on the IC.

However, I also remembered this
http://www.proto-advantage.com/store/product_info.php?products_id=3D3200115
proto-advantage sells individual paste stencils, 0.5CC syringes of 63/37
paste, and squeegee's so if youre doing a lot of IC's you could be
reflowing them onto paste and probably get a lot more consistent results.
($11 for the stencil $3 for paste, and $0.50 for squeegee)
-Jon
--=20
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