Desoldering smd: braid or hot air station?

[CharlotteSwiss]

I stole some old electronic boards to do some desoldering tests (smd component).
I have both the desoldering braid and a Chinese hot air station: the hot air station I took it on purpose to unsolder smd...
But today's tests disappointed me 
Two pin smd: according to my theory, a hot air temperature of 300 °, a low speed, use a small round nozzle and rotate over the smd .. would have been enough and it would have unsoldered easily. Actually I had to set 400 °, and many times pushing the smd the pads of the board were also detached ... 
With the braid, on the other hand, I can quite well unsolder the two-pin smd. Maybe today I learned that to unsolder a two pin smd you don't need a hot air station?
 
Maybe old electronic boards have solders that are difficult to unsolder?
Which procedure is best for unsoldering two pin smd?
I'm a disaster... 
Charlotte

[John B]

I use a Quick 861DW and have never had issues desoldering components. Desolder braid can't get rid of the surface film of solder and therefore the component will still have a pretty strong connection to the pad, more than enough to rip it off. I use a fine nozzle and don't spread the heat around too much. The solder should visibly change when it melts, then the chip will lift off easily.

[hugo]

You do not need a  hot air station for desoldering:   

[CharlotteSwiss]

You do not need a  hot air station for desoldering:   

oh yes, but I would like to avoid using flux for desoldering; and then I have to learn how to unsolder with hot air 
thanks

[CharlotteSwiss]

I use a Quick 861DW and have never had issues desoldering components. Desolder braid can't get rid of the surface film of solder and therefore the component will still have a pretty strong connection to the pad, more than enough to rip it off. I use a fine nozzle and don't spread the heat around too much. The solder should visibly change when it melts, then the chip will lift off easily.

I paid 5 times less for my station. Yes true, with the braid there is a surface film but in the tests I have not even detached a pitch with the braid. While with the air I detached many pitches. Maybe I was pushing the component too hard with a tip while heating ...
However in the tests with 380 ° .. after 10 seconds the tin did not melt ...
But with such a long time, there is no risk of causing damage to pitches or neighboring parts?
I'm confused 
Maybe there is some trick I don't know ..
thanks

[Howardlong]

Depends on how many layers & power planes: they will sink away heat. If one of the pads is on a flood fill, on a thermal via, or a thermal relief on a flood, it'll take longer too.

I usually use soldering tweezers for 2 pad SMDs, but you can use hot air. I run mine at 350C and full speed, but it's usually used for removing medium sized QFNs & QFPs rather than small smds. The first time I use it in a session, it takes a few tens of seconds extra for the hot air iron to warm its own thermal mass compared to using it soon afterwards.

Yes, you will need braid too, to clean up afterwards.

[CharlotteSwiss]

Depends on how many layers & power planes: they will sink away heat. If one of the pads is on a flood fill, on a thermal via, or a thermal relief on a flood, it'll take longer too.

I usually use soldering tweezers for 2 pad SMDs, but you can use hot air. I run mine at 350C and full speed, but it's usually used for removing medium sized QFNs & QFPs rather than small smds. The first time I use it in a session, it takes a few tens of seconds extra for the hot air iron to warm its own thermal mass compared to using it soon afterwards.

Yes, you will need braid too, to clean up afterwards.

Ok so anyway for the two-pin smd (medium size) it still takes a few tens of seconds to unsolder (I was convinced that it would unsolder in 3-4 seconds).
Air flow then I will set it high (scale 1-10, I thought 2-3 was enough). Of course the track is excellent for cleaning up the pitches.
Maybe my mistake is to force with a small crowbar while I'm warming .. that's why in the tests I detached many pitches ..

thanks 

[timenutgoblin]

I have had success desoldering and reusing SMD parts including resistors, capacitors, sot-23 packages and SOIC packages using either a soldering iron or hot air station. Sometimes the SMD parts are glued or cemented to the PCB which makes them stubborn to remove. Heat can be used to break the surface tension between the SMD part and the glue/cement. Sometimes the PCB has a heavy ground plane which can act as a heatsink which may require preheating. The only force that is holding an SMD part to a PCB is surface tension. There is surface tension in the glue/cement if used and solder regardless of whether it is melted or not. I recommend using tweezers to lift the SMD part up off the PCB when the SMD part is ready to be removed.

[CharlotteSwiss]

I have had success desoldering and reusing SMD parts including resistors, capacitors, sot-23 packages and SOIC packages using either a soldering iron or hot air station. Sometimes the SMD parts are glued or cemented to the PCB which makes them stubborn to remove. Heat can be used to break the surface tension between the SMD part and the glue/cement. Sometimes the PCB has a heavy ground plane which can act as a heatsink which may require preheating. The only force that is holding an SMD part to a PCB is surface tension. There is surface tension in the glue/cement if used and solder regardless of whether it is melted or not. I recommend using tweezers to lift the SMD part up off the PCB when the SMD part is ready to be removed.

However, if I unsalt a smd (2 pin) generally then you change it; so it doesn't matter if it breaks, the important thing is not to lift the pitches; tweezers ok, but don't overdo it to pull ahead of time. Today I made this mistake, and I raised many pitches ...
thanks 

[twospoons]

I find hot air + hot plate to be the best, especially for larger chips, or boards with big copper planes.  120C-150C preheat with the hot plate, then 350C air.  The preheat means to don't have to sit there roasting a chip for 3 minutes to get it to melt - usually only takes 10-20 secs of hot air to push the joints past melt temp.

Same setup is good for soldering SMT too - paste, place and reflow in one hit.

[CharlotteSwiss]

I find hot air + hot plate to be the best, especially for larger chips, or boards with big copper planes.  120C-150C preheat with the hot plate, then 350C air.  The preheat means to don't have to sit there roasting a chip for 3 minutes to get it to melt - usually only takes 10-20 secs of hot air to push the joints past melt temp.

Same setup is good for soldering SMT too - paste, place and reflow in one hit.

in the test yesterday I used the adapter with 3mm round end, I was about 1 centimeter away from the smd, 380 degrees. But I saw that the tin did not turn liquid. Maybe this board is very old and the tin could be difficult to unsolder, maybe I try with other boards ... 

[Berni]

Hot air works great when you use it right.

Hotplate helps with large boards with lots of copper mass, but for most cases its not needed.

You want to use a big nozzle of >= 5mm and plenty of air flow at temperatures of 320 to 400°C depending on the difficulty of the job. Do NOT point at the chip, all this does is cook the IC. You move the hot air around the board in a circle (something like 5 cm in diameter) this preheats the surrounding area to keep it from pulling so much heat, then narrow down on the chip and start moving in circles around the chip to heat up the board in that area. Once it is ready to go move the hot air gun farther away from the board and start pointing directly at the chip. Going farther away reduces the temperature, since at this point you just want to keep it molten for long enough to do your thing, if the solder grabs again just come a bit closer again.

Also wrapping the rest of the PCB in aluminum foil helps a lot. This is because it prevents the board from radiating heat away on the bottom side. Foil or kapton tape can also be used to protect any sensitive plastic connectors that might be right next to the chip you are working on.

[CharlotteSwiss]

Hot air works great when you use it right.

Hotplate helps with large boards with lots of copper mass, but for most cases its not needed.

You want to use a big nozzle of >= 5mm and plenty of air flow at temperatures of 320 to 400°C depending on the difficulty of the job. Do NOT point at the chip, all this does is cook the IC. You move the hot air around the board in a circle (something like 5 cm in diameter) this preheats the surrounding area to keep it from pulling so much heat, then narrow down on the chip and start moving in circles around the chip to heat up the board in that area. Once it is ready to go move the hot air gun farther away from the board and start pointing directly at the chip. Going farther away reduces the temperature, since at this point you just want to keep it molten for long enough to do your thing, if the solder grabs again just come a bit closer again.

Also wrapping the rest of the PCB in aluminum foil helps a lot. This is because it prevents the board from radiating heat away on the bottom side. Foil or kapton tape can also be used to protect any sensitive plastic connectors that might be right next to the chip you are working on.

thanks Berni
as for the heating plate, i don't understand what could help in desoldering for example a two pin smd.
Regarding your analysis, I agree, but I am not considering the desoldering of multi-pin ICs, for those I have square adapters of different sizes suitable for the case.
I was talking about desoldering a simple two-pin smd (type 1206) with hot air. However from what you wrote, I started to understand some of my mistakes: I have to use higher temperatures also for smd (I had set 300 ° as the smd balance them even at 280 ° ..); air desoldering takes time, and does not resolve in a few seconds; maybe a 3mm nozzle is too small
With next tests I hope to do better 

[CharlotteSwiss]

Ideally you use whatever technique is best for the situation. But braid and a solder sucker will not lift smd legs so you are going to get better results with low melt alloy or hot air. I'd work towards these tools in the following order.

Solder sucker, braid, desoldering alloy (chip quik etc), hot air, preheater and get a desoldering gun if you are doing a lot of through hole desoldering.

Don't be afraid to use flux as it makes it easier to reflow certain joints before desoldering. Even if you just use the flux that is in the solder by adding a little more. Flux reduces the surface tension and allows better wetting of the solder so makes it easier to both apply and remove (especially crusty oxidized joints).

I didn't understand well (I'm not good in English ..); so are you saying that before desoldering I could use some flux on the soldered pins of the smd? Does this help melt the solder tin better? I have both a water flux and a chip quik..
thanks 

[Berni]

thanks Berni
as for the heating plate, i don't understand what could help in desoldering for example a two pin smd.
Regarding your analysis, I agree, but I am not considering the desoldering of multi-pin ICs, for those I have square adapters of different sizes suitable for the case.
I was talking about desoldering a simple two-pin smd (type 1206) with hot air. However from what you wrote, I started to understand some of my mistakes: I have to use higher temperatures also for smd (I had set 300 ° as the smd balance them even at 280 ° ..); air desoldering takes time, and does not resolve in a few seconds; maybe a 3mm nozzle is too small
With next tests I hope to do better 

For just simple resistors and capacitors all you need is a soldering iron.

Set the soldering iron to a much higher temperature than you normally use for soldering, such as 360°C. heat up one pad and add a big blob of solder on it, do the same to the other pad too, then start quickly alternating the iron between the two pads. Eventually one pad stays hot enough for you to get to the other one and you can use the soldering iron tip to push the capacitor off the pads and lift the iron up, the capacitor will typically stick to the irons tip and you can just flick it off onto the table. Fast and easy.

The adding of solder to the capacitors pins will leave flux there anyway. This flux helps make a nice clean ball on the pin so its welcome anyway. You just need something for cleaning flux from the board. There are PCB cleaning sprays out there (such as  Kontakt Chemie PCC http://www.kontaktchemie.com/koc/KOCproductdetail.csp?division=&product=KONTAKT%20PCC&ilang=all&plang=all ) or just get some Isopropanol Alcohol (IPA) or pure Ethanol and a brush to scrub your board (or google some of the diy flux cleaner recopies online). You just put the stuff on, scrub a bit and then while it off with a paper towel, you can use compressed air to get the cleaner out from under chips and connectors (or just blowing with your mouth helps, just don't spit on your board). Flux is easy to clean with the right tools. Same cleaners are also good for cleaning any other gunk or crap off circuit boards. Even just using dish soap and water works fine for cleaning PCBs, just make sure to dry it off really well in that case (hair drier or an oven at 120°C)

[CharlotteSwiss]

For just simple resistors and capacitors all you need is a soldering iron.

Set the soldering iron to a much higher temperature than you normally use for soldering, such as 360°C. heat up one pad and add a big blob of solder on it, do the same to the other pad too, then start quickly alternating the iron between the two pads. Eventually one pad stays hot enough for you to get to the other one and you can use the soldering iron tip to push the capacitor off the pads and lift the iron up, the capacitor will typically stick to the irons tip and you can just flick it off onto the table. Fast and easy.

The adding of solder to the capacitors pins will leave flux there anyway. This flux helps make a nice clean ball on the pin so its welcome anyway. You just need something for cleaning flux from the board. There are PCB cleaning sprays out there (such as  Kontakt Chemie PCC http://www.kontaktchemie.com/koc/KOCproductdetail.csp?division=&product=KONTAKT%20PCC&ilang=all&plang=all ) or just get some Isopropanol Alcohol (IPA) or pure Ethanol and a brush to scrub your board (or google some of the diy flux cleaner recopies online). You just put the stuff on, scrub a bit and then while it off with a paper towel, you can use compressed air to get the cleaner out from under chips and connectors (or just blowing with your mouth helps, just don't spit on your board). Flux is easy to clean with the right tools. Same cleaners are also good for cleaning any other gunk or crap off circuit boards. Even just using dish soap and water works fine for cleaning PCBs, just make sure to dry it off really well in that case (hair drier or an oven at 120°C)

thanks Berni; with the soldering iron I used the braid, but I had also heard about this method that you wrote; new welding brings flux and facilitates. To clean I have always used Isopropanol Alcohol and I am fine. As I specified, with the soldering iron I already get good results in desoldering two-pin smd; but to make sense of the money wasted on the hot air station, I wanted to learn how to use that to unsolder two-pin smd too. An alternative, just to learn a new thing.

Tonight I go to the workshop and do more tests with hot air. Yes, I love spending evenings among the electronic components. I'll let you know if I've been able to improve
 

[CharlotteSwiss]

I didn't understand well (I'm not good in English ..); so are you saying that before desoldering I could use some flux on the soldered pins of the smd? Does this help melt the solder tin better? I have both a water flux and a chip quik.

Flux makes solder flow easier as it displaces the oxides and reduces the surface tension. No need to use if it you apply fluxed solder or chip quik as you have already reflowed the solder which has the same effect. For clean up, flux makes cheap or old braid work better as well.

You should watch the old Pace videos on youtube.
https://www.youtube.com/c/paceworldwide/playlists

Rework & Repair Lessons 1 - 8
Basic Soldering Lessons 1 - 9
Adventures in Repair

thanks, tomorrow i will watch the video 

[CharlotteSwiss]

In light of the new advice, I did other two-pin smd desoldering tests: temperature 380-400 (better 400), air flow at maximum, instead of the pliers I used a tweezers of the pointed ones, simply holding it pointed at the smd without pushing: I unsoldered about 30 smd, no ruined pitch. The problem was the low temperature, calculating that if I set 380 ° on the air station, I believe that after 1 cm from the terminal it is much less ... I have not tried with 350 °, I imagine that in any case after many tens of seconds even so it will desolder. The riddle could be: 390 ° and 10-20 seconds better, or 360 ° and 30-40 seconds?
Come on tonight it was already much better, happy.
 

[Berni]

Yeah hot air temperature is not the same as soldering iron temperature.

You get different results with the same temperature if you just change the nozzle size, airflow, distance...etc. The hotter you go the faster you can get the job done, but it means you have to be more alert to back off the distance when it does melt or you risk burning the PCB.

But still the quickly alternating between the ends is the fastest way to get resistors and capacitors off, takes like 3 seconds. The benefit of hot air comes in with components with more pins or tricky components with pins under it such as LGA packages, inductors with bottom pads etc... Anyone that is working often with SMD components should have a hot air station. It makes dealing with chips sooooo much easier and you can pick up a perfectly good hot air station for $40 from china. No need to spend lots of money on some fancy one.

EDIT:
Oh and about desoldering braid, its not really all that good at actual desoldering (i use a pump or hot air for that), but that does not make it useless. The stuff is excellent at sucking up excess solder. If you hand solder a fine pitch SSOP, TQFP etc and short the pins, the braid is great at sucking that solder bridge out of there while still leaving enough solder to keep the pin soldered. It is also good at cleaning up footprints after removing a chip. If you just removed a chip and want nice clean flat pads on the PCB to hand solder a new one, then running some hot desoldering braid over those pads cleans them up as good as new. Same for cleaning up that ChipQuik low melting point solder after using it (You MUST clean it since the alloys with regular solder and turns its mechanical properties into crap)

[twospoons]

If you really want to go fast with 2-pin smd then two fine tip soldering irons works great. With one in each hand you can melt both joints and lift the smd away.

[CharlotteSwiss]

If you really want to go fast with 2-pin smd then two fine tip soldering irons works great. With one in each hand you can melt both joints and lift the smd away.

Rapid? no no, I'm very slow 
interesting suggestion, thanks 

[CharlotteSwiss]

Yeah hot air temperature is not the same as soldering iron temperature.

You get different results with the same temperature if you just change the nozzle size, airflow, distance...etc. The hotter you go the faster you can get the job done, but it means you have to be more alert to back off the distance when it does melt or you risk burning the PCB.

But still the quickly alternating between the ends is the fastest way to get resistors and capacitors off, takes like 3 seconds. The benefit of hot air comes in with components with more pins or tricky components with pins under it such as LGA packages, inductors with bottom pads etc... Anyone that is working often with SMD components should have a hot air station. It makes dealing with chips sooooo much easier and you can pick up a perfectly good hot air station for $40 from china. No need to spend lots of money on some fancy one.

EDIT:
Oh and about desoldering braid, its not really all that good at actual desoldering (i use a pump or hot air for that), but that does not make it useless. The stuff is excellent at sucking up excess solder. If you hand solder a fine pitch SSOP, TQFP etc and short the pins, the braid is great at sucking that solder bridge out of there while still leaving enough solder to keep the pin soldered. It is also good at cleaning up footprints after removing a chip. If you just removed a chip and want nice clean flat pads on the PCB to hand solder a new one, then running some hot desoldering braid over those pads cleans them up as good as new. Same for cleaning up that ChipQuik low melting point solder after using it (You MUST clean it since the alloys with regular solder and turns its mechanical properties into crap)

in the tests last night I did not burn any adjacent component or the pcb. With hot air, however, 3 seconds I could not unsolder anything ... the fastest to detach were smd resistors (very small size), but certainly more than 3 seconds.
Tonight I dreamed of this technique to unsolder 2-pin smd: soldering iron and braid to remove the bulk of the small soldered duw ... and then hot air (a not high temperature might be enough) to detach the smd from the pcb, it should come off in a moment..
thanks 

[Berni]

Hot air is slow because it needs to heat up the board to solder melting temperature, since the pin is soldered to the board it will be at a similar temperature as the board. Less solder will not help since the board has many times more thermal mass than the little bit of solder.

The reason why just quickly alternating between the 2 pins with a soldering iron is so much faster (those 3 seconds) is because the soldering iron directly touches the pad, so the only thing limiting heat transfer is the thermal conductivity of the soldering iron tip and the solder itself. The board is not thermally conductive enough to overcome that and sink away heat. Only thing faster than this is using two soldering irons (as suggested by twospoons) to grab the component between the irons and lift it off while heating both sides, this brings the desoldering time down to 1 second. But it takes more setup to grab a 2nd soldering iron and warm it up, so i only use this method when i have a lot of 2 pin components to remove, like for example i placed the wrong value resistor in 20 places on a board)

Hot air is rarely the tool of choice for working with just simple 2 pin passive components. The one time where hot air is a better choice than a soldering iron is when working with very small parts such as 0201 or perhaps 0402. Since they are literally as big as a grain of salt makes it difficult to accurately poke with a huge soldering iron, so using hot air and tweezers tends to work better (of course under a microscope, even if you have good eye sight).

[CharlotteSwiss]

Hot air is slow because it needs to heat up the board to solder melting temperature, since the pin is soldered to the board it will be at a similar temperature as the board. Less solder will not help since the board has many times more thermal mass than the little bit of solder.

The reason why just quickly alternating between the 2 pins with a soldering iron is so much faster (those 3 seconds) is because the soldering iron directly touches the pad, so the only thing limiting heat transfer is the thermal conductivity of the soldering iron tip and the solder itself. The board is not thermally conductive enough to overcome that and sink away heat. Only thing faster than this is using two soldering irons (as suggested by twospoons) to grab the component between the irons and lift it off while heating both sides, this brings the desoldering time down to 1 second. But it takes more setup to grab a 2nd soldering iron and warm it up, so i only use this method when i have a lot of 2 pin components to remove, like for example i placed the wrong value resistor in 20 places on a board)

Hot air is rarely the tool of choice for working with just simple 2 pin passive components. The one time where hot air is a better choice than a soldering iron is when working with very small parts such as 0201 or perhaps 0402. Since they are literally as big as a grain of salt makes it difficult to accurately poke with a huge soldering iron, so using hot air and tweezers tends to work better (of course under a microscope, even if you have good eye sight).

Ok I misunderstood, I thought 3 seconds was referring to the hot air, not the soldering iron.
In the test on small smd (I think 0402) it is quite fast even with the air and pushing gently to the side with the tweezers, they come off immediately. For the terminal I think the smallest is better (for smd), mine is 3mm round: so I don't heat up adjacent areas too much.
After these tips I could say that for smd 2 pin it is better to use the soldering iron (air maybe for the smaller ones); while for smd> 2 pin better to use hot air to desolder.
When i have time i will continue my tests also with smd> 2pin .. and then i will try the soldering with smd air
(but I have already seen that it is enough to hold the smd on the tinned pads with tweezers, heat with air and ok it soldering)
 
thanks

[CharlotteSwiss]

found the deception for which I could not unsolder the 2 pin smd using the hot air station: I used the small terminal (3 mm), I did some tests by detecting the air temperature, and with this terminal if you are going to 1 centimeter from the weld, the air has a temperature of 80 ° lower than that set on the station.
While using a terminal of at least 5mm, and remaining about 5 mm from the soldering, the detected temperature is about the set one; in fact tonight I tried to unsolder with the 5mm terminal and I can unsolder in a range of 300-380 ° (better 380 °, it comes off immediately in about 2 seconds ..)
Great