JP4316827B2 - Laser processing method and laser processing apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laser processing method and a laser processing apparatus for processing a hole connecting a surface and a target inner layer into a processing target by irradiating pulsed laser light a plurality of times.
[0002]
[Prior art]
FIG. 6 is a side view of the multilayer printed board. The multilayer printed circuit board 8 includes an upper layer (surface layer) 8a, a plurality of inner layers (intermediate layers) 8b, 8c,... And a back layer 8z. When processing a hole (hereinafter referred to as “upper layer” from the surface to the target inner layer) that reaches the target inner layer (for example, the inner layer 8b) from the surface in such a multilayer substrate, the processing is performed using laser light. Then, processing efficiency can be improved. However, since the thickness of the upper layer varies, if the processing conditions are determined according to the case where the thickness of the upper layer is the largest, the inner layer is damaged where the thickness of the upper layer is thin. For this reason, it is necessary to process the upper layer without damaging the inner layer.
[0003]
Therefore, in Japanese Patent Laid-Open No. 5-261777, the processing state of a hole is estimated from the emission spectrum of a plume (plasma-like object) generated during processing, and laser light irradiation is performed before damaging the target inner layer. I try to stop.
[0004]
In Japanese Patent Laid-Open No. 10-85976, the laser output is controlled by detecting the reflected light from the target inner layer.
[0005]
[Problems to be solved by the invention]
However, the former of the above prior art does not disclose a specific method for detecting the plume and a specific method for controlling the laser light after the processing end signal is detected. For this reason, it is possible to effectively select the processing end signal from the laser beam for processing and to minimize damage to the inner layer, and to prevent smear (the upper layer component remaining on the surface of the inner layer, when the inner layer is a copper foil. In order not to exist, it is unclear how the laser beam should be controlled when a signal is obtained.
[0006]
Further, since the latter of the prior art uses reflected light as the processing end signal, it is difficult to detect the processing end when the reflectance of the inner layer is low.
[0007]
The object of the present invention is to solve the above-described problems in the prior art and minimize damage to the inner layer when machining a hole that connects the surface and the intended inner layer in a multilayer structure to be machined. It is in providing the laser processing method and laser processing apparatus which do not have smear.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the first means is a laser processing method for processing a hole connecting a surface and a target inner layer into a processing target by irradiating a pulsed laser beam a plurality of times for each target position. In this case, for each target position, a standard number of times of irradiation required to remove the upper layer of the average thickness with the laser beam of the first energy is obtained, and a first number of times of irradiation that is less than the determined number of times of irradiation is obtained. The laser beam having the first energy is irradiated with the first number of times of irradiation, and then the laser beam having the second energy smaller than the energy of the laser beam having the first number of irradiations is irradiated, and the second After the intensity of the radiated light emitted by the inner layer processed by the laser beam having the energy of a predetermined value or more becomes a predetermined value or more, the second number of times of irradiating the laser beam having the second energy at the target position. Further irradiation And wherein the door.
[0010]
The second means measures the time from the start of the output of the laser light until the intensity of the emitted light becomes equal to or greater than a predetermined value every time the laser light is output. When the measured time is shorter than a predetermined time, it is determined that the inner layer is exposed .
[0011]
A third means is a laser processing apparatus comprising a radiated light detecting means for detecting radiated light emitted by a processing target processed by a laser beam, wherein the laser beam is placed in an optical path of the laser light reaching the processing target. Polarization means for defining the polarization direction and shutter means are arranged, and the radiation detecting means blocks the laser beam component for processing whose polarization direction is defined by the polarization means reflected from the object to be processed and the radiation. Selection means for transmitting light, measurement means for measuring the intensity of the emitted light, a first number of times of irradiation of the laser light by the first energy, and a second by a second energy smaller than the first energy. setting means for setting the number of times of irradiation, the first laser light energy after irradiated by the first irradiation times, performs laser light irradiation by the second energy, the emitted light Characterized in that the intensity is provided with control means for irradiating a laser beam of the second energy to the radiation position of the emitted light after becoming more predetermined value by the second number of times of irradiation, the.
[0013]
In addition, the fourth means is the third means in which, every time the laser light is output, the time from when the output of the laser light is started until the intensity of the radiated light becomes a predetermined value or more. Measuring means for measuring, and determining means for determining that the inner layer is exposed when the time measured by the measuring means is shorter than a predetermined time are provided.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
<First Embodiment>
Hereinafter, the present invention will be described based on the illustrated embodiments.
[0015]
FIG. 1 is a configuration diagram of a laser beam machine according to the first embodiment of the present invention.
[0016]
On the optical path of the laser oscillator 1, a polarizing plate 2, a shutter 23, an aperture 3, a mirror 5 of the scanner 4, an fθ lens 7, and a processing target 8 are arranged.
[0017]
The shutter 23 includes an electro-optic element (hereinafter referred to as “EO element”) 24 and a polarizing plate 25 whose polarization plane is parallel to the polarization plane of the polarizing plate 2. The EO element 24 to which a voltage is applied has a function of rotating the polarization plane of incident light by an angle proportional to the applied voltage, and the incident voltage can be changed by changing the voltage applied to the EO element 24 from 0 to a half-wave voltage. Light can be polarized from 0 to 90 degrees. Since the shutter 23 has a configuration in which the polarizing plate 25 is disposed on the emission side of the EO element 24, the opening degree of the shutter 23 is changed from fully open (the applied voltage is 0) by changing the voltage applied to the EO element 24. It can be changed at a high speed up to the fully closed state (applied voltage is a half-wave voltage).
[0018]
The mirror 5 is supported by the output shaft of the motor 6 and can be positioned at any angle around the axis of rotation perpendicular to the paper surface. An object to be processed 8 (here, a multilayer printed board) is fixed to an XY stage 9.
[0019]
A detector 10 is arranged so as to face the multilayer printed board 8. The detector 10 includes a wavelength selection unit 11, a polarization selection unit 12, a lens 13, and a PD (photodiode) 14. The wavelength selection unit 11 transmits light having a wavelength unique to the material of the inner layer 8b radiated by the inner layer 8b processed by the laser light (hereinafter referred to as “radiated light”) and does not transmit other light. The polarization selection means 12 is configured by combining a quarter wavelength plate and a polarizing plate. The PD 14 is connected to the processing circuit 20.
[0020]
The processing circuit 20 controls the laser driver 21 that drives the laser oscillator 1 and the shutter driver 22 that drives the shutter 23 based on the output signal of the PD 14.
[0021]
Next, the operation of this embodiment will be described.
[0022]
FIG. 2 is a diagram showing temporal changes in the laser light intensity and the emitted light intensity according to the first embodiment of the present invention, where the solid line shows the laser light and the dotted line shows the emitted light. In the figure, P1 is the peak power value of the laser beam, and Ith is the threshold value of the detection signal intensity, that is, the emitted light intensity.
[0023]
After controlling the scanner 4 and the XY stage 9 to two-dimensionally position the center of the optical path of the laser beam at the processing position, the laser oscillator 1 is operated to output the laser beam in a pulsed manner. Laser light whose optical path output from the laser oscillator 1 is parallel to the paper surface passes through the polarizing plate 2 and the shutter 23 , is shaped by the aperture 3, enters the fθ lens 7 through the scanner 4, and is processed 8 The image is formed on the top. A part of the laser light makes a hole in the upper layer 8 a, and a part of the laser light is reflected by the upper layer 8 a and enters the detector 10. The wavelength selection unit 11 transmits the radiated light, and does not transmit the laser beam (hereinafter referred to as “processing laser beam”) supplied to the processing unit. In addition, the polarization selection unit 12 is a laser beam component for processing that could not be removed by the wavelength selection unit 11 (as will be described later, the polarization plane of the processing laser beam may be rotated by the shutter 23, so the upper layer 8a The reflected laser light may include polarized light other than the polarized light component defined by the polarizing plate 2). Therefore, light other than the emitted light that has passed through the wavelength selecting unit 11 is polarized light selecting unit 12. Is hardly transmitted. Therefore, the intensity of the signal output from the PD 14 is small while the upper layer 8a is being processed, that is, while no emitted light is generated.
[0024]
When a part of the upper layer 8a is removed and the processing laser light is irradiated onto the inner layer (in this case, the inner layer 8b in FIG. 6), the inner layer 8b emits radiated light. The emitted light passes through the wavelength selection unit 11 and the polarization selection unit 12 and is collected by the lens 13 to irradiate the PD 14. The PD 14 that has received the irradiation light outputs a light reception signal to the processing circuit 20.
[0025]
The processing circuit 20 compares the value of the received light signal with a preset value , determines that the upper layer 8a has been substantially removed when the received light signal is equal to or greater than the preset value, and for the purpose of removing smear, Further, the laser beam is irradiated to the processing portion a predetermined number of times (excess pulse in the drawing), and the processing at the position is finished.
[0026]
Thus, since the drilling process is stopped after detecting that the inner layer 8b has been processed, even if the thickness of the upper layer 8a varies, the upper layer 8a is reliably processed without damaging the inner layer 8b. In addition, it is possible to prevent smear from remaining in the processed portion.
[0027]
In addition, since the reflected light reflected by the processing object 8 is generally elliptically polarized light including linearly polarized light, the polarization selecting means 12 may be configured by a single polarizing plate.
[0028]
Further, although an EO element is used as the shutter 23 , an acousto-optic element (AO element) may be used.
[0029]
Here, when a plurality of holes are made in a region that can be scanned by the scanner 4, pulsed laser light is continuously irradiated for each processing portion until the intensity of the emitted light becomes a predetermined value or more, and then If the laser beam energy value is reduced and each hole is further irradiated with several pulses of laser light, the laser power can be adjusted once regardless of the number of holes to be processed. Control becomes easy and processing efficiency can be improved.
[0030]
By the way, when the intensity of the output signal of the PD 14, that is, the intensity of the emitted light is compared with a preset value (threshold), the inner layer 8 b may be damaged if the threshold is increased in order to avoid the influence of noise or the like. On the other hand, when the threshold value is reduced, the removal of the upper layer 8a may be insufficient. For this reason, it is necessary to perform a sufficient confirmation test in advance to determine the threshold value.
[0031]
Therefore, if the generation of synchrotron radiation is confirmed not only by the intensity of the synchrotron radiation but also by other means, the amount of confirmation tests can be reduced, and the reliability of determining whether the inner layer has been exposed is further improved. Can be made.
[0032]
<Second Embodiment>
FIG. 3 is a diagram showing temporal changes in the laser light intensity and the emitted light intensity according to the second embodiment of the present invention, where the solid line shows the laser light and the dotted line shows the emitted light.
[0033]
When the inner layer 8b is exposed, the intensity of the detection signal increases almost simultaneously with the laser light irradiation as shown in FIG. In addition, when smear is present, the appearance timing of the detection signal is delayed or the intensity is small as compared with the case where the inner layer 8b is exposed, as shown in FIG. Further, if the inner layer is not exposed, as shown in FIG. (C), components of the processing laser light not threshold divided by the wavelength selection means 11 and the polarization selecting means 12 is detected as noise.
[0034]
Therefore, the time t0 is experimentally obtained in advance until the intensity of the detection signal becomes equal to or higher than a predetermined value (S in the figure) after the laser light is output when the inner layer 8b is exposed. Then, at the time of processing, the time t is compared with the time t0 until the intensity of the detection signal is equal to or greater than a predetermined value (S in the figure) after the laser beam is output. If it is determined that the bottom has reached the inner layer 8b, the determination accuracy is improved, so that the processing accuracy can be improved and damage to the inner layer can be prevented.
[0035]
By the way, although smear can be reliably removed by further irradiating laser light after the intensity of the emitted light exceeds a predetermined value, the inner layer 8b may be damaged.
[0036]
<Third Embodiment>
FIG. 4 is a diagram showing the relationship between the waveform of the laser beam and the detection signal according to the third embodiment of the present invention.
[0037]
The peak power value P1 and pulse width T1 of the laser beam are determined, and the number of pulses Nav necessary for removing the upper layer 8a in this case is calculated in advance from the average thickness of the upper layer 8a. Then, processing is performed with the peak power value P1 until the number of processing pulses approaches Nav, and thereafter processing is performed with a peak power value P2 smaller than the peak power value P1 (however, the pulse width is the same). In this case, it is practical to determine the number of pulses for switching the peak power value so that the inner layer 8b starts to be exposed when processing at the peak power P2 in consideration of the variation in the thickness of the upper layer 8a. It is.
[0038]
In the case of FIG. 4, since the output signal of the PD 14 increased during the second irradiation after decreasing the peak power value, it was determined that the inner layer 8b was exposed at this point, and then the laser beam was irradiated twice more. Processing has been completed.
[0039]
Further, as shown in FIG. 5, after the number of machining pulses approaches Nav, the peak power value is not changed, and even if the subsequent pulse width T2 is smaller than the pulse width T1 until the inner layer 8b is exposed, The same result as in the case of FIG. 4 can be obtained.
[0040]
In the case of FIG. 5, since the output signal of the PD 14 is increased at the first irradiation after reducing the pulse width, it is determined that the inner layer 8b is exposed at this time, and then the laser beam is irradiated twice more for processing. Has ended.
[0041]
In this way, since the energy of the laser beam when the inner layer 8b is exposed is small, damage to the inner layer 8b can be suppressed, and smear can be almost removed.
[0042]
The peak power value and the pulse width can be easily changed by adjusting the voltage applied to the EO element 24.
[0043]
In any of the above cases, the processing reliability can be improved by comparing the intensity of the emitted light when the laser beam is last irradiated with a preset value.
[0044]
Further, although the peak power value or pulse width of the laser beam is changed by the EO element 24, the output of the laser oscillator 1 may be changed.
[0045]
【The invention's effect】
As described above, according to the present invention, it is determined that the hole bottom has reached the inner layer by the radiated light radiated from the inner layer, so that it is not affected by the reflectance of the inner layer.
[0046]
In addition, the polarization defining means in the detector removes most of the processing laser light reflected by the processing portion in combination with the action of the polarization defining means provided in the optical path of the laser light. Light can be detected with high accuracy. In addition, smear can be reliably removed by irradiating laser light after detecting the emitted light. In addition, damage to the inner layer can be suppressed by reducing the energy of the laser light near the end of processing.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a laser beam machine according to the present invention.
FIG. 2 is a diagram illustrating a relationship between a waveform of a laser beam and a detection signal in the present invention.
FIG. 3 is a diagram showing temporal changes in laser light intensity and emitted light intensity in the present invention.
FIG. 4 is a diagram showing the relationship between the waveform of a laser beam and a detection signal in the present invention.
FIG. 5 is a diagram showing a relationship between a waveform of a laser beam and a detection signal in the present invention.
FIG. 6 is a side view of a multilayer printed board.
[Explanation of symbols]
10 Detector 20 Processing Circuit 21 Laser Driver

Claims (4)

In a laser processing method of irradiating a pulsed laser beam a plurality of times for each target position and processing a hole connecting a surface and a target inner layer into a processing target,
For each target position, a standard number of irradiations required to remove the upper layer of the average thickness with the laser beam having the first energy is obtained, and a first number of irradiations less than the obtained number of irradiations is determined. Every
After irradiating the laser beam of the first energy for the first number of times of irradiation, irradiating a laser beam of a second energy smaller than the energy of the laser beam for the first number of irradiations,
After the intensity of the radiated light emitted from the inner layer processed by the laser beam having the second energy becomes equal to or higher than a predetermined value, the second laser beam having the second energy is predetermined at the target position . The number of times of irradiation is further irradiated. Each time the laser beam is output, the time from when the output of the laser beam is started until the intensity of the radiated light becomes a predetermined value or more is measured,
The laser processing method according to claim 1, wherein the inner layer is determined to be exposed when the measured time is shorter than a predetermined time. In a laser processing apparatus provided with a radiant light detection means for detecting radiant light emitted by a workpiece processed by laser light,
A polarizing unit that defines a polarization direction of the laser beam and a shutter unit are disposed in the optical path of the laser beam reaching the processing target,
A selection means for blocking the laser light component for processing whose polarization direction is defined by the polarization means reflected from the object to be processed and transmitting the radiation light to the radiation light detection means;
Measuring means for measuring the intensity of the emitted light;
Setting means for setting the first number of times of irradiation of the laser beam with the first energy and the second number of times of irradiation with the second energy smaller than the first energy ;
After irradiating the laser beam of the first energy at the first number of irradiations, irradiating the laser beam with the second energy,
And control means for irradiating with the second number of times of irradiation of the laser beam of the second energy to the radiation position of the emitted light after the intensity of the emitted light is equal to or greater than the predetermined value, it was provided that A featured laser processing apparatus. Measuring means for measuring the time from when the output of the laser light is started until the intensity of the radiated light reaches a predetermined value or more each time the laser light is output;
A determination unit that determines that the inner layer is exposed when a time measured by the measurement unit is shorter than a predetermined time;
The laser processing apparatus according to claim 3, wherein:

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