From ‘blobby solder joints’ and ‘wonky’ pins to finishing touches, Pimoroni have an excellent ‘Ultimate Guide to Soldering‘ written by their own head of digital content Sandy Macdonald. They use a Raspberry Pi Zero W to demonstrate many of the proper procedures and pitfalls of soldering – such as bridged connections or solder blobs. Since the Zero W typically requires two long rows of header pins to solder it’s a good device for you to test your skills and proficiency with the iron on. (When you have to focus on soldering 40 pins you can really get in a groove, and also see where your shortcomings are.)
This guide will aim to cover everything you need to know, and probably a fair bit you don’t need to know, about soldering. Soldering isn’t an easy skill to learn, although it’s easy to do it badly, but there are lots of tips that aren’t immediately obvious that can help you out a bunch.
Read much more here.