de-soldering IC's

Always cut the pins and remove the plastic. Then go about desoldering.

greg

Snip all the pins and remove them one by one is the best way to avoid PCB damage.

--
*Santa's helpers are subordinate clauses*

    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

As others have said, if the IC is not to be saved, cut the pins at the substrate with diagonal cutters and remove each pin one at a time. The only thing I would add is to use a solder sucker such as at:

A cautionary note: Desoldering PWBs requires a degree of skill. Practice on scrap boards before attempting it on something you do not want to damage. It will prove to be a wise investment of your time.

Like they say, snipping the pins first makes it a lot easier.

The solder braid should wick out your holes better than sticking wires through them. You sometimes need to put a little solder on the braid to get your heat flow happening (just like your iron tip). Remember the solder is wicking towards the heat so you can run it up by moving the soldering iron ahead of it. Practice on junk.

The best solder suckers (besides braid) are the spring loaded push rod types. they'll usually clear out the clipped pin and most of the solder, leaving just a little clean up for the braid. Avoid the plastic versions and get the metal body ones. Keep them clean.

There are some specialized solder tips for weller soldering irons that will unsolder a row of connections at a time, but that's more for high volume work.

We used to have one of the vacuum unsoldering stations, but from what I've seen, the user has to spend a lot of time keeping it clean and unclogged, another high volume kind of thing.

There's lots of tricks, but the best tool is patience.

As all the others have said, cut the pins and then take out one at a time. This is especially true if the board is double sided, or has thru' plated holes, or internal ground / power planes. However, if you want to save the IC, you can usually do it with a sucker and braid, on a single sided board at least, but the trick is, before trying to unsolder the pins, heat each one, and add new solder first. It's a fact that new solder works and flows better than old. That said, though, if the board is recent, and manufactured using lead-free solder, you will struggle, no matter what desoldering aids you use.

Arfa

Dave wrote in message news:czDPf.22828$Ui.9828@edtnps84...

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I've used this technique for about 20 years and although I have a proper vacuum assist de-solder station I rarely use it, prefering the following.

De-soldering ICs Use a hot-air paint-stripper,1400W,500 degree centigrade,with 2 level heat control to prolong element life. Activity may appear fearsome but it is no worse than a flow-solder bath.Pre-heat for one minute then apply to pcb,make extractor tool to pull ic from component side. Make an IC extractor from an old large pair,10 inch, of circlip pliers,the jaws need to open out enough to clip around the ends of up to 64 pin ICs with enough force to overcome the mechanical force of the situation where all the pins are angled relative to the PCB holes.Forge around both of the original circlip pins,one joggle at right angle to clear the heigth of the ICs and a slight inwards joggle to make purchase on the underside of the IC,grinding a wedge angle to the points helps particularly where there is no clearance between IC and pcb. Use this technique for salvaging (working order) up to 64 pin ics ( when practised ),other components, sm and even repair (tracks are not dislodged).For repair work beware of spatter of molten solder causing solder bridges on adjascent compoents because if you are doing the job properly,ie not dislodging pcb tracks the IC must be pulled out with some force and the board tends to flex so possibility of flicking solder. The secret is to be as quick as possible,idealy the body of the extracted ic will be just about handleable rather than too hot to touch.Try practising on a board with close packed TTL chips or similar and aim for an extraction rate of something like one every 2 seconds.Between boards keep the hot air gun running on low power setting (not switching off).Don't rest the gun against the board when heating as vibration seems to affect the element life also don't allow the board to flex back onto the gun for the same reason.Hold the gun so airflow is angled to the board as solder spat directly into the nozzle can kill the element. About the only components that cannot be removed with this technique are parts moulded in soft plastic,e.g. crystal sockets,rf coils with plastic former (IF coils usually OK) some DIP switches. Even these are desolderable intact if the body of the component is previously cooled with a blast of aerosol freezer spray.

SAFETY NOTE:- ensure good ventilation, use safety goggles because trapped water etc in the capaillary structure of glass fibre reinfiorced PCB can super- heat to steam and jet out molten solder,also it is possible to overlook small electrolytic capacitors on the solder side of the board which of coarse explode with the direct heat of the hot air gun and beware of very slight risk of combustion of adjascent flammable parts especially where components have extra (un-noticed) mechanical bonding leading to extended duration of heating activity.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

It seems that gravity is working against me... I am putting the solder braid on top, and it isn't drawing the solder up and out of the hole. I guess I can try it from the bottom.

manufactured

The board is at least 5 years old. The solder seems to take quite a bit of heat to melt, I don't know if that would indicate lead-free. I've done a bit of desoldering of things like capacitors, transistors, etc. and have not run into this type of problem. I was ready to chuck the whole mess in the trash after 2 hours last night... I am going to try adding new solder next time

When using the desoldering pump, do you heat one side of the board and apply the pump to the other? My pump has a plastic or teflon tip and I worry about it melting. I guess I'll try it and see what happens.

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This is the best idea I've heard since someone suggested solder reflow using the toaster oven (which, btw, I haven't tried yet). I have a heat gun someplace, will check the rating on it and see if it will work.

Dave

If the board is 5 years old, it is unlikely that it has been manufactured using lead-free solder. I think you will find that it's just that the solder has chemically aged, and also formed an oxide layer on its surface, which can be quite hard, and a good heat insulator. New solder added before unsoldering is definitely the order of the day, in these cases.

The tip on the solder sucker will melt - but only after it's unsoldered like

500 joints. Put the iron on the side of the joint. Add some new solder. Let it all cook for 2-3 seconds, then push the tip of the sucker firmly against the other side of the joint, into the molten solder, whilst still holding the iron tip, exactly where it was. When you release the sucker, it will take the old solder off clean. Some people prefer to place the nozzle over the end of the wire or pin. This is fine also, but don't push the nozzle all the way down to the board, and don't remove the iron tip from the joint. Just lean the nozzle over, away from the iron tip. I prefer the former method as, if the component leg that you're sucking is large, it can block the nozzle to the point where there is not enough space around it for the solder to be sucked off the joint.

Arfa

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You definitely need a tool to pull the IC off the board as soon as the solder is non-solid/breaking up ie before even fully melted quite possibly. An old pair of long nose pliers with the ends ground down so the remnant tips can be bent inwards to grab the ends of the IC would probably be sufficient to show the method works. Also definitely practise on an old/scrap board first as it needs that confidence because otherwise pointing a glowing hot element and 300 degree C or so blast of hot air at a pcb is not a natural thing to do.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

All right, already. I went and got some godd#mn flux about a year ago after reading one of your posts. Still not sure exactly when to use it or how much to use... seems to leave a bit of a mess on my board when the job is done, i.e. doesn't come off with isopropanol and a Q-tip.

Nope. No fancy desoldering station for me, one more piece of electronic gear in my workshop and I'll be in divorce court for sure. I like the $5 desoldering braid. I may learn to like my $15 desoldering pump if I figure out the technique.

I'm not 100% sure I understand your technique but hey, it's worth a try. I generally work at my bench; I may need some sort of protective glove to make it shake given it weighs >150kg and is lag-bolted into a concrete wall. Or maybe I could try a card table.

I used some flux yesterday. It worked. It worked very well. It worked so well I had to clean up the mess on the other side of my board! Part of my bungling component removal technique is to destroy at least one metal pad (metal circle on PCB with no trace attached). If one is trying to solder in a new component, it's tough to get the solder to flow to the other side of the board without the metal pad... the solder tends to want accumulate on my iron instead of flowing onto the heated component lead. Ahh, enter the flux. I used it on two of my IC pins and yowza! Solder went right through the hole and dripped off the pin on the other side before I realized it!

Thanks for the advice and the entertaining manner in which it was delivered.

Dave

For stubborn holes, cut the end of the solder wick at a slanted angle to form a sharp point. Stick the pointed end in the hole. Do use liquid or paste flux and fresh solder with the wick if it's not working. Usually the issue is your soldering iron tip needing some fresh solder.

Don't forget to clean up the board with something like rubbing alcohol and q-tips.

If the circuit board has solder pads on both sides then it is very difficult to remove with the braid method. If the pads are on one side only then you need to make sure that their is no solder between the pins and the holes. Hope this helps.

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