1. Field of the Invention
The present invention relates generally to the cutting of brittle materials to define, for example, a ceramic board used for an electrical device such as a printed circuit board, or a semiconductor wafer; to a cutting system suitable for carrying out the cutting method; and to a chip material obtained by laser cutting. The invention relates more particularly to such a cutting method and cutting system for initiating a clean cut in a board or chip material by controlling the initial parameters of the cut.
2. Description of the Related Art
Laser cutting is a preferred method of cutting a workpiece because it is substantially free of dust, dross cracking, and cutting allowance. Typically, laser cutting is performed by establishing an initial crack under thermal stress, and then by propagating the crack in the direction initiated by the crack itself. Laser cutting is considered quite suitable for cutting brittle materials such as silicon wafers and electronic circuit boards.
One prior art laser cutting method, disclosed in Japanese Patent Laid-Open No. 4-37492, forms a fine hole by emission of a laser beam, wherein laser cutting starts from a micro-crack generated around the fine hole. However, this method suffers from the lack of control over the direction of the crack generated by the first piercing, and in turn, over the direction of the cutting direction determined by the initial crack. Thus, the accuracy of the cutting direction is reduced.
Another laser cutting method is disclosed in Japanese Patent Laid-Open No. 4-167985. According to this method, a modified layer is formed along a predetermined cutting line, and cutting is performed by scanning the cutting line with a laser beam. The method of JP-4-167985 suffers from the increased number of working steps necessary for forming the modified layer along the predetermined cutting line.
Japanese Patent Laid-Open No. 6-39572 discloses a laser cutting method wherein cutting is performed by multiple scanning of the laser beam using a rotating mirror. JP 6-39572 suffers from poor cutting accuracy in any case other than a linear cut.
Moreover, each of these prior art methods is incapable of accurately cutting a board which has a pattern (such as a metallized wiring) that is high in laser absorptivity, because the laser beam absorption tends to cause damage to the board.