Solder doesn't melt

Question

If I solder something and wait about 24 hours, I can't remove it anymore. I am using a soldering iron at 350 degrees C. I tried turning it up but it still won't melt. Even when it does melt, it's pasty. Also, when melting solder from the wire of solder, it sometimes also doesn't melt. New tips always melt it, so is it because my tip is too old? But new tips always get dirty after one use so it would be ridiculous to change to a new tip every time. DeOxit only gets rid of the blue so that doesn't do anything useful. Does using lead solder help? (I'm using a lead free with rosin core solder) I'm using a wet sponge but it doesn't do anything useful. Won't you get lead poisoning if you use leaded solder?

Answer 1

New tips always melt it, so is it because my tip is too old?

This sounds like you're trying to melt solder by touching a "dry" tip to it. That doesn't work well, because the thermal contact is very bad; you wet the solder tip with fresh solder. The fresh solder should spread evenly on the tip and cover it. Then, touching the existing solder with your liquid solder will establish a "heat bridge" and melt the solder quickly.

If fresh solder applied to your tip doesn't wet the tip correctly, you might need to clean it from oxide. Doing that, do try to work at lower temperature – depending on the solder alloy and the flux in the solder wire, that might simply be too hot and lead to an abundance of corrosion on the tip.

But new tips always get dirty after one use

No, that's not true. Quite frankly, I clean my tips less often than I should, but I can still use them for years.

it would be ridiculous to change to a new tip every time.

I concur.

DeOxit only gets rid of the blue so that doesn't do anything useful.

Whatever DeOxit is, and whatever "the blue" is in this context! Cleaning a non-corroded solder tip is usually just wiping it with a moist non-melting sponge or with a brass "pot scrubber" thing. If a tip has been terribly abused for months and is a oxidized mess, careful mechanical abrasion to get to blank copper (or solder-compatible metal) is what you'd do as a very last resort. Usually, this doesn't even happen. As said, a normal tip under usual care (which means wiping it once in a while when hot) will never need to be treated with anything chemical to remove oxide, aside from with fresh solder.

This all sounds like a combination of different factors:

• too high temperature
• wrong solder (are you perhaps using plumbing or hard jewellery solder?)
• aggressive cleaning products

Answer 2

Your tip and the solder joint are most likely oxidized. Insufficient flux is the most likely cause. Try solder from a reputable brand, like Kester. I recommend K100LD.

The iron tip will also oxidize if you leave it hot for a long time. Don't leave it on when you're not actively using it. If you have a high quality iron it will likely heat up in seconds. I turn mine off every time I set it down.

You can sometimes revitalize a tip by applying solder all over it and cleaning it with a brass sponge. There's also these little trays of top cleaning chemical you can buy, which you dip the tip into. Search chipquick tip cleaner. This is rarely needed if you use good practices to limit oxidation. I've used mine only once or twice, but it is very powerful.

Answer 3

But new tips always get dirty after one use

Yes they do. The tip must be cleaned every time just before soldering a joint [or a rapid (10 to 15 seconds) sequence of joints. It takes a few seconds for oxide to form]**. As others have indicated, use a damp sponge or brass tip cleaner.

There is usually a coating over part of the tip that will accept solder. Apply solder to the tip then wipe it off. The tip should be shiny silver and clean. This is called tinning. Do this every time. Keep the tip shiny silver always.

Do not sand or file a tip.

** Thanks @TonyM