Buck Regulator Explosions
Check C4 and the connections around it carefully.  This sounds like the integrated switch FET is ending up in linear mode, and therefore dissipating a lot of power.  C4 is part of the charge pump that creates the gate voltage for this internal N-channel FET.  If this charge pump is not working, then the FET can't be fully turned on.

I once accidentally connected the charge pump cap to the wrong side of the inductor, and got similar symptoms.  Mine weren't quite as spectacular, but the output voltage was regulated at low currents, and the chip got hot.

Added

When debugging a switching power supply, the first thing to do is to look at the waveform going into the inductor.  That is very diagnostic, and various subtle things can be seen from its details.

Show us the waveform over at least one complete pulse with a relatively light load.  That will tell us a lot.  When capturing this trace, make sure to ground the scope probe properly to a solid ground node near the switching chip.

Scope trace



This is a rather annoying scope trace.  You've got plenty of vertical room, yet have the gain set to 5 V/div.  There is very little detail per cycle because there are too many cycles on the screen.  And the worst is that the zero volt are in random places not lined up with a division, making it more work than necessary to see the voltage.

If you want someone to spend their free time looking at your problem, show some respect, by taking some care and paying attention to the details.

I'm outta here.