
SMD reflow with a blowtorch (2016) - luu
https://lab.whitequark.org/notes/2016-04-28/smd-reflow-with-a-blowtorch/
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jacquesm
Lovely hack :) I used blowtorches in my poor days to rapidly desolder
components. Take a bucket, fill it with water to about 3/4 full, hang your PCB
upside down over the bucket. Heat evenly with blowtorch. Part will desolder
themselves, gravity pulls them down as the solder melts and when they're free
they drop in the bucket for instant cooling. You can get quite aggressive like
that without damaging parts. This trick works for both SMD as well as hole
through components, but _not_ when the legs have been folded over.

In no time you'll have a good pile of parts for experimenting or building new
stuff, you can even de-solder very large ICs using this.

~~~
eqvinox
I used to whack PCBs onto the table to get things off (after heating something
with some shitty underpowered soldering iron.) Just because I didn't have
proper tweezers, and the solder would quickly solidify again...

People looked at me with serious "WTF?" faces whenever I soldered somewhere
away from home ;D

Still do whack the soldering iron itself to get excess solder off. Obviously
not with the tip but the handle, so the solder just continues onto the mat and
makes a nice small splat. (No it doesn't fly off, it quickly solidifies on
landing due to the splat increasing the contact area for heat transmission.
Doesn't even damage the mat...)

You just gotta know how to help yourself with the tools available!

~~~
sneak
Mitch Altman taught me that trick! I use it all the time now.

I went up to him to ask for some desoldering braid at a conference, and he
showed it to me. Life-changing! I don’t know why I didn’t think to do it
myself.

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ur-whale
Whitequark's lab notebook [1] is sheer pleasure to read through (if you're int
that sort of things, obviously).

[1] [https://lab.whitequark.org/](https://lab.whitequark.org/)

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retSava
(Don't mean this to sound negative)

I guess you make use of what you have, but if you are at the level of doing
smd reflow, there are significantly better tools at a low cost (hobbyist-level
too).

For smd rework I'd say better to use a cheap hot air station. Plenty of cheap
ones that work ok, at least much better than such an imprecise tool as a
blowtorch.

For prototyping, you can buy kits with a toaster oven + controller that works
pretty well for reflow. You plug the power cable of the oven to the
controller, and the controller switch it on and off according to the temp
profile. Works pretty well, we use one at work for small runs.

~~~
MrBuddyCasino
You kind of missed the point here, which was that it is surprisingly doable
using a ghetto-ass blowtorch when the correct tools aren't available, which is
counter-intuitive. I would have expected this to go spectacularly wrong and
leave a charred PCB, which it most certainly didn't ("When holding the tip of
the flame ~15cm away from the PCB, it took over a minute to get the solder to
melt and wet the plane.").

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lukego
This is remarkably similar to the DIY version of a high-end soldering
technique I've just learned about called Vapor Phase Soldering.

I'm waiting for a bottle of Galden LS230 to arrive so that I can try this DIY
method on some whacking great big Xilinx BGAs:
[https://m.youtube.com/watch?v=czwRntpEzgg](https://m.youtube.com/watch?v=czwRntpEzgg)

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baybal2
> Something to note is that torch exhaust contains a substantial amount of
> water vapor, which readily condenses on cold areas of the PCB.

Reflow + wet PCB/parks === no go. If they will have to redo that in an hour or
so, they will get popcorn on PCB or components.

~~~
MrBuddyCasino
Can you elaborate? I never heard the term popcorn used in that way.

~~~
eqvinox
[https://en.wikipedia.org/wiki/Moisture_sensitivity_level](https://en.wikipedia.org/wiki/Moisture_sensitivity_level)

If you order parts from a major distributor (arrow, avnet, digikey, mouser,
etc.), everything comes with appropriate humidity indicators where needed.
Pretty much anything that is something + plastic around it will be affected to
some extent.

I haven't seen things go "popcorn", but broken off edges and cracks across a
package... yeah.

Add: that said, moisture from a blowtorch probably won't have such an effect;
you need to get it nice and deep into the package and unable to come back out.

Add(2): this is also why ziplock bags make good outer semiconductor packaging.
Make sure you properly zip them back up whenever possible.

Add(3): a quick look through my semiconductor stack (SMT ICs, mostly QFN, some
SOP, no BGAs) is about 30% MSL3, 45% MSL2 and 25% MSL1 or unmarked.

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StavrosK
This is great to know! One question I have is what the actual technique the
author used is (ie distance and time), because they mention that it took a
minute for solder to melt at 15cm and I'm not sure if that was what worked
best in the end.

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Animats
I thought that was Jeri Ellsworth. Thinks things through from first
principles. But no, it's a _another_ red-haired woman who thinks like Feynman.

~~~
jcoffland
> it's a another red-haired woman

Why is it significant that this post was from a woman or that she has red
hair? This comment sounds like a backhanded compliment, at best.

