JP2006350292A - Laser beam switching device and laser beam machining apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser beam switching device and a laser beam machining apparatus. <P>SOLUTION: The device selectively guides an input laser beam (110) to a first output laser beam (140a) and/or a second output laser beam (140b). The device is equipped with: a beam separating element (115) installed for the purpose of spatially separating the input laser beam (110) into a first partial beam (120a) and a second partial beam (120b); and a beam superposing element (135) installed and arranged for the purpose of spatially and coherently superposing the two partial beams (120a, 120b) and converting the two partial beams (120a, 120b) to the first output laser beam (140a) and/or the second output laser beam (140b). The laser beam machining apparatus is also disclosed that is provided with a laser light source (105), the above device (100), a first deflector (180a) and a second deflector (180b) and that is designed to machine a workpiece. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an apparatus for selectively irradiating an input laser beam with a first output laser beam and / or a second output laser beam. Furthermore, the present invention relates to a laser processing apparatus for processing an object to be processed, particularly for drilling and / or forming an electronic circuit carrier, using the laser processing apparatus comprising the above laser beam conversion apparatus.

  Today, electronic assemblies that are being miniaturized are often constructed on multilayer circuit carriers, especially multilayer circuit boards. At that time, it is necessary to contact a specific conductive layer of the circuit board. This is accomplished by drilling a blind hole or through hole in the layer and contacting it, and then coating the hole with conductive metallization. In this way, circuit paths can be formed not only in two dimensions but also in three dimensions so that the space required for the electronic assembly is considerably reduced.

Usually, electronic circuit boards are perforated by pulsed laser radiation in special laser processing equipment for the electronics field. Usually, a CO ₂ or solid state laser such as Nd: YAG or Nd: YVO ₄ is used as the laser light source. An important feature of a competitive laser processing device is on the one hand the throughput, ie the number of holes that can be drilled in a certain time, and on the other hand the purchase price of the laser processing device. Accordingly, laser processing apparatuses have been developed in which a laser beam emitted from one laser source is selectively directed to one of two output optical paths by an optical switch element. Each output optical path is provided with a deflecting device and an imaging optical system, whereby each output beam is applied to a different target position on one or several workpieces. A corresponding device for drilling holes in a circuit board using several laser beams is known, for example, from Japanese Patent Application Publication No. 2002-11854.

  Also known are mechanically pivotable reflectors that selectively irradiate various spatially separated optical paths with a laser beam. In this process, the input laser beam is deflected in different directions depending on the respective tilt of the reflector. Such a mechanical swivel reflector is disadvantageous in that the switching time is relatively long due to the mass inertia of the reflector. Generally at least 100 μs, already at 10 kHz pulse repetition frequency, a determined switch between the two output laser beams is not possible in the time between two successive laser pulses.

  Japanese published patent application 2003-53576 discloses an apparatus and method in which a laser beam is deflected in various directions by an acousto-optic modulator (AOM). Here, standing sound waves are generated in the quartz and function as a diffraction grating for laser beam incidence on the quartz. AOM is disadvantageous in that it has a limited crystal robustness and lifetime and can usually generate only a small deflection angle. Another disadvantage is that the intensity of the laser beam is not completely deflected in a specific direction corresponding to a specific diffraction order. Rather, laser radiation intensity that should not be ignored is always directed to different diffraction orders.

  Japanese Patent Application Publication No. 2003-126982 discloses a laser processing apparatus including an electro-optic modulator (EOM) as a beam switching element, and this EOM functions in cooperation with a polarization dependent reflector. Similarly, when the EOM is electrically activated, the polarization direction of the laser beam impinging on the polarization-dependent reflector so that the laser beam is selectively directed to one of two optical paths connected downstream of the polarization-dependent reflector. Is intentionally affected. However, the laser radiation hitting the EOM is never perfectly linearly polarized, and the rotation angle of the polarization direction created by the EOM is always blurred by a certain amount, so some of the remaining intensity will always be in the path of the protruding laser beam. to go into. In addition, the use of EOM is (a) a relatively high voltage is required for EOM operation, and (b) the expected service life of EOM is unknown, especially when the power density of the deflected laser beam is high. There is a disadvantage in that (c) EOM is a relatively expensive optical component.

Japanese published patent 2002-11584 Japanese Patent Publication No. 2003-53576 Japanese Patent Publication No. 2003-126982

  It is an object of the present invention to provide an apparatus for selectively directing an input laser beam to a first output laser beam and / or a second output laser beam, in a simple manner and precisely, for both output laser beams. It is to provide a device capable of switching laser beams quickly and simultaneously. It is a further object of the present invention to provide a laser processing apparatus that uses the above laser beam conversion apparatus in an advantageous manner for processing a workpiece quickly and precisely.

  This object is achieved by an apparatus for selectively directing an input laser beam to a first output laser beam and / or a second output laser beam having the features of independent claim 1. The apparatus of the present invention comprises a beam separation element arranged to spatially separate an input laser beam into a first partial beam and a second partial beam, and two partial beams spatially overlapped into two parts. A beam superposition element disposed and arranged to convert the beam into a first output laser beam and / or a second output laser beam. The two partial beams are superimposed such that the intensity of the two output laser beams depends on the relative phase shift between the two partial beams at the beam superposition element. This is because the apparatus of the present invention forms an interferometer in which the intensity distribution between both output laser beams is freely adjustable by changing the path length of the partial beams by half the wavelength. Is realized by coherently overlapping. According to the present invention, the optical path length is provided in the first partial beam, and the optical path length of the first partial beam is changed by the optical driving element installed so as to change between the beam separation element and the beam superposition element. To do.

  The invention is based on the recognition that it is possible to freely adjust the intensity distribution between two output optical paths by coherently superimposing two partial beams using an interferometer. For example, coherent polymerization between both partial beams guides the input laser beam to the first output laser beam as long as they have exactly the same path length. Since the two partial beams interfere destructively with each other in this direction, there is no intensity directed to the second output laser beam. If the optical path length of the first partial beam changes by half the wavelength, then coherent polymerization of both partial beams will not produce any output for the first output laser beam due to destructive interference. Constructive interference occurs between both partial beams in the direction of the second output laser beam so that the overall intensity of the input laser beam moves to the second output laser beam.

  Of course, coherent superposition of the two partial beams is possible only when the difference in optical path length between the two partial beams is smaller than the length of interference of the laser beams.

  Still further, the apparatus according to the present invention can also be used to selectively direct an input laser beam to more than two output laser beams. This is achieved by the cooperative action of several inventive switching devices (switching devices) connected in series in a cascade. In this way, it is possible to intentionally direct the input laser beam to three, four, or more output laser beams.

  According to a second aspect of the present invention, a first light receiver optically connected to the first output laser beam is further provided. For the purpose of adjusting the intensity of the first output laser beam, the light receiver is further connected to the actuating element, for example via a wire. The optical coupling with the first output laser beam is preferably done via a beam separation element that guides only a small amount of the intensity of the first output laser beam to the receiver. The light receiver is, for example, a conventional photodiode. Preferably, the connection between the receiver and the actuating element is performed via the electrical output of the receiver, which outputs an output voltage during the operation of the receiver, whose level is applied to the receiver. It is directly proportional to the intensity of the light currently hit.

  According to claim 3, there is further provided a second light receiver optically coupled to the second output laser beam and connected to the actuating element for the purpose of adjusting the intensity of the second output laser beam. This makes it possible to adjust the actuating element particularly precisely, so that it is possible to switch between two different operating conditions in a well-defined manner. In the first operating condition, the entire intensity of the input laser beam is directed to the first output laser beam and the intensity of the second output laser beam is at least close to zero. In the second operating condition, the intensity of the first output laser beam is approximately zero and the overall intensity of the input laser beam is directed to the second output laser beam.

  According to claim 4, the actuating element comprises a mechanically adjustable mirror. As explained above, only a very small mirror movement compared to the laser wavelength is required to switch the input laser beam between the optical paths of the two spatially separated output laser beams. This is because in the case of mirror movement shifts, the two partial beams are also spatially overlapped with each other to the extent that coherent polymerization between the two partial beams is ensured, regardless of the current position of the mirror. This means that the beam shift of the first partial beam related to the mirror movement is very small (almost no). Therefore, the beam shift can be ignored at good approach.

  According to claim 5, the actuating element is mechanically adjustable, wherein the relative phase shift between the two partial beams is generated by placing a light-transmissive refractive medium in the optical path of the first partial beam. Refracting optical element. This may be of different thickness so that, for example, the associated phase adjustment between both partial beams can be adjusted by moving or rotating the optical element. The optical path of the first partial beam is affected by the optical element as long as the optical element is shaped so that not only the output surface of the optical element but also the input surface is perpendicular to the optical path of the second partial beam. Phase shift can be performed without. Thus, if the apparatus is perfectly tuned so that the spatial interference of the two partial beams in the beam superimposing element is not affected at all by the adjustment of the optical element, both partial beams can be completely overlapped. Thus, the input laser beam can be deliberately directed to only one output laser beam with high precision, or to both output laser beams with a precisely defined intensity distribution.

  According to claim 6, the actuating element comprises a piezoelectric drive which enables the actuating element to be adjusted particularly fast. Therefore, even if the repetition rate of the input laser beam is high, the intensity of the output laser beam can be switched between two optical paths between two consecutive pulses.

  The second object is achieved by a laser processing device having the features of independent claim 7 for processing a workpiece, in particular for drilling and / or forming an electronic circuit carrier. The laser processing apparatus according to the present invention is a laser light source for generating an input laser beam, and for selectively guiding the input laser beam to the first output laser beam and / or the second output laser beam. A laser beam conversion device (switching device) according to any one of 1 to 6, a first deflection device provided in a first output optical path, a second deflection device provided in a second output optical path, Have Two deflection devices are provided on at least one workpiece to match the two output laser beams to a predetermined target position.

  The laser processing apparatus according to the present invention enables mutual processing of materials at two processing positions. During the processing by the first output laser beam, the second deflecting device reaches the target position where the second output laser beam reaches immediately after the processing by the first output laser beam is completed by switching the laser beam conversion device. Adapted. Switching the output intensity between the optical path of the first output laser beam and the optical path of the second output laser beam requires only a short shift of the optical actuating element at the light wavelength of the input laser beam. If a suitable drive is used, beam switching between two successive pulses of the pulsed laser oscillator can be achieved. Thus, the secondary processing time occurs due to the jumping movement of the deflector between the various spaced target positions, which can be completely eliminated in material processing.

  Usually, the deflecting device has two galvanometers rotatably supported around mutually perpendicular axes so that the laser beam guided via the two galvanometer mirrors is guided to any target position in the processing region. It is a so-called galvo system in which the mirror is moved.

  Further advantages and features of the present invention can be obtained from the following exemplary description in a preferred embodiment.

The laser processing apparatus according to the present embodiment shown in the figure has a laser light source 105 that emits a suitable pulsed input laser beam 110 in the near-ultraviolet spectral region, visible spectral region, or near-infrared spectral region. In the case of an infrared laser beam, a CO ₂ laser is particularly preferable as the laser light source, and in the case of a laser light source that emits in the visible or near-ultraviolet spectral region, the fundamental wavelength is determined by a known method using a nonlinear crystal mounted in the laser light source 105. A diode-pumped solid-state laser that is changed to multiplication is preferably used.

  Further, the laser processing apparatus includes a coherent beam switching apparatus 100 that selectively guides the input laser beam 110 to the optical path of the first output laser beam 140a and / or the optical path of the second output laser beam 140b. The coherent beam switching device 100 causes the input laser beam 110 to strike (incident) a beam splitter 115 that separates the input laser beam 110 into two partial beams, a first partial beam 120a and a second partial beam 120b. Are provided in association with the laser light source 105. The intensity of the two partial beams is almost the same. The second partial beam 120b is incident on a further beam splitter 135 via a stationary mirror 121b. The first partial beam 120a is also incident on the further beam splitter 135 via the movable mirror 121a. In the beam splitter 135, the two partial beams 120a and 120b are coherently overlapped, and due to the phase relationship between the two partial beams 120a and 120b, the overlapped laser beam becomes the optical path of the first output laser beam 140a and / Or guided to the optical path of the second output laser beam 140b.

  Separating the input laser beam 110 into two partial beams 120a and 120b and subsequently coherently superimposing the two partial beams 120a and 120b corresponds to beam separation and beam combination in a Mach-Zehnder interferometer To do. The optical path length of the first partial beam 120a is changed by moving the movable mirror 121a by the piezoelectric drive unit 171 representing the optical actuating element 170 together with the movable mirror 121a. The variation in optical path length automatically changes the relative phase relationship between the two partial beams 120a and 120b, resulting in the optical path of the first output laser beam 140a and the optical path of the second output laser beam 140b. The intensity distribution of the laser radiation can be adjusted freely by placing an interferometer between them.

  In the apparatus described here, the two partial beams 120a run such that the two output laser beams run perpendicular to each other immediately after the beam splitter 135 where the two partial beams 120a and 120b are coherently superimposed. And 120b run in parallel in pairs. The second output laser beam 140b is reflected by the stationary mirror 141b so that the entire laser processing apparatus can be adjusted in a simple manner. Thereby, the two output laser beams 140a and 140b are respectively applied (incident) to the deflecting devices 180a and 180b in the optical paths parallel to each other.

  Each of the deflectors 180a and 180b is provided with an optical system (not shown), particularly a so-called fθ optical system. As a result, the output laser beams 140a and 140b deflected by the deflecting devices 180a and 180b are focused on the corresponding target positions of the workpiece (not shown). During processing of the material, the mutual laser processing between the first output laser beam 140a and the second output laser beam 140b allows the deflection device related to the other laser beam to be moved to the first target position if necessary. It can be adjusted in advance to a new second target position away from. Thus, for further laser processing with the other output laser beam, after the material processing with one output laser beam is completed, the intensity of one output laser beam decreases to zero and the other output laser beam becomes Only the phase relationship between the two partial beams 120a and 120b needs to be changed to increase to the maximum value. Since only a very short path is required to produce the required phase shift, switching between two consecutive pulses is also possible in a pulsed laser emitting laser radiation with a repetition rate in the range of several megahertz. can do.

  To ensure precise adjustment of the movable mirror 121a, separate beam splitters 145a and 145b are provided for each of the two output laser beams 140a and 140b, which in each case is a fraction of the intensity of each output laser beam. A part is guided to each of the photodetectors 150a and 150b. The two photodetectors 150a and 150b are so-called photodiodes, for example, and supply an output signal proportional to the intensity of light striking the light receiving surface of the photodiode. The two photodetectors 150a and 150b are coupled (connected) to the comparison circuit 160 via signal lines 151a and 151b, respectively, where the difference between the output signals of the two photodetectors 150a and 150b is an analog circuit. Obtained by. The amplifier 165 is connected downstream of the comparison circuit 160 via the signal line 161, and this amplifier is coupled (connected) to the piezoelectric drive unit 171 via another signal line 166. In order to allow selective switching of the intensity of the input laser beam 110 to the first output laser beam 140a or the second output laser beam 140b, the difference between the detection signal of the photodetector 150a and the detection signal of the photodetector 150b. Is actuated by the amplifier 165 so that is as large as possible. This is accurately obtained when the intensity of one of the two output laser beams is maximum while the intensity of another output laser beam is minimum, preferably zero.

  As described above, the two photodetectors 150a and 150b, the comparison circuit 160, the amplification circuit 165, and the piezoelectric drive unit 171 are transferred to the first output laser beam 140a and the second output laser beam 140b together with the corresponding signal lines. A control loop for adjusting the intensity distribution of the input laser beam 110 to a predetermined value.

  In summary:

  A coherent beam switching device 100 comprising a Mach-Zehnder interferometer and a control loop for optimally matching the intensities of the two output laser beams 140a and 140b is emitted by the laser light source 105 in a simple manner, quickly and accurately. It is possible to convert (switch) the input laser beam 110 to the first deflector 180a and / or the second deflector 180b. In addition to the two beam splitters 115 and 135, the Mach-Zehnder interferometer includes two reflectors, a static reflector 121b and a variable reflector 121a. The control loop accurately includes two separate beam splitters 145a and 145b, two photodetectors 150a and 150b, electronic circuits 160 and 165 with appropriate signal lines 151a, 151b, 161 and 166, and variable reflector 121a. A drive unit 171 is provided for movement.

Single FIG. 1 shows a beam in which two partial beams of a Mach Zehnder interferometer are coherently superimposed and selectively directed to a first output laser beam and / or a second output laser beam. It is a figure which shows roughly the laser processing apparatus which has a switching apparatus.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 ... Coherent beam switching apparatus, 105 ... Laser light source, 110 ... Input laser beam, 115 ... Beam splitter, 120a ... First partial beam, 120b ... Second partial beam, 121a ... Movable mirror, 121b ... Static mirror, 135 ... Beam splitter, 140a ... First output laser beam, 140b ... Second output laser beam, 145a ... Separation beam splitter, 145b ... Separation beam splitter, 150a ... Photo detector, 150b ... Photo detector, 151a ... Signal line, 151b ... signal line 160 ... comparison circuit 161 ... signal line 165 ... amplifier 166 ... signal line 170 ... optical actuator element 171 ... piezoelectric drive unit 180a ... deflecting device 180b ... deflecting device

Claims (7)

An apparatus for selectively directing an input laser beam (110) to a first output laser beam (140a) and / or a second output laser beam (140b),
A beam separation element (115) installed to spatially separate the input laser beam (110) into a first partial beam (120a) and a second partial beam (120b);
The two partial beams (120a, 120b) are spatially overlapped, and the two partial beams (120a, 120b) are combined with the first output laser beam (140a) and / or the second output laser beam (140b). A beam polymerization element (135) installed and arranged to convert to
The intensity of the two output laser beams (140a, 140b) depends on the relative phase shift between the two partial beams (120a, 120b) in the beam superposition element (135);
Further, the optical path length of the first partial beam (120a) is provided between the beam separation element (115) and the beam superimposing element (135). A laser beam switching device comprising an optical actuating element (170) installed as described above.   Further, a first photoreceiver (optically coupled to the first output laser beam (140a) and connected to the actuating element (170) for the purpose of controlling the intensity of the first output laser beam (140a). 150. The device of claim 1, comprising 150a).   Further, a second light receiver (150b) optically coupled to the second output laser beam (140b) and connected to the actuating element (170) for the purpose of controlling the intensity of the second output laser beam (140b). The device according to claim 1.   4. A device according to claim 1, wherein the actuating element (170) comprises a mechanically adjustable mirror (121a).   4. The device according to claim 1, wherein the actuating element (170) comprises a mechanically adjustable refractive optical element.   Device according to claim 4 or 5, characterized in that the actuating element (170) comprises a piezoelectric drive (171). A laser processing apparatus for processing a workpiece, in particular for drilling and / or forming an electronic circuit carrier,
A laser light source (105) for generating an input laser beam (110);
7. The device according to claim 1, for selectively directing the input laser beam (110) to a first output laser beam (140 a) and / or a second output laser beam (140 b). An apparatus (100);
A first deflector (180a) provided in the optical path of the output laser beam (140a);
A second deflecting device (180b) provided in the optical path of the output laser beam (140b),
The two deflection devices (180a, 180b) are provided on at least one workpiece to match the two laser beams (140a, 140b) with a predetermined target position.

Images