Laser processing apparatus, method for operating the same, and method for processing a workpiece using the same.

Abstract

This invention relates to a laser processing apparatus and a method for operating it. [Solution] The laser processing apparatus can perform a process of forming vias in a workpiece by irradiating a workpiece formed on a second material with laser energy having a wavelength in which the first material is more reflective than the second material, thereby causing the laser energy to be incident on the first material. The laser processing apparatus may include a back reflection detection system that can capture a back reflection signal corresponding to a portion of the laser energy irradiated onto the workpiece and reflected by the first material, and generate a sensor signal based on the captured back reflection signal, and a controller that is communicatively coupled to the output of the back reflection detection system and can control the remainder of the via formation process based on the sensor signal.

Description

Technical Field

[0001] Embodiments of the present invention relate to a laser processing apparatus and a method of operating the same. Technical Background

[0002] A printed circuit board (PCB) is typically formed from conductive layers laminated on a dielectric substrate. The PCB can be double-sided or multi-layered. A double-sided PCB includes two conductive layers laminated on both sides of a common dielectric substrate. A multi-layered PCB typically has conductive layers interposed between a plurality of dielectric substrates and one or more conductive layers laminated on its outer surfaces.

[0003] Dielectric substrates are usually provided as composite materials formed from a matrix material (e.g., epoxy resin) and a reinforcing material (e.g., glass fiber woven fabric). Such dielectric substrates necessarily have a non-uniform composition as shown in FIG. 1. Referring to FIG. 1, the glass fiber woven fabric (shown as white and gray fibers) appears to be surrounded by the matrix material (shown in black). The composition of the dielectric substrate varies depending on the position. For example, at the position of "A", the dielectric substrate contains a relatively large amount of reinforcing material and a relatively small amount of matrix material. At the position of "B", the dielectric substrate contains only the matrix material. At the position of "C", the dielectric substrate contains less reinforcing material than at the position of "A" and more than at the position of "B", and contains more matrix than at the position of "A" and less than at the position of "C". A schematic cross-sectional view of a part of a PCB including a dielectric substrate as described with respect to FIG. 1 is shown in FIG. 2. Referring to FIG. 2, a conductor 20 (also referred to herein as the "upper conductor") is provided on the first surface of the dielectric substrate 24, and another conductor 24 (also referred to herein as the "bottom conductor") is provided on the second surface of the dielectric substrate 24. The dielectric substrate 24 is shown as including a matrix material 26 and a reinforcing material 28.

[0004] Vias, whether through-hole or non-through-hole vias, can be perforated within a PCB using a laser (e.g., using a laser perforation process). A schematic cross-sectional view of a non-through-hole via formed in a PCB shown in Figure 2 is shown in Figure 3. Referring to Figure 2, a non-through-hole via 30 can be formed using a laser perforation "punch" process in which a laser energy beam is irradiated at a single location on the PCB to remove the dielectric substrate 24 so as to form an opening in the upper conductor 20 and expose a portion of the bottom conductor 22 within the non-through-hole via 30. However, the matrix and reinforcing materials of the dielectric substrate 24 are often not processed with the same efficiency by the laser. Matrix materials are typically easier to process than reinforcing materials. Also, there may be variations in the surface reflectivity and / or thickness of the upper conductor 20 across different regions of the PCB. As a result, if the same perforation parameters (e.g., pulse width, peak pulse power) are used to form non-through-holes at different locations within the dielectric substrate, there will be some inherent variation in the morphology of the resulting non-through-holes. The morphological characteristics of a non-through via hole may include the degree to which the upper conductor protrudes from the sidewall of the hole formed in the dielectric substrate 24 (also known as "overhang") and the ratio of the diameter of the non-through via hole 30 in the bottom conductor 22 to the diameter of the non-through via hole 30 in the upper conductor 20 (also known as "taper"). Generally, it is preferable that each via be characterized by a relatively small overhang and a relatively large taper. Therefore, variations in the morphological characteristics of a non-through via hole depending on its location are undesirable for high-performance PCBs and associated processing yields.

[0005] The aforementioned fluctuation problem can be mitigated to some extent by processing the PCB using a laser wavelength that is relatively unresponsive to variations in the composition of the dielectric substrate. For example, a carbon dioxide laser can generate laser energy at a wavelength of ~9.4 μm, which is linearly absorbed by the matrix and reinforcing materials but mainly reflected by the conductor (i.e., copper) exposed by non-penetrating via holes. It is generally known that removing the reinforcing material 28 requires more energy than removing the matrix material 26 (even with a laser wavelength of ~9.4 μm). However, even if the energy required to remove a portion of the dielectric substrate 24 varies based on the relative amounts of matrix material 26 and reinforcing material 28 within it, the matrix and reinforcing materials of the dielectric substrate 24 can usually be reliably removed without damaging (e.g., melting) the bottom conductor 22.

[0006] The aforementioned fluctuation problem can be further reduced by using multiple laser pulses to form a single non-penetrating via hole. In this case, the first pulse is irradiated to form an opening in the upper conductor 20, and all subsequent pulses are irradiated to remove the remaining dielectric substrate 24 without damaging the bottom conductor 22. A proposed improvement to this “multi-pulse processing” technique typically involves adjusting the pulse energy of the second or subsequent laser pulses based on the intensity of the laser light reflected by the bottom conductor 22 (generally understood to correspond to the size of the area of ​​the bottom conductor 22 exposed by the non-penetrating via hole 30). Summary

[0007] One embodiment of the present invention can be broadly characterized as a laser processing apparatus for performing a process of forming vias in a workpiece by irradiating a workpiece formed on a second material with laser energy having a wavelength such that the first material is more reflective than the second material, thereby causing the laser energy to be incident on the first material. The laser processing apparatus may include a back reflection detection system that can capture a back reflection signal corresponding to a portion of the laser energy irradiated onto the workpiece and reflected by the first material, and generate a sensor signal based on the captured back reflection signal, and a controller that is communicatively coupled to the output of the back reflection detection system and can control the remainder of the via formation process based on the sensor signal.

[0008] Other embodiments of the present invention can be broadly characterized as a method comprising: irradiating a workpiece formed on a second material with a laser pulse having a wavelength such that the first material is more reflective than the second material; inducing the laser pulse into the first material to form vias in the workpiece; capturing a back-reflected signal corresponding to a portion of the laser energy irradiated onto the workpiece and reflected by the first material; generating a sensor signal based on the captured back-reflected signal; processing the sensor signal to determine how the remainder of the process should be carried out to form the vias; and carrying out the remainder of the process based on the processing of the sensor signal.

[0009] A further embodiment of the present invention is a laser processing apparatus capable of performing a process of forming vias in a workpiece by irradiating a workpiece formed on a second material with laser energy having a wavelength such that the first material is more reflective than the second material, thereby causing the laser energy to be incident on the first material, the laser processing apparatus comprising: a back reflection detection system capable of capturing a back reflection signal corresponding to a portion of the laser energy irradiated onto the workpiece and reflected by the first material, and generating a sensor signal based on the captured back reflection signal; and a controller communicatively coupled to the output of the back reflection detection system, wherein the non-transient computer-readable medium used with the laser processing apparatus is characterized in that, when executed by the controller, it stores instructions causing the controller to control the process based on the sensor signal. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 shows an example of the arrangement of reinforcing materials within the matrix material of a composite dielectric substrate that can be processed by laser according to an embodiment of the present invention.

[0011] [Figure 2] Figure 2 shows a schematic cross-sectional view of a portion of the PCB, including the dielectric substrate as described in Figure 1.

[0012] [Figure 3] Figure 3 shows a schematic cross-sectional view of a non-through via formed in the PCB shown in Figure 2.

[0013] [Figure 4] Figure 4 schematically shows a laser processing apparatus according to one embodiment of the present invention.

[0014] [Figure 5]Figure 5 schematically shows a back reflection detection system for the laser processing apparatus shown in Figure 4, according to one embodiment of the present invention.

[0015] [Figure 6] Figure 6 is a graph showing the signal intensity of the back-reflected signal, exemplified by the back-reflected detection system described with reference to Figures 4 and 5 according to an embodiment of the present invention, as a function of time (i.e., during the formation of a non-penetrating via hole). Detailed explanation

[0016] The following describes examples of embodiments with reference to the attached drawings. Unless explicitly stated, the sizes, positions, and distances between components, features, and elements in the drawings are not necessarily to scale and are exaggerated for ease of understanding. Similar numbers throughout the drawings represent similar elements. Therefore, identical or similar numbers may be mentioned by reference to other drawings even if they are not mentioned or described in the corresponding drawings. Furthermore, elements without reference numbers may also be mentioned by reference to other drawings.

[0017] The terms used in this specification are for the sole purpose of describing specific exemplary embodiments and are not intended to be limiting. Unless otherwise specifically defined, all terms used herein (including technical and scientific terms) have the same meaning as generally understood by those skilled in the art. Where used herein, singular nouns are intended to include plural nouns unless the context explicitly indicates otherwise. Furthermore, the terms “equipped with” and / or “equipped with” should be understood to identify the presence of a described feature, integer, step, operation, element, and / or component, but not to exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. Unless otherwise specifically indicated, where a range of values ​​is given, that range includes the upper and lower limits, as well as the sub-range between the upper and lower limits of that range. Unless otherwise specifically indicated, terms such as “first” and “second” are used solely to distinguish elements from one another. For example, one node may be called the “first node,” and similarly another node may be called the “second node,” or vice versa.

[0018] Unless otherwise specified, “approximately,” “around,” and “substantially” mean that quantities, sizes, proportions, parameters, and other quantities and characteristics are not, and do not need to be, exact, and may be approximate, and may be larger or smaller, as needed, or to reflect tolerances, conversion factors, rounding, measurement errors, and other factors known to those skilled in the art. In this specification, spatially relative terms such as “below,” “down,” “below,” “up,” and “above” may be used to facilitate explanation when describing the relationship between one element or feature and another element or feature, as shown in the figures. It should be understood that spatially relative terms are intended to include different orientations in addition to those shown in the figures. For example, an element described as being “below” or “below” another element or feature would face “above” the other element or feature if the object in the figure were inverted. Thus, the exemplary term “below” may include both upward and downward orientations. If the object is facing a different direction (for example, if it is rotated 90 degrees or is in a different direction), the spatially relative descriptors used herein may be interpreted accordingly.

[0019] Section headings used herein are for organizational purposes only, unless otherwise specified, and should not be construed as limiting the subject matter discussed. It will be understood that many different forms, embodiments, and combinations are conceivable without departing from the spirit and teachings of this disclosure, and that this disclosure should not be construed as limiting to the examples of embodiments described herein. Rather, these examples and embodiments are provided to fully convey the scope of this disclosure to those skilled in the art, as it is complete and all-encompassing.

[0020] I. Overview

[0021] Figure 4 schematically shows a laser processing apparatus according to one embodiment of the present invention.

[0022] Referring to the embodiment shown in FIG. 4, a laser processing apparatus 100 (also simply referred to as "apparatus" in this specification) for processing a workpiece 102 can be characterized as including a laser source 104 for generating a laser energy beam, a beam modulator 106, a scanner 108, a stage 110, and a scan lens 112.

[0023] As described in more detail below, the beam modulator 106 operates to selectively and variably attenuate the laser energy beam propagating from the laser source 104. As a result, the laser energy beam emerging from the beam modulator 106 along the beam path 114 can have a lower optical power than the optical power of the laser energy beam entering the beam modulator 106 along the beam path 114. As used herein, the term "beam path" means the path along which the laser energy in the laser energy beam moves when the laser energy beam propagates from the laser source 104 to the scan lens 112.

[0024] The scanner 108 diffracts, reflects, refracts, or the like, or any combination thereof (i.e., "deflects" the laser energy beam) the laser energy beam generated by the laser source 104 and optionally deflected by the beam modulator 106 so as to deflect the beam path 114 toward the scan lens 112. When deflecting the beam path 114 toward the scan lens 112, the scanner 108 can deflect the beam path 114 at any angle within a certain angular range (such as shown at 116), for example, which is measured with respect to the optical axis of the scan lens 112.

[0025] The laser energy deflected toward the scan lens 112 is typically focused by the scan lens 112 so as to irradiate the workpiece 102 and transmits along the beam axis. The laser energy irradiating the workpiece 102 can be characterized as having a Gaussian spatial intensity profile or a non-Gaussian (i.e., "shaped") spatial intensity profile (e.g., "top hat" spatial intensity profile, super-Gaussian spatial intensity profile, etc.).

[0026] As used herein, the term "spot size" means the diameter or maximum spatial width of the laser energy beam irradiated at a position (also referred to as "process spot", "spot position" or more simply "spot") where an area of the workpiece 102 at least partially machined by the irradiated laser energy beam intersects the beam axis. In the discussion herein, the spot size is measured as the radial distance or transverse distance from the beam axis to where the optical intensity drops to at least 1 / e 2 of the light intensity at the beam axis. Generally, the spot size of the laser energy beam is minimum at the beam waist. When irradiating the workpiece 102, the laser energy in the beam can be characterized as hitting the workpiece 102 with a spot size in the range of 2 μm to 200 μm. However, it can be understood that the spot size can be smaller than 2 μm or larger than 200 μm. Thus, the laser energy beam irradiating the workpiece 102 can have a spot size larger than, smaller than, or equal to 2 μm, 3 μm, 5 μm, 7 μm, 10 μm, 15 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 80 μm, 100 μm, 150 μm, 200 μm, etc., or a spot size between any of these values.

[0027] The apparatus 100 may also include one or more optical elements (e.g., beam traps, beam expanders, beam shapers, beam splitters, apertures, filters, collimators, lenses, mirrors, prisms, polarizers, phase retarders, diffractive optical elements (commonly known in the art as DOEs), refractive optical elements (commonly known in the art as ROEs), or any combination thereof) for focusing, expanding, collimating, shaping, polarizing, filtering, splitting, combining, cropping, absorbing, or modifying, adjusting, directing, or otherwise performing actions on the laser energy beam as it propagates along the beam path 114.

[0028] A. Laser source

[0029] In one embodiment, the laser source 104 can generate laser pulses. Therefore, the laser source 104 may include a pulsed laser source, a CW laser source, a QCW laser source, a burst-mode laser, or any combination thereof. If the laser source 104 includes a QCW laser source or a CW laser source, the laser source 104 may be operated in pulsed mode or non-pulsed mode, but may further include a pulse gating unit (e.g., an acousto-optic (AO) modulator (AOM), a beam chopper, etc.) that temporally modulates the beam of laser radiation output from the QCW laser source or CW laser source. Although not shown, the apparatus 100 may optionally include one or more harmonic generating crystals (also known as "wavelength conversion crystals") configured to convert the wavelength of light output by the laser source 104. However, in other embodiments, the laser source 104 may be provided as a QCW laser source or a CW laser source and may not include a pulse gating unit. Thus, the laser source 104 can be broadly characterized as capable of generating a laser energy beam that can manifest as a series of laser pulses, or as a continuous or quasi-continuous laser beam. This laser energy beam can then propagate along the beam path 114. While many embodiments described herein describe laser pulses, it should be understood that a continuous or quasi-continuous beam can be used instead, or in addition to, laser pulses, where appropriate or required.

[0030] The laser energy output from the laser source 104 may have one or more wavelengths in the ultraviolet (UV), visible, or infrared (IR) region of the electromagnetic spectrum. The laser energy in the UV region of the electromagnetic spectrum may have one or more wavelengths in the range of 10 nm (or around) to 385 nm (or around), such as 100 nm, 121 nm, 124 nm, 157 nm, 200 nm, 334 nm, 337 nm, 351 nm, 380 nm, or wavelengths between any of these values. The laser energy in the visible green light region of the electromagnetic spectrum may have one or more wavelengths in the range of 500 nm (or around) to 560 nm (or around), such as 511 nm, 515 nm, 530 nm, 532 nm, 543 nm, 568 nm, or wavelengths between any of these values. The laser energy in the IR region of the electromagnetic spectrum may have one or more wavelengths in the range of 750 nm (or around) to 15 μm (or around), such as 600 nm to 1000 nm, 752.5 nm, 780 nm to 1060 nm, 799.3 nm, 980 nm, 1047 nm, 1053 nm, 1060 nm, 1064 nm, 1080 nm, 1090 nm, 1152 nm, 1150 nm to 1350 nm, 1540 nm, 2.6 μm to 4 μm, 4.8 μm to 8.3 μm, 9.4 μm, 10.6 μm, or wavelengths in any of these values.

[0031] When the laser energy beam is represented as a series of laser pulses, the laser pulses output by the laser source 104 may have a pulse width or pulse duration (i.e., based on the full width at half maximum (FWHM) of the optical power in the pulse with respect to time) in the range of 10 fs to 900 ms. However, it can be understood that the pulse duration may be shorter than 10 fs or longer than 900 ms. Thus, at least one laser pulse output by the laser source 104 is 10fs, 15fs, 30fs, 50fs, 100fs, 150fs, 200fs, 300fs, 500fs, 600fs, 750fs, 800fs, 850fs, 900fs, 950fs, 1ps, 2ps, 3ps, 4ps, 5ps, 7ps, 10ps, 15ps, 25ps, 50ps, 75ps, 100ps, 200ps, 500ps, 1ns, 1.5ns, 2ns, 5ns, 10ns, 20ns, 50ns, 100 The pulse duration can be shorter than ns, 200ns, 400ns, 800ns, 1000ns, 2μs, 5μs, 10μs, 15μs, 20μs, 25μs, 30μs, 40μs, 50μs, 100μs, 300μs, 500μs, 900μs, 1ms, 2ms, 5ms, 10ms, 20ms, 50ms, 100ms, 300ms, 500ms, 900ms, 1s, etc., or shorter than any of these values, longer than these values, or equal to these values.

[0032] The laser pulses output by the laser source 104 can have an average power in the range of 5mW to 50kW. However, it can be understood that the average power may be less than 5mW or greater than 50kW. Thus, the laser pulses output by the laser source 104 can have an average power of 5mW, 10mW, 15mW, 20mW, 25mW, 50mW, 75mW, 100mW, 300mW, 500mW, 800mW, 1W, 2W, 3W, 4W, 5W, 6W, 7W, 10W, 15W, 18W, 25W, 30W, 50W, 60W, 100W, 150W, 200W, 250W, 500W, 2kW, 3kW, 20kW, 50kW, etc., or an average power less than, greater than, or equal to any of these values.

[0033] The laser source 104 can output laser pulses at pulse repetition rates in the range of 5 kHz to 5 GHz. However, it can be understood that the pulse repetition rate may be lower than 5 kHz or higher than 5 GHz. Thus, the laser source 104 can output laser pulses at pulse repetition rates lower than, higher than, or equal to 5 kHz, 50 kHz, 100 kHz, 175 kHz, 225 kHz, 250 kHz, 275 kHz, 500 kHz, 800 kHz, 900 kHz, 1 MHz, 1.5 MHz, 1.8 MHz, 1.9 MHz, 2 MHz, 2.5 MHz, 3 MHz, 4 MHz, 5 MHz, 10 MHz, 20 MHz, 50 MHz, 60 MHz, 100 MHz, 150 MHz, 200 MHz, 250 MHz, 300 MHz, 350 MHz, 500 MHz, 550 MHz, 600 MHz, 900 MHz, 2 GHz, 10 GHz, or any value between these values.

[0034] In addition to wavelength, average power, pulse duration, and pulse repetition rate when the laser energy beam is represented as a series of laser pulses, the laser energy beam irradiated onto the workpiece 102 can be characterized by one or more other properties such as pulse energy and peak power. This laser pulse is sufficient (W / cm²) to process the workpiece 102 (for example, to form one or more feature parts). 2 Light intensity (measured at), (J / cm²) 2 To irradiate the workpiece 102 at the process spot, the fluence (measured by) can be selected (for example, based on one or more other characteristics such as wavelength, pulse duration, average power and pulse repetition rate, spot size, etc., as needed).

[0035] Examples of laser types that can characterize the laser source 104 include gas lasers (e.g., carbon dioxide lasers, carbon monoxide lasers, excimer lasers, etc.), solid-state lasers (e.g., Nd:YAG lasers, etc.), rod lasers, fiber lasers, photonic crystal rod / fiber lasers, passive mode-locked solid bulk or fiber lasers, dye lasers, mode-locked diode lasers, pulsed lasers (e.g., ms pulsed lasers, ns pulsed lasers, ps pulsed lasers, fs pulsed lasers), CW lasers, QCW lasers, etc., or any combination thereof. Depending on the configuration, a gas laser (e.g., a carbon dioxide laser) may be configured to operate in one or more modes (e.g., CW mode, QCW mode, pulsed mode, or any combination thereof).

[0036] B. Beam Modulator

[0037] As described above, the beam modulator 106 operates to selectively and variably attenuate the laser energy beam propagating from the laser source 104. The beam modulator 106 may include one or more systems such as a variable neutral filter, an acousto-optic (AO) modulator (AOM), an AO deflector (AOD), a liquid crystal variable attenuator (LCVA), a VOA utilizing a microelectromechanical system (MEMS), an optical attenuator wheel, a polarization / waveplate filter, or any combination thereof.

[0038] i. Embodiments relating to AOD as a beam modulator

[0039] If the beam modulator 106 is provided as one or more AOMs or AODs, or any combination thereof, the beam modulator 106 can also operate to diffract the laser energy beam generated by the laser source 104 so as to deflect the beam path 114 relative to the scanner 108. In one embodiment, the beam modulator 106 can also operate to move the beam axis relative to the workpiece 102 along the X-axis (or X direction), the Y-axis (or Y direction), or a combination thereof (for example, by deflecting the beam path 114 within a certain angular range, as shown by 118). Although not shown, the Y-axis (or Y direction) can be understood to mean an axis (or direction) perpendicular to the illustrated X-axis (or X direction) and Z-axis (or Z direction).

[0040] In one embodiment, the beam modulator 106 may be provided as an AO deflector (AOD) system. This AOD system comprises one or more AODs, each having an AO cell formed from a material such as crystalline germanium (Ge), gallium arsenide (GaAs), chalcite (PbMoO4), tellurium dioxide (TeO2), quartz, glassy SiO2, arsenic trisulfide (As2S3), lithium niobate (LiNbO3), or any combination thereof. It will be understood that the material forming the AO cell depends on the wavelength of the laser energy propagating along the beam path 114 to be incident on the AO cell. For example, if the wavelength of the deflected laser energy is in the range of 2 μm (or around that) to 20 μm (or around that), materials such as crystalline germanium can be used; if the wavelength of the deflected laser energy is in the range of 1 μm (or around that) to 11 μm (or around that), materials such as gallium arsenide or arsenic trisulfide can be used; and if the wavelength of the deflected laser energy is in the range of 200 nm (or around that) to 5 μm (or around that), materials such as glassy SiO2, quartz, lithium niobate, chalcedony, and tellurium dioxide can be used.

[0041] As will be understood by those skilled in the art, optical optical (AO) technology (e.g., AOD, AOM, etc.) utilizes the diffraction effect caused by one or more sound waves propagating through the AO cell (along the "diffraction axis" of the AOD) to diffract an incident light wave (i.e., a laser energy beam in the context of this application) simultaneously propagating through the AO cell (along the "optical axis" within the AOD). Diffraction of the incident laser energy beam produces a diffraction pattern that typically includes zero-order and first-order diffraction peaks, and may also include other higher-order (e.g., second-order, third-order, etc.) diffraction peaks. As is known in the art, the portion of the laser energy beam diffracted at the zero-order diffraction peak is called the "zero-order" beam, and the portion of the laser energy beam diffracted at the first-order diffraction peak is called the "first-order" beam, and so on. Generally, the zero-order beam and other-order beams (e.g., the first-order beam) propagate along different beam paths as they exit the AO cell (e.g., through the optical output side of the AO cell). For example, the zero-order beam propagates along the zero-order beampath, and the primary beam propagates along the primary beampath. Unless otherwise explicitly stated in this specification, the beampath 114 exiting the AO cell corresponds to the primary beampath. Although not shown, the apparatus 100 includes one or more beam dumps or traps, as known in the art, arranged and configured to absorb laser energy propagating from the beam modulator 106 along any beampath other than the zero-order beampath or the primary beampath.

[0042] Sound waves are typically input to the AO cell by applying RF drive signals (e.g., from one or more drivers of the beam modulator 106) to an ultrasonic converter element. The characteristics of the RF drive signals (e.g., amplitude, frequency, phase, etc.) can be controlled (based on one or more control signals output by controller 122, component-specific controllers, or any combination thereof) to adjust how the incident light waves are diffracted.

[0043] For example, the frequency of a given RF drive signal determines the angle at which the beam path 114 is deflected. As is known in the art, the angle Θ at which the beam path 114 is deflected can be calculated as follows.

[0044]

number

[0045] Here, λ is the optical wavelength of the laser energy beam, f is the frequency of the applied RF drive signal, and v is the speed of sound waves in the AO cell. If the frequency of the applied RF drive signal consists of multiple frequencies, the beam path 114 is deflected at multiple angles simultaneously.

[0046] Furthermore, the amplitude of the applied RF drive signal can affect the diffraction efficiency of the AOD. As used herein, the term "diffraction efficiency" refers to the proportion of energy in the laser energy beam incident on the AOD that is diffracted into the primary beam within the AO cell of the AOD. Therefore, diffraction efficiency can be expressed as the ratio of the optical power of the primary beam generated by the AOD to the optical power of the incident laser energy beam incident on the AOD. Thus, the amplitude of the applied RF drive signal can significantly affect the optical power in the primary beam output by the AOD. In this way, the beam modulator 106 can operate to attenuate the incident laser energy beam in a desired manner when driven by an applied RF signal having a desired or suitable amplitude. It should also be noted that the diffraction efficiency of the AOD can also vary as a function of the frequency of the RF drive signal applied to drive the AOD.

[0047] The central axis (also referred to herein as the “rotation axis”) around which the beam path 114 exiting the AO cell is rotated (for example, with respect to the beam path 114 when incident on the AO cell) is orthogonal to both the diffraction axis of the AO cell and the optical axis along the direction in which the incident laser energy beam propagates within the AO cell when the AOD is operated or driven to diffract the incident laser energy beam. In this way, the AOD deflects the incident beam path 114 within a plane (also referred to herein as the “deflection plane”) that includes (or otherwise substantially parallel to) the diffraction axis of the AO cell and the optical axis within the AO cell. In this specification, the spatial range over which the AOD can deflect the beam path 114 within the deflection plane is referred to herein as the “scan region” of the AOD. Thus, the first scan region of the beam modulator 106 can be considered to correspond to the scan region of a single AOD (for example, if the beam modulator 106 includes a single AOD), or to the combined scan region of multiple AODs (for example, if the beam modulator 106 includes multiple AODs).

[0048] During the operation of the beam modulator 106, an RF drive signal is repeatedly supplied to one or more ultrasonic transducers of the beam modulator 106. The rate at which the RF drive signal is supplied is also called the "update rate" or "refresh rate". For example, the update rate of the beam modulator 106 may be greater than or less than 8kHz, 10kHz, 20kHz, 30kHz, 40kHz, 50kHz, 75kHz, 80kHz, 100kHz, 250kHz, 500kHz, 750kHz, 1MHz, 5MHz, 10MHz, 20MHz, 40MHz, 50MHz, 75MHz, 100MHz, 125MHz, 150MHz, 175MHz, 200MHz, 225MHz, 250MHz, or any value between these values.

[0049] ii. Additional explanation regarding the use of beam modulators to move the beam axis

[0050] In one embodiment, the beam modulator 106 can operate (either alone or in cooperation with the scanner 108) to move the beam axis relative to the workpiece 102. The movement of the beam axis by the beam modulator 106 is generally limited to scanning, moving, or positioning a process spot within a first scan area projected by the scan lens 112. Generally, depending on one or more factors such as the configuration of the beam modulator 106, the position of the beam modulator 106 along the beam path 114, the beam size of the laser energy beam incident on the beam modulator 106, and the spot size, the first scan area may extend in either the X or Y direction to a distance shorter than, longer than, or equal to, 0.01 mm, 0.04 mm, 0.1 mm, 0.5 mm, 1.0 mm, 1.4 mm, 1.5 mm, 1.8 mm, 2 mm, 2.5 mm, 3.0 mm, 3.5 mm, 4.0 mm, 4.2 mm, 5 mm, 10 mm, 25 mm, 50 mm, 60 mm, or any of these values. As used herein, the term "beam size" means the diameter or width of the laser energy beam, and is measured from the beam axis to 1 / e of the light intensity along the propagation axis along the beam path 114. 2 It can be measured as a radial or transverse distance down to the point where it drops down. The maximum dimension of the first scan area (for example, in a plane containing the X and Y axes (hereinafter referred to as the "XY plane")) may be greater than, equal to, or less than the maximum dimension (measured in the XY plane) of features formed on the workpiece 102 (e.g., openings, recesses, vias, trenches, etc.).

[0051] In one embodiment, the AOD system includes at least one single-element AOD (e.g., one, two, three, four, five, six, etc.), at least one multi-element AOD (e.g., one, two, three, four, five, six, etc.), or any combination thereof. In this specification, an AOD system containing only one AOD is referred to as a "single-cell AOD system," and an AOD system containing more than one AOD is referred to as a "multi-cell AOD system." As used herein, a "single-element" AOD means an AOD having only one ultrasonic converter element acoustically coupled to an AO cell, and a "multi-element" AOD includes two or more ultrasonic converter elements acoustically coupled to a common AO cell. An AOD system may be provided as a single-axis AOD system (for example, capable of deflecting the beam axis along a single axis) by deflecting the beam path 114 in a corresponding manner, or as a multi-axis AOD system (for example, capable of deflecting the beam axis along one or more axes, e.g., along the X-axis, along the Y-axis, or along any combination thereof). Generally, a multi-axis AOD system may be provided as a single-cell AOD system or a multi-cell AOD system. A multi-cell multi-axis AOD system typically includes multiple AODs, each capable of deflecting the beam axis along a different axis. For example, a multi-cell multi-axis system may include a first AOD (e.g., a single-element or multi-element AOD system) capable of deflecting the beam axis along one axis (e.g., along the X-axis) and a second AOD (e.g., a single-element or multi-element AOD) capable of deflecting the beam axis along a second axis (e.g., along the Y-axis). A single-cell multi-axis system typically includes a single AOD capable of deflecting the beam axis along two axes (e.g., along the X-axis and Y-axis). For example, a single-cell multi-axis system may include two or more ultrasonic conversion elements acoustically coupled to orthogonally arranged planes, faces, or sides of a common AO cell.

[0052] The beam modulator 106 can be characterized as having a “first positioning speed,” which means the speed at which the beam modulator 106 positions (and thereby moves the beam axis) a process spot to any position within a first scan area. In this specification, this range is also called the first positioning bandwidth. In this specification, the reciprocal of the first positioning speed is called the “first positioning period,” which means the shortest time it takes for the position of the process spot to change from one location within the first scan area to another location within the first scan area. Therefore, the beam modulator 106 can be characterized as having a first positioning period that is longer than or less than 200 μs, 125 μs, 100 μs, 50 μs, 33 μs, 25 μs, 20 μs, 15 μs, 13.3 μs, 12.5 μs, 10 μs, 4 μs, 2 μs, 1.3 μs, 1 μs, 0.2 μs, 0.1 μs, 0.05 μs, 0.025 μs, 0.02 μs, 0.013 μs, 0.01 μs, 0.008 μs, 0.0067 μs, 0.0057 μs, 0.0044 μs, 0.004 μs, or any of these values.

[0053] When the laser energy beam output by the laser source 104 is represented as a series of laser pulses, the beam modulator 106 can be operated to change the beam path 114 at different angles. In one embodiment, the update rate is greater than or equal to the pulse duration of each laser pulse. Thus, when the AOD is driven at a fixed RF drive frequency (or a set of fixed RF drive frequencies), the laser pulses penetrate the AO cells of the AOD. By maintaining the fixed RF drive frequency (or a set of fixed RF drive frequencies) applied to the AOD while the laser pulses are penetrating the AO cells of the AOD, the laser pulses can generally be deflected uniformly over the entire pulse duration of the laser pulses, and for this reason is sometimes called "full pulse deflection". However, in other embodiments, the update rate may be shorter than the pulse duration of the laser pulses, and thus the laser pulses can penetrate the AO cells of the AOD when the RF drive frequency (or a frequency within a set of RF drive frequencies) is changed. By changing the RF drive frequency applied to the AOD as the laser pulse passes through the AOD's AO cell, the laser pulse input to the AOD can be temporally divided, which is sometimes called "partial pulse deflection" or "pulse slicing." To reduce the diffraction efficiency of the AOD to zero or a significant degree (so that substantially the laser energy incident on the AOD propagates along the zero-order beampath), the laser pulse input to the AOD can be temporally divided (i.e., pulse slicing) by changing the amplitude of the applied RF drive signal (for example, to zero or a small amplitude, where a small proportion of the energy is diffracted to the primary beampath).

[0054] When pulse slicing is performed, the laser pulses exiting the AOD have a shorter pulse duration than the laser pulse input to the AOD. As used herein, the laser pulse input to the AOD is also called the “mother pulse,” and the laser pulses that are temporally separated from the mother pulse and exit the AOD along the beam path 114 are also called “pulse slices.” While the pulse slicing technique is applied herein to temporally divide a laser pulse, it will be understood that these techniques can be similarly applied to temporally divide a laser energy beam represented as a continuous or quasi-continuous laser beam.

[0055] C. Scanner

[0056] Generally, the scanner 108 can operate to move the beam axis relative to the workpiece 102 along the X-axis (or X direction), the Y-axis (or Y direction), or a combination thereof.

[0057] The movement of the beam axis relative to the workpiece 102 by the scanner 108 is generally limited so that the process spot can be scanned, moved, or positioned within a second scan area projected by the scan lens 112. Generally, depending on one or more factors such as the configuration of the scanner 108, the position of the scanner 108 along the beam path 114, the beam size of the laser energy beam incident on the scanner 108, and the spot size, the second scan area may extend to a distance longer than the corresponding distance of the first scan area in either the X or Y direction. From this perspective, the second scan area may extend to a distance shorter than, longer than, or equal to, 1 mm, 25 mm, 50 mm, 75 mm, 100 mm, 250 mm, 500 mm, 750 mm, 1 cm, 25 cm, 50 cm, 75 cm, 1 m, 1.25 m, 1.5 m, or any of these values. The maximum dimension of the second scan region (for example, in the XY plane) may be greater than, equal to, or less than the maximum dimension (measured in the XY plane) of the features formed on the workpiece 102 (e.g., openings, recesses, vias, trenches, scribe lines, conductive traces, etc.).

[0058] In terms of the configuration described herein, the beam axis movement performed by the beam modulator 106 can be superimposed on the beam axis movement performed by the scanner 108. Therefore, the scanner 108 can scan the first scan area within the second scan area.

[0059] Generally, the positioning speed at which the scanner 108 can position a process spot at any position within the second scan area (thus moving the beam axis within the second scan area and / or scanning the first scan area within the second scan area) is smaller than the range of the first positioning bandwidth (also referred to herein as the "second positioning bandwidth"). In one embodiment, the second positioning bandwidth is in the range of 500 Hz (or around there) to 8 kHz (or around there). For example, the second positioning bandwidth may be higher than, equal to, or lower than 500 Hz, 750 Hz, 1 kHz, 1.25 kHz, 1.5 kHz, 1.75 kHz, 2 kHz, 2.5 kHz, 3 kHz, 3.5 kHz, 4 kHz, 4.5 kHz, 5 kHz, 5.5 kHz, 6 kHz, 6.5 kHz, 7 kHz, 7.5 kHz, 8 kHz, or any of these values ​​or between them.

[0060] In one embodiment, the scanner 108 may be provided as a galvanometer mirror system including two galvanometer mirror components: a first galvanometer mirror component (e.g., an X-axis galvanometer mirror component) configured to move the beam axis along the X-axis relative to the workpiece 102, and a second galvanometer mirror component (e.g., a Y-axis galvanometer mirror component) configured to move the beam axis along the Y-axis relative to the workpiece 102. However, in other embodiments, the scanner 108 may be provided as a galvanometer mirror system including only a single galvanometer mirror component configured to move the beam axis along both the X-axis and the Y-axis relative to the workpiece 102. In yet another embodiment, the scanner 108 may be provided as a rotating polyhedron mirror system, an AOD system, or any combination thereof.

[0061] D Stage

[0062] Stage 110 can move the workpiece 102 relative to the scan lens 112, thereby moving the workpiece 102 relative to the beam axis. The movement of the workpiece 102 relative to the beam axis is generally limited to scanning, moving, or positioning process spots within a third scan region. Depending on one or more factors such as the configuration of Stage 110, the third scan region may extend to a distance longer than or equal to the corresponding distance of the second scan region in the X, Y, or any combination thereof. However, generally, the maximum dimension of the third scan region (e.g., in the XY plane) is greater than or equal to the corresponding maximum dimension (measured in the XY plane) of the features formed on the workpiece 102. If necessary, Stage 110 may be able to move the workpiece 102 relative to the beam axis within a scan region extending in the Z direction (e.g., over a range of 1 mm to 50 mm). Thus, the third scan region may extend along the X, Y, and / or Z directions.

[0063] As described above, the apparatus 100 may use a so-called "stacked" positioning system as the stage 110. This "stacked" positioning system allows the workpiece 102 to move while the positions of components other than the workpiece, such as the beam modulator 106, scanner 108, and scan lens 112, are stationary within the apparatus 100 (for example, via one or more supports, frames, etc., as known in the art). In other embodiments, the stage 110 may be arranged and operated to move one or more components, such as the beam modulator 106, scanner 108, scan lens 112, or any combination thereof, while the workpiece 102 remains stationary.

[0064] In yet another embodiment, the stage 110 may be provided as a so-called “split-axis” positioning system, in which one or more components, such as a beam modulator 106, a scanner 108, a scan lens 112, or any combination thereof, are transported by one or more linear or rotary stages (e.g., mounted on a frame or gantry), and the workpiece 102 is transported by one or more other linear or rotary stages. In such an embodiment, the stage 110 includes one or more linear or rotary stages that are arranged and operable to move one or more components, such as a scan head (e.g., including a scanner 108 and a scan lens 112), and one or more linear or rotary stages that are arranged and operable to move the workpiece 102. For example, the stage 110 may include a Y-stage that moves the workpiece 102 along the Y-direction and an X-stage that moves the scan head along the X-direction.

[0065] In one embodiment of stage 110 including a Z-stage, the Z-stage may be positioned and configured to move the workpiece 102 along the Z-direction. In this case, the Z-stage may be transported by one or more of the other stages described above for moving or positioning the workpiece 102, or transport one or more of the other stages described above for moving or positioning the workpiece 102, or any combination thereof. In another embodiment of stage 110 including a Z-stage, the Z-stage may be positioned and configured to move the scan head along the Z-direction. Thus, when stage 110 is provided as a split-axis positioning system, the Z-stage may transport the X-stage, or be transported by the X-stage. By moving the workpiece 102 or the scan head along the Z-direction, the spot size on the workpiece 102 can be changed.

[0066] In yet another embodiment, one or more components, such as the scanner 108 and the scan lens 112, may be transported by a multi-axis articulated robot arm (e.g., a 2-axis, 3-axis, 4-axis, 5-axis, or 6-axis arm). In such an embodiment, the scanner 108 and / or the scan lens 112 may be transported by the end effector of the robot arm, if necessary. In yet another embodiment, the workpiece 102 may be transported directly on the end effector of the multi-axis articulated robot arm (i.e., without the stage 110). In yet another embodiment, the stage 110 may be transported on the end effector of the multi-axis articulated robot arm.

[0067] E. Scan Lens

[0068] Generally, the scan lens 112 (for example, provided as either a simple lens or a composite lens) is typically configured to focus a laser energy beam directed along the beam path to generate a beam waist that may be located at or near a desired process spot. The scan lens 112 may be provided as an f-theta lens, a telecentric lens, an axicon lens (in which case a series of beam waists are generated, resulting in multiple process spots offset from each other along the beam axis), or any combination thereof. The scan lens 112 may be provided as a non-telecentric lens (as illustrated), a f-theta lens, a telecentric lens, an axicon lens (in which case a series of beam waists are generated, resulting in multiple process spots offset from each other along the beam axis), or any combination thereof.

[0069] In one embodiment, the scan lens 112 is provided as a fixed focal length lens and is connected to a movable scan lens positioner (e.g., a lens actuator, not shown) to change the position of the beam waist along the beam axis. For example, the lens actuator may be provided as a voice coil capable of linearly translating the scan lens 112 along the Z direction. In this case, the scan lens 112 may be formed from a material such as fused silica, optical glass, zinc selenide, zinc sulfide, germanium, gallium arsenide, or magnesium fluoride. In another embodiment, the scan lens 112 is provided as a variable focal length lens (e.g., a zoom lens, or a so-called "liquid lens" incorporating technology currently offered by COGNEX, VARIOPTIC, etc.) that can be operated (e.g., via a lens actuator) to change the position of the beam waist along the beam axis. By changing the position of the beam waist along the beam axis, the spot size on the workpiece 102 can be changed.

[0070] In embodiments where the device 100 includes a lens actuator, the lens actuator may be coupled to the scan lens 112 (for example, to allow the scan lens 112 to move relative to the scanner 108 within the scan head). Alternatively, the lens actuator may be coupled to the scan head (for example, to allow the scan head itself to move when the scan lens 112 and the scanner 108 move together). In other embodiments, the scan lens 112 and the scanner 108 are integrated into different housings (for example, so that the housing into which the scan lens 112 is integrated is movable relative to the housing into which the scanner 108 is integrated).

[0071] F. Controller

[0072] Generally, the device 100 includes one or more controllers, such as a controller 122, for controlling or facilitating the control and operation of the device 100. In one embodiment, the controller 122 is communicatively connected (via one or more wired or wireless serial or parallel communication links, such as USB, RS-232, Ethernet, Firewire, Wi-Fi, RFID, NFC, Bluetooth, Li-Fi, SERCOS, MARCO, EtherCAT, or any combination thereof) to one or more components of the device 100, such as a laser source 104, a beam modulator 106, a scanner 108, a stage 110, a lens actuator, a scanning lens 112 (if provided as a variable focal length lens), and fixtures, so that these components operate in response to one or more control signals output by the controller 122.

[0073] For example, the controller 122 can control the operation of the beam modulator 106 to selectively and variably attenuate the laser energy beam incident on the beam modulator 106, or to deflect the beam path 114 (for example, to cause relative movement between the beam axis and the workpiece so as to cause relative motion between the process spot and the workpiece 102 along a path or trajectory (also referred to herein as the “process trajectory”)), or a combination thereof. Similarly, the controller 122 can control the operation of the scanner 108, the stage 110, or any combination thereof to cause relative movement between the beam axis and the workpiece so as to cause relative movement between the process spot and the workpiece 102 along the process trajectory.

[0074] Generally, the controller 122 includes one or more processors capable of generating the aforementioned control signals when executing instructions. The processors may be provided as programmable processors capable of executing instructions (e.g., one or more general-purpose computer processors, microprocessors, digital signal processors, or any combination thereof). Instructions executable by the processors may be implemented as software, firmware, or in any preferred form of circuitry, including programmable logic devices (PLDs), field-programmable gate arrays (FPGAs), field-programmable object arrays (FPOAs), application-specific integrated circuits (ASICs) (including digital circuits, analog circuits, and mixed analog / digital circuits), or any combination thereof. Instruction execution may occur on a single processor, distributed across multiple processors, in parallel across multiple processors within a single device or across a network of devices, or in similar manner, or in any combination thereof.

[0075] In one embodiment, the controller 122 includes a tangible medium such as computer memory accessible by the processor (e.g., via one or more wired or wireless communication links). As used herein, “computer memory” includes magnetic media (e.g., magnetic tape, hard disk drives, etc.), optical disks, volatile or non-volatile semiconductor memory (e.g., RAM, ROM, NAND flash memory, NOR flash memory, SONOS memory, etc.), and may be locally accessible, remotely accessible (e.g., via a network), or a combination thereof. Generally, instructions may be stored as computer software (e.g., executable code, files, instructions, library files, etc.). Such computer software can be written in, for example, C, C++, Visual Basic, Java, Python, Tel, Perl, Scheme, Ruby, assembly language, hardware description languages ​​(e.g., VHDL, VERILOG, etc.) and can be easily created by those skilled in the art from the descriptions provided herein. Computer software is typically stored in one or more data structures transmitted by computer memory.

[0076] Although not shown in the figures, one or more drivers (e.g., RF drivers, servo drivers, line drivers, power supplies, etc.) may be communicatively coupled to the inputs of one or more components, such as the laser source 104, beam modulator 106, scanner 108, stage 110, lens actuator, and (if provided as a variable focal length lens) scan lens 112, to control such components. Thus, one or more components, such as the laser source 104, beam modulator 106, scanner 108, stage 110, lens actuator, and (if provided as a variable focal length lens) scan lens 112, can also be considered to include any suitable drivers known in the art. Each driver typically includes an input to which a controller 122 is communicatively coupled, and the controller 122 is capable of generating one or more control signals (e.g., trigger signals). These control signals may be transmitted to the inputs of one or more drivers associated with one or more components of the apparatus 100. Thus, components such as the laser source 104, beam modulator 106, scanner 108, stage 110, lens actuator, and (if provided as a variable focal length lens) scan lens 112 are configured to respond to control signals generated by the controller 122.

[0077] Although not shown, one or more additional controllers (e.g., component-specific controllers) may, as needed, be communicably connected to the inputs of drivers communicably connected to (and associated with) components such as the laser source 104, beam modulator 106, scanner 108, stage 110, lens actuator, and (if provided as a variable focal length lens) scan lens 112. In this embodiment, each component-specific controller may be communicably connected to controller 122 and capable of generating one or more control signals (e.g., trigger signals) in response to one or more control signals received from controller 122. These one or more control signals may then be transmitted to the inputs of drivers communicably connected to it. In this embodiment, the component-specific controllers may be operable in the same manner as described with respect to controller 122.

[0078] In other embodiments where one or more component-specific controllers are provided, a component-specific controller associated with a component (e.g., a laser source 104) may be communicatively coupled to a component-specific controller associated with another component (e.g., a beam modulator 106). In this embodiment, one or more of the component-specific controllers may generate one or more control signals (e.g., trigger signals) in response to one or more control signals received from one or more other component-specific controllers.

[0079] G. Rear reflection detection system

[0080] As described above, when forming non-penetrating via holes at different locations within the dielectric substrate 24 using the same drilling parameters, some morphological variation is likely to occur among the ultimately produced non-penetrating via holes (for example, due to the non-uniformity of the inherent composition of the dielectric substrate 24, variations in the surface reflectance / thickness of the upper conductor 20, etc.). To reduce the possibility of undesirable morphological variation, the apparatus 100 is equipped with a back reflection detection system 124. The output of the back reflection detection system 124 can be used (alone or in cooperation with the controller 122) to perform a adaptive processing method in which one or more parameters of the process used to form non-penetrating via holes (e.g., pulse width, average power, peak power, pulse energy, number of laser pulses, etc., or any combination thereof) are set based on one or more characteristics of the back reflection signal.

[0081] Generally, back-reflected signals are those that are reflected by the workpiece 102 from a portion of the laser energy beam irradiated onto the workpiece 102 (for example, during the process of forming non-penetrating via holes). Depending on the material of the workpiece 102 being processed and the wavelength of the laser energy beam irradiated onto the workpiece 102 during laser processing, the workpiece 102 may reflect at least a portion of the laser energy beam irradiated from the scan lens 112. For example, the laser energy beam may have a wavelength of approximately 9.4 μm, and the workpiece 102 may be provided as a PCB as described above with respect to Figures 1 and 2. In this case, an effective proportion of the laser energy beam irradiated onto the workpiece 102 may be reflected by the upper conductor 20 and returned to the scan lens 112. When processing the workpiece 102 (i.e., the PCB described above) to form non-penetrating via holes 30 terminated at the bottom conductor 22, a portion of the laser energy beam irradiated onto the bottom conductor 22 may also be reflected by the bottom conductor 22. It should be noted that one or more components of the dielectric substrate 24 (e.g., resin material 26, reinforcing material 28, or a combination thereof) may also reflect some of the laser energy beam, but typically the amount reflected is much less than the amount that can be reflected by the upper conductor 20 or the bottom conductor 22.

[0082] In Figure 4, the back reflection detection system 124 is shown to be positioned on the beam path 114 between the beam modulator 106 and the scanner 108 (so as to be optically coupled to the optical output of the beam modulator 106 and the optical input of the scanner 108). Thus, the back reflection detection system 124 can operate to capture at least a portion of the back reflection signal from a position along the beam path 114 between the beam modulator 106 and the scanner 108. However, it can be understood that the back reflection detection system 124 may also be configured to capture at least a portion of the back reflection signal from one or more other suitable or desired positions along the beam path 114 (e.g., between the laser source 104 and the beam modulator 106, between the scanner 108 and the scan lens 112, between the scan lens 112 and the workpiece 102, or any combination thereof).

[0083] Furthermore, the rear reflection detection system 124 can operate to convert the captured rear reflection signal into an electronic signal (also referred to herein as the "sensor signal"). The sensor signal can then be processed (for example, by the rear reflection detection system 124 or the controller 122) to determine whether further machining is required to form a non-through via hole in the workpiece 102. If necessary, the sensor signal is processed (for example, by the rear reflection detection system 124 or the controller 122) to determine how further machining is required to form a non-through via hole in the workpiece 102. Examples of embodiments relating to the configuration and operation of the rear reflection detection system 124 and the processing of the sensor signal are described in more detail below.

[0084] III. Examples of Embodiments Related to a Rear Reflection Detection System

[0085] Referring to Figure 5, the back reflection detection system 124 may include, for example, a polarizing beam splitter 500, a waveplate 502 (e.g., a quarter-wave plate), a lens 504, and a detector 506 (e.g., a photodetector). During the process of forming a non-penetrating via hole (for example, as described above with respect to Figure 3), the laser energy beam propagates from the beam modulator 106 along the beam path 114 and subsequently passes through the polarizing beam splitter 500, waveplate 502, scanner 108, and scanning lens 112 to irradiate the workpiece 102 (for example, provided as a PCB as described above with respect to Figures 1 and 2).

[0086] In the illustrated embodiment, the laser energy beam has a wavelength (e.g., ~9.4 μm) that is at least partially reflectable by one or more materials of the workpiece 102. Therefore, a portion of the irradiated laser energy beam is reflected by the workpiece 102 and subsequently propagates through the scanning lens 112, scanner 108, and waveplate 502 (e.g., along beam path 114 or along a different beam path). The reflected light is polarized by the waveplate 502 before being incident on the polarizing beam splitter 500. The polarizing beam splitter 500 then reflects the reflected light that has passed through the waveplate 502 toward the lens 504 (e.g., along beam path 510 toward lens 504). The lens 504 focuses the reflected light onto the detector 506. In this case, the operation of polarizing the back-reflected light at the waveplate 502 during the formation of non-penetrating via holes in the workpiece 102 and reflecting the back-reflected light along beam path 510 constitutes "capturing" the back-reflected signal.

[0087] Generally, the detector 506 can operate to convert incident reflected light (propagating from lens 504 along path 510) into an electric current and output this current as the sensor signal described above (for example, to controller 122). Therefore, the output of detector 506 varies depending on the intensity of the reflected light incident on it.

[0088] IV. Explanation of Backward Reflected Signals

[0089] Figure 6 is a graph showing the signal intensity of an exemplary back-reflected signal captured by the back-reflected signal detection system 124 as a function of time (during the formation of a non-penetrating via hole according to an embodiment of the present invention). That is, the graph shown in Figure 6 shows the signal intensity of an exemplary back-reflected signal captured when a typical initial (i.e., first) laser pulse is irradiated onto the workpiece 102 (e.g., provided as a PCB as described above with respect to Figures 1 and 2) to form a non-penetrating via hole (e.g., as described above with respect to Figure 3).

[0090] For illustrative purposes, it can be assumed that the initial laser pulse on which the captured back-reflected signal shown in Figure 6 is based has a pulse duration in the range of approximately 10 μs to 11 μs and a pulse energy sufficient to form an opening in the upper conductor 22 of the PCB and remove a portion of the dielectric substrate 24 beneath it. However, it can be understood that the initial laser pulse may have a pulse duration shorter than 10 μs or longer than 11 μs. According to the embodiments described herein, the pulse energy of the initial laser pulse irradiated onto the workpiece 102 in the process of forming a non-penetrating via hole in the workpiece 102 is sufficient to form an opening in the upper conductor 20 by a process known as “indirect ablation” and also sufficient to remove a portion of the dielectric substrate 24 exposed by the opening by a process known as “direct ablation”.

[0091] Direct ablation of the material in workpiece 102 occurs when the primary cause of ablation is thermal decomposition of the material due to energy absorption by the material in the irradiated laser energy beam (e.g., linear absorption, nonlinear absorption, or any combination thereof). Indirect ablation of the material in workpiece 102 (also known as "lift-off") occurs when the primary cause of ablation is melting and vaporization due to heat transferred from an adjacent material that absorbs energy in the laser energy beam ultimately irradiated onto workpiece 102. Considerations for material removal by indirect (and direct) ablation are known in the art and are described in International Publication WO 2017 / 044646 A1. In this case, the upper conductor 20 reflects a portion of the initial laser pulse irradiated onto workpiece 102, and the upper conductor 20 becomes hot as a result of irradiation by the initial laser pulse. Heat is dissipated or transferred from the upper conductor 20 to the region of the dielectric substrate 24 below the region of the upper conductor 20 that is irradiated with the initial laser pulse. As a result, over time, heat transferred from the upper conductor 20 accumulates in the region of the dielectric substrate 24, causing that region to vaporize. If the irradiated region of the upper conductor 20 does not reach a temperature above its processing threshold temperature, the vaporization of the region of the dielectric substrate 24 acts to create a pocket or space below the irradiated region of the upper conductor 20 (for example, a high-pressure region containing pressurized heating gas, particles, etc., generated during the vaporization of the dielectric substrate 24). Subsequently, when the region of the upper conductor 20 irradiated by the initial laser pulse reaches the processing threshold temperature, the pressure increase in the pocket below becomes sufficient to eject the irradiated region of the upper conductor 20 from the workpiece, thereby "indirectly ablating" the upper conductor 20 and exposing the dielectric substrate 24 below it.

[0092] Returning to Figure 6, the backreflected signal associated with the initial laser pulse can be characterized as comprising a primary intensity period 600 with relatively high intensity, followed by a secondary intensity period 602 with relatively low intensity. In the example shown in Figure 6, the backreflected signal is fairly constant for approximately the first 6 μs (e.g., with a relatively high signal intensity of about 0.5 au). Thereafter, the signal intensity drops sharply (e.g., over a period of about 1 μs to 1.5 μs), then the decrease in signal intensity becomes more gradual (e.g., over a period of about 2.5 μs), and then increases again briefly to a secondary peak 604 (e.g., to about 0.1 au), before decreasing to zero.

[0093] The progression of the signal intensity of the back-reflected signal encodes the dynamics of the indirect ablation process associated with the formation of non-penetrating via holes. For example, the relatively high signal intensity during the primary intensity period 600 corresponds to the light reflected by the upper conductor 20 when the processing of the non-penetrating via hole began using the first laser pulse. During this time, heat transferred from the upper conductor 20 accumulates in the dielectric substrate 24, causing the dielectric substrate 24 to vaporize and form a pocket consisting of pressurized heating gas, particles, etc. The subsequent sharp decrease in signal intensity indicates that the irradiated area of ​​the upper conductor 20 exceeds its processing threshold temperature, and the increased pressure in the pocket below causes the irradiated area of ​​the upper conductor 20 to erupt, thus directly exposing the dielectric substrate 24 below to the initial laser pulse. Therefore, the duration t1 of the primary intensity period 600 corresponds to the time it takes for the irradiated laser pulse to form an opening in the upper conductor 20. The signal intensity peak 604 during the secondary intensity period 602 indicates that a portion of the dielectric substrate 24 was removed by the first laser pulse, exposing a portion of the bottom conductor 22 (an operation also referred to herein as forming an opening within the dielectric substrate 24). The decrease to near zero signal intensity at 608 indicates the end of the laser pulse striking the workpiece surface.

[0094] A. Embodiments relating to captured back-reflected signal characteristics

[0095] As described above, the back reflection detection system 124 can operate to convert the back reflection signal (captured when the initial laser pulse is irradiated onto the workpiece 102) into a sensor signal representing the captured back reflection signal. The sensor signal can be processed (for example, by the back reflection detection system 124 or the controller 122, or a combination thereof) to identify one or more characteristics of the captured back reflection signal that can be represented by or obtained from the sensor signal. It will be understood that the sensor signal can be processed using one or more suitable signal processing techniques known in the art to identify one or more characteristics of the captured back reflection signal. Exemplary embodiments of such characteristics of the captured back reflection signal are described in more detail below.

[0096] i. Duration of the primary intensity period

[0097] One embodiment of the characteristics of the captured back-reflected signal that can be used to make processing decisions is the duration t1 of the primary intensity period 600. In Figure 6, the duration of the primary intensity period 600 is measured based on the time relative to the full width at half maximum (FWHM) of the signal intensity of the captured back-reflected signal. However, in other embodiments, the primary intensity period may be considered to coincide with the end of the rise time of the initial laser pulse from which the back-reflected signal is captured. The pulse rise time can be considered as the time interval required for the leading edge of the laser pulse to rise from 10% to 90% of the peak pulse amplitude. Also, as shown in Figure 6, the duration t2 represents the period from the end of the primary intensity period 600 to the end of the laser pulse.

[0098] Given the above definitions of durations t1 and t2, it should be clear that as t1 decreases, t2 increases. And as t1 increases, t2 decreases. Experiments conducted by the applicant tend to show that non-penetrating via holes associated with captured back-reflected signals having a relatively short duration of t1 (i.e., a relatively long duration of t2) tend to have an undesirably large overhang, and non-penetrating via holes associated with captured back-reflected signals having a relatively long duration of t1 (i.e., a relatively short duration of t2) tend to have an undesirably large taper.

[0099] ii. Integration of the region within the secondary intensity period

[0100] Another embodiment of the characteristics of the captured back-reflected signal that can be used to make a processing decision is the integrated area of ​​the signal from the end of t1 to the end of the laser pulse, which captures both the second-order peak 604 (indicating the formation of an aperture in the dielectric substrate 24) and the total length of time the laser energy is irradiated onto the dielectric substrate 24.

[0101] iii. Other Embodiments of Captured Back-Reflected Signal Characteristics

[0102] Other embodiments of the characteristics of the captured back-reflected signal that can be used to make processing decisions include the signal intensity at the secondary peak of the captured back-reflected signal (e.g., 604 as shown in Figure 6) and the signal intensity at the primary peak (i.e., the highest signal intensity) of the captured back-reflected signal (e.g., 606 as shown in Figure 6).

[0103] B. Embodiment relating to the comparison between captured back reflection signal characteristics and reference back reflection signal characteristics

[0104] Once identified, the captured backreflected signal characteristic (or other data representing it) can be compared to a reference backreflected signal characteristic associated with that captured backreflected signal characteristic (for example, in the backreflected detection system 124 or controller 122, or a combination thereof). For example, if the captured backreflected signal characteristic is the aforementioned duration t1 of the primary intensity period, the associated reference backreflected signal characteristic would be some reference value or range for the duration t1 of the primary intensity period. If the captured backreflected signal characteristic is the aforementioned integrated area of ​​the signal during the secondary intensity period, the associated reference backreflected signal characteristic would be some reference value or range for the integrated area.

[0105] It can be understood that such comparisons are possible by processing the sensor signal (for example, using one or more suitable signal processing techniques known in the art), by processing data associated with the identified characteristics, or similarly, or by any combination thereof. It can be further understood that the reference value or reference range of the associated data-referenced back-reflected signal characteristics may correspond to one or more parameters of the portion of the initial laser pulse irradiated onto the workpiece 102 up to the time the back-reflected signal characteristics were captured (e.g., duration, peak power, spot size, wavelength, etc.), one or more parameters of the workpiece 102 (e.g., material composition of the upper conductor 20, thickness of the upper conductor 20, material composition of the dielectric substrate 24, thickness of the dielectric substrate 24, etc.), or any combination thereof. For example, the reference value or reference range for the duration t1 of the primary intensity period may be (a) a decrease due to an increase in the peak power of the initial laser pulse or an increase due to a decrease in the peak power of the initial laser pulse, an increase due to an increase in the thickness of the upper conductor 20 or a decrease due to a decrease in the thickness of the upper conductor 20, or (b) a decrease if the upper conductor 20 is covered with an energy-absorbing coating, or (c) an increase or decrease due to the composition of the matrix material 26, or (d) something similar, or any combination thereof. These reference values ​​or reference ranges may be obtained or determined through empirical observation, computational simulation or diagnosis, or any combination thereof.

[0106] V. Embodiments relating to adaptive processing

[0107] Apparatus 100 can be used to perform an adaptive processing method in which one or more parameters of the process used to form non-penetrating via holes (e.g., pulse width, average power, peak power, pulse energy, number of laser pulses, or any combination thereof) are set based on a comparison of the captured back-reflected signal characteristics (or other data representing them) with an associated reference back-reflected signal characteristics. In this case, the process used to form non-penetrating via holes can generally be characterized as a “punching” process that requires at least one laser pulse to be irradiated onto a single desired location in the workpiece 102 (provided as the PCB described above with reference to Figures 1 and 2). The first laser pulse irradiated onto the workpiece 102 to form a particular non-penetrating via hole is referred to herein as the “initial laser pulse.” Subsequent laser pulses irradiated onto the workpiece 102 to form a particular non-penetrating via hole are referred to herein as “supplementary laser pulses,” or may be labeled according to their order in a series of laser pulses irradiated onto the workpiece 102 to form a particular non-penetrating via hole (e.g., “second laser pulse,” “third laser pulse,” “final laser pulse,” etc.).

[0108] Since the initial laser pulse is to be irradiated onto the workpiece 102, the initial laser pulse is characterized by a set of laser pulse parameters (also referred to herein as “initial laser pulse parameters”) such as wavelength, pulse duration, temporal optical power profile, peak power associated with the temporal optical power profile, spot size, and pulse energy. Generally, the pulse duration of any laser pulse can be adjusted by controlling the operation of the laser source 104 in any manner known in the art, by controlling the operation of the beam modulator 106 (for example, to perform pulse slicing as described above), or by similar methods, or by any combination thereof. Examples of temporal optical power profiles that the initial laser pulse may have include rectangular, chair (low to high, high to low, or a combination thereof), and ramp (increasing and / or decreasing in a stepwise, linear, or nonlinear manner, or a combination thereof). The time-optical power profile (and thus the peak power) of any laser pulse can be adjusted by controlling the operation of the laser source 104 in any way known in the art, by controlling the operation of the beam modulator 106, or by similar methods, or by any combination thereof.

[0109] Generally, the initial laser pulse parameters are set so that a non-penetrating via hole (e.g., a non-penetrating via hole 30 as illustrated in Figure 3) with desired characteristics (e.g., overhang, taper, or any combination thereof) is formed at a reference position in the workpiece 102 using only the initial laser pulse. The reference position may be a position in the workpiece 102 corresponding to, for example, position "B" or position "C" (both shown in Figure 1). Therefore, the setting of the initial laser pulse parameters may vary depending on the configuration of the workpiece 102, and the determination of the reference pulse energy amount may be determined empirically or computationally. Furthermore, one or more of the aforementioned back-reflected signal characteristics (e.g., the duration t1 of the primary intensity period, the integrated area of ​​the signal during the secondary intensity period, etc.) can be determined empirically (e.g., by irradiating the workpiece 102 with a laser pulse having initial laser pulse parameters as described above, and capturing and processing the resulting captured back-reflected signal), obtained computationally, obtained by similar methods, or obtained by any combination thereof, and can be set as a reference value or reference range for the back-reflected signal characteristics associated with the initial laser pulse irradiated onto the workpiece 102 during the "punching" process that forms non-penetrating via holes at any position in the workpiece 102.

[0110] In one embodiment, the initial laser pulse irradiated onto the workpiece 102 may have a wavelength in the range of 9 μm (or around there) to 11 μm (or around there) (e.g., wavelengths such as 9.4 μm (or around there), 10.6 μm (or around there)), a pulse duration in the range of 5 μs (or around there) to 20 μs (or around there), a rectangular (or at least substantially rectangular) temporal optical power profile, a peak power in the range of 250 W (or around there) to 2 kW (or around there), and a spot size in the range of 30 μm (or around there) to 90 μm (or around there). It will also be understood that the initial laser pulse irradiated onto the workpiece 102 may have other characteristics (e.g., pulse duration, temporal optical power profile, peak power, spot size, pulse energy, etc.) such that the initial laser pulse is set to process the workpiece 102, and may have a wavelength shorter than 9 μm (e.g., in the ultraviolet or visible green region of the electromagnetic spectrum). It should be noted that when the wavelength is changed to the ultraviolet or visible-green region of the electromagnetic spectrum, the initial laser pulse is replaced by the first set of laser pulses, each of which has a pulse duration in the ns or ps range (e.g., in the range of 10 ns (or around) to 1 ps (or around)) and the laser pulses are irradiated at a pulse repetition rate in the range of 100 MHz (or around) to 5 GHz (or around).

[0111] An adaptive processing method is applied to the workpiece 102 to perform a "punch" process that creates non-penetrating via holes at arbitrary locations within the workpiece 102. An initial laser pulse (with initial laser pulse parameters) is irradiated onto the workpiece 102. At least a portion of the light in the initial laser pulse is reflected by the workpiece 102 (i.e., by the upper conductor 20) and returns to the scan lens 112, where it is subsequently captured as described above with respect to Figure 5. The resulting captured backreflection signal is then processed to identify one or more captured backreflection signal characteristics (or other data representing them) associated with the initial laser pulse (e.g., as described above). Such characteristics can then be compared (e.g., as described above) (e.g., in the backreflection detection system 124, in the controller 122, or similar locations, or any combination thereof). As will be described in more detail below, the controller 122 may operate to control the operation of one or more components of the apparatus 100 (e.g., the laser source 104, the beam modulator 106, or any combination thereof) based on the comparison results.

[0112] In one embodiment, the captured backreflected signal characteristic associated with the initial laser pulse is the duration t1 of the primary intensity period. Therefore, the duration t1 of the primary intensity period is compared to a predetermined reference value or range. In another embodiment, the captured backreflected signal characteristic associated with the initial laser pulse is the integrated area of ​​the signal during the secondary intensity period. Therefore, the integrated area of ​​the signal during the secondary intensity period is compared to a predetermined reference value or range. In yet another embodiment, the captured backreflected signal characteristic associated with the initial laser pulse is a combination of the characteristics described above. Therefore, the captured characteristics are compared to predetermined reference values ​​or ranges for each of these characteristics.

[0113] If the duration t1 of the primary intensity period associated with the initial laser pulse is greater than the associated reference value or reference range, this indicates that the initial laser pulse (with the initial laser pulse parameters) is not sufficient to form an opening in the upper conductor 20 or to form a non-penetrating via hole with the desired properties (e.g., in the sense of tapering). If the duration t1 of the primary intensity period of the initial laser pulse is smaller than the associated reference value or reference range, this indicates that the initial laser pulse is not sufficient to form a non-penetrating via hole with the desired properties (e.g., in the sense of overhang), or may damage (undesirably melt or remove) the bottom conductor 22 that is ultimately exposed within the non-penetrating via hole.

[0114] If a comparison between the captured back-reflected signal characteristics and a reference value or range associated with them indicates that the initial laser pulse is insufficient to form a non-penetrating via hole with desired characteristics (e.g., as described above), the controller 122 may output one or more control signals (e.g., to the laser source 104, the beam modulator 106, or any combination thereof) to ensure that a non-penetrating via hole with desired characteristics (e.g., in the sense of taper and overhang) is formed. For example, as can be seen (e.g., from Figure 6), the duration t1 of the primary intensity period and the integrated area of ​​the signal during the secondary intensity period can be identified from the captured back-reflected signal associated with the initial laser pulse before the entire initial laser pulse irradiates the workpiece 102. Therefore, one or more control signals output by the controller 122 may act to adjust the initial laser pulse parameters (e.g., to adjust the temporal optical power by increasing or decreasing the instantaneous power of the initial laser pulse, to increase or decrease the pulse duration of the initial laser pulse, or similar actions, or any combination thereof). Instead of, or in addition to, modifying the initial laser pulse parameters of the initial laser pulse, one or more control signals output by the controller 122 can act to cause one or more supplemental laser pulses to irradiate the workpiece 102 after the entire initial laser pulse has irradiated the workpiece 102. As used herein, modification of one or more initial laser pulse parameters or irradiation of supplemental laser pulses, such as being initiated by the controller 122 (for example, when the controller 122 outputs one or more control signals as a result of the comparison described above), is referred herein to as an "adaptive response" to the captured backreflected signal characteristics.

[0115] If the duration t1 of the primary intensity period associated with the initial laser pulse is greater than the associated reference value or reference range, the controller 122 may operate to adjust the temporal optical power profile (e.g., by increasing the instantaneous power of the initial laser pulse) and / or increase the pulse duration of the initial laser pulse. In one embodiment, the laser pulse parameters described above are adjusted in a predetermined manner regardless of how much greater the duration t1 of the primary intensity period of the initial laser pulse is than the associated reference value or reference range. In other embodiments, the laser pulse parameters described above are adjusted in a predetermined manner corresponding to the difference in the duration t1 of the primary intensity period of the initial laser pulse with respect to the reference value or reference range associated with the initial laser pulse. If one or more supplemental laser pulses are irradiated onto the workpiece 102, any of these supplemental laser pulses may be characterized by laser pulse parameters that are the same as or different from the initial laser pulse parameters (e.g., to reduce the rate at which the dielectric substrate 24 is removed by the supplemental laser pulse). Generally, the method by which the controller 122 performs an adaptive response can be predetermined (for example, based on empirical observation, computational simulation, or any combination thereof), determined in real time (for example, by interpolation of predetermined data), similar to this, or any combination thereof.

[0116] If the duration t1 of the primary intensity period associated with the initial laser pulse is smaller than the associated reference value or reference range, the controller 122 may operate to adjust the temporal optical power profile (e.g., by reducing the instantaneous power of the initial laser pulse) and / or reduce the pulse duration of the initial laser pulse. In one embodiment, the laser pulse parameters described above are adjusted in a predetermined manner regardless of how small the duration t1 of the primary intensity period of the initial laser pulse is compared to the associated reference value or reference range. In other embodiments, the laser pulse parameters described above are adjusted in a predetermined manner corresponding to the difference in the duration t1 of the primary intensity period of the initial laser pulse relative to the reference value or reference range associated with the initial laser pulse. If one or more supplemental laser pulses are irradiated onto the workpiece 102, any of these supplemental laser pulses may be characterized by laser pulse parameters that are the same as or different from the initial laser pulse parameters (e.g., to increase the rate at which the dielectric substrate 24 is removed by the supplemental laser pulse). Generally, the method by which the controller 122 performs an adaptive response can be predetermined (for example, based on empirical observation, computational simulation, or any combination thereof), determined in real time (for example, by interpolation of predetermined data), similar to this, or any combination thereof.

[0117] VII. Conclusion

[0118] The above describes embodiments and examples of the present invention and should not be construed as limiting thereto. For example, while adaptive processing methods are described above with respect to non-through via hole formation processes, it will be understood that these adaptive processing methods can be extended to through via hole formation methods and the like. Although several specific embodiments and examples have been described with reference to the drawings, those skilled in the art will readily recognize that many improvements are possible to the disclosed embodiments and examples and other embodiments without departing significantly from the novel teachings and advantages of the present invention. Therefore, all such improvements are intended to fall within the scope of the present invention as defined in the claims. For example, those skilled in the art will understand that the subject matter of any sentence or paragraph, example or embodiment can be combined with the subject matter of some or all of other sentences or paragraphs, examples or embodiments, unless such combinations are mutually exclusive. Therefore, the scope of the present invention should be determined by the following claims and their equivalents.

Claims

1. A laser processing apparatus for performing a process of forming vias in a workpiece by irradiating a workpiece formed on a second material with laser energy having a wavelength such that the first material is more reflective than the second material, thereby causing the laser energy to be incident on the first material, A back reflection detection system capable of capturing a back reflection signal corresponding to a portion of the laser energy irradiated onto the workpiece and reflected by the first material, and generating a sensor signal based on the captured back reflection signal, A controller that is communicably connected to the output of the back reflection detection system, and is capable of controlling the remainder of the process in which the vias are formed based on the sensor signal. A laser processing device equipped with the following features.

2. The laser processing apparatus according to claim 1, wherein the laser energy irradiated onto the workpiece is represented as at least one laser pulse, and the controller can at least partially control the process by controlling the pulse energy of the at least one laser pulse.

3. The laser processing apparatus according to claim 1, wherein the laser energy irradiated onto the workpiece is represented as at least one laser pulse, and the controller can at least partially control the process by controlling the pulse width of the at least one laser pulse.

4. The laser processing apparatus according to claim 1, wherein the laser energy irradiated onto the workpiece is represented as at least one laser pulse, and the controller can at least partially control the process by controlling the number of laser pulses irradiated onto the workpiece.

5. The laser processing apparatus according to claim 1, wherein the controller can at least partially control the process by controlling the average power of the laser energy.

6. The laser processing apparatus according to claim 1, wherein the controller can at least partially control the process by controlling the peak power of the laser energy.

7. The laser processing apparatus according to claim 1, wherein the laser energy irradiated onto the workpiece is represented as a laser pulse, and the controller can control the process by which the vias are formed when the laser pulse is irradiated onto the workpiece.

8. The laser processing apparatus according to claim 1, further comprising a laser source capable of generating the aforementioned laser energy.

9. The laser processing apparatus according to claim 1, further comprising a beam modulator capable of modulating the laser energy.

10. A process is performed to form vias in a workpiece by irradiating a workpiece formed on a second material with a laser pulse having a wavelength that makes the first material more reflective than the second material, thereby causing the laser pulse to incident on the first material. A back-reflected signal corresponding to a portion of the laser energy irradiated onto the workpiece and reflected by the first material is captured. A sensor signal is generated based on the captured back reflection signal. To process the sensor signal and determine how the remainder of the process should be carried out to form the via, Based on the processing of the sensor signal, the remainder of the process is performed. method.

11. The method according to claim 10, wherein the laser energy irradiated onto the workpiece is represented as at least one laser pulse, and performing the remainder of the process includes adjusting the pulse energy of the at least one laser pulse.

12. The method according to claim 10, wherein the laser energy irradiated onto the workpiece is represented as at least one laser pulse, and performing the remainder of the process includes adjusting the pulse width of the at least one laser pulse.

13. The method according to claim 10, wherein the laser energy irradiated onto the workpiece is represented as at least one laser pulse, and performing the remainder of the process includes adjusting the number of laser pulses irradiated onto the workpiece.

14. The method according to claim 10, wherein performing the remainder of the process includes adjusting the average power of the laser energy.

15. The method according to claim 10, wherein performing the remainder of the process includes adjusting the peak power of the laser energy.

16. The method according to claim 10, wherein the laser energy irradiated onto the workpiece is represented as a laser pulse, and the remainder of the process is performed while the laser pulse is irradiated onto the workpiece.

17. A laser processing apparatus capable of performing a process of forming vias in a workpiece by irradiating a workpiece formed on a second material with laser energy having a wavelength such that the first material is more reflective than the second material, thereby causing the laser energy to be incident on the first material, the laser processing apparatus comprising: a back reflection detection system capable of capturing a back reflection signal corresponding to a portion of the laser energy irradiated onto the workpiece and reflected by the first material, and generating a sensor signal based on the captured back reflection signal; and a controller communicatively connected to the output of the back reflection detection system, wherein the non-transient computer-readable medium for use with the laser processing apparatus, the non-transient computer-readable medium stores instructions that, when executed by the controller, cause the controller to control the process based on the sensor signal.

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