CurtPalme.com Home Theater Forum

PaulB

Just been unsoldering a couple things on the LVPS but boy, what a job that turned out to be! I just could not get the solder out of a couple of the holes on the pcb, been at it for over an hour and only just got it done Evil or Very Mad

Is it me or does trying to unsolder stuff sometimes turn into nightmare city for anyone else? I eventually had to push the soldering iron temperature way up before I can get the old stuff wicked away, even then I ended up pushing a needle through one of the holes 'cause I just could not get the last fragments of solder out no matter what I did!

I think its because its old type solder on th pcb that doesn't melt quite as easily as the modern stuff perhaps, dunno.

Got a desoldering pump but I prefer to wick Shocked

Nightmare.

stefuel · Posted: Thu Sep 17, 2009 12:27 am Post subject:

I don't even bother any more. When you remove a through hole component, there is usually a convex dimple on the solder pad after removal of the part. I have a tiny drill that I use. It only takes a few seconds to do. It doesn't over heat the board and the new part fits and solders right in. Wink

wallace123456 · Joined: 14 Aug 2006 Posts: 2236 Location: Northwest VA area

My experience is, the older the solder, the harder it is to heat up. Solder suckers work better on a pcb than wick, for me at least.

I'll sometimes burn a little solder on the tip and leave a small amount on. Then apply the soldering iron tip to the spot where I want to un-solder. Sometimes it helps get the solder flowing.

wallace

betel · Posted: Thu Sep 17, 2009 1:17 am Post subject:

There may be an oxidized layer on the solder surface inhibiting the flow of heat. Might try putting some flux on it first. Just a guess though. Also remember many manufactures are now using lead-free solder. Much higher melting temperatures.

Nashou66 · Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY

I just leave it there and use my hot air station to heat up the holes and slide the part through the soft solder Very Happy

Athanasios

beun · Joined: 28 Jun 2006 Posts: 676

Another way is to actually add some new solder and use solder wick. You are than usually still left with a bit of solder in the hole. To get that out use a flux pen and some more wick. Works usually for me.

joatmon · Joined: 17 Mar 2009 Posts: 127 Location: Ottawa, Ontario

It's simply a case of not enough heat. A preheater can work wonders - so can a third hand holding a hot air rework tool over the area you are working on.

If you want hard, try removing a through hole mounted 1.0V 50A DC-DC power supply from a 30+ layer circuit board...

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

**Curt Palme** · Posted: Thu Sep 17, 2009 3:17 am Post subject:

I had a bunch of Barco 1208 V boards that I accidentally stuck in an 808 before I realized that that sends overvoltage to a bunch of the chips on the sub board. I think I had 4 here that I completely screwed up. Barco sub boards are doublesided and through plated. As I found shorted chips, I used the following trick:

-cut the chip out with side cutters, leaving the chip leads intact on the board.
- use tiny pliers to pull the leads out from the component side while using a soldering iron to heat the pad from the underside.
-then I had a clean pad, but yes, that solder dimple between top and bottom was a PITA to get the solder out of, esp. when the pad was in really tight quarters.
- I then switched to an air compressor, to blow the air through the hole. That worked EVERY time, except for the solder splatters on each side of the board on occasion. Since the solder was being cooled as it was blown out of the holes, and the pads/parts around the solder were cold, it turned out the solder didn't stick, and could be easily scraped away with a fingernail or a toothbrush. I had a 16 pin chip replacement (with IC socket in case it ever smoked again) down to about 15 minutes by the time I was done, and I saved every board except one.

PaulB · Posted: Thu Sep 17, 2009 6:40 am Post subject:

Some wonderful ideas there guys, didn't even know that the problem had a name - solder dimple, very descriptive!

I'll follow up on these ideas, so simple some of them, the drill in particular is one that appeals to me. I just had a look and realised I have tiny drill bits the right size Thumbs Up

Theres me trying to push a needle through the dimple - what a plonker!

I've tried the adding solder trick normally with great success but this time all I was doing was feeding the dimple monster more solder to replace the stuff I did manage to get out - extremely frustrating that I just could not get that last bit out of there.

Glad to see I'm in good company and that its not just me. I just presumed there was only a couple ways to desolder, now I realise that your only limited by your ingenuity and the tools you have at hand. My eyes have been well and truely opened!

Brilliant, brilliant ideas guys, many, many thanks.

Ile · Posted: Thu Sep 17, 2009 7:34 am Post subject:

I use so small soldering iron tip that it fit to hole and then suck melted solder with pump from pcb other side.

PaulB · Posted: Thu Sep 17, 2009 8:05 am Post subject:

Ile · Posted: Thu Sep 17, 2009 11:46 am Post subject:

Round 0.4 mm is probably smallest for my Weller WHS-40.
http://www.tooled-up.com/Product.asp?PID=12390
With old oxidated solders I have been added some fresh solder first.

CIR Engineering · Posted: Thu Sep 17, 2009 2:16 pm Post subject:

beun · Joined: 28 Jun 2006 Posts: 676

The solder flux and wick really helps to suck the dimple out, blowing like Curt describes also works really well.

draganm · Joined: 08 Mar 2006 Posts: 8990 Location: Colorado

Craig's right, stay away from dill bits. Not only will you lift a trace but can easilly strip the through-hole plating out of the PCB.

Sparky015 · Posted: Thu Sep 17, 2009 10:48 pm Post subject:

Paul, there are a few ways to skin this cat. As others have said, stay away from mechanical things like drilling, or pushing really hard with your tip. You will destroy your board, and your tip. Also, stay away from jacking up the heat, as that will also ruin your board and shorten the life of your solder tip. Techicians trick, solder some new solder on top of the old, then use your solder wick or mechanical desoldering tool. Or, invest in an air powered desoldering unit. Expensive, but pays for itself by not ruining any traces. Also make sure to keep your solder tip in good condition by melting some solder on it before shutting it off. Good lucK!

stefuel · Posted: Thu Sep 17, 2009 11:56 pm Post subject:

Robert A. Hill · Joined: 19 May 2006 Posts: 182 Location: Simpsonville, SC

To clean out holes, I use a clean copper wire as a wick. Sand the wire to remove any coating or oxidation, apply a little flux to the wire and on the solder in the hole. Heat the wire ( not the pad) until it is hot enough to melt the solder in the hole. push the wire thru the hole and remove it. The solder will wet the clean wire and the solder wlll come out of the hole when you remove the wire. It never takes more than one repeat to clear a hole. This minimizes damage to the pad by reducing heating of the pad area.

**Curt Palme** · Posted: Fri Sep 18, 2009 2:11 am Post subject: