L _ Technical Field

Embodiments described herein relate generally to techniques for forming features, such as vias, in a workpiece.

II. Technical Background

Laser processes are often employed to form vias (e.g., blind via, through vias, or a combination thereof) in workpieces such as printed circuit boards (both rigid and flexile varieties). Laser processes that may be used to form vias are typically classified as either a “punch” process, or a “trepan” process, but the two processes can be combined. During a punch process, a beam of laser energy is directed onto the workpiece is kept stationary while the via is formed. In contrast, during a trepan process, the beam of laser energy is moved relative to the workpiece to form the via. The set of control parameters used to form a via (e.g., wavelength, pulse energy, peak power, pulse duration, pulse repetition rate, number of pulses, whether and how the beam of laser energy is moved relative to the workpiece, or the like or any combination ) is commonly referred as a “processing recipe.”

Typically, a laser process is carried out by repeatedly executing the same processing recipe at multiple locations on a workpiece to sequentially form many vias. When vias are formed in this way, the resulting geometry of a particular via (e.g., via diameter, taper, overhang, etc.) in the sequence can depend not only on the values of the parameters in the processing recipe, but also on the laser energy used to form any vias before the particular via is formed.

Generally, “via diameter” is understood to refer to the diameter or maximum width of a via opening at the surface of a workpiece; “taper” is understood to refer to the ratio of the diameter of a via at the bottom thereof to the diameter of the via at the top thereof; and “overhang” (when the workpiece is formed as a layered construction of multiple components, and the via extends through at least two of the components) is understood to refer to the degree to which an upper component extends over the sidewall of a lower component. For example, a via formed according to a processing recipe having a relatively high pulse energy may have a larger via diameter than a via formed according to a processing recipe having a relatively low pulse energy. The effect of pulse energy on other aspects of via geometry such as taper and overhang are also well known.

In a particular example, the via geometry of a via that is not formed first in the sequence can depend on the laser energy that was previously delivered to the workpiece during formation of preceding vias in the sequence, if the via was formed in close temporal proximity and in close spatial proximity to the formation of any of the preceding vias. In this case, laser energy absorbed by the workpiece can be converted into heat during formation of the vias. Heat accumulated in the workpiece during via formation (i.e., at a location in the workpiece where a via is actively being formed) can dissipate to other locations in the workpiece (e.g., to a location where a subsequent via is to be formed during a later period in time). If a subsequent via is formed before enough heat dissipates from the location in the workpiece where it is to be formed, then the geometry of the subsequent via can vary significantly from the geometry of a preceding via that was formed before it. This can be undesirable if the preceding and subsequent vias were intended to have the same (or about the same) via geometries.

In order to minimize possible thermally-induced variation in via geometry in a workpiece (thereby ensuring that the vias have, at least, about the same via geometries), one could simply ensure that successively-formed vias are not formed in close temporal proximity to one another. This approach, however, may lead to undesirably low throughput. Thus, a conventional alternative approach is to define the via drilling sequence such that the spatial distance between vias that are to be successively formed is always greater that some predetermined threshold distance. In this alternative approach, throughput can be improved somewhat because successively-formed vias are formed in close temporal proximity and variation in via geometry is maintained because successively-formed vias are not formed in close spatial proximity to one another.

SUMMARY

One embodiment can be characterized as a method that includes: forming a plurality of vias in a workpiece by directing a beam of laser energy to the workpiece, wherein forming the plurality of vias comprises: (a) forming a first via according to a first processing recipe at a first location within the workpiece, wherein the first processing recipe is characterized by a set of parameters; and (b) after forming the first via, forming a second via after according to a second processing recipe at a second location within the workpiece, wherein the second processing recipe is characterized by the set of parameters. A value for at least one parameter in the set of parameters for the second processing recipe is different from a value for the at least one parameter in the set of parameters for the first processing recipe in a manner that corresponds to the distance between the first location and the second location.

Another embodiment can be characterized as a method that includes: forming a plurality of vias in a workpiece by directing a beam of laser energy to the workpiece, wherein forming the plurality of vias comprises: (a) forming a first via according to a first processing recipe in which a first pulse energy is delivered to a first location within the workpiece to form the first via; and (b) after forming the first via, forming a second via according to a second processing recipe in which a second pulse energy is delivered to a second location within the workpiece to form the second via, wherein the second pulse energy is less than the first pulse energy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a laser-processing apparatus according to one embodiment.

FIG. 2 schematically illustrates an exemplary spatial arrangement of vias to be formed within a workpiece using the apparatus shown in FIG. 1 and an associated drilling sequence, according to one embodiment.

FIG. 3 schematically illustrates an exemplary relationship of optical power in a beam of laser energy delivered to a workpiece to sequentially form vias within the workpiece as a function of distance between successively-formed vias.

DETAILED DESCRIPTION

Example embodiments are described herein with reference to the accompanying drawings. Unless otherwise expressly stated, in the drawings the sizes, positions, etc., of components, features, elements, etc., as well as any distances therebetween, are not necessarily to scale, but are exaggerated for clarity. In the drawings, like numbers refer to like elements throughout. Thus, the same or similar numbers may be described with reference to other drawings even if they are neither mentioned nor described in the corresponding drawing. Also, even elements that are not denoted by reference numbers may be described with reference to other drawings.

The terminology used herein is for the purpose of describing particular example 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 forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should be recognized that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Unless otherwise specified, a range of values, when recited, includes both the upper and lower limits of the range, as well as any sub-ranges therebetween. Unless indicated otherwise, terms such as “first,” “second,” etc., are only used to distinguish one element from another. For example, one node could be termed a “first node” and similarly, another node could be termed a “second node”, or vice versa.

Unless indicated otherwise, the term “about,” “thereabout,” etc., means that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but may be approximate and/or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art. Spatially relative terms, such as “below,” “beneath,” “lower,” “above,” and “upper,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element or feature, as illustrated in the FIGS. It should be recognized that the spatially relative terms are intended to encompass different orientations in addition to the orientation depicted in the FIGS. For example, if an object in the FIGS, is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the exemplary term “below” can encompass both an orientation of above and below. An object may be otherwise oriented (e.g., rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may be interpreted accordingly.

The section headings used herein are for organizational purposes only and, unless explicitly stated otherwise, are not to be construed as limiting the subject matter described. It will be appreciated that many different forms, embodiments and combinations are possible without deviating from the spirit and teachings of this disclosure and so this 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 thorough and complete, and will convey the scope of the disclosure to those skilled in the art.

L System - Overview

FIG. 1 schematically illustrates a laser-processing apparatus in accordance with one embodiment of the present invention.

Referring to the embodiment shown in FIG. 1, a laser-processing apparatus 100 (also referred to herein simply as an “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.

As discussed in greater detail below, the beam modulator 106 is operative to selectively, and variably, attenuate the beam of laser energy propagating from the laser source 104. As a result, the beam of laser energy propagating along beam path 114 from the beam modulator 106 may have an optical power that is less than that of the beam of laser energy propagating along beam path 114 into the beam modulator 106. As used herein, the term “beam path” refers to the path along which laser energy in the beam of laser energy travels as it propagates from the laser source 104 to the scan lens 112.

The scanner 108 is operative to diffract, reflect, refract, or the like, or any combination thereof, the beam of laser energy generated by the laser source 104 and, optionally, deflected by the beam modulator 106 (i.e., to “deflect” the beam of laser energy) so as to deflect the beam path 114 to scan lens 112. When deflecting the beam path 114 to the scan lens 112, the scanner 108 can deflect the beam path 114 by any angle (e.g., as measured relative to the optical axis of the scan lens 112) within a range of angles (as indicated at 116).

As used herein, the term “spot size” refers to the diameter or maximum spatial width of the beam of laser energy delivered at a location (also referred to as a “process spot,” “spot location” or, more simply, a “spot”) where the beam axis intersects a region of the workpiece 102 that is to be, at least partially, processed by the delivered beam of laser energy. For purposes of discussion herein, spot size is measured as a radial or transverse distance from the beam axis to where the optical intensity drops to, at least, 1/e ² of the optical intensity at the beam axis. Generally, the spot size of the beam of laser energy will be at a minimum at the beam waist. Once delivered to the workpiece 102, laser energy within the beam can be characterized as impinging the workpiece 102 at a spot size in a range from 2 pm to 200 pm. It will be appreciated, however, that the spot size can be made smaller than 2 pm or larger than 200 pm. Thus, the beam of laser energy delivered to the workpiece 102 can have a spot size greater than, less than, or equal to 2 pm, 3 pm, 5 pm, 7 pm, 10 pm, 15 pm, 30 pm, 35 pm, 40 pm, 45 pm, 50 pm, 55 pm, 80 pm, 100 pm, 150 pm, 200 pm, etc., or between any of these values.

The apparatus 100 may also include one or more other optical components (e.g., beam traps, beam expanders, beam shapers, beam splitters, apertures, filters, collimators, lenses, mirrors, prisms, polarizers, phase retarders, diffractive optical elements (commonly known in the art as DOEs), refractive optical elements (commonly known in the art as ROEs), or the like or any combination thereof) to focus, expand, collimate, shape, polarize, filter, split, combine, crop, absorb, or otherwise modify, condition, direct, etc., the beam of laser energy as it propagates along beam path 114.

A. Laser Source

In one embodiment, the laser source 104 is operative to generate laser pulses. As such, the laser source 104 may include a pulse laser source, a CW laser source, a QCW laser source, a burst mode laser, or the like or any combination thereof. In the event that the laser source 104 includes a QCW or CW laser source, the laser source 104 may be operated in a pulsed mode, or may be operated in a non-pulsed mode but further include a pulse gating unit (e.g., an acoustooptic (AO) modulator (AOM), a beam chopper, etc.) to temporally modulate beam of laser radiation output from the QCW or CW laser source. Although not illustrated, the apparatus 100 may optionally include one or more harmonic generation crystals (also known as “wavelength conversion crystals”) configured to convert a wavelength of light output by the laser source 104. In another embodiment, however, the laser source 104 may be provided as a QCW laser source or a CW laser source and not include a pulse gating unit. Thus, the laser source 104 can be broadly characterized as operative to generate a beam of laser energy, which may manifested as a series of laser pulses or as a continuous or quasi-continuous laser beam, which can thereafter be propagated along the beam path 114. Although many embodiments discussed herein make reference to laser pulses, it should be recognized that continuous or quasi-continuous beams may alternatively, or additionally, be employed whenever appropriate or desired.

Laser energy output by the laser source 104 can have one or more wavelengths in the ultraviolet (UV), visible or infrared (IR) range of the electromagnetic spectrum. Laser energy in the UV range of the electromagnetic spectrum may have one or more wavelengths in a range from 10 nm (or thereabout) to 385 nm (or thereabout), such as 100 nm, 121 nm, 124 nm, 157 nm, 200 nm, 334 nm, 337 nm, 351 nm, 380 nm, etc., or between any of these values. Laser energy in the visible, green range of the electromagnetic spectrum may have one or more wavelengths in a range from 500 nm (or thereabout) to 560 nm (or thereabout), such as 511 nm, 515 nm, 530 nm, 532 nm, 543 nm, 568 nm, etc., or between any of these values. Laser energy in the IR range of the electromagnetic spectrum may have one or more wavelengths in a range from 750 nm (or thereabout) to 15 pm (or thereabout), 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 pm to 4 pm, 4.8 pm to 8.3 pm, 9.4 pm, 10.6 pm, etc., or between any of these values.

When the beam of laser energy is manifested as a series of laser pulses, the laser pulses output by the laser source 104 can have a pulse width or pulse duration (i.e., based on the fullwidth at half-maximum (FWHM) of the optical power in the pulse versus time) that is in a range from 10 fs to 900 ms. It will be appreciated, however, that the pulse duration can be made smaller than 10 fs or larger than 900 ms. Thus, at least one laser pulse output by the laser source 104 can have a pulse duration less than, greater than or equal to 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 ns, 200 ns, 400 ns, 800 ns, 1000 ns, 2 ps, 5 ps, 10 ps, 15 ps, 20 ps, 25 ps, 30 ps, 40 ps, 50 ps, 100 ps, 300 ps, 500 ps, 900 ps, 1 ms, 2 ms, 5 ms, 10 ms, 20 ms, 50 ms, 100 ms, 300 ms, 500 ms, 900 ms, 1 s, etc., or between any of these values.

Laser pulses output by the laser source 104 can have an average power in a range from 5 mW to 50 kW. It will be appreciated, however, that the average power can be made smaller than 5 mW or larger than 50 kW. Thus, 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 between any of these values.

Laser pulses can be output by the laser source 104 at a pulse repetition rate in a range from 5 kHz to 5 GHz. It will be appreciated, however, that the pulse repetition rate can be less than 5 kHz or larger than 5 GHz. Thus, laser pulses can be output by the laser source 104 at a pulse repetition rate 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 between any of these values.

In addition to wavelength, average power and, when the beam of laser energy is manifested as a series of laser pulses, pulse duration and pulse repetition rate, the beam of laser energy delivered to the workpiece 102 can be characterized by one or more other characteristics such as pulse energy, peak power, etc., which can be selected (e.g., optionally based on one or more other characteristics such as wavelength, pulse duration, average power and pulse repetition rate, spot size, etc.) to irradiate the workpiece 102 at the process spot at an optical intensity (measured in W/cm ² ), fluence (measured in J/cm ² ), etc., sufficient to process the workpiece 102 (e.g., to form one or more features, such as any of the aforementioned vias).

Examples of types of lasers that the laser source 104 may be characterized as 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 mode- locked solid-state bulk or fiber lasers, dye lasers, mode-locked diode lasers, pulsed lasers (e.g., ms-, ns-, ps-, fs-pulsed lasers), CW lasers, QCW lasers, or the like or any combination thereof. Depending upon their configuration, gas lasers (e.g., carbon dioxide lasers, etc.) may be configured to operate in one or more modes (e.g., in CW mode, QCW mode, pulsed mode, or any combination thereof).

B. Beam Modulator

As mentioned above, the beam modulator 106 is operative to selectively, and variably, attenuate the beam of laser energy propagating from the laser source 104. Examples of the beam modulator 106 can include one or more systems such as a variable neutral density filter, an acousto-optical (AO) modulator (AOM), an AO deflector (AOD), a liquid crystal variable attenuator (LCVA), a micro-electro-mechanical system (MEMS)-based VOA, an optical attenuator wheel, a polarizer/waveplate filter, or the like or any combination thereof. i. Embodiments Concerning an AOD as the Beam Modulator

If the beam modulator 106 is provided as one or more AOMs or AODs, or any combination thereof, the beam modulator 106 may also be operated to diffract, reflect, refract, or the like, or any combination thereof, the beam of laser energy generated by the laser source 104 and so as to deflect the beam path 114 toward the scanner 108. In one embodiment, the beam modulator 106 can also be operated to impart movement of the beam axis relative to the workpiece 102 along the X-axis (or direction), a Y-axis (or direction), or a combination thereof (e.g., by deflecting of the beam path 114 within a range of angles (as indicated at 118). Although not illustrated, the Y-axis (or Y-direction) will be understood to refer to an axis (or direction) that is orthogonal to the illustrated X- and Z-axes (or directions).

In one embodiment, the beam modulator 106 can be provided as an AO deflector (AOD) system, which includes one or more AODs, each having an AO cell formed of a material such as crystalline germanium (Ge), gallium arsenide (GaAs), wulfenite (PbMoO4), tellurium dioxide (TeO2), crystalline quartz, glassy SiO2, arsenic trisulfide (AS2S3), lithium niobate (LiNbOs), or the like or any combination thereof. It will be appreciated that the material from which the AO cell is formed will depend upon the wavelength of the laser energy that propagates along the beam path 114 so as to be incident upon the AO cell. For example, a material such as crystalline germanium can be used where the wavelength of laser energy to be deflected is in a range from 2 pm (or thereabout) to 20 pm (or thereabout), materials such as gallium arsenide and arsenic trisulfide can be used where the wavelength of the beam of laser energy to be deflected is in a range from 1 pm (or thereabout) to 11 pm (or thereabout), and materials such as glassy SiO2, quartz, lithium niobate, wulfenite, and tellurium dioxide can be used where the wavelength of laser energy to be deflected is in a range from 200 nm (or thereabout) to 5 pm (or thereabout).

As will be recognized by those of ordinary skill, AO technologies (e.g., AODs, AOMs, etc.) utilize diffraction effects caused by one or more acoustic waves propagating through the AO cell (i.e., along a “diffraction axis” of the AOD) to diffract an incident optical wave (i.e., a beam of laser energy, in the context of the present application) contemporaneously propagating through the AO cell (i.e., along an “optical axis” within the AOD). Diffracting the incident beam of laser energy produces a diffraction pattern that typically includes zeroth- and first-order diffraction peaks, and may also include other higher-order diffraction peaks (e.g., second-order, third-order, etc.). As is known in the art, the portion of the diffracted beam of laser energy in the zeroth-order diffraction peak is referred to as a “zeroth-order” beam, the portion of the diffracted beam of laser energy in the first-order diffraction peak is referred to as a “first-order” beam, and so on. Generally, the zeroth-order beam and other diffracted-order beams (e.g., the first-order beam, etc.) propagate along different beam paths upon exiting the AO cell (e.g., through an optical output side of the AO cell). For example, the zeroth-order beam propagates along a zeroth-order beam path, the first-order beam propagates along a first-order beam path, and so on.

Acoustic waves are typically launched into the AO cell by applying an RF drive signal (e.g., from one or more drivers of the beam modulator 106) to the ultrasonic transducer element. Characteristics of the RF drive signal (e.g., amplitude, frequency, phase, etc.) can be controlled (e.g., based on one or more control signals output by the controller 122, a component- specific controller, or the like or any combination thereof) to adjust the manner with which the incident optical wave is diffracted.

For example, the frequency of the applied RF drive signal will determine the angle to which the beam path 114 is deflected. As is known in the art, the angle, 0, by which the beam path 114 is deflected is can be calculated as follows: where 2 is the optical wavelength of beam of laser energy, /is the frequency of the applied RF drive signal, and v is the velocity of the acoustic wave in the AO cell. If the frequency of the applied RF drive signal is composed of multiple frequencies, then the beam path 114 will be deflected simultaneously by multiple angles.

Further, the amplitude of an applied RF drive signal can have an effect on the diffraction efficiency of the AOD. As used herein, the term “diffraction efficiency” refers to the proportion of energy in a beam of laser energy incident upon an AOD that gets diffracted within the AO cell of the AOD into the first-order beam. Diffraction efficiency may thus be represented as the ratio of the optical power in the first-order beam produced by the AOD to the optical power of the incident beam of laser energy incident upon the AOD. Thus, the amplitude of the applied RF drive signal can have a large effect on the optical power in the first-order beam output by the AOD. Thus, the beam modulator 106 can be operated to desirably attenuate an incident beam of laser energy upon being driven by an applied RF signal having a desired or otherwise suitable amplitude. It should also be noted that the diffraction efficiency of an AOD can also change as a function of the frequency of the RF drive signal applied to drive the AOD.

The first-order beam path exiting the AO cell can typically be regarded as the beam path 114 that has been rotated or deflected within the AO cell. Unless otherwise expressly stated herein, the beam path 114 exiting the AO cell corresponds to the first-order beam path. The axis (also referred to herein as the “rotation axis”) about which the beam path 114 exiting the AO cell is rotated (e.g., relative to the beam path 114 as it is incident upon the AO cell) is orthogonal to both the diffraction axis of the AO cell and the optical axis along which the incident beam of laser energy propagates within the AO cell when the AOD is operated or driven to diffract the incident beam of laser energy. The AOD thus deflects an incident beam path 114 within a plane (also referred to herein as a “plane of deflection”) that contains (or is otherwise generally parallel to) the diffraction axis of the AO cell and the optical axis within the AO cell. The spatial extent across which an AOD can deflect the beam path 114 within the plane of deflection is herein referred to as the “scan field” of that AOD. Accordingly, the first scan field of the beam modulator 106 can be considered to correspond to the scan field of a single AOD (e.g., in the event the beam modulator 106 includes a single AOD) or to correspond to combined scan fields of multiple AODs (e.g., in the event the beam modulator 106 includes multiple AODs).

During operation of the beam modulator 106, RF drive signals are repeatedly applied to one or more ultrasonic transducers of the beam modulator 106. The rate with which the RF drive signals are applied is also referred to as the “update rate” or “refresh rate.” For example, the update rate of the beam modulator 106 can be greater than, equal to 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 between any of these values. ii. Additional Discussion Concerning Use of the Beam Modulator to Impart Movement of the Beam Axis

In one embodiment, the beam modulator 106 can be operated so as to impart movement of the beam axis relative to the workpiece 102 (i.e., either alone or in conjunction with the scanner 108). Movement of the beam axis by the beam modulator 106 is generally limited such that the process spot can be scanned, moved or otherwise positioned within a first scan field projected by a scan lens 112. Generally, and depending upon one or more factors such as the configuration of the beam modulator 106, the location of the beam modulator 106 along the beam path 114, the beam size of the beam of laser energy incident upon the beam modulator 106, the spot size, etc., the first scan field may extend, in any of the X- or Y-directions, to a distance that is 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 between any of these values. As used herein, the term “beam size” refers to the diameter or width of the beam of laser energy, and can be measured as a radial or transverse distance from the beam axis to where the optical intensity drops to 1/e ² of the optical intensity at the axis of propagation along the beam path 114. A maximum dimension of the first scan field (e.g., in a plane containing the X- and Y-axes, herein referred to as the “X-Y plane”) may be greater than, equal to or less than a maximum dimension (as measured in the X-Y plane) of a feature (e.g., an opening, a recess, a via, a trench, etc.) to be formed in the workpiece 102.

In one embodiment, the AOD system includes at least one (e.g., one, two, three, four, five, six, etc.) single-element AOD, at least one (e.g., one, two, three, four, five, six, etc.) multielement AOD, or the like or any combination thereof. An AOD system including only one AOD is herein referred to as a “single-cell AOD system,” and an AOD system including more than one AOD is herein referred to as a “multi-cell AOD system.” As used herein, a “single-element” AOD refers to an AOD having only one ultrasonic transducer element acoustically coupled to the AO cell, whereas a “multi-element” AOD includes at least two ultrasonic transducer elements acoustically coupled to a common AO cell. The AOD system may be provided as single-axis AOD system (e.g., operative to deflect the beam axis along a single axis) or as a multi-axis AOD system (e.g., operative to deflect the beam axis along one or more axes, such as along the X-axis, along the Y- axis, or any combination thereof) by deflecting the beam path 114 in a corresponding manner. Generally, a multi-axis AOD system can be provided as a single- or multi-cell AOD system. A multi-cell, multi-axis AOD system typically includes multiple AODs, each operative to deflect the beam axis along a different axis. For example, a multi-cell, multiaxis system can include a first AOD (e.g., a single- or multi-element AOD system) operative to deflect the beam axis along one axis (e.g., along the X- axis), and a second AOD (e.g., a single- or multi-element AOD) operative to deflect the beam axis along a second axis (e.g., along the Y- axis). A single-cell, multi-axis system typically includes a single AOD operative to deflect the beam axis along two axes (e.g., along the X- and Y-axes). For example, a single-cell, multi-axis system can include at least two ultrasonic transducer elements acoustically coupled to orthogonally-arranged planes, facets, sides, etc., of a common AO cell.

The update rate of the beam modulator 106 can also be considered as a “first positioning rate,” which refers to the rate with which the beam modulator 106 positions the process spot at any location within the first scan field (thus moving the beam axis). The inverse of the first positioning rate is herein referred to as the “first positioning period,” and thus refers to the minimum amount of time that elapses before the position of the process spot is changed from one location within the first scan field to another location within the first scan field. Thus, the beam modulator 106 can be characterized as having a first positioning period that is greater than, equal to or less than 200 ps, 125 ps, 100 ps, 50 ps, 33 ps, 25 ps, 20 ps, 15 ps, 13.3 ps, 12.5 ps, 10 ps, 4 ps, 2 ps, 1.3 ps, 1 ps, 0.2 ps, 0.1 ps, 0.05 ps, 0.025 ps, 0.02 ps, 0.013 ps, 0.01 ps, 0.008 ps, 0.0067 ps, 0.0057 ps, 0.0044 ps, 0.004 ps, etc., or between any of these values.

When the beam of laser energy output by the laser source 104 is manifested as a series of laser pulses, the beam modulator 106 can be operated to deflect the beam path 114 by different angles. In one embodiment, the first positioning period is greater than or equal to the pulse duration of each of the laser pulses. Accordingly, a laser pulse can transit through the AO cell of an AOD while the AOD is driven at a fixed RF drive frequency (or a fixed set of RF drive frequencies). Maintaining a fixed RF drive frequency (or a fixed set of RF drive frequencies) applied to an AOD while a laser pulse is transiting through the AO cell of the AOD generally results in uniformly deflecting the laser pulse for the entire pulse duration of the laser pulse and, so, can also be referred to as “whole-pulse deflection.” In another embodiment, however, the first positioning period can be less than the pulse duration of a laser pulse; so the laser pulse can transit through the AO cell of the AOD while the RF drive frequency (or the frequencies within the set of RF drive frequencies) is varied.

C. Scanner

Generally, the scanner 108 is operative to impart movement of the beam axis relative to the workpiece 102 along the X-axis (or direction), the Y-axis (or direction), or a combination thereof.

Movement of the beam axis relative to the workpiece 102, as imparted by the scanner 108, is generally limited such that the process spot can be scanned, moved or otherwise positioned within a second scan field projected by a scan lens 112. Generally, and depending upon one or more factors such as the configuration of the scanner 108, the location of the scanner 108 along the beam path 114, the beam s ize of the beam of laser energy incident upon the scanner 108, the spot size, etc., the second scan field may extend, in any of the X- or Y-directions to a distance that is greater than a corresponding distance of the first scan field. In view of the above, the second scan field may extend, in any of the X- or Y-directions, to a distance 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 between any of these values. A maximum dimension of the second scan field (e.g., in the X-Y plane) may be greater than, equal to or less than a maximum dimension (as measured in the X-Y plane) of a feature (e.g., an opening, a recess, a via, a trench, a scribe line, a conductive trace, etc.) to be formed in the workpiece 102.

In view of the configuration described herein, it should be recognized that any movement of the beam axis imparted by the beam modulator 106 can be superimposed by movement of the beam axis imparted by the scanner 108. Thus, the scanner 108 is operative to scan the first scan field within the second scan field.

Generally, the positioning rate with which the scanner 108 is capable of positioning the process spot at any location within the second scan field (thus moving the beam axis within the second scan field and/or scanning the first scan field within the second scan field) spans a range (also referred to herein as the “second positioning bandwidth”) that is less than the first positioning bandwidth. In one embodiment, the second positioning bandwidth is in a range from 500 Hz (or thereabout) to 8 kHz (or thereabout). For example, the second positioning bandwidth can 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 between any of these values.

In one embodiment, the scanner 108 can be provided as a galvanometer mirror system including two galvanometer mirror components, i.e., a first galvanometer mirror component (e.g., an X-axis galvanometer mirror component) arranged to impart movement of the beam axis relative to the workpiece 102 along the X-axis and a second galvanometer mirror component (e.g., a Y-axis galvanometer mirror component) arranged to impart movement of the beam axis relative to the workpiece 102 along the Y- axis. In another embodiment, however, the scanner 108 may be provided as a galvanometer mirror system including only a single galvanometer mirror component arranged to impart movement of the beam axis relative to the workpiece 102 along the X- and Y- axes. In yet other embodiments, the scanner 108 may be provided as a rotating polygon mirror system, etc. It will thus be appreciated that, depending on the specific configuration of the scanner 108 and the beam modulator 106, the second positioning bandwidth may be greater than or equal to the first positioning bandwidth.

D. Stage

The stage 110 is operative to impart movement of a workpiece 102 relative to the scan lens 112, and, consequently, impart movement of the workpiece 102 relative to the beam axis. Movement of a workpiece 102 relative to the beam axis is generally limited such that the process spot can be scanned, moved or otherwise positioned within a third scan field. Depending upon one or more factors such as the configuration of the stage 110, the third scan field may extend, in the X-direction, the Y-direction, or any combination thereof, to a distance that is greater than or equal to a corresponding distance of the second scan field. Generally, however, a maximum dimension of the third scan field (e.g., in the X-Y plane) will be greater than or equal to a corresponding maximum dimension (as measured in the X-Y plane) of any feature to be formed in the workpiece 102. Optionally, the stage 110 may be operative to move the workpiece 102 relative to the beam axis within a scan field that extends in the Z-direction (e.g., over a range between 1 mm and 50 mm). Thus, the third scan field may extend along the X-, Y- and/or Z- directions.

In view of the configuration described herein, it should be recognized that movement of the process spot relative to the workpiece 102 (e.g., as imparted by the beam modulator 106 and/or the scanner 108) can be superimposed by movement of the workpiece 102 as imparted by the stage 110. Thus, the stage 110 is operative to scan the first scan field and/or second scan field within the third scan field. Generally, the positioning rate with which the stage 110 is capable of positioning the workpiece 102 at any location within the third scan field (thus moving the workpiece 102, scanning the first scan field within the third scan field, and/or scanning the second scan field within the third scan field) spans a range (also referred to herein as the “third positioning bandwidth”) that is less than the second positioning bandwidth. In one embodiment, the third positioning bandwidth is less than 500 Hz (or thereabout). For example, the third positioning bandwidth can be equal to or less than 500 Hz, 250 Hz, 150 Hz, 100 Hz, 75 Hz, 50 Hz, 25 Hz, 10 Hz, 7.5 Hz, 5 Hz, 2.5 Hz, 2 Hz, 1.5 Hz, 1 Hz, etc., or between any of these values.

In one embodiment, the stage 110 is provided as one or more linear stages (e.g., each capable of imparting translational movement to the workpiece 102 along the X-, Y- and/or Z- directions), one or more rotational stages (e.g., each capable of imparting rotational movement to the workpiece 102 about an axis parallel to the X-, Y- and/or Z-directions), or the like or any combination thereof. In one embodiment, the stage 110 includes an X- stage for moving the workpiece 102 along the X-direction, and a Y-stage supported by the X-stage (and, thus, moveable along the X-direction by the X-stage) for moving the workpiece 102 along the Y- direction.

As described thus far, the apparatus 100 could employ a so-called “stacked” positioning system as the stage 110, which enables the workpiece 102 to be moved while positions of other components such as the beam modulator 106, scanner 108, scan lens 112, etc., are kept stationary within the apparatus 100 (e.g., via one or more supports, frames, etc., as is known in the art) relative to the workpiece 102. In another embodiment, the stage 110 may be arranged and operative to move one or more components such as the beam modulator 106, scanner 108, scan lens 112, or the like or any combination thereof, and the workpiece 102 may be kept stationary.

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

In one embodiment in which the stage 110 includes a Z-stage, the Z-stage may be arranged 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 aforementioned stages for moving or positioning the workpiece 102, may carry one or more of the other aforementioned stages for moving or positioning the workpiece 102, or any combination thereof. In another embodiment in which the stage 110 includes a Z-stage, the Z-stage may be arranged and configured to move the scan head along the Z-direction. Thus, in the case where the stage 110 is provided as a splitstage 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 result in a change in spot size at the workpiece 102.

In still another embodiment, one or more components such as the beam modulator 106, scanner 108, scan lens 112, etc., may be carried by an articulated, multi-axis robotic arm (e.g., a 2-, 3-, 4-, 5-, or 6-axis arm). In such an embodiment, the scanner 108 and/or scan lens 112 may, optionally, be carried by an end effector of the robotic arm. In yet another embodiment, the workpiece 102 may be carried directly on an end effector of an articulated, multi-axis robotic arm (i.e., without the stage 110). In still another embodiment, the stage 110 may be carried on an end effector of an articulated, multi-axis robotic arm.

E. Scan Lens

The scan lens 112 (e.g., provided as either a simple lens, or a compound lens) is generally configured to focus the beam of laser energy directed along the beam path, typically so as to produce a beam waist that can be positioned at or near the desired process spot. The scan lens 112 may be provided as an non-telecentric f-theta lens (as shown), a telecentric f-theta lens, an axicon lens (in which case, a series of beam waists are produced, yielding a plurality of process spots displaced from one another along the beam axis), or the like or any combination thereof.

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) operative to move the scan lens 112 (e.g., so as to change the position of the beam waist along the beam axis). For example, the lens actuator may be provided as a voice coil operative to linearly translate the scan lens 112 along the Z-direction. In this case, the scan lens 112 may be formed of a material such as fused silica, optical glass, zinc selenide, zinc sulfide, germanium, gallium arsenide, magnesium fluoride, etc. In another embodiment, the scan lens 112 is provided as a variable-focal length lens (e.g., a zoom lens, or a so-called “liquid lens” incorporating technologies currently offered by COGNEX, VARIOPTIC, etc.) capable of being actuated (e.g., via a lens actuator) to change the position of the beam waist along the beam axis. Changing the position of the beam waist along the beam axis can result in a change in spot size at the workpiece 102.

In an embodiment in which the apparatus 100 includes a lens actuator, the lens actuator may be coupled to the scan lens 112 (e.g., so as to enable movement of the scan lens 112 within the scan head, relative to the scanner 108). Alternatively, the lens actuator may be coupled to the scan head (e.g., so as to enable movement of the scan head itself, in which case the scan lens 112 and the scanner 108 would move together). In another embodiment, the scan lens 112 and the scanner 108 are integrated into different housings (e.g., such that the housing in which the scan lens 112 is integrated is movable relative to the housing in which the scanner 108 is integrated).

F. Controller

Generally, the apparatus 100 includes one or more controllers, such as controller 122, to control, or facilitate control of, the operation of the apparatus 100. In one embodiment, the controller 122 is communicatively coupled (e.g., over one or more wired or wireless, serial or parallel, communications links, such as USB, RS-232, Ethernet, Firewire, Wi-Fi, RFID, NFC, Bluetooth, Ei-Fi, SERCOS, MARCO, EtherCAT, or the like or any combination thereof) to one or more components of the apparatus 100, such as the laser source 104, the beam modulator 106, the scanner 108, stage 110, the lens actuator, the scan lens 112 (when provided as a variable- focal length lens), etc., which are thus operative in response to one or more control signals output by the controller 122.

For example, the controller 122 may control an operation of the beam modulator 106 to selectively, and variably, attenuate the beam of laser energy incident thereto, to deflect the beam path 114 (e.g., to impart relative movement between the beam axis and the workpiece so as to cause 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. Likewise, the controller 122 can control an operation of the scanner 108, the stage 110, or any combination thereof, to impart relative movement between the beam axis and the workpiece so as to cause relative movement between the process spot and the workpiece 102 along a process trajectory.

Generally, the controller 122 includes one or more processors operative to generate the aforementioned control signals upon executing instructions. A processor can be provided as a programmable processor (e.g., including one or more general purpose computer processors, microprocessors, digital signal processors, or the like or any combination thereof) operative to execute the instructions. Instructions executable by the processor(s) may be implemented software, firmware, etc., or in any suitable form of circuitry including programmable logic devices (PLDs), field-programmable gate arrays (FPGAs), field-programmable object arrays (FPOAs), application- specific integrated circuits (ASICs) - including digital, analog and mixed analog/digital circuitry - or the like, or any combination thereof. Execution of instructions can be performed on one processor, distributed among processors, made parallel across processors within a device or across a network of devices, or the like or any combination thereof.

In one embodiment, the controller 122 includes tangible media such as computer memory, which is accessible (e.g., via one or more wired or wireless communications links) by the processor. As used herein, “computer memory” includes magnetic media (e.g., magnetic tape, hard disk drive, etc.), optical discs, volatile or non-volatile semiconductor memory (e.g., RAM, ROM, NAND-type flash memory, NOR-type flash memory, SONOS memory, etc.), etc., and may be accessed locally, remotely (e.g., across a network), or a combination thereof. Generally, the instructions may be stored as computer software (e.g., executable code, files, instructions, etc., library files, etc.), which can be readily authored by artisans, from the descriptions provided herein, e.g., written in C, C++, Visual Basic, Java, Python, Tel, Perl, Scheme, Ruby, assembly language, hardware description language (e.g., VHDL, VERILOG, etc.), etc. Computer software is commonly stored in one or more data structures conveyed by computer memory.

Although not shown, one or more drivers (e.g., RF drivers, servo drivers, line drivers, power sources, etc.) can be communicatively coupled to an input 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 (when provided as a variable-focal length lens), etc., for controlling 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 (when provided as a variable-focal length lens), etc., can be considered to also include any suitable driver, as is known in the art. Each of such drivers would typically include an input communicatively coupled to the controller 122 and the controller 122 is operative to generate one or more control signals (e.g., trigger signals, etc.), which can be transmitted to the input(s) of one or more drivers associated with one or more components of the apparatus 100. Components such as the laser source 104, the beam modulator 106, the scanner 108, the stage 110, lens actuator, the scan lens 112 (when provided as a variable-focal length lens), etc., are thus responsive to control signals generated by the controller 122.

Although not shown, one or more additional controllers (e.g., component-specific controllers) may, optionally, be communicatively coupled to an input of a driver communicatively coupled to a component (and thus associated with the component) such as the laser source 104, the beam modulator 106, the scanner 108, the stage 110, the lens actuator, the scan lens 112 (when provided as a variable-focal length lens), etc. In this embodiment, each component-specific controller can be communicatively coupled to the controller 122 and be operative to generate, in response to one or more control signals received from the controller 122, one or more control signals (e.g., trigger signals, etc.), which can then be transmitted to the input(s) of the driver(s) to which it is communicatively coupled. In this embodiment, a component-specific controller may be operative as similarly described with respect to the controller 122.

In another embodiment in which one or more component- specific controllers are provided, the component- specific controller associated with one component (e.g., the laser source 104) can be communicatively coupled to the component-specific controller associated with one component (e.g., the beam modulator 106, etc.). In this embodiment, one or more of the component- specific controllers can be operative to 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.

II. Embodiments Concerning Reduction in Variability of Via Geometry

FIG. 2 schematically illustrates an exemplary spatial arrangement of vias to be formed within a workpiece (whether by punch processing or by trepan processing) using the apparatus shown in FIG. 1 and an associated drilling sequence determined by the route-determination technique, according to one embodiment. This FIG. is a plan view illustrating a state where a workpiece 102 (e.g., a printed circuit board) has been secured onto the stage 110, and depicts positions of seven vias (i.e., labelled “1,” “2,” “3,” ... “7”) within a scan field (e.g., the scan field of the beam modulator 106 or of the scanner 108, or a combination thereof) projected onto the workpiece 102 by the scan lens 112. FIG. 3 schematically illustrates an exemplary relationship of optical power in a beam of laser energy delivered to a workpiece to sequentially form vias within the workpiece as a function of distance between successively-formed vias.

As mentioned above, a conventional approach to minimizing possible thermally-induced variation of via geometry in a workpiece involves defining a via drilling sequence in which the spatial distance between vias that are to be successively formed is always greater that some predetermined threshold distance. While this approach provides higher processing throughput than simply ensuring that successively-formed vias are not in close temporal proximity to one another, the processing throughput is still not optimal because a distance between a pair of successively-formed vias may be greater than a distance from a via in the pair of successively- formed vias to some other neighboring via to be formed in the workpiece 102. Thus, according to embodiments described herein, the via drilling sequence in which vias are to be formed is determined (e.g., at the controller 122, etc.) by any suitable route-determination technique known in the art (e.g., by solving a travelling salesman problem, etc.) that does not require the distance between successively-formed vias to be greater than some predetermined threshold distance. By doing so, the total distance between all pairs of successively-formed vias defined according to the via drilling sequence can be minimized or otherwise reduced compared to the conventional approach discussed above. Thus, the route-determination technique according to embodiments of the present invention produces a via drilling sequence in which at least some pairs of successively-formed vias are formed both in close temporal proximity and in close spatial proximity to one another. To minimize possible thermally-induced variation of via geometry (thereby ensuring that the vias have, at least, about the same via geometries), the processing recipe executed to form a particular via will vary depending on the distance between the location in the workpiece 102 where the particular via is to be formed and the location of a via in the workpiece 102 to be formed before the particular via.

For example, in FIG. 2, the numbers associated with each via indicate an exemplary via drilling sequence in which vias are to be formed within the workpiece 102, as determined by the route-determination technique according to embodiments of the present invention. Thus, the via “1” is to be formed first, via “2” is to be formed second, via “3” is to be formed third, via “4” is to be formed fourth, and so on. Thus, vias “1” and “2” are an example of successively-formed vias, as are vias “2” and “3”, vias “3” and “4”, vias “4” and “5”, vias “5” and “6”, and vias “6” and “7.” Vias “1” and “2” are formed in close temporal proximity to one another, as are vias “2” and “3”, vias “3” and “4”, vias “4” and “5”, vias “5” and “6”, and vias “6” and “7.” In other embodiment, however, a via such as via “7” may not be formed in close temporal proximity to via “6.” As between a set of vias, any via formed earlier than another via can be referred to as a “preceding via” and any via formed later than another via can be referred to as a “subsequent via.” Thus, as between vias “1” and “2,” via “1” is a preceding via and via “2” is a subsequent via; as between vias “1.” “2” and “3,” vias “1” and “2” are preceding vias and via “3” is a subsequent via; as between vias “2” and “3,” via “2” is a preceding via and via “3” is a subsequent via; as between vias “3” and “4,” via “3” is a preceding via and via “4” is a subsequent via; and the like. In the example shown in FIG. 2, vias “1” and “2” are formed in close spatial proximity to one another, as are vias “1” and “3”, vias “2” and “3”, vias “3” and “4”, and vias “5” and “6.” Vias “4” and “5” are not formed in close spatial proximity to one another, and via “7” is not formed in close spatial proximity to any other via.

Because vias “1” and “2” are formed in close temporal proximity and in close spatial proximity to one another, as are vias “2” and “3”, vias “3” and “4”, and vias “5” and “6,” there is a possibility that vias “2,” “3,” “4” and “6” (e.g., in terms of diameter, taper, overhang, or the like or any combination thereof) will exhibit the thermally-induced geometry variation discussed above relative to the geometry of the other vias “1,” “5,” and “7.”

To minimize possible thermally-induced variation of via geometry for vias such as vias “2,” “3,” “4” and “6,” the processing recipe executed to form these vias can be varied depending on the distance between the location in the workpiece 102 where the these vias are to be formed and the location of the via in the workpiece 102 to be formed before it. That is, the processing recipe executed to form via “2” can be varied (e.g., relative to the processing recipe executed to form via “1”) depending on the distance between the location in the workpiece 102 where vias “1” and “2” are to be formed; the processing recipe executed to form via “3” can be varied (e.g., relative to the processing recipe executed to form via “2”) depending on the distance between the location in the workpiece 102 where vias “2” and “3” are to be formed; the processing recipe executed to form via “4” can be varied (e.g., relative to the processing recipe executed to form via “3”) depending on the distance between the location in the workpiece 102 where vias “3” and “4” are to be formed; and the processing recipe executed to form via “6” can be varied (e.g., relative to the processing recipe executed to form via “5”) depending on the distance between the location in the workpiece 102 where vias “5” and “6” are to be formed.

In one embodiment, the processing recipe executed to form a via can be varied by adjusting the optical power (or pulse energy) in the beam of laser energy ultimately delivered to the via. In this case, the optical power (or pulse energy) can be adjusted by controlling an operation of the beam modulator 106 to produce an attenuated beam of laser energy such that the optical power (or pulse energy) in the beam of laser energy ultimately delivered to each via corresponds to the inter-via distance, (d), between successively-formed vias. As used herein, the term “inter-via distance” (d) refers to the distance between successively-formed vias. In the example shown in FIG. 2, the inter-via distance, d, between vias “4” and “5” and between vias “6” and “7” is greater than a first predetermined threshold distance (e.g., diong in FIG. 3) and, therefore, pulse energy delivered to the workpiece to form vias “5” and “7” can be relatively high (e.g., pehigh in FIG. 3). Further in the example shown in FIG. 2, the inter-via distance, d, between vias “1” and “2” is less than a second predetermined threshold distance (e.g., dshort in FIG. 3) and, therefore, pulse energy delivered to the workpiece to form via “2” can be relatively low (e.g., peiow in FIG. 3). If the inter-via distance, d, between successively-formed vias is between the first threshold distance and the second threshold distance, then the pulse energy to be delivered can vary in exact or approximate correspondence with the inter-via distance between the successively-formed vias.

For example, in FIG. 2, the inter-via distance between vias “1” and “2,” is below the second predetermined threshold distance and, therefore, the pulse energy delivered to the workpiece to form via “2” can be equal to (or at least substantially equal to) peiow (e.g., as shown in FIG. 3). The inter-via distance between vias “2” and “3,” between vias “3” and “4” and between vias “5” and “6” is between the first predetermined threshold distance and the second threshold distance and, therefore, the pulse energy delivered to the workpiece to form vias “3,” “4” and “6” can be between peiow and pehigh (e.g., as shown in FIG. 3). The inter-via distance between vias “4” and “5” and between vias “6” and “7” is greater than the first predetermined threshold distance and, therefore, the pulse energy delivered to the workpiece to form vias “5” and “7” can be equal to (or at least substantially equal to) pehigh (e.g., as shown in FIG. 3). In one embodiment, the optical power (or pulse energy, pe) delivered to the workpiece to form a subsequent via can be calculated as follows: It should be recognized that the optical power (or pulse energy) delivered to the workpiece 102 to form a subsequent via can be calculated in any other suitable or desired manner. It should also be noted that the first via in any via-processing sequence would be formed using a relatively high pulse energy (e.g., pehigh in FIG. 3). Generally, the values for pehigh, pei _ow , diong and, dshort can be selected or otherwise set based on one or more factors such as the materials to be processed during via formation, the wavelength of the beam of laser energy delivered to the workpiece during via formation, the average power of the beam of laser energy delivered to the workpiece during via formation, or the like or any combination thereof. When the workpiece 102 is provided as a printed circuit board and the beam of laser energy is produced by a high- power carbon dioxide laser, the pehigh can be in a range from 1-10 mJ (or thereabout), peiow can be in a range from 60%-90% (or thereabout) of pehigh, di _ong can be greater than 1 mm (or thereabout), and dshort can be in a range from 0 to 300 pm (or thereabout).

III. Conclusion

The foregoing is illustrative of embodiments and examples of the invention, and is not to be construed as limiting thereof. Although a few specific embodiments and examples have been described with reference to the drawings, those skilled in the art will readily appreciate that many modifications to the disclosed embodiments and examples, as well as other embodiments, are possible without materially departing from the novel teachings and advantages of the invention. Accordingly, all such modifications are intended to be included within the scope of the invention as defined in the claims. For example, skilled persons will appreciate that the subject matter of any sentence, paragraph, example or embodiment can be combined with subject matter of some or all of the other sentences, paragraphs, examples or embodiments, except where such combinations are mutually exclusive. The scope of the present invention should, therefore, be determined by the following claims, with equivalents of the claims to be included therein.