JP5167187B2 - Laser drilling method - Google Patents

Description

  The present invention relates to a laser drilling method for drilling a drilling object such as a printed circuit board with a laser, and an apparatus for executing the processing method.

  Along with the downsizing and high-density mounting of electronic devices, printed circuit boards are mainly multilayer wiring boards in which a plurality of boards are stacked. In a multilayer wiring board, it is necessary to electrically connect conductive layers between substrates stacked one above the other. Therefore, a via hole (hole) reaching the lower conductive layer is formed in the insulating layer of the multilayer wiring board, and conductive plating is applied to the inside of the via hole to electrically connect the conductive layers between the substrates stacked vertically. doing.

For the formation of the via hole, a high-power carbon dioxide laser (CO ₂ laser) or a UV laser using harmonics of YAG is used with the miniaturization of the via hole. Further, high-speed processing is realized by scanning a laser beam by using a beam scanning optical system in which a flat mirror (galvano mirror; hereinafter referred to as “mirror”) and an fθ lens are combined. The mirror is connected to the drive unit (motor) of the galvano scanner device via a mount member, positioned at a desired angle following high-speed oscillation and positioning of the motor, and reflects the laser beam in the intended direction. To do.

  The laser beam reflected by the mirror changes its beam shape, that is, its cross-sectional shape perpendicular to the optical axis of the beam, according to the flatness of the reflecting surface of the mirror. Further, the beam mode, that is, the energy distribution in the cross-sectional direction perpendicular to the optical axis also changes as the beam shape changes. In the galvano scanner device, the laser beam reflected by the mirror is imaged on the processing surface by the fθ lens, so the flatness of the mirror at the time of laser beam reflection (irradiation time) affects the shape of the processed hole. That is, if the flatness of the mirror is excellent, the quality of the processed hole, that is, the accuracy such as the roundness, the hole depth, and the taper angle of the hole can be increased.

  As a technique for correcting aberrations of a projection optical system such as a mirror or an Fθ lens that constitutes a laser processing apparatus, there is a technique of correcting using an adaptive mirror (Patent Document 1). Further, as a technique for measuring the static flatness that affects the aberration of the mirror, a Fizeau laser interferometer and a fringe scan analysis type measurement system have been known (Patent Document 2).

JP 2005-103630 A JP 2001-099624 A

  In the galvano scanner device, immediately after the mirror is positioned, the vibration accompanying the oscillation is generated in the mirror, so that the processing quality is deteriorated.

  However, in the case of the technique disclosed in Patent Document 1, the purpose is to correct static aberrations of optical system parts, particularly astigmatism and chromatic aberration caused by the Fθ lens. It cannot be applied to dynamic mirror flatness changes when the is operating. Further, there are various mirror operation patterns, and the difference in flatness between the static state and the dynamic state is not constant, so it is difficult to improve the quality of the processed hole.

  Moreover, although the technique of patent document 2 is effective in the measurement of static flatness, it cannot measure the dynamic mirror flatness assuming actual machining.

  In addition, in order to prevent the vibration accompanying the oscillation of the mirror from deteriorating the quality of the hole, if the laser is irradiated after a sufficient time has elapsed after positioning the mirror, the processing efficiency is lowered.

  An object of the present invention is to solve the above-mentioned problems and to provide a laser processing method capable of processing a high-quality hole without reducing the processing speed.

  In order to solve the above-described problems, the present invention deflects the optical axis of the laser beam output from the laser oscillator by swinging a flat mirror fixed to the shaft end of the drive shaft, thereby making the laser beam non- In a laser drilling method for positioning at a desired position of a workpiece, the mirror has a predetermined amount of deformation in the flatness of the mirror when the mirror is swung. The time from the time when the mirror enters a predetermined positioning allowable range to the time when the laser is irradiated to the processing part is determined as a processing condition based on the obtained time. It is characterized in that it is determined in advance.

  According to the present invention, a high-quality hole can be machined without reducing the machining speed.

It is a block diagram of the dynamic flatness test | inspection system in embodiment of this invention. It is a block diagram of the mirror positioning device in FIG. It is a figure which shows the relationship between the position of a mirror when a mirror is rock | fluctuated, and the shape of a mirror reflective surface. It is a figure which shows the structure of the optical system of the laser drilling apparatus to which this invention is applied. It is a time chart which shows the timing of the laser processing at the time of applying this invention.

  Hereinafter, embodiments of the present invention will be described.

  First, a means for measuring the deformation of the mirror accompanying the swinging will be described.

  FIG. 1 is a configuration diagram of a dynamic flatness inspection system.

  The dynamic flatness inspection system includes a galvano scanner device that is an object to be measured and a measurement optical system. The galvano scanner device includes a galvano scanner 2, a galvano control unit 3 that controls the galvano scanner, and a control device 4. The measurement optical system includes a pulse generator 7, a laser oscillator 8, collimator lenses 10, 11, 14, and 15, a beam splitter 12, a reference mirror 13, a CCD camera 16, an image processing device 17, and a control device that controls these units. It consists of four. In the present embodiment, the galvano scanner 2 is the object to be measured, the image processing unit 17 performs an operation based on the Fourier transform interference measurement method from the image photographed by the CCD camera 16, and the shape of the reflecting surface is quantified, By outputting the result to the control device 4, the deformation of the mirror accompanying the swing is measured.

  In the galvano scanner device, the mirror 1 is fastened to an output shaft 2j of a motor built in the galvano scanner 2 via a mirror mount member (not shown). The galvano scanner 2 is connected to the control device 4 via the galvano control unit 3 and is under the control of the control device 4. The galvano control unit 3 drives the galvano scanner 2 in accordance with a command from the control device 4 to position the mirror 1 and outputs an arrival signal to the control device 4 when the mirror 1 reaches the target position. A timer 6 built in the control device 4 sets a delay time T by a setting device 5. When the delay time T elapses, the timer 6 operates the laser oscillator 8 and the CCD camera 16 which is a light receiving device via the pulse generator 7. A mirror positioning device 30 is disposed behind the galvano scanner 2.

  2A and 2B are configuration diagrams of the mirror positioning device 30, in which FIG. 2A is a front view and FIG. 2B is a side view. As shown in the figure, the mirror positioning device 30 includes a holder 31, a holder support device 32 that supports the holder 31 in a swingable manner, a motor 33 that swings the holder 31, and a holder support device 32 that is 3 xyz. The moving device 34 is configured to move in the axial direction. The holder 31 is formed with a hole that fits into the motor case of the galvano scanner 2. When the motor case of the galvano scanner 2 is fitted into the hole of the holder 31 and fixed by means not shown, the axis of the swing axis of the mirror 1 is coaxial with the swing axis of the holder 31. A laser source 40 and a sensor 41 are arranged so as to face the holder 31. When the mirror 1 is arranged perpendicular to the laser light 9r output from the laser source 40 and reflected by the beam splitter 12, the sensor 41 outputs the laser light output from the laser source 40 and reflected by the mirror 1. It arrange | positions in the position which injects perpendicularly. The moving device 34, the laser source 40, and the sensor 41 are connected to the control device 4, and the moving device 34 and the laser source 40 are controlled by the control device 4.

  In the measurement optical system, the laser oscillator 8 outputs laser light having a wavelength satisfying the measurement optical system resolution. Here, the laser oscillator 8 is a UV laser oscillator that outputs laser light having a wavelength of 355 nm. The laser oscillator 8 outputs a pulsed laser beam based on a command from the timer 6. The pulse generator 7 is a device for determining the waveform (pulse width and peak value) of the laser light 9 output from the laser oscillator 8. Then, the waveform is determined so that the boundary and contrast of interference fringes described later are clear.

  The collimator lenses 10 and 11 enlarge or reduce the beam diameter of the laser light 9 output from the laser oscillator 8 to a size that can irradiate the entire reflection surface of the mirror 1. The beam splitter 12 transmits 50% of the incident laser light 9 and reflects the rest. A reference mirror 13 is arranged on the transmission side of the beam splitter 12. The flatness of the reflecting surface of the reference mirror 13 is several nm, and the distance from the beam splitter 12 to the reflecting surface is A. The reflection surface of the reference mirror 13 is perpendicular (90 degrees) to the optical axis of the laser light 9 output from the laser oscillator 8.

  Collimator lenses 14 and 15 and a CCD camera 16 are arranged on the optical axis of the laser beam 9 reflected by the reference mirror 13 and reflected by the beam splitter 12. The collimator lenses 14 and 15 reduce the beam diameter of the laser light 9 reflected by the beam splitter 12 to a beam diameter equal to or smaller than the observation element size of the CCD camera 16. An image processing device 17 is connected to the CCD camera 16. The operation of the image processing device 17 will be described later.

  In the dynamic flatness inspection system configured as described above, the holder 31 holds the motor case of the galvano scanner 2 in advance. At this time, the reflecting surface of the mirror 1 is arranged at the center (θ = 0) of the swing range of the mirror 1. Then, the moving device 34 is operated, and the reflecting surface of the mirror 1 is positioned at a distance A from the beam splitter 12. In this state, the laser source 40 is operated to check the output of the sensor 41, and the reflection surface of the mirror 1 is reflected by the beam splitter 12 with respect to the optical axis of the laser light 9 (laser light 9r indicated by a dotted line in FIG. 2). Make sure it is vertical. If it is not vertical, the motor 33 is operated so that the reflecting surface of the mirror 1 is positioned (oscillated) perpendicularly to the optical axis of the laser beam 9r reflected by the beam splitter 12. The setting device 5 inputs the swing angle θ1 of the mirror 1 (there are cases where θ1 is 0, positive, and negative) and the delay time T to the control device 4.

  When a start button (not shown) is turned on, the control device 4 first instructs the galvano control unit 3 to swing the mirror 1 to an angle θ1, which is a previously input angle, and the mirror 1 swings by θ1 degree. When positioned at the moved position, the galvano controller 3 is instructed to move (swing) the mirror 1 from the current position (angle θ1) to the angle 0 (θ = 0). The galvano control unit 3 swings the mirror 1 and outputs a positioning completion signal to the control device 4 when the mirror 1 falls within the allowable range. When receiving the positioning completion signal, the control device 4 turns on the timer 6. The timer 6 waits for the designated delay time T (T includes T = 0) to elapse. When the delay time T elapses, the timer 6 causes the laser oscillator 8 to output a pulsed laser and the CCD camera 16 Open the shutter.

  The pulsed laser light 9 output from the laser oscillator 8 is adjusted in outer shape to be larger than the reflecting surface of the mirror 1 by the collimator lenses 10 and 11 and enters the beam splitter 12. In the beam splitter 12, 50% passes through the beam splitter 12 and enters the reference mirror 13, and the other 50% is reflected by the beam splitter 12. Hereinafter, the laser beam 9 transmitted through the beam splitter 12 is referred to as a transmitted laser beam 9t, and the laser beam 9 reflected by the beam splitter 12 is referred to as a reflected laser beam 9r.

  50% of the transmitted laser beam 9t transmitted through the beam splitter 12 and reflected by the reference mirror 13 is transmitted through the beam splitter 12 and returned to the laser oscillator 8, and the remaining laser beam (hereinafter referred to as transmitted / reflected laser beam 9tr). ) Is reflected by the beam splitter 12 and enters the CCD camera 16 via the collimator lenses 14 and 15. On the other hand, the reflected laser light 9 r reflected by the beam splitter 12 enters the mirror 1 and is reflected by the mirror 1. 50% of the laser light 9r reflected by the mirror 1 is reflected by the beam splitter 12 and returns to the laser oscillator 8, and the remaining laser light (hereinafter referred to as reflection / transmission laser light 9rt) passes through the beam splitter 12, The light enters the CCD camera 16 through the collimator lenses 14 and 15. The CCD camera 16 takes the incident reflected / transmitted laser beam 9rt and transmitted / reflected laser beam 9tr as image data and sends them to the image processing unit 17.

  When the reflection surface of the mirror 1 is deformed, the transmission / reflection laser light 9tr reflected by the reference mirror 13 and the reflection / transmission laser light 9rt reflected by the reflection surface of the galvano mirror 1 interfere with each other, resulting in interference fringes. . The image processing unit 17 performs a calculation based on the Fourier transform interferometry, digitizes the shape of the reflecting surface, and outputs the result to the control device 4.

  The Fourier transform interferometry method is described in the literature (Basic theory of sub-fringe interferometer measurement, author: Mitsuo Takeda (The University of Electro-Communications), Section 3.3, FIG. 7), and thus detailed description is omitted. To do.

  FIG. 3 is a diagram showing the relationship between the position of the mirror 1 and the shape of the mirror reflection surface when the mirror is swung by 10 degrees, where (a) shows the position of the mirror 1 and (b) to (e). Indicates the three-dimensional shape of the mirror reflecting surface. Note that 0 in (a) is the target position coordinate, and the dotted line is the allowable positioning range of the mirror 1, and is set, for example, around ± 0.001 ° with respect to the target position coordinate (eg ± 10 °). This range is arbitrary, but is set to, for example, about 1/10000 of the mirror swing width or less. (B) shows the three-dimensional shape of the mirror reflecting surface in a stationary state, (c) shows the three-dimensional shape of the mirror reflecting surface at time T0, and (d) shows the three-dimensional shape of the mirror reflecting surface at time T1. The shape (e) shows the three-dimensional shape of the mirror reflecting surface at time T2.

  In the figure, the deformation of the mirror reflecting surface in a stationary state, here, the difference between the highest and the lowest of the reflecting surface is taken, but the amount of deformation is 236 nm, when the mirror 1 enters the allowable range ( The deformation of the mirror reflection surface at time T0) is 255 nm, the deformation of the mirror reflection surface at time T1 after 50 μs from time T0 is 208 nm, and the deformation of the mirror reflection surface at time T2 after 950 μs from time T0 is 235 nm. Therefore, if the laser is irradiated after time T1 when 50 μs of deformation of the mirror reflecting surface has elapsed, the processing quality can be improved.

  By the way, the degree of deformation of the mirror reflecting surface varies depending on the swing angle θ of the mirror 1. Therefore, all the relationships between the swing angle θ and the deformation of the mirror reflecting surface are obtained in advance within the operating range of the mirror 1. That is, for example, the deformation of the mirror reflecting surface is measured every time 10 μs elapses from time T0 at every swing angle of 0.1 degree. A delay time T is set in addition to the pulse intensity and the pulse-on time, which are conventionally determined laser processing conditions (irradiation conditions). In this way, a hole with excellent quality can be processed, and the shortest time in which the deformation of the mirror reflecting surface can be set can be set, so that the processing speed does not decrease so much. The measured value and the set delay time T are stored in a memory (not shown) of the control device 4 as a table, for example, so that the CPU of the control device 4 can refer to the table immediately.

  FIG. 4 is a configuration diagram of an optical system of a laser drilling apparatus to which the present invention is applied, and the same components as those in FIG.

  The optical system of the laser drilling apparatus includes a laser oscillator 8, a beam diameter adjuster 20, a pulse shaper 21, first and second galvano scanners 2a and 2b, and first and second galvano controllers 3a, 3b, and the Fθ lens 22 and a processing control device 52 for controlling them are basically configured. As the laser oscillator 8, a carbon dioxide gas laser or a UV laser is selected according to the processing application. Here, the laser oscillator 8 is a carbon dioxide laser oscillator that outputs a laser beam 9 having a wavelength of 9.4 μm. The laser light 9 output from the laser oscillator 8 is shaped in outer diameter by a beam diameter adjuster 20 and is pulsed by an acousto-optic pulse shaper (hereinafter referred to as “AOM”) 21 based on processing conditions. The energy-controlled laser light 9k whose energy is controlled is branched to the processing optical axis. The non-energy control laser beam 9d other than the energy control laser beam 9k is irradiated to a damper (not shown) and converted into heat.

  The energy control laser beam 9k is applied in the XY direction on the printed circuit board as the work 50 by the first and second mirrors 1a and 1b positioned in the swinging direction by the first and second galvano scanners 2a and 2b. Positioned. The energy control laser beam 9k reflected by the first and second mirrors 1a and 1b is collected by the Fθ lens 22 and enters a desired position of the workpiece 50 placed on the XY table 51.

  In this way, when laser processing is performed by entering the workpiece 50 at a desired position, the laser oscillator 8, the AOM 21, and the first and second galvano controllers 3a and 3b are controlled synchronously by the controller 52. The The control device 52 outputs an operation command to the first and second galvano scanners 2a and 2b in accordance with the setting of the laser processing conditions and the processing pattern, and monitors the operation state of both. When the positioning operation of the first and second mirrors 1a and 1b is completed, the control device 52 outputs a laser output signal to the laser oscillator 8 and outputs a laser beam 9, and also issues a pulse shaping command to the AOM 21. Output. The pulse shaping command shapes the laser beam 9k used for machining based on the machining conditions. By this command, the laser beam 9k is branched by the AOM 21 on the machining optical axis, and the non-energy control laser beam 9d and the energy control laser beam are split. It is output as 9k.

  Next, the operation of each part in laser processing will be described.

  FIG. 5 is a time chart of laser processing when the present invention is applied, and shows an example in which laser light is irradiated twice by one galvano operation. In addition, (a) in the figure shows the shape of the oscillated laser pulse, and the vertical axis represents the energy intensity. (B) shows the laser output signal, (c) shows the AOM output signal, and (d) shows the operating state of the galvano scanner. (E) is the position of the mirror, and the vertical axis is the angle. Note that the dotted line in (e) is the allowable positioning range of the mirror (target position is 0), and it is necessary to irradiate the laser within this range in order to maintain the hole quality. Here, in order to facilitate understanding, it is assumed that only the mirror 1a operates.

  When the mirror 1a driven to swing by the galvano scanner 2 enters a swing allowable range θa set in advance with respect to the swing axis (time T0), the control device 52 determines that the galvano movement positioning is completed and stopped. To do. Next, the control device 52 outputs a laser output signal to the laser oscillator 8 after the time t set in the processing conditions has elapsed (time T1). As described above, this time t is a feature of the present invention. At time T1 after the elapse of time t from time T0, laser light 9 is output from the laser oscillator 8, and an AOM signal is sent to the AOM 21 with a delay time P from the control device 52. The AOM signal is continuously output for a length of time Q, and also plays a role of pulse shaping. When the time Q elapses, the AOM signal is cut off, but the laser output signal is continuously output until the time R elapses thereafter. This completes the first laser irradiation.

  After the time D has elapsed since the first laser output signal is output, the control device 52 outputs the second laser output signal, and the output signal to the AOM 21 is output in conjunction with the first condition. After the two laser irradiations are completed, the first and second mirrors 1a and 1b start moving to the next processing position. This operation is repeated until the machining is completed. In the case of a mirror with a small change in dynamic flatness, or when it is required to improve the processing speed rather than the hole quality, the time t can be set to 0.

1 Mirror 2j Oscillating shaft 8 Laser oscillator 9 Laser light T0 Time

Claims (1)

The optical axis of the laser beam outputted from the laser oscillator is deflected by swinging the flat mirror with respect to the drive shaft, the laser beam is positioned at a desired position of the workpiece, and the workpiece is In the laser drilling method for drilling,
The amount of deformation of the flatness of the mirror when the mirror is swung is obtained in advance in accordance with the passage of time starting from the time when the mirror enters the positioning allowable range set in advance with respect to the target position coordinates. In addition, based on the obtained result, a time from when the mirror enters a preset positioning allowable range until the laser beam is irradiated onto the workpiece is preset as a processing condition. Laser drilling method.