JP2007111749A - Laser beam machining device and laser beam machining method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce time for machining the objects to be machined, and to prevent deterioration in the side face shape of the hole to be formed. <P>SOLUTION: A pulse laser beam is emitted from a laser light source 1 is made incident on a pulse chopping means 2. The pulse chopping means 2 chops a plurality of laser pulses separated on a time-base from one original laser pulse of the incident pulse laser beams. A controller 12 memorizes the positions of a plurality of the points to be machined on the objects 10a, 10b to be machined, and controls the laser light source 1, the pulse chopping means 2 and moving mechanisms 11a, 11b in such a manner that the plurality of laser pulses chopped from the first original laser pulse are made incident on the first point to be machined, a plurality of laser pulses chopped from a second original laser pulse emitted after the first original laser pulse are made incident on at least one other point to be machined, and thereafter, a laser pulse chopped from a third original laser pulse emitted after the second original laser pulse is made incident on the first point to be machined. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a laser processing apparatus and a laser processing method, and more particularly to a laser processing apparatus and a laser processing method mainly for drilling.

  Laser processing is the mainstream for via-hole processing of build-up substrates. Mobile phones, etc., which are the final product, are becoming highly functional and lightweight, and the number of via holes tends to increase accordingly. Since laser drilling time is proportional to the number of via holes to be formed, shortening of the laser processing time is required.

  As a method for performing laser drilling, two types of methods are known: multi-shot continuous irradiation processing, commonly known as burst processing, single-shot repeated irradiation processing, and so-called cycle processing.

  Burst processing is a method of forming via holes by continuously irradiating a plurality of shots at a predetermined laser frequency after positioning of the galvano scanner is completed. As a substrate to be processed, there is a conformal substrate or the like in which a copper foil at a portion where a via hole is formed is removed by etching or the like, and a resin layer under the copper foil is exposed.

  In Patent Document 1 below, laser processing is performed in which one of pulse laser beams traveling in two optical paths is divided into a plurality of laser pulses on a time axis by a pulse chopper, and a resin layer is burst processed by the plurality of divided laser pulses. A method and laser processing apparatus are provided.

  The cycle machining will be described. After the positioning of the galvano scanner is completed, a process of irradiating a laser pulse to the processing point for only one shot and then irradiating the other processing point on the workpiece with the laser pulse for each shot is defined as one cycle. After the irradiation of the processing point that needs to be processed is completed, as the second cycle, the galvano scanner is positioned so that the first processing point is irradiated with the laser pulse again, and after one shot of the laser pulse is irradiated, A laser pulse is also irradiated to other workpiece points on the workpiece one shot at a time. This cycle is repeated until all the machining points have been processed.

JP 2004-98121 A

  When the substrate is processed using the burst processing method, particularly when the above-described conformal substrate is processed, the shape of the via hole to be formed becomes a barrel shape. This is due to the fact that a plurality of laser pulses are continuously irradiated to the same processing point, heat is accumulated around the processing portion, and the side surface of the hole is excessively removed.

  Further, in the cycle processing, the shot interval of the laser pulse per hole becomes long, so that the side surface shape of the hole can be prevented from being deteriorated due to heat accumulation during processing, such as burst processing. However, since it takes time to position the galvano scanner, the processing time is generally longer than the burst processing.

  The objective of this invention is providing the laser processing apparatus and laser processing method which can shorten the time which processes a process target object, and can prevent deterioration of the side shape of the hole formed.

  According to one aspect of the present invention, a laser light source that emits a pulse laser beam and a pulse laser beam emitted from the laser light source are incident and separated from one original laser pulse of the incident pulse laser beam on a time axis. A pulse cutting means for cutting out the plurality of laser pulses, a stage for holding the workpiece at a position where the pulse laser beam that has passed through the pulse cutting means is incident, and a workpiece to be held on the stage. A moving mechanism that moves one of the path of the pulse laser beam and the workpiece relative to the other so that the incident position of the pulse laser beam moves, and the positions of a plurality of workpiece points on the workpiece are stored. A plurality of laser pulses cut out from the first original laser pulse are incident on the first workpiece point, and the first workpiece point is incident on at least one other workpiece point. After a plurality of laser pulses cut out from the second original laser pulse emitted after the laser pulse are incident, the third laser beam emitted after the second original laser pulse is further applied to the first workpiece point. There is provided a laser processing apparatus having the laser light source, the pulse cutting means, and a control device for controlling the moving mechanism so that a laser pulse cut out from the original laser pulse enters.

  According to another aspect of the present invention, a plurality of laser pulses cut out from a first original laser pulse emitted from a laser light source so as to be separated on a time axis are converted into a first workpiece on a workpiece. A plurality of laser pulses cut out from the second original laser pulse emitted from the laser light source after the first original laser pulse, and a second workpiece point of the object to be processed. And after the second original laser pulse, one laser pulse cut out from the third original laser pulse emitted from the laser light source is incident on the first processing point. There is provided a laser processing method having a process.

  As the first cycle, after a plurality of laser pulses cut out from the first original laser pulse are incident on the first workpiece point on the workpiece, the first original laser is applied to each of the other workpiece points. A plurality of laser pulses cut out from the original laser pulse after the pulse are incident, and holes are formed respectively. After the first cycle, as a second cycle, only one laser pulse is incident again on the first processing point, and laser pulses are incident on the other processing points one shot at a time to complete the hole processing. Since the interval between the plurality of laser pulses irradiated to each workpiece point in the first cycle is shorter than the conventional one, machining in a short time is possible.

  Further, another laser beam is processed between the time when the laser pulse cut out from the first original laser pulse enters the first workpiece point and the time when the laser pulse cut out from the third original laser pulse enters. The time necessary for the laser pulse cut out from the second original laser pulse to enter the point elapses. Therefore, since the side surface of the hole formed in the 1st to-be-processed point is cooled in the meantime, deterioration of the side surface shape by heat storage can be prevented.

FIG. 1 shows a schematic diagram of a laser processing apparatus according to an embodiment of the present application. The laser light source 1 emits a pulse laser beam. As the laser light source 1, for example, a CO ₂ laser is used.

  The pulsed laser beam emitted from the laser light source 1 enters the pulse extractor 2. The pulse extractor 2 cuts out a plurality of laser pulses separated on the time axis from one original laser pulse of the incident pulse laser beam and emits them to the optical path A. The remaining component that has not exited the optical path A is absorbed by the beam damper 3. For the pulse extractor 2, for example, an acousto-optic device (AOM) is used. As another pulse extractor, a combination of an electro-optical element (Electro-Optic Modulator, EOM) and a polarizing beam splitter may be used.

  The pulse laser beam extracted by the pulse extractor 2 is shaped into, for example, a circular shape by a mask 4 having a through hole, then reflected by a folding mirror 5 and incident on a branching optical system 6. The branching optical system 6 branches the incident pulse laser beam into a pulse laser beam traveling on the first optical path B and a pulse laser beam traveling on the second optical path C.

  The pulsed laser beam traveling in the first optical path B is incident on the galvano scanner 8a. The galvano scanner 8a includes a pair of swingable reflecting mirrors, and scans the pulse laser beam in a two-dimensional direction. The pulse laser beam scanned by the galvano scanner 8a passes through the fθ lens 9a and enters the workpiece 10a, and the workpiece 10a is processed. The workpiece 10a is placed on the movable surface of the XY stage 11a. The fθ lens 9a forms an image of the through hole of the mask 4 on the surface of the workpiece 10a.

  The galvano scanner 8a scans the laser beam so that the pulsed laser beam is incident on the target position in the scannable region on the surface of the workpiece 10a according to a command from the control device 12. The XY stage 11a arranges a desired area on the surface of the workpiece 10a within the scannable area of the galvano scanner 8a according to a command from the control device 12.

  The pulse laser beam traveling in the second optical path C is reflected by the folding mirror 7, enters the workpiece 10b via the galvano scanner 8b and the fθ lens 9b, and the workpiece 10a is processed at the same time. Processing of the processing object 10b is performed. The workpiece 10b is placed on the movable surface of the XY stage 11b. The operations of the galvano scanner 8b, the fθ lens 9b, and the XY stage 11b are the same as those of the galvano scanner 8a, the fθ lens 9a, and the XY stage 11a disposed in the first optical path B, respectively.

  FIG. 2 shows a cross-sectional view of the workpiece 10a. A copper layer 22 is formed on the surface of the resin layer 21, and an inner wiring pattern 23 is embedded in the resin layer 21. The resin layer 21 is made of, for example, polyimide, and the inner layer wiring pattern 23 is made of, for example, copper. Moreover, the opening 22a which penetrates the copper layer 22 by chemical etching etc. is formed in the copper layer 22, and the workpiece 10a has comprised the structure of the conformal board | substrate. The pulse laser beam 30 is irradiated with the center of the opening 22a as a processing point.

  The beam spot of the irradiated pulsed laser beam 30 on the surface of the workpiece 10a has a size including the opening 22a. Assume that the beam spot of the pulsed laser beam 30 and the aperture 22a are circular. For example, an opening 22 a having a diameter of 150 μm is formed in the copper layer 22. The depth from the bottom surface of the opening 22a to the inner layer wiring pattern 23 is, for example, 60 μm. A pulse laser beam 30 having a beam spot diameter of 300 μm is irradiated toward the center of the opening 22a. When the pulse laser beam 30 is irradiated, the bottom surface of the opening 22a is etched to form a hole.

  The processing object 10b is also a conformal substrate having a basic structure similar to that of the processing object 10a.

  Below, the laser processing method in the Example of this application is explained in full detail.

  FIG. 3A shows the original laser pulse waveform of one of the pulse laser beams emitted from the laser light source 1. From the laser light source 1, for example, an original laser pulse with a pulse width of 100 μs is emitted.

FIG. 3B shows a laser pulse waveform cut out from the original laser pulse in FIG. Here, the original laser pulse incident on the pulse extractor 2 is divided into two laser pulses. The pulse energy density required for processing the resin is about 10 J / cm ² , and it is necessary to set the pulse width to 10 to 20 μs from the maximum output of the laser oscillator, the size of the beam spot, and the like. . This condition depends on the laser oscillator to be used, the size of the hole to be processed, and the like. As an example, the pulse width of the divided first laser pulse can be 15 μs, and the pulse width of the second laser pulse can be 10 μs. Thus, by controlling the pulse extractor 2, the pulse width of the second and subsequent laser pulses extracted from the original laser pulse can be made shorter than the pulse width of the first laser pulse.

  In the following, a pulse laser beam irradiation method according to an embodiment of the present application will be described in comparison with a reference method combining burst processing and cycle processing. In addition, since the process of the process target object 10a and 10b is performed in the same procedure, the process of the process target object 10a by the laser pulse which passes along the 1st optical path B is demonstrated here.

  FIG. 4A shows a timing chart of pulse laser beam irradiation by the method of the reference example. In the method of the reference example, the irradiation of the pulse laser beam is roughly divided into two cycles. In the first cycle, two shots of the original laser pulse are respectively emitted to the workpiece points respectively associated with a plurality (here, n) of openings on the workpiece 10a, which are stored in the control device 12 in advance. It is a cycle by burst processing.

  First, in step A1-1, positioning is performed by controlling the galvano scanner 8a or the XY stage 11a so that the first workpiece point is irradiated with the laser pulse, and then the original laser pulse is irradiated with two shots. One processing point is processed. Next, in step A1-2, positioning is performed by controlling the galvano scanner 8a so that the second processing point is irradiated with the laser pulse, and then the original laser pulse is irradiated with two shots. A processing point is processed. Such a process is performed until the n-th workpiece point is processed.

  The second cycle is a cycle in which the original laser pulse is irradiated one shot at a time to the n workpiece points that have been subjected to burst processing in the first cycle. First, in step A2-1, positioning is performed by controlling the galvano scanner 8a so that the laser pulse is again irradiated to the first workpiece point, and one shot of the original laser pulse is irradiated. Next, in step A2-2, positioning is performed by controlling the galvano scanner 8a so that the second workpiece point is irradiated with the laser pulse, and then the original laser pulse is irradiated with one shot. Such a process is performed until the n-th workpiece point is processed.

  In the method of the reference example, the following restrictions occur when the laser pulse is irradiated.

The CO ₂ laser oscillator generally has a characteristic that the maximum duty cycle decreases linearly when the pulse repetition frequency (hereinafter simply referred to as “frequency”) increases. As an example, when a laser oscillator having a maximum duty cycle of 10% when the frequency is 1000 Hz is used, the maximum pulse width when oscillating at a frequency of 1000 Hz is 100 μs. When operating at a frequency of 1000 Hz, a laser pulse having a pulse width longer than 100 μs cannot be output. Thus, when the frequency is determined, the maximum pulse width of the laser pulse that can be output under the condition is determined. Conversely, when the desired pulse width is determined, the maximum frequency at which a laser pulse with that pulse width can be output is determined.

  As described above, depending on conditions such as the characteristics of the laser oscillator and the size of the hole to be processed, as an example, the pulse width necessary for processing the resin is 10 to 20 μs. It is assumed that the pulse width of the laser pulse irradiated in the first cycle is 14 μs. When the pulse width is determined, the maximum frequency at which a laser pulse having the pulse width can be output is obtained. For example, the maximum frequency is 3000 Hz. When the frequency is 3000 Hz, the period of the two original laser pulses is about 0.33 ms. The period of the two original laser pulses cannot be made shorter than this.

  In each step, it takes time to determine the irradiation position by controlling the galvano scanner 8a. When the object to be processed is processed using the galvano scanner 8a according to the embodiment of the present application, it takes 1 ms to perform alignment from the (n-1) th processing point to the nth processing point. Similarly, the second cycle requires 1 ms for alignment.

  FIG. 4B shows a timing chart of pulse laser beam irradiation according to the embodiment of the present application. Also in the embodiment of the present application, the irradiation of the pulse laser beam is roughly divided into two cycles. In the first cycle, two shots are cut out from one original laser pulse at each processing point respectively associated with a plurality of (here, n) openings on the processing object 10a stored in the control device 12 in advance. It is a cycle by burst processing to irradiate.

  First, in step B1-1, after the irradiation positioning is performed by controlling the galvano scanner 8a or the XY stage 11a so that the first processing point is irradiated with the laser pulse, it is cut out from the first original laser pulse. The laser pulse is irradiated by two shots, and the first processing point is processed. Next, in step B1-2, after performing irradiation positioning by controlling the galvano scanner 8a so that the second processing point is irradiated with the laser pulse, the laser pulse cut out from the second original laser pulse Are irradiated with two shots, and the second processing point is processed. Such a process is performed until the n-th workpiece point is processed.

  The second cycle is a cycle in which each of the n processing points subjected to the burst processing in the first cycle is irradiated with one shot of the laser pulse cut from the original laser pulse to process the processing point. is there.

  If the pulse width of the laser pulse cut out in the second cycle is the same as the pulse width of the original laser pulse irradiated in the second cycle of the reference example, a difference in processing time from the reference example occurs in the first cycle. In the method of the reference example, the original laser pulse emitted from the laser light source 1 is irradiated to each workpiece point without performing optical modulation by two shots. However, in the embodiment of the present application, the original laser pulse is emitted from the laser light source 1. Two laser pulses are cut out from one original laser pulse and irradiated to one processing point. Due to the difference in the laser pulse irradiation method in the first cycle, the time required for processing is shortened.

  The time required for the process A1-2 in the reference example is compared with the time required for the process B1-2 in the example of the present application. First, in the process A1-2, as described above, when the original laser pulse having a pulse width of 14 μs is used, 1 ms for adjusting the irradiation position, the period of the two original laser pulses is about 0.33 ms, and the second original laser is used. The pulse width of the pulse is about 0.01 ms, and the time required to process one hole is about 1.34 ms in total.

  On the other hand, in the first cycle of the processing method according to the embodiment, a time of 1 ms required for positioning the galvano scanner 8a elapses from the time when one original laser pulse is emitted until the next original laser pulse is emitted. The period of the original laser pulse is set to the sum of the time 1 ms required for this positioning and the pulse width. In order to cut out two laser pulses necessary for processing, the pulse width of the original laser pulse is set to 100 μs. Then, the period of the original laser pulse is 1.1 ms, and the frequency is 909 Hz. This frequency satisfies the condition of the frequency that can be output with respect to the pulse width of the laser pulse due to the characteristics of the laser oscillator described above. From FIG. 3B, the time width required for two laser pulses to enter one hole is 0.095 ms. When this time is combined with the time 1 ms required for positioning as described above, the time required for processing per hole in the first cycle of the example is 1.095 ms, which is shorter than the reference example.

  The process of aligning the same workpiece point again and irradiating the laser pulse in the second cycle requires the same time for both the method of the reference example and the embodiment of the present application. This shortens the entire process. Therefore, the processing time per hole according to the embodiment of the present application is shortened by about 0.245 ms compared to the method of the reference example.

  Moreover, in the Example of this application, deterioration of the side surface shape of the hole formed in the workpiece 10a can be prevented.

  FIG. 5A shows a cross-sectional view of the workpiece 10a when a hole is formed only by burst machining. When only the burst processing is performed on the workpiece 10a, a hole 21a as shown in FIG. This is due to the fact that a plurality of laser pulses are continuously irradiated to the same processing point, so that heat is accumulated around the processing portion and the side surface of the hole is excessively removed.

  FIG. 5B shows a cross-sectional view of the workpiece 10a processed by the method according to the embodiment of the present application. When the workpiece 10a is machined by the method according to the embodiment of the present application, the laser pulse is incident on the first workpiece point in the first cycle, and then the laser pulse is incident on the first workpiece point again in the second cycle. In the first cycle, a time required for the laser pulse to enter another processing point in the first cycle elapses. Therefore, since the side surface of the hole formed at the first workpiece point is cooled in the meantime, deterioration of the side surface shape due to heat accumulation can be prevented in the process of forming the hole. Therefore, a hole 21b having a small side depression is formed in the workpiece 10a.

  In the above embodiment, two laser pulses are incident on each workpiece point in the first cycle, but three or more laser pulses may be incident. In general, when burst processing is performed, the last incident laser pulse greatly deteriorates the shape of the hole. In the above-described embodiment, in the first cycle, a plurality of laser pulses are incident on one processing point at a period as short as that of conventional burst processing. However, the last shot required for processing is incident in the second cycle. For this reason, unlike the normal burst processing, it is possible to reduce the deterioration of the hole shape caused by the last one shot.

  In the above embodiment, the pulse width of the second laser pulse out of the two laser pulses incident on one hole in the first cycle is shorter than the pulse width of the first laser pulse. When three or more laser pulses are incident in the first cycle, the pulse width of each laser pulse of the laser pulse group incident later is set to be larger than the pulse width of each laser pulse of the laser pulse group incident earlier. It is preferable to shorten it. By using such a pulse train, the shape of the hole can be maintained with higher quality.

  However, since the deterioration of the hole shape due to the plurality of laser pulses incident on the first cycle is slight, the pulse widths of the plurality of laser pulses incident on the first cycle may all be equal.

  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.

It is the schematic of the laser processing apparatus used in the Example of this application. It is sectional drawing of the processing target object in the Example of this application. (A) is a diagram showing a waveform of a pulse laser beam before being cut out by a pulse extractor, and (B) is a pulse obtained by cutting out the pulse laser beam shown in FIG. 3 (A) with a pulse extractor. It is a diagram which shows the waveform of a laser beam. (A) is a diagram which shows the emission signal of the pulse laser beam in the conventional method, (B) is a diagram which shows the emission signal of the pulse laser beam by the Example of this application. (A) is a cross-sectional view of an object to be processed when only burst processing is performed, and (B) is a cross-sectional view of the object to be processed when processed by the method according to the embodiment of the present application.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser light source 2 Pulse extractor 3 Beam damper 4 Mask 5, 7 Folding mirror 6 Branching optical system 8a, 8b Galvano scanner 9a, 9b f (theta) lens 10a, 10b Processing object 11a, 11b XY stage 12 Controller 21 Resin layer 21a, 21b Hole 22 Copper layer 22a Opening 23 Inner layer wiring pattern 30 Pulse laser beam A, B, C Optical path

Claims (7)

A laser light source for emitting a pulsed laser beam;
Pulse cutting means for cutting out a plurality of laser pulses separated on the time axis from one original laser pulse of the incident pulse laser beam that is incident on the pulse laser beam emitted from the laser light source;
A stage for holding a workpiece at a position where a pulsed laser beam is incident via the pulse cutting means;
A moving mechanism for moving one of the path of the pulsed laser beam and the workpiece relative to the other so that the incident position of the pulsed laser beam on the workpiece held by the stage moves;
The positions of a plurality of processing points on the processing object are stored, a plurality of laser pulses cut out from the first original laser pulse are incident on the first processing point, and at least one other processing point After a plurality of laser pulses cut out from the second original laser pulse emitted after the first original laser pulse are incident on the first processed laser beam, the second original laser pulse is further applied to the first workpiece point. A laser processing apparatus comprising: the laser light source, the pulse cutting means, and a control device that controls the moving mechanism so that a laser pulse cut out from a third original laser pulse emitted later is incident. The control device includes the laser light source, the pulse cutting means, and the pulse cutting means so that only one of the laser pulses cut from the third original laser pulse is incident on the first workpiece point. The laser processing apparatus according to claim 1 which controls a moving mechanism.   The control device causes the pulse width of the second and subsequent laser pulses on the time axis to be shorter than the pulse width of the first laser pulse among the plurality of laser pulses extracted from the first original laser pulse. The laser processing apparatus according to claim 1, wherein the pulse cutting means is controlled.   Further, a pulse laser beam emitted from the pulse cutting means is incident on the workpiece through the first optical path and a pulse incident on another workpiece through the second optical path. The laser processing apparatus according to any one of claims 1 to 3, further comprising a branching optical system for branching into a laser beam. A step of causing a plurality of laser pulses extracted so as to be separated on the time axis from a first original laser pulse emitted from a laser light source to be incident on a first workpiece point on a workpiece;
A step of causing a plurality of laser pulses cut out from a second original laser pulse emitted from the laser light source to be incident on a second workpiece point of the workpiece after the first original laser pulse;
Laser processing including, after the second original laser pulse, one laser pulse cut out from the third original laser pulse emitted from the laser light source is incident on the first processing point. Method.   Among the plurality of laser pulses cut out from the original laser pulse, the pulse cutting means is controlled so that the pulse width of the second and subsequent laser pulses on the time axis is shorter than the pulse width of the first laser pulse. The laser processing method according to claim 5, further comprising a step. The object to be processed has a structure in which a metal layer and a resin layer are laminated, and each of the first and second processed points on the object to be processed is a plurality of openings provided in the metal layer. The size of the beam spot of the pulsed laser beam that is associated with any one and is applied to the first and second workpiece points on the workpiece includes a corresponding opening provided in the metal layer. The laser processing method according to claim 5 or 6.

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