I was repairing an iPhone 6s today, just the 4.7 inch display. I had the battery plugged in while I was doing this. As I plugged in the LCD, I’ve seen smoke rise up. Was it because of the adhesive gasket around the connectors for the LCD & digitizer connectors. That maybe I had accidentally pinch in the adhesive within the connectors or was it because i didn’t disconnected the battery.

I'm all late to this comment, but to those replacing their ipad mini ' for the first time. Here's a tip:to remove the LCD use floss or sewing spring. Feed to one corner then to the other one, then just slide it to the top and back down then lift up.