The problem of bunched up solder or peaks as you lift the iron from the solder is caused by the iron being slightly too cool for the job and the solder being used. Looking at the conditions causing the problems may lead to a better solution.
If the problem is caused by the iron being slightly too cool to let the solder flow properly, this can be caused by a number of things.
- If your iron is too low power, you may start out well and have the problem develop as you solder.
- If your iron is high enough power and you're using a 'rheostat' or dimmer controller, this has the effect of lowering the iron's power and the problem will occur as above.
- 50/50 (tin/lead) solder requires a hotter iron than 60/40 (tin/lead) solder to keep the molten metal flowing properly.
The best possible soldering iron controller is a genuine temperature controlled iron, where the iron’s controller maintains the tip temperature by applying full power to the heater when the tip cools slightly, but otherwise just 'idles'. If you can't get (or afford) one of these, possibly the best would be to get a higher power iron or throw away the 'rheostat' or dimmer 'controller'.
If the problem still occurs, then use 60/40 solder – which melts and solidifies in a narrower range than 50/50 - or perhaps do the soldering in shorter 'bursts', letting the iron recover for a couple of minutes before starting again.
In any case you need to match the speed of movement and the speed of feeding the solder to the iron according to the capability of the iron to adequately melt the solder.
Also you have to ensure that the foil has been properly fluxed and tinned.