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As high power LEDs develop rapidly, sapphire substrate on which LED's chips are grown, cannot meet the needs of the increasing performance any longer. Therefore, transfer of the devices from the former sapphire substrates to more thermally and electrically conductive receptor substrates is recommended. Laser peeling has been a new technology of separating films of GaN from the substrate on which they are grown. Experience shows that the films can be debonded intactly when the laser parameters are well controlled. In this contribution, the mechanics of the laser-assisted debonding of GaN films on sapphire, silicon and copper substrates is considered so that the specific parameters can be optimized in order to achieve a feasible process scheme that may be used in the industry. During the simulation, the knowledge of interfacial crack generation between dissimilar materials is considered to be the essential principle of the process of "liftoff". Failure of the interfaces results in the debonding. Whatever, the films of chips should not be damaged in the duration of the "lift-off" process. A few important issues such as temperature distribution, stress distribution and energy release rate are raised in terms of examining whether the films are likely to be damaged.