Yep a good iron is key. I’ve built a lot of diy modules and so far have gotten them all working. I’m not so sure how but I’ve been lucky. I should probably stop now to keep my perfect record. It’s fairly easy though if you have an iron with temperature control and solder fast but work slow. Double check every component before you place it as it’s far easier to spot and fix mistakes when your placing a component than after it’s soldered