Solder does not stick to tip of soldering iron?

Basic question here, but it's driving me insane!

The solder does not seem to stick to the tip of my soldering iron. After the iron heats up, the tip appears black (sometimes on all sides and sometimes on one side), then either it doesn't melt the solder at all, or it I fiddle around with it for a while; it melts the solder, but the solder rolls into itself into a ball and doesn't stick to the tip.

I've seen this many times while soldering before and usually it's solved by cleaning the tip on a soldering sponge or cooling it down and scraping the tip off with a blade, but I have scraped this particular one many times and still it's the same problem: it heats up and gets black, then the solder doesn't stick to it.

It doesn't help that this soldering iron has a very fine tip and I have to use it to solder very tiny chips and wires under a microscope (I'm just starting to learn soldering under microscopes).

Any ideas on what I can do?

PS: Is scraping the tip a bad idea? I have been doing it with my other bigger soldering irons and it seemed to work (at least in most cases) but I am not sure whether it is a good solution or not.

Answer

First question: How long have you had the tip? You could probably easily and cheaply replace it. If the iron doesn't have replaceable tips, get rid of it!

If you've not had the tip long, then a few pointers to keep in mind:

• When the iron is not being used, keep some solder on the tip. This prevents oxidation and corrosion.


• When using the iron, keep a little solder on the tip when the iron is in the stand. Wipe clean before using. Avoid excessive wiping on a wet sponge as this can cause temperature fluctuations which expand and contract the metal, and stress the tip. Consider using brass shavings instead of a wet sponge.


• Never use sandpaper or abrasives to clean the tip. Also avoid dipping it into flux to clean. (Except for re-tinning which should be infrequent.)


• Use a good quality solder. Old solder can have contaminants which leave behind residue and basically make soldering more difficult. (By "old" I mean solder that's been around collecting dust, not necessarily that it has a short shelf life.)

Finally, if you've got a cheap iron, it may be too hot or cold and not melting solder at the correct temperature. Consider getting a temperature controlled unit. I could recommend a Hakko FX-888D for ~ $100 US, see also this tutorial.

Some additional soldering tip pointers: