Laser processing apparatus and laser processing method

Abstract

To prevent insufficient processing of an interlayer insulating layer and over-processing of a conductor layer, when performing boring processing on the interlayer insulating layer using a laser beam.SOLUTION: A laser processing apparatus that performs boring processing by emitting a laser beam to an interlayer insulating layer of a build-up layer in which the resin-based interlayer insulating layer and a metal-based conductor layer are laminated, comprises: an AOM 2 which transmits or blocks the laser beam emitted from a laser light source 1; a beam scanning mechanism 6 which deflects the laser beam to scan a boring processing position; an Fθ lens 7 which makes the deflected laser beam perpendicularly incident on the surface of the interlayer insulating layer and focuses it; a bandpass filter 9 which transmits plasma light in a predetermined wavelength in the plasma light generated by the focused laser beam; a light sensor 10 which outputs an electric signal with intensity corresponding to the received intensity of the plasma light in the predetermined wavelength; and a processing control device 12 which causes the transmission and blocking of the laser beam and scanning of the boring processing position by the laser beam to be performed on the basis of the changes in the output signal intensity.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a laser processing apparatus and a laser processing method for performing hole drilling of via holes by irradiating an insulating layer of a printed wiring board with a laser beam.

Background Art

[0002] In recent years, in the technical field of printed wiring boards, for the purpose of high density of electronic circuits, for example, a single-layer or a plurality of build-up layers are laminated on a core substrate formed by laminating a conductor layer made of copper or the like on one or both sides of a base insulating layer made of resin or the like, and a multilayer printed wiring board is formed.

[0003] The build-up layer is formed by alternately laminating, for example, an interlayer insulating layer made of resin or the like and a conductor layer made of copper or the like. And via holes penetrating the interlayer insulating layer are formed in the build-up layer, and the conductor layer of the core substrate and the conductor layer of the build-up layer and the conductor layers of the plurality of build-up layers are electrically connected by via hole conductors provided in the via holes.

[0004] Since the via holes, which are through holes for via hole conductors, are extremely small in diameter and numerous, a laser processing apparatus is usually used for drilling the via holes in the interlayer insulating layer of the build-up layer of the printed wiring board. As such a laser processing apparatus, conventionally, for example, the one described in Patent Document 1 is known.

[0005] In this laser processing apparatus, an AOD (acousto-optic deflector) and a galvanometer mirror deflect a laser beam emitted from a laser light source, and an Fθ lens makes the deflected laser beam perpendicularly incident on the surface of the interlayer insulating layer and converge at the incident position. When performing hole drilling of a large number of via holes with the laser beam, the incident position is gradually moved by the above deflection to scan the hole drilling position. When the hole drilling positions are far apart, the printed wiring board is horizontally moved largely by an X-Y table that horizontally supports the printed wiring board.

[0006] In this laser processing apparatus, a dichroic beam splitter is disposed on the optical path of the laser beam, and the laser beam transmitted through the dichroic beam splitter is used to drill via holes in the interlayer insulating layer. When plasma light such as copper is generated from the conductor layer under the interlayer insulating layer due to the drilling process, the plasma light returns along the optical path of the laser beam and is reflected laterally from the optical path of the laser beam by the dichroic beam splitter. A photosensor for receiving the plasma light such as copper is provided on the side of the dichroic beam splitter, and the photosensor outputs an electrical signal to the processing control means according to the received light amount. Based on the change in this electrical signal, the processing control means controls the operations of the AOD, the galvanometer mirror, and the X-Y table to start and stop the emission of the laser beam, scan the drilling position of the interlayer insulating layer with the laser beam, and move the incident position of the laser beam.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, in the above conventional laser processing apparatus, since a dichroic beam splitter is disposed on the optical path of the laser beam, the following problems exist. (1) Since the laser beam on the optical path is partially reflected and partially absorbed by the dichroic beam splitter, the intensity of the laser beam irradiated on the interlayer insulating layer of the printed wiring board decreases. (2) Since the laser beam on the optical path is powerful, the need for maintenance and replacement of the dichroic beam splitter arises due to optical degradation. (3) A dichroic beam splitter is required such that the wavelength of the laser beam is mostly transmitted and the wavelength of the plasma light is mostly reflected. When these wavelengths are close to each other, the transmission wavelength band and the reflection wavelength band cannot be completely separated, and the wavelength of the laser beam is also strongly reflected. For this reason, the strong reflected light of the laser beam from the printed wiring board also enters the optical sensor, which may cause a decrease in the S / N ratio of the optical sensor output signal or damage to the optical sensor.

Means for Solving the Problem

[0009] A laser processing apparatus of the present invention, which aims to solve the problems of the above-mentioned conventional laser processing apparatus, irradiates a laser beam onto a build-up layer in which a resin-made interlayer insulation layer and a conductor layer made of a metal such as copper constituting a printed wiring board are laminated to perform hole drilling processing of via holes, and has the following configuration.

[0010] That is, the laser processing apparatus of the present invention includes a laser light source that emits a laser beam, beam control means that passes or blocks the laser beam emitted from the laser light source, beam scanning means that deflects the laser beam that has passed through the beam control means to scan the hole opening processing position of the interlayer insulation layer, and an Fθ lens that vertically incident the laser beam deflected by the beam scanning means on the surface of the interlayer insulation layer and converges it at the incident position.

[0011] Further, the laser processing apparatus of the present invention includes one or more band-pass filters arranged in the vicinity of the Fθ lens, which transmit plasma light of a specific wavelength corresponding to a metal such as copper that forms the conductor layer among the plasma light generated by the hole drilling processing of the interlayer insulation layer by the laser beam converged by the Fθ lens, and an optical sensor that is paired with the band-pass filter, receives the plasma light of the specific wavelength that has passed through the band-pass filter, and outputs an electrical signal having an intensity corresponding to the received light intensity.

[0012] Furthermore, the laser processing apparatus of the present invention includes processing control means for causing the beam control means to pass or block the laser beam and causing the beam scanning means to scan the hole drilling position of the interlayer insulating layer by deflecting the laser beam based on a change in the output signal intensity of the optical sensor.

[0013] Moreover, the laser processing method of the present invention, which aims to solve the problems of the processing method in the above conventional laser processing apparatus, is a method of irradiating a laser beam onto a build-up layer in which a resin interlayer insulating layer and a conductor layer made of a metal such as copper constituting a printed wiring board are laminated to perform hole drilling, and includes the following steps.

[0014] That is, the laser processing method of the present invention includes a step of a laser light source emitting a laser beam, a step of the beam control means passing or blocking the laser beam emitted from the laser light source, a step of the beam scanning means deflecting the laser beam that has passed through the beam control means to scan the hole drilling position of the interlayer insulating layer, and a step of causing the laser beam deflected by the beam scanning means to be incident perpendicularly to the surface of the interlayer insulating layer by an Fθ lens and converging it at the incident position.

[0015] Furthermore, the laser processing method of the present invention includes a step of allowing plasma light of a specific wavelength corresponding to a metal such as copper forming the conductor layer among the plasma light generated by the hole drilling of the interlayer insulating layer by the laser beam converged by the Fθ lens to pass through a band-pass filter disposed near the Fθ lens, and a step of receiving the plasma light of the specific wavelength that has passed through the band-pass filter with an optical sensor and outputting an electrical signal having an intensity corresponding to the received intensity of the plasma light of the specific wavelength from the optical sensor.

[0016] Furthermore, in the laser processing method of the present invention, based on the change in the output signal intensity of the optical sensor, the processing control means causes the beam control means to pass and block the laser beam and the beam scanning means to scan the hole drilling position of the interlayer insulating layer by deflecting the laser beam.

Advantages of the Invention

[0017] In the laser processing apparatus and the laser processing method of the present invention, for example, a laser beam of a short-pulse UV laser emitted from a laser light source is passed or blocked by a beam control means having, for example, an acousto-optic modulator (AOM), and the laser beam that has passed through the beam control means is deflected by a beam scanning means having, for example, an acousto-optic deflector (AOD) and / or a galvanometer mirror to scan the hole drilling position of the interlayer insulating layer. During the scanning, the Fθ lens makes the laser beam deflected by the beam scanning means perpendicularly incident on the interlayer resin layer and converge at the incident position. As a result, the laser beam drills a large number of via holes penetrating the interlayer resin layer. Then, among the plasma light generated during the hole drilling of the interlayer insulating layer by the laser beam converged by the Fθ lens, the plasma light of a specific wavelength corresponding to a metal such as copper constituting the conductor layer is selectively transmitted by a band-pass filter disposed near the Fθ lens. When the beam scanning means has an AOD, the beam control means may use the AOD of the beam scanning means in combination instead of having an AOM, and pass or block the laser beam by deflection by the AOD.

[0018] Furthermore, in the laser processing apparatus and the laser processing method of the present invention, the optical sensor receives the plasma light of a specific wavelength selectively transmitted by the band-pass filter and outputs an electrical signal having an intensity corresponding to the received intensity. Then, based on the change in the output signal intensity of the optical sensor, the processing control means causes the beam control means to pass and block the laser beam and the beam scanning means to scan the hole drilling position of the interlayer insulating layer by deflecting the laser beam.

[0019] Therefore, according to the laser processing apparatus and the laser processing method of the present invention, since the basic optical path of the laser processing apparatus is not changed, there are no adverse effects on processing and wavelength restrictions as in the prior art. Therefore, the following effects can be obtained. (1) Since there is no dichroic beam splitter on the optical path of the laser beam, the intensity of the laser beam irradiated on the interlayer insulating layer of the printed wiring board does not decrease. (2) Since there is no dichroic beam splitter on the optical path of the laser beam, there is no need for maintenance or replacement of the dichroic beam splitter due to optical degradation. (3) The band-pass filter blocks the strong reflected light of the laser beam and selectively transmits only the plasma light emitted from the printed wiring board and having a specific wavelength corresponding to a metal such as copper constituting the conductor layer. Since the optical sensor receives the plasma light of the specific wavelength, it is possible to prevent a decrease in the S / N ratio of the sensor output signal and damage to the optical sensor.

[0020] The laser processing apparatus of the present invention may further include a printed wiring board moving means for supporting the printed wiring board and moving it parallel to the surface of the printed wiring board to relatively move the incident position of the laser beam from the Fθ lens with respect to the printed wiring board. Thereby, in the region where via holes are dense, the incident position of the laser beam is gradually moved by deflection by the beam scanning means, while in the region where there are no via holes, the incident position of the laser beam can be moved more greatly than by the beam scanning means by moving the printed wiring board by the printed wiring board moving means. Therefore, a high positional accuracy and a high moving speed of the incident position of the laser beam can be obtained over a wide range of the printed wiring board.

[0021] In addition, in the laser processing apparatus of the present invention, the laser light source emits a short-pulse UV laser beam, and the processing control means counts the number of signals from the optical sensor having an intensity exceeding a specified intensity, and when the number of signals exceeding the specified intensity reaches a specified number, the beam control means may block the short-pulse UV laser beam. Here, as the specified intensity, a signal intensity indicating that copper plasma from the conductor layer exposed in the via hole formed in the interlayer insulating layer is received is set. Further, as the specified number, the number of signals exceeding the specified intensity indicating that the number of pulses of the laser beam required to secure the bottom diameter of the via hole has been reached is set.

[0022] Accordingly, it is possible to know that a via hole has been formed from the signal exceeding the specified intensity, and it is possible to know that the bottom diameter of the via hole has been secured from the reaching of the number of signals exceeding the specified intensity to the specified number. Therefore, by blocking the short-pulse UV laser beam by the beam control means when the number of signals exceeding the specified intensity reaches the specified number and stopping the incidence of the laser beam on the interlayer insulating layer, it is possible to prevent insufficient processing of the interlayer insulating layer and excessive processing of the conductor layer.

Brief Description of the Drawings

[0023]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0024] Hereinafter, embodiments of a laser processing apparatus and a laser processing method according to the present invention will be described with reference to the drawings. FIG. 1 is an explanatory diagram showing the configuration of an embodiment of the laser processing apparatus of the present invention, and FIG. 2 is an explanatory diagram showing a laser processing method according to an embodiment of the present invention by the laser processing apparatus of that embodiment.

[0025] The laser processing apparatus of this embodiment shown in FIG. 1 irradiates a laser beam onto a build-up layer in which a resin interlayer insulating layer and a copper conductor layer constituting a printed wiring board are laminated, and drills a via hole penetrating the interlayer insulating layer. Here, the build-up layer may be laminated on a core substrate to constitute a printed wiring board, or may constitute a printed wiring board alone without a core substrate.

[0026] The laser processing apparatus of this embodiment includes a short-pulse laser oscillator 1 as a laser light source that emits a short-pulse laser beam B, and a pulse control mechanism 2 as beam control means for passing or blocking the laser beam B emitted from the laser oscillator 1. The short-pulse laser oscillator 1 is a normal laser oscillator that emits a laser beam B of a short-pulse UV laser of the third harmonic (wavelength 355 nm) of, for example, a UV-YAG (yttrium aluminum garnet) laser. The pulse control mechanism 2 is a normal acousto-optic modulator (AOM) that passes or blocks the laser beam B by deflecting the laser beam B at high speed within a predetermined plane at an angle corresponding to the frequency of the input ultrasonic wave.

[0027] The laser processing apparatus of this embodiment also includes, for example, a beam shaper 3, a mask 4, and a mirror 5. The beam shaper 3 deforms the cross-sectional shape of the laser beam B that has passed through the pulse control mechanism 2 into, for example, a rectangular shape suitable for drilling. The mask 4 narrows the laser beam B to a predetermined thickness, and the mirror 5 changes the optical path direction of the narrowed laser beam B and directs it toward a beam scanning mechanism 6 described later. Any one or more of the beam shaper 3, the mask 4, and the mirror 5 can be omitted if not necessary in the optical path configuration.

[0028] The laser processing apparatus of this embodiment further includes a beam scanning mechanism 6 as beam scanning means for deflecting the laser beam B whose optical path direction has been changed by the mirror 5 to scan the hole drilling position of the interlayer insulating layer, an Fθ lens 7, and an X-Y table 8 as printed wiring board moving means. The beam scanning mechanism 6 has both an acousto-optic deflector (AOD) and a galvanometer mirror in the illustrated example. The AOD slightly deflects the laser beam B within two predetermined planes orthogonal to each other by an acousto-optic configuration similar to that of the AOM of the pulse control mechanism 2. Further, in this embodiment, the galvanometer mirror sequentially reflects the laser beam B slightly deflected by the AOD with two mirrors facing each other and rotated around two axes orthogonal to each other by motors, respectively, to deflect it more greatly than the AOD in the X-Y direction. Note that the beam scanning mechanism 6 may have only either the AOD or the galvanometer mirror depending on, for example, the size of the hole drilling region of the interlayer insulating layer.

[0029] The Fθ lens 7 makes the laser beam deflected by the beam scanning mechanism 6 perpendicularly incident on the surface of the interlayer insulating layer of the printed wiring board W horizontally supported by the X-Y table 8 and converge at the incident position. The X-Y table 8 sucks and horizontally supports, for example, a disk-shaped wafer that constitutes a plurality of printed wiring boards W by negative pressure, and moves the wafer and thus the printed wiring board W in the X-Y direction, which is a horizontal direction parallel to and orthogonal to each other on the surface of the printed wiring board, by a motor-driven moving mechanism. Thereby, the incident position of the laser beam B from the Fθ lens 7 can be moved more greatly relative to the interlayer insulating layer on the surface of the interlayer insulating layer of the printed wiring board W than the deflection by the beam scanning mechanism 6. Note that the X-Y table 8 may, for example, support the printed wiring board W at a fixed position, and horizontally move, in the X-Y direction, the optical configuration from, for example, the mirror 5 to the Fθ lens 7 together with the pair of the band-pass filter 9 and the optical sensor 10 by a motor-driven moving mechanism.

[0030] The laser processing apparatus of this embodiment further includes a pair of one or more, in the illustrated example, a plurality of band-pass filters 9 and optical sensors 10 disposed in the vicinity around the Fθ lens 7, a signal synthesizer 11, and a processing control device 12 as processing control means.

[0031] The band-pass filter 9 selectively transmits, as light of a specific wavelength among the plasma light generated during the via hole machining of the interlayer insulating layer of the printed wiring board W by the laser beam converged by the Fθ lens 7, for example, the plasma light of copper as the metal forming the conductor layer at the bottom of the via. There are a plurality of peaks in the emission spectrum of the plasma light of copper, such as around 325 nm, around 295 nm, and around 280 nm. The band-pass filter 9 preferably transmits plasma light of, for example, 320 to 330 nm and absorbs or reflects the rest. In addition, when a metal film such as nickel or gold other than copper is provided on the surface of the copper pad formed by the conductor layer at the bottom of the via for improving the connectivity of the via hole conductor or the like, the light of a specific wavelength may include the plasma light of the metal other than copper.

[0032] The optical sensor 10 receives the plasma light of copper transmitted through the band-pass filter 9 and outputs an electrical signal RS having an intensity corresponding to the received intensity. It is desirable that the pair of the band-pass filter 9 and the optical sensor 10 is arranged so as not to interfere with the laser beam B and the optical axis has an angle as large as possible with respect to the surface of the printed wiring board W. For example, it is located at a position where the laser beam B does not directly hit, around the Fθ lens or under the Fθ lens.

[0033] When the light receiving area is small, a plurality of pairs of the band-pass filter 9 and the optical sensor 10 are preferable. When the light receiving area is large, one pair may be sufficient. The size, number, and arrangement are selected so that the conductor layer exposed at the bottom of the via can be detected with high sensitivity. When a plurality of optical sensors 10 are installed, the signal synthesizer 11 outputs a synthesized electrical signal RSC obtained by synthesizing the electrical signals RS from those optical sensors 10, indicating the received intensity obtained by adding the received intensities of those optical sensors 10.

[0034] The processing control device 12 is specifically composed of a normal computer having at least a central processing unit (CPU) and a memory, and executes the following processes based on a program previously provided to the computer. That is, the processing control device 12 sets and stores a specified intensity DP indicating that it has received the plasma light of copper from the conductor layer exposed at the via bottom of the via hole formed in the interlayer insulating layer. Further, the processing control device 12 sets and stores a specified number DC indicating the number of combined electrical signals RSC exceeding the specified intensity DP corresponding to the number of pulses of the laser beam B required to secure the via bottom diameter of the via hole. Note that the specified intensity DP and the specified number DC can be obtained in advance through experiments, simulations, etc.

[0035] Then, the processing control device 12 inputs the combined electrical signal RSC from the signal synthesizer 11, compares the combined electrical signal RSC with the specified intensity DP, counts the number of times the combined electrical signal RSC exceeds the specified intensity DP, and determines whether the number of signals exceeding the specified intensity DP has reached the specified number DC.

[0036] Based on the result of this determination, until the number of times the combined electrical signal RSC exceeds the specified intensity DP reaches the specified number DC, the processing control device 12 allows the laser beam B emitted from the laser oscillator 1 to pass through the pulse control mechanism 2 as it is. Also, when the processing control device 12 determines that the number of times the combined electrical signal RSC exceeds the specified intensity DP has reached the specified number DC, it outputs a blocking signal SS to the pulse control mechanism 2 to block the laser beam B emitted from the laser oscillator 1. Next, the processing control device 12 outputs a control signal CS to the deflection mechanism 6 and the X-Y table 8 to deflect and / or horizontally move the laser beam B. Thereby, the processing control device 12 can cause the incident position of the laser beam B to be changed to the next drilling position, and thus the scanning of a large number of drilling positions by the laser beam B and the movement of the laser beam B between relatively distant drilling positions.

[0037] This laser processing method of this embodiment shown in FIG. 2 uses the laser processing apparatus of the embodiment shown in FIG. 1 to irradiate a laser beam B onto a build-up layer in which a resin interlayer insulating layer and, for example, a conductor layer made of copper that constitute a printed wiring board W are laminated, and to perform a drilling process for a via hole that penetrates the interlayer insulating layer.

[0038] In this laser processing method of this embodiment, first, on the X-Y table 8, a flat wafer that constitutes a large number of printed wiring boards W in which a resin interlayer insulating layer L1 and a copper conductor layer L2 that form a build-up layer are laminated is placed with its interlayer insulating layer L1 side facing upward. Next, the X-Y table 8 is operated by the processing control device 12 to adsorb and support the wafer and thus the printed wiring board W, and to move it in two directions perpendicular to each other in the horizontal plane, and relatively, to position the initial incidence position of the laser beam B from the Fθ lens 7 at the first drilling position of the printed wiring board W.

[0039] Next, in this laser processing method of this embodiment, a laser beam B of a short-pulse UV laser is emitted from the laser oscillator 1, the laser beam B is passed through as it is by the pulse control mechanism 2, and then, for example, it is deformed into a rectangular cross-sectional shape suitable for drilling by a beam shaper 3, narrowed to a predetermined thickness by a mask 4, and the optical path direction is changed by a mirror 5 and directed toward the beam scanning mechanism 6.

[0040] Then, the beam scanning mechanism 6 slightly deflects the laser beam B by, for example, AOD and then deflects it more greatly than AOD by a galvanometer mirror and passes it through the Fθ lens 7. The Fθ lens 7 vertically incidences the laser beam B onto the surface of the first drilling position of the printed wiring board W and converges it at the incidence position.

[0041] By repeatedly irradiating the first drilling position of the pulsed laser beam B, as shown in FIG. 2, first, the resin forming the interlayer insulating layer L1 of the printed wiring board W is melted or thermally decomposed into plasma, and a hole is formed at that position. Then, when the depth of the hole reaches the thickness of the interlayer insulating layer L1 and the hole penetrates to form a via hole H, the opening diameter (via bottom diameter) of the via hole H in the interlayer insulating layer L1 gradually expands. When the via bottom diameter expands to a certain extent, the surface of the copper forming the conductor layer L2 of the printed wiring board W facing the interlayer insulating layer L1 side is melted or thermally decomposed into plasma by the laser beam B passing through the via hole H, and a dent begins to form at the position of the via hole H. At this time, plasma light L is emitted from the plasma of the resin and copper that have become plasma, and the plasma light L is radiated outside the printed wiring board W through the via hole H.

[0042] In the laser processing method of this embodiment, among the radiated plasma light L, the plasma light from the copper plasma P is selectively transmitted through the band-pass filter 9 and received by the optical sensor 10, and the optical sensor 10 outputs an electrical signal RS with an intensity corresponding to the received light intensity. The electrical signals RS from the plurality of optical sensors 10 are synthesized by the signal synthesizer 11, and the synthesized electrical signal RSC is output to the signal synthesizer 11.

[0043] Furthermore, in the laser processing method of this embodiment, the processing control device 12 stores the specified intensity DP of the synthesized electrical signal RSC indicating that the plasma light from the copper plasma P from the conductor layer L2 exposed at the via bottom of the via hole H formed in the interlayer insulating layer L1 has been received. Also, the processing control device 12 stores the specified number DC indicating the number of synthesized electrical signals RSC exceeding the specified intensity DP corresponding to the number of pulses of the laser beam B required to ensure the via bottom diameter of the via hole H. Then, the processing control device 12 inputs the synthesized electrical signal RSC from the signal synthesizer 11, compares the synthesized electrical signal RSC with the specified intensity DP, counts the number of times the synthesized electrical signal RSC exceeds the specified intensity DP, and determines whether the number of signals exceeding the specified intensity DP has reached the specified number DC.

[0044] In the laser processing method of this embodiment, as a result of the above determination, until the number of times the combined electrical signal RSC exceeds the specified intensity DP reaches the specified number DC, the pulse control mechanism 2 is allowed to pass the laser beam B emitted from the laser oscillator 1 as it is by the processing control device 12. Then, when the number of times the combined electrical signal RSC exceeds the specified intensity DP reaches the specified number DC, the processing control device 12 outputs a blocking signal SS to the pulse control mechanism 2 to block the laser beam B emitted from the laser oscillator 1. Next, the processing control device 12 outputs a control signal CS to the beam scanning mechanism 6 and the X-Y table 8 to deflect and / or horizontally move the laser beam B, thereby changing the incident position of the laser beam B to the next drilling position.

[0045] In this way, the incident position of the laser beam B is successively changed from the first drilling position of the printed wiring board W to the next drilling position, and then to other drilling positions, and the laser beam B scans a large number of drilling positions in sequence. At these drilling positions of the printed wiring board W, the through holes H in the interlayer insulating layer L1 are drilled in the same manner as at the first drilling position.

[0046] Therefore, according to the laser processing apparatus and the laser processing method of this embodiment, the following effects can be obtained. (1) Since the dichroic beam splitter is not arranged on the optical path of the laser beam B, the intensity of the laser beam B irradiated on the interlayer insulating layer of the printed wiring board W does not decrease. (2) Since the dichroic beam splitter is not arranged on the optical path of the laser beam B, there is no need for maintenance or replacement of the dichroic beam splitter due to optical degradation. (3) The band-pass filter 9 blocks the strong reflected light of the laser beam B and receives only the plasma light L emitted from the printed wiring board W, and selectively transmits the plasma light of the copper plasma P among them. Since the optical sensor 10 receives the plasma light of the copper plasma P, it is possible to prevent a decrease in the S / N ratio of the sensor output signal and damage to the optical sensor 10.

[0047] Furthermore, the laser processing apparatus of this embodiment includes an X-Y table 8 that supports the printed wiring board W and moves the printed wiring board W parallel to its surface to relatively move the incident position of the laser beam from the Fθ lens with respect to the printed wiring board. Therefore, according to the laser processing apparatus and the laser processing method of this embodiment, in the region where via holes are dense, the incident position of the laser beam B is gradually moved by deflection in the beam scanning mechanism 6, while in the region without via holes, the incident position of the laser beam B can be greatly moved by the X-Y table 8. Therefore, according to the laser processing apparatus and the laser processing method of this embodiment, high positional accuracy and high moving speed of the incident position of the laser beam B can be obtained over a wide range of the printed wiring board W.

[0048] Also, according to the laser processing apparatus and the laser processing method of this embodiment, the laser light source 1 emits a short-pulse UV laser beam, and the processing control device 12 counts the number of signals from the optical sensor 10 with an intensity exceeding the specified intensity DP, and when the number of signals exceeding the specified intensity DP reaches the specified number DC, the pulse control mechanism 2 blocks the laser beam B of the short-pulse UV laser. Here, as the specified intensity DP, the signal intensity indicating that the plasma light of the copper plasma P from the conductor layer exposed in the via hole formed in the interlayer insulating layer is received is set. Also, as the specified number DC, the number of signals exceeding the specified intensity DP indicating that the number of pulses of the laser beam B required to secure the via bottom diameter of the via hole has been reached is set.

[0049] Thereby, it can be known that a via hole has been formed from the signal exceeding the specified intensity DP, and it can be known that the via bottom diameter of the via hole has been secured from the reaching of the number of signals exceeding the specified intensity DP to the specified number DC. Therefore, by blocking the short-pulse UV laser beam in the pulse control mechanism 2 when the number of signals exceeding the specified intensity DP reaches the specified number DC and stopping the incidence of the laser beam B on the interlayer insulating layer, insufficient processing of the interlayer insulating layer and excessive processing of the conductor layer can be prevented.

[0050] In particular, in the case of a short-pulse (nanoseconds, picoseconds, femtoseconds of about 5 nanoseconds or less) UV laser, copper processing progresses with each irradiation pulse. Therefore, according to the laser processing apparatus and the laser processing method of this embodiment, the processing amount of the copper pad, which is the conductor layer forming the via bottom, can be suppressed within an allowable range.

[0051] As described above based on the illustrated embodiment, the laser processing apparatus and the laser processing method of this invention are not limited to the above-described embodiment, and can be appropriately changed as needed within the scope described in the claims.

Explanation of Reference Numerals

[0052] 1 Short-pulse laser oscillator 2 Acousto-optic modulator (AOM) 3 Beam shaper 4 Mask 5 Mirror 6 Beam scanning mechanism 7 Fθ lens 8 X-Y table 9 Band-pass filter 10 Optical sensor 11 Signal synthesizer 12 Processing control device B Laser beam CS Control signal DC Designated number DP Designated intensity H Via hole (through hole) L Plasma light L1 Interlayer insulating layer L2 Conductor layer P Plasma of copper RS Electrical signal RSC Composite electrical signal SS Shut-off signal W Printed wiring board

Claims

1. A laser processing apparatus for performing drilling on a build-up layer in which a resin interlayer insulating layer and a metal conductor layer constituting a printed wiring board are laminated, by irradiating a laser beam, comprising: a laser light source that emits a laser beam; beam control means for passing or blocking the laser beam emitted from the laser light source; beam scanning means for deflecting the laser beam that has passed through the beam control means to scan the drilling position of the interlayer insulating layer; an Fθ lens that perpendicularly incident the laser beam deflected by the beam scanning means on the surface of the interlayer insulating layer and converges it at the incident position; one or more band-pass filters disposed in the vicinity of the Fθ lens, for transmitting plasma light of a specific wavelength corresponding to the metal forming the conductor layer among the plasma light generated by the drilling of the interlayer insulating layer by the laser beam converged by the Fθ lens; an optical sensor that is paired with the band-pass filter, receives the plasma light of the specific wavelength that has passed through the band-pass filter, and outputs an electrical signal having an intensity corresponding to the received light intensity; processing control means for causing the beam control means to pass and block the laser beam and causing the beam scanning means to scan the drilling position of the interlayer insulating layer by deflecting the laser beam, based on a change in the output signal intensity of the optical sensor; and comprising the above.

2. The laser processing apparatus according to claim 1, wherein the metal forming the conductor layer is copper.

3. The laser processing apparatus according to claim 1, further comprising printed wiring board moving means for supporting the printed wiring board and moving the printed wiring board parallel to its surface, so as to relatively move the incident position of the laser beam from the Fθ lens with respect to the printed wiring board.

4. The laser processing apparatus according to claim 1, wherein the laser light source emits a short-pulse UV laser beam, the processing control means counts the number of signals from the optical sensor having an intensity exceeding a specified intensity indicating that the plasma light of the specific wavelength from the conductor layer exposed in the via hole formed in the interlayer insulating layer has been received, and when the number of signals exceeding the specified intensity reaches a specified number indicating the number of pulses of the laser beam required to ensure the bottom diameter of the via hole, causes the beam control means to block the short-pulse UV laser beam.

5. A laser processing method for performing drilling on a build-up layer in which a resin interlayer insulating layer and a metal conductor layer constituting a printed wiring board are laminated, wherein: a step of a laser light source emitting a laser beam; a step of a beam control means passing or blocking the laser beam emitted from the laser light source; a step of a beam scanning means deflecting the laser beam that has passed through the beam control means to scan the hole drilling position of the interlayer insulating layer; a step of vertically incidenting the laser beam deflected by the beam scanning means on the surface of the interlayer insulating layer with an Fθ lens and converging it at the incident position; a step of allowing plasma light of a specific wavelength corresponding to the metal forming the conductor layer among the plasma light generated by the hole drilling of the interlayer insulating layer by the laser beam converged by the Fθ lens to pass through a band-pass filter disposed one or more in the vicinity of the Fθ lens; a step of receiving the plasma light of the specific wavelength that has passed through the band-pass filter with an optical sensor and outputting an electrical signal having an intensity corresponding to the received intensity of the plasma light of the specific wavelength from the optical sensor; a step of a processing control means causing the beam control means to pass and block the laser beam and the beam scanning means to scan the hole drilling position of the interlayer insulating layer by deflecting the laser beam based on a change in the output signal intensity of the optical sensor; is included.

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