Butch Harmon shares an incredibly simple drill to stop chipping yips in this Golf Digest post. It may be hard to believe something so simple can help, but it addresses the problem directly.
What is Butch's drill? Simply this: Practice chipping normally but let go with your trailing hand at impact.
I've written about this cause before, because it's one of the same problems that screws up your putting. If you flip your wrists at impact, it's because you stop turning through the shot. Your shoulders and arms stop moving at the ball, so your wrists have to finish the shot... and the only way they can do that is to flip the club.
By letting go of the club with your trailing hand at impact, your lead hand and arm will be forced to continue the swinging motion. This drill is a simple way to teach your body to keep turning all the way to your finish.
Dead simple, but the simple fixes are often the best.