Where did I go wrong? - stuck screw

Hello,

I'm an amateur iPhone repairer who is into destroying iPhones. At least, that is what I seem to be accomplishing despite my best efforts. So I'm just looking for a postmortem here on what I did wrong.

This iPhone SE was working perfectly fine when I opened it up. I had opened it once before to replace the home button, so I had removed the metal plate covering the screen and touch connections so that I separate the screen from the phone's base. However, now when I wanted to separate the screen again, I discovered the screw that I'd put into the metal plate indicated by the red circle was refusing to yield. I had made absolutely certain that was the same screw that was there before.

I tried packing tape over the screw then pressing down with the screw-driver, I tried gaff tape and I tried epoxy-gluing a wooden skewer onto the top of the screw. None of those worked. So I took a hobby drill with the smallest drill bit I had, set the spin to counter-clockwise and drilled into the top of the screw head with increasing pressure (this was not an impact drill). After small metal filings emerged from the screw head, the screw finally came loose and emerged. There was a little scraping on the metal plate.

The phone shows a totally black screen now and will not show any indication of working. The top of the screen will get warm when the device is charging.

Obviously, I've damaged the mainboard. If I was in the same situation again, I would not know what to do, so I'm just wondering if anyone could tell me what I did wrong here.

Here's some photographs of it while inside the frame. Did anyone want it taken out to show underneath?

UPDATE: So I got some isopropyl alcohol, pulled out the logic board (but kept that annoying underside connector connected) and started spraying and brushing it down with a toothbrush. There were some metal filings underneath that could have interfered with the underside circuitry of the logic board. This is how it looks now that it's clean.

I connected everything back up again.

and the issue is still the same. If I charge while the phone is open, I can feel the top of the display getting hot.

So I dunked the logic board in 100% isopropyl alcohol for 10 minutes.

I let it dry for 20 minutes then plugged everything back in. Still nothing.