JP3673255B2 - Laser processing method and laser processing apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laser processing apparatus and a laser processing method in which a laser beam is incident on a workpiece by controlling the size of a cross section.
[0002]
[Prior art]
FIG. 5 is a schematic view showing a conventional laser processing apparatus. A pulse laser beam is emitted from a laser light source 30, for example, an Nd: YAG laser. The emitted pulsed laser beam is incident on the homogenizer 31. The homogenizer 31 emits the shaped laser beam after shaping the intensity distribution so that the incident laser beam becomes top flat at the position of the mask 32 having a circular through hole, for example. The cross section of the laser beam is shaped into a circle by the mask 32. The laser beam emitted from the mask 32 passes through the imaging lens 33 and enters the workpiece 34 placed on the stage 35. The processing object 34 is, for example, a printed board. The imaging lens 33 images the circular through-hole of the mask 32 on the workpiece 34. A circular hole is opened in the workpiece 34 at the position where the laser beam is incident.
[0003]
6A to 6C are schematic graphs showing the intensity distribution in the cross section of the laser beam. FIG. 6A shows the intensity distribution in the cross section of the laser beam before being emitted from the laser light source 30 and entering the homogenizer 31. A Gaussian distribution is shown in which the intensity is strong at the center of the beam cross section, and the intensity decreases toward the periphery. FIG. 6B shows the intensity distribution at the position of the mask 32 of the laser beam emitted from the homogenizer 31. The intensity distribution in the laser beam cross section is substantially uniform. FIG. 6C shows the intensity distribution in the beam cross section of the laser beam whose cross-sectional shape is shaped into a circle by the mask 32. By passing through the circular through hole of the mask 32, the peripheral portion of the laser beam having the top flat pulse energy distribution shown in FIG. 6B is cut. Therefore, the pulse energy of the laser beam emitted from the mask 32 is smaller than that before entering the mask 32. (For example, see Patent Document 1.)
Further, the diameter of the hole to be drilled in the workpiece 34 is controlled by shaping the cross-sectional shape of the beam with a mask having through holes of different sizes.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 2002-23099
[Problems to be solved by the invention]
In conventional laser processing, a large energy loss has occurred in the mask when the beam cross-section is shaped into a required shape.
[0006]
An object of the present invention is to provide a laser processing apparatus and a laser processing method with high energy utilization efficiency.
[0007]
[Means for Solving the Problems]
According to one aspect of the present invention, a laser light source that emits a laser beam and a laser beam emitted from the laser light source are incident, and the intensity distribution in the beam spot of the laser beam on a virtual homogenized surface is uniform. And a variable magnification transfer optical system that can form an image of the beam spot on the homogenized surface on the surface of the workpiece and change the imaging magnification, and the beam homogenizer includes the laser A laser beam emitted from a light source is incident, and a first aspherical lens having a focal length that increases as it advances from the incident position of the center of the laser beam to the periphery, and a laser beam transmitted through the first aspherical lens. A second aspherical lens having a focal length that decreases as it enters and advances from the incident position at the center of the laser beam to the periphery. A laser processing apparatus in which the intensity distribution in the beam spot of the laser beam transmitted through the second aspherical lens is uniformly closer than the intensity distribution of the laser beam emitted from the laser light source. Is provided.
[0008]
When laser processing is performed using this laser processing apparatus, energy loss when controlling the shape and size of the cross section of the laser beam can be reduced, so that laser processing can be performed with high energy utilization efficiency.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic diagram of a laser processing apparatus used in a laser processing method according to an embodiment of the present invention. A laser beam is emitted from a laser light source 1, for example, an Nd: YAG laser. The cross-sectional shape of the emitted pulse laser beam is, for example, a circle. The intensity distribution in the beam cross section shows a Gaussian distribution as shown in FIG.
[0012]
The laser beam is incident on a flat top optics (FTO) 2. The flat top optics 2 includes an aspheric lens optical system. When a laser beam having a circular cross-sectional shape and a Gaussian intensity distribution in the cross-section is incident, the laser beam is converted into a laser beam having a circular cross-sectional shape and a top-flat intensity distribution. The shaping of the cross-sectional shape and the conversion of the intensity distribution are simultaneously performed by passing a laser beam through the aspherical lens. The flat top optics 2 will be described in detail later.
[0013]
The laser beam emitted from the flat top optics 2 passes through the variable magnification transfer optical system 3 and enters a workpiece 4 placed on the stage 5. The workpiece 4 is, for example, a printed board. The variable magnification transfer optical system 3 transfers the cross-sectional shape of the laser beam at a predetermined position onto the workpiece 4. A hole in the shape of the transferred image is opened at the position on the workpiece 4 where the laser beam is incident. The variable magnification transfer optical system 3 can change (switch) the transfer magnification. By changing the transfer magnification, the cross-sectional size of the laser beam incident on the workpiece 4 can be controlled. Thereby, the size of the hole to be formed can be changed. Unlike the case where the cross-sectional size of the laser beam is controlled by the size of the through hole of the mask, when the variable magnification transfer optical system 3 is used, there is no energy loss due to the control of the beam size. This is because vignetting does not occur in the laser beam incident on the workpiece 4 because no mask is used.
[0014]
FIG. 2 is a diagram for explaining the function of the flat-top optics 2. The flat top optics 2 includes two aspheric lenses 11 and 12. The focal length of the aspherical lens 11 is longer toward the periphery of the lens. The focal length of the aspherical lens 12 is shorter toward the periphery of the lens. For example, the aspherical lens 11 is formed of a concave lens at the center and a convex lens at the periphery. The focal length of the concave lens is negative. Therefore, the focal length of the aspheric lens includes a negative value. For example, that the focal length is longer in the peripheral portion of the aspheric lens 11 means that the numerical value including the sign indicating the focal length is larger in the peripheral portion.
[0015]
The laser beam 10 enters the aspheric lens 11. The intensity of the laser beam 10 in the cross section has a Gaussian distribution as shown in FIG. 6A, with the intensity being strong at the center of the cross section and decreasing as it goes to the periphery. When transmitted through the aspherical lens 11, the central portion 13 of the strong laser beam 10 becomes a divergent light beam and enters the aspherical lens 12. A peripheral portion 14 of the laser beam 10 having a low intensity becomes a condensed light beam and enters the aspherical lens 12. The laser beam emitted from the aspheric lens 12 is parallel to the laser beam 10 immediately before entering the aspheric lens 11. The two aspherical lenses 11 and 12 make the intensity in the cross section of the laser beam 10 close to uniform, and the laser beam 15 is emitted. At the homogenized surface 16, the uniformity of intensity in the cross section of the laser beam 15 is the highest.
[0016]
FIG. 3A is a schematic graph showing the intensity distribution of the laser beam 15 on the homogenized surface 16. The laser beam 15 incident on the flat top optics 2 is converted so that the intensity distribution on the homogenized surface 16 is substantially uniform.
[0017]
FIG. 3B is a schematic view of the cross-sectional shape of the laser beam 15 on the homogenized surface 16 as viewed from the optical axis direction of the laser beam. The beam has a circular cross-sectional shape. The circular beam spot on the homogenizing surface 16 is imaged on the workpiece 4 at a desired imaging magnification by the variable magnification transfer optical system 3. For example, a hole corresponding to the size and shape of the formed image is formed on the workpiece 4.
[0018]
Next, the workpiece 4 is moved by the stage 5. The variable magnification transfer optical system 3 changes the imaging magnification while maintaining a conjugate relationship between the homogenized surface 16 and the surface of the processing object 4, and causes the beam spot on the homogenized surface 16 to be reflected on the surface of the processing object 4. To form an image. At the imaging position, there is a hole corresponding to the size and shape of the image formed. Thereby, holes of different sizes can be formed at different positions on the workpiece 4. While the workpiece 4 is being moved, the laser oscillation is stopped or the laser beam is shielded so that the laser beam does not enter the workpiece 4.
[0019]
FIG. 4 is a schematic view of a laser processing apparatus in which a galvano scanner 20 is added to the laser processing apparatus shown in FIG. Other constituent elements are all the same as those of the laser processing apparatus of FIG. The galvano scanner 20 can scan the laser beam to open holes of different sizes at different positions on the workpiece 4.
[0020]
By design, flat-top optics can obtain laser beams with various cross-sectional shapes having a top-flat intensity distribution in the cross-section. Further, when flat top optics are used, the beam shape can be shaped with almost no energy loss.
[0021]
When controlling the shape and size of the laser beam, energy loss can be almost eliminated, so that laser processing can be performed with high energy utilization efficiency.
[0022]
Conventionally, the size of the through-hole of the mask is changed to change the cross-sectional size of the beam, and the laser beam is incident on the object to be processed at a constant imaging magnification to perform the processing. In the laser processing method according to the embodiment, a cross section having a constant size on a uniform surface is imaged on a processing object by changing the imaging magnification with a variable magnification transfer optical system and processed.
[0023]
As mentioned above, although this invention was demonstrated along the Example, this invention is not limited to these. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.
[0024]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a laser processing method and a laser processing apparatus with high energy utilization efficiency.
[Brief description of the drawings]
FIG. 1 is a schematic view of a laser processing apparatus used in a laser processing method according to an embodiment.
FIG. 2 is a diagram for explaining functions of flat-top optics.
3A is a schematic graph showing a distribution of pulse energy density per pulse in a cross section of a laser beam emitted from a flat top optics, and FIG. 3B emits the flat top optics. It is the schematic which looked at the cross-sectional shape of the obtained pulse laser beam from the optical axis direction of the laser beam.
FIG. 4 is a schematic view of a laser processing apparatus used in a laser processing method according to an embodiment.
FIG. 5 is a schematic view showing a conventional laser processing apparatus.
6A, 6B, and 6C are schematic graphs showing a distribution of pulse energy density in a cross section of a one-shot pulse laser beam.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Laser light source 2 Flat top optics 3 Variable magnification transfer optical system 4 Work object 5 Stage 10 Laser beam 11 Aspherical lens 12 Aspherical lens 13 Central part 14 Peripheral part 15 Laser beam 16 Homogenizing surface 20 Galvano scanner 30 Laser light source 31 Homogenizer 32 Mask 33 Imaging lens 34 Object 35 Stage

Claims (4)

A laser light source for emitting a laser beam;
A beam homogenizer that makes the laser beam emitted from the laser light source incident, and makes the intensity distribution in the beam spot of the laser beam uniformly on the virtual homogenization surface;
A variable magnification transfer optical system capable of forming an image of the beam spot on the homogenized surface on the surface of the workpiece and changing the imaging magnification;
The beam homogenizer is
A first aspherical lens having a focal length that increases as the laser beam emitted from the laser light source enters and proceeds from the incident position of the center of the laser beam to the periphery;
A laser beam that has passed through the first aspherical lens is incident, and a second aspherical lens that has a focal length that decreases as it advances from the incident position at the center of the laser beam to the periphery, A laser processing apparatus in which an intensity distribution of a laser beam transmitted through an aspheric lens in a beam spot on the homogenized surface is closer to the intensity distribution of a laser beam emitted from the laser light source.   2. The laser processing apparatus according to claim 1, wherein the uniformity of the intensity distribution in the beam cross section of the laser beam that has passed through the beam homogenizer is the highest on the homogenized surface.   3. The laser processing apparatus according to claim 1, wherein the homogenized surface and the surface of the workpiece are in a conjugate relationship even when the magnification of the variable magnification transfer optical system is changed.   The laser processing apparatus according to any one of claims 1 to 3, wherein no vignetting occurs before the laser beam emitted from the laser light source reaches the object to be processed.

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