JP2000176661A - Laser beam machining method and its device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a laser beam machining method and its device capable of enhancing reproducibility of high quality machining. SOLUTION: As a laser beam machining method, in the case of forming an optical system provided with an aperture 3 in the optical path of a laser beam from a laser generator 4 to the lens, an intensity distribution is detected for the laser beam passing through the aperture 3 and, on the basis of the detected information, the laser beam diameter through the aperture 3 is adjusted for the machining.

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, and more particularly to a laser processing method and a laser processing apparatus for performing high-quality via holes and through holes on a material such as a printed circuit board. It is about.

[0002]

2. Description of the Related Art The principle of an image transfer optical system is shown in FIG. FIG.
In the figures, 1 is a processing (imaging) lens, 2 is a laser beam, 3 is an aperture, and 4 is a laser oscillator. Also,
a is the distance between the processing lens 1 and the aperture 3, b is the distance between the processing lens 1 and the transfer position, f is the processing lens 1
Is the focal length. The laser beam 2 oscillated from the laser oscillator 4 is limited by the aperture 3, and the laser beam 2 shaped by the aperture 3 is transferred to the position "b". By changing the aperture diameter, an arbitrary hole diameter can be obtained.

Conventionally, in such an optical system, processing conditions are defined by a fluence (energy density) and an energy amount at a processing point. Therefore, as a method of changing these parameters, a method of changing the waveform (pulse width, peak output) of the laser beam oscillated from the laser oscillator 4 by the amount of electric power supplied to the laser oscillator 4 or the like, A method of changing the beam diameter, and a method using both of them have been used.

[0004] According to such a definition, FIG.
The result is that the beams of the two modes shown in (b) are equivalent. FIG. 9 and FIG. 10 show the results when processing is performed with these two types of beams. FIG. 9 shows a result obtained by processing with a beam having a high center of the beam intensity distribution and a result obtained by performing penetration processing with a beam having a flat beam intensity distribution. The material to be processed is glass epoxy, the thickness is 0.4 mm, the diameter of the processing hole is 0.2 mm, and the energy at the processing point is 15 mJ. For each case, the change in the cross-sectional diameter of the machined hole when the machined hole (pierced hole) is performed is shown. In the graph of FIG. 9, the higher the value on the horizontal axis, the closer to the surface of the workpiece, that is, the laser incident side. In the case of drilling with a laser beam whose center of the beam intensity distribution is high as shown in FIG. 8A, the diameter becomes extremely small as the drilling proceeds with respect to the diameter on the beam incident side in the depth direction. Become. In contrast, FIG.
In the case of drilling a hole with a laser beam having a flat beam intensity distribution as shown in (b), the change in diameter in the depth direction is small.

FIG. 10 shows a comparison of a case where blind holes are formed in a printed circuit board by using such two types of beams. The horizontal axis of the graph shown in FIG. 10 is the laser power (mJ) at the processing position. The vertical axis indicates the damage rate to the copper foil in the inner layer portion of the printed circuit board. In this case, the damage rate is a ratio when the number of holes where the copper foil surface is molten is 1000 holes. The melting frequency increases as the beam diameter on the aperture decreases, and decreases as the beam diameter increases. Note that the thickness of the copper foil is 18 μm.

[0006]

As described above, in the conventional laser processing method and apparatus, the concept of processing conditions based on the relationship between the laser power at the processing point in the image transfer optical system and the diameter of the processing hole, etc. Then, the reproducibility of high quality processing was poor.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a laser processing method and a laser processing apparatus capable of improving reproducibility of high-quality processing.

[0008]

According to the present invention, there is provided a laser processing method comprising: forming an optical system having an aperture in an optical path of a laser beam from a laser oscillator to a lens; The laser beam intensity distribution is detected, and processing is performed by adjusting the laser beam diameter at the aperture based on the detected information.

[0009] Further, a laser processing apparatus according to the present invention comprises:
In a laser processing apparatus for forming an optical system having an aperture in an optical path of a laser beam from a laser oscillator to a lens, a variable optical means for changing a laser beam diameter at the aperture, and the laser passing through the aperture Intensity distribution detecting means for detecting the intensity distribution of the beam;
Beam diameter control means for controlling the variable optical means based on information detected by the intensity distribution detection means.

[0010] The laser processing method according to the present invention comprises:
When forming an optical system provided with an aperture in the optical path of the laser beam from the laser oscillator to the lens, the laser power before passing through the aperture and the laser power after passing through the aperture are detected. The processing is performed by adjusting the diameter of the laser beam at the aperture based on the laser beam.

Further, a laser processing apparatus according to the present invention is a laser processing apparatus for forming an optical system having an aperture in an optical path of a laser beam from a laser oscillator to a lens, wherein the laser beam diameter at the aperture is reduced. Variable optical means for changing, first power detecting means for detecting laser power before passing through the aperture, second power detecting means for detecting laser power after passing through the aperture, and the two power detecting means Beam diameter control means for controlling the variable optical means based on the detection information.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 A laser processing method and apparatus according to a first embodiment of the present invention will be described with reference to FIGS. As a method of changing the laser beam diameter on the aperture 3, as shown in FIG. 1, a movable lens 5 as a variable optical means is installed between the aperture 3 and the laser oscillator 4, and the movable lens 5 A method of changing the diameter of the laser beam on the aperture 3 by appropriately changing the position of the collimator lens is considered.

The cause of the generation of the two types of beams as shown in FIG. 8 is the laser beam diameter on the aperture 3. In FIG. 2, when the laser beam diameter on the aperture 3 is small as shown in FIG.
The intensity of the center of the shape of the laser beam cut out by the above is high, and this is transferred to the processing point. On the other hand, as shown in FIG. 2 (b), when the laser beam diameter on the aperture 3 is large, the intensity of the laser beam cut out by the aperture 3 is flat, so that the intensity is generally uniform even at the processing point. Is transferred as a perfect distribution.

FIG. 3 shows the shape of the beam intensity distribution on the aperture 3. In FIG. 3, the entire intensity of the intensity distribution of the portion of the laser beam passing through the hole of the aperture 3 is H, and the difference from the highest intensity portion to the lowest intensity portion is h. This is reflected in the intensity distribution at the processing point. When the position of the collimating lens 5 is changed and the beam diameter on the aperture 3 is changed, the ratio of these two numerical values, h / H, changes.

FIG. 4 shows the relationship between the h / H and the processing. In FIG. 4, the relationship between h / H and the damage rate of the inner layer copper foil of the processed substrate is examined with an aperture diameter of φ4.0 mm. The vertical axis indicates the rate of damage to the copper foil in the inner layer portion of the printed circuit board. The horizontal axis is h / H. In this case, the damage rate means that the number of holes where the copper foil surface is molten is 100
It is shown as a ratio when 0-hole machining is performed. The substrate used was glass epoxy, a thickness of 0.1 mm, and an inner copper foil t of 18 μm. From the results in FIG. 4, it is understood that h / H needs to be kept at 30% or less.

Embodiment 2 As described in the first embodiment, h / H changes depending on the beam diameter on the aperture. Therefore, the relationship between the laser power at the exit of the laser oscillator 4 and the laser power after passing through the aperture is replaced. Is possible. FIG. 5 shows (h / H × 1) in FIG.
00 (%)) is replaced with (laser power after passing through aperture / laser power at laser oscillator exit) (hereinafter referred to as utilization rate as appropriate). Although the utilization rate does not become the same value with respect to h / H, it can be seen from FIG. 5 that good quality processing is possible if the utilization rate is maintained at 35% or less.

By replacing h / H (or beam diameter on the aperture, collimating lens position) with the utilization factor, a power measuring device is installed after the laser oscillator exits and after passing through the aperture, and the laser power at two locations can be measured. Since the usage rate can be easily obtained, management is simple. Further, by using the apparatus configuration as shown in FIG. 6 and always keeping the utilization below a certain set value, the reproducibility of processing is improved.
The function of the device shown in FIG. 6 will be described below. The aperture 3 is installed, and a necessary power is input after passing through the aperture 3 (processing point). The first power detection means (not shown) provided in the laser oscillator 4 checks the output value of the laser oscillator 4 under the current laser output condition. Change the pulse width, peak, etc., so that the utilization rate becomes the set value. The laser output after passing through the aperture 3 (processing point) is measured, for example, by using the power sensor 8 as the second power detecting means. If the measurement result is large for the required power by the control device 9 as the beam diameter control means, a command is issued to move the collimating lens 5 in a direction to increase the beam diameter on the aperture 3, and the measurement result is small. For example, a command is issued to move the collimator lens 5 in a direction to reduce the beam diameter on the aperture 3. The collimator lens 5 is moved by a drive unit using a ball screw 7 and a motor 10, which constitutes a part of the variable optical unit.

[0018]

As described above, according to the present invention,
By finding the appropriate position in terms of the beam profile at the processing point, the ratio between the aperture diameter and the beam diameter on the aperture in the image transfer optical system, the effect of improving the reproducibility of high-quality processing can be improved. is there.

Further, by replacing the relationship between the laser beam diameter and the aperture diameter with the relationship between the laser power at the laser oscillator exit and the laser power after passing through the aperture, an appropriate beam position can be obtained. is there.

[Brief description of the drawings]

FIG. 1 is a diagram showing an optical path system in which a laser beam diameter on an aperture is varied in a laser processing method according to an embodiment of the present invention.

FIG. 2 is a diagram showing a difference in beam shape depending on an aperture diameter and a laser beam diameter.

FIG. 3 is a diagram showing a laser beam profile on an aperture.

FIG. 4 is a diagram showing a relationship between a copper foil damage rate and h / H.

FIG. 5 is a diagram showing a relationship between a copper foil damage rate and a utilization rate.

FIG. 6 is a schematic configuration diagram showing a laser processing apparatus according to an embodiment of the present invention.

FIG. 7 is a diagram illustrating the principle of an image transfer optical system.

FIG. 8 is a diagram showing a profile of a laser beam at a processing point.

FIG. 9 is a diagram showing a relationship between a processing hole depth (thickness) and a hole diameter in a cross section.

FIG. 10 is a diagram showing a relationship between a laser power and a copper foil damage rate.

[Explanation of symbols]

 Reference Signs List 1 processing lens 2 laser beam 3 aperture 4 laser oscillator 5 movable lens 6 total reflection mirror 7 ball screw 8 power sensor 9 control device 10 motor a distance between aperture and processing lens b distance between processing lens and transfer position f processing lens focal length E1 , E2 energy d1, d2 beam diameter

Claims (4)

[Claims] When forming an optical system having an aperture in an optical path of a laser beam from a laser oscillator to a lens, an intensity distribution of the laser beam passing through the aperture is detected. A laser processing method, wherein the laser beam diameter at the aperture is adjusted to perform the processing. 2. A laser processing apparatus for forming an optical system having an aperture in an optical path of a laser beam from a laser oscillator to a lens, wherein said variable optical means changes a laser beam diameter at said aperture; Laser processing comprising: intensity distribution detecting means for detecting the intensity distribution of the laser beam passing through; and beam diameter controlling means for controlling the variable optical means based on information detected by the intensity distribution detecting means. apparatus. 3. When forming an optical system having an aperture in an optical path of a laser beam from a laser oscillator to a lens, a laser power before passing through the aperture and a laser power after passing through the aperture are detected. A laser processing method wherein the laser beam diameter at the aperture is adjusted based on the detection information to perform processing. 4. A laser processing apparatus for forming an optical system having an aperture in an optical path of a laser beam from a laser oscillator to a lens, wherein said variable optical means changes a laser beam diameter at said aperture; A first power detecting means for detecting a laser power before passing, a second power detecting means for detecting a laser power after passing the aperture, and the variable optical means based on information detected by the two power detecting means. A laser processing apparatus comprising: a beam diameter control means for controlling.