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Does your method work for QFN and DFN? I currently find them to be the biggest headache in prototyping. If you coat some solder on the chip and board using an i

Does your method work for QFN and DFN? I currently find them to be the biggest headache in prototyping. If you coat some solder on the chip and board using an iron and then reflow with a hot air station, it's easy to miss a few pins underneath due to uneven solder distribution; on the other hand, if you use solder paste and reflow with hot air, again, due to uneven solder distribution, you'll short some pins and miss others, and there is no straightforward way to fix it, the thing gets even worse when solder on the ground pad suddenly melts and causes unwanted movements (during rework) that misaligns the chip. I got my board working only by pure luck. I'd like to hear your recommendation.

elcritch 7y ago
QFN/DFN are pain, but I've had decent luck with them using the toaster oven method. Of course that's using a solder mask from JLC PCB, as without the mask you just end up with the incorrect amount of solder. Still you get the occasional missed pin you need to re-solder but it works.
- bcaa7f3a8bbc 7y ago
  > Still you get the occasional missed pin you need to re-solder but it works. How? Did you mean to remove all the existing solder, reapply the paste, and reflow again (can that even be done on an already populated board, where do you place the mask/stencil?), or it's something else?
  - elcritch 7y ago
    More of just putting a bead of solder on a soldering iron tip and fixing that pin (best with a microscope setup). If you get the technique just so, you can do a form of "drag soldering" to fix a missing pin or two. Otherwise you can do a quick dab with a bead of solder since with most QFN's you can still see the side of the pin but you may need to rotate the board. I think there are a bunch of great youtube videos on doing that. Getting a proper solders for QFN's really does best with a proper metal stencil. If you use JCL PCB, use their "electropolishing" option otherwise on fine pins the paste sticks more. Removing and reflowing the part is tricky and often damages the part. Also to not ruin other parts of the board, a heat gun is often easier. We've never really tried reflowing parts unless a board didn't "bake" properly.
- sokoloff 7y ago
  Confirm you meant to say stencil rather than solder mask there? (Solder mask is the colored material over the board, while a stencil is a separate piece of metal with holes cut to allow solder paste application with a squeegee.)
  - elcritch 7y ago
    > Confirm you meant to say stencil rather than solder mask there? Yes, stencil is what I meant to say. The "mask" part of solder mask seems to throw me everytime I mean to say stencil, as in I want to mask the parts of the board _not_ to solder. Someways I wish English were more like Swiss/German or Hebrew.
kennywinker 7y ago
All the ic’s on the board I used this technique on had leads, so I can’t comment on how dfn/qfn parts would work. Pan+sand would definitely be the first thing I try tho
- bcaa7f3a8bbc 7y ago
  Thanks for the confirmation anyway!

elcritch 7y ago

QFN/DFN are pain, but I've had decent luck with them using the toaster oven method. Of course that's using a solder mask from JLC PCB, as without the mask you just end up with the incorrect amount of solder. Still you get the occasional missed pin you need to re-solder but it works.

bcaa7f3a8bbc 7y ago
> Still you get the occasional missed pin you need to re-solder but it works. How? Did you mean to remove all the existing solder, reapply the paste, and reflow again (can that even be done on an already populated board, where do you place the mask/stencil?), or it's something else?
- elcritch 7y ago
  More of just putting a bead of solder on a soldering iron tip and fixing that pin (best with a microscope setup). If you get the technique just so, you can do a form of "drag soldering" to fix a missing pin or two. Otherwise you can do a quick dab with a bead of solder since with most QFN's you can still see the side of the pin but you may need to rotate the board. I think there are a bunch of great youtube videos on doing that. Getting a proper solders for QFN's really does best with a proper metal stencil. If you use JCL PCB, use their "electropolishing" option otherwise on fine pins the paste sticks more. Removing and reflowing the part is tricky and often damages the part. Also to not ruin other parts of the board, a heat gun is often easier. We've never really tried reflowing parts unless a board didn't "bake" properly.
sokoloff 7y ago
Confirm you meant to say stencil rather than solder mask there? (Solder mask is the colored material over the board, while a stencil is a separate piece of metal with holes cut to allow solder paste application with a squeegee.)
- elcritch 7y ago
  > Confirm you meant to say stencil rather than solder mask there? Yes, stencil is what I meant to say. The "mask" part of solder mask seems to throw me everytime I mean to say stencil, as in I want to mask the parts of the board _not_ to solder. Someways I wish English were more like Swiss/German or Hebrew.

kennywinker 7y ago

All the ic’s on the board I used this technique on had leads, so I can’t comment on how dfn/qfn parts would work. Pan+sand would definitely be the first thing I try tho

bcaa7f3a8bbc 7y ago
Thanks for the confirmation anyway!