QFN is doable at home, though more difficult than TQFP leads or larger SOIC-chips. Still, far too many components are QFN today so its a good skill to pickup.
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The techninque is:
1. Reflow soldering brings the _whole_ board to soldering temperatures, and then relies upon surface-tension to pull all the devices into proper place.
2. Solder paste is applies ahead of time. You can cleanup solder paste with a toothpick before you bring the board up to temperature. Solder paste tends to go bad pretty quickly however. When doing prototypes, opt for the more expensive low-melt solder paste to minimize potential heat damage.
3. Prefer to use a stencil to apply solder paste. But its more than doable to be sloppy with a syringe and then rely upon the solder mask + surface tension to magically cleanup things during reflow temperatures.
4. Use a hot-air gun to fix any issues. The #1 issue you'll have is tombstoning, QFNs or TQFP chips are usually pretty good about settling into place. For TQFP issues (ex: bridging), you'll need solder-wick + soldering iron. EDIT: And flux: lots of flux helps. Also, flux goes bad, so throw away Flux all the time and keep buying new batches.
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BGA is also doable at home btw, thanks to the above principles. But its even harder than QFN. The real issue of BGAs is that you're looking at 4-layer minimum, maybe 6, 8, or 10-layer designs. There's also substantial grounding and other advanced PCB concepts you need before you can layout a BGA-capable PCB.
Its not so much the physical activity of soldering that's hard or difficult for BGAs. Its all the theory you need to study to breakout BGAs + minimize inductance + deal with impedance matching and trace-length matching.
I find hand soldering QFN is faster, easier and more reliable than (T)QFP once you got enough practice. If you need to rework the QFN part the key is to FLOOD the footprint with good solder flux from a syringe. Do not use one of those flux pens, those do not dispense enough flux.
> If you need to rework the QFN part the key is to FLOOD the footprint with good solder flux from a syringe.
I've never tried this but this makes a lot of sense in my mind's eye. I'll try this next time I have such an issue.
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TQFP seems nice because I can sloppily shove tons of solder down, and then just wick up all the excess solder with solder wick. In fact, I purposefully over-solder all the TQFP joints for this practice. (Too much solder during reflow, and then just a quick cleanup step with a soldering iron later).
QFN is doable at home, though more difficult than TQFP leads or larger SOIC-chips. Still, far too many components are QFN today so its a good skill to pickup.
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The techninque is:
1. Reflow soldering brings the _whole_ board to soldering temperatures, and then relies upon surface-tension to pull all the devices into proper place.
2. Solder paste is applies ahead of time. You can cleanup solder paste with a toothpick before you bring the board up to temperature. Solder paste tends to go bad pretty quickly however. When doing prototypes, opt for the more expensive low-melt solder paste to minimize potential heat damage.
3. Prefer to use a stencil to apply solder paste. But its more than doable to be sloppy with a syringe and then rely upon the solder mask + surface tension to magically cleanup things during reflow temperatures.
4. Use a hot-air gun to fix any issues. The #1 issue you'll have is tombstoning, QFNs or TQFP chips are usually pretty good about settling into place. For TQFP issues (ex: bridging), you'll need solder-wick + soldering iron. EDIT: And flux: lots of flux helps. Also, flux goes bad, so throw away Flux all the time and keep buying new batches.
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BGA is also doable at home btw, thanks to the above principles. But its even harder than QFN. The real issue of BGAs is that you're looking at 4-layer minimum, maybe 6, 8, or 10-layer designs. There's also substantial grounding and other advanced PCB concepts you need before you can layout a BGA-capable PCB.
Its not so much the physical activity of soldering that's hard or difficult for BGAs. Its all the theory you need to study to breakout BGAs + minimize inductance + deal with impedance matching and trace-length matching.