how desolder smd components. Best technique?

[GGMM]

Hello,

Despite my tests with a hot air station, I am not convinced of the result to strip memories to 56 legs.
It seems on my PCB there is weld  on the top of the legs, which makes the operation more difficult.
With my ram test bar, the legs were more "glued" from the bottom and thus easier to desolder.

---->> See post Oscilloscope YOKOGAWA DL1640
https://www.eevblog.com/forum/repair/oscilloscope-yokogawa-ld1640/

I don’t want to damage the circuit board.
I would like to have your opinions and experience on another technique.
I would like to warm up the 56 legs with one blow with one head. I don’t know if it’s commercially available, but you can make it with a copper rod. (I have some)
see this example:
https://www.elektormagazine.fr/magazine/elektor-201307/20836
You’ve already tested, I think I’m less likely to destroy.
Then I thought I’d cut off the legs and unsheathe one, but we’d need a surgical clamp. I don’t know if this exists for integrated circuits

your opinion
cdt

[cantata.tech]

Here's one way, unfortunately this product is no longer sold here https://youtu.be/UmD7F0--7Lc

There's also a few other videos on youtube showing different ways.

I researched this because I need to do it, but haven't tried yet.

[GGMM]

hello,
I think I’ll try this technique.



Either with rigid copper recovered in an electrical cable, but I also believe to have at least a 2 mm rigid copper rod.
Make a precise template, and try before on my test ram.
Well put some solder on the copper bar and flow on the circuit. It should be maybe better than the hot air.


cdt

[MBI_TECH]

If you have a good iron - I personally would and have just used solderwick. Those pins are large enough to get a tip on and flux and wick it off. If you have trouble lifting the pin off of the pad I use an angled dental tool, while heating the pin get behind it with dental pick and lift it off the pad, using the adjacent pin for leverage.

[Audiorepair]

There's another method.

Cut through all the legs with a Craft knife with a new blade.

Then you can remove the chip body and then remove all the pins one by one without having to heat up the PCB unnecessarily.

[wraper]

Hot air is the safest thing. Everything else is much more prone to accidentally damaging pads and traces. Making that contraption for soldering iron is simply ridiculous when you have a hot air station. The major problem with hot air is when you have heat sensitive components nearby, like electrolytic capacitors or connectors. But I just make heat shields from no longer needed stainless steel PCB stencils.

[Audiorepair]

Hot air is the safest thing. Everything else is much more prone to accidentally damaging pads and traces. Making that attachment for soldering iron is simply ridiculous when you have a hot air station.

Agree, there is no way I would attempt such a Heath Robinson method, that's just going to end in tears.

Before I became skilled enough at hot air, I used the cut the legs off method, and never had any problem with damaging anything.
Even now I will often do this instead of hot air, as I consider it far less risky.

The only problem can be when the IC is glued to the PCB, when you really don't want to chisel it off, as it might then launch itself through through the still soldered legs, and take pad, tracks and components with it.
But you can always carefully remove all the cut legs before chiseling if this is the case.


Also, if you don't know whether the IC is glued to the PCB before you try and remove it, any method such as the Heath Robinson one and even hot air, really is going to end in tears, as you will have to supply enough heat to melt the glue without destroying the PCB in the process, something I have found to be impossible in the past with certain manufacturers.
This is when cutting legs/chiseling is the only real option.

[wraper]

Before I became skilled enough at hot air, I used the cut the legs off method, and never had any problem with damaging anything.
Even now I will often do this instead of hot air, as I consider it far less risky.

Cutting legs of SMD parts is risky. When you cut terminal, side cutters push it away from the IC package which may have enough force to lift the pad if terminal is rigid enough. Also it's problematic to do on fine pitch parts.

The only problem can be when the IC is glued to the PCB, when you really don't want to chisel it off, as it might then launch itself through through the still soldered legs, and take pad, tracks and components with it.
But you can always carefully remove all the cut legs before chiseling if this is the case.

If there is some space around IC, my method is heating it with hot air till solder melts. Adhesive is softened too. Then while continuing applying hot air, gently rotate IC back and forth without lifting with pliers until adhesive gives up.

[Audiorepair]

Before I became skilled enough at hot air, I used the cut the legs off method, and never had any problem with damaging anything.
Even now I will often do this instead of hot air, as I consider it far less risky.

Cutting legs of SMD parts is risky. When you cut terminal, side cutters push it away from the IC package which may have enough force to lift the pad if terminal is rigid enough. Also it's problematic to do on fine pitch parts.

If you use a very sharp new blade there is little risk. I never mentioned using cutters.

I have never had a problem doing this, and I have done it a lot.

I have had, however, problems removing an SMD op-amp with hot air, when I didn't know the IC was glued to the PCB.
The PCB was cheap crap, and it blistered well before the glue became soft enough to remove the IC.

[wasedadoc]

Chipquik. (Unless the chip has a ground pad soldered underneath!)

[wraper]

The PCB was cheap crap, and it blistered well before the glue became soft enough to remove the IC.

I guess it was on phenolic board. Those can blister when vapors from absorbed moisture try to escape during heating. It's better to not use hot air on those. Or leave PCB in oven for like an hour or a few at >80^oC to dry it.

[Audiorepair]

The PCB was cheap crap, and it blistered well before the glue became soft enough to remove the IC.

I guess it was on phenolic board. Those can blister when vapors from absorbed moisture try to escape during heating. It's better to not use hot air on those. Or leave PCB in oven for like an hour or a few at >80^oC to dry it.

No this is contemporary Mackie/Behringer/Soundcraft etc.

Often each SMD op-amp is secured with a blob of cement to the PCB.
Hot air DOES NOT WORK.  You have to cut the legs and chisel them off.

[wraper]

Often each SMD op-amp is secured with a blob of cement to the PCB.
Hot air DOES NOT WORK.  You have to cut the legs and chisel them off.

I have yet to see something of opamp size which cannot be twisted off while solder in molten. Adhesive is way less resistant to shear forces. Even when cutting terminals, I would still twist it off rather than brutally chisel it.

[tautech]

Overlay original solder with new low temp silver bearing solder. Suck most off. Use PCB preheater and hot air with Kapton tape to protect any parts remaining or sensitive ones.

Some PSB's are populated both sides so components are glued on and therefore other strategies are required.

[Audiorepair]

Often each SMD op-amp is secured with a blob of cement to the PCB.
Hot air DOES NOT WORK.  You have to cut the legs and chisel them off.

I have yet to see something of opamp size which cannot be twisted off while solder in molten. Adhesive is way less resistant to shear forces. Even when cutting terminals, I would still twist it off rather than brutally chisel it.

Yes, but cutting off the legs and chiseling means you don't have to heat the whole PCB to solder melting temperatures in the first place, with the inherent risks in doing that.

There is nothing particularly brutal about chiseling off an IC body from its cement bond IMHO.
Far more brutal surely is to subject everything else to huge amounts of heat when you don't need to do that.

[wraper]

Often each SMD op-amp is secured with a blob of cement to the PCB.
Hot air DOES NOT WORK.  You have to cut the legs and chisel them off.

I have yet to see something of opamp size which cannot be twisted off while solder in molten. Adhesive is way less resistant to shear forces. Even when cutting terminals, I would still twist it off rather than brutally chisel it.

Yes, but cutting off the legs and chiseling means you don't have to heat the whole PCB to solder melting temperatures in the first place, with the inherent risks in doing that.

There is nothing particularly brutal about chiseling off an IC body from its cement bond IMHO.
Far more brutal surely is to subject everything else to huge amounts of heat when you don't need to do that.

You can twist it on cold too. Much less risk of tearing off solder resist.

[GGMM]

hello,

If you want to cut the legs of the  integrated mémory, don’t you have to have a pair of scissors like that rather than a clamp for electronics. It is teletically small.

yes:  ?
https://www.amazon.fr/s?k=mini+ciseau+de+precision+ongles&__mk_fr_FR=%C3%85M%C3%85%C5%BD%C3%95%C3%91&crid=1SN51738UJ0G4&sprefix=mini+ciseau+de+precision+ongles%2Caps%2C83&ref=nb_sb_noss

no:  !!!
https://www.amazon.fr/s?k=pince+coupante+%C3%A9lectronicien&adgrpid=1349101703137585&hvadid=84319321101869&hvbmt=be&hvdev=c&hvlocphy=126456&hvnetw=o&hvqmt=e&hvtargid=kwd-84319381478034%3Aloc-66&hydadcr=14872_2289459&tag=hydfrmsn-21&ref=pd_sl_3hx7sk0u3y_e

the problem is the gap between the legs, it is less than 0.5 mm

if you have other choices?

cdt

[Lunasix]

As already said, hot air !!! Easy and fast for those packages, but needs some practice. All other methods are risky and should be avoided when hou have hot air.
Desolder the component should be done in 10 to 20 seconds max.

[Bud]

If you want to cut the legs of the  integrated mémory, don’t you have to have a pair of scissors like that rather than a clamp for electronics.

You use a sharp knife for that, not scissors and not cutters. You cut through the legs one by one right where they are molded in the IC body. Care is needed to apply just enough force to cut through leg metal and not allow the knife to fall through and touch the PCB which may damage the traces under the IC. Once all legs are cut, remove the IC body and unsolder the cut legs from the PCB one by one using a regular soldering iron.

Edit: watch here: https://youtu.be/IjVMSCFc5rY?t=1195

[nigelwright7557]

I used to just cut pins with side cutters and remove them one by one.

I now use hot air gun.
However a bit of patience is needed as it can take quite a while to heat up IC and pcb to solder melting oint.

Some people use "low melt" solder which speeds up process.