CDI stands for "Capacitive discharge ignition"
It is probably one of the most reliable type of ignition systems made for ATVs, snowmobile and other applications. If your problem is no longer under warranty I would suggest that you try to get some kind of guarantee or other assurance from the dealer that replacing it will cure the problem. It is a fairly expensive part!
Some possible causes for premature failure are:
1. welding on any part of your quad or attached parts such as a plow or winch mount without disconnecting the unit.
2. Incorrectly wired accesories
3.loose battery connections causing arcing which in turn can result in voltage spikes. Any of these can cause failure but in the majority of cases it will result in a total failure of the CDI box. (Not a temperature related intermittent failure as you describe)