6 ms·

SMD reflow with a blowtorch (2016)

49 points by luu 7y ago

retSava 7y ago
(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.
- agumonkey 7y ago
  It's cool to know that it's 'doable' even though I guess it require acrobatic levels of control and high charring rates :)
- MrBuddyCasino 7y ago
  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.").
- jacquesm 7y ago
  One hallmark of the 'true hacker' is that they get the job done, no matter what the tools at hand (or even no tools, in some cases). This post is one of the very few posts on the homepage right now that to me makes HN worth reading. Using a brute force tool to do something extremely delicate.
- wiml 7y ago
  > if you are at the level of doing smd reflow, there are significantly better tools What do you mean by "at the level of doing reflow"? Techniques like this demonstrate that "the level" of doing reflow is much more attainable by resource-constrained hackers than people sometimes think. Many years ago, when my personal time-vs-money tradeoff was different, I made a number of surface mount PCBs by doing reflow over an ordinary candle or paraffin lamp. I would balance the PCB on a piece of metal shim to act as a heat spreader and keep the board from getting sooty. It worked really quite well up to a couple square inches — the trick was learning how to follow a preheat profile to keep the small passives from tombstoning.
jacquesm 7y ago
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.
- omgtehlion 7y ago
  Well, if you do not really want to damage parts, you better not cool them too rapidly (in the water), better leave them to cool slowly.
  - jacquesm 7y ago
    The heat is mostly still in the connectors at that point which are all metal. That won't suffer from the shock of cooling down whereas the residual heat in the pins could easily damage a sensitive chip if not cooled.
- eqvinox 7y ago
  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!
  - dicknuckle 7y ago
lukego 7y ago
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
ur-whale 7y ago
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/
baybal2 7y ago
> 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 7y ago
  Can you elaborate? I never heard the term popcorn used in that way.
  - eqvinox 7y ago
    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.
Animats 7y ago
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 7y ago
  > 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.
StavrosK 7y ago
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.

49 points by luu 7y ago

(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.

agumonkey 7y ago
It's cool to know that it's 'doable' even though I guess it require acrobatic levels of control and high charring rates :)
MrBuddyCasino 7y ago
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.").
jacquesm 7y ago
One hallmark of the 'true hacker' is that they get the job done, no matter what the tools at hand (or even no tools, in some cases). This post is one of the very few posts on the homepage right now that to me makes HN worth reading. Using a brute force tool to do something extremely delicate.
wiml 7y ago
> if you are at the level of doing smd reflow, there are significantly better tools What do you mean by "at the level of doing reflow"? Techniques like this demonstrate that "the level" of doing reflow is much more attainable by resource-constrained hackers than people sometimes think. Many years ago, when my personal time-vs-money tradeoff was different, I made a number of surface mount PCBs by doing reflow over an ordinary candle or paraffin lamp. I would balance the PCB on a piece of metal shim to act as a heat spreader and keep the board from getting sooty. It worked really quite well up to a couple square inches — the trick was learning how to follow a preheat profile to keep the small passives from tombstoning.

jacquesm 7y ago

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.

omgtehlion 7y ago
Well, if you do not really want to damage parts, you better not cool them too rapidly (in the water), better leave them to cool slowly.
- jacquesm 7y ago
  The heat is mostly still in the connectors at that point which are all metal. That won't suffer from the shock of cooling down whereas the residual heat in the pins could easily damage a sensitive chip if not cooled.
eqvinox 7y ago
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!
- dicknuckle 7y ago

lukego 7y ago

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

ur-whale 7y ago

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/

baybal2 7y ago

> 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 7y ago
Can you elaborate? I never heard the term popcorn used in that way.
- eqvinox 7y ago
  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.

Animats 7y ago

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 7y ago
> 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.

StavrosK 7y ago

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.