I believe you are incorrect in your approach. Try using NO2 to super cool it and then try to pop them out. You are right that the diodes would get hot, but hot enough to melt solder? If they did get hot enough to melt solder, then the solder would melt during normal use... and well that's just not going to work. I'd say it is either an epoxy or thermal glue. The best way to take off glue is to either use alcohol or cooling it.
I'd soak it in alcohol and then freeze the mess out of it and watch it pop right out.
It's definitely solder. Probably a paste they apply and then heat. Its melting point is higher than normal operating temperature. But I have been told that these diodes can withstand heat higher than the melting point off solder. The internal parts are welded so they can withstand the heat of the semiconductor chip which has to reach a pretty high temp.
Research what happens to that metal when it is cooled, does it expand or shrink? Would the solder become brittle and release the diode if popped when the temperature is reduced that far? What do the diodes we receive look like? Signs of melted solder or fractured?
Well then, there's your answer. How about around the rim? Edit: well, that might not say anything if it doesn't have solder on the rim, that part might be only compression fitted and the back side soldered.
Yeah that's the other thing. I noticed when I pressed it out its also compression fit. They knew what they where doing when they made this thing. So heat won't just make them fall out. It's going to take a refined method.
Use a bandsaw on the side of the block. It's soft brass. just cut slow.
And if you figure out a good way share it here. Keeping this a secret is the most idiotic thing I have heard of. I don't know why *certain* people treat it like an ancestral secret of the highest order.
Heat the back with a big solder gun and push down between the pins so you don't heat the others as much? You could make an inductive loop the diameter of one diode back and apply heat in just that area fast while pressing between the pins so the instant it melts you push it out.
Ugh, reading this makes me want to get a block and try!
Edit: by looking at DTR's picture, it seems he has some "scratch" marks on the solder, or whatever it is, where he may have pride it when he heated or froze it, or whatever he did. Lol, I hope this helps?