http://web.archive.org/web/20240512204543/https://en.wikipedia.org/wiki/Nuclear_weapon_design
(Archive link in case it's changed.)
This article is a surprisingly entertaining read for a few reasons:
- one or more people who wrote it clearly have very strong opinions about how nuclear weapons should be built
- the article contains a surprising amount of detail, including stuff that seems like it'd be classified or at least censored
- due to both of the above, there's a ton of
[citation needed]that I doubt will ever be resolved
It is finicky. That's why only a handful of countries have actually managed to create their own thermonuclear warheads. It's more about being able to build the needed infrastructure and acquire the source material than understanding the physics.