I assembled a board a few days ago where I feel I might have made a bit of a mistake. It had a Li-ion battery charger and a boost converter to run a fan, and the datasheets for those parts suggested layouts with lots of pours for thermal management. I did the layout according to the recommendations and ended up not including any thermal relief on most of the parts connected to the pours. Needless to say, that made soldering parts to the board harder. I got it done, but some of it was pretty ugly.
So the question is: what’s the right way to deal with thermal relief and pours? If you’re putting big areas of copper everywhere to move heat away from components, it seems as though thermal relief is the last thing you want, since it increases the thermal resistance between the parts and the pours, but at least for hand soldering, not having thermal relief makes life quite difficult during assembly.
Which leads to a related question: do you still need thermal relief when you’re reflowing boards? It seems to me that the main argument for thermal relief is that you want to increase the pad-to-pour thermal resistance so that when you heat the pad up with your iron, you can get it to soldering temperature quickly without heat leaking out into the pour. If you’re reflowing, isn’t the whole board (pads, pours, substrate, parts) all at the same temperature anyway? What’s the benefit of thermal relief then?
(This all seems like something that should be obvious, but it’s not to me…)