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Best results with lead free solder
When using lead free (silver) solder for the first time, you are probably much disappointed. The
solder joint looks not nice, looks unreliable, and badly done. Well, and that is probably just what it
is. Lead-free soldering is not more difficult, but mostly it is A NOTHER process, and you probably
don't know that. All you need to do is change the way you are soldering, and you can have very nice
results. Lead-free soldering was always done to get solder joints of higher stability. So... what
keeps you from doing it? .
Here is a typical problem situation:
You want to add a wire to an existing connection. The solder joint gets too big and dirty, and the
more solder you take the worse it gets . The components around it start to over heat, and the
solder is not flowing still. So you take some more solder from the roll, but the flux that is inside
doesn't do the job very good, and the solder joint looks as if a young boy has done it. Higher solder
temperature makes it worse, and at lower temperature also.
You want to make a normal joint, but it doesn't look nice. So you take some more solder, and re
melt the joint to make it look better. Like as you were used from normal solder. However now
comes the surprise. The extra solder doesn't flow nice at all. You re flow it again. And again? After
a while the components around it are burned, and/or the the PC board cracks off the solder pads .
You remove everything and try it again.
What causes this problem?
Here is the difference. W ith lead solder, the moment it melts, and there is some flux, it will flow nicely.
The flux is active from the very moment the solder has melted, and lead solder melts at such a "low"
temperature, the flux will not burn away quickly, doing it's job all of the time.
Not so with lead-free solder. The flux is initially not working. You need to understand this . You have to
heat up the joint, until the flux starts to burn away, which means really it is quite hot. It is this very
moment, where the flux burns away, the solder suddenly flows nice, and after that is nti functional, and
you have to remove the solder iron. However, this moment is short, since the burning flux is disappearing
quickly. This makes the moment of good solder flow so short, and you can only make small solder joints,
like solder two little wires together. The moment you need to do something larger, you simple need to
apply extra flux, or even apply it a few times . I have tried everything, but I find this the only way. For best
optical results, you can remove the flux residue with alcohol, and it will look very nice.
This is a liquid flux, of highest possible concentration, so as much as possible will
stay on the object. It looks like honey. If for some reason you find it too thick, you
can use alcohol to make it thinner.
You can also use it to prepare printed circuit boards before soldering. For this
application, mix 1 part of the liquid solder flux with 1 part alcohol. Paint the PCB
with this, let is dry on the air for one hour, or dry it with air from a hair dryer. W hen
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Ordering code: dry, solder the PCB the normal way. Don't bother how it looks afterwards, you can
610-007-76 remove the residue nicely with 100% pure alcohol.
Hint: Resin in a good glue. So keep the bottle clean before you close it. If in any
case you glue the lid on, with spoiled residue, you can open it after warming the lid
with very hot water, or leave the closed bottle in alcohol a few hours .
How to apply extra flux?
The good old way, to dip the solder iron into some flux is not working with lead free solder. The flux is
burning away already on the solder iron. The small residue that is left, will not spread over the solder joint
insufficient, and you may just burn the components .
Process for larger solder joints:
1. Apply liquid flux on all surfaces that you want to solder. Use as much as you can apply on it. Better
take too much as too little, any residue can be very easily wiped off afterwards with a cloth and
2. W ith litz wires, apply liquid flux solder before you solder them. Then pre solder those very thin,
before soldering finally into the solder joint that they are intended for.
3. Solder the normal way. I you have enough solder, but you feel there is not enough flux, let cool
down the joint, paint as much liquid flux on is as you can and re solder.
4. If that will not help, here is another method. Empty half of the bottle content in some small metal
container. (Like the metal lid of some bottles) Let it dry in there until you have a sticky paste, of
which you can apply as much as you need then. W ith this it will always work nice.
5. Smaller joints will need less attention, the above is for larger, more difficult joints .
6. Once you have this technique under control, you will not understand why you ever had problems
with it :)
7. Conclusion: You do need to apply extra flux, when soldering lead free. There is no other good way.
Hint: For clean de soldering we sell an excellent, and low cost de soldering iron. (Check under "tools" in