Desoldering smd: braid or hot air station?

[richard.cs]

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.

This is my preferred technique for 2-pin, and sometimes 3 or 4 pin if you can get the irons in at the right angle. It's very quick, maybe 2-3 seconds to remove a component Anything with more pins I use hot air.

[CharlotteSwiss]

Ok two soldering irons, but now that I understand which terminal to use and the right temperature, I have seen that in less than 2 seconds the smallest smd (2 pins) are desoldered, while for the medium-large ones (always 2 pins) in about 3 seconds slip away which is a pleasure ..

[tautech]

Ok two soldering irons, but now that I understand which terminal to use and the right temperature, I have seen that in less than 2 seconds the smallest smd (2 pins) are desoldered, while for the medium-large ones (always 2 pins) in about 3 seconds slip away which is a pleasure ..

If you are using a Hakko type iron get some K style tips for removal of SMD passives:
https://www.hakko.com/english/products/hakko_fx838_tips.html

[CharlotteSwiss]

I use Ersa not Hakko; however i have a tip about how the K, i will do some tests 

[tautech]

Many SMD PCB's are not laid out with rework in mind and even simple rework often requires hot air but as you have discovered the PB free muck solder is not always easy to work with.
In cases of rework on modern PCB's the addition of some lead based solder can make rework life much easier.

[CharlotteSwiss]

yes of course, I already had to add 60/40 solder to then facilitate the desoldering 

[perieanuo]

hi,
that's no arguing here, hotair is the way to go, just learn the technique and the gotcha's.
desoldering with braid, hammer or other medieval methods it's a joke
what do you do if a bga chip arrives on you bench, stretch the braid underneath?
one of my old bosses from a french R&D company that r&q-eed and prototyped + manufactured electronic modules desoldered with braid and 1kg soldering material wasted per chip, when he hit BGA he came to me and said "ok, pierre, let's do it your way" (hotair desoldering, of course). later, you will add heating plate for tough works
so, learn the good way, no some gizmos that will make you finally a bad image as a pro (even a beginner will eventually became a pro, right? that's the idea, to progress, not to find cheezy methods)
regards, pierre

[CharlotteSwiss]

ok,
for multi-pin components (IC ...) there is no discussion about the use of hot air ONLY; in this topic I wanted to understand if it was better the air or the braid for SMD with TWO pins: after testing I realized by myself that it is better to use hot air also for SMD with two pins. For THT components I think it is better to solder and sucking pump
My 2 cents 

[CharlotteSwiss]

tonight i did some two pin smd soldering tests (2mm long); I did not use flux (even if I still have it), tip 0,8 mm (I also used flat tip 1,6mm, but better with the 0,8 one), soldering temperature 280 ° but I preferred 300 °.
As a method I put a little tin on the tip and soldered 1 pin ok, then the second pin with the wire: I thought it was more difficult, solders came out quite well. 

[jpanhalt]

Whenever I do something like that, after the additional pin(s) are soldered, I remelt the original to relieve an stress I may have introduced.

[CharlotteSwiss]

I too would have thought of having to solder the first pin again; but after testing I saw that even with a small amount of solder on the tip to solder the first pin, the solder on it looked good
Perhaps the same pond could be heated again; adding more tin would be too much

[jpanhalt]

I am not referring to what the joint looks like.   A good looking solder joint may actually apply more stress as it is stronger.  There are many articles about the adverse effects of stress on solder joints and components.

Assume you have an SOIC-8 component, you solder one pin, then align the other pins a little bit better with a little twist.  You have added stress to that first pin.  Even two-lead components (e.g., SMD capacitors) can suffer that.  It only takes a second to relieve that potential stress.

Anyway, it's what I do.  In fact, my first joint usually needs a little more solder, as I depend on a little tinning for the "soldering" that holds it in place.  My hands today are nowhere near as steady as they once were.  So, the second hand in most cases isn't to apply solder, but to hold the component in place while I heat that first joint.

[CharlotteSwiss]

thanks for the contribution, now I understand: I want to clarify that when I soldering the first pin (I was referring to two-pin smd), I keep it pretty still .. even a few moments after soldering, so in theory it should not suffer any strees. I then did traction tests on the component, nothing to do, it didn't come off at all in the world   

[CharlotteSwiss]

One of the doubts I have about the soldering of multi-pin smd is: use the technique by dragging the soldering iron, or better to solder with hot air? Maybe the answer could come from the pin spacing of the component, I don't know .. I'll have to experiment 

[Berni]

Both work well.

I tend to prefer drag soldering since to use hot air you need to fist tin the pads really well beforehand. So if im running around the footprint with a soldering iron i might as well just solder the thing then and there. Shorts are easily solved with some extra flux or desoldering braid.

But i do tend to prefer hot air for QFNs. They are usually pretty small, so easy to heat up the area, and they often have heat dissipation power pads under them

[tautech]

Just find what works best for you with the gear you have on hand.
Interesting alternative method:


More ideas here:
https://www.eevblog.com/forum/beginners/so-surface-mount-it-is/

[CharlotteSwiss]

thanks for the links, Taut 

Berni... true what you say, but it scares me enough to have to remove all the bridges that are created with the dragging of the tip. However with the gun I have unsoldered many SMD multi pin, as soon as I can I will play to figure out which method could be easier for me.
thanks 

[Berni]

I don't even care about the bridges when drag soldering, in fact i try to leave some bridges because that means there is enough solder, so that i know all the pins got soldered properly.

It's easier to just not care and fix the shorted pins later, rather than be super careful not to short any in the first place. The process for getting rid of the shorts is so simply add some flux and drag the soldering iron along again with a dry tip. This tends to grab any solder bridges and pull the along until the end of the row of pins, leaving you with just a short on the last 2 to 5 pins. This then easily gets sucked away by placing some desoldering braid on top, pressing down a soldering iron on top to heat it up and lifting it away as soon as it starts wicking up solder. Sometimes it pulls away too much solder leaving the last few pins looking a bit dry. In that case i just add a tiny bit of solder to the iron and go back to touch them up slightly(sometimes also adding a bit more flux). At the end i use some PCB cleaner spray to clean off the flux residue.

I only do the careful pin by pin method on the larger chips like SOIC

[CharlotteSwiss]

ok, in august i will do some tests on soldering of smd IC; i will try both pin to pin, drag, hot air ...
So if I understand correctly, ONLY soic components are suitable for using the pin to pin method?
Maybe we need to evaluate the distance between two adjacent pins I guess ..
thanks 

[Berni]

Not that anything smaller than SOIC (1.27mm pitch) is unsuitable, but more that the level of skill to do it reliably quickly goes up. I need to do it under a microscope to properly see what i am doing and it is pretty slow. Also SOIC chips tend to have a fairly low number of pins, usually somewhere between 8 and 16 pins, the largest ones tend to get to 28 pins, so the speed does not matter as much.

But when you get to something like a 160pin TQFP with 0.5mm pitch its going to take a while to do it one pin at a time. So it makes the speed gain of drag soldering much more of a advantage. I might still do it pin by pin on a small 8 pin TSOP chip, since the cleanup effort afterwards is higher with drag soldering.

For the fastest ways of soldering and desoldering tiny chips the best sources are youtube channels that repair electronics. The ones that have been doing this on a daily basis for the past few years have found all the best ways of soldering stuff.

[CharlotteSwiss]

ok thanks Berni, i will do various tests on multi pins and see what will be the best option for me: i don't care about speed, but the best way to do a clean job without damage.
I have to look for a table with all types of existing smd ICs, it might be useful to know which chips are on the market and their pin sizes.
For chips with 100 closely spaced pins, I can't even imagine how it could be possible to do pin to pin .. maybe with a tin nullity on the tip without wire ... 

[CharlotteSwiss]

I was training to solder 2 pin smd (also 1.2mm wide measure); with the 0.8mm tip I saw that I can weld, while with the 0.5 mm tip I had big problems, it is difficult to heat the soldering area.
I think this 0.5 mm tip should only be used for micro smd 0.5 mm wide and that's it, no other use maybe ... 

My procedure is to put some solder on the tip, place the smd and solder one pin ... then solder the other pin with the wire.
But watching this video (from 7.30)

https://youtu.be/fYInlAmPnGo?t=451

use another method: put the drop on the pitch, then drag the smd into position and ok, I knew this technique too. But the thing that amazes me is that when the welding has already been done, it puts flux on the welds and heats up.
Does this procedure make sense? 

[Terry Bites]

Braid aka solder wick and flux. It sometimes helps to put some new solder on top of the old solder to get a hot puddle going for the wick.
Tales from the solderwick chronicles.

[Berni]

Well how else would you solder a 2 pin component? Tinning one pin and sticking it on while its hot is the only way i know of doing it.

[CharlotteSwiss]

Braid aka solder wick and flux. It sometimes helps to put some new solder on top of the old solder to get a hot puddle going for the wick.
Tales from the solderwick chronicles.

thanks Terry
I solved the problem of desoldering, I can both with braid and with hot air; first for testing I unsoldered 50 smd without problems and without ruining any pitch (without disturbing the flux)