JP6385294B2 - Laser processing apparatus and laser processing method - Google Patents

Description

  The present invention relates to a laser processing apparatus and a laser processing method.

  Patent Document 1 below discloses a laser processing machine for punching a multilayer printed board. A beam expander, an aspherical lens, a mask, a transfer lens, a galvano scanner, and an fθ lens are arranged in this order on the beam path from the laser light source of the laser processing machine to the object to be processed. The beam expander is composed of two convex lenses and changes the beam size of the laser beam. The aspheric lens makes the beam profile uniform.

JP, 2014-183152, A

  The position of the beam waist near the output end of the laser beam output from the laser light source is imaged at the position of the aspheric lens, and the beam size is enlarged. By setting the beam size at the position of the aspheric lens to a target value, a target beam profile can be obtained. In this case, the position of the beam waist of the laser beam becomes an object point, and the position of the aspheric lens becomes an image point.

  It is desirable to change the beam profile on the processing surface depending on the processing object and application. For example, in drilling a copper foil of a printed wiring board, a preferable beam profile is not the same depending on the presence / absence of surface treatment of the copper foil and the thickness of the copper foil. A preferable beam profile is different between drilling a copper foil and drilling a resin layer. Furthermore, a preferable beam profile differs also in the drilling process which exposes the surface of the copper foil of an inner layer, and the drilling process which forms a through hole.

  In the conventional laser beam machine, the beam profile obtained by the aspheric lens can be changed by changing the beam size and the divergence angle of the laser beam at the position of the aspheric lens. By adjusting the positions of the two convex lenses of the beam expander, the beam size and divergence angle of the laser beam can be changed.

  However, when the beam size is changed, the position of the object point having a conjugate relationship with the position of the aspherical lens shifts from the position of the beam waist. For this reason, the stability of the beam profile is lowered. In addition, when a beam expander is configured with two convex lenses, it is difficult to independently change the beam size and the divergence angle. In order to increase the degree of freedom of beam profile adjustment, it is desirable to independently adjust the beam size and divergence angle.

  An object of the present invention is to provide a laser processing apparatus capable of increasing the degree of freedom of beam profile adjustment and increasing the stability of the beam profile. Another object of the present invention is to provide a laser processing method capable of increasing the degree of freedom of beam profile adjustment and increasing the stability of the beam profile.

According to one aspect of the invention,
A laser light source for outputting a laser beam;
A beam expander that changes the beam size of the laser beam output from the laser light source;
An aspheric lens that changes the beam profile of the laser beam that has passed through the beam expander;
A mask for shaping the beam cross section of the laser beam that has passed through the aspheric lens;
A laser beam that has passed through the mask, and a focus lens disposed in the path of the laser beam between the workpiece and the workpiece,
The beam expander, see contains at least three lenses are configured to be able to change the relative position in the optical axis direction, by changing the relative position of the lens, the incident position of the aspheric lens A laser processing apparatus capable of independently adjusting the divergence angle and beam size of the laser beam is provided.

According to another aspect of the invention,
Beam expander to vary the beam size, a non-spherical lens, a laser processing method for entering a mask for shaping the beam cross section, and the focus lens by way sequentially a laser beam in the object to change the beam profile,
The beam expander, see contains at least three lenses are configured to be able to change the relative position in the optical axis direction, by changing the relative position of the lens, the incident position of the aspheric lens The divergence angle and beam size of the laser beam can be adjusted independently,
Adjusting the position of the lens of the beam expander based on the target shape of the beam profile on the surface of the workpiece;
After adjusting the position of the lens, there is provided a laser processing method including a step of performing laser processing by making a laser beam incident on the processing object .

  By configuring the beam expander with at least three or more lenses, the beam size and divergence angle of the laser beam at the position of the aspherical lens can be changed independently.

FIG. 1 is a schematic diagram of a laser processing apparatus according to an embodiment. FIG. 2 is a graph showing an example of the relationship between the beam size and divergence angle of the laser beam incident on the aspheric lens and the beam profile at the mask position. 3A and 3B are partial cross-sectional views of a printed circuit board to be laser processed. 3C and 3D are partial cross-sectional views of a printed circuit board to be laser processed. 4A and 4B are partial cross-sectional views of a printed circuit board to be laser processed. FIG. 5 is a flowchart of a method for performing laser processing using the laser processing apparatus according to the embodiment.

  FIG. 1 shows a schematic diagram of a laser processing apparatus according to an embodiment. The laser light source 10 outputs a pulse laser beam. For the laser light source 10, for example, a carbon dioxide laser, an Nd: YAG laser, or the like is used. The pulse laser beam output from the laser light source 10 passes through the beam expander 11, the aspheric lens 12, the mask transmittance adjusting optical system 13, the mask 14, the collimation lens 15, the folding mirror 16, the galvano scanner 17, and the objective lens 18. Then, the light enters the processing object 40. The workpiece 40 is held on the moving stage 35.

  The beam expander 11 enlarges the beam size of the laser beam and changes the spread angle of the laser beam. For example, the beam expander 11 is configured such that the beam waist position in the vicinity of the emission surface (surface from which the laser beam is output) of the laser light source 10 and the position of the aspherical lens 12 have a conjugate relationship. . In other words, the beam waist position becomes the projection source 101 to the aspherical lens 12. The beam expander 11 includes at least three lenses 111 and a moving mechanism 112. The moving mechanism 112 can change the relative positions of the three lenses 111 in the optical axis direction. As the lens 111, for example, a plano-convex lens is used.

  The aspherical lens 12 diverges the laser beam near the optical axis and converges the laser beam near the outer periphery. As a result, the beam profile of the Gaussian beam is changed. When the laser beam incident on the aspheric lens 12 is adjusted to a standard beam size and divergence angle, the beam profile approaches a uniform profile. In FIG. 1, the cross-sectional shape of the aspherical lens 12 is drawn with more emphasis than the actual curvature.

  The mask transmittance adjusting optical system 13 changes the beam size at the position of the mask 14. The mask 14 includes a light shielding part and a transmission window (for example, an opening) provided in the light shielding part. The cross section of the laser beam is shaped by the mask 14. For example, a rotating mask provided with a plurality of transmission windows having different sizes may be used as the mask 14. The rotary mask can rotate around a rotation axis parallel to the optical axis. By changing the position of the rotary mask in the rotational direction, a transmission window of a desired size can be arranged in the laser beam path. By adjusting the mask transmittance adjusting optical system 13 to change the beam size at the position of the mask 14, it is possible to change the ratio (transmittance) of the power at which the laser beam passes through the mask 14.

  The collimation lens 15 and the objective lens 18 function as a focus lens. Specifically, the transmission window of the mask 14 is imaged on the surface of the workpiece 40 by the collimation lens 15 and the objective lens 18. An fθ lens is used as the objective lens 18. The galvano scanner 17 swings the traveling direction of the laser beam in a two-dimensional direction. By operating the galvano scanner 17, the incident position of the laser beam can be moved within the scannable range on the surface of the workpiece 40.

  The moving stage 35 moves the workpiece 40 in a two-dimensional direction parallel to the surface. By combining the movement of the incident position of the laser beam by the galvano scanner 17 and the movement of the workpiece 40 by the moving stage 35, the entire area of the workpiece 40 larger than the scanable range by the galvano scanner 17 can be processed. it can.

  The control device 36 controls the laser light source 10, the moving mechanism 112 of the beam expander 11, the galvano scanner 17, and the moving stage 35. Various parameters applied during laser processing are input from the input device 37 to the control device 36.

  FIG. 2 shows an example of the relationship between the beam size and divergence angle of the laser beam incident on the aspheric lens 12 and the beam profile at the position of the mask 14. The horizontal axis in FIG. 2 represents the beam size of the laser beam, and the vertical axis represents the spread angle of the laser beam. The divergence angle of the converging laser beam is negative, the divergence angle of the diverging laser beam is positive, and the divergence angle of the parallel light beam is 0 °.

  Under the condition that the divergence angle is constant, the beam profile shows a tendency that the light intensity at the central portion decreases and the light intensity at the peripheral portion increases as the beam size increases. Under the condition that the beam size is constant, the beam profile shows a tendency that the light intensity at the central portion decreases and the light intensity at the peripheral portion increases as the divergence angle increases.

  As an example, a top-flat beam profile is obtained in the standard state where the beam size is standard and the divergence angle is 0 ° (ie, parallel light flux). When the beam size is increased from the standard state, the beam profile has a shape with a depressed center, and when the beam size is decreased, the beam profile has a shape with a raised center. When the divergence angle is increased from the standard state, the beam profile has a shape with a depressed center, and when the divergence angle is decreased, the beam profile has a shape with a raised center.

  When both the beam size and the divergence angle are increased from the standard state, the beam profile shows a shape in which the center is greatly depressed. When both the beam size and the divergence angle are reduced from the standard state, the beam profile shows a shape in which the center is greatly raised. When the beam size is increased from the standard state and the divergence angle is decreased, the beam profile approaches a top flat shape. Even if the beam size is reduced from the standard state and the divergence angle is increased, the beam profile approaches the shape of a top flat.

  By adjusting the position of the lens 111 of the beam expander 11 (FIG. 1), the beam size and divergence angle of the laser beam incident on the aspherical lens 12 can be changed. In the embodiment, the beam expander 11 includes three or more lenses 111 and can change the relative positions of the three lenses 111. Therefore, the beam size and the divergence angle can be changed independently with the position of the projection source 101 fixed. Therefore, the incident condition to the aspherical lens 12 can be set at an arbitrary position in the two-dimensional coordinates of the beam size and the divergence angle shown in FIG.

  Since the transmission window of the mask 14 is imaged on the surface of the workpiece 40 by the collimation lens 15 and the objective lens 18, the beam profile in the transmission window of the mask 14 is projected onto the surface of the workpiece 40. .

  A command for designating a beam profile of a laser beam used for processing is input from the input device 37 (FIG. 1). Based on the input command, the control device 36 controls the moving mechanism 112 so that the beam profile at the position of the mask 14 becomes the beam profile specified by the command. At this time, the position of the lens 111 is adjusted under the condition that the position of the projection source 101 does not change. Instead of inputting a command, the position of the lens 111 may be adjusted manually.

  When the beam expander 11 is composed of two lenses, it is difficult to independently adjust the beam size and divergence angle of the laser beam. Specifically, when one of the beam size and the divergence angle is adjusted, the other is uniquely determined. Normally, the divergence angle increases as the beam size is increased. For this reason, the incident condition to the aspherical lens 12 can be changed only along one line rising to the right in the two-dimensional coordinates of the beam size and the spread angle shown in FIG.

  Furthermore, when the beam expander 11 is composed of two lenses, if the beam size and the divergence angle are adjusted, the position of the projection source 101 to the position of the aspherical lens 12 changes. That is, the projection source 101 is displaced from the position of the beam waist. For this reason, the stability of the beam profile on the surface of the workpiece 40 is lowered.

  In the embodiment shown in FIGS. 1 and 2, the incident condition to the aspherical lens 12 can be set at an arbitrary position within the two-dimensional coordinates of the beam size and the divergence angle shown in FIG. For this reason, the freedom degree of selection of a beam profile increases. Since the degree of freedom in selecting the beam profile is high, it is possible to optimize the beam profile according to various materials and structures of the workpiece and various processing applications.

  The beam size and divergence angle of the laser beam output from the laser light source 10 (FIG. 1) changes with time. By adjusting the position of the lens 111 (FIG. 1) of the beam expander 11, it is possible to compensate for changes in the beam profile due to changes in beam size and divergence angle over time. For this reason, even if the laser light source changes with time, the beam profile can be maintained in a suitable state, and high-quality processing can be performed.

  Furthermore, in the embodiment, even if the beam profile is changed, the position of the projection source 101 on the aspherical lens 12 is not changed, so that the stability of the beam profile can be maintained high.

  Next, an example of a method for drilling a printed circuit board using the laser processing apparatus according to the embodiment will be described with reference to FIGS. 3A to 3D. 3A to 3D are partial cross-sectional views of a printed circuit board that is the workpiece 40. FIG.

  As shown in FIG. 3A, the inner layer conductive pattern 42 is disposed in a partial region of the surface of the core substrate 41. A resin layer 43 is disposed on the core substrate 41 and the inner conductive pattern 42. An upper conductive film 44 is disposed on the resin layer 43. For the inner layer conductive pattern 42 and the upper layer conductive film 44, for example, copper foil is used.

  As shown in FIG. 3B, a via hole 45 is formed in the upper conductive film 44 by causing a pulse laser beam 50 to enter the workpiece 40. The pulse laser beam 50 has, for example, a top flat beam profile, and the upper conductive film 44 penetrates in one shot.

  As shown in FIG. 3C, the pulse laser beam 51 is incident on the resin layer 43 exposed on the bottom surface of the via hole 45 to drill the resin layer 43. As a result, the inner conductive pattern 42 is exposed on the bottom surface of the via hole 45. The pulse laser beam 51 has, for example, a beam profile that is raised at the center. For the processing until the inner layer conductive pattern 42 is exposed, a multi-shot pulse laser beam 51 is used. The side surface of the via hole 45 is inclined downward so that the cross section of the via hole 45 becomes smaller.

  As shown in FIG. 3D, the side surface of the via hole 45 is steeply inclined by making the pulse laser beam 52 enter the bottom surface of the via hole 45. The pulse laser beam 52 has a beam profile with a depressed center.

  With reference to FIGS. 4A and 4B, another example of a method for drilling a printed circuit board using the laser processing apparatus according to the embodiment will be described.

  As shown in FIG. 4A, conductive films 47 and 48 are disposed on the upper and lower surfaces of the resin core substrate 46, respectively. For the conductive films 47 and 48, for example, copper foil is used.

  As shown in FIG. 4B, a pulse laser beam 55 is incident on the workpiece 40 to form a through hole 49 that penetrates the workpiece 40. The pulse laser beam 55 has, for example, a top flat beam profile. In order to form the through hole 49, a multiple shot pulse laser beam 55 is used.

  As shown in FIG. 3A to FIG. 3D and FIG. 4A to FIG. 4B, high-quality drilling is performed by optimizing the beam profile according to the material to be processed, the shape of the hole to be formed, the type of processing, etc. Can be performed.

  FIG. 5 shows a flowchart of a method for performing laser processing using the laser processing apparatus shown in FIG. First, the workpiece 40 is placed on the moving stage 35 (FIG. 1).

  In step S1, the target shape of the beam profile of the pulse laser beam used for processing is determined based on the material and processing type of the processing object 40 (FIG. 1). Examples of the material include resin and copper. As an example of the processing type, processing for forming a via hole 45 that stops processing in the middle of the processing target object 40 (FIGS. 3B and 3C), processing for forming a through hole 49 penetrating the processing target object 40 (FIG. 4B), A process for shaping the shape of the side surface of the via hole 45 (FIG. 3D) and the like can be mentioned.

  In step S2, the position of the lens 111 of the beam expander 11 (FIG. 1) is adjusted based on the target shape of the beam profile. In this step, for example, a command for designating the target shape of the beam profile is input from the input device 37 (FIG. 1). The position of the lens 111 is adjusted by the control device 36 controlling the moving mechanism 112 in accordance with the input command. As another method, the operator may manually adjust the position of the lens 111.

In step S3, the control device 36 controls the galvano scanner 17 and the laser light source 10 (FIG. 1) to perform one cycle of laser processing within one scannable range. Here, the “ scannable range” means a range in which a laser beam can be incident by operating the galvano scanner 17 while the moving stage 35 is stationary. “One cycle” means a step in which a pulsed laser beam is incident on every work point (position where a hole is to be formed) within one scannable range one shot at a time.

  In step S4, it is determined whether or not the processing within the scanning processing range is completed. As an example, when the via hole 45 does not reach the inner conductive pattern 42 as shown in FIG. 3B, or when the side surface of the via hole 45 is not shaped as shown in FIG. Determined. As shown in FIG. 3D, when the side surface of the via hole 45 is shaped, it is determined that the processing is finished.

  If the machining within the scannable range has not been completed, the process returns to step S1 and the machining within the same scannable range is continued. When the processing within the scannable range is completed, it is determined in step S5 whether or not the entire processing of the processing object 40 has been completed. If the entire area has not been processed, the moving stage 35 (FIG. 1) is moved in step S6 to place the unprocessed area of the processing object 40 within the scanning processing range. Thereafter, the process returns to step S1, and processing of the scannable range is newly started. When the processing of the entire area of the processing object 40 is completed, the processing is ended and the processing object 40 is taken out from the moving stage 35.

  In the embodiment shown in FIG. 5, focusing on one processing point, the target shape of the beam profile is determined for each shot. For this reason, as shown in FIGS. 3B to 3D, the beam profile can be changed during the machining of one workpiece point. Thereby, the via hole 45 having a target shape can be formed.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

DESCRIPTION OF SYMBOLS 10 Laser light source 11 Beam expander 12 Aspherical lens 13 Mask transmittance adjustment optical system 14 Mask 15 Collimation lens 16 Folding mirror 17 Galvano scanner 18 Objective lens 35 Moving stage 36 Control device 37 Input device 40 Processing object 41 Core substrate 42 Inner layer Conductive pattern 43 Resin layer 44 Upper conductive film 45 Via hole 46 Core substrate 47, 48 Conductive film 49 Through hole 50, 51, 52, 55 Pulse laser beam 101 Projection source 111 Lens 112 Moving mechanism

Claims (3)

A laser light source for outputting a laser beam;
A beam expander that changes the beam size of the laser beam output from the laser light source;
An aspheric lens that changes the beam profile of the laser beam that has passed through the beam expander;
A mask for shaping the beam cross section of the laser beam that has passed through the aspheric lens;
A laser beam that has passed through the mask, and a focus lens disposed in a path of the laser beam between the workpiece and the workpiece,
The beam expander, see contains at least three lenses are configured to be able to change the relative position in the optical axis direction, by changing the relative position of the lens, the incident position of the aspheric lens Laser processing apparatus capable of independently adjusting the divergence angle and the beam size of the laser beam . further,
A moving mechanism for moving the lens of the beam expander;
A control device for controlling the moving mechanism;
An input device for inputting a command for designating a beam profile of a laser beam used for processing;
The laser processing apparatus according to claim 1, wherein the control device controls the moving mechanism based on the command input from the input device. Beam expander to vary the beam size, a non-spherical lens, a laser processing method for entering a mask for shaping the beam cross section, and the focus lens by way sequentially a laser beam in the object to change the beam profile,
The beam expander, see contains at least three lenses are configured to be able to change the relative position in the optical axis direction, by changing the relative position of the lens, the incident position of the aspheric lens The divergence angle and beam size of the laser beam can be adjusted independently,
Adjusting the position of the lens of the beam expander based on the target shape of the beam profile on the surface of the workpiece;
A laser processing method comprising: adjusting a position of the lens and then performing laser processing by causing a laser beam to enter the processing object .

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