JP2015186818A - Laser processing device and laser processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser processing device capable of appropriately determining the quality of a laser pulse even when a frequency fluctuates.SOLUTION: A beam scanner causes a pulse laser beam to be incident to a workpiece, and moves an incident position on the surface. A photo-detector measures a physical amount dependent on pulse energy of each laser pulse. A route switcher switches a pulse laser beam route between a first route where the pulse laser beam is incident to the workpiece and a second route where it is not incident to the workpiece. While controlling the beam scanner so that the pulse laser beam is incident to a position of a working point based on a working order, a control device measures a physical amount dependent on pulse energy, and determines an acceptable range of the physical amount based on the distribution of the physical amount. At least part of the laser pulses in which the physical amount measured by the photo-detector falls within the acceptable range is propagated along the first route, and the laser pulses that are out of the acceptable range are propagated along the second route during processing.

Description

  The present invention relates to a laser processing apparatus and a laser processing method for performing laser processing by sequentially applying a pulse laser beam to a plurality of processing points defined on the surface of a processing object.

  A technique for drilling a printed circuit board using a pulsed laser beam is disclosed in Patent Document 1 below. In the method disclosed in Patent Document 1, when a laser pulse having a pulse energy smaller than an allowable value is incident on the printed circuit board, an additional laser pulse is incident on the portion, thereby compensating for the shortage of the pulse energy. .

  In the method disclosed in Patent Document 2 below, the energy of the rising portion of the laser pulse is detected. If the detection result is within an allowable range, the subsequent portion of the laser pulse is incident on the object to be processed. If the detection result is out of the allowable range, the laser pulse is not incident on the workpiece. Thereby, it is possible to prevent a defective laser pulse having insufficient energy or excessive energy from entering the object to be processed.

Japanese Patent No. 2858236 JP 2009-148812 A

  In order to appropriately determine the allowable range of the pulse energy of the laser pulse and the allowable range of the energy of the rising portion of the laser pulse, various evaluation experiments must be performed with different pulse energies. It is also possible to determine the allowable range of pulse energy based on the variation of pulse energy when the laser light source is operating normally. With this method, the allowable range can be easily determined.

  The pulse energy depends on the pulse repetition frequency (hereinafter simply referred to as “frequency”). For this reason, if the frequency at the time of laser processing varies, the variation in pulse energy increases. When the variation of the pulse energy increases, the pulse energy may deviate from the initially determined allowable range even if the laser light source is operating normally. If it is determined whether the laser pulse is good or defective based on the initially determined allowable range, the laser pulse output during normal operation may be determined to be defective.

  An object of the present invention is to provide a laser processing apparatus and a laser processing method capable of appropriately determining whether a laser pulse is good or bad even if the frequency fluctuates.

According to one aspect of the invention,
A laser light source that outputs a pulsed laser beam;
A stage for holding the workpiece,
A beam scanner that causes the pulse laser beam output from the laser light source to enter the object to be processed and moves an incident position on the surface of the object to be processed;
A photodetector for measuring a physical quantity depending on pulse energy of each laser pulse of the pulse laser beam output from the laser light source;
A path switcher that switches a path of the pulse laser beam output from the laser light source between a first path incident on the workpiece and a second path not incident on the workpiece;
The positions of a plurality of processing points on the surface of the processing object and the processing order are stored, and the beam scanning is performed based on the positions of the processing points, the processing order, and the detection results of the photodetector. And a control device for controlling the path switch,
The controller is
The physical quantity depending on the pulse energy of each laser pulse is measured by the photodetector while controlling the beam scanner so that the pulse laser beam is incident on the position of the processing point based on the processing order. And performing a pre-processing preparation procedure for determining an allowable range of the physical quantity based on the distribution of the physical quantity,
After the pre-processing preparatory procedure, during processing of the workpiece, at least a part of the laser pulse whose physical quantity measured by the photodetector is within the allowable range is transferred to the first path. A laser processing apparatus is provided that propagates along the second path for laser pulses that are propagated along and out of the allowable range.

According to another aspect of the invention,
Measuring the physical quantity of each laser pulse depending on the pulse energy while controlling the beam scanner so that the pulsed laser beam is incident on the position of the determined processing point in the determined processing order; ,
Determining an allowable range of the physical quantity based on the distribution of the measured physical quantity;
A step of performing laser processing by causing a pulse laser beam to enter the position of the processing point on the processing target in the processing order, and
In the laser processing step, the physical quantity of each laser pulse of the pulse laser beam is measured, and when the measurement result is within the allowable range, at least a part of the laser pulse is incident on the processing object. When the measurement result is out of the allowable range, a laser processing method is provided in which the laser pulse is not incident on the object to be processed.

  Since the pulse laser beam is actually output while controlling the beam scanner and the physical quantity depending on the pulse energy is measured, the variation in the pulse energy due to the variation in the frequency of the pulse laser beam during processing determines the allowable range. Reflected. Therefore, it is possible to appropriately determine whether the laser pulse is good or bad.

FIG. 1 is a schematic diagram of a laser processing apparatus according to an embodiment. FIG. 2 shows a trigger signal trg, a laser pulse Lp1 incident from a path switch, a laser pulse Lp2 propagating through a machining path, a laser pulse Lp3 propagating through a damper path, a control signal con for controlling the path switch, and light detection It is a graph which shows an example of the timing chart and waveform of detection signal det transmitted to a control device from a device. FIG. 3A is a timing chart when a laser pulse is output from the laser light source at a constant frequency, and FIG. 3B is a histogram of determination energy when the laser pulse is output at a constant frequency. FIG. 4A is a schematic plan view of an object to be processed, FIG. 4B is a timing chart of laser pulses during processing, and FIG. 4C is a histogram of determination energy of laser pulses during processing. FIG. 5 is a flowchart of the laser processing method according to the embodiment. 6A is a timing chart of the laser pulse output from the laser light source in step S1, and FIG. 6B is a histogram of determination energy of the laser pulse output at the timing shown in FIG. 6A. FIG. 7 is a chart showing the correspondence between the processing point arrangement pattern and the allowable range.

  FIG. 1 shows a schematic diagram of a laser processing apparatus according to an embodiment. The laser processing apparatus according to the embodiment is, for example, a laser drill for drilling a printed board. When the laser light source 10 receives the trigger signal trg from the control device 50, the laser light source 10 outputs a pulse laser beam. For example, a carbon dioxide laser is used for the laser light source 10.

  The pulse laser beam output from the laser light source 10 enters the irradiation optical system 11. The irradiation optical system 11 changes at least one of the divergence angle and the beam diameter of the pulse laser beam. The pulse laser beam that has passed through the irradiation optical system 11 enters the aperture 13. The irradiation optical system 11 also has a function of uniformizing the beam profile at the position of the aperture 13. The aperture 13 shapes the beam cross section.

  The pulsed laser beam that has passed through the aperture 13 enters the path switch 15. The path switch 15 receives the control signal con from the control device 50 and switches the path of the pulse laser beam between the processing path 16 and the damper path 17. For the path switch 15, for example, an acousto-optic element (AOD) is used. A path along which the input laser pulse Lp1 goes straight corresponds to the damper path 17, and a path where the laser pulse is diffracted corresponds to the machining path 16.

  The laser pulse Lp2 propagating along the processing path 16 is deflected by the folding mirror 18 and enters the beam scanner 20. The beam scanner 20 is controlled by the control device 50 to swing the traveling direction of the pulse laser beam in a two-dimensional direction. For the beam scanner 20, for example, a pair of galvano scanners is used.

  The pulsed laser beam that has passed through the beam scanner 20 passes through the objective lens 21 and enters the workpiece 40. For the objective lens 21, for example, an fθ lens is used. The workpiece 40 is, for example, a printed board to be drilled. The workpiece 40 is held on the stage 23. The stage 23 is moved in a two-dimensional direction parallel to the surface of the workpiece 40 by the moving mechanism 24. The moving mechanism 24 is controlled by the control device 50.

  By the objective lens 21, the opening of the aperture 13 is reduced and projected onto the surface of the workpiece 40. By changing the traveling direction of the pulse laser beam by the beam scanner 20, the incident position of the pulse laser beam can be moved on the surface of the workpiece 40.

  The laser pulse Lp3 propagating along the damper path 17 enters the partial reflection mirror 30. The laser pulse transmitted through the partial reflection mirror 30 enters the beam damper 31. The laser pulse reflected by the partial reflection mirror 30 enters the photodetector 32. For the photodetector 32, for example, an energy meter having sensitivity in the wavelength region of the pulse laser beam output from the laser light source 10 is used. A detection signal det from the photodetector 32 is input to the control device 50.

  The control device 50 includes a storage device 51. The storage device 51 stores position information of a plurality of processing points of the processing object 40, processing order, and various information necessary for control.

  In FIG. 2, a trigger signal trg, a laser pulse Lp1 incident on the path switch 15, a laser pulse Lp2 propagating through the machining path 16, a laser pulse Lp3 propagating through the damper path 17, a control signal con that controls the path switch 15, 4 shows an example of a timing chart and a waveform of a detection signal det transmitted from the photodetector 32 to the control device 50.

  When the trigger signal trg rises at time t1, the laser pulse Lp1 rises at time t2 with a slight delay. At this time, the output path of the path switch 15 is switched to the damper path 17. For this reason, the laser pulse Lp3 propagating through the damper path 17 rises.

  The photodetector 32 detects the laser pulse Lp3 and transmits a detection signal det to the control device 50. The magnitude of the detection signal det is substantially proportional to the power of the laser pulse Lp3. The control device 50 integrates the detection signal det until a time t3 when a certain time has elapsed from the rising time t2. The integration result is stored in the storage device 51.

  At time t <b> 4, the control device 50 transmits a control signal con for switching to the machining path 16 to the path switch 15. When the output path of the path switch 15 is switched from the damper path 17 to the machining path 16, the laser pulse Lp3 falls and the laser pulse Lp2 rises. As the laser pulse Lp3 falls, the detection signal det of the photodetector 32 also becomes zero.

  At time t <b> 5, the control device 50 transmits a control signal con that switches to the damper path 17 to the path switch 15. When the output path of the path switcher 15 is switched from the machining path 16 to the damper path 17, the laser pulse Lp3 rises and the laser pulse Lp2 falls. As the laser pulse Lp3 rises, the detection signal det of the photodetector 32 also rises.

  At time t6, the trigger signal trg falls. As a result, the laser pulse Lp1 and the laser pulse Lp3 fall. As the laser pulse Lp3 falls, the detection signal det of the photodetector 32 also falls.

  The value obtained by integrating the detection signal det of the photodetector 32 from time t2 to time t3 (the area of the hatched portion in FIG. 2) corresponds to the energy of the rising portion of the laser pulse Lp1. If the pulse width of the laser pulse Lp2 cut out for processing from the laser pulse Lp1 is constant, the pulse energy of the laser pulse Lp2 and the energy of the rising portion of the laser pulse Lp1 have a correlation. For this reason, the normality of the pulse energy of the laser pulse Lp2 can be determined from the energy of the rising portion of the laser pulse Lp1. The energy at the rising portion of the laser pulse Lp1 is referred to as “determination energy”. The determination energy is a physical quantity that depends on the pulse energy.

  The time from time t2 to time t3 is determined based on the average rise time of the laser pulse Lp1. As the time from time t2 to time t3, an average time until the power of the laser pulse Lp1 reaches the steady state may be adopted, or until the power of the laser pulse Lp2 reaches 90% of the power in the steady state. Average time may be employed.

As a physical quantity that depends on the pulse energy, the power of the rising portion of the laser pulse Lp1 may be employed instead of the energy of the rising portion. If the power of only one point on the time axis in the rising portion is adopted as a physical quantity depending on the pulse energy, the reliability of the pulse energy estimated from the power is lowered. By adopting the power at a plurality of locations on the time axis in the rising portion as a physical quantity depending on the pulse energy, the reliability of the pulse energy estimated from the power can be improved.

  FIG. 3A shows a timing chart when the laser pulse Lp1 is output from the laser light source 10 at a constant frequency.

  FIG. 3B shows a histogram of determination energy when the laser pulse Lp1 is output at a constant frequency. The horizontal axis represents determination energy, and the vertical axis represents frequency. When the laser light source 10 is operating normally, the distribution of determination energy substantially follows a normal distribution. When the average value of determination energy is represented by m and the standard deviation is represented by σ, the determination energy of most laser pulses Lp1 falls within the range of m ± 3σ (hereinafter referred to as normal range D0).

  FIG. 4A shows a schematic plan view of the workpiece 40. A plurality of workpiece points 41 are defined on the surface of the workpiece 40. Drilling is performed by making the laser pulse Lp2 (FIG. 1) incident on the workpiece point 41. The processing order of the workpiece point 41 is determined in advance. In FIG. 4A, an example of the processing order is indicated by arrows. As shown in FIG. 4A, the distance from the processed point 41 to be processed to the next point 41 to be processed is not constant but varies. When the moving distance of the incident position of the pulse laser beam becomes longer, the settling time of the beam scanner 20 becomes longer. For this reason, during the processing of the workpiece 40, the frequency of the pulse laser beam is not constant, but varies according to the moving distance of the incident position of the pulse laser beam.

  FIG. 4B shows an example of a timing chart of the pulse laser beam output from the laser light source 10 during the processing period. As shown in FIG. 4B, the frequency of the pulsed laser beam varies.

  FIG. 4C shows a histogram of determination energy when the frequency of the pulse laser beam varies. For comparison, a histogram of determination energy when the frequency of the pulse laser beam is constant is indicated by a broken line. In general, the pulse energy of the pulse laser beam output from the laser light source 10 depends on the frequency. For example, in a carbon dioxide laser, the pulse energy tends to decrease as the frequency increases.

  The variation in determination energy due to the variation in frequency is superimposed on the variation in determination energy when the frequency is constant in the variation in determination energy when the frequency varies. For this reason, when the frequency varies, the variation in determination energy increases. If the frequency is not constant, the determination energy may deviate from the normal range D0 even when the laser light source 10 is operating normally.

  When control is performed using only a laser pulse whose determination energy is included in the normal range D0 for laser processing, a laser pulse having determination energy deviating from the normal range D0 despite the laser light source 10 operating normally. It will not be used for processing. For this reason, the utilization efficiency of laser energy will fall. In the embodiment described below, it is possible to suppress a decrease in utilization efficiency of laser energy due to variation in determination energy under the condition where the laser light source 10 is operating normally.

  FIG. 5 shows a flowchart of a laser processing method according to the embodiment. In step S1, a pulsed laser beam is output from the laser light source 10 by controlling the laser light source 10 and the beam scanner 20 based on the position of the processing point 41 (FIG. 4A) of the processing object 40 and the processing order. To do. At this time, the path switch 15 keeps the output path switched to the damper path 17. For this reason, the pulse laser beam does not enter the stage 23. However, since the beam scanner 20 is controlled, the frequency of the pulse laser beam reflects variations in the settling time of the beam scanner 20.

  FIG. 6A shows a timing chart of the laser pulse Lp1 output from the laser light source 10 in step S1. The frequency of the pulse laser beam in step S1 varies as with the frequency of the pulse laser beam during the processing period shown in FIG. 4B. Since the beam scanner 20 is controlled based on the actual position of the processing point 41 and the processing sequence, the degree of variation in the frequency of the pulse laser beam in step S1 is the frequency of the pulse laser beam during processing. The degree of variation is the same.

  The measurement result of the photodetector 32 is input to the control device 50. The control device 50 obtains the determination energy of each laser pulse Lp1 and stores the obtained determination energy in the storage device 51.

  In step S2, an allowable range R1 of determination energy is determined based on the distribution of determination energy.

  With reference to FIG. 6B, a method for determining the allowable range R1 of the determination energy will be described. FIG. 6B shows a histogram of determination energy. For comparison, the distribution of determination energy when the frequency of the pulse laser beam is constant is indicated by a broken line. The average value of the distribution of determination energy obtained in step S1 is represented by m1, and the standard deviation is represented by σ1. As an example, the upper limit value of the allowable range R1 is m1 + 3σ1, and the lower limit value is m1-3σ1. The allowable range R1 when the frequency varies is wider than the normal range R0 when the frequency is constant, according to the spread of the variation in determination energy.

  In step S3 (FIG. 5), the workpiece 40 is placed on the stage 23 (FIG. 1). In step S4, the beam scanner 20 is operated to wait until the pulse laser beam beam scanner 20 is set. When the beam scanner 20 is settled, one laser pulse Lp1 is output from the laser light source 10 in step S5. At the output start time of the laser pulse Lp1, the output path of the path switch 15 is switched to the damper path 17. Therefore, the light intensity detection signal det from the light detector 32 is input to the control device 50. The control device 50 calculates determination energy based on the detection signal det input from the photodetector 32.

  In step S6, it is determined whether or not the determination energy is within the allowable range R1. If the determination energy is out of the allowable range R1, after the fall of the laser pulse Lp1, the process returns to step S5 to output the next laser pulse Lp1. If the determination energy is within the allowable range R1, the laser pulse Lp2 (FIG. 2) is cut out from the laser pulse Lp1 and propagated along the machining path 16 by controlling the path switch 15 in step S7. . The laser pulse Lp2 is incident on the workpiece 40 and drilling is performed.

  In step S8, it is determined whether or not the processing of all the processing points 41 has been completed. When the unmachined workpiece point 41 remains, the process returns to step S4 and the next workpiece point 41 is machined. When processing is performed by making a plurality of laser pulses incident on one processing point 41, cycle mode processing or burst mode processing is applied.

  In cycle mode machining, each time one laser pulse is incident on one workpiece point 41, the incident position is moved to the next workpiece point 41. The procedure of making one shot of laser pulses incident on all the machining points 41 is one cycle, and by repeating this cycle a plurality of times, a desired number of shots of laser pulses can be incident on the machining points 41. it can. When performing cycle mode machining, it is determined in step S8 that machining has been completed when the cycle has been repeated a desired number of times.

  In burst mode machining, a laser beam having a desired number of shots is continuously incident on one workpiece point 41, and then the workpiece point 41 to be machined next is machined. When performing the burst mode processing, when the previous laser pulse and the next laser pulse are incident on the same processing point 41, it is not necessary to operate the beam scanner 20 in step S4.

  When the processing of all the processing points 41 is completed, it is determined in step S9 whether or not an unprocessed processing object 40 having the same arrangement pattern of the processing points 41 remains. When the unprocessed workpiece 40 remains, the process returns to step S3, and the workpiece 40 to be processed next is placed on the stage 23. If there is no unprocessed workpiece 40 left, the processing procedure ends.

  When processing the processing target 40 having an arrangement pattern different from the arrangement pattern of the processing points 41 of the processing target 40 processed immediately before, the pre-processing preparation procedure in steps S1 to S2 is executed, and the allowable range is reached. R1 is newly determined.

  In the above embodiment, even if the laser pulse Lp1 has the determination energy deviating from the normal range R0 shown in FIG. 6B, the laser pulse whose determination energy is within the allowable range R1 is used for processing. For this reason, the fall of the utilization efficiency of a laser energy can be suppressed. When the operation of the laser light source 10 becomes unstable and the determination energy deviates from the allowable range R1, the laser pulse Lp1 is not used for processing. For this reason, it is possible to prevent a deterioration in processing quality due to the incidence of the laser pulse Lp2 having insufficient or excessive pulse energy.

  In the said Example, before starting the process of the some workpiece 40 with the same arrangement pattern of the to-be-processed point 41, the pre-process procedure of step S1-step S2 (FIG. 5) is implemented, and tolerance | permissible_range R1 It was determined. A correspondence relationship in which the determined allowable range R1 and the arrangement pattern of the workpiece points 41 are associated may be stored in the storage device 51.

  FIG. 7 shows an example of this correspondence. For each arrangement pattern of the points to be processed 41, a lower limit value and an upper limit value of the allowable range R1 are stored. When the arrangement pattern of the workpiece points 41 of the workpiece 40 to be processed next is stored in the correspondence table of FIG. 7, Steps S1 to S2 (FIG. 2) can be omitted. In step S <b> 6, it may be determined whether the determination energy is within the allowable range R <b> 1 stored in the storage device 51.

  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 Irradiation optical system 13 Aperture 15 Path | route switch 16 Processing path | route 17 Damper path | route 18 Folding mirror 20 Beam scanner 21 Objective lens 23 Stage 24 Moving mechanism 30 Partial reflection mirror 31 Beam damper 32 Photo detector 40 Processing object 41 Covered object Processing point 50 Control device 51 Storage devices Lp1, Lp2, Lp3 Laser pulse con Control signal det Detection signal trg Trigger signal R0 Normal range R1 Allowable range

Claims (7)

A laser light source that outputs a pulsed laser beam;
A stage for holding the workpiece,
A beam scanner that causes the pulse laser beam output from the laser light source to enter the object to be processed and moves an incident position on the surface of the object to be processed;
A photodetector for measuring a physical quantity depending on pulse energy of each laser pulse of the pulse laser beam output from the laser light source;
A path switcher that switches a path of the pulse laser beam output from the laser light source between a first path incident on the workpiece and a second path not incident on the workpiece;
The positions of a plurality of processing points on the surface of the processing object and the processing order are stored, and the beam scanning is performed based on the positions of the processing points, the processing order, and the detection results of the photodetector. And a control device for controlling the path switch,
The controller is
The physical quantity depending on the pulse energy of each laser pulse is measured by the photodetector while controlling the beam scanner so that the pulse laser beam is incident on the position of the processing point based on the processing order. And performing a pre-processing preparation procedure for determining an allowable range of the physical quantity based on the distribution of the physical quantity,
After the pre-processing preparatory procedure, during processing of the workpiece, at least a part of the laser pulse whose physical quantity measured by the photodetector is within the allowable range is transferred to the first path. A laser processing apparatus that propagates along the second path, laser pulses that are propagated along and out of the allowable range.   The laser processing apparatus according to claim 1, wherein the control device determines an upper limit value and a lower limit value of the allowable range based on a standard deviation of the physical quantity.   When the arrangement pattern of the workpiece points of the workpiece to be processed next is different from the arrangement pattern of the workpiece points of the workpiece to be processed immediately before, the control device processes the workpiece to be processed next. 3. The laser processing apparatus according to claim 1, wherein the permissible range is newly determined by executing the pre-processing preparation procedure before performing the process.   The laser processing apparatus according to claim 1, wherein the physical quantity is energy at a rising portion of the laser pulse. Measuring the physical quantity of each laser pulse depending on the pulse energy while controlling the beam scanner so that the pulsed laser beam is incident on the position of the determined processing point in the determined processing order; ,
Determining an allowable range of the physical quantity based on the distribution of the measured physical quantity;
A step of performing laser processing by causing a pulse laser beam to enter the position of the processing point on the processing target in the processing order, and
In the laser processing step, the physical quantity of each laser pulse of the pulse laser beam is measured, and when the measurement result is within the allowable range, at least a part of the laser pulse is incident on the processing object. And a laser processing method in which the laser pulse is not incident on the object to be processed when the measurement result is out of the allowable range.   The laser processing method according to claim 5, wherein an upper limit value and a lower limit value of the allowable range are determined based on a standard deviation of the physical quantity.   The laser processing method according to claim 5, wherein the physical quantity is energy at a rising portion of the laser pulse.

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