Laser processing apparatus and laser processing method

Abstract

To form an opening close to a desired state 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 conditions of 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 irradiation with the laser beam LB to the controller 5. The controller 5 is configured to reduce the processability of the laser beam LB and continue the irradiation of the laser beam LB when recognizing the change in the irradiation part by the laser beam LB from the sensor output SO.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 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 diameter. [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 irradiation conditions of the laser beam, and a sensor for outputting a sensor output based on plasma light emitted from the wiring board by irradiation with the laser beam to the controller. The controller is configured to reduce the processing ability of the laser beam and continue the irradiation when it recognizes a change in the irradiation area by the laser beam from the sensor output.

[0006] A laser processing method of the present invention is a laser processing method for a wiring board, the laser processing method including: irradiating a surface of the wiring board with a laser beam to form an opening in an insulating layer of the wiring board to expose a part of a conductor layer covered by the insulating layer; and causing plasma light emitted from the wiring board by the irradiation of the laser beam to be incident on a sensor, thereby causing the sensor to output a sensor output based on the plasma light. The forming of the opening includes, when a change in the irradiated area by the laser beam is recognized from the sensor output, reducing the processability of the laser beam and continuing the irradiation of the laser beam.

[0007] According to the embodiment of the present invention, it is believed that an opening closer to the desired state can be formed in the insulating layer of the wiring board while minimizing damage to the underlying conductor layer. [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. 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, 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 conditions 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 using 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 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 may 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 be simply referred to as the "integrated sensor output value" below. Note that 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. Alternatively, the integrated sensor output value may be a total value obtained by adding up the product of the sensor output SO for each of multiple irradiations at that one processing position and a unit time corresponding to the irradiation period, for all sensor outputs at that one processing position from the start of processing.

[0027] The integrated sensor output value may also be a definite integral of a function with respect to time of the sensor output SO obtained by each of the repeated irradiations of the pulsed laser beam LB. That is, the relationship between the sensor output SO obtained by each of the repeated irradiations of the pulsed laser beam LB (see FIGS. 6A to 6D) and the elapsed time from the start of irradiation is approximated by a function of an appropriate order. Furthermore, a definite integral of the function with respect to the elapsed time until each of the repeated irradiations of the pulsed laser beam LB is calculated. Then, each of the definite integrals may be used as the integrated sensor output value up to each of the repeated irradiations to form the aperture S31 by the laser beam LB.

[0028] One function of the determination unit 53 is to compare the calculation result of the calculation unit 51 with a predetermined threshold stored in the memory unit 52 to determine whether or not there has been a change in the location irradiated with the laser beam LB. 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. Based on the determination result of the determination unit 53, the irradiation start / stop control unit 54 sends a signal to control the start and stop of emission of the laser beam LB from 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 a signal to control the energy density and power of the laser beam LB emitted by the light source 2. When the laser beam LB is emitted in pulses, the irradiation condition control unit 55 may output a signal to control the irradiation period and pulse width based on the determination result of the determination unit 53. Furthermore, the irradiation condition control unit 55 may output a signal 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. Based on the judgment result of the judgment 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.

[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 a "predetermined first threshold value" (described later) for the sensor output SO. The storage unit 52 may also store a "predetermined second threshold value" and a "predetermined third threshold value" (described later) for the sensor output integrated 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] Based on the sensor output SO, the controller 5 controls the stopping of irradiation of the wiring board S with the laser beam LB, the irradiation conditions of the laser beam LB, the irradiation position of the laser beam LB, etc. 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.

[0033] In the laser processing apparatus 1 of the embodiment, the controller 5 is configured to recognize a change in the area irradiated by the laser beam LB on the wiring board S, which is the processing target, from the sensor output SO. The controller 5 is further configured, upon recognizing a change in the area irradiated by the laser beam LB, to reduce the processing ability of the laser beam LB and continue the irradiation of the laser beam LB onto the wiring board S. For example, a program built into a microcomputer or the like constituting the controller 5 may include a command to cause the controller 5 to reduce the processing ability of the laser beam LB and continue the irradiation when the controller 5 recognizes a change in the area irradiated by the laser beam LB from the sensor output SO.

[0034] In the following explanation, the statement that "controller 5 is configured (to perform a specific process)" includes the gist 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] As an example of a means for reducing the processability of the laser beam LB, the controller 5 is configured to reduce the processability of the laser beam LB by reducing the energy density of the laser beam LB. It is believed that reducing the energy density can easily reduce the processability of the laser beam LB. However, the processability of the laser beam LB is not limited to reducing the energy density, and may be reduced by any means capable of reducing the rate at which the opening S31 is made larger or deeper. For example, the processability of the laser beam LB may be reduced by narrowing the pulse width of the laser beam LB.

[0036] In the laser processing device of the embodiment, when a change in the area irradiated by the laser beam LB is recognized, the laser beam LB's processability is reduced and irradiation continues, rather than immediately stopping irradiation when a change in the spectrum of plasma light or when a predetermined number of irradiations of laser light is reached as in Patent Document 1. Therefore, compared to conventional drilling methods such as Patent Document 1, it may be possible to form an opening S31 that is closer to the desired state, for example, in terms of the opening diameter, while minimizing damage to the conductor layer S1.

[0037] <Changes in the irradiated area> 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] That is, the intensity of the plasma light PL increases as the irradiated area transitions from insulating layer S2 to conductor layer S1. Furthermore, the amount of wavelength components specific to the constituent material of 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. Then, the level and frequency of sensor output SO change according to the photoelectric conversion characteristics of sensor 6. Therefore, controller 5 can recognize the change in the irradiated area by laser beam LB.

[0042] Therefore, in one embodiment, controller 5 may be configured to recognize a change in the location irradiated by laser beam LB from a change in the level of sensor output SO corresponding to a change in the intensity of plasma light PL. For example, controller 5 may compare sensor output SO with a predetermined first threshold in determination unit 53, and recognize a change in the location irradiated by laser beam LB from a comparison result that sensor output SO is equal to or greater than the predetermined first threshold. As one example, the first threshold may be a value between 10% and 20% of the maximum value of sensor output SO obtained when laser beam LB is irradiating conductor layer S1.

[0043] Furthermore, the "integrated sensor output value" calculated by irradiating the same location on the wiring substrate S to be processed with the pulsed laser beam LB multiple times is considered to correlate with the progress of the formation of the opening S31 after each irradiation with the pulsed laser beam LB. Therefore, the controller 5 may be configured to recognize a change in the location irradiated with the laser beam LB when the integrated sensor output value satisfies a predetermined condition. For example, the "predetermined condition" may be that the rate of increase in the integrated sensor output value after a single irradiation with the laser beam LB is equal to or greater than a predetermined second threshold. In this case, the "predetermined condition" may be, for example, an increase rate of 40% or more and 60% or less. Alternatively, the "predetermined condition" may be that the integrated sensor output value reaches a predetermined second threshold. In this case, the "predetermined second threshold" is set based on the results of, for example, confirming in advance the correlation between the integrated sensor output value and the progress of the formation of the opening S31.

[0044] Furthermore, since the integrated sensor output value is considered to have a correlation with the progress of the formation of the opening S31, the controller 5 may be further configured to terminate processing at each processing position (one processing position) currently being processed when the integrated sensor output value reaches a predetermined third threshold. The "predetermined third threshold" is set, for example, from the results of confirming in advance the correlation between the integrated sensor output value and the progress of the opening S31. By terminating processing at each processing position when the integrated sensor output value reaches the predetermined third threshold, it may be possible to form an opening close to the desired state.

[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. 2The test was performed by irradiating the workpiece with a pulsed laser beam. The pulse width of the laser beam was 10 nsec, and the pulse frequency was 200 kHz. The test results shown in Figures 6A to 7D were performed by disabling the function of controller 5 (see Figure 1), which reduces the workability of the workpiece when it detects changes in the irradiated area due to the laser beam.

[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 portion of conductor layer S1 is exposed at the bottom of opening S31 that reaches conductor layer S1 than 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 materials that make up conductor layer S1, so the results shown in Fig. 6C show 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 may be difficult to understand, an opening S31 having a larger diameter than the opening S31 of FIG. 7C is formed, as will be described later. The conductor layer S1 is exposed at the bottom surface of the opening S31 with this larger diameter. Therefore, the results shown in FIG. 6D show a sensor output that is even greater than that of 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 aperture S31, the images of which are shown in Figures 7A to 7D, the aperture diameter at the bottom of each aperture S31 was measured using the measurement function of the observation device. The aperture diameters at the bottom of aperture S31 shown in Figures 7A, 7B, 7C, and 7D were 0 μm, approximately 4.2 μm, approximately 6.4 μm, and approximately 7.0 μm, respectively. The results of the investigation shown in Figures 6A to 6D and 7A to 7D indicate that by continuing to irradiate the laser beam even when the laser beam irradiation location on the wiring board to be processed changes from an insulating layer to a conductive layer, an aperture with a larger aperture diameter at the bottom can be formed. As a result, it may be possible to form an aperture that is closer to the desired state.

[0054] <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.

[0055] 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.

[0056] Specifically, when the laser processing apparatus 1 of FIG. 1 is used, in 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, the beam splitter 4, the galvanometer mirror unit 8, and the objective lens 3, and irradiates the surface of the wiring substrate S. 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 the 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.

[0057] An opening S31 can be formed at a predetermined location on the wiring substrate S by irradiating the laser beam LB to the predetermined location. In the laser processing method of the embodiment, forming the opening S31 includes continuing the irradiation of the laser beam LB while reducing the processing ability of the laser beam LB when a change in the location irradiated by the laser beam LB is recognized from the sensor output SO.

[0058] In the laser processing method of the embodiment, reducing the processability of the laser beam LB may include reducing the energy density of the laser beam LB. It is considered that reducing the energy density can easily reduce the processability of the laser beam LB. Furthermore, in the laser processing method of the embodiment, reducing the processability of the laser beam LB may include narrowing the pulse width of the laser beam LB emitted in pulses from the light source 2. In the laser processing method of the embodiment, the processability of the laser beam LB may be reduced by any method, not limited to the energy density or pulse width.

[0059] As described above with respect to the laser processing apparatus of the embodiment, the intensity of the plasma light PL changes in response to changes in the constituent material of the wiring substrate S irradiated by the laser beam LB, and the sensor output SO also changes. Therefore, from the sensor output SO, a change in the irradiated area by the laser beam LB from the insulating layer S2 to the conductor layer S1 can be recognized using, for example, the controller 5 shown in FIG. 1 . Therefore, in the laser processing method of the embodiment, a change in the irradiated area by the laser beam LB may be recognized from a change in the level of the sensor output SO in response to a change in the intensity of the plasma light PL. For example, the sensor output SO may be compared with a predetermined first threshold, and a change in the irradiated area by the laser beam LB may be recognized when the sensor output SO is equal to or exceeds the predetermined first threshold. As an example, the first threshold may be a value between 10% and 20% of the maximum value of the sensor output SO obtained when the laser beam LB irradiates the conductor layer S1.

[0060] As explained with respect to the laser processing apparatus of the embodiment, 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 is considered to have a correlation with the progress state of the formation of the opening S31. To be able to utilize this correlation, the laser processing method of the embodiment may further include calculating the integrated sensor output value.

[0061] That is, the laser processing method of the embodiment may include repeatedly irradiating a single processing position on the wiring substrate S with a pulsed laser beam LB multiple times. Furthermore, the laser processing method of the embodiment may include 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. In the laser processing method of the embodiment, a change in the irradiated portion by the laser beam LB may be recognized when the integrated sensor output value satisfies a predetermined condition. For example, the "predetermined condition" may be that the rate of increase in the integrated sensor output value due to a single irradiation of the laser beam LB is equal to or greater than a predetermined second threshold. Alternatively, the "predetermined condition" may be that the integrated sensor output value reaches a predetermined second threshold.

[0062] 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. Alternatively, the integrated sensor output value may be a total value obtained by adding up the product of the sensor output SO for each of multiple irradiations of one processing position and a unit time corresponding to the irradiation period, for all sensor outputs from the start of processing at that one processing position. Furthermore, as described with respect to the laser processing apparatus of the embodiment, the integrated sensor output value may be a definite integral of the time function of the sensor output SO obtained by each of multiple repeated irradiations of the pulsed laser beam LB.

[0063] Furthermore, since the integrated sensor output value is considered to have a correlation with the progress of the formation of the opening S31, in the laser processing method of the embodiment, when the integrated sensor output value reaches a predetermined third threshold, processing at the processing position currently being processed (one processing position) may be terminated. By terminating processing at each processing position when the integrated sensor output value reaches the predetermined third threshold, it may be possible to form an opening close to the desired state at each processing position.

[0064] As explained above, in the laser processing apparatus and laser processing method of the embodiment, the laser beam continues to be irradiated even after a change in the irradiated area by the laser beam is recognized. Therefore, it is considered possible to form an opening that is closer to the desired state than in conventional laser processing apparatuses and methods that stop irradiation when a change in the irradiated area by the laser beam is detected.

[0065] Furthermore, in the laser processing apparatus and laser processing method of the embodiment, when a change in the irradiated area by the laser beam is recognized, the processability of the laser beam is reduced and irradiation is continued. Therefore, by continuing to process the insulating layer, the formed opening can be made closer to the desired state, while damage to the conductor layer due to continued irradiation can be suppressed by reducing the processability of the laser beam. Therefore, it is thought that penetration of the conductor layer due to continued irradiation after the irradiated area by the laser beam has changed from the insulating layer to the conductor layer can be prevented.

[0066] 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 may be preferable for forming small diameter openings. However, because short-wavelength, short-pulse laser beams have high processability for copper, continuing to irradiate the laser beam while maintaining processability after the laser beam irradiated portion has changed into a conductor layer is likely to cause excessive damage to the conductor layer. In contrast, with the laser processing apparatus and laser processing method of the embodiment, once the change in the irradiated portion due to the laser beam is detected, irradiation is continued with a laser beam with reduced processability. 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.

[0067] 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]

[0068] 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 conditions 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 is configured to, when recognizing a change in the area irradiated with the laser beam from the sensor output, reduce the processability of the laser beam and continue the irradiation.

2. The laser processing apparatus according to claim 1, The controller is configured to recognize the change in the irradiated area from a change in the level of the sensor output in response to a change in the intensity of the plasma light.

3. The laser processing apparatus according to claim 1, the controller has a calculation unit that calculates an integrated value of the sensor output from the start of processing at one processing position on the wiring board for each of a plurality of irradiations of the laser beam at the one processing position, The controller is configured to recognize a change in the irradiated area when the integrated value satisfies a predetermined condition.

4. 2. The laser processing apparatus according to claim 1, wherein the controller is configured to reduce the processing efficiency by lowering the energy density of the laser beam.

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 includes, when a change in the area irradiated with the laser beam is recognized from the sensor output, reducing the processability of the laser beam and continuing the irradiation of the laser beam.

7. In a laser processing method according to a sixth aspect of the present invention, the step of reducing the processability includes reducing the energy density of the laser beam.

8. 7. A laser processing method according to claim 6, wherein the change in the irradiated portion is recognized from a change in the level of the sensor output in response to a change in the intensity of the plasma light.

9. The laser processing method according to claim 6, further comprising: 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 the plurality of irradiations of the laser beam from the start of processing at the one processing position; The change in the irradiated area is recognized when the integrated value satisfies a predetermined condition.

Images