There's a secret to soldering directly onto a host wall. It works best when you're dealing with a host that has some sort of internal removable pill.
It doesn't matter if it's copper or aluminum. You need to have some pliers on hand. Take the pill, and set it on your stove's burner. Flip the heat up to high. Once the entire pill is host enough, you'll be able to dissolve solder onto it. It works really well if you have an internal "edge" where you can let a bit of solder pool.
Basically (and you have to do this realtively quickly), melt some solder onto your heated pill, then with pliers, move the pill to another burner that is OFF, take your lead, and hold it in the "pool of solder", while blowing slightly to hasten the cool-down. You may have to hold the wire steady for 20 seconds while the temperature drops enough for the solder to solidify.
It sounds long and complicated, but it's actually really simple. The big challenge in trying to solder to a host or pill directly, is that they are natural heatsinks that pull heat away from the localized area you're trying to solder. The solution, is to just get the entire host or pill really really hot. It's not actually that difficult to solder to aluminum, absent the issue of the host dissipating all your heat.
I do this on occasion. I'm increasingly looking for newer and better was to tap case feeds, because I'm not crazy about using case-pins on diodes. For one, it implies that your Aixiz module needs to have an unobstructed connection to the host. Sometimes, this makes it difficult to use thermal compound effectively. I'm starting to see some value in using arctic silver in a lot more areas of my builds, and then finding alternative ways to either tap the host feed, or at least provide a "backup" host feed.
