Much has been said that I heartily agree with. Including use of extra
flux! However, I'm a real believer in stencils. They can be made cheaply
usng a Silhouette Cameo or Portrait (half the cost of the Cameo). During
the Dorkbot PDX group build of the Bus Pirate 4, IIRC, 20+ boards were
built with only one failure we couldn't clear. All done using stencils
made with the Cameo (Thanks, Travis!). Pretty much the only SMT
soldering failures I've had were when I tried to smear on the paste.
Just doesn't work for me. YMMV.
I also strongly agree with Dave on creating your own footprints for the
parts. Making the pads narrow enough to allow solder mask between the
pads (usually make pads .24mm for .5mm pad to pad spacing) and
lengthening them slightly (Dave suggested .2mm; I've used .15mm). Note
this is for prototyping - other rules may be used for production.
On 3/12/2015 5:21 PM, Brad Burleson wrote:
On Thu, Mar 12, 2015 at 11:44 AM, David Madden <[email protected]> wrote:
I've had pretty good luck with solder paste in a syringe, smear across
the pads (and center), then hot-plate.
While I've never done a QFN32, I have done more than a few QFN10's and
I wanted to add... the less paste on the center ground pad the better.
I had some stencils made with a large ground pad for the QFN10 and it
was a disaster. When I re-sized the ground pad to 20% the original
size my success rate (w/ a little hand re-work) went up to nearly
100%.
I've also made a few just like David says and all you have to do is
make sure a little bit of paste is on EVERY pad (and less is more).
Good luck,
Brad.
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