JP2003053570A - Method and device for laser beam machining - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a device for laser beam machining by which the damage of an inner layer is suppressed to the minimum and a smear is not made at the part to be machined when a hole which connects the surface and a target inner layer is machined on a work having a multilayer structure. SOLUTION: A radiated light radiated by the inner layer when machined is detected with a detector 10. A processing circuit 20 decides that the hole bottom reaches the target inner layer when the value of the output signal of the detector 10 reaches a prescribed value or greater. The processing circuit 20 drives a laser driver 21 for removing the smear, and the hole is additionally irradiated with the laser beam at prescribed times. In this case, it is effective when the energy of the additionally irradiated laser beam is set smaller.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser processing method and a laser processing apparatus for irradiating a pulsed laser beam a plurality of times to process a hole for connecting a surface and a target inner layer to a processing target.

[0002]

2. Description of the Related Art FIG. 6 is a side view of a multilayer printed circuit board. The multilayer printed circuit board 8 includes an upper layer (front surface layer) 8a, a plurality of inner layers (intermediate layers) 8b, 8c, ... And a back surface layer 8z.
It consists of and. A hole reaching the target inner layer (for example, the inner layer 8b) from the surface of such a multilayer substrate (hereinafter, the surface to the target inner layer is referred to as "upper layer").
In the case of processing, the processing efficiency can be improved by processing using laser light. 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. Therefore, it is necessary to process the upper layer so as not to damage the inner layer.

Therefore, in JP-A-5-261577, a plume (plasma-like object) generated by machining
The processing state of the hole is estimated from the emission spectrum of the laser and the irradiation of the laser beam is stopped before the target inner layer is damaged.

In Japanese Patent Laid-Open No. 10-85976, the laser output is controlled by detecting the reflected light from the target inner layer.

[0005]

However, the former of the above-mentioned prior arts 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. Therefore, a method of effectively selecting the processing end signal from the laser light for processing, and minimizing damage to the inner layer, and smear (when the inner layer is the upper layer component remaining on the inner layer surface and the inner layer is copper foil) It is unclear what kind of signal should be obtained and how to control the laser light in order to prevent the existence of the (.

Further, in the latter of the above-mentioned conventional techniques, since the reflected light is used as the processing end signal, it is difficult to detect the processing end when the reflectance of the inner layer is low.

The object of the present invention is to solve the above-mentioned problems in the prior art, to minimize damage to the inner layer when processing a hole for connecting the surface and the target inner layer to a processing target of a multilayer structure, and (EN) Provided are a laser processing method and a laser processing apparatus that do not allow smear to exist in a processing portion.

[0008]

To achieve the above object, the first means is to irradiate a pulsed laser beam a plurality of times for each target position to form a hole for connecting the surface and a target inner layer. In the laser processing method of processing the object to be processed, after the intensity of the radiated light emitted by the inner layer processed by the laser light becomes a predetermined value or more, the laser light of a predetermined number of times at the target position is further It is characterized by irradiation.

In this case, the energy value of the laser light to be applied after the intensity of the emitted light exceeds a predetermined value is set to be a value smaller than the energy values up to that point. Further, a standard irradiation number of the laser light is set for each target position, and the energy value of the laser light is made smaller than the energy value up to that point before the irradiation number is reached. Furthermore, each time the laser light is output, the time from the start of the output of the laser light until the intensity of the emitted light is equal to or more than a predetermined value is measured,
When the measured time is shorter than a predetermined time, it is determined that the inner layer is exposed.

A second means is a laser processing method for irradiating a pulsed laser beam a plurality of times for each target position to process a hole for connecting a surface and a target inner layer as a processing target, in the target position. It is characterized in that the intensity of the radiated light at the time of the last irradiation of the laser light is measured for each time, and the measured value is compared with a predetermined value to judge the quality of the processing.

A third means is a laser processing apparatus provided with radiation light detecting means for detecting radiation light emitted by a processing object processed by laser light, and reflected by the radiation light detecting means from the processing object. Selection means for blocking the laser light and transmitting the emitted light, measuring means for measuring the intensity of the emitted light, setting means for setting the number of times of irradiation, and intensity of the emitted light is a predetermined value or more. And a control means for irradiating the laser light to the position where the radiated light is radiated after the number of times set by the setting means, the control means radiating the target inner layer of the processing target. After the light intensity exceeds a predetermined value, the laser beam is further irradiated to the hole processing target position.

In this case, a polarization regulating means for regulating the polarization direction of the laser light is arranged in the optical path of the laser light reaching the object to be processed, and the laser of the polarization direction regulated by the polarization regulating means by the selecting means is arranged. It is also possible to block the light.

Further, each time the laser light is output, a measuring means for measuring the time from the start of the output of the laser light until the intensity of the radiated light exceeds a predetermined value, and the measuring means. A determining unit may be provided to determine that the inner layer is exposed when the time measured in step 2 is shorter than a predetermined time.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION <First Embodiment> The present invention will be described below based on the illustrated embodiments.

FIG. 1 is a block diagram of a laser processing machine according to a first embodiment of the present invention.

On the optical path of the laser oscillator 1, a polarizing plate 2,
Shutter 23, aperture 3, mirror 5 of scanner 4,
The fθ lens 7 and the processing target 8 are arranged.

The shutter 23 is an electro-optical element (hereinafter,
It is called "EO element". ) 24 and a polarizing plate 25 whose plane of polarization is parallel to the plane of polarization of the polarizing plate 2. The voltage-applied EO element 24 has a function of rotating the plane of polarization of incident light by an angle proportional to the applied voltage. By changing the voltage applied to the EO element 24 from 0 to a half-wave voltage, the incident light is incident. Light can be polarized from 0 to 90 degrees. Since the shutter 23 has a configuration in which the polarizing plate 25 is arranged on the emission side of the EO element 24, the EO element 2
By changing the voltage applied to the shutter 4,
The opening degree of 3 can be changed at a high speed from fully open (applied voltage is 0) to fully closed (applied voltage is half-wavelength voltage).

The mirror 5 is supported on the output shaft of the motor 6,
It can be positioned at any angle around the axis of rotation perpendicular to the paper surface. Processing target 8 (here, multilayer printed circuit board)
Are fixed to the XY stage 9.

A detector 10 is arranged so as to face the multilayer printed circuit board 8. The detector 10 includes a wavelength selecting unit 11, a polarization selecting unit 12, a lens 13 and a P.
And a D (photodiode) 14. The wavelength selecting means 11 is an inner layer 8 processed by laser light.
light having a wavelength peculiar to the material of the inner layer 8b radiated by b (hereinafter,
It is called "synchronized light". ) Is transmitted and other light is not transmitted. Further, the polarization selecting means 12 is configured by combining a quarter wavelength plate and a polarizing plate. The PD 14 is connected to the processing circuit 20.

The processing circuit 20 controls the laser driver 21 for driving the laser oscillator 1 and the shutter driver 22 for driving the shutter 23 based on the output signal of the PD 14.

Next, the operation of this embodiment will be described.

FIG. 2 is a diagram showing temporal changes in laser light intensity and emitted light intensity according to the first embodiment of the present invention. The solid line shows laser light and the dotted line shows emitted light. .
In the figure, P1 is the peak power value of the laser light, and Ith is the threshold value of the detection signal intensity, that is, the emitted light intensity.

After controlling the scanner 4 and the XY stage 9 to two-dimensionally position the center of the optical path of the laser light at the processing position, the laser oscillator 1 is operated to output the laser light in pulses. The laser light output from the laser oscillator 1 and having an optical path parallel to the paper surface passes through the polarizing plate 2 and the shutter 22, the outer shape is shaped by the aperture 3, and enters the fθ lens 7 through the scanner 4 to be processed 8. Is imaged on. Then, a part of the laser light makes a hole in the upper layer 8a, and a part of the laser light is reflected by the upper layer 8a and enters the detector 10. The wavelength selection unit 11 transmits the radiated light, and does not transmit the laser light (hereinafter, referred to as “processing laser light”) supplied to the processing unit. Further, the polarization selection means 12 is
The processing laser light component that could not be completely removed by the wavelength selection means 11 (as will be described later, the polarization plane of the processing laser light may be rotated by the shutter 23, so the laser light reflected by the upper layer 8a may be The polarized light other than the polarized light component defined by the polarizing plate 2 may be included.), So that light other than the radiated light that has passed through the wavelength selecting means 11 hardly passes through the polarized light selecting means 12. Therefore, the intensity of the signal output from the PD 14 is low while the upper layer 8a is being processed, that is, while the emitted light is not generated.

When part of the upper layer 8a is removed and the inner layer (here, the inner layer 8b in FIG. 6) is irradiated with the processing laser light, the inner layer 8b emits radiated light. The emitted light passes through the wavelength selecting means 11 and the polarization selecting means 12, and the lens 13
The light is condensed by and is irradiated onto the PD 14. The PD 14 that receives the irradiation light outputs a light reception signal to the processing circuit 20.

The processing circuit 20 compares the value of the received light signal with a preset value, determines that the upper layer 8a is almost removed when the received light signal is equal to or more than the preset value, and aims at removing smear. , Irradiating the processing point with laser light a predetermined number of times (excess pulse in the figure),
The processing at that position is completed.

As described above, 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 can be reliably removed without damaging the inner layer 8b. In addition to being processed, it is possible to prevent smear from remaining in the processed portion.

Since the reflected light reflected by the object 8 to be processed is generally elliptically polarized light including linearly polarized light, the polarization selecting means 12 may be composed of one polarizing plate.

Although the EO element is used as the shutter 3, an acousto-optic element (AO element) may be used.

Here, when a plurality of holes are formed in the area which can be scanned by the scanner 4, pulsed laser light is continuously irradiated to each processing point until the intensity of the emitted light exceeds a predetermined value. After that, if the energy value of the laser light 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. Therefore, the control becomes easy and the processing efficiency can be improved.

By the way, when comparing the intensity of the output signal of the PD 14, that is, the intensity of the radiated light with a preset value (threshold value), the inner layer 8b may be damaged if the threshold value is increased to avoid the influence of noise or the like. is there. On the other hand, if the threshold value is made small, the removal of the upper layer 8a may be insufficient.
Therefore, it is necessary to perform a sufficient confirmation test in advance to determine the threshold value.

Therefore, if the generation of the radiated light is confirmed not only by the intensity of the radiated light but also by other means, the amount of confirmation test can be reduced, and the reliability of the determination that the inner layer is exposed can be reduced. Can be further improved.

<Second Embodiment> FIG. 3 shows a second embodiment of the present invention.
FIG. 6 is a diagram showing temporal changes in laser light intensity and emitted light intensity according to the embodiment of the present invention, in which a solid line shows laser light and a dotted line shows emitted light.

When the inner layer 8b is exposed, FIG.
As shown in, the intensity of the detection signal increases almost at the same time when the laser light is irradiated. Further, when smear is present, the timing of appearance of the detection signal is delayed as compared with the case where the inner layer 8b is exposed, as shown in FIG.
The strength is small. Further, when the inner layer is not exposed, the component of the processing laser light which is not completely removed by the wavelength selecting means 11 and the polarization selecting means 12 is detected as noise, as shown in FIG.

Therefore, when the inner layer 8b is exposed, the time t0 is experimentally obtained in advance until the intensity of the detection signal exceeds a predetermined value (S in the figure) after the laser light is output. deep. Then, at the time of processing, the time t is compared with the time t0 until the intensity of the detection signal becomes equal to or more than a predetermined value (S in the figure) after the laser light is output, and when the time t is the time t0 or less, If it is determined that the bottom has reached the inner layer 8b, the accuracy of determination is improved, so that the processing accuracy can be improved and damage to the inner layer can be prevented.

By the way, although the smear can be surely removed by further irradiating the laser beam after the intensity of the emitted light exceeds the predetermined value, the inner layer 8b may be damaged in some cases.

<Third Embodiment> FIG. 4 shows a third embodiment of the present invention.
It is a figure which shows the relationship of the waveform of a laser beam and a detection signal which concern on embodiment of this.

The peak power value P1 of the laser beam and the pulse width T1 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, the processing is performed with the peak power value P1 until the number of processing pulses approaches Nav, and thereafter, the processing is performed with the peak power value P2 (however, the pulse width is the same) smaller than the peak power value P1. In this case, the number of pulses for switching the peak power value is the upper layer 8a.
It is practical to determine the inner layer 8b so that the inner layer 8b starts to be exposed while processing with the peak power P2 in consideration of the variation in the thickness.

In the case of FIG. 4, since the output signal of the PD 14 increased during the second irradiation after the peak power value was decreased, it was determined that the inner layer 8b was exposed at this point, and the laser beam was further irradiated twice. Irradiation has been finished.

Further, as shown in FIG. 5, after the machining pulse number approaches Nav, the peak power value is not changed and the subsequent pulse width T2 is made smaller than the pulse width T1 until the inner layer 8b is exposed. However, the same result as in the case of FIG. 4 can be obtained.

In the case of FIG. 5, the pulse width is reduced to 1
Since the output signal of the PD 14 increased during the second irradiation, it was determined that the inner layer 8b was exposed at this point, and then the laser beam was irradiated twice more to complete the processing.

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 the smear can be almost removed.

The peak power value and the pulse width can be easily changed by adjusting the voltage applied to the EO element 24.

Further, in any of the above cases, the reliability of processing can be improved by comparing the intensity of the emitted light at the time of the last irradiation with the laser light with a preset value.

Further, although the peak power value or pulse width of the laser light is changed by the EO element 24, the output of the laser oscillator 1 may be changed.

[0045]

As described above, according to the present invention,
Since it is determined that the bottom of the hole has reached the inner layer by the radiant light emitted by the inner layer, there is no influence of the reflectance of the inner layer.

Further, the polarization defining means in the detector removes most of the processing laser light reflected by the processing part in combination with the action of the polarization defining means for defining the polarization provided in the optical path of the laser light. Therefore, the emitted light can be accurately detected. Moreover, the smear can be surely removed by irradiating the laser light after detecting the emitted light. In addition, damage to the inner layer can be suppressed by reducing the energy of the laser beam near the end of processing.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a laser processing machine according to the present invention.

FIG. 2 is a diagram showing a relationship between a laser light waveform 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 a relationship between a waveform of laser light and a detection signal in the present invention.

FIG. 5 is a diagram showing a relationship between a waveform of laser light and a detection signal in the present invention.

FIG. 6 is a side view of a multilayer printed circuit board.

[Explanation of symbols]

10 detector 20 Processing circuit 21 Laser driver

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H05K 3/00 H05K 3/00 N 3/46 3/46 XY // B23K 101: 42 B23K 101: 42 (72) Inventor Hiroshi Aoyama 2100 Kamiimazumi, Ebina City, Kanagawa Prefecture F-term inside Hitachi Via Mechanics Co., Ltd. (reference) 4E068 AF01 CA02 CB01 CB10 CC01 CD05 DA11 5E346 FF03 GG15 HH07 5F072 GG05 HH06 JJ05 KK05 MM05 MM17 YY06

Claims (8)

[Claims] 1. A laser processing method for irradiating a pulsed laser beam for each target position a plurality of times to process a hole for connecting a surface and a target inner layer to a processing target, wherein the laser beam is used for processing. A laser processing method, further comprising: irradiating the target position with the laser light a predetermined number of times after the intensity of the radiated light emitted from the inner layer reaches or exceeds a predetermined value. 2. The energy value of the laser beam irradiated after the intensity of the emitted light exceeds a predetermined value, which is smaller than the energy values up to that point. 1. The laser processing method described in 1. 3. A standard number of times of irradiation of the laser beam is set for each target position, and before the number of times of irradiation is reached,
The laser processing method according to claim 1, wherein the energy value of the laser light is made smaller than the energy value up to that point. 4. Each 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 reaches a predetermined value or more is measured, and the measured time is preset. The inner layer is determined to be exposed when the time is shorter than a predetermined time.
4. The laser processing method according to any one of items 1 to 3. 5. A laser processing method for irradiating a pulsed laser beam a plurality of times at each target position to process a hole connecting a surface and a target inner layer as a processing target, wherein the laser beam is processed at each target position. A laser processing method, characterized in that the intensity of the emitted light at the time of the last irradiation with light is measured, and the measured value is compared with a predetermined value to judge the quality of the processing. 6. A laser processing apparatus provided with radiation light detection means for detecting radiation light emitted from a processing object processed by laser light, wherein the radiation light detecting means receives the laser light reflected from the processing object. Selection means for blocking and transmitting the emitted light, measuring means for measuring the intensity of the emitted light, setting means for setting the number of irradiations, and the emission after the intensity of the emitted light exceeds a predetermined value. A control means for irradiating the position where the light is emitted with the laser light the number of times set by the setting means is provided, and the control means is the intensity of the emitted light emitted by the target inner layer of the processing target. After the value exceeds a predetermined value,
A laser processing apparatus, which further irradiates the laser beam to a hole processing target position. 7. An optical path of the laser light reaching a processing object,
7. The laser processing according to claim 6, further comprising: a polarization defining unit that defines a polarization direction of the laser beam, and the selection unit blocks the laser beam having the polarization direction defined by the polarization defining unit. apparatus. 8. A measuring unit for measuring the time from the output of the laser beam until the intensity of the radiated light reaches a predetermined value or more each time the laser beam is output, and the measuring unit. The laser processing apparatus according to claim 6 or 7, further comprising: a determining unit that determines that the inner layer is exposed when the time measured in step 3 is shorter than a predetermined time.