LASER IRRADIATION METHOD AND LASER IRRADIATION APPARATUS

A laser irradiation apparatus including: a photonic crystal surface emitting laser (PCSEL) element configured to emit a laser beam; a laser head configured to focus the laser beam emitted from the PCSEL element by a focusing lens thereof in an optical transmission path by spatial propagation; and a moving mechanism configured to irradiate the laser beam focused by the focusing lens onto an object to be irradiated with the laser beam at any irradiation position within a Rayleigh length range regardless of a beam waist position of the laser beam in an optical axis direction by a movement of the focusing lens relative to the object to be irradiated along the optical axis direction of the laser beam.

TECHNICAL FIELD

The present disclosure relates to a laser irradiation method and a laser irradiation apparatus.

BACKGROUND ART

A technique is known which is for soldering an electronic component such as a semiconductor chip to a printed substrate using laser light and a solder. Patent Literature 1 discloses a method of soldering an electronic component to a printed substrate.

In the method disclosed in Patent Literature 1, for example, laser light such as a YAG laser enters a laser irradiation part through an optical fiber from a laser oscillator. The entered laser light has a direction which is changed by a deflection mirror and is scanned at an equal speed on the printed substrate. A plurality of soldering points where the electronic component is soldered are arranged on a scanning locus of the laser light on the printed substrate. Each soldering point is irradiated with the laser light due to an output of the laser light being ON by a Q-switch. The electronic component is soldered to the printed substrate by irradiating each soldering point with the laser light.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

In the method disclosed in Patent Literature1, the YAG laser is exemplified, but if the deflection mirror is not used, a diode laser (semiconductor laser) using a Fabry-Perot resonator is used as a laser light source in a general laser soldering apparatus. The laser light radiated from the Fabry-Perot resonator has an elliptical-beam cross section because an emission diameter and a beam spread angle of the laser light differ in a horizontal direction and a vertical direction. Therefore, the beam cross section of the laser light is shaped into a circle by a Fiber Coupled Laser Diode (FCLD) in which an optical fiber is coupled to a diode laser.

In addition to the YAG laser, a direct diode laser (DDL) using a diode laser, which is a pump light source of a fiber laser in a general laser soldering apparatus, is also available in the market as a laser light source for processing. A collimating lens converts divergent laser light emitted from an end of an optical fiber for beam shaping into collimated light at a point closer to the optical fiber than the deflection mirror. The laser light collimated by the collimating lens is focused by a focusing lens and is used to irradiate each soldering point. An energy density of the laser beam focused by the focusing lens has a Gaussian distribution both before and after collimation performed by the collimating lens. It is necessary to irradiate each soldering point with a laser beam having a high energy density, and therefore a focusing lens is used which has a short focal length and reduces a beam diameter of a laser beam having an energy density of a Gaussian distribution. The Rayleigh length of the laser beam of which beam diameter is reduced by the focusing lens with a short focal length becomes short in accordance with the focal length of the focusing lens.

If the Rayleigh length of the laser beam is short, when a position of each soldering point is deviated in a height direction from a normal position, it is not possible to irradiate each soldering point with a laser beam having a necessary energy density. A position of each soldering point may be deviated in the height direction from the normal position due to warping of the printed substrate, for example. A position of each soldering point may be deviated in the height direction from the normal position depending on a rising state of a solder previously arranged on the printed substrate. If a position of each soldering point is deviated in the height direction and a position to be irradiated with the laser beam is no longer within the Rayleigh length range of the focused laser beam, it is not possible to irradiate each soldering point with a laser beam having a necessary energy density.

One aspect of the present disclosure provides a laser irradiation method comprising: entering a laser beam emitted from a photonic crystal surface emitting laser element to a focusing lens by spatial propagation; and irradiating the laser beam focused by the focusing lens onto an object to be irradiated with the laser beam at any irradiation position within a Rayleigh length range regardless of a beam waist position of the laser beam in an optical axis direction of the laser beam.

One aspect of the present disclosure provides a laser irradiation apparatus comprising: a photonic crystal surface emitting laser element configured to emit a laser beam; a laser head configured to focus the laser beam emitted from the photonic crystal surface emitting laser element by a focusing lens thereof in an optical transmission path by spatial propagation of the laser beam; and a moving mechanism configured to irradiate the laser beam onto an object to be irradiated with the laser beam at any irradiation position within a Rayleigh length range regardless of a beam waist position of the laser beam in an optical axis direction by a movement of the focusing lens relative to the object to be irradiated along the optical axis direction of the laser beam.

In one aspect of the present disclosure, a laser beam emitted from a photonic crystal surface emitting laser element is focused by a focusing lens and irradiated onto an object to be irradiated at any irradiation position within a Rayleigh length range. The laser beam emitted from the photonic crystal surface emitting laser element has a Gaussian waveform intensity distribution in a beam radial direction, and in a case of a Watt class element size, a beam angle in an optical axis direction is spread substantially absent and the laser beam is collimated. Therefore, it is not necessary to collimate the laser beam emitted from the photonic crystal surface emitting laser element by a collimating lens. Since a collimating lens is not necessary, an optical transmission path for entering a laser beam to a collimating lens is not necessary, and a laser beam can be entered to a focusing lens by means of spatial propagation.

Generally, a laser beam having a Gaussian waveform intensity distribution naturally radiates and diverges toward an optical axis direction of the laser beam from a laser light source, even if the laser beam is collimated light. Since the intensity of the laser beam is low at a hem portion of the Gaussian waveform, that is, at a peripheral edge portion in a beam radial direction of the laser beam, the laser beam attenuates toward an optical axis direction from a laser light source. However, at a propagation distance of the laser light of the laser soldering apparatus of the present disclosure, the collimated light does not substantially diverge or attenuate.

Further, if the area of a radiation region of the laser beam in the laser light source increases, a diffraction effect is suppressed and the beam comes to have a plane wave, and therefore collimated light having substantially no beam spread angle in an optical axis direction is obtained.

In other words, since the area of the radiation region of the photonic crystal surface emitting laser element becomes the area of the collimated light, the Rayleigh length of the light focused by the focusing lens can be longer than that of a general laser soldering apparatus.

In accordance with a laser irradiation method and a laser irradiation apparatus according to one aspect of the present disclosure, it is possible to irradiate an object to be irradiated, with a laser beam having a necessary energy density at a position in a wide range in an optical axis direction of the laser beam.

DESCRIPTION OF EMBODIMENT

The present embodiment will be described below with reference to the drawings. The same or equivalent parts or components are denoted with the same reference numerals throughout the drawings.

The following embodiment exemplifies an apparatus and the like for embodying technical ideas of the present disclosure. The technical ideas of the present disclosure do not specify a material, shape, configuration, arrangement, function, and the like of each component to the following.

A laser irradiation apparatus for performing a laser irradiation method according to the present embodiment will be described below with reference to the drawings.FIG.1Ais a diagram showing an entire configuration example of the laser irradiation apparatus according to the present embodiment.FIG.1Bis a diagram showing the relationship between a beam waist position and a position of the Rayleigh length of a laser beam that has been focused by a focusing lens shown inFIG.1A.FIG.2Ais a diagram showing a configuration example of a photonic crystal surface emitting laser element of a laser oscillator in the laser irradiation apparatus shown inFIG.1A.

As shown inFIG.1A, a laser irradiation apparatus100according to an embodiment includes: a photonic crystal surface emitting laser element110ofFIG.2Aconfigured to emit a laser beam LB; a laser head24configured to focus the laser beam LB emitted from the photonic crystal surface emitting laser element110by a focusing lens27thereof in an optical transmission path by spatial propagation of the laser beam LB; and moving mechanisms22,23, and24configured to irradiate the laser beam LB focused by the focusing lens27onto an object to be irradiated W with the laser beam LB at any irradiation position within a Rayleigh length ZRrange ofFIG.1Bregardless of a beam waist BW position ofFIG.1Bof the laser beam LB in an optical axis direction by a movement of the focusing lens27relative to the object to be irradiated W along the optical axis direction of the laser beam LB.

Details of the laser irradiation apparatus100according to the present embodiment will be described below.

A case will be described where the laser irradiation apparatus100shown inFIG.1Ais an example of a laser soldering apparatus for performing soldering to an object to be irradiated with laser light. The laser irradiation apparatus100may be a laser cutting machine for cutting an object to be irradiated with laser light, a laser welding machine for welding, a surface modifying apparatus for modifying a surface of an object to be irradiated, or a marking apparatus for marking an object to be irradiated.

As shown inFIG.1A, the laser irradiation apparatus100includes a laser oscillator11, a laser processing unit15, and a protection unit30for protecting the laser beam LB emitted from the laser oscillator11and transmitted to the laser processing unit15.

The laser oscillator11includes the Photonic crystal Surface Emitting Lasers (PCSEL) element110(hereinafter abbreviated as “PCSEL element110”) shown inFIG.2A. The PCSEL element110emits the laser beam LB. The laser beam LB emitted by the PCSEL element110has a Gaussian waveform intensity distribution in a beam radial direction of the laser beam LB.

Generally, a laser beam having a Gaussian waveform intensity distribution naturally radiates and diverges toward an optical axis direction of the laser beam from a laser light source, even if the laser beam is collimated light. Since the intensity of the laser beam is low at a hem portion of the Gaussian waveform, that is, at a peripheral edge portion in a beam radial direction of the laser beam, the laser beam attenuates more as it moves away from a laser light source in an optical axis direction. However, at a propagation distance of the laser light of the laser soldering apparatus of the present disclosure, the collimated light does not substantially diverge or attenuate.

Further, when the area of a radiation region of the laser beam in the laser light source increases, a diffraction effect is suppressed, the beam comes to have a plane wave, and therefore collimated light having substantially no beam spread angle in an optical axis direction is obtained. In the following description, the “collimated light having substantially no beam spread angle in the optical axis direction” will be referred to as “collimated light” or “substantially collimated light”.

The laser beam LB having the Gaussian waveform intensity distribution, which is emitted from the PCSEL element110, passes through the focusing lens27and then is irradiated onto the object to be irradiated W as shown inFIG.1A. When the laser beam LB is focused by the focusing lens27, as shown inFIG.1B, a spot size (radius) W(Z) at a focusing point of the focused laser beam LB takes the minimum value W0at a certain point on an optical axis. The point at which the spot size W(Z) in the focused laser beam LB becomes the minimum value W0is referred to as a beam waist BW. A spot size W(Z) of the focused laser beam LB at a position away from the beam waist BW by the Rayleigh length ZRis √{square root over (2)} times the spot size W0of the laser beam LB at the beam waist BW.

There are two positions which are away from the beam waist BW by the Rayleigh length ZR, one of the two positions is on a side closer to the focusing lens27shown inFIG.1Athan the position of the beam waist BW of the focused laser beam LB, and the other of the two positions is on a side opposite to the focusing lens27. A focal depth b of the focused laser beam LB shown inFIG.1Bis a distance between a position away from the beam waist BW toward the focusing lens27side by the Rayleigh length ZR, and a position away from the beam waist BW toward the side opposite to the focusing lens27by the Rayleigh length ZR. The position away from the beam waist BW toward the focusing lens27side by the Rayleigh length ZRis referred to as an inner focus position, and the inner focus position is shown as “Pi” inFIG.1B. Further, the position away from the beam waist BW toward the side opposite to the focusing lens27by the Rayleigh length ZRis referred to as an outer focus position, and the outer focus position is shown as “Po” inFIG.1B. At the inner focus position Pi and the outer focus position Po, a cross-sectional area of the laser beam LB is twice a cross-sectional area of the laser beam LB at the beam waist BW. InFIG.1B, θ indicates a divergence angle of the laser beam LB focused by the focusing lens27.

In the laser irradiation method and the laser irradiation apparatus of the present disclosure described below, a range from the beam waist BW ofFIG.1Bof the laser beam LB focused by the focusing lens27shown inFIG.1Ato positions away from the beam waist BW by the Rayleigh length ZRis set as a use range for soldering of the object to be irradiated W.

FIG.2Ashows a case where the laser oscillator11includes a plurality of PCSEL elements110. The plurality of PCSEL elements110can be regularly arranged in a two-dimensional manner. The two-dimensional and regular arrangement is, for example, a square lattice shape in which each PCSEL element110is arranged in correspondence with each vertex of the square as shown inFIG.2A. However, the arrangement is not limited thereto, and other arrangements may be used such as other lattice shapes including a hexagonal lattice shape in which each PCSEL element110is arranged in correspondence with each vertex of the hexagon, or concentric circles.

In an example shown inFIG.2A, the plurality of PCSEL elements110are mounted on a common circuit board111. When the plurality of PCSEL elements110are mounted on the common circuit board111, each PCSEL element110can be electrically driven in parallel. By electrically driving each PCSEL element110in parallel, each PCSEL element110can emit the laser beam LB of the same intensity. However, an input current of each PCSEL element110may be individually adjusted in order to adjust the individual difference of each PCSEL element110. In that case, it is not necessary to mount the PCSEL on the common board111, but the PCSEL may be mounted on individual boards.

The circuit board111may be divided into a plurality of parts as shown by dashed lines inFIG.2A. When the circuit board111is divided into a plurality of parts, the plurality of PCSEL elements110mounted on each circuit board111are regularly arranged in a two-dimensional manner. When each PCSEL element110is mounted on each circuit board111, an t current of each PCSEL element110can be individually set. When an input current of each PCSEL element110is individually set, the intensity of a laser beam LB emitted by each PCSEL element110can be adjusted according to a position irradiated with each laser beam LB.

The plurality of PCSEL elements110of the laser oscillator11may be regularly arranged in a one-dimensional manner. The number of the PCSEL elements110of the laser oscillator11may be one instead of being more than one. The number and arrangement of the PCSEL elements110of the laser oscillator11may be determined, for example, according to the layout of parts of an object to be irradiated which is subjected to processing such as soldering by means of irradiation with the laser beam LB.

FIG.2Bis a perspective view showing a detailed configuration example of each PCSEL element110shown inFIG.2A. As shown inFIG.2B, each PCSEL element110is configured by laminating a substrate112, an n-type cladding layer113, an active layer114, a carrier block layer115, a photonic crystal layer116, a p-type cladding layer117, a p-type contact layer118, and a back electrode119. InFIG.2B, the carrier block layer115and the photonic crystal layer116are shown in a separated state so that a configuration of the photonic crystal layer116can be easily seen.

A Distributed Bragg Reflector (DBR) layer (not shown) is provided between the p-type cladding layer117and the p-type contact layer118. The distributed bragg reflector layer reflects light directing toward the back electrode119in an emission direction. A plurality of holes121are formed in the photonic crystal layer116.

A ring-shaped window electrode122is provided on a surface of the substrate112. A window part123by an Anti-Reflection (AR) coat layer is provided on an inner side of the window electrode122. The window part123serves as an emission surface of a laser beam LB from each PCSEL element110.

In each PCSEL element110, light generated in the active layer114due to the energization between the back electrode119and the window electrode122is diffracted in a direction of 90 degrees or 180 degrees in the holes121of the photonic crystal layer116which exhibits a binding effect on the light. A standing wave along a crystal direction is generated inside the photonic crystal layer116due to the interference of the diffracted light.

The diffraction of the light in the holes121occurs not only in a direction in a plane of the photonic crystal layer116but also in a direction orthogonal to this plane. Among light extracted from the photonic crystal layer116, light traveling toward the substrate112passes through the window part123on the inner side of the window electrode122and is radiated to the outside of each PCSEL element110. Among the light extracted from the photonic crystal layer116, light traveling toward the back electrode119is reflected by the distributed bragg reflector layer. The light reflected by the distributed bragg reflector layer passes through the window part123together with the light traveling toward the substrate112, and is radiated to the outside of each PCSEL element110. The light radiated through the window part123of each PCSEL element110becomes coherent light.

Each PCSEL element110emits coherent light radiated through the window part123as the laser beam LB. The laser beam LB emitted by each PCSEL element110is substantially collimated light in a watt class. The laser beam LB emitted by each PCSEL element110has a Gaussian waveform intensity distribution in a beam radial direction.

The laser oscillator11shown inFIG.1Aoutputs the laser beam LB emitted by each energized PCSEL element110. When the plurality of energized PCSEL elements110emit laser beams LB, the laser beams LB output by the laser oscillator11become multi-beams.

The laser processing unit15has a processing table21, an X-axis carriage22, a Y-axis carriage23, and a processing head24fixed to the Y-axis carriage23. A printed substrate W to be processed with the laser beam LB is mounted on the processing table21.

The X-axis carriage22is formed into a gate shape and is movable in an X-axis direction on the processing table21by spanning the printed substrate W. The Y-axis carriage23is movable in a Y-axis direction perpendicular to the X-axis direction on the X-axis carriage22. The X-axis carriage22and Y-axis carriage23can move the entire processing head24including a nozzle26relatively to the printed substrate W on the processing table21along a surface of the printed substrate W in the X-axis direction, the Y-axis direction, or any combination direction of the X-axis and the Y-axis.

Instead of moving the processing head24along the surface of the printed substrate W in the X-axis direction and Y-axis direction, a position of the processing head24may be fixed and the printed substrate W or the processing table21on which the printed substrate W is mounted may move in the X-axis direction and the Y-axis direction.

The processing head24as a laser head has a bend mirror25for reflecting the laser beam LB propagated in the protection unit30, and the nozzle26for emitting the laser beam LB reflected by the bend mirror25to the printed substrate W on the processing table21. The processing head24further has the focusing lens27for focusing the laser beam LB reflected by the bend mirror25and emitting the laser beam from the nozzle26. The focusing lens27is movable in the processing head24in a Z-axis direction perpendicular to the X-axis and Y-axis.

Instead of moving the focusing lens27in the processing head24in the 2-axis direction, a position of the focusing lens27may be fixed in the processing head24, and the printed substrate W or the processing table21on which the printed substrate W is mounted may move in the Z-axis direction.

The X-axis carriage22, Y-axis carriage23, and processing head24function as moving mechanisms for moving the printed substrate W, which is an object to be irradiated, relative to the processing head24in the X-axis direction, Y-axis direction, and Z-axis direction. That is, it is sufficient if the laser irradiation apparatus100has a moving mechanism for moving the processing head24relative to the surface of the printed substrate W.

The protection unit30has a mirror housing32connected to the laser oscillator11with a bellows optical path cover31therebetween, and a mirror housing35connected to the mirror housing32with a bellows optical path cover34therebetween. The mirror housing32houses an X-axis bend mirror33and the mirror housing35houses a Y-axis bend mirror36.

The optical path cover31protects, from external elements, the laser beam LB emitted by each PCSEL element110of the laser oscillator11and directed to the X-axis bend mirror33. The optical path cover34protects, from external elements, the laser beam LB reflected by the X-axis bend mirror33and directed to the Y-axis bend mirror36. The laser beam LB reflected by the Y-axis bend mirror36is reflected by the bend mirror25of the processing head24and emitted from the nozzle26of the processing head24toward the processing table21.

In the protection unit30, the laser beam LB is transmitted from the laser oscillator11to the focusing lens27of the processing head24by means of spatial propagation except for reflection by the X-axis bend mirror33, Y-axis bend mirror36, and bend mirror25. The spatial propagation is performed by means of wireless transmission without spectroscopy, focusing, and transmission using an optical transmission path. The protection unit30may directly connect the laser oscillator11and the processing head24with bellows optical path cover. In this case, the mirror housings32and35, the X-axis bend mirror33, and the Y-axis bend mirror36can be omitted.

According to above the configuration, the laser irradiation apparatus100transmits the laser beam LB emitted from the laser oscillator11to the processing head24by means of the protection unit30, irradiates the printed substrate W with the laser beam having a high energy density to perform soldering to the printed substrate W.

A laser light source for processing such as soldering has changed from a gas laser of CO2 to a solid laser such as YAG (a crystal of a garnet structure by a compound oxide of yttrium and aluminum) and a slab laser, and then to a fiber laser. A direct diode laser (DDL) using a diode laser, which is a pump light source for a fiber laser, is available in the market as the laser light source for processing.

An example of the DDL is a Fabry-Perot diode laser.FIG.3is a diagram showing a principle of laser beam emission by the Fabry-Perot diode laser used as the laser light source for processing.

In a Fabry-Perot (hereinafter abbreviated as “FP”) diode laser200shown inFIG.3, an optical resonator is configured in which left and right end surfaces201and202in the diagram serve as mirrors, and light reciprocates between both of the mirrors. A light-emitting part203for emitting a laser beam LB1, located at the right end surface202has an elongated line shape, and has a dimension of, for example, about 100 μm horizontally and less than 1 μm vertically. A divergence angle of the laser beam LB1emitted from the light-emitting part203is, for example, a full. angle of 10 degrees horizontally and a full angle of 60 degrees vertically. Therefore, the quality of the laser beam LB1emitted from the FP diode laser200differs greatly in the vertical direction and the horizontal direction.

Therefore, when the FP diode laser200is used as the laser light source for processing, a complicated optical system is required to form a shape of an emitted beam. Further, when the FP diode laser200is used as the laser light source for processing, it is necessary to focus the laser beam LB1so that the energy density distribution is uniform.

Each issue of the beam shape and the energy density distribution is solved by inputting the laser beam LB1emitted from the light-emitting part203of the FP diode laser200into an optical fiber and configuring a fiber coupled laser diode (hereinafter abbreviated as “FCLD”). In the FCLD, while the laser beam LB1is transmitted in the optical fiber, the laser beam LB1can be shaped to have a circular-beam cross section, and the energy density distribution of the laser beam LB can be made uniform.

FIG.4Ais a diagram showing an example of a soldering operation performed on a printed substrate by a general laser soldering apparatus using the FCLD as a laser light source.FIG.4Bis a diagram showing an example of an operation when soldering is performed on a printed substrate by the laser soldering apparatus ofFIG.4Ausing a line-shaped laser beam.

A laser beam emitted from an end surface of the optical fiber of the FCLD becomes divergent light in which a diameter of a beam cross section gradually increases. In a laser soldering apparatus using the FCLD emitting divergent light as a laser light source, as shown inFIG.4A, laser beams LB1as divergent light emitted from end surfaces of optical fibers LF of the FCLDs are collimated by collimating lenses205of the processing heads204. The collimated laser beams LB1are focused by the focusing lenses206and are irradiated onto solders (not shown) arranged at soldering points P1of terminals of an electrical component D1on the printed substrate W.

When the electrical component D1having terminals on both sides is soldered, if the terminals on both sides are not soldered to the soldering points P1simultaneously, the electrical component D1is fixed in a cantilevered manner due to terminals on only one side being soldered before terminals on the other side, and therefore the electrical component D1may be inclined relative to the printed substrate W. When the electrical component D1is inclined, terminals on the other side are separated from the printed substrate W, and it becomes difficult to solder the terminals to the soldering points P1. In order to avoid the inclination of the electrical component D1due to soldering, as shown inFIG.4A, it is effective to solder the terminals on both sides of the electrical component D1simultaneously using the laser beams LB1from the plurality of processing heads204.

When a plurality of terminals are present on each side of the electrical component D1, as shown inFIG.4B, a beam shaping element207is arranged between a collimating lens205and a focusing lens206of each processing head204, and a laser beam LB2is shaped into a line shape by the beam shaping element207. The shaped line laser beam LB2spans a plurality of soldering points P1corresponding to a plurality of terminals on each side of the electrical component D1, and is irradiated onto solders (not shown) of the soldering points P1.

Incidentally, in the high-power FP diode laser200used for a processing application, many longitudinal modes are oscillated, and the wavelength width of oscillation spectrums reaches 2 to 4 nm at half maximum. In addition, in the high-power FP diode laser200, the temperature dependence of the wavelength is large, and a wavelength shift of 0.25 to 0.3 nm/° C. is observed due to a temperature change of a cooling part or a change in a heat radiation amount due to a difference in the output.

FIG.5Ais a diagram showing a case where outputs of the laser beams LB1and LB2are increased by increasing the length of the optical resonator in the FP diode laser200.FIG.5Bis a diagram showing a case where outputs of the laser beams LB1and LB2are increased by increasing the width of the light-emitting part203in the FP diode laser200.

In the FP diode laser200, outputs of the laser beams LB1and LB2can be increased by increasing the length of the optical resonator as shown inFIG.5Aor by increasing the width of the light-emitting part203as shown inFIG.5B.

However, when the length of the optical resonator is increased, since the width of the light-emitting part203does not change, the brightness of a laser beam emitted from the light-emitting part203increases, the light-emitting part203causes Catastrophic optical damage (COD), and therefore there are limitations on the increase in outputs. Further, when the width of the light-emitting part203is increased, the quality of a laser beam in a horizontal direction, which is lower than that in a vertical direction, further deteriorates, and it becomes difficult to focus a laser beam and input a laser beam to a fiber.

FIG.5Cis a diagram showing an example of a focusing optical path of the laser beam LB1emitted by the FCLD in the laser soldering apparatus ofFIG.4A. The laser beam LB1emitted by the FP diode laser200is collimated by the collimating lens205, then focused by the focusing lens206, and irradiated onto the soldering points P1.

Since the focal length of the collimating lens205is limited by a lens diameter, it is not possible to increase the focal length. When the priority is to reduce a beam diameter of the laser beam LB1at the soldering point P1so that a necessary energy density can be obtained at the soldering point P1, it is necessary to reduce the focal length of the focusing lens206.

When the focal length of the focusing lens206is reduced, the Rayleigh length of the focused laser beam LB1is reduced. If the Rayleigh length of the laser beam LB1is short, when a position of the soldering point P1deviates in the Z-axis direction due to warping of the printed substrate W, the position of the soldering point P1is likely to be outside a range of the Rayleigh length of the laser beam LB1, for example.

Incidentally, as is well known, the Rayleigh length of the laser beam LB1is a distance between the focusing point of the laser beam LB1and a position where a beam cross-sectional area of the laser beam LB1is twice a beam cross-sectional area at the focusing point. The focusing lens206side from the beam waist position of the laser beam LB1is referred to as an inner focus side, and an opposite side of the focusing lens206is referred to as an outer focus side. The range of the Rayleigh length extends to both the inner focus side and the outer focus side.

The focal depth of the Rayleigh length indicates a range where a focusing diameter of the laser beam LB1by the focusing lens206is equal to or less than √{square root over (2)} times the focusing point, and therefore, in the focal depth of the Rayleigh length, the energy density of the laser beam LB1is reduced to half of the highest energy density of the focusing point at the maximum. In the range of the Rayleigh length of the laser beam LB1, the focal depth is not necessarily applicable to all laser processing. However, at least when the laser beam LB1is used for soldering at the soldering point P1, by using the focal depth as the Rayleigh length, the laser beam LB1having the necessary energy density can be irradiated onto the soldering point P1.

However, as described above, when the position of the soldering point P1is outside the range of the Rayleigh length of the laser beam LB1, it is not possible to irradiate the soldering point P1with the laser beam LB1having the necessary energy density, and soldering may not be performed appropriately.

FIG.6Ais a graph showing an example of the relationship between the focal length of the focusing lens206and a beam diameter of the focused laser beam LB1when the laser beam LB1emitted by the FCLD is collimated and then focused by the focusing lens206.FIG.6Bis a graph showing an example of the relationship between the focal length of the focusing lens206shown inFIG.6Aand the Rayleigh length of the focused laser beam LB1.

FIG.6Ashows the laser beam LB1emitted by the FCLD when the laser beam LB1emitted from the FP diode laser200is input to the optical fiber, and a wavelength λ of the laser beam LB1is 948 nm. A core diameter φ of the optical fiber of the FCLD is 100 μm, a numerical aperture NA thereof is 0.2, and a focal length f of the collimating lens205for collimating the laser beam LB1emitted by the FCLD is 40 mm.

Generally, in many cases, a beam diameter of a laser beam used for soldering is about 100 to 400 μm. As can be seen from the relationship shown inFIG.6A, in order to reduce a beam diameter of the laser beam LB1to 100 to 400 μm, it is necessary to use a focusing lens206having a focal length of 40 to 160 mm. As can be seen from the relationship shown inFIG.6B, the Rayleigh length of the laser beam LB1focused by the focusing lens206having a focal length of 40 to 160 mm is about 4 mm at the longest.

In the laser soldering apparatus shown inFIG.4A or4B, even if each soldering point P1is deviated by only several millimeters in the Z-axis direction, a position thereof is outside a range of the Rayleigh length of the laser beam LB1or LB2, and it is not possible to irradiate each soldering point P1with the laser beam LB1or LB2having a necessary energy density.

Meanwhile, when meeting a space requirement in a laser soldering apparatus is a priority, another problem occurs. There are space limitations on a lens diameter of the collimating lens205shown inFIG.5Cand a distance from an end surface of the optical fiber LF to the collimating lens205in the optical axis direction of the laser beam LB1. Therefore, there are upper limitations on the length of the focal length of the collimating lens205.

In addition, since it is not possible to use a lens with a long focal length for the collimating lens205, there is a demand to shorten the focal length of the focusing lens206such that the necessary energy density can be obtained at the soldering point P1. However, in order to ensure a necessary distance, there are lower limitations on a distance from a surface of the focusing lens206to the soldering point P1on a focal position of the focusing lens206(also referred to as a working distance) in the optical axis direction of the laser beam LB1.

Therefore, when meeting a space requirement in a laser soldering apparatus is a priority, it becomes difficult to sufficiently reduce a beam diameter of the laser beam LB1at the soldering point P1such that the necessary energy density can be obtained at the soldering point P1.

In the laser irradiation apparatus100of the present embodiment shown inFIGS.1A,1B,2A, and2B, the PCSEL element110used in the laser oscillator11oscillates in a single mode. The PCSEL element110having a radiation region φ 1 mm oscillates substantially with collimated light, for example. The PCSEL element110emits collimated light as the laser beam LB, and therefore a collimating lens for collimating the laser beam LB becomes unnecessary. Accordingly, in meeting a space requirement in the laser irradiation apparatus100, it is not necessary to consider the presence of a collimating lens and a focal length.

FIG.7is a diagram showing an example of a focusing optical path of the laser beam LB emitted by the PCSEL element110shown inFIG.2Bin the laser irradiation apparatus100shown inFIG.1A. The laser beam LB emitted by the PCSEL element110is focused by the focusing lens27and then irradiated onto a soldering point P of the printed substrate W.

Since the PCSEL element110oscillates in a single mode, the quality of the laser beam LB emitted by the PCSEL element110is higher than the quality of the laser beam LB1or LB2ofFIG.4A or4Bemitted by the FCLD. Therefore, even if the focusing lens27having a long focal length is used, it is possible to reduce a beam diameter of the laser beam LB to a beam diameter sufficient to obtain the necessary energy density at the soldering point P of the printed substrate W.

Since a lens having a longer focal length than the focusing lens206can be used for the focusing lens27, and a beam diameter of a beam entering the focusing lens27is small, it is possible to increase the Rayleigh length ZRof the coherent light of the laser beam LB focused by the focusing lens27and expand a range of the Rayleigh length ZR. Since the range of the Rayleigh length ZRof the coherent light is expanded, even if the position of the soldering point P1is deviated in the Z-axis direction due to warping of the printed substrate W, the position of the soldering point P1is less likely to be outside the range of the Rayleigh length ZRof the coherent light. Therefore, even if the position of the soldering point P1is deviated in the Z-axis direction, it is possible to easily irradiate the soldering point P1with the coherent light of the laser beam LB having the necessary energy density.

The laser beam LB is emitted from the window part123on the inner side of the window electrode122on an anode side of the PCSEL element110shown inFIG.2B, for example. When a diameter φ of the window part123is 1 mm and a focal length f of the focusing lens27is 100 mm, a beam diameter φ of the laser beam LB at the focal position of the focusing lens27is 200 μm, for example. Since the laser beam LB entering the focusing lens27is coherent light with a small beam diameter φ of 1 mm, the long Rayleigh length ZRcan be ensured. Since the diameter of the focusing lens27can be reduced, a space necessary for the arrangement of the focusing lens27can be minimized.

FIG.8Ais a diagram showing that the PCSEL element110shown inFIG.2Bconfines light in an in-plane direction by means of a photonic crystal and radiates light in a vertical direction.FIG.8Bis a diagram showing an example of increasing a radiation area of a laser beam in the PCSEL element110shown inFIG.2Band achieving higher output.

When a current is supplied to the PCSEL element110shown inFIG.2B, the laser beam LB is emitted from the window part123of the PCSEL element110as shown inFIG.8A. The laser beam LB emitted from the window part123is radially emitted from a central axis passing through the center of the window electrode122. Since the PCSEL element110can oscillate in a single mode irrelevant to the area of the window part123thereof, as shown inFIG.8B, when the radiation area of the laser beam LB is increased in order to increase the output of the laser beam LB, reversely a beam spread angle of the laser beam LB becomes small.

Since an output of the laser irradiation apparatus100is required to have a watt level, the radiation region of the PCSEL element110has a large diameter, and in accordance with this, the beam spread angle of the laser beam LB becomes smaller. Therefore, in the PCSEL element110of the laser irradiation apparatus100, the laser beam LB can be focused to have a sufficiently small beam diameter by the focusing lens27even if a collimating lens is not used.

The laser beam LB emitted by the PCSEL element110has excellent longitudinal mode characteristics, and therefore an oscillation spectrum of the laser beam LB is less than 0.1 nm at half maximum, and the wavelength shift by temperature is also less than 0.1 nm/° C. Therefore, the change in the wavelength of the laser beam LB due to the change in the output of the laser beam LB is small. Further, the PCSEL element110oscillating in a single mode can optically control the emitted laser beam LB easily because the laser beam has a circular shape and has the Gaussian waveform intensity distribution. Therefore, the PCSEL element110can easily respond to an increase in the output of the laser beam LB.

FIG.9Ais a graph showing example of the relationship between the focal length of the focusing lens27for focusing the single mode laser beam LB emitted by the PCSEL element110shown inFIG.2Bin the laser irradiation apparatus100shown inFIG.1A, and the beam diameter of the focused laser beam LB.FIG.9Bis a graph showing an example of the relationship between the focal length of the focusing lens27shown inFIG.9Aand the Rayleigh length ZRof the focused laser beam LB.FIG.9Ashows the relationship between the focal length of the focusing lens27in the PCSEL element110and the beam diameter of the focused laser beam LB, and in the PCSEL element110, the wavelength λ of the laser beam LB is 948 nm, the beam quality M2is 1.5, and a diameter φ of the window part123is 1 mm, for example.

The laser beam LB emitted by the PCSEL element110is substantially collimated light with a high quality and a small divergence angle because the laser beam is in a single mode, and therefore the laser beam LB enters the focusing lens27with a small beam diameter even if the laser beam is not collimated by the collimating lens. When the focusing lens27with a focal length of 60 mm to 110 mm is used, as shown inFIG.9A, a beam diameter of the laser beam LB at the focal position of the focusing lens27can be 100 to 200 μm, for example. Further, the Rayleigh length ZRof the laser beam LB focused by the focusing lens27with a focal length of 60 mm to 110 mm is 5 to 20 mm as can be seen from the relationship shown inFIG.9B.

In the laser irradiation apparatus100shown inFIG.1A, even if the soldering point P is deviated by several millimeters in the Z-axis direction, the laser beam LB can be irradiated onto the soldering point P within the range of the Rayleigh length ZRof the laser beam LB. When a focusing lens27having a focal length of 120 mm is used as the focusing lens27, according to the relationship shown inFIG.9B, even at a position deviated by 20 mm or more in the Z-axis direction from the focal position of the focusing lens27, the positon of the soldering point P is less likely to be outside the range of the Rayleigh length ZRof the coherent light of the laser beam LB.

Similar to the Rayleigh length of the laser beam LB1shown inFIG.5C, the Rayleigh length ZRof the laser beam LB shown inFIG.1Bindicates a distance between the focusing point of the laser beam LB and a position where a beam cross-sectional area of the laser beam LB is twice a beam cross-sectional area at the focusing point. That is, the range of the Rayleigh length ZRextends to both the inner focus side and the outer focus side.

In the focal depth b of the Rayleigh length ZR, the energy density of the laser beam LB is reduced to half of the highest energy density of the focusing point at the maximum. However, at least to the extent that the laser irradiation method and the laser irradiation apparatus of the present disclosure are applied to soldering of the present embodiment, the laser beam LB having the necessary energy density can be irradiated onto the soldering point P by setting the focal depth to the Rayleigh length ZR.

When the soldering point P is deviated in the Z-axis direction, a position of the printed substrate W irradiated with the laser beam LB may be deviated from the position of the soldering point P in at least one direction of the X-axis direction and the Y-axis direction. In this case, a relative position of the printed substrate W and the processing head24is adjusted such that the position of the soldering point P is irradiated with the laser beam LB.

In the laser irradiation apparatus100of the present embodiment, it is possible to increase the Rayleigh length ZRof the laser beam LB focused by the focusing lens27, and in the wide range of the Rayleigh length ZR, the laser beam LB for processing having the necessary energy density can be irradiated onto the printed substrate W.

The PCSEL element110for emitting the laser beam LB from the window part123thereof may be all PCSEL elements110mounted on the circuit board111, or a part of the PCSEL elements110. When only a part of the PCSEL elements110emits the laser beam LB, unnecessary laser beams LB emitted from other PCSEL elements110may be blocked by a shutter. Alternatively, it is possible to stop the supply of a current to PCSEL elements110which are not required to emit laser beams LB.

When a laser beam LB is irradiated onto one soldering point P of the printed substrate W, a PCSEL element emitting a laser beam LB may be limited to one PCSEL element110corresponding to a position of the soldering point P, for example. Further, when a plurality of soldering points P are simultaneously irradiated with laser beams LB, a plurality of PCSEL elements110corresponding to each soldering point P can emit the laser beams LB simultaneously. When the plurality of PCSEL elements110emit the laser beams LB, multi-spot beams by the plurality of laser beams LB are irradiated onto each soldering point P of the printed substrate W.

When laser beams LB are simultaneously emitted from all PCSEL elements110, multi-spot beams irradiated onto the printed substrate W form a pattern in which the arrangement of the plurality of PCSEL elements110is reduced by focusing performed by the focusing lens27.

The circuit board111for supplying a current to the PCSEL element110may be a single circuit board common to all PCSEL elements110, or may be a plurality of circuit boards individually corresponding to each PCSEL element110. When the circuit board111is the single circuit board, it is advantageous to supply a current of the same magnitude to each PCSEL element110. When the circuit board111is the plurality of circuit boards individually corresponding to each PCSEL element110, it is advantageous to individually control an output of a laser beam LB by each PCSEL element110.

Each PCSEL element110can emit a laser beam LB of an output according to the area of the back electrode119. The ring-shaped window part123can be sized such that the laser beam LB of the output according to the area of the back electrode119is emitted without being blocked, for example. By increasing the area of a back electrode119of each PCSEL element110and setting the area of the window part123according to the area of the back electrode119, the radiation area of the laser beam LB can be increased and the output of the laser beam LB can be increased.

FIG.10is a diagram showing examples of optical paths of laser beams LB radiated by two PCSEL elements110ofFIG.2Bof the laser oscillator11shown inFIG.1A. When the laser beams LB radiated by the two PCSEL elements110ofFIG.10are focused by the focusing lens27and then irradiated onto two irradiation positions of the printed substrate W, it is necessary to adjust an interval of the laser beams LB in accordance with an interval of the irradiation positions.

The interval of the laser beams LB varies depending on how much irradiation positions of the printed substrate W irradiated with the laser beams LB are deviated in the Z-axis direction from a focal position (Z=0 mm) of the focusing lens27. Further, the interval of the laser beams LB varies depending on the focal length of the focusing lens27.

FIG.11is a graph showing an example of the relationship between a beam interval and the focal length of the focusing lens27of the two laser beams LB shown inFIG.10. When a position where the two laser beams LB intersect is set as Z=0 mm,FIG.10shows a beam interval at a position which is deviated by Z mm from the position in the inner focus side or the outer focus side.

When an interval between the irradiation positions of the printed substrate W is 6 mm and the focal length of the focusing lens27is 120 mm, an interval between the two laser beams LB is 6 mm at a position which is deviated by about 40 mm from the position of the focal point (Z=0 mm), for example. When the focal length of the focusing lens27is 200 mm, an interval between the two laser beams LB is 6 mm at a position which is deviated by 60 mm from the position of the focal point (Z=0 mm).

Therefore, when a focusing lens27having a focal length of 120 mm is used, whether the Rayleigh length ZRof a focused laser beam LB is 40 mm or more is confirmed. Further, when a focusing lens27having a focal length of 200 mm is used, whether the Rayleigh length ZRof a focused laser beam LB is 60 mm or more is confirmed.

When the Rayleigh length ZRis equal to or longer than the length to be compared, by deviating the positions irradiated with the laser beams LB by a distance according to the focal length of the focusing lens27from the focal position of the focusing lens27, the two laser beams LB can be irradiated onto the printed substrate W at an interval equal to an interval between the irradiation positions. A direction in which the printed substrate W is deviated can be either the inner focus side or the outer focus side. The processing head24may be deviated instead of the printed substrate W.

FIG.12Ais a diagram showing a position of each laser beam LB in a range of the Rayleigh length ZRwhen the two laser beams LB shown inFIG.10are focused by one focusing lens27having a focal length of 120 mm for each distance from a focal plane of the focusing lens27.FIG.12Bis a diagram showing a position of each laser beam LB in a range of the Rayleigh length ZRwhen the two laser beams LB shown inFIG.10are focused by one focusing lens27having a focal length of 200 mm for each distance from a focal plane of the focusing lens27.

In bothFIGS.12A and12B, a position of the printed substrate W is deviated from a position of the focal plane of the focusing lens27in a range of the Rayleigh length ZRof the laser beam LB, and accordingly soldering can be performed simultaneously at different positions of the printed substrate W by irradiating the positions with the laser beams LB. The position of the printed substrate W deviated from the position of the focal plane of the focusing lens27can be either the inner focus side or the outer focus side.

The positions of the printed substrate W irradiated with the laser beams LB that have been focused by the focusing lens27shown inFIG.1Amay be limited in a range of the Rayleigh length ZRfrom the beam waist BW to the inner focus position Pi shown inFIG.1B. The positions of the printed substrate W irradiated with the laser beams LB that have been focused by the focusing lens27may be limited in a range of the Rayleigh length ZRfrom the beam waist BW to the outer focus position Po shown inFIG.1B.

At a position where the laser beams LB partially overlap, the printed substrate W can be irradiated with the laser beams LB that are partially overlapped and form a line shape.

In the above embodiment, a case has been described in which an operation to be performed on an object to be irradiated with a laser beams LB is a processing operation such as soldering. However, an operation to be performed on an object to be irradiated with a laser beams LB is not limited to a processing operation. Examples of the operation to be performed on the object to be irradiated with the laser beams LB may include face detection by means of a face authentication system, laser treatment in an ophthalmic practice, and the like.

Further, one PCSEL element110may emit laser beams LB simultaneously in a plurality of directions by means of multi-beam radiation.

According to the configuration described above, it is possible to disclose a laser irradiation method comprising:entering a laser beam emitted from a photonic crystal surface emitting laser element to a focusing lens by spatial propagation; andirradiating the laser beam focused by the focusing lens onto an object to be irradiated with the laser beam at any irradiation position within a Rayleigh length range regardless of a beam waist position of the laser beam in an optical axis direction of the laser beam.

It is sufficient if the irradiation position of the laser beam is within the Rayleigh length range of the laser beam focused by the focusing lens. Therefore, the irradiation position of the laser beam may be set to an inner focus position on a side closer to the focusing lens than the beam waist position, or an outer focus position on an opposite side of the focusing lens from the beam waist position. Laser beams emitted from a plurality of photonic crystal surface emitting laser elements arranged in a two-dimensional manner may be irradiated onto the object to be irradiated at a plurality of irradiation positions. Each of the irradiation positions may be set to a position where two adjacent laser beams partially overlap in a beam radial direction of the laser beams, among the plurality of laser beams emitted from the plurality of photonic crystal surface emitting laser elements arranged in a two-dimensional manner.

The laser beams emitted from the plurality of photonic crystal surface emitting laser elements arranged in a two-dimensional manner and a diameter of the focusing lens may be individually set in correspondence with the irradiation positions of the laser beams emitted from the plurality of photonic crystal surface emitting laser elements.

The plurality of laser beams emitted from the plurality of photonic crystal surface emitting laser elements arranged in a two-dimensional manner may be irradiated onto an object to be irradiated with multi-spot beams. The multi-spot beams form a pattern in which the arrangement of the plurality of photonic crystal surface emitting laser elements is reduced by focusing performed by the focusing lens. The plurality of photonic crystal surface emitting laser elements may be individually mounted on circuit boards and arranged in a one-dimensional manner or a two-dimensional manner. The plurality of photonic crystal surface emitting laser elements may be mounted on a single circuit board. Inputs to the plurality of photonic crystal surface emitting laser elements may be individually controlled.

The disclosure of the present application relates to the subject matter of Japanese Patent Application No. 2022-006521, filed on Jan. 19, 2022, the entire disclosed content of which is incorporated herein by reference.