Letting your left wrist break down at impact causes fats, thins and chunks (see top right photo). This happens because you're in too much a hurry to get the clubhead to the ball. In good chip swings, the hands reach impact first, not the clubhead.
The simple fix? Less hand action. Try this: Take your normal grip, then remove your right hand from the handle. Wrap it around your left hand as shown (right, bottom), using your right thumb to press the back of your left hand onto the handle for extra stability. Now chip. Use the pressure from your right hand to keep your left wrist flat through impact, letting your hands reach the ball first without excessively "dragging" the handle. Groove the feel, then go back to your normal grip. Still flipping it? Put more weight over your front foot, as I'm doing in the photo at left, and add a little body rotation. Your chipping is about to get so good, you'll almost want to miss the green.