Why does my solder bubble ?

[aneng]

I've been using lead-free solder for ages and had no problems with it.  Recently, I got a roll of good quality (Multicore/Loctite) 60/40 and it's doing the weirdest thing...  It seems to have a lot of gas (presumably the rosin / flux) venting off as it melts, and when I remove the iron, it continues to bubble for a second and invariably sets just as a bubble has popped - leaving an ugly looking hole in the side of the joint, OR, it will bubble up and not quite pop, leaving a sealed bubble on the joint.  What am I doing wrong here ?  What's the best way to avoid this phenomenon ?

Thanks !

[cs.dk]

To high temperature maybe? I have never seen that before, I also got Multicore/Loctice branded solder, it should be in the top of solders.

Do you have a picture? That sometimes explains more than a thousand words.

[wraper]

Try to preheat the joint a bit before applying solder. Solder will flow better and lower amount of gas will be entrapped in the hole.

[aneng]

I thought about it being too much heat.  I'm only using a cheap Antex 25W mains iron.  It's not temp controlled, so its element is heating continually.  I wouldn't have noticed it with the lead free stuff as that's probably better suited to the higher bit temp.  Oh well, it looks like I'll just have to buy that Hakko FX-888D I've been lusting after.   

[Ian.M]

Stick it on a light dimmer and turn the temperature down a bit!  If that doesn't help, then a proper TC solderstation wont either.  However its more likely to be a contaminated or low quality PCB outgassing than your new solder, and it will do that at any reasonable soldering temperature, with worse problems the longer you dwell on a joint.  (you cant bake the gas out by dwelling longer as that tends to lift the track, or worse)

[Cubdriver]

I've never used the lead free solder (other than in plumbing, where I despise it), but as a thought, are you using the same iron tip, and if so how long have you been using it with the leaded solder?  Purely speculation on my part, but could it be cross contamination with the non-leaded residue that might still be on the iron tip?  (Obviously this isn't the case if you're using a new tip.)  If you haven't swapped tips and happen to have a spare, it can't hurt to try switching.

Additionally, what are you soldering to/on?  A circuit board?  Could there be trapped moisture present that's boiling off as you solder?

I've never seen bubbling like what you describe in leaded solder, and am interested in hearing what the cause ultimately turns out to be.

-Pat

[Dago]

You need a proper temperature controlled soldering iron. Otherwise you will boil and burn the flux as you noticed.

[tautech]

Stick it on a light dimmer and turn the temperature down a bit! 

+1
Exactly what I used for years until i needed/could afford a rework station.
Some used to use a bulb in series with the iron that could be switched in for low heat or out for full heat, this can be a useful cheap fix too.

[SteveLy]

Like others have said, it sounds like your iron is too hot. If you haven't got one, then a temperature controlled soldering iron/station would be a good investment - even if all you can afford is the "world's cheapest" (they have gotten better since Dave made this video):



If you can't or don't want to get a new iron, you can still make do by adapting the way you use your iron to the task and materials at hand. Practice on old junk boards. If your iron is hot, you just need to work faster.