To disable tanks, continuous attack from the sides or rear works.
Depending on your quality of shot, and a bit of luck, it can take anything between a single shot(2x 40mm) to 10 volleys until a Panzer breaks down and is seriously damaged.
To pop a Panzer, its much more difficult. You need to hit exactly the rooftop of the tank with at least more than 45 degrees angle. When the angle is right and the shot landed is perfect, even a single shot will blow up a Panzer.