JP2001042372A - Processing laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce as much as possible the fluctuation in output power in a processing laser device irradiating a subject to be processed with a wavelength converted laser beam and processing it. SOLUTION: The laser beam emitted from a laser light source 11 is made incident on a non-linear optical crystal 1 of an LBO, a CLBO, etc., and is wavelength converted to be emitted from the non-linear optical crystal 1. The temp. of the non-linear optical crystal 1 is measured by a sensor 3 to be sent to a controller 5 through a sensor amplifier 4. An optimum phase matching angle that maximum output power is obtained for the temp. of the non-linear optical crystal is stored beforehand in the controller 5, and the controller 5 drives a drive device 6 according to the temp. of the measured non-linear optical crystal 1, and adjusts the angle of the crystal axis of the non-linear optical crystal 1 by an angle moving mechanism 7 to control it so as to become the optimum phase matching angle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to processing such as drilling and marking by generating harmonic laser light using a nonlinear optical crystal and irradiating the object to be irradiated such as a multilayer printed board with the harmonic laser light. The present invention relates to a processing laser device that performs the following.

[0002]

2. Description of the Related Art Lasers are used for forming via holes in printed circuit boards, cutting films and metals, and the like. As a laser for processing a printed circuit board, a wavelength of 262 to 35 is used.
A 5 nm high output, high repetition ultraviolet laser light source is used. FIG. 5 shows a schematic configuration of a processing laser device 10 for performing processing by wavelength conversion using a nonlinear optical crystal. Laser light emitted from the laser light source 11 is condensed by the condenser lens 12 and enters the nonlinear optical crystal 1. A part of the laser light incident on the nonlinear optical crystal 1 is wavelength-converted and emitted from the nonlinear optical crystal 1, and the emitted light is condensed by the condenser lens 13 and irradiated on the workpiece 14. As the nonlinear optical crystal 1 used, for example, L
BO, CLBO and the like.

The angle between the crystal axis and the optical axis of the above-described nonlinear optical crystal 1 is maintained at an angle called a phase matching angle at which the wavelength conversion efficiency is maximized. However, since this angle depends on the temperature of the crystal, It is known that when the temperature changes, the output laser power changes. Therefore, the nonlinear optical crystal 1 is controlled so that its temperature becomes constant. The temperature control of the nonlinear optical crystal 1
A temperature measuring element such as a thermocouple 15 is brought into contact with the surface of
The entire nonlinear optical crystal is covered with a heating means such as a heater 17 or a cooling means such as a Peltier element. And thermocouple 1
5 is input to a temperature controller 16 (hereinafter, referred to as a temperature controller 16). The temperature controller 16 feeds back the measured temperature of the nonlinear optical crystal so as to be a preset temperature, controls the input of a heating unit or a cooling unit, and adjusts the temperature of the nonlinear optical crystal 1. Further, in order to adjust the phase matching angle of the nonlinear optical crystal 1, the nonlinear optical crystal 1 is mounted on an angle adjusting mechanism 7 driven by a driving device.

FIG. 5 shows a case where the nonlinear optical crystal 1 is heated using the heater 17. Hereinafter, a case where the nonlinear optical crystal is heated will be described as an example. The output from the processing laser device 10 is adjusted as follows. The nonlinear optical crystal 1 is heated to a predetermined temperature and is controlled to a constant temperature. In this state, the laser light from the laser light source 11 is incident on the nonlinear optical crystal 1, and the wavelength-converted and output laser light is received by a power monitor (not shown). While watching the display on the power monitor, the phase matching angle of the nonlinear optical crystal 1 is adjusted so that the value is maximized, and the angle at which the nonlinear optical crystal 1 is arranged is determined. When performing a via hole processing or the like of a multilayer printed board by the processing laser device described above, a laser beam is applied to a shutter or a Q-hole.
The workpiece is irradiated intermittently with pulsed laser light by being turned on / off by the SW.

FIG. 6 shows how a via hole is formed by a laser beam. As shown in FIG. 1A, usually, a plurality of irradiation areas A1, A2,... Are formed on a single substrate, and each irradiation area A1, A2,. Is provided. Then, the laser light emitted from the processing laser device is scanned by a control means such as a galvanometer, and is positioned at each hole-forming position of the multilayer printed board,
A via hole processing is performed by irradiating each of the drilling positions with a pulsed laser beam a plurality of times.

That is, as shown in FIG. 1D, the full width at half maximum (pulse width at half the peak value) is several tens ns.
To several hundred ns, and the repetition frequency is several kHz to several tens.
A laser pulse of kHz is applied a plurality of times to each of the drilled locations in the area A1 as shown in FIG. 3 (c) to perform drilling processing. The laser light is moved, and the operation of making a hole is repeated in the same manner. Then, when all the holes in the area A1 are completed, the laser light is turned off, the laser light is moved to the next area A2, and similar drilling is performed, as shown in FIG. Hereinafter, similarly, each area A1, A of the multilayer printed board
The drilling process of 2,... Is sequentially performed, and when the drilling of one multilayer printed board is completed, the multilayer printed board is replaced and the next printed board is processed. Here, the number of laser shots is, for example, 1 to 30 shots for processing one hole. In FIG. 6C, the size of the laser light gradually increases immediately after the start of the emission of the laser light, but this is an output fluctuation due to a rise in the internal temperature of the nonlinear optical crystal, as described later.

As described above, when a processing laser device is used for processing a via hole or the like of a multilayer printed board, a processed work (multilayer printed board) is replaced with an unprocessed work, or a single multilayer printed board is processed. Therefore, an operation such as moving an area to be irradiated with a laser beam is required (this operation is called “setup change”). This setup change time is usually several seconds to several tens of seconds (sometimes several minutes).
Take it. During the setup change, the laser light is not emitted from the laser light source as described with reference to FIG.
The processing laser device does not output a laser. After the completion of the setup change, the laser light is emitted from the laser light source, and the work is irradiated with the wavelength-converted laser light.

[0008]

The refractive index of the above-mentioned nonlinear optical crystal changes depending on the temperature. Therefore, the self-heating of the nonlinear optical crystal itself accompanying the generation of the laser light causes a problem that the optimum angle between the optical axis and the crystal axis changes due to the generation of the laser light, and the output fluctuates. for that reason,
Usually, the nonlinear optical crystal is heated or cooled by the heating means or the cooling means as shown in FIG. 5 and the ambient temperature is kept constant. However, as described with reference to FIG. 6, when light needs to be generated intermittently at time intervals of several to several tens of seconds, it is difficult to keep the light constant because the temperature changes transiently. FIG. 7 is a diagram showing a change in power of laser light emitted from the nonlinear optical crystal immediately after the start of laser light emission.
The figure shows the case where the crystal is used and the temperature of the CLBO crystal is controlled to be constant as described above. As shown in the figure, the laser power gradually increases immediately after the start of laser emission.

When the laser light output changes as shown in FIG.
For example, in the case of via hole processing, the depth of the hole of the via hole changes, and in the case of cutting processing, the shape of the cut surface is disordered,
Practical problems arise. In practice, the fluctuation of the laser light output is 1
It is demanded to keep it within 0%. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a processing laser device that performs processing by irradiating a workpiece with laser light whose wavelength has been converted using a nonlinear optical crystal, It is an object of the present invention to minimize fluctuations in the output power of the laser beam after stopping the emission of the laser beam due to a setup change or the like as much as possible, thereby enabling good processing.

[0010]

According to the present invention, there is provided a processing laser device comprising: a temperature measuring means for measuring a temperature of a nonlinear optical crystal; and an angle moving mechanism for adjusting an angle of a crystal axis of the nonlinear optical crystal. And a control means for controlling the angle moving mechanism based on the temperature of the nonlinear optical crystal measured by the temperature measuring means, wherein the control means has a maximum output power with respect to the temperature of the nonlinear optical crystal. The obtained optimal phase matching angle is stored in advance. Then, the angle of the nonlinear optical crystal is controlled by the control means in accordance with the temperature of the nonlinear optical crystal, and the nonlinear optical crystal is adjusted to a phase matching angle at which the maximum output power is obtained. In the present invention, since the configuration described above, regardless of the temperature change of the nonlinear optical crystal, the angle of the nonlinear optical crystal can be maintained at an angle that maintains an optimal phase matching angle with respect to the crystal temperature, Fluctuations in the output power of the laser light can be reduced. For this reason, good processing is possible in the processing laser device.

[0011]

FIG. 1 is a diagram showing an embodiment of the present invention. FIG. 1 shows only a laser light source, a nonlinear optical crystal, and a control system for controlling the angle of the nonlinear optical crystal, and other components are omitted. In FIG. 1, 1
Reference numeral 1 denotes a laser light source, and 1 denotes a nonlinear optical crystal such as LBO or CLBO. The nonlinear optical crystal 1 is placed in a holder 2, and the temperature of the nonlinear optical crystal 1 is measured by a sensor 3. Although not shown, the nonlinear optical crystal 1 is heated to a desired temperature by a heater. Reference numeral 4 denotes a sensor amplifier for amplifying the output of the sensor 3, and reference numeral 5 denotes a control device including a computer or the like.

Next, the operation of this embodiment will be described.
Before that, first, the relationship between the crystal temperature and the wavelength conversion efficiency and the relationship between the crystal temperature and the phase matching angle will be described. In general,
The wavelength conversion efficiency η of the nonlinear optical crystal can be expressed by the following equation (1). η∝ ｛sin ² (ΔkL / 2)｝ / (ΔkL / 2) ² (1) where L is the optical distance of the nonlinear optical crystal, and Δk is the distance between the laser beam entering and exiting the nonlinear optical crystal. This is the difference between the wave numbers and is expressed by the following equation (2).

Λ1 and λ2 are the wavelengths of the laser beam incident on the nonlinear optical crystal, λ3 is the wavelength of the wavelength-converted laser beam emitted from the nonlinear optical crystal, and ni is the refractive index for the wavelength λi. It is determined by the incident angle (θ) of the incident light with respect to the coordinates, its polarization direction (φ), and the temperature (T) of the nonlinear optical crystal. That is, the refractive index n can be expressed as a function of θ, φ, and T as shown in the following equation (3). n = f (θ, φ, T) (3)

Therefore, from the equations (1), (2) and (3), the wavelength conversion efficiency η can be expressed as a function of the temperature T of the nonlinear optical crystal. FIG. 2 shows an example in which the wavelength conversion efficiency η with respect to the crystal temperature is obtained from the above equations (1), (2) and (3). FIG.
In the graph, the horizontal axis represents the temperature difference from the crystal temperature To at which the output power becomes maximum at a certain phase matching angle, and the vertical axis represents conversion efficiency. As shown in the figure, when the crystal temperature is at the optimum phase matching angle at To, the conversion output is reduced whether the crystal temperature is higher or lower than To. FIG. 3 is a diagram showing an example of the relationship between the temperature difference of the nonlinear optical crystal and the phase matching angle shift.
In the figure, the horizontal axis shows the temperature difference of the crystal, and the vertical axis shows the angle deviation from the phase matching angle. For example, when the phase matching angle when the crystal temperature is To is θo, the crystal temperature is + 5 ° C
When the shift (To + 5) ° C. is reached, the phase matching angle becomes about 0.4.
mrad shift, θo + 0.4 mrad. here,
The relationship between the temperature difference ΔT and the phase matching angle shift Δθ is represented by Δθ =
If f (ΔT) is expressed, when the temperature of the nonlinear optical crystal increases by ΔT due to self-heating accompanying laser beam irradiation, the phase matching angle of the nonlinear optical crystal shifts by Δθ = f (ΔT).

Therefore, when the temperature of the crystal temperature is To and the crystal axis of the crystal is set to the phase matching angle θo at which the maximum conversion efficiency is at that time, the conversion efficiency becomes maximum immediately after the laser beam irradiation. When the temperature of the nonlinear optical crystal rises by ΔT due to self-heating accompanying laser beam irradiation,
The phase matching angle deviates from θo by Δθ. In other words, even if the relationship between the optical axis of the laser beam and the crystal axis of the nonlinear optical crystal is set to the optimum phase matching angle θo when the crystal temperature is To, the temperature of the crystal is not affected by the laser beam irradiation. When ΔT increases due to heating, the phase matching angle shifts by Δθ = f (ΔT), and the conversion efficiency decreases. Therefore, in this embodiment, the temperature of the nonlinear optical crystal is measured, and the angle of the crystal axis of the nonlinear optical crystal is adjusted according to the measured temperature so that the nonlinear optical crystal always maintains an optimal phase matching state. did.

Returning to FIG. 1, the operation of this embodiment will be described below. The laser light emitted from the laser light source 11 is LB
Incident on a nonlinear optical crystal 1 such as O, CLBO, etc .;
The wavelength is converted into a harmonic such as a third harmonic, and the light is emitted from the nonlinear optical crystal 1. The temperature of the nonlinear optical crystal 1 is measured by the sensor 3 and sent to the control device 5 via the sensor amplifier 4. The control device 5 drives the driving device 6 based on the output of the sensor amplifier 4 and adjusts the angle of the crystal axis of the nonlinear optical crystal 1 with respect to the optical axis of the incident laser beam by the angle moving mechanism 7. The optimal phase matching angle at which the maximum output power is obtained for the temperature of the nonlinear optical crystal as shown in FIG. 3 is stored in the control device 5 in advance. An optimum phase matching angle according to the temperature of the nonlinear optical crystal is determined, and control is performed so that the angle of the crystal axis of the nonlinear optical crystal 1 becomes the optimum phase matching angle. FIG. 4 is a time chart showing the operation of this embodiment. The operation of this embodiment will be described with reference to FIG.

In FIG. 4, (a) shows the on / off state of the laser, (b) shows the temperature of the nonlinear optical crystal, and (c) shows the optimum phase matching angle of the crystal with respect to the crystal temperature.
Adjusts the angle of the crystal axis in accordance with the measured temperature so that the optimum phase matching angle is obtained. (D) is a laser output obtained when the angle of the crystal axis is controlled by the controller 5 as described above. (E) and (f) show the laser output when the angle of the nonlinear optical crystal is not controlled, and (e) shows the optimum phase matching angle when the crystal temperature is T1 (see the dotted line in FIG. 3 (b)). (F) shows that the phase matching angle is set to be an optimum angle when the crystal temperature is T2 (see the dotted line in FIG. 3 (b)). Shows the case.

In this embodiment, it is assumed that the temperature of the nonlinear optical crystal is To before the start of laser beam irradiation, and the phase matching angle is set to θo at which the maximum efficiency is obtained at the temperature To. When the laser light is turned on as shown in FIG. 4A, the temperature of the nonlinear optical crystal 1 rises as shown in FIG. The temperature of the nonlinear optical crystal 1 measured by the sensor 3 is input to the control device 5. Control device 5
From the relationship between the temperature difference of the nonlinear optical crystal and the amount of phase shift shown in FIG. 3, an adjustment amount Δθ of the phase matching angle according to the temperature rise ΔT of the nonlinear optical crystal 1 is obtained. Is adjusted to be θo + Δθ. Thereby, the angle of the nonlinear optical crystal 1 is adjusted as shown in FIG. 4C, and the angle of the nonlinear optical crystal 1 becomes the optimum phase matching angle θo + Δθ at the temperature To + ΔT. For this reason,
As shown in FIG. 4D, the laser output is maintained at a substantially constant level. The control device 5 repeats the operation, and adjusts the angle of the nonlinear optical crystal so as to maintain the optimum phase matching angle.

Here, when the angle adjustment of the nonlinear optical crystal is not performed as described above, the laser output is as shown in FIGS.
become that way. That is, when the phase matching angle is equal to the crystal temperature T
In the case where the angle is set to be an optimum angle at 1 and T2, the conversion efficiency of the nonlinear optical crystal becomes maximum when the crystal temperature is T1 and T2. It increases as the temperature approaches T2, and decreases when the temperature of the crystal exceeds T1 and T2. Therefore, in this case, the laser output fluctuates as shown in FIGS. As described above, in the present invention, the temperature of the nonlinear optical crystal is measured, and the angle of the nonlinear optical crystal is adjusted accordingly, so that the optimal phase matching state is maintained regardless of the temperature change of the nonlinear optical crystal. It is possible,
Fluctuations in the laser output can be reduced. Therefore, when applied to a processing laser device, it is possible to perform good processing.

It is also conceivable to measure the output power of the laser device with a power meter or the like and adjust the temperature or angle of the nonlinear optical crystal so that the output power becomes constant. Although this method is effective in a laser device that constantly outputs laser light, in the case of a laser device in which laser light is intermittently output according to the present invention, this method can effectively reduce output fluctuation. I can't control it. That is, when the above method is applied to a laser device that outputs laser light intermittently, during a period in which no laser light is output, the control system for keeping the output power constant does not operate, and the laser light is output. The control system is activated each time it is performed. Therefore, the output power of the laser light fluctuates transiently every time the laser light is output. In contrast, in the case of the present embodiment, even when the laser light is not output, the angle of the nonlinear optical crystal is always adjusted based on the temperature of the nonlinear optical crystal. The maximum output can be maintained immediately after the laser emission, and the output power does not undergo the above-mentioned transient fluctuation, and the output power can be stably controlled to be constant.

[0021]

As described above, a temperature measuring means for measuring the temperature of a nonlinear optical crystal is provided in a processing laser device.
An angle moving mechanism for adjusting the angle of the crystal axis of the nonlinear optical crystal, and a control means for controlling the angle moving mechanism based on the temperature of the nonlinear optical crystal measured by the temperature measuring means are provided. The optimal phase matching angle at which the maximum output power is obtained is stored in advance with respect to the temperature of the nonlinear optical crystal, and the angle of the crystal axis of the nonlinear optical crystal is controlled in accordance with the temperature of the nonlinear optical crystal. Since the optical crystal is adjusted to the phase matching angle at which the maximum output power is obtained, the fluctuation of the output power of the laser light can be reduced, which is favorable in a processing laser device in which the laser light is output intermittently. Processing is possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a crystal temperature and a conversion efficiency.

FIG. 3 is a diagram showing a relationship between a temperature difference of a nonlinear optical crystal and a phase matching angle shift.

FIG. 4 is a time chart showing the operation of the embodiment of the present invention.

FIG. 5 is a diagram showing a schematic configuration of a processing laser device that performs processing by wavelength conversion.

FIG. 6 is a diagram showing a state of via hole processing by laser light.

FIG. 7 is a diagram showing a change in power of laser light immediately after the start of laser light emission.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Nonlinear optical crystal 2 Holder 3 Sensor 4 Sensor amplifier 5 Control device 6 Drive device 7 Angle movement mechanism 11 Laser light source

Claims (1)

[Claims] 1. A method for generating a harmonic laser beam using a nonlinear optical crystal, intermittently irradiating the object to be irradiated with the harmonic laser beam, and performing a work of removing a hole, marking, or the like in the object to be irradiated. A processing laser device, wherein the processing laser device includes a temperature measuring unit that measures a temperature of the nonlinear optical crystal, an angle moving mechanism that adjusts an angle of a crystal axis of the nonlinear optical crystal, and a temperature measurement unit that measures the temperature. Control means for controlling the angle movement mechanism based on the temperature of the nonlinear optical crystal, wherein the control means determines an optimal phase matching angle at which the maximum output power is obtained with respect to the temperature of the nonlinear optical crystal. Stored in advance, by the control means, to control the angle of the crystal axis of the nonlinear optical crystal according to the temperature of the nonlinear optical crystal,
A processing laser device wherein an angle of a nonlinear optical crystal is adjusted to a phase matching angle at which a maximum output power is obtained.