Method for dividing composite material

A method for dividing a composite material in which a brittle material layer and a resin layer are laminated, the method comprising:

• a resin removing step of irradiating the resin layer with a laser beam oscillated from a first laser source along a scheduled dividing line of the composite material to remove a resin forming the resin layer, to thereby form a processing groove along the scheduled dividing line;
• after the resin removing step, a brittle material removing step of irradiating the brittle material layer with a laser beam oscillated from an ultrashort pulsed laser source along the scheduled dividing line to remove a brittle material forming the brittle material layer, to thereby form a processing mark along the scheduled dividing line;
• and
• after the brittle material removing step, a brittle material layer dividing step of applying heat to the brittle material layer from an opposite side to the resin layer along the scheduled dividing line to generate thermal stress in the brittle material layer, to thereby divide the brittle material layer,
• in the brittle material layer dividing step, thermal stress is generated in the brittle material layer by irradiating the brittle material layer with a laser beam oscillated from a second laser source from an opposite side to the resin layer;
• in the brittle material layer dividing step, a spot diameter of the laser beam oscillated from the second laser source at an irradiation position on the brittle material layer is 0.6 mm or more to 2 mm or less;
• in the resin removing step, the resin forming the resin layer is removed in a manner so that one part thereof remains as a residue having a thickness of 1 to 30 μm;
• and
• in the brittle material layer dividing step, after thermal stress is generated in the brittle material layer, a mechanical external force is applied to the brittle material layer along the scheduled dividing line.