Let's Make Robots!

soldering iron allergic to solder

Im just starting to make my Start Here Robot, but I'm having real problems soldering. 

The solder just will not stick to the soldering iron, or the contacts on my picaxe 28x1. Its so frustrating. I have done soldering before an never had this problem, only difference being that I used to use my Grandads 40 year old soldering iron, and this time I am using a new one that I bought - its pretty cheap and cheerful but it still melts the solder. It just doesnt "flow". The solder is just the stuff that came with the iron, lead free stuff, not rosin cored, but I am using separate flux. 

I have cleaned the tip repeatedly with a wet sponge, i am using flux on the tip before I start trying to solder and I am heating up the pins i am soldering, then adding the solder. I cant tin the tip though because the solder just wont stick to it :(

 

Any help would be really appreciated

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Maybe something like wire glue would work for you... but I have never tried it before so I can't say how good it works.

Well, it was the solder :)

I got some Draper 60/40 rosin cored solder and it works a treat. Spent about 10mins getting the tip tinned up, but now it is nice and shiny and the solder flows like......well....solder

I got some (IMHO) excellent results. Quite tidy considering its my first time soldering in many many years, and I have never done anything this finnicky before. 

What I have learnt from this whole experience = Dont use lead free solder. Its rubbish. 

Thanks for letting us know the 60/40 solder worked.  Always good to know the final solution to these things.  Any faint desire I had to use lead free solder is now gone for good.  I am getting old a little lead might be good in my diet, (just kidding) ...LOL.

sometimes it happens that the tip of the iron develops some kind of oxide layer on it or the solder wire or the board has little impurities on the surface, in these cases usually the solder won't melt properly or won't stick onto the surface.

what i do is rub the tip of the iron and/or the board with a small piece of sand paper. a damp cloth or sponge may work but not as good as a sand paper.

You shouldn't sand your tip. Sanding it will cause damage to the tip.

The tip is usually copper plated with another metal.  The heat, solder, and flux eat away copper.  If you sand, you remove the plating and eventually expose the copper.  Once the copper is exposed it will erode VERY quickly.  You can clean the tip with a green scrubbing pad and water, alcohol, or flux.  I usually dip the hot tip into flux then wipe it on a damp, not dripping wet, sponge.  

...sanding will thin down the tip of the iron pretty much. I was suggested sanding by DanM when I reffered a thick tip iron to him and said that I wanted the tip to be finer. To clear the tip, sponge (or cloth) dipped in water should suffice with daily use. However, the most ideal solution will be to use a brass cleaner for iron (unluckily, I'm yet to find one in my local market as most of them have steel cleaners and I think that steel cleaners may damage the copper tip).

i rub the tip of my soldering once or twice on a mild sand paper sometimes, is it still bad?

 

The only thing I can relate to is the balling up of your solder.

I have an variable temperature soldering iron and use a 60:40 solder with rosin core and no external flux. When I touch the solder on my tip, the solder balls up and falls down onto my table but going about 4-6mm higher, there is the hotspot of my iron and the solder melts and flows properly. This is, to the best of my knowledge, due to the tip having inappropriate temperature. Solder flows only beyond its melting point and if temperature of the tip is inappropriate, the solder will not flow. The iron tins properly when I apply the solder to it at its hotspot. It took considerable searching from my side to find the hotspot of my iron. Try tinning your iron on various spots (get crazy and try tinning even parts you'd not apply solder to). If done properly, you'd have a working iron.

However, I know solder may be a problem as well. I have seen a bit of flux applied to the solder working fabulously for me. However, since you use flux, I'd like you to check the temperature. It is most probably the cause of your problem. Maybe get the tip checked for temperature (from people who have soldering tip thermometers).

There are different varieties of lead free solder, but in general they are all terrible, especially for less experienced people.  Even commercial manufacturers have trouble with it under very controlled conditions.  It is so bad that the laws requiring its use make exceptions for mission-critical equipment, like military, space, and infrastructure (public works, electric grid, etc).  I think you will have much better luck with 60-40 or even better 63-37 if you can find it.  There are different fluxes for lead-based and lead-free solder, too, so make sure you use the right one with the right solder.