I think the key phrase in Malcolm's reply is "using an adequate iron". I have two soldering irons. One is a temperature controlled 50 watt jobbie which struggles on a motor casing. It takes an age for the solder to melt, by which time everything has got worryingly hot. The other iron is a 120 watt Weller. It's not temperature controlled, takes about ten minutes to heat up and, size wise, is a bit of a monster but, for soldering capacitors on etc., the solder flows within a second or so and the heating is very localised.
Hope this helps.
Mike