A real quick write-up here, reposted from my Facebook post:
I get an ungodly amount of questions regarding hand placement on a back squat. Besides my height, it’s the most frequent question I’m asked. Here is the answer:
I keep my hands close to my shoulders, I keep my thumb off the bar, and I keep the bar in my fingers instead of in my palm. I do this because if the bar is in my palm, my elbows will flare back and I will push the bar forward into my neck as I stand up. That will cause my chest to stay down while my ass rises, turning it into a good morning. By keeping my elbows relatively down and the bar in my fingers, I cannot push the bar into my neck, thus keeping my back angle the same on both the descent and ascent. My way may work for you, it may not. Either way, it works for me, that’s all I care about.
If you are having trouble with your chest caving on your ascent, try squatting to parallel for a few weeks. This will force you to slow down your descent and rely on your own strength to get out of the bottom, rather than a rebound which takes you out of tension and then put you back under the weight during the hardest part of the lift.