Laser processing device, method of operating same, and method of using same to process a workpiece

Abstract

The laser processing apparatus can perform a process of forming a via in a workpiece having a first material formed on a second material by irradiating the workpiece with laser energy having a wavelength that is more reflective of the first material than the second material, and causing the laser energy to be incident on the first material. The laser processing apparatus can include a back reflection detection system operable to capture a back reflection signal corresponding to a portion of the laser energy irradiated on the workpiece and reflected from the first material and generate a sensor signal based on the captured back reflection signal, and a controller communicatively coupled to an output of the back reflection detection system, the controller operable to control the remainder of the process in which the via is formed based on the sensor signal.

Description

[Technical Field]

[0001] TECHNICAL FIELD Embodiments of the present invention relate to a laser processing apparatus and a method for operating the same.

[0002] Printed circuit boards (PCBs) are typically formed from conductive layers stacked on a dielectric substrate. PCBs can be double-sided or multi-layered. A double-sided PCB contains two conductive layers stacked on either side of a common dielectric substrate. A multi-layer PCB typically has multiple dielectric substrates with conductive layers sandwiched between them and one or more conductive layers stacked on the outer surfaces of the substrates.

[0003] Dielectric substrates are typically provided as composite materials formed from a matrix material (e.g., epoxy resin) and a reinforcing material (e.g., woven glass fiber cloth). Such dielectric substrates necessarily have a heterogeneous composition, as shown in FIG. 1. Referring to FIG. 1, the woven glass fiber cloth (shown as white and gray fibers) is seen surrounded by a matrix material (shown in black). The composition of the dielectric substrate varies depending on the location. For example, at location "A," the dielectric substrate contains a relatively large amount of reinforcing material and a relatively small amount of matrix material. At location "B," the dielectric substrate contains only matrix material. At location "C," the dielectric substrate contains less reinforcing material than at location "A" and more than at location "B," and more matrix than at location "A" and less than at location "C." A schematic cross-sectional view of a portion of a PCB including a dielectric substrate such as that described with reference to FIG. 1 is shown in FIG. 2. Referring to FIG. 2, a conductor 20 (also referred to herein as the "top conductor") is provided on a first side of a dielectric substrate 24, and another conductor 22 (also referred to herein as the "bottom conductor") is disposed on a 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 blind-hole vias or through-hole vias, can be drilled in a PCB using a laser (e.g., using a laser drilling process). A schematic cross-sectional view of a blind-hole via formed in the PCB shown in FIG. 2 is shown in FIG. 3. Referring to FIG. 2, a blind-via hole 30 can be formed using a laser drilling “punch” process in which a laser energy beam is directed at a single location on the PCB to remove the dielectric substrate 24 to form an opening in the top conductor 20 and expose a portion of the bottom conductor 22 within the blind-via hole 30. However, the matrix and reinforcement materials of the dielectric substrate 24 often are not processed with the same efficiency by a laser. The matrix material is typically processed more easily than the reinforcement material. Also, there may be variations in the surface reflectivity and / or thickness of the top conductor 20 across different regions of the PCB. As a result, when identical drilling parameters (e.g., pulse width, peak pulse power) are used to form blind-via holes at different locations within the dielectric substrate, there will be some inherent variation in morphology between the resulting blind-via holes. The topographical characteristics of the blind-via holes may include the degree to which the top conductor extends beyond the sidewall of the hole formed in the dielectric substrate 24 (also known as "overhang") and the ratio of the diameter of the blind-via hole 30 in the bottom conductor 22 to the diameter of the blind-via hole 30 in the top conductor 20 (also known as "taper"). Generally, it is preferred that each via be characterized by a relatively small overhang and a relatively large taper. Thus, position-dependent variations in the topographical characteristics of blind-via holes are undesirable for high-performance PCBs and associated processing yields.

[0005] The above-mentioned variability problem can be somewhat reduced by processing PCBs using laser wavelengths that are relatively insensitive to variations in the dielectric substrate composition. For example, a carbon dioxide laser can generate laser energy at a wavelength of ∼9.4 μm that is linearly absorbed by the matrix and reinforcement materials but may be primarily reflected by the conductors (i.e., copper) exposed by blind via holes. It is generally known that more energy is required to remove the reinforcement material 28 than to remove the matrix material 26 (even with a laser wavelength of ∼9.4 μm). However, even though the energy required to remove a portion of the dielectric substrate 24 varies based on the relative amounts of matrix material 26 and reinforcement material 28 therein, it is generally possible to reliably remove the matrix and reinforcement materials of the dielectric substrate 24 without damaging (e.g., melting) the bottom conductors 22.

[0006] The above-mentioned variability problem can be further reduced by using multiple laser pulses to form a single blind via hole. In this case, a first pulse is applied to form an opening in the top conductor 20, and all subsequent pulses are applied to remove the remaining dielectric substrate 24 without damaging the bottom conductor 22. Proposed improvements to this "multiple pulse processing" technique typically involve adjusting the pulse energy of the second or subsequent laser pulses based on the intensity of the laser light reflected from the bottom conductor 22 (generally understood to correspond to the size of the area of ​​the bottom conductor 22 exposed by the blind via hole 30). Overview

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

[0008] Another embodiment of the present invention can be broadly characterized as a method of irradiating a workpiece having a first material formed on a second material with laser pulses having a wavelength that is more reflective from the first material than from the second material, performing a process of forming a via in the workpiece by causing the laser pulses to be incident on the first material, capturing backreflected signals corresponding to a portion of the laser energy irradiated on the workpiece and reflected from the first material, generating a sensor signal based on the captured backreflected signals, processing the sensor signal to determine how the remainder of the process should be performed to form the via, and performing the remainder of the process based on the processing of the sensor signal.

[0009] Yet another embodiment of the present invention can be broadly characterized as a non-transitory computer-readable medium for use with a laser processing apparatus capable of performing a process of forming a via in a workpiece having a first material formed on a second material by irradiating the workpiece with laser energy having a wavelength that is more reflective of the first material than the second material, and causing the laser energy to be incident on the first material, the laser processing apparatus comprising: a backreflection detection system operable to capture backreflection signals corresponding to a portion of the laser energy irradiated on the workpiece and reflected from the first material and generate a sensor signal based on the captured backreflection signals; and a controller communicatively coupled to an output of the backreflection detection system, the non-transitory computer-readable medium having stored thereon instructions that, when executed by the controller, cause the controller to control the process based on the sensor signal. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 illustrates an example arrangement of reinforcement material within a matrix material of a composite dielectric substrate that can be machined by a laser according to an embodiment of the present invention.

[0011] [Figure 2] FIG. 2 shows a schematic cross-sectional view of a portion of a PCB including a dielectric substrate as described with respect to FIG.

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

[0013] [Figure 4] FIG. 4 is a schematic diagram showing a laser processing apparatus according to an embodiment of the present invention.

[0014] [Figure 5]FIG. 5 is a schematic diagram illustrating a back reflection detection system of the laser processing apparatus shown in FIG. 4 according to one embodiment of the present invention.

[0015] [Figure 6] FIG. 6 is a graph illustrating signal strength of an exemplary back-reflected signal as a function of time (i.e., during the formation of a blind via hole) from the back-reflected sensing system described with respect to FIGS. 4 and 5, in accordance with an embodiment of the present invention. Detailed Description

[0016] Examples of embodiments will now be described with reference to the accompanying drawings. Unless explicitly stated, in the drawings, the sizes, positions, etc. of components, features, elements, etc., and the distances therebetween, are not necessarily to scale and have been exaggerated for clarity. Like numbers refer to like elements throughout the drawings. Thus, the same or similar numbers may be described with reference to other drawings even if they are not mentioned or described in the corresponding drawings. Also, elements without reference numbers may be described with reference to other drawings.

[0017] The terminology used in the specification is for the purpose of describing particular exemplary embodiments only and is not intended to be limiting. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art. As used herein, the singular is intended to include the plural unless the content clearly dictates otherwise. Furthermore, it should be understood that the terms "comprises" and / or "comprising," when used herein, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. Unless otherwise indicated, when a range of values ​​is recited, the range includes the upper and lower limits, as well as any subranges between the upper and lower limits of the range. Unless otherwise indicated, terms such as "first" and "second" are used merely to distinguish elements from one another. For example, one node can be referred to as a "first node," and similarly, another node can be referred to as a "second node," or vice versa.

[0018] Unless otherwise indicated, terms such as "about," "around," "substantially," and the like mean that amounts, sizes, compositions, parameters, and other quantities and characteristics are not, and need not be, exact and may be approximate and / or larger or smaller, as appropriate, or to reflect tolerances, conversion factors, rounding, measurement error, and the like, as well as other factors known to those skilled in the art. Spatially relative terms such as "lower," "below," "lower side," "upper," and "above" may be used herein for ease of description when describing the relationship of an element or feature to another element or feature, as depicted in the figures. It should be understood that spatially relative terms are intended to encompass different orientations in addition to those depicted in the figures. For example, an element described as being "lower" or "below" another element or feature would be oriented "above" that other element or feature if the object in the figure were inverted. Thus, the exemplary term "lower" can encompass both an orientation of upper and lower. If the object is oriented in other ways (e.g., rotated 90 degrees or at other orientations), the spatially relative descriptors used herein may be interpreted accordingly.

[0019] The section headings used herein, unless specifically stated, are for organizational purposes only and should not be construed as limiting the subject matter described. It will be understood that many different forms, embodiments, and combinations are possible without departing from the spirit and teachings of the present disclosure, and that the present disclosure should not be construed as limited to the example embodiments set forth herein. Rather, these examples and embodiments are provided so that this disclosure will be complete and all-inclusive, and will fully convey the scope of the disclosure to those skilled in the art.

[0020] I. Overview

[0021] FIG. 4 is a schematic diagram of a laser processing device according to one embodiment of the present invention.

[0022] Referring to the embodiment shown in FIG. 4, a laser processing apparatus 100 (also referred to herein simply as “apparatus”) for processing a workpiece 102 can be characterized as including a laser source 104 for generating a beam of laser energy, 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 exiting the beam modulator 106 along the beam path 114 may 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" refers to the path traveled by laser energy in the laser energy beam as it propagates from the laser source 104 to the scan lens 112.

[0024] Scanner 108 operates to diffract, reflect, refract, or the like, or any combination thereof, the laser energy beam generated by laser source 104 and optionally deflected by beam modulator 106 (i.e., to "deflect" the laser energy beam), so as to deflect beam path 114 towards scan lens 112. In deflecting beam path 114 towards scan lens 112, scanner 108 may deflect beam path 114 by any angle within a range of angles (as shown at 116) (e.g., as measured relative to the optical axis of scan lens 112).

[0025] The laser energy deflected toward the scan lens 112 is typically focused by the scan lens 112 to impinge on the workpiece 102 and transmitted to propagate along the beam axis. The laser energy impinging on 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., a "top hat" spatial intensity profile, a super-Gaussian spatial intensity profile, etc.).

[0026] As used herein, the term "spot size" refers to the diameter or maximum spatial width of the laser energy beam impinging on a location where the beam axis intersects with an area of ​​the workpiece 102 that is at least partially processed by the impinging laser energy beam (also referred to as a "process spot," "spot location," or more simply, "spot"). For purposes of discussion herein, spot size refers to the distance from the beam axis where the optical intensity is at least 1 / e of the optical intensity at the beam axis. 2 The spot size of the laser energy beam is measured as the radial or transverse distance down to the beam waist. Generally, the spot size of the laser energy beam is smallest at the beam waist. When irradiated onto the workpiece 102, the laser energy in the beam can be characterized as striking the workpiece 102 with a spot size ranging from 2 μm to 200 μm. However, it will be understood that the spot size can be less than 2 μm or greater than 200 μm. Thus, the laser energy beam irradiated onto the workpiece 102 can have a spot size greater than, less 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), etc., or any combination thereof) to focus, expand, collimate, shape, polarize, filter, split, combine, crop, absorb, or otherwise modify, condition, direct, or otherwise modify the laser energy beam as it propagates along the beam path 114.

[0028] A. Laser Source

[0029] In one embodiment, the laser source 104 is capable of generating laser pulses. As such, the laser source 104 may include a pulsed laser source, a CW laser source, a QCW laser source, a burst-mode laser, or the like, or any combination thereof. If the laser source 104 includes a QCW or CW laser source, the laser source 104 may be operated in a pulsed or non-pulsed mode and may further include a pulse gating unit (e.g., an acousto-optic (AO) modulator (AOM), a beam chopper, or the like) that temporally modulates the beam of laser radiation output from the QCW or CW laser source. Although not shown, the apparatus 100 may optionally include one or more harmonic generation crystals (also known as “wavelength conversion crystals”) configured to convert the wavelength of the light output by the laser source 104. However, in other embodiments, the laser source 104 may be provided as a QCW or CW laser source and may not include a pulse gating unit. As such, laser source 104 can be broadly characterized as being capable of generating a laser energy beam that may be expressed as a series of laser pulses or as a continuous or quasi-continuous laser beam, which may then propagate along beam path 114. While many of the embodiments described herein refer to laser pulses, it should be understood that a continuous or quasi-continuous beam may be used instead or in addition 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) regions of the electromagnetic spectrum. Laser energy in the UV region of the electromagnetic spectrum may have one or more wavelengths in the range of 10 nm (or thereabouts) to 385 nm (or thereabouts), such as 100 nm, 121 nm, 124 nm, 157 nm, 200 nm, 334 nm, 337 nm, 351 nm, 380 nm, etc., or wavelengths between any of these values. Laser energy in the visible green region of the electromagnetic spectrum may have one or more wavelengths in the range of 500 nm (or thereabouts) to 560 nm (or thereabouts), such as 511 nm, 515 nm, 530 nm, 532 nm, 543 nm, 568 nm, etc., or wavelengths between any of these values. Laser energy in the IR region of the electromagnetic spectrum may have one or more wavelengths in the range of 750 nm (or thereabouts) to 15 μm (or thereabouts), 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, etc., or wavelengths between any of these values.

[0031] When the laser energy beam is represented as a train 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) ranging from 10 fs to 900 ms, although it will be understood that the pulse duration may be shorter than 10 fs or longer than 900 ms. Thus, the at least one laser pulse output by the laser source 104 may be 10 fs, 15 fs, 30 fs, 50 fs, 100 fs, 150 fs, 200 fs, 300 fs, 500 fs, 600 fs, 750 fs, 800 fs, 850 fs, 900 fs, 950 fs, 1 ps, 2 ps, 3 ps, 4 ps, 5 ps, 7 ps, 10 ps, ​​15 ps, 25 ps, 50 ps, ​​75 ps, 100 ps, ​​200 ps, ​​500 ps, ​​1 ns, 1.5 ns, 2 ns, 5 ns, 10 ns, 20 ns, 50 ns, 100 The pulse duration may be shorter than, longer than, or equal to ns, 200 ns, 400 ns, 800 ns, 1000 ns, 2 μs, 5 μs, 10 μs, 15 μs, 20 μs, 25 μs, 30 μs, 40 μs, 50 μs, 100 μs, 300 μs, 500 μs, 900 μs, 1 ms, 2 ms, 5 ms, 10 ms, 20 ms, 50 ms, 100 ms, 300 ms, 500 ms, 900 ms, 1 s, etc., or any value between these values.

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

[0033] Laser source 104 can output laser pulses at a pulse repetition rate ranging from 5 kHz to 5 GHz. However, it will be appreciated that the pulse repetition rate can be less than 5 kHz or greater than 5 GHz. Thus, laser source 104 can output laser pulses at pulse repetition rates less than, greater 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, etc., or any value between these values.

[0034] In addition to wavelength, average power, pulse duration and pulse repetition rate if the laser energy beam is represented as a series of laser pulses, the laser energy beam irradiated onto the workpiece 102 may be characterized by one or more other properties, such as pulse energy, peak power, etc. The laser pulses may be of a magnitude sufficient (W / cm) to process the workpiece 102 (e.g., to form one or more features). 2 Light intensity, measured in J / cm 2 The laser beam can be selected (e.g., based on one or more other characteristics, such as wavelength, pulse duration, average power and pulse repetition rate, spot size, etc., as needed) to irradiate the workpiece 102 at the process spot with a fluence (measured in λ / 2).

[0035] Examples of types of lasers that may characterize 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, passively modelocked solid-state bulk or fiber lasers, dye lasers, modelocked diode lasers, pulsed lasers (e.g., ms pulsed lasers, ns pulsed lasers, ps pulsed lasers, fs pulsed lasers), CW lasers, quasi-CW lasers, etc., or any combination thereof. In some configurations, gas lasers (e.g., carbon dioxide lasers, etc.) may be configured to operate in one or more modes (e.g., CW mode, quasi-CW 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 density filter, an acousto-optic (AO) modulator (AOM), an AO deflector (AOD), a liquid crystal variable attenuator (LCVA), a microelectromechanical system (MEMS) based VOA, an optical attenuator wheel, a polarization / waveplate filter, or the like, or any combination thereof.

[0038] i. Embodiments relating to AODs as beam modulators

[0039] When the beam modulator 106 is provided as one or more AOMs or AODs, or any combination thereof, the beam modulator 106 may also be operable to diffract the beam of laser energy 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 may also be operable to move the beam axis relative to the workpiece 102 along an X-axis (or X-direction), a Y-axis (or Y-direction), or a combination thereof (e.g., by deflecting the beam path 114 through a range of angles, as shown at 118). Although not shown, the Y-axis (or Y-direction) should be understood to mean an axis (or direction) that is orthogonal 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 that includes one or more AODs, each having an AO cell formed from a material such as crystalline germanium (Ge), gallium arsenide (GaAs), pyrophorite (PbMoO), tellurium dioxide (TeO), quartz, vitreous SiO, arsenic trisulfide (AsS), lithium niobate (LiNbO), or the like, or any combination thereof. It will be appreciated that the material forming the AO cell will depend on the wavelength of the laser energy propagating along the beam path 114 to be incident on the AO cell. For example, materials such as crystalline germanium can be used when the wavelength of the deflected laser energy is in the range of 2 μm (or thereabouts) to 20 μm (or thereabouts), materials such as gallium arsenide and arsenic trisulfide can be used when the wavelength of the deflected laser energy is in the range of 1 μm (or thereabouts) to 11 μm (or thereabouts), and materials such as vitreous SiO2, quartz, lithium niobate, pyrite, and tellurium dioxide can be used when the wavelength of the deflected laser energy is in the range of 200 nm (or thereabouts) to 5 μm (or thereabouts).

[0041] As will be appreciated by those skilled in the art, AO technology (e.g., AODs, AOMs, etc.) utilizes the diffraction effect produced by one or more acoustic waves propagating through the AO cell (along the “diffraction axis” of the AOD) to diffract an incident light wave (i.e., in the context of this application, a laser energy beam) 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- and first-order diffraction peaks, but may also include other diffraction peaks of higher orders (e.g., second, third, etc.). As known in the art, the portion of the laser energy beam diffracted at the zero-order diffraction peak is referred to as the “zero-order” beam, the portion of the laser energy beam diffracted at the first-order diffraction peak is referred to as the “first-order” beam, and so on. Generally, the zero-order beam and other order beams (e.g., first-order beams) propagate along different beam paths as they exit the AO cell (e.g., through the light output side of the AO cell). For example, a zero-order beam propagates along a zero-order beam path, a first-order beam propagates along a first-order beam path, etc. Unless expressly stated otherwise herein, beam path 114 exiting the AO cell corresponds to the first-order beam path. Although not shown, apparatus 100 includes one or more beam dumps or traps, as known in the art, positioned and configured to absorb laser energy propagating from beam modulator 106 along any beam path other than the zero-order beam path or the first-order beam path.

[0042] Acoustic waves are typically input to the AO cell by applying RF drive signals (e.g., from one or more drivers of beam modulator 106) to the ultrasonic transducer elements. The characteristics (e.g., amplitude, frequency, phase, etc.) of the RF drive signal can be controlled (e.g., based on one or more control signals output by controller 122, component-specific controllers, etc., or any combination thereof) to tailor the way in which incident optical waves are diffracted.

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

[0044]

number

[0045] where λ is the optical wavelength of the laser energy beam, f is the frequency of the applied RF drive signal, and v is the velocity of the acoustic waves in the AO cell. If the frequency of the applied RF drive signal is comprised of multiple frequencies, then the beam path 114 will be deflected through 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 fraction of energy in a laser energy beam incident on the AOD that is diffracted into a first-order beam within the AO cells of the AOD. Thus, diffraction efficiency can be expressed as the ratio of the optical power of the first-order 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 first-order beam output by the AOD. Thus, the beam modulator 106, when driven by an applied RF signal having a desired or preferred amplitude, can operate to desirably attenuate the incident laser energy beam. It should also be noted that the diffraction efficiency of an AOD can vary as a function of the frequency of the RF drive signal applied to drive the AOD.

[0047] The axis (also referred to herein as the “axis of rotation”) about which the beam path 114 exiting the AO cell is rotated (e.g., relative to the beam path 114 as it enters the AO cell) is orthogonal to both the diffraction axis of the AO cell and the optical axis along 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. Thus, the AOD deflects the incident beam path 114 within a plane (also referred to herein as the “deflection plane”) that contains (or is otherwise substantially parallel to) the diffraction axis of the AO cell and the optical axis within the AO cell. The spatial extent over which the AOD can deflect the beam path 114 within the deflection plane is referred to herein as the “scan region” of that AOD. Accordingly, the first scan region of the beam modulator 106 can be considered to correspond to the scan region of a single AOD (e.g., if the beam modulator 106 includes a single AOD) or to the combined scan regions of multiple AODs (e.g., if the beam modulator 106 includes multiple AODs).

[0048] During operation of the beam modulator 106, an RF drive signal is repeatedly applied to one or more ultrasonic transducers of the beam modulator 106. The rate at which the RF drive signal is applied is also referred to as the "update rate" or "refresh rate." For example, the update rate of the beam modulator 106 may be greater than or less than 8 kHz, 10 kHz, 20 kHz, 30 kHz, 40 kHz, 50 kHz, 75 kHz, 80 kHz, 100 kHz, 250 kHz, 500 kHz, 750 kHz, 1 MHz, 5 MHz, 10 MHz, 20 MHz, 40 MHz, 50 MHz, 75 MHz, 100 MHz, 125 MHz, 150 MHz, 175 MHz, 200 MHz, 225 MHz, 250 MHz, etc., 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 (either alone or in cooperation with the scanner 108) is operable 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 the 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, spot size, etc., of the laser energy beam incident on the beam modulator 106, the first scan region may extend in either the X or Y direction to a distance less than, greater 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, etc., or any value between these values. As used herein, the term "beam size" refers to the diameter or width of the laser energy beam, and refers to the distance from the beam axis where the light intensity is 1 / e of the light intensity at the axis of propagation along the beam path 114. 2 The maximum dimension of the first scan area (e.g., in a plane containing the X-axis and Y-axis (herein referred to as the "XY plane")) may be greater than, equal to, or less than the maximum dimension (measured in the XY plane) of a feature (e.g., opening, recess, via, trench, etc.) to be formed in the workpiece 102.

[0051] In one embodiment, the AOD system includes at least one (e.g., 1, 2, 3, 4, 5, 6, etc.) single-element AOD, at least one (e.g., 1, 2, 3, 4, 5, 6, etc.) multi-element AOD, etc., or any combination thereof. As used herein, an AOD system including only one AOD is referred to as a "single-cell AOD system," and an AOD system including more than one AOD is referred to as a "multi-cell AOD system." As used herein, a "single-element" AOD means an AOD with only one ultrasonic transducer element acoustically coupled to an AO cell, and a "multi-element" AOD includes two or more ultrasonic transducer elements acoustically coupled to a common AO cell. The AOD system may be provided as a single-axis AOD system (e.g., capable of deflecting the beam axis along a single axis) or as a multi-axis AOD system (e.g., capable of deflecting the beam axis along one or more axes, e.g., along the X-axis, the Y-axis, or any combination thereof) by deflecting the beam path 114 in a corresponding manner. 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 its 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 its 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 its 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 its beam axis along two axes (e.g., along the X-axis and the Y-axis). For example, a single-cell multi-axis system may include two or more ultrasound transducer elements acoustically coupled to orthogonally arranged planar faces, facets, sides, etc. of a common AO cell.

[0052] The beam modulator 106 can be characterized as having a "first positioning speed," which refers to the speed at which the beam modulator 106 positions the process spot (and thereby moves the beam axis) at any location within the first scan area. This range is also referred to herein as the first positioning bandwidth. The inverse of the first positioning speed is referred to herein as the "first positioning period," which refers to 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. Thus, the beam modulator 106 can be characterized as having a first positioning period that is greater 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, etc., or a value between 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 equal to or greater than the pulse duration of each laser pulse. Thus, the laser pulses are transmitted through the AO cells of the AOD when the AOD is driven at a fixed RF drive frequency (or a set of fixed RF drive frequencies). By maintaining a fixed RF drive frequency (or a set of fixed RF drive frequencies) on the AOD when the laser pulses are transmitted through the AO cells of the AOD, the laser pulses can generally be uniformly deflected over their entire pulse duration, sometimes referred to as “full pulse deflection.” However, in other embodiments, the update rate can be shorter than the pulse duration of the laser pulses, thereby allowing the laser pulses to be transmitted through the AO cells of the AOD when the RF drive frequency (or a frequency within the set of RF drive frequencies) is being changed. By varying the RF drive frequency applied to the AOD as the laser pulse passes through the AO cell of the AOD, the laser pulse input to the AOD can be split in time, which is sometimes referred to as "partial pulse deflection" or "pulse slicing." The laser pulse input to the AOD can be split in time (i.e., pulse slicing) by varying the amplitude of the applied RF drive signal (e.g., to zero or a small amplitude such that a small percentage of the energy is diffracted into the first beam path) to reduce the diffraction efficiency of the AOD to zero or a significant degree (so that substantially all of the laser energy incident on the AOD propagates along the zeroth beam path).

[0054] When pulse slicing is performed, the laser pulse exiting the AOD has a pulse duration that is shorter than the pulse duration of the laser pulse input to the AOD. As used herein, the laser pulse input to the AOD is also referred to as a "mother pulse," and the laser pulse that is separated in time from the mother pulse and exits the AOD along beam path 114 is also referred to herein as a "pulse slice." While pulse slicing techniques are applied herein to separate laser pulses in time, it will be understood that these techniques may similarly be applied to separate in time a beam of laser energy that is represented as a continuous or quasi-continuous laser beam.

[0055] C. Scanner

[0056] Generally, the scanner 108 is operable 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] Beam axis movement by the scanner 108 relative to the workpiece 102 is generally limited to allow scanning, moving, or positioning of the process spot 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, the spot size, etc., the second scan area may extend a distance in either the X or Y direction that is greater than the corresponding distance of the first scan area. In view of the above, the second scan area may extend a distance in either the X or Y direction that is less than, greater 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, etc., or any value between these values. The maximum dimension of the second scan area (e.g., in the XY plane) may be greater than, equal to, or smaller than the maximum dimension (measured in the XY plane) of a feature (e.g., opening, recess, via, trench, scribe line, conductive trace, etc.) formed in the workpiece 102.

[0058] In view of the configurations 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. This allows the scanner 108 to scan a first scan area within a second scan area.

[0059] Generally, the positioning speed at which the scanner 108 can position the process spot anywhere within the second scan area (thereby moving the beam axis within the second scan area and / or scanning the first scan area within the second scan area) ranges less than the first positioning bandwidth (also referred to herein as the "second positioning bandwidth"). In one embodiment, the second positioning bandwidth ranges from 500 Hz (or thereabouts) to 8 kHz (or thereabouts). For example, the second positioning bandwidth may be greater than, equal to, or less 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, etc., or any value between these values.

[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 translate 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 translate 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 translate the beam axis along the X-axis and the Y-axis relative to the workpiece 102. In still other embodiments, the scanner 108 may be provided as a rotating polygon mirror system, an AOD system, or the like, or any combination thereof.

[0061] D. Stage

[0062] The 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 allow scanning, moving, or positioning of a process spot within a third scan region. Depending on one or more factors, such as the configuration of the stage 110, the third scan region may extend in the X direction, the Y direction, or any combination thereof, to a distance greater than or equal to the corresponding distance of the second scan region. However, typically, 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 a feature to be formed on the workpiece 102. If desired, the stage 110 can 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 direction, the Y direction, and / or the Z direction.

[0063] As previously mentioned, apparatus 100 may use a so-called "stacked" positioning system for stage 110, which allows workpiece 102 to be moved while other components, such as beam modulator 106, scanner 108, scan lens 112, etc., remain stationary within apparatus 100 relative to workpiece 102 (e.g., via one or more supports, frames, etc., as known in the art). In other embodiments, stage 110 may be configured and operated to move one or more components, such as beam modulator 106, scanner 108, scan lens 112, etc., or any combination thereof, while workpiece 102 remains stationary.

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

[0065] In one embodiment in which the stage 110 includes 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 carried by one or more of the other stages described above for moving or positioning the workpiece 102, or may carry one or more of the other stages described above for moving or positioning the workpiece 102, or any combination thereof. In other embodiments in which the stage 110 includes a Z-stage, the Z-stage may be positioned and configured to move the scan head along the Z-direction. Thus, if the stage 110 is provided as a split-axis positioning system, the Z-stage may carry or be carried by the X-stage. Moving the workpiece 102 or the scan head along the Z-direction can change the spot size at the workpiece 102.

[0066] In yet other embodiments, one or more components, such as scanner 108, scan lens 112, etc., may be carried by a multi-axis articulated robotic arm (e.g., a two-axis, three-axis, four-axis, five-axis, or six-axis arm). In such embodiments, scanner 108 and / or scan lens 112 may be carried by an end effector of the robotic arm, as needed. In yet other embodiments, workpiece 102 may be carried directly (i.e., without stage 110) on the end effector of the multi-axis articulated robotic arm. In yet other embodiments, stage 110 may be carried on the end effector of the multi-axis articulated robotic arm.

[0067] E. Scan lens

[0068] Generally, the scan lens 112 (e.g., provided as either a simple lens or a compound lens) is typically configured to focus a laser energy beam directed along a beam path to produce 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 produced, resulting in multiple process spots offset from one another along the beam axis), or the like, or any combination thereof. The scan lens 112 may be provided as a non-telecentric lens (as shown), an f-theta lens, a telecentric lens, an axicon lens (in which case a series of beam waists are produced, resulting in multiple process spots offset from one another along the beam axis), or the like, or any combination thereof.

[0069] In one embodiment, the scan lens 112 is provided as a fixed focal length lens and is coupled to a scan lens positioner (e.g., a lens actuator, not shown) that can move the scan lens 112 (e.g., to change the position of the beam waist along the beam axis). For example, the lens actuator can be provided as a voice coil that can linearly translate the scan lens 112 along the Z direction. In this case, the scan lens 112 can be formed from materials such as fused silica, optical glass, zinc selenide, zinc sulfide, germanium, gallium arsenide, magnesium fluoride, etc. In other embodiments, 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 actuated (e.g., via a lens actuator) to change the position of the beam waist along the beam axis. Varying the position of the beam waist along the beam axis can change the spot size at the workpiece 102.

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

[0071] F. Controller

[0072] Generally, apparatus 100 includes one or more controllers, such as controller 122, for controlling or facilitating the control and operation of apparatus 100. In one embodiment, controller 122 is communicatively coupled (e.g., 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, etc., or any combination thereof) to one or more components of apparatus 100, such as laser source 104, beam modulator 106, scanner 108, stage 110, lens actuator, scan lens 112 (if provided as a variable focal length lens), fixture, etc., such that these components operate in response to one or more control signals output by controller 122.

[0073] For example, the controller 122 may 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 (e.g., to effect relative movement between the beam axis and the workpiece to effect relative movement between the process spot and the workpiece 102 along a path or trajectory (also referred to herein as a "process trajectory")), or a combination thereof. Similarly, the controller 122 may control the operation of the scanner 108, the stage 110, etc., or any combination thereof, to effect relative movement between the beam axis and the workpiece to effect relative movement between the process spot and the workpiece 102 along a process trajectory.

[0074] Typically, the controller 122 includes one or more processors operable to execute instructions to generate the control signals described above. The processor may be provided as a programmable processor (e.g., one or more general-purpose computer processors, microprocessors, digital signal processors, etc., or any combination thereof) operable to execute instructions. The instructions executable by the processor may be implemented as software, firmware, etc., or any suitable form of circuitry (including digital, analog, or mixed analog / digital circuitry) including programmable logic devices (PLDs), field programmable gate arrays (FPGAs), field programmable object arrays (FPOAs), application-specific integrated circuits (ASICs), etc., or any combination thereof. Execution of the instructions may occur on a single processor, distributed across multiple processors, in parallel across multiple processors within a device or across a network of devices, or the like, or any combination thereof.

[0075] In one embodiment, the controller 122 includes tangible media, 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.), etc., and may be locally accessible, remotely accessible (e.g., over a network), or any combination thereof. Generally, instructions may be stored as computer software (e.g., executable code, files, instructions, etc., library files, etc.). Such computer software may 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.), etc., and may be readily produced by one of ordinary skill in the art from the description provided herein. Computer software is typically stored in one or more data structures carried by the computer memory.

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

[0077] Although not shown, one or more additional controllers (e.g., component-specific controllers) may optionally be communicatively coupled to inputs of drivers communicatively coupled to (and associated with) components such as laser source 104, beam modulator 106, scanner 108, stage 110, lens actuator, and scan lens 112 (if provided as a variable focal length lens). In this embodiment, each component-specific controller may be communicatively coupled 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. The one or more control signals may then be transmitted to inputs of the driver communicatively coupled thereto. In this embodiment, the component-specific controllers may be operable in a manner similar to that 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., laser source 104) may be communicatively coupled to a component-specific controller associated with a component (e.g., beam modulator 106, etc.). In this embodiment, one or more of the component-specific controllers may generate one or more control signals (e.g., trigger signals, etc.) in response to one or more control signals received from one or more other component-specific controllers.

[0079] G. Back reflection detection system

[0080] As discussed above, when the same drilling parameters are used to form blind-via holes at different locations within the dielectric substrate 24, some variation in morphology between the final blind-via holes is likely (e.g., due to inherent compositional non-uniformities in the dielectric substrate 24, variations in the surface reflectivity / thickness of the top conductor 20, etc.). To reduce the possibility of undesirable morphological variations, the apparatus 100 includes a back-reflection sensing system 124. The output of the back-reflection sensing system 124 can be used (alone or in conjunction with the controller 122) to perform an adaptive processing recipe in which one or more parameters of the process used to form the blind-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, the back-reflected signal is a reflection from the workpiece 102 of a portion of the laser energy beam irradiated onto the workpiece 102 (e.g., during a process of forming a blind via hole). 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, it is possible that 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 FIGS. 1 and 2. In this case, a significant percentage of the laser energy beam irradiated onto the workpiece 102 may reflect off the top conductor 20 and return to the scan lens 112. When the workpiece 102 (i.e., the PCB described above) is processed to form a blind via hole 30 that terminates in the bottom conductor 22, a portion of the laser energy beam irradiated onto the bottom conductor 22 may also be reflected off the bottom conductor 22. It should be noted that one or more components of the dielectric substrate 24 (e.g., the resin material 26, the reinforcing material 28, or a combination thereof) may also reflect a portion of the laser energy beam, but typically the amount reflected is much less than the amount reflected by the top conductor 20 or the bottom conductor 22.

[0082] 4, the back-reflection detection system 124 is shown disposed on the beam path 114 at a position 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 is operable 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 will be appreciated that the back-reflection detection system 124 may be configured to capture at least a portion of the back-reflection signal from any other suitable or desired position or 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, etc., or any combination thereof).

[0083] Additionally, the back-reflection sensing system 124 may operate to convert the captured back-reflection signal into an electronic signal (also referred to herein as a "sensor signal"). The sensor signal may then be processed (e.g., by the back-reflection sensing system 124 or the controller 122) to determine whether the workpiece 102 needs to be further processed to form a blind-via hole. If necessary, the sensor signal is processed (e.g., by the back-reflection sensing system 124 or the controller 122) to determine how the workpiece 102 needs to be further processed to form a blind-via hole. Example embodiments of the configuration and operation of the back-reflection sensing system 124 and the processing of the sensor signal are described in more detail below.

[0084] III. Example Embodiments of a Retroreflective Sensing System

[0085] 5, the back-reflection detection system 124 may include, for example, a polarizing beam splitter 500, a wave plate 502 (e.g., a quarter-wave plate), a lens 504, and a detector 506 (e.g., a photodetector). During the process of forming a blind via hole (e.g., as described above with respect to FIG. 3), a laser energy beam propagates from the beam modulator 106 along the beam path 114, and subsequently passes through the polarizing beam splitter 500, the wave plate 502, the scanner 108, and the scan lens 112 to illuminate the workpiece 102 (e.g., provided as a PCB as described above with respect to FIGS. 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. Thus, a portion of the incident laser energy beam reflects off the workpiece 102 and subsequently propagates (e.g., along beam path 114 or along a different beam path) through the scan lens 112, the scanner 108, and the wave plate 502. The reflected light is polarized by the wave plate 502 before entering the polarizing beam splitter 500. Thus, the polarizing beam splitter 500 reflects the reflected light that passes through the wave plate 502 toward the lens 504 (e.g., along beam path 510 toward the lens 504). The lens 504 focuses the reflected light onto the detector 506. In this case, the act of polarizing the back-reflected light at the wave plate 502 and reflecting the back-reflected light along the beam path 510 during the formation of a blind via hole in the workpiece 102 constitutes "capturing" the back-reflected signal.

[0087] In general, detector 506 is operable to convert incident reflected light (propagating from lens 504 along path 510) into an electrical current and output this current (e.g., to controller 122) as the sensor signal described above. Thus, the output of detector 506 varies with the intensity of the reflected light incident thereon.

[0088] IV. Back-reflected signal description

[0089] 6 is a graph illustrating the signal strength of an exemplary back-reflection signal captured by the back-reflection detection system 124 as a function of time (during the formation of a blind via hole, in accordance with an embodiment of the present invention). That is, the graph shown in FIG. 6 illustrates the signal strength of an exemplary back-reflection signal captured when a typical initial (i.e., first) laser pulse is applied to the workpiece 102 (e.g., provided as a PCB as described above with respect to FIGS. 1 and 2) to form a blind via hole (e.g., as described above with respect to FIG. 3).

[0090] For illustrative purposes, the initial laser pulse on which the captured backreflection signal shown in FIG. 6 is based has a pulse duration ranging between approximately 10 μs and 11 μs, and is located on the top conductor of the PCB. 20 It can be assumed that the initial laser pulse has sufficient pulse energy to form an opening in the top conductor 20 and remove a portion of the underlying dielectric substrate 24. However, it will 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 on the workpiece 102 in the process of forming a blind via hole in the workpiece 102 is sufficient to form an opening in the top conductor 20 by a process known as "indirect ablation," and is 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 material in the workpiece 102 occurs when ablation is primarily due to thermal decomposition of the material due to absorption of energy by the material in the impinging laser energy beam (e.g., linear absorption, nonlinear absorption, or any combination thereof). Indirect ablation of material in the workpiece 102 (also known as "lift-off") occurs when ablation is primarily due to melting and vaporization due to heat transferred from adjacent material that ultimately absorbs the energy in the laser energy beam impinging on the workpiece 102. Considerations for material removal by indirect ablation (and direct ablation) are known in the art and are described in International Publication No. WO 2017 / 044646 A1. In this case, the top conductor 20 reflects a portion of the initial laser pulse impinging on the workpiece 102, and the top conductor 20 heats up as a result of irradiation by the initial laser pulse. Heat is dissipated or transferred from the top conductor 20 to the area of ​​the dielectric substrate 24 below the area of ​​the top conductor 20 irradiated by the initial laser pulse. Thus, over time, the heat transferred from the top conductor 20 accumulates in the area of ​​the dielectric substrate 24, vaporizing that area. If the irradiated area of ​​the top conductor 20 is not at or above its processing threshold temperature, the vaporization of the area of ​​the dielectric substrate 24 acts to create a pocket or space (e.g., a high-pressure region containing pressurized, heated gas, particles, etc., produced during vaporization of the dielectric substrate 24) below the irradiated area of ​​the top conductor 20. If the area of ​​the top conductor 20 irradiated by the initial laser pulse then reaches its processing threshold temperature, the pressure increase within the pocket below may be sufficient to eject the irradiated area of ​​the top conductor 20 from the workpiece, thereby "indirectly ablating" the top conductor 20 and exposing the underlying dielectric substrate 24.

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

[0093] The evolution of the signal intensity of the backreflected signal encodes the dynamics of the indirect ablation process associated with the formation of the blind-via hole. For example, the relatively high signal intensity during the primary intensity period 600 corresponds to light reflected from the top conductor 20 when the first laser pulse initiates the machining of the blind-via hole. During this time, the dielectric substrate 24 accumulates heat transferred from the top conductor 20, vaporizing the dielectric substrate 24 and forming a pocket of pressurized, heated gas, particles, and the like. The subsequent abrupt drop in signal intensity indicates that the irradiated region of the top conductor 20 has risen above its machining threshold temperature, and the increased pressure within the underlying pocket causes the irradiated region of the top conductor 20 to erupt, thereby directly exposing the underlying dielectric substrate 24 to the initial laser pulse. Thus, the duration t1 of the primary intensity period 600 corresponds to the time it takes for the irradiating laser pulse to form an opening in the top conductor 20. A signal intensity peak 604 in the secondary intensity period 602 indicates that a portion of the dielectric substrate 24 has been removed by the first laser pulse, exposing a portion of the bottom conductor 22 (an operation also referred to herein as forming an opening in the dielectric substrate 24). A drop to near zero signal intensity at 608 indicates the end of the laser pulse striking the workpiece surface.

[0094] A. Embodiments Relating to Captured Backreflected Signal Characteristics

[0095] As described above, the back-reflection detection system 124 may operate to convert the back-reflection signal (captured as the initial laser pulse irradiates the workpiece 102) into a sensor signal representative of the captured back-reflection signal. The sensor signal may be processed (e.g., 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 may be represented by or derived from the sensor signal. It will be appreciated that the sensor signal may be processed using one or more suitable signal processing techniques as 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 a characteristic of the captured backreflected signal that can be used to make processing decisions is the duration t1 of the first intensity period 600. In FIG. 6, the duration of the first intensity period 600 is measured based on the time to full width at half maximum (FWHM) of the signal intensity of the captured backreflected signal. However, in other embodiments, the first intensity period may be considered to coincide with the end of the rise time of the initial laser pulse from which the backreflected signal is captured. The pulse rise time may 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 FIG. 6, duration t2 represents the time from the end of the first intensity period 600 to the end of the laser pulse.

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

[0099] ii. Integral of the area within the second intensity period

[0100] Another embodiment of a characteristic of the captured backreflected signal that can be used to make processing decisions is the integrated area of ​​the signal from the end of t1 to the end of the laser pulse, which captures both the secondary peak 604 (indicating the formation of an aperture in the dielectric substrate 24) and the total length of time that the laser energy is applied to the dielectric substrate 24.

[0101] iii. Other Example Embodiments of Captured Backreflected Signal Characteristics

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

[0103] B. Embodiments Relating to Comparison Between Captured and Reference Backreflected Signal Characteristics

[0104] Once identified, the captured backreflected signal characteristic (or other data representative thereof) can be compared (e.g., by backreflected detection system 124 or controller 122, or a combination thereof) to a reference backreflected signal characteristic associated with the captured backreflected signal characteristic. 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 will be appreciated that such a comparison can be made by processing the sensor signal (e.g., using one or more suitable signal processing techniques as known in the art), by processing data associated with the identified characteristics, or the like, or by any combination thereof. It will further be appreciated that the reference value or range for the associated data-based back-reflected signal characteristic can correspond to one or more parameters of the portion of the initial laser pulse that has been applied to the workpiece 102 up to the time the back-reflected signal characteristic was captured (e.g., duration, peak power, spot size, wavelength, etc.), one or more parameters of the workpiece 102 (e.g., material composition of the top conductor 20, thickness of the top conductor 20, material composition of the dielectric substrate 24, thickness of the dielectric substrate 24, etc.), or the like, or any combination thereof. For example, the reference value or range for the duration t1 of the primary intensity period can be (a) a decrease with increasing peak power of the initial laser pulse or an increase with decreasing peak power of the initial laser pulse, an increase with increasing thickness of the top conductor 20 or a decrease with decreasing thickness of the top conductor 20, or (b) a decrease if the top conductor 20 is coated with an energy absorbing coating, or (c) an increase or decrease depending on the composition of the matrix material 26, or (d) the like, or any combination thereof. These reference values ​​or ranges can be obtained or identified through empirical observation, computational simulation, diagnostics, or the like, or any combination thereof.

[0106] V. Adaptive Processing Embodiments

[0107] The apparatus 100 can be used to perform adaptive machining techniques in which one or more parameters of the process used to form the blind-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 a comparison of the captured backreflection signal characteristics (or other data representative thereof) described above with associated reference backreflection signal characteristics. In this case, the process used to form the blind-via holes can be generally characterized as a “punch” process, which requires that at least one laser pulse be applied to a single desired location on the workpiece 102 (provided as the PCB described above with reference to FIGS. 1 and 2 ). The first laser pulse applied to the workpiece 102 to form a particular blind-via hole is referred to herein as the “initial laser pulse.” Subsequent laser pulses applied to the workpiece 102 to form a particular blind-via hole are referred to herein as “supplemental laser pulses,” or may be labeled according to their order in the sequence of laser pulses applied to the workpiece 102 to form a particular blind-via hole (e.g., “second laser pulse,” “third laser pulse,” “final laser pulse,” etc.).

[0108] As 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 (e.g., to perform pulse slicing, as described above), or the like, or by any combination thereof. Examples of temporal optical power profiles that the initial laser pulse may have include rectangular, chair-shaped (low to high, high to low, or a combination thereof), ramp-shaped (increasing and / or decreasing in a stepped manner or linearly or nonlinearly continuously, or a combination thereof). The temporal optical power profile (and thus peak power) of any laser pulse can be adjusted by controlling the operation of laser source 104 in any manner known in the art, by controlling the operation of beam modulator 106, or the like, or by any combination thereof.

[0109] Typically, the initial laser pulse parameters are set so that a blind via hole (e.g., the blind via hole 30 shown illustratively in FIG. 3 ) having desired characteristics (e.g., an overhang, a taper, or any combination thereof) can be formed at a reference position within the workpiece 102 using only the initial laser pulse. The reference position may be, for example, a position within the workpiece 102 corresponding to a position such as position “B” or position “C” (both shown in FIG. 1 ). Thus, the settings 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. One or more of the above-mentioned backreflection signal characteristics (e.g., duration t1 of the primary intensity period, integrated area of ​​the signal during the secondary intensity period, etc.) can then be empirically determined (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 backreflection signal), computationally obtained, obtained by similar methods, or any combination thereof, and set as reference values ​​or reference ranges for the backreflection signal characteristics associated with the initial laser pulse irradiated to the workpiece 102 during the ``punch'' process of forming a blind via hole at any location within 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 thereabouts) to 11 μm (or thereabouts) (e.g., wavelengths of 9.4 μm (or thereabouts), 10.6 μm (or thereabouts), etc.), a pulse duration in the range of 5 μs (or thereabouts) to 20 μs (or thereabouts), a rectangular (or at least substantially rectangular) temporal optical power profile, a peak power in the range of 250 W (or thereabouts) to 2 kW (or thereabouts), and a spot size in the range of 30 μm (or thereabouts) to 90 μm (or thereabouts). It will be appreciated that the initial laser pulse irradiated onto the workpiece 102 may have a wavelength shorter than 9 μm (e.g., in the ultraviolet or visible green region of the electromagnetic spectrum), provided that other characteristics (e.g., pulse duration, temporal optical power profile, peak power, spot size, pulse energy, etc.) are configured such that the initial laser pulse is capable of processing the workpiece 102. 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 an initial set of laser pulses, each having a pulse duration in the ns or ps range (e.g., in the range of 10 ns (or thereabouts) to 1 ps (or thereabouts)), and the laser pulses are emitted at a pulse repetition rate in the range of 100 MHz (or thereabouts) to 5 GHz (or thereabouts).

[0111] To perform an adaptive machining method to perform a “punch” process to form a blind via hole at a desired location within the workpiece 102, an initial laser pulse (having initial laser pulse parameters) is irradiated onto the workpiece 102. At least a portion of the light in the initial laser pulse reflects off the workpiece 102 (i.e., off the top conductor 20) and back to the scan lens 112, where it is then captured as described above with respect to FIG. 5 . The resulting captured backreflection signal is then processed (e.g., as described above) to identify one or more captured backreflection signal characteristics (or other data representative thereof) associated with the initial laser pulse. Such characteristics may then be compared (e.g., as described above) with one or more associated reference backreflection signal characteristics (e.g., in the backreflection detection system 124, in the controller 122, or the like, or any combination thereof). As described in more detail below, the controller 122 may be operable to control the operation of one or more components of the apparatus 100 (e.g., the laser source 104, the beam modulator 106, etc., or any combination thereof) based on the comparison results.

[0112] In some embodiments, the captured back-reflected signal characteristic associated with the initial laser pulse is the duration t1 of the primary intensity period. Thus, the duration t1 of the primary intensity period is compared to a predetermined reference value or reference range for the duration t1 of the primary intensity period. In some embodiments, the captured back-reflected signal characteristic associated with the initial laser pulse is the integrated area of ​​the signal during the secondary intensity period. Thus, the integrated area of ​​the signal during the secondary intensity period is compared to a predetermined reference value or reference range for the integrated area of ​​the signal during the secondary intensity period. In other embodiments, the captured back-reflected signal characteristic associated with the initial laser pulse is a combination of the above-mentioned characteristics. Thus, the captured characteristics are each compared to a predetermined reference value or reference range for these characteristics.

[0113] If the duration t1 of the primary intensity period associated with the initial laser pulse is greater than its associated reference value or range, this indicates that the initial laser pulse (with the initial laser pulse parameters) is not sufficient to form an opening in the top conductor 20 or to form a blind via hole with the desired characteristics (e.g., in terms of taper). If the duration t1 of the primary intensity period of the initial laser pulse is less than its associated reference value or range, this indicates that the initial laser pulse is not sufficient to form a blind via hole with the desired characteristics (e.g., in terms of overhang) or may end up damaging (undesirably melting or removing) the bottom conductor 22 exposed in the blind via hole.

[0114] If the comparison between the captured backreflected signal characteristics and the associated reference values ​​or ranges indicates that the initial laser pulse is not sufficient to form a blind-via hole having the desired characteristics (e.g., as described above), the controller 122 can output one or more control signals (e.g., to the laser source 104, the beam modulator 106, etc., or any combination thereof) to ensure that a blind-via hole having the desired characteristics (e.g., in terms of taper and overhang) is formed. For example, as can be seen (e.g., from FIG. 6 ), the integrated area of ​​the signal during the duration t1 of the primary intensity period and the secondary intensity period can be identified from the captured backreflected signal associated with the initial laser pulse before the entire initial laser pulse is irradiated onto the workpiece 102. Thus, the one or more control signals output by the controller 122 can 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 the like, or any combination thereof). Alternatively, or in addition to modifying the initial laser pulse parameters of the initial laser pulse, the one or more control signals output by the controller 122 may act to cause one or more supplemental laser pulses to be irradiated onto the workpiece 102 after the entire initial laser pulse has been irradiated onto the workpiece 102. As used herein, modifying one or more initial laser pulse parameters or irradiating supplemental laser pulses as initiated by the controller 122 (e.g., upon output of one or more control signals by the controller 122 as a result of the comparison described above) is referred to herein as an "adaptive response" to the captured backreflected signal characteristics.

[0115] If the duration t1 of the primary intensity period duration associated with the initial laser pulse is greater than its associated reference value or reference range, the controller 122 can 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 above-mentioned laser pulse parameters are adjusted in a predetermined manner regardless of how large the duration t1 of the primary intensity period of the initial laser pulse is relative to its associated reference value or reference range. In another embodiment, the above-mentioned laser pulse parameters are adjusted in a predetermined manner corresponding to a difference in the duration t1 of the primary intensity period of the initial laser pulse relative to its associated reference value or reference range. If one or more supplemental laser pulses are irradiated onto the workpiece 102, any of these supplemental laser pulses can 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). In general, the manner in which the adaptive response is effected by the controller 122 may be predetermined (e.g., based on empirical observation, computational simulation, etc., or any combination thereof), may be determined in real time (e.g., by interpolation of predetermined data), or the like, or any combination thereof.

[0116] If the duration t1 of the primary intensity period associated with the initial laser pulse is less than its associated reference value or reference range, the controller 122 can operate to adjust the temporal optical power profile (e.g., by reducing the instantaneous power of the initial laser pulse) and / or decrease the pulse duration of the initial laser pulse. In one embodiment, the above-mentioned laser pulse parameters are adjusted in a predetermined manner regardless of how small the duration t1 of the primary intensity period of the initial laser pulse is relative to its associated reference value or reference range. In another embodiment, the above-mentioned laser pulse parameters are adjusted in a predetermined manner corresponding to a difference in the duration t1 of the primary intensity period of the initial laser pulse relative to its associated reference value or reference range. If one or more supplemental laser pulses are irradiated onto the workpiece 102, any of these supplemental laser pulses can 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). In general, the manner in which the adaptive response is effected by the controller 122 may be predetermined (e.g., based on empirical observation, computational simulation, etc., or any combination thereof), may be determined in real time (e.g., by interpolation of predetermined data), or the like, or any combination thereof.

[0117] VII. Conclusion

[0118] The foregoing describes embodiments and examples of the present invention and is not to be construed as limiting thereof. For example, while adaptive processing methods are described above with respect to blind via hole formation processes, it will be understood that these adaptive processing methods may also be extended to through via hole processing methods, etc. While several specific embodiments and examples have been described with reference to the drawings, those skilled in the art will readily recognize that many modifications to the disclosed embodiments and examples and other embodiments are possible without significantly departing from the novel teachings and advantages of the present invention. Accordingly, all such modifications are intended to be included 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, paragraph, example, or embodiment can be combined with part or all of the subject matter of any other sentence, paragraph, example, or embodiment, except where such combinations are mutually exclusive. The scope of the present invention should therefore be determined by the following claims and any equivalents thereof to which they may be included.

Claims

1. A laser processing apparatus for performing a process of forming a via in a workpiece, the via extending through the first material and into the second material, by irradiating a workpiece, the first material being formed on a second material, with laser energy having a wavelength that is more reflective than the first material, the laser energy being represented as a series of laser pulses including an initial laser pulse and at least one supplemental laser pulse, the laser energy being incident on the workpiece, the laser processing apparatus comprising: a backreflection detection system operable to capture a backreflection signal corresponding to a portion of the laser energy irradiated on and reflected from the workpiece; a controller communicatively coupled to an output of the retroreflective sensing system, comparing at least one characteristic of the backreflected signal captured during the initial laser pulse with at least one associated reference backreflected signal characteristic to determine whether the initial laser pulse is sufficient to at least one of: i) form an opening in the first material; and ii) remove a portion of the second material; controlling irradiation of the at least one supplemental laser pulse based on the comparison to form the via. with a controller that works like this A laser processing device comprising:

2. The laser processing apparatus of claim 1, wherein the controller is capable of at least partially controlling the process by controlling the pulse energy of the at least one supplemental laser pulse.

3. The laser processing apparatus of claim 1, wherein the controller is capable of at least partially controlling the process by controlling the pulse width of the at least one supplemental laser pulse.

4. The laser processing apparatus of claim 1, wherein the controller is capable of at least partially controlling the process by controlling the number of laser pulses irradiated onto the workpiece.

5. The laser processing apparatus of claim 1 , wherein the controller is capable of controlling the process at least in part by controlling the average power of the laser energy.

6. The laser processing apparatus of claim 1 , wherein the controller is capable of controlling the process at least in part by controlling a peak power of the laser energy.

7. The laser processing apparatus of claim 1 , further comprising a laser source capable of generating the laser energy.

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

9. a process of irradiating a workpiece having a first material formed on a second material with laser energy having a wavelength that is more reflective than the first material, the laser energy being represented as a series of laser pulses including an initial laser pulse and at least one supplemental laser pulse, and forming a via in the workpiece, the via extending through the first material and into the second material, by directing the laser pulses at the workpiece; capturing a backreflection signal corresponding to a portion of the laser energy irradiated onto and reflected from the workpiece during the initial laser pulse; comparing, via a controller, at least one characteristic of the captured back-reflected signal with at least one associated reference back-reflected signal characteristic to determine whether the initial laser pulse is sufficient to at least one of: i) form an aperture in the first material; and ii) remove a portion of the second material; controlling, via the controller, the application of the at least one supplemental laser pulse based on the comparison to form the via. method.

10. The method described in claim 9, wherein controlling the irradiation of the at least one supplemental laser pulse includes adjusting the pulse energy of the at least one supplemental laser pulse.

11. The method described in claim 9, wherein controlling the irradiation of the at least one supplemental laser pulse includes adjusting the pulse width of the at least one supplemental laser pulse.

12. The method described in claim 9, wherein controlling the irradiation of the at least one supplemental laser pulse includes adjusting the number of laser pulses irradiated onto the workpiece.

13. 10. The method of claim 9, wherein controlling the delivery of the at least one supplemental laser pulse comprises adjusting an average power of the laser energy.

14. 10. The method of claim 9, wherein controlling the delivery of the at least one supplemental laser pulse comprises adjusting a peak power of the laser energy.

15. 1. A laser processing apparatus capable of performing a process of forming a via in a workpiece, the workpiece comprising: irradiating a workpiece, the workpiece comprising a first material formed on a second material, with laser energy having a wavelength that is more reflective than the first material, the laser energy being represented as a series of laser pulses including an initial laser pulse and at least one supplemental laser pulse; the laser energy being incident on the workpiece, the workpiece forming a via that extends through the first material and into the second material; the laser processing apparatus comprising: a back-reflection detection system operable to capture a back-reflection signal corresponding to a portion of the laser energy irradiated on and reflected from the workpiece; and a controller communicatively coupled to an output of the back-reflection detection system, the laser energy being represented as a series of laser pulses including an initial laser pulse and at least one supplemental laser pulse; and a controller communicatively coupled to an output of the back-reflection detection system, the laser energy being represented as a series of laser pulses including an initial laser pulse and at least one supplemental laser pulse, the medium, when executed by the controller, causing the controller to: comparing at least one characteristic of the backreflected signal captured during the initial laser pulse with at least one associated reference backreflected signal characteristic to determine whether the initial laser pulse is sufficient to at least one of: i) form an opening in the first material; and ii) remove a portion of the second material; Controlling the irradiation of the at least one supplemental laser pulse to form the via based on the comparison. A non-transitory computer-readable medium having instructions stored thereon.

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