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From: Jon Slaughter on 27 Dec 2009 19:17
Thanks guys. I'll have to get some paste and see how it turns out. The main
problem is that a simple toaster oven or waffle iron is too small for my
boards. Maybe with some type of flat pan iron it will be possible or using a
hot air gun(after all, it takes them off pretty easily)?

Anyone know where I can get some solder paste on the cheap and easy and
possibly non RoHS(i.e., leaded)?


From: Robert Baer on 28 Dec 2009 01:27
Jon Slaughter wrote:
> Any have any tips for QFN packages by hand without a stencil? The main
> problem is that there seems to be no easy way to check/fix to make sure
> the leads are soldered since they are completely under the package. I
> was thinking of using puting solder paste on the pads by hand and
> attempting to properly align the IC. The problem I see is that most
> likely the solder paste will end up between the pads rather than on them
> and I'll probably end up with shorted pads. Does the solder on the
> solder mask tend to "run" to the copper? (after all, isn't that what the
> solder resist is for?)
>
> If I have the right amount of paste in the right places and the ic is
> somewhat closely aligned will it align itself?
Well, i have never tried them, but IF the particular units in
question have the lands extended to the side of the package, then i
would first tin the PC pads, drop the part on top, align as best
possible, and use iron on a "corner" pad to "drop" (or align) in place.
The capillary action forces by the solder should align the device
reasonable sized parts.
One can see if the part rotates some / too much; use a toothpick on
"far" end to prevent that; let it cool.
Inspect, if all OK then work a pad on the "far" end to "lock" the
part in place.
The rest of the pins will be a piece of cake.

Maybe..this will also work if no extension (no metal on package sides).
From: Robert Baer on 28 Dec 2009 01:37
Jon Slaughter wrote:
> Thanks guys. I'll have to get some paste and see how it turns out. The
> main problem is that a simple toaster oven or waffle iron is too small
> for my boards. Maybe with some type of flat pan iron it will be possible
> or using a hot air gun(after all, it takes them off pretty easily)?
>
> Anyone know where I can get some solder paste on the cheap and easy and
> possibly non RoHS(i.e., leaded)?
>
>
Are you in the states?
How about a 100g syringe of Sn96.5Ag3.5?
From: Nico Coesel on 28 Dec 2009 19:21
Robert Baer <robertbaer(a)localnet.com> wrote:

>
> Maybe..this will also work if no extension (no metal on package sides).

I wouldn't design those packages in. They are hard to get right by the
assemblers and you can't check the joints visually.

--
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
nico(a)nctdevpuntnl (punt=.)
--------------------------------------------------------------
From: EE123 on 28 Dec 2009 19:59



Try this website:
www.everythingRF.com


Select "articles"
Select "RF PCB Design"

There is a PDF there titled:
"PCB Design and Assembly for QFN Packages"

Good luck,
Dave


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