The percussion technique should be vigorous and rhythmical, but it should not involve pain. If the patient does complain of pain, this means that your hand may not be cupped properly and needs to be softened or readjusted. When done properly, you should hear a hollow sound with each percussion.
Chest percussion should be done over the ribs, with careful attention to avoiding percussing over the spine, breastbone, or lower back to prevent damage to internal organs. Percussion may, or may not, be accompanied by vibration.
Mechanical percussive devices are also available as an alternative to manual chest percussion. Compare prices of percussive devices.