Laser processing apparatus and laser processing method

Abstract

To form an opening having an area close to a desired opening area in an insulating layer of a wiring board.SOLUTION: The laser processing device 1 of the embodiment forms, in the insulating layer S2, an opening S1 that exposes a part of the conductive layer S31 covered with the insulating layer S2 of the circuit board S. The laser processing apparatus 1 includes a light source 2 that emits a laser beam LB, an objective lens 3 that condenses the laser beam LB on the surface of the wiring board S, a controller 5 that controls irradiation with the laser beam LB, and a sensor 6 that outputs a sensor output SO based on plasma light PL emitted from the wiring board S by the irradiation with the laser beam LB to the controller 5. The controller 5 is configured to calculate an integrated value from the start of processing at one processing position for the sensor outputs SO for each of the plurality of irradiations of the laser beam LB to the one processing position, and to end the formation of the opening S31 at the one processing position when the integrated value satisfies a predetermined condition.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a laser processing apparatus and a laser processing method. [Background technology]

[0002] Patent Document 1 discloses a drilling method and a laser processing apparatus for forming a laser-machined hole that extends from a first member to a second member by irradiating a laser beam onto a workpiece composed of a first member and a second member that are connected together. In the method and processing apparatus disclosed in Patent Document 1, minimum and maximum values ​​are set in advance for the number of shots of a pulsed laser beam. The irradiation of the pulsed laser beam is stopped based on the magnitude relationship between these minimum and maximum values ​​and the number of shots of the pulsed laser beam that have already been irradiated, and on changes in the spectrum emitted by plasma due to irradiation with the pulsed laser beam. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-43198 Summary of the Invention [Problem to be solved by the invention]

[0004] In the hole-drilling method and laser processing device disclosed in Patent Document 1, the irradiation of the pulsed laser beam is stopped when the spectrum of the plasma changes or when the number of pulsed laser beam irradiations reaches a preset number of shots, so the laser-processed hole may not necessarily have the desired opening area. [Means for solving the problem]

[0005] The laser processing apparatus of the present invention is a laser processing apparatus for forming an opening in an insulating layer of a wiring board to expose a part of a conductor layer covered by the insulating layer, and includes a light source for emitting a laser beam, an objective lens for focusing the laser beam on a surface of the wiring board, a controller for controlling the irradiation of the laser beam, and a sensor for outputting a sensor output based on plasma light emitted from the wiring board by the irradiation of the laser beam to the controller. The controller is configured to calculate an integrated value of the sensor output for each of a plurality of irradiations of the laser beam at a processing position on the wiring board from the start of processing at the processing position, and to terminate the formation of the opening at the processing position by the irradiation of the laser beam when the integrated value satisfies a predetermined condition.

[0006] A laser processing method for a wiring board includes: irradiating a surface of the wiring board with a laser beam to form an opening in an insulating layer of the wiring board, exposing a portion of a conductor layer covered by the insulating layer; and causing a sensor to emit plasma light emitted from the wiring board by the irradiation of the laser beam, thereby causing the sensor to output a sensor output based on the plasma light. The forming of the opening includes repeatedly irradiating a processing position on the wiring board with the laser beam a plurality of times; calculating an integrated value of the sensor output for each of the plurality of laser beam irradiations from the start of processing at the processing position; and terminating the formation of the opening at the processing position by irradiating the laser beam when the integrated value satisfies a predetermined condition.

[0007] According to the embodiment of the present invention, it is believed that an opening having an area at the bottom that is closer to the desired opening area can be formed in the insulating layer of the wiring substrate. [Brief explanation of the drawings]

[0008] [Figure 1]1 is a schematic diagram showing an example of the overall configuration of a laser processing apparatus according to an embodiment of the present invention; [Figure 2] 1 is a cross-sectional view showing an example of a wiring substrate processed by a laser processing apparatus and method according to an embodiment; [Figure 3] 1 is a cross-sectional view showing an example of a processing state by a laser processing apparatus and method according to an embodiment; [Figure 4A] 1 is a cross-sectional view showing an example of a progress state of processing by the laser processing apparatus and method according to an embodiment. [Figure 4B] 1 is a cross-sectional view showing an example of a progress state of processing by the laser processing apparatus and method according to an embodiment. [Figure 5] FIG. 4 is a diagram showing an example of frequency characteristics of a filter in the laser processing apparatus according to the embodiment. [Figure 6A] FIG. 4 is a diagram showing an example of an actual measurement result of a sensor output of the laser processing apparatus according to the embodiment. [Figure 6B] FIG. 4 is a diagram showing an example of an actual measurement result of a sensor output of the laser processing apparatus according to the embodiment. [Figure 6C] FIG. 4 is a diagram showing an example of an actual measurement result of a sensor output of the laser processing apparatus according to the embodiment. [Figure 6D] FIG. 4 is a diagram showing an example of an actual measurement result of a sensor output of the laser processing apparatus according to the embodiment. [Figure 7A] 6B is an observation image of the opening formed at the time when the actual measurement result of FIG. 6A was obtained. [Figure 7B] An observation image of the opening formed at the time when the actual measurement result of Figure 6B was obtained. [Figure 7C] An observation image of the opening formed at the time when the actual measurement result of Figure 6C was obtained. [Figure 7D] An observation image of the opening formed at the time when the actual measurement results of Figure 6D were obtained. [Figure 8] 10 is a diagram showing the results of a survey of the correlation between the integrated sensor output value and the opening area of ​​the opening of the laser processing device according to the embodiment. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] A laser processing apparatus and a laser processing method according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 schematically illustrates the overall configuration of a laser processing apparatus 1, which is an example of a laser processing apparatus according to an embodiment. FIG. 2 illustrates a cross-sectional view of a wiring board S, which is an example of an object to be processed by the laser processing apparatus and the laser processing method according to an embodiment. FIG. 3 illustrates an example of a processing state at a location irradiated with a laser beam by the laser processing apparatus and the laser processing method according to an embodiment. Note that the laser processing apparatus 1 in FIG. 1 is merely an example of a laser processing apparatus according to an embodiment. The laser processing apparatus according to an embodiment may include optional components and / or functional blocks other than those included in the laser processing apparatus 1 in FIG. 1, or may not include some of the components included in the laser processing apparatus 1. Furthermore, a wiring board processed by the laser processing apparatus and the laser processing method according to an embodiment may have any structure different from the structure of the wiring board S shown in FIG. 2. The laser processing apparatus and the laser processing method according to an embodiment can be applied to a wiring board having any structure including at least one conductor layer and one insulating layer covering the conductor layer.

[0010] <Configuration of laser processing device according to embodiment> As shown in Fig. 1, the laser processing apparatus 1 includes a light source 2 that emits a laser beam LB, an objective lens 3 that focuses the laser beam LB, a controller 5 that controls the irradiation of the laser beam LB, and a sensor 6 that detects incident light and outputs an output (sensor output SO) corresponding to that light. The laser processing apparatus 1 in Fig. 1 also includes a beam splitter 4, an acousto-optic modulator (AOM) 7 that modulates the laser beam LB emitted from the light source 2 by the acousto-optic effect, a galvanometer mirror unit 8, a table 10, and two filters 61 and 62. In the laser processing apparatus 1 in Fig. 1, the object to be processed is a wiring board S, and the objective lens 3 focuses the laser beam LB on the surface of the wiring board S.

[0011] The light source 2 is composed of any laser oscillator capable of emitting a laser beam LB. The light source 2 may emit a pulsed laser beam LB. As an example, the light source 2 emits a UV laser beam having a wavelength of 355 nm, which is a third harmonic of a UV-YAG laser. A UV laser beam has excellent linearity and is suitable for forming a minute opening S31, and therefore may be preferable as the laser beam LB used in the laser processing apparatus 1 of the embodiment. However, the laser beam LB is not limited to a UV laser beam, and may be a laser beam of any wavelength that can drill a hole in the wiring board S.

[0012] The AOM 7 deflects and / or intensity-modulates the laser beam LB emitted from the light source 2 in accordance with characteristics such as the frequency and / or amplitude of a high-frequency band control signal sent from the controller 5. The AOM 7 may start or stop the irradiation of the laser beam LB onto the wiring board S by starting or stopping the deflection or modulation operation in accordance with the control signal sent from the controller 5.

[0013] The galvanometer mirror unit 8 includes a pair of reflecting mirrors 81 and a driver for rotating each of the reflecting mirrors 81. Each driver rotates the two reflecting mirrors 81 around mutually orthogonal rotation axes in response to a control signal sent from the controller 5. The pair of reflecting mirrors 81 rotated in the desired direction deflects the laser beam LB in the desired direction. This allows fine adjustment of the irradiation position of the laser beam LB on the wiring board S.

[0014] The objective lens 3 makes the laser beam LB incident on the objective lens 3 from the galvanometer mirror unit 8 perpendicular to the surface of the wiring substrate S to be processed, and focuses the laser beam LB at the incident position. In other words, the objective lens 3 functions as a so-called fθ lens. The objective lens 3 can be any optical lens that can focus the laser beam LB at the incident position on the surface of the wiring substrate S.

[0015] The table 10 supports the wiring board S, which is placed on the table 10 to form the opening S31. The table 10 moves the wiring board S relatively to the irradiated laser beam LB, for example, by reciprocating in two directions perpendicular to each other. The table 10 may be an XY table, for example, but may also be any movable table that can position any position on the wiring board S at the irradiation position of the laser beam LB. The movement of the table 10 is preferably controlled by a controller 5.

[0016] The wiring board S illustrated in FIG. 2 includes a core substrate S4 and conductor layers S1 and insulating layers S2 alternately stacked on both sides of the core substrate S4. Each conductor layer S1 is covered with an insulating layer S2 stacked on the opposite side of the core substrate S4. The conductor layer S1 is formed of, for example, copper, but may be formed of any metal other than copper. The insulating layer S2 is formed primarily of, for example, epoxy resin, but may also be formed primarily of a thermosetting resin other than epoxy resin, such as bismaleimide triazine resin (BT resin), or a thermoplastic resin such as fluororesin. Each insulating layer S2 has via conductors S3 formed therein, connecting the conductor layers sandwiching each insulating layer S2. The via conductors S3 are formed in openings S31 penetrating each insulating layer S2. By using the laser processing apparatus 1 and the laser processing method of the embodiment, an opening such as the opening S31 shown in Figures 1 and 2 is formed in the insulating layer of the wiring board, which penetrates the insulating layer and exposes a portion of the conductor layer covered by the insulating layer.

[0017] When the surface of the wiring substrate S is irradiated with the laser beam LB, a plasma state is generated at the irradiated location due to temperature rise and ionization, and plasma light PL is emitted, as shown in Fig. 3. For example, when the laser beam LB irradiates the conductor layer S1 as shown in Fig. 3, plasma light PL is emitted that mainly contains a wavelength specific to the material (e.g., copper) that makes up the conductor layer S1.

[0018] In the laser processing apparatus 1 of this embodiment, beam splitter 4 is disposed in the optical path LP of laser beam LB between light source 2 and objective lens 3. Beam splitter 4 transmits laser beam LB, which enters first light incident / exit surface 41 from the light source 2 side, to the objective lens 3 side, i.e., the wiring substrate S side. Furthermore, beam splitter 4 reflects plasma light PL, which enters second light incident / exit surface 42 opposite first light incident / exit surface 41, so that it deviates from the optical path LP of laser beam LB. In other words, beam splitter 4 reflects plasma light PL, which is emitted from wiring substrate S in response to irradiation with laser beam LB and enters from the wiring substrate S side, in a direction different from both the traveling direction of laser beam LB and the opposite direction.

[0019] 1 reflects the incident plasma light PL in a second direction D2 different from the first direction D1 along the optical path LP of the laser beam LB. Alternatively, the beam splitter 4 may reflect only light of at least a specific wavelength from the incident plasma light PL in the second direction D2. For example, the beam splitter 4 may reflect light of a specific wavelength from the plasma light PL incident on the second light input / output surface 42 in the second direction D2, which is at an angle of approximately 90 degrees to the first direction D1. The beam splitter 4 may be a dichroic beam splitter that transmits or reflects light of a specific wavelength from the light incident on each light input / output surface.

[0020] The wavelength band of light that beam splitter 4 transmits from first light incident / exit surface 41 to second light incident / exit surface 42 may include, for example, 355 nm, which is the wavelength of UV laser light. Furthermore, the specific wavelength of light that beam splitter 4 reflects in second direction D2 of plasma light PL that is incident on second light incident / exit surface 42 may be the wavelength of plasma light emitted by conductor layer S1 of wiring substrate S in response to irradiation with laser beam LB. For example, the specific wavelength may be a wavelength of 230 to 326 nm of plasma light emitted when copper is irradiated with laser beam LB.

[0021] Beam splitter 4 may transmit, to first light incident / exit surface 41, light of a wavelength different from the wavelength of light reflected in second direction D2 from plasma light PL incident on second light incident / exit surface 42. The wavelength band of light that beam splitter 4 transmits to first light incident / exit surface 41 from plasma light PL incident on second light incident / exit surface 42 may include the wavelength of plasma light emitted by constituent materials of wiring substrate S other than conductor layer S1 in response to irradiation with laser beam LB. For example, even if resins such as epoxy resin that constitute insulating layer S2, glass used as a reinforcing material, or silicon oxide or alumina that constitute particles added to insulating layer S2 emit plasma light, the plasma light can be prevented from entering sensor 6. The wavelength band of light that beam splitter 4 transmits from second light incident / exit surface 42 to first light incident / exit surface 41 may be, for example, a wavelength band of 336 to 1200 nm.

[0022] Beam splitter 4 may reflect, in second direction D2, all light of all wavelengths of plasma light PL that is incident on second light incident / exit surface 42. Even if plasma light PL is reflected in this way, by providing filters 61 and / or 62 as described below, it is possible to allow only light of desired wavelengths of plasma light PL to be incident on sensor 6.

[0023] 1, a sensor unit 60 is configured by a sensor 6, a filter 61, and a filter 62. The sensor unit 60 is arranged in the second direction D2 so that the plasma light PL reflected by the beam splitter 4 in the second direction D2 enters the sensor unit 60. The filters 61 and 62 are provided between the beam splitter 4 and the sensor 6. Of the light reflected by the beam splitter 4 in the second direction D2, light of a specific wavelength band passes through the filters 61 and 62 and enters the sensor 6.

[0024] Sensor 6 outputs to controller 5 a sensor output SO based on the plasma light PL reflected in second direction D2 by beam splitter 4. Specifically, sensor 6 detects the light that reaches sensor 6 from the plasma light PL reflected by beam splitter 4. Sensor 6 outputs sensor output SO, which is an electrical signal having a level or frequency corresponding to, for example, the intensity of the detected light. Sensor 6 may, for example, be a photomultiplier tube capable of detecting light with high sensitivity and high speed. However, sensor 6 may also use any photoelectric conversion element, such as a photodiode or phototransistor, that can output an electrical signal having characteristics corresponding to the intensity of incident light. Note that the "intensity" of light such as plasma light PL may, for example, be the energy of light flowing through a unit area per unit time (Poynting vector or power density).

[0025] The controller 5 is configured by an integrated circuit device (IC) such as a microcomputer, a programmable logic device, or a field programmable gate array that performs predetermined operations according to instructions from a built-in program. The controller 5 may be configured by any of these ICs and its peripheral components. The IC such as the microcomputer that configures the controller 5 and its peripheral components function as the calculation unit 51, judgment unit 53, irradiation start / stop control unit 54, irradiation condition control unit 55, and irradiation position control unit 56 of the controller 5 according to the algorithm of a program (execution program) that is executed sequentially. In the example of FIG. 1, the controller 5 further includes a memory unit 52 that stores a predetermined threshold value for the sensor output SO output by the sensor 6.

[0026] The calculation unit 51 performs a predetermined calculation commanded by the execution program, for example, a predetermined calculation on the sensor output SO, and outputs the calculation result to the judgment unit 53. As one function, the calculation unit 51 is configured to calculate an integrated value of the sensor output SO for each of multiple irradiations of the pulsed laser beam LB at one processing position on the wiring board S to be processed, from the start of processing at that one processing position. This integrated value will hereinafter also be simply referred to as the "integrated sensor output value." As an example, the integrated sensor output value may be a simple sum of the sensor outputs SO from the start of processing at that one processing position.

[0027] One function of the determination unit 53 is to determine whether the integrated sensor output value satisfies a predetermined condition set in advance for controlling the laser beam LB. For example, the determination unit 53 may compare the integrated sensor output value obtained by the calculation of the calculation unit 51 with a predetermined threshold value stored in the storage unit 52 to determine whether the integrated sensor output value satisfies the predetermined condition. The determination unit 53 then provides the determination result to the irradiation start / stop control unit 54, the irradiation condition control unit 55, and / or the irradiation position control unit 56.

[0028] The irradiation start / stop control unit 54 sends signals to control the start and stop of emission of the laser beam LB by the light source 2 and / or the on / off switching of the AOM 7 based on the determination result of the determination unit 53. The irradiation condition control unit 55 outputs signals to control the energy density and power of the laser beam LB when emitted by the light source 2 based on the determination result of the determination unit 53. When the laser beam LB is emitted in pulses, the irradiation condition control unit 55 may output signals to control the irradiation cycle and pulse width based on the determination result of the determination unit 53. Furthermore, the irradiation condition control unit 55 may output signals to control the degree of intensity modulation of the laser beam LB by the AOM 7 based on the determination result of the determination unit 53. The irradiation position control unit 56 outputs signals to control the deflection of the laser beam LB by the AOM 7 and / or the galvanometer mirror unit 8, as well as the start, stop, and movement direction of the table 10, based on the determination result of the determination unit 53.

[0029] The storage unit 52 may be included in a microcomputer or the like that mainly constitutes the controller 5, or may be a memory device provided separately from an IC such as a microcomputer. The storage unit 52 may store numerical values, time, number of times, conditional expressions, and the like related to predetermined conditions that are set in advance for the integrated sensor output value to control the laser beam LB. As an example, the storage unit 52 may store a "predetermined first threshold value" (described later) for the integrated sensor output value.

[0030] When the laser processing apparatus 1 of the embodiment forms an opening S31 in the insulating layer S2 of the wiring board S, a pulsed laser beam LB, for example in the UV band, is emitted from the light source 2. The laser beam LB is modulated and / or deflected by the AOM 7, and is further deflected in a predetermined direction by the galvanometer mirror unit 8 before entering the objective lens 3. The laser beam LB focused by the objective lens 3 then irradiates the surface of the wiring board S at a desired processing position. When the laser beam LB irradiates the conductor layer S1, plasma light PL is emitted from the wiring board S, which includes light with a wavelength specific to the constituent material of the conductor layer S1.

[0031] The plasma light PL passes through objective lens 3 in the direction opposite to the traveling direction of laser beam LB, is further deflected by galvanometer mirror unit 8, and enters beam splitter 4 from second light input / output surface 42. Of the plasma light PL, at least that part having a wavelength specific to the constituent material of conductor layer S1 is reflected by beam splitter 4 in second direction D2. Of the plasma light PL, that part having a wavelength specific to the constituent material of conductor layer S1 enters sensor 6. Sensor 6 outputs sensor output SO, which has a level corresponding to, for example, the intensity of the incident light, to controller 5.

[0032] The controller 5 controls, based on the sensor output SO, the stopping of irradiation of the wiring board S with the laser beam LB, the irradiation conditions of the laser beam LB, and the irradiation position of the laser beam LB. That is, based on the sensor output SO, the controller 5 performs control such as stopping the irradiation of the laser beam LB, adjusting the irradiation conditions of the laser beam LB such as the energy density, pulse width, and irradiation period, and moving the irradiation position of the laser beam LB from one irradiation position to the next. In particular, in the laser processing apparatus 1 of the embodiment, the controller 5 is configured to control the irradiation of the laser beam LB based on the above-mentioned integrated value of the sensor output.

[0033] Specifically, in the laser processing apparatus 1 of the embodiment, the controller 5 calculates an integrated sensor output value, and when the integrated sensor output value satisfies a predetermined condition, the controller 5 terminates the formation of the opening S31 by irradiating the laser beam LB at the processing position for which the integrated sensor output value is calculated. The "processing position for which the integrated sensor output value is calculated" is the position in the wiring substrate S that is currently irradiated with the laser beam LB when the integrated sensor output value satisfies the predetermined condition in multiple irradiations of the laser beam LB at the same position. As an example, when the controller 5 recognizes that the integrated sensor output value satisfies the predetermined condition, a built-in program such as a microcomputer constituting the controller 5 may include a command to immediately or after a predetermined time has elapsed to terminate irradiation of the laser beam LB at the processing position that is currently irradiated with the laser beam LB.

[0034] In the following explanation, the statement that "controller 5 is configured (to perform a specific process)" implies that the execution program built into the microcomputer or the like that constitutes controller 5 contains instructions that cause controller 5 to perform that specific process.

[0035] In the laser processing device of the embodiment, the formation of the opening S31 at the processing position irradiated with the laser beam LB at that time is terminated when the integrated value of the sensor output satisfies a predetermined condition, rather than stopping the irradiation when the spectrum of the plasma light changes or when a predetermined number of irradiations of the laser light is reached as in Patent Document 1. Therefore, as will be described in detail below, it is believed that it is possible to form an opening S31 whose bottom surface has an area closer to the desired opening area.

[0036] <Changes in plasma light> 4A and 4B show the progress of processing in the laser processing apparatus and laser processing method of the embodiment before reaching the state shown in Fig. 3. The processing state of the irradiated part by the laser processing apparatus and laser processing method of the embodiment changes in the order of Fig. 4A, Fig. 4B, and Fig. 3.

[0037] When the area irradiated by the laser beam LB on the wiring board S to be processed changes from the insulating layer S2 to the interface between the insulating layer S2 and the conductor layer S1, and then to the conductor layer S1, and the conductor layer S1 is irradiated with the laser beam LB, plasma light PL is emitted from the wiring board S. For example, as shown in FIG. 4A, while the laser beam LB is irradiating the insulating layer S2, almost no plasma light is emitted. Even if plasma light is emitted, its intensity is slight, and the slightly emitted plasma light does not include almost any wavelength specific to the material (e.g., copper) that constitutes the conductor layer S1.

[0038] Next, as shown in FIG. 4B, when the laser beam LB starts to irradiate the conductor layer S1 at the interface between the insulating layer S2 and the conductor layer S1, plasma light PL containing a wavelength specific to the constituent material of the conductor layer S1 starts to be emitted.

[0039] When the laser beam LB irradiates the conductor layer S1 (see Figure 3), plasma light PL, which mainly contains wavelengths specific to the material (e.g., copper) that constitutes the conductor layer S1, is emitted with a higher intensity than the plasma light PL emitted in the processing state shown in Figure 4B.

[0040] That is, the intensity of the plasma light PL increases as the irradiation location shifts from insulating layer S2 to conductor layer S1. Furthermore, the amount of wavelength components specific to the material constituting conductor layer S1 increases in the plasma light PL. Therefore, the intensity of the plasma light PL incident on sensor 6 via beam splitter 4 and filters 61 and 62 increases. The level and frequency of sensor output SO then change according to the photoelectric conversion characteristics of sensor 6. Therefore, the "integrated sensor output value," calculated by integrating the sensor output SO for each of multiple irradiations of laser beam LB at the same location, is thought to increase with each irradiation of laser beam LB as the irradiation location shifts to conductor layer S1.

[0041] As will be described later, the integrated sensor output value has a specific relationship with the opening area of ​​the bottom surface of the opening S31 formed by multiple irradiations of the laser beam LB for which the integrated sensor output value has been calculated. Based on this specific relationship, the controller 5 in the laser processing apparatus 1 of the embodiment is configured to terminate the formation of the opening S31 at the processing position irradiated with the laser beam LB at that time when the integrated sensor output value satisfies a predetermined condition.

[0042] For example, when the integrated sensor output value satisfies a predetermined condition, the controller 5 may immediately stop the irradiation of the laser beam LB, thereby ending the formation of the opening S31 at the processing position at that time. As another example, when the integrated sensor output value satisfies a predetermined condition, the controller 5 may continue the irradiation of the laser beam LB for a predetermined time and then stop the irradiation, thereby ending the formation of the opening S31 at the processing position at that time, so as to reliably form the opening S31 having the desired opening area.

[0043] For example, the "predetermined condition" may be that the integrated sensor output value reaches a predetermined first threshold. That is, the controller 5 may be configured to terminate irradiation of the laser beam LB at the processing position currently being irradiated with the laser beam LB when the integrated sensor output value reaches the predetermined first threshold. The "predetermined first threshold" may be, for example, the value of the integrated sensor output value corresponding to the median of the allowable range for the opening area of ​​the bottom surface of the opening S31. By terminating the formation of an opening at the processing position currently being irradiated with the laser beam LB when the integrated sensor output value reaches the predetermined first threshold, it may be possible to form an opening having a bottom surface area close to the desired opening area.

[0044] In another example, the "predetermined condition" may be that the rate of increase of the integrated sensor output value due to one irradiation of the laser beam LB (hereinafter also referred to as the "unit increase rate") is within the range of a predetermined second threshold. In this case, the "predetermined second threshold" may be, for example, 40% or more and 60% or less. The reason for this is that a too large unit increase rate indicates that the laser beam LB has just started to irradiate the conductor layer S1, and a too small unit increase rate indicates that the change in the opening formation state for each irradiation of the laser beam LB has saturated.

[0045] <Filter characteristics> FIG. 5 shows an example of the wavelength characteristics of the gain (or attenuation rate) of filters 61 and 62. The characteristics of filter 61 are shown by curve C1, and the characteristics of filter 62 are shown by curve C2. As shown in FIG. 5, filter 61 may be a bandstop filter that significantly attenuates or blocks light in a specific wavelength band including wavelength f1. Filter 61 may also be a notch filter that significantly attenuates only light in an extremely narrow wavelength band. Filter 61 may have a stopband that includes the wavelength of laser beam LB emitted from light source 2. If filter 61 has such a stopband, even if the laser beam emitted from the light source is unintentionally transmitted or reflected toward sensor 6 (see FIG. 1), the laser beam is prevented from reaching sensor 6 and being erroneously detected by sensor 6. For example, if the light source emits a UV laser beam having a wavelength of 355 nm, the wavelength f1 included in the stopband shown in FIG. 5 may be 355 nm.

[0046] On the other hand, as shown in FIG. 5, filter 62 may be a bandpass filter that transmits only light in a specific wavelength band including wavelength f2 and attenuates or blocks light in other wavelength bands. Filter 62 preferably transmits only light in the wavelength band of plasma light emitted by the conductor layer of the wiring board to be processed when irradiated with a laser beam from a light source. For example, the wavelength band of light transmitted by filter 62 may be the wavelength band of plasma light emitted when copper is irradiated with a laser beam from a light source. Therefore, wavelength f2 included in the pass band indicated by curve C2 in FIG. 5 may be 326 nm.

[0047] <Examples of sensor output measurements and opening observations> 6A to 6D show examples of measured sensor outputs SO obtained by forming openings in an insulating layer of a wiring board using the laser processing apparatus 1 of the embodiment illustrated in FIG. 1. In FIGS. 6A to 6D, the vertical axis represents the level (voltage) of the sensor output SO measured when a pulsed laser beam is repeatedly applied to the same location on the wiring board in a plan view. In FIGS. 6A to 6D, the horizontal axis represents the time axis, indicating the progression of time as the laser beam is repeatedly applied. The height of the vertical bar at each point on the horizontal axis represents the level of the sensor output SO measured at that point with a single pulsed laser beam. Furthermore, each opening already formed at the time the measurement results shown in FIGS. 6A to 6D were obtained was cut along its axial direction and observed from diagonally above each opening. Images obtained from this observation are shown in FIGS. 7A to 7D. The observed images in FIGS. 7A to 7D correspond to openings formed by irradiation with the laser beams whose sensor output measurement results are shown in FIGS. 6A to 6D, respectively. As is clear from the cross-sectional images of the openings after each irradiation of the laser beam in Figures 7A to 7D, the investigations whose results are shown in Figures 6A to 6D were carried out on the formation of different openings.

[0048] FIG. 6A shows the sensor output SO measured by five repeated laser beam irradiations. FIGS. 6B, 6C, and 6D show the sensor output SO measured by eight, eleven, and fourteen repeated laser beam irradiations, respectively. Accordingly, FIGS. 7A, 7B, 7C, and 7D are images of apertures formed by five, eight, eleven, and fourteen repeated laser beam irradiations, respectively. The investigations whose results are shown in FIGS. 6A-6D and 7A-7D involved laser irradiation of an 8.5 μm thick insulating layer covering a 2.5 μm thick conductor layer, using a wavelength of 355 nm and an energy density of 0.82 J / cm. 2 The laser beam had a pulse width of 10 nsec and a pulse frequency of 200 kHz.

[0049] As shown in Fig. 6A, the level of the sensor output SO for each of the five laser beam irradiations is approximately 0 V. That is, as shown in Fig. 7A, the opening S31 formed in the insulating layer S2 by the five laser beam irradiations does not penetrate the insulating layer S2, so that no plasma light is emitted from the wiring substrate S, or even if a small amount of plasma light is emitted, the plasma light contains almost no wavelength components specific to the copper or other materials that make up the conductor layer S1. Therefore, almost no light reaches the sensor 6 shown in Fig. 1, and only the sensor output SO of approximately 0 V is measured.

[0050] In the actual measurement results shown in FIG. 6B, a substantial level of sensor output SO was measured by the last two laser beam irradiations. The last laser beam irradiation measured a sensor output SO of approximately 0.2 V. Referring to FIG. 7B, eight laser beam irradiations formed an opening S31 reaching the conductor layer S1, slightly exposing the surface of the conductor layer S1 through the opening S31. This causes plasma light to be emitted from the wiring substrate S. This plasma light contains wavelength components specific to the copper and other components that make up the conductor layer S1. Because this wavelength component reaches the sensor 6 in FIG. 1, a sensor output SO greater than 0 V was measured. In the laser beam irradiations for which the sensor output SO is shown in FIG. 6B, the irradiated area of ​​the laser beam LB is believed to be near the interface between the insulating layer S2 and the conductor layer S1, as shown in FIG. 4B.

[0051] In the actual measurement results shown in Fig. 6C, the level of the sensor output SO rose to approximately 0.4 V in the final two irradiations. Referring to Fig. 7C, a larger area of ​​conductor layer S1 is exposed at the bottom of opening S31 that reaches conductor layer S1 than the exposed area of ​​conductor layer S1 in Fig. 7B. Therefore, the intensity of the plasma light emitted from wiring board S is higher than during irradiation, for which the sensor output is shown in Fig. 6B. In addition, the emitted plasma light contains wavelength components specific to the copper and other components that make up conductor layer S1, so the results shown in Fig. 6C provide a higher level of sensor output SO than in Fig. 6B.

[0052] The measurement results shown in Fig. 6D show a sensor output SO that is even greater than the sensor output SO of the measurement results shown in Fig. 6C. Referring to Fig. 7D, although it is somewhat difficult to see, the conductor layer S1 is exposed over an area at the bottom of opening S31 that is larger than the exposed area of ​​conductor layer S1 in Fig. 7C, as will be described later. Therefore, the results shown in Fig. 6D show a sensor output that is even greater than that in Fig. 6C. In the final irradiation of the laser beam, for which the sensor output SO is shown in Figs. 6C and 6D, it is believed that the area irradiated with the laser beam is mainly the conductor layer, similar to the processing state illustrated in Fig. 3 previously referenced.

[0053] In observing the openings S31 whose images are shown in FIGS. 7A to 7D, the opening diameter and opening area at the bottom of each opening S31 were measured using the measurement function of the observation device. The opening diameters at the bottom of the openings S31 shown in FIGS. 7A, 7B, 7C, and 7D were 0 μm, approximately 4.2 μm, approximately 6.4 μm, and approximately 7.0 μm, respectively. The opening areas at the bottom of the openings S31 shown in FIGS. 7A, 7B, 7C, and 7D were 0 μm, approximately 4.2 μm, approximately 6.4 μm, and approximately 7.0 μm, respectively. 2 , about 13.8μm 2 , about 35.8μm 2 , and approximately 40.4 μm 2 It was.

[0054] 6A to 6D and 7A to 7D, it can be seen that by continuing to irradiate the laser beam even after it has started to irradiate the conductor layer on the wiring board to be processed, it is possible to form an opening with a larger opening area at the bottom. It is believed that it is possible to form an opening with an area at the bottom that is closer to the desired opening area.

[0055] <Correlation between sensor output integrated value and opening area> Figure 8 shows the relationship between the integrated sensor output (horizontal axis) and the bottom opening area (vertical axis) of the opening formed at each processing position, obtained by irradiating a pulsed laser beam 5 to 14 times at each of many processing positions on a wiring board. The pulsed laser beam was irradiated at a fixed cycle and for a fixed irradiation time (pulse width) per irradiation. The integrated sensor output shown on the horizontal axis of Figure 8 is the integrated value obtained by adding up the product of the sensor output for each irradiation and the unit time corresponding to the pulsed laser beam irradiation cycle for all sensor outputs for each processing position. In Figure 8, the different numbers of irradiations (5 to 14) are distinguished by different symbols (e.g., ○ and △). The results shown in Figure 8 indicate a specific relationship, approximated by a straight line L, between the integrated sensor output obtained from repeated pulsed laser beam irradiation and the bottom opening area of ​​the opening formed by the repeated irradiation.

[0056] 8 has been found, and therefore, as described above, when the integrated sensor output value satisfies the "predetermined condition," it is determined that an opening of the desired opening area has been formed, and processing by irradiating the laser beam can be stopped immediately or after a predetermined time has elapsed. In other words, the integrated sensor output value can be used to determine whether to stop processing by irradiating the laser beam to form the opening.

[0057] Therefore, the calculation unit 51 (see FIG. 1) of the controller 5 may calculate the product of the irradiation period of a plurality of laser beams at a fixed period to one processing position and the sensor output for each irradiation of the laser beam, and calculate the sum (total value) of these products from the start of processing at the one processing position as the integrated sensor output value. In other words, the integrated sensor output value may be, for example, a total value obtained by adding up the product of the sensor output for each irradiation of a plurality of laser beams at a fixed period to one processing position and the unit time corresponding to the irradiation period of the laser beam, for all sensor outputs from the start of processing at the one processing position.

[0058] 8 is the sum of the sensor outputs themselves, it is believed that a specific relationship exists between the sum (integrated value) and the opening area of ​​the bottom surface of the opening, simply by changing the slope of the line L. Therefore, the control unit 5 may be configured, for example, by the calculation unit 51 to calculate, as the sensor output integrated value, the sum (total value) of the sensor outputs for each of multiple laser beam irradiations to one processing position from the start of processing at that one processing position.

[0059] In the repeated laser beam irradiation, the irradiation time and irradiation cycle of each irradiation do not have to be constant. Even in this case, the sum of the products of the irradiation time of each of the multiple laser beam irradiations and the sensor output at each irradiation time from the start of processing is considered to have a specific relationship with the opening area of ​​the opening formed by the multiple laser beam irradiations, similar to that shown in Figure 8.

[0060] Therefore, the control unit 5 may be configured to, for example, calculate the product of the irradiation time for each of the multiple laser beam irradiations on a single processing position and the sensor output for each irradiation time, and then calculate the sum (total value) of these products from the start of processing at the single processing position as the integrated sensor output value. That is, the integrated sensor output value may be, for example, a total value obtained by adding up the product of the sensor output for each of the multiple laser beam irradiations on a single processing position and the irradiation time for each irradiation, for all sensor outputs from the start of processing at the single processing position. When the control unit 5 calculates the integrated sensor output value in this manner, the degree of freedom in setting the time conditions for the multiple laser beam irradiations may be increased. Furthermore, since the specific irradiation time is incorporated into the calculation, it may be possible to more accurately form an opening having a bottom area close to the desired opening area.

[0061] Furthermore, from the results shown in FIG. 8, it is believed that the definite integral of the time function of the sensor output obtained with each repeated irradiation of the laser beam may be used to determine whether to stop the laser beam processing to form the opening. That is, as shown in FIGS. 6A to 6D, the relationship between the sensor output obtained with each repeated irradiation of the pulsed laser beam and the elapsed time from the start of irradiation is approximated by a function of an appropriate order. Furthermore, the definite integral of the function with respect to the elapsed time until each repeated irradiation is calculated, and a specific relationship is identified between each definite integral and the opening area of ​​the opening formed up to each irradiation, as shown in the example of FIG. 8. Then, based on the identified relationship, the definite integral of the sensor output may be used as the integrated sensor output value to determine whether to stop the laser beam processing to form the opening.

[0062] Therefore, in the laser processing apparatus of the embodiment, the control unit 5 may be configured to derive a mathematical formula (function) that indicates the relationship between the sensor output obtained at each irradiation of the repetitive laser beam and the elapsed time from the start of irradiation. Furthermore, the control unit 5 may be configured to calculate, for the derived mathematical formula, a definite integral value from the start of the repetitive laser beam irradiation to the time of each irradiation as the sensor output integrated value. Then, the determination unit 53 (see FIG. 1) may be configured to determine whether the definite integral value calculated as the sensor output integrated value satisfies the above-mentioned "predetermined condition."

[0063] <Laser processing method according to the embodiment> The laser processing method of the embodiment mainly includes, as steps to be executed, some of the operations, controls, and electrical or optical processes performed by each component, such as the controller of the laser processing apparatus of the embodiment. The laser processing method of the embodiment may be performed using the laser processing apparatus of the embodiment, or may be performed without using the laser processing apparatus of the embodiment. Below, the laser processing method of the embodiment will be described using the laser processing apparatus 1 of the embodiment as an example, with reference to FIG. 1 and the like again and using the reference numerals assigned to FIG. 1. Note that, in the following description, even if not specifically mentioned, the operations, controls, and various processes performed by each component described with respect to the laser processing apparatus of the embodiment may also be included in the laser processing method of the embodiment.

[0064] The laser processing method of the embodiment is a laser processing method for a wiring board such as the wiring board S exemplified in Fig. 1. The laser processing method of the embodiment includes forming an opening S31 in an insulating layer S2 of the wiring board S, exposing a part of the conductor layer S1 covered by the insulating layer S2, by irradiating a surface of the wiring board S with a laser beam LB. The laser processing method of the embodiment further includes causing plasma light PL emitted from the wiring board S by irradiation with the laser beam LB to be incident on a sensor 6, thereby causing the sensor 6 to output a sensor output SO based on the plasma light PL.

[0065] Specifically, when the laser processing apparatus 1 of FIG. 1 is used to implement the laser processing method of this embodiment, a pulsed UV laser beam LB is emitted from the light source 2. The laser beam LB passes through the AOM 7, beam splitter 4, galvanometer mirror unit 8, and objective lens 3, irradiating the surface of the wiring substrate S. By irradiating a predetermined location on the wiring substrate S with the laser beam LB, an opening S31 can be formed at that predetermined location. When the laser beam LB irradiates the conductor layer S1, plasma light PL containing light with a wavelength specific to the material constituting the conductor layer S1 is emitted. The plasma light PL passes through the objective lens 3 and galvanometer mirror unit 8 and enters the beam splitter 4. At least the plasma light PL having a wavelength specific to the material constituting the conductor layer S1 is reflected by the beam splitter 4 in the second direction D2, passes through filters 61 and 62, and enters the sensor 6. The sensor 6 outputs a sensor output SO having a level corresponding to, for example, the intensity of the incident light.

[0066] As explained with respect to the laser processing apparatus of the embodiment, the intensity of the plasma light PL changes in accordance with changes in the constituent material of the wiring substrate S irradiated by the laser beam LB, and the sensor output SO also changes. Furthermore, the integrated value of the sensor output SO (integrated sensor output value) calculated by irradiating the same position on the wiring substrate S to be processed with the pulsed laser beam LB multiple times has a specific relationship with the opening area of ​​the bottom surface of the opening S31 formed. To utilize this relationship, the laser processing method of the embodiment further includes calculating the integrated sensor output value.

[0067] That is, forming the opening S31 in the laser processing method of the embodiment includes repeatedly irradiating a single processing position on the wiring substrate S with, for example, a pulsed laser beam LB multiple times. Furthermore, forming the opening S31 in the laser processing method of the embodiment also includes calculating an integrated sensor output value, which is an integrated value of the sensor output SO for each of the multiple irradiations of the laser beam LB from the start of processing at the single processing position. Furthermore, forming the opening S31 in the laser processing method of the embodiment also includes ending the formation of the opening S31 at the single processing position by irradiating the laser beam LB when the integrated sensor output value satisfies a predetermined condition. Because the opening S31 is formed in these steps, it is believed possible to form an opening S31 having a bottom area closer to the desired opening area, as described with respect to the laser processing apparatus of the embodiment.

[0068] In the laser processing method of the embodiment, as one example, when the integrated sensor output value satisfies a predetermined condition, the irradiation of the laser beam LB may be stopped immediately, thereby terminating the formation of the opening S31 at the processing position at that time. As another example, when the integrated sensor output value satisfies a predetermined condition, the irradiation of the laser beam LB may be continued for a predetermined time and then stopped, thereby terminating the formation of the opening S31 at the processing position at that time, so as to reliably form the opening S31 having the desired opening area.

[0069] For example, the "predetermined condition" may be that the integrated sensor output value reaches a predetermined first threshold. That is, the predetermined condition may be satisfied when the integrated sensor output value reaches the predetermined first threshold. The "predetermined first threshold" may be, for example, the integrated sensor output value corresponding to the median of the allowable range for the opening area of ​​the bottom surface of the opening S31. It is believed that by terminating the formation of an opening at the processing position during irradiation with the laser beam LB when the integrated sensor output value reaches the predetermined first threshold, an opening having an area on the bottom surface close to the desired opening area can be formed. In another example, the "predetermined condition" may be that the unit increase rate of the integrated sensor output value is within the range of a predetermined second threshold. In this case, the "predetermined second threshold" may be, for example, 40% or more and 60% or less.

[0070] In the laser processing method of the embodiment, the integrated sensor output value may also be a simple sum of the sensor outputs SO from the start of processing at one processing position. Therefore, calculating the integrated sensor output value in the laser processing method of the embodiment may include calculating the sum of the sensor outputs SO for each of multiple irradiations of the laser beam LB at one processing position from the start of processing at the one processing position.

[0071] Furthermore, the integrated sensor output value may be a total value obtained by adding up the product of the sensor output SO for each of the multiple irradiations of the laser beam LB at one processing position and a unit time corresponding to the irradiation period, for all sensor outputs SO from the start of processing at that one processing position. When multiple irradiations of the laser beam LB are repeated at a fixed period and for a fixed irradiation time per irradiation, the integrated sensor output value may be the sum of the products of the sensor output SO for each irradiation and the irradiation period. Therefore, calculating the integrated sensor output value in the laser processing method of the embodiment may include calculating the product of the irradiation period of the multiple irradiations of the laser beam LB at a fixed period at one processing position and each sensor output SO for each irradiation of the laser beam LB, and then calculating the sum of the products from the start of processing at that one processing position.

[0072] Furthermore, the integrated sensor output value may be a total value obtained by adding up the product of the sensor output SO for each of the multiple irradiations of the laser beam LB at one processing position and the irradiation time of each irradiation, for all sensor outputs SO from the start of processing at that one processing position. Therefore, calculating the integrated sensor output value in the laser processing method of the embodiment may include calculating the sum of the products of the irradiation times of each of the multiple irradiations of the laser beam LB at one processing position and the sensor output SO for each of those irradiation times from the start of processing at that one processing position.

[0073] Furthermore, the integrated sensor output value may be a definite integral of a function with respect to time of the sensor output SO obtained by each of the multiple repeated irradiations of the laser beam LB, as described with respect to the laser processing apparatus of the embodiment. Therefore, calculating the integrated sensor output value in the laser processing method of the embodiment may include deriving a mathematical formula (function) that indicates the relationship between the sensor output SO obtained by each of the multiple irradiations of the laser beam LB and the elapsed time from the start of the multiple irradiations, and calculating a definite integral of the derived mathematical formula up to the time of each irradiation.

[0074] <Understanding the correlation between the sensor output integrated value and the opening area> The laser processing method of the embodiment may further include grasping in advance the correlation between the integrated sensor output value and the opening area of ​​the bottom surface of the opening to be formed, as shown in previously referenced Fig. 8. That is, the laser processing method of the embodiment may include repeatedly irradiating the same position of a wiring board that preferably has the same structure and material as the wiring board to be processed with a test laser beam a plurality of times (Step A), and acquiring the opening area of ​​the bottom surface of the opening to be formed at that same position after each of the plurality of irradiations of the test laser beam (Step B).

[0075] The laser processing method of the embodiment may further include acquiring a reference integrated value by integrating the sensor output for each of the multiple irradiations of the test laser beam at the same position from the start of irradiation of the test laser beam (Step C). The correlation between the reference integrated value up to each irradiation of the multiple irradiations of the test laser beam and the opening area acquired in Step B after each irradiation is considered to directly indicate the correlation between the opening area of ​​the bottom of the opening formed by the laser processing method of the embodiment and the sensor output integrated value.

[0076] Therefore, the laser processing method of the embodiment may further include setting (step D) a "predetermined condition" that is a condition for ending processing at one processing position, based on the correlation between the opening area acquired in step B and the reference integrated value acquired in step C. For example, a "first threshold value" that is a determination index for ending processing at one processing position regarding the sensor output integrated value may be set based on the correlation between the opening area acquired in step B and the reference integrated value.

[0077] The correlation between the reference integrated value and the opening area of ​​the opening to be formed may be grasped using the laser processing apparatus 1 of the embodiment shown in Fig. 1. Preferably, the test laser beam used has substantially the same processability for the insulating layer of the wiring board to be processed, such as the wiring board S, as the laser beam used to process the wiring board in the laser processing method of the embodiment.

[0078] As described above, the laser processing apparatus and method of the embodiment use the integrated sensor output value to determine when processing is complete, which is believed to enable the formation of an opening with a bottom area closer to the desired opening area than conventional laser processing apparatuses and methods. Furthermore, damage to the conductor layer caused by excessive laser beam irradiation is believed to be reduced. For example, penetration of the conductor layer due to excessive laser beam irradiation is believed to be prevented.

[0079] As wiring patterns on wiring boards become increasingly finer, smaller diameter via conductors are required. Small diameter via conductors require smaller diameter openings, and the use of a short-wavelength, short-pulse laser beam is sometimes preferable for forming small diameter openings. However, because short-wavelength, short-pulse laser beams are highly effective at processing copper, excessive and continuous laser beam irradiation can easily cause excessive damage to the conductor layer. In contrast, in the laser processing apparatus and laser processing method of the embodiment, a sensor output integrated value having a specific relationship with the opening area of ​​the opening to be formed is used to determine the end of processing to form the opening. Therefore, it is believed that irradiation with a laser beam that is neither too strong nor too weak can be achieved. In other words, it is believed that excessive damage to the conductor layer is unlikely to occur. Therefore, the laser processing apparatus and laser processing method of the embodiment may be particularly suitable for forming small diameter via conductors and for manufacturing wiring boards with fine wiring patterns.

[0080] The laser processing apparatus of the embodiment is not limited to one having the structure exemplified in Fig. 1 and the structure exemplified in this specification. For example, the functions of the filters 61 and 62 may be provided in the beam splitter 4 or the sensor 6. Furthermore, the laser processing apparatus of the embodiment may have any components other than the components shown in Fig. 1. Furthermore, the laser processing method of the embodiment is not limited to the method described with reference to Fig. 1. Any steps may be added to the laser processing method of the embodiment in addition to the steps described above, and some of the steps described above may be omitted. [Explanation of symbols]

[0081] 1. Laser processing equipment 2 light source 3 Objective Lenses 4 Beam splitter 5 Controller 51 Arithmetic section 6 sensors 61 Filter (Band-stop filter) LB laser beam LP optical path PL Plasma Light SO Sensor output S wiring board S1 Conductor layer S2 insulating layer S31 opening

Claims

1. 1. A laser processing apparatus for forming an opening in an insulating layer of a wiring board to expose a part of a conductor layer covered by the insulating layer, a light source that emits a laser beam; an objective lens that focuses the laser beam on the surface of a wiring substrate; a controller for controlling the irradiation of the laser beam; a sensor that outputs a sensor output based on plasma light emitted from the wiring substrate by irradiation with the laser beam to the controller; Equipped with The controller Calculating an integrated value of the sensor output from the start of processing at one processing position of the wiring board for each of a plurality of irradiations of the laser beam at the one processing position, and When the integrated value satisfies a predetermined condition, the formation of the opening at the one processing position by irradiating the laser beam is terminated.

2. The laser processing apparatus according to claim 1, The controller is configured to terminate the formation of the opening at the one processing position by irradiating the laser beam when the integrated value reaches a predetermined first threshold value.

3. 2. A laser processing apparatus according to claim 1, wherein the controller is configured to calculate, as the integrated value, the sum of the sensor output from the start of processing for each of multiple irradiations of the laser beam to the one processing position.

4. A laser processing apparatus according to claim 1, wherein the controller is configured to calculate, as the integrated value, the sum of the product of the irradiation time of each of the laser beams applied to the processing position multiple times and the sensor output during each of the irradiation times from the start of the processing.

5. The laser processing apparatus according to claim 1, further comprising: a beam splitter that transmits the laser beam and reflects the plasma light emitted from the wiring substrate so as to deviate from the optical path of the laser beam; a filter having a stop band that includes the wavelength of the laser beam; Equipped with the beam splitter is disposed in the optical path between the light source and the objective lens; The filter is disposed between the beam splitter and the sensor.

6. A laser processing method for a wiring board, the laser processing method comprising: forming an opening in an insulating layer of the wiring board by irradiating a surface of the wiring board with a laser beam, the opening exposing a part of a conductor layer covered by the insulating layer; Plasma light emitted from the wiring substrate by irradiation with the laser beam is incident on a sensor, and the sensor outputs a sensor output based on the plasma light; Including, forming the opening Repeating the irradiation of the laser beam to one processing position of the wiring substrate a plurality of times; calculating an integrated value of the sensor output for each of a plurality of irradiations of the laser beam from the start of processing at the one processing position; When the integrated value satisfies a predetermined condition, the formation of the opening at the one processing position by irradiating the laser beam is terminated.

7. 7. A laser processing method according to claim 6, wherein the predetermined condition is satisfied when the integrated value reaches a predetermined first threshold value.

8. A laser processing method according to claim 6, wherein calculating the integrated value includes calculating the sum of the sensor output for each of a plurality of irradiations of the laser beam at the one processing position from the start of processing.

9. A laser processing method according to claim 6, wherein calculating the integrated value includes calculating the sum of the product of the irradiation time of each of the laser beams applied to the one processing position multiple times and the sensor output for each of the irradiation times from the start of processing.

10. The laser processing method according to claim 6, further comprising: Repeating irradiation of the test laser beam to the same position on the wiring board multiple times; acquiring an opening area of ​​the opening formed at the same position after each of a plurality of irradiations of the test laser beam; acquiring a reference integrated value by integrating the sensor output for each of a plurality of irradiations of the test laser beam at the same position from the start of irradiation of the test laser beam; setting the predetermined condition based on a correlation between the opening area and the reference integrated value; Contains:

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