News Column

Patent Issued for Laser Scribe Processing Method

July 30, 2014



By a News Reporter-Staff News Editor at Journal of Engineering -- A patent by the inventor Kajikawa, Toshikazu (Kobe, JP), filed on June 10, 2010, was published online on July 15, 2014, according to news reporting originating from Alexandria, Virginia, by VerticalNews correspondents.

Patent number 8779327 is assigned to Seishin Trading Co., Ltd. (Hyogo, JP).

The following quote was obtained by the news editors from the background information supplied by the inventors: "The present invention relates to a laser scribe processing method for use in processing hard and brittle materials and the like.

"As a means for cutting circuit boards and the like equipped with electronic parts, laser processing has been widely used. In laser processing, a laser beam emitted from a light source is converged using an optical system for irradiation such as a lens, and a laser converged spot (beam waist) having an elevated power density is irradiated onto a board to cut the board.

"As a material entity of the board, a hard and brittle material has been used. Hard and brittle materials are classified into noncrystalline hard and brittle materials typified by glass materials, and crystalline hard and brittle materials typified by sapphire and the like. For example, when a laser beam is, irradiated onto a board formed from a noncrystalline hard and brittle material, concomitant with formation of melt processing marks and thermally altered portions on a part of the board as a result of the thermal processing, irregular cracks are formed that result from strain stress generated concurrently with thermal processing. Such cracks are formed in various directions on the surface of the board, and the direction of this formation has been known to be affected by asymmetry, wavefront aberration and the like of the optical system for irradiation or the laser beam. In addition, crystalline materials have orientations along which cleavage is likely to occur (cleavage plane). When a board configured from such a crystalline material is subjected to laser processing, cracks are generally formed along a cleavage planar direction of the crystalline material that configures the board. Accordingly, cracks formed in various directions on the surface and the interior of a board by laser processing are believed to make it possible to cut the board nonuniformly (asymmetrically), and to cut in a desired cutting direction difficult.

"With regard to such generation of cracks, as a means for preventing generation of cracks, JP-A No. 2008-93706 discloses (A) a laser processing method in which a processing is carried out while relatively shifting a laser beam with respect to an object to be processed, and the method is characterized in that the laser beam has an elliptical beam shape having a long axis along a relative shifting direction on an irradiated face of the object to be processed, and that light intensity distribution along the long axis direction is asymmetric. In addition, as a means for cutting a board utilizing generation of cracks, JP-A No. 2007-260749 discloses (B) a laser processing method in which first laser light is converged to the vicinity of the surface of the object to be processed to form an initial crack, and the cut crack is developed on the object to be processed from the initial crack as a starting point, whereby cutting of the object to be processed is executed.

"However, according to the laser processing method (A) described above, a special light converging optical system is needed for preventing generation of cracks. In addition, according to the laser processing method (B), cutting is executed using thermal stress generated by irradiating with a laser beam onto a hard and brittle material of the board; however, problems of causing deformation of the board and occurrence of nonuniform torn surface may be raised when such thermal stress is great. Moreover, since it is necessary to provide a cooling step in which a cooling medium is sprayed on the region irradiated with laser, problems in terms of preparation and production may be involved."

In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventor's summary information for this patent: "The present invention was made in view of the foregoing problems, and an object of the invention is to provide a laser scribe processing method in which multiple pairs of beam spots are formed on the surface of a board concurrently with irradiation with a laser beam in laser scribe processing of a board formed from a hard and brittle material such as glass or sapphire, and in which the direction of cutting the board can be adjusted to agree with a desired direction by controlling the direction of extension of cracks formed with the multiple pairs of beam spots.

"An aspect of the invention made for the purpose of solving the foregoing problems is a laser scribe processing method of forming cracks that run along a scribe direction of a processing target substance using a light source that emits a laser beam, and an optical system for irradiation that leads the laser beam onto a processing target substance, the method including:

"an emission step of emitting a laser beam from the light source;

"a splitting step of splitting the laser beam into an ordinary light component and an extraordinary light component having different travel directions;

"a light converging step of converging the ordinary light component and the extraordinary light component to form multiple pairs of beam spots; and

"an irradiation step of intermittently irradiating with the laser beam having multiple pairs of beam spots in a scribe direction of the processing target substance.

"The laser processing method is a laser scribe processing method in which a crack along a scribe direction of a processing target substance is formed using a light source that emits a laser beam, and an optical system for irradiation that leads the laser beam onto a processing target substance. Specifically, provided is a method in which: an emitted laser beam is split into an ordinary light component and an extraordinary light component, which are allowed to travel toward each different directions, followed by light converging; thus formed multiple pairs of beam spots are simultaneously irradiated onto a processing target substance; and the processing target substance is cut using cracks formed between the multiple pairs of beam spots. Accordingly, by concomitantly forming multiple pairs of beam spots spaced with one another on a processing target substance, cracks having directionality but having fewer heat affected layers can be effectively formed and extended. As a result, uniform and symmetrical cutting of the processing target substance can be realized. In addition, by intermittently irradiating the processing target substance in a scribe direction thereof with the laser beam thus having multiple pairs of beam spots, cracks that extend on a straight line that connects between the multiple pairs of beam spots are linked, whereby the processing target substance can be cut uniformly and symmetrically while minimizing the influences from thermal stress.

"For splitting into an ordinary light component and an extraordinary light component in the splitting step, a birefringent prism disposed in the optical system for irradiation may be used. By using such a birefringent prism, splitting of the laser beam into the ordinary light component and the extraordinary light component can be realized concomitantly with travelling of thus split ordinary light component and extraordinary light component toward different directions. As a result, simplification and improvement of operability of the device configuration can be achieved.

"The directions of splitting of the ordinary light component and the extraordinary light component may be adjusted such that the directions of splitting of a pair of beam spots in the irradiation step run along the scribe direction of the processing target substance. When the directions of splitting of the ordinary light component and the extraordinary light component are adjusted in this manner, directions of splitting of the a pair of beam spots spaced apart can be adjusted so as to meet the scribe direction of the processing target substance. Therefore, cracks can be effectively extended with respect to the scribe direction; and the extension direction of the cracks can be controlled, whereby crack formation along the desired direction is enabled. As a result, breakage of the processing target substance can be executed uniformly and symmetrically.

"The directions of splitting of the ordinary light component and the extraordinary light component may be adjusted such that the directions of splitting of a pair of beam spots in the irradiation step run along the cleavage plane of the processing target substance. For example, when the processing target substance is formed from a hard and brittle material such as sapphire, the directions of splitting of the ordinary light component and the extraordinary light component are adjusted to adjust the directions of splitting of the a pair of beam spots spaced apart so as to run along the cleavage plane of the processing target substance. Thus, the cracks can be extended along the cleavage plane, and uniform and symmetrical cutting with respect to the desired direction can be realized using the extension of the cracks.

"For adjusting the directions of splitting of a pair of beam spots in the irradiation step, a birefringent prism which is disposed in the optical system for irradiation, and is rotatable around the optical axis of the optical system for irradiation may be used. Adapting such a birefringent prism rotatable around the optical axis of the optical system for irradiation enables: (1) the laser beam to be split into the ordinary light component and the extraordinary light component; (2) the ordinary light component and extraordinary light components to concomitantly travel toward the different directions; and further (3) the directions of splitting of the ordinary light component and the extraordinary light component to be easily adjusted also in the face perpendicular to the optical axis of the optical system for irradiation.

"The directions of splitting of the ordinary light component and the extraordinary light component may be adjusted such that the distance between centers of the a pair of beam spots in the irradiation step is adjusted. Adjusting the directions of splitting of the ordinary light component and the extraordinary light component of the split laser beam enables the distance between centers of the a pair of beam spots to be adjusted to meet the adjustment. By thus adjusting to give an optimal value of the distance between centers of the a pair of beam spots depending on the type and properties as well as the processing characteristics and the like of the processing target substance, formation and extension of the crack on the straight line that connects between the a pair of beam spots can be effectively realized, and the formation and extension of the crack can be easily controlled.

"The distance between centers of the a pair of beam spots in the irradiation step is preferably adjusted to 0.2 times or greater and 50 times or less of the diameter of the spot (may be also referred to as 'spot diameter'). When the distance between centers of the a pair of beam spots falls within this range, the formation and extension of the crack on the straight line that connects between a pair of beam spots can be most effectively realized. As a result, a straight and stable crack can be formed and extended along the scribe direction of the processing target substance, and cutting of the processing target substance can be executed even more uniformly and symmetrically.

"In the splitting step, a half-wave plate which is disposed in the optical system for irradiation and is rotatable around the optical axis of the optical system for irradiation may be used to adjust the intensity ratio of the ordinary light component to the extraordinary light component. Adjusting the intensity ratio of the ordinary light component to the extraordinary light component using a polarization rotation element such as this half-wave plate enables the power density of the multiple pairs of beam spots to be controlled, and the extension direction of the crack formed with the multiple pairs of beam spots to be adjusted. As a result, generation of a thermal effect layer which is most appropriate for the type and properties as well as the processing characteristics of the processing target substance, and the cutting direction of the processing target substance can be easily adjusted.

"The spot diameter of multiple pairs of beam spots formed in the irradiation step is preferably 0.3 .mu.m or greater and 300 .mu.m or less. When the spot diameter falls within this range, cracks formed on the a straight line that connects multiple pairs of beam spots can be even more greatly extended, and thus uniform and symmetrical cutting of the processing target substance can be easily realized while minimizing the influences of thermal stress.

"The optical system for irradiation may further have a quarter-wave plate. When the quarter-wave plate is provided, linear polarization of the laser beam is converted into circular polarization, and thus influences of polarization are eliminated, whereby stabilization of processing characteristics can be easily ensured.

"The term 'scribe direction' as referred to herein means a direction of the laser beam intermittently irradiated onto a processing target substance. The term 'cutting direction' means a direction of breakage generated on the processing target substance. The term 'directions of splitting of a pair of beam spots' means directions of splitting of a pair of beam spots formed from an ordinary light component and an extraordinary light component, and also directions of splitting in a face that is perpendicular to the optical axis of the optical system for irradiation. The term 'distance between centers of the a pair of beam spots' means the distance between substantially circular center points each formed by a pair of beam spots formed from the ordinary light component and the extraordinary light component in a face that is perpendicular to the optical axis of the optical system for irradiation. The term 'optical axis of the optical system for irradiation' means the optical axis of a portion of the irradiation target substance to be the object of contrast of this optical axis.

"As described in the foregoing, uniform and symmetrical cutting of the processing target substance can be effectively and easily executed according to the laser scribe processing method of the present invention by irradiating with a laser beam to concomitantly form multiple pairs of beam spots on the processing target substance, and by controlling cracks formed with the multiple pairs of beam spots so as to extend in a direction along which the processing target substance is likely to be broken. Moreover, the laser scribe processing method of the present invention includes convenient and simple steps, and thus enables formation and control of the extension direction of cracks to be easily carried out. Therefore, improvement of operation efficiency can be achieved."

URL and more information on this patent, see: Kajikawa, Toshikazu. Laser Scribe Processing Method. U.S. Patent Number 8779327, filed June 10, 2010, and published online on July 15, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8779327.PN.&OS=PN/8779327RS=PN/8779327

Keywords for this news article include: Seishin Trading Co., Seishin Trading Co. Ltd.

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Source: Journal of Engineering


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