What screws for attaching 1/2" ply to 3/4" ply?
You'll need to pilot and counter-sink screws like that, or try switching to a self piloting, self counter-sinking screw like Gold Star or similar. The problem with all purpose screws is that the blunt tip just flexes the fibers out of the way, reducing the amount of material the threads can get a hold of. With a screw that short it doesn't get enough bite to pull the head flush so it strips out. With a Gold Star, the burr on the tip severs the fibers, allowing the threads to bite in all the way around,  then the nibs on the bugle help the head burrow in so you don't have to counter-sink.