What is a ‘lead free’ PCB? OK, it’s one that’s got no lead in it – that’s pretty obvious – but lead-free reflow process is typically run at higher temperature that for a leaded process. So can you run leaded solder on a lead free PCB? Sure – but sometimes there are packages with solder attached already – e.g. Ball Grid Arrays – if those have lead-free balls, and you try to mix with leaded process, then there’s a danger that the solder balls on the BGA won’t metl completely resulting in poor connections. So you can sometimes run leaded solder on lead free, but caution advised. When we do in-house prototype runs through our own reflow oven, we typcially used leaded solder as it’s a bit more tolerant to temperature variations – with lead-free, often have to push the temerature to avoid cold spots, and the variations in the hot spots can cuase discolouration (or in exreme casers, warping, delamination and even charring!) – so for a ‘on the lab bench’ process, running leaded is usually the best way.