A method of manufacturing a flat panel display device is disclosed. In one embodiment, the method includes: i) forming a plurality of light emitting units on a first substrate, each of the plurality of light emitting units including a light emitting element, ii) providing a second substrate, iii) placing glass frits between the first and second substrates, iv) radiating a first laser beam, having a first intensity, on one of the first and second substrates, wherein the first laser is configured to melt the grass frits and combine the first and second substrates and v) radiating a second laser beam, having a second intensity, on the first irradiated region so as to anneal the first or second substrate, wherein the second intensity is different from the first intensity. According to one embodiment, the substrate cutting quality can be simply improved.