This may be a silly question but do you have to solder on both sides of a two sided PCB or does the solder run? I would assume that the solder will not run, but how do you solder the top surface if the component obscures the connections? IC sockets for instance would obscure the top face.

 

Usually no, sometimes yes.
Commercially produced boards usually have through plated vias, which means that the pads on opposite sides are electrically connected before you start soldering.
Often the pad on the component side doesn't need electrically connecting anyway. On DIY boards without through plated vias, sometimes soldering both sides of a component is used to connect the layers at that point, if you are designing the board yourself you know if that needs doing, if it's a kit then it should be mentioned if required.

 

With through hole plated boards you solder from the "non-component" side only. The solder will wick up into the plated through hole. You typically want the solder to wick at least 75% up into the hole for a good quality joint.

 

Thank you both.

I've recently bought PCB Wizard and on a congested board using the double sided option makes the board so much neater. I suppose that technically it makes no difference, but omitting jumper wires would be nice.