The density in the pit of an exploding nuclear weapon is not especially high. The trigger only has to compress the core to greater than the critical density so even only a 50% density increase is sufficient. Carey Sublette's nuclear weapon design site says:

The convergent shock wave of an implosion can compress solid uranium or plutonium by a factor of 2 to 3.

If we take a 100kg mass the density required to form a black hole is of the order of $10^{75}~\text{kg/m}^3$, which is many, many orders of magnitude greater than the density of plutonium or uranium. The bottom line is that the density obtained in a nuclear explosion is so many orders of magnitude greater than anything achieved in a nuclear bomb that it is beyond any conceivable human technology.

The density in the pit of an exploding nuclear weapon is not especially high. The trigger only has to compress the core to greater than the critical density so even only a 50% density increase is sufficient. Carey Sublette's nuclear weapon design site says:

The convergent shock wave of an implosion can compress solid uranium or plutonium by a factor of 2 to 3.

If we take a 100kg mass the density required to form a black hole is of the order of $10^{75}~\text{kg/m}^3$, which is many, many orders of magnitude greater than the density of plutonium or uranium. The bottom line is that the density required is so many orders of magnitude greater than anything achieved in a nuclear bomb that it is beyond any conceivable human technology.