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
As far as I understand it, nukes are pretty easy to put together with modern tech. The problem is finding enough fissile material of the right grade. That takes a massive industrial effort.