JP2003285188A - Laser beam machining device and machining method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser beam machining device capable of making holes into several layers composed of different materials without changing pulse frequency. <P>SOLUTION: A linear polarized pulse laser beam is emitted from a laser beam source 1. The pulse laser beam emitted from the laser source carries out incidence to a polarization direction control element 2. The polarization direction control element can change the polarization direction of the pulse laser beam by controlling from the outside. The reducing element 4 reduces the strength of the pulse laser beam, whose polarization direction is controlled by the polarization direction control element 2, in accordance of the polarization direction. A holding means 7 holds the machining substance 20. A condenser lens 6 condenses the pulse laser beam reduced by the reducing element on the machining substance held by the holding means. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser processing apparatus and a processing method, and more particularly to a laser processing apparatus and a processing method for forming a hole by making a pulsed laser beam incident on a processing target.

[0002]

2. Description of the Related Art Inner wiring, resin layer,
A laser beam may be incident on the printed wiring board on which the upper layer film is formed to form a hole that penetrates the upper layer film and the resin layer and exposes a part of the inner layer wiring. The inner layer wiring and the upper layer film are usually formed of copper. The upper layer film is less likely to be etched by the laser beam than the resin layer.
For example, when using a pulsed laser beam having a wavelength of 351 nm in the ultraviolet region, the pulse energy required to form a hole in the upper layer film is about 20 J / cm ² , whereas it is necessary to form a hole in the resin layer. Pulse energy is about 2 J / cm
^{Is 2} .

When forming a hole in the upper layer film, the pulse energy of the laser beam is set to 20 J / cm ² or more. When a hole is formed through the upper layer film, the pulse energy is reduced to 2
The resin layer is processed by lowering it to about J / cm ² . Since the inner layer wiring is not etched by the pulse energy of ² J / cm ² , a hole penetrating the resin layer can be formed without damaging the inner layer wiring.

[0004]

Adjustment of the pulse energy of a solid-state laser is usually performed by changing the pulse frequency. For example, increasing the pulse frequency decreases the pulse energy. Therefore, when the hole penetrating the upper layer film is formed, the pulse frequency is increased to process the resin layer. However, if the pulse frequency is changed, the quality of the laser beam, for example, the stability of pulse energy, the divergence angle, the beam profile, etc. also change.

Further, the output of a solid-state laser oscillator is generally adjusted at a specific pulse frequency. Therefore, the output at pulse frequencies other than the adjusted pulse frequency of the output varies among the laser oscillators. For example, if the output is adjusted with the pulse frequency when forming the upper layer film, the output when forming the resin layer varies among the apparatuses.

An object of the present invention is to provide a laser processing apparatus and a processing method capable of making holes in a plurality of layers made of different materials without changing the pulse frequency.

[0007]

According to one aspect of the present invention, a laser light source that emits a linearly polarized pulse laser beam and a pulse laser beam emitted from the laser light source are incident, and are controlled from the outside. A polarization direction control element capable of changing the polarization direction of the pulse laser beam, an attenuating element for attenuating the intensity of the pulse laser beam whose polarization direction is controlled by the polarization direction control element depending on the polarization direction, and an object to be processed. There is provided a laser processing apparatus having a holding means for holding the pulse laser beam and a condenser lens for condensing the pulse laser beam attenuated by the attenuating element on the object to be processed held by the holding means.

According to another aspect of the present invention, at least a first layer, a second layer and a third layer have a laminated structure in which they are laminated in this order, and the second layer is the first layer. And a step of preparing a processing object formed of a material which is more easily etched by the laser beam than the material of the third layer, and attenuation of a linearly polarized pulsed laser beam whose attenuation amount changes depending on the polarization direction. A step of making a pulsed laser beam which is incident on the element and attenuated into a third layer of the object to be processed to form a hole penetrating the third layer; and a pulsed laser beam which is made incident on the attenuating element By changing the polarization direction of the pulse laser beam to increase the attenuation amount of the pulsed laser beam, and the attenuated pulsed laser beam is incident on the second layer on the bottom surface of the hole formed in the third layer of the workpiece, Penetrate the second layer,
Forming a hole exposing a portion of the first layer.

By adjusting the attenuation amount of the pulse laser beam, the pulse energy density of the laser beam on the surface of the object to be processed can be changed without changing the output of the laser light source. As a result, processing can be performed with a laser beam having a pulse energy density suitable for the material in which the holes are to be formed.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a laser according to an embodiment of the present invention.
The schematic of the processing apparatus is shown. The laser light source 1 is for processing
Emit a pulsed laser beam. The laser light source 1 is
Solid-state dielectric using a solid dielectric containing
Laser and a wavelength conversion element.
The loose laser beam is a linearly polarized third harmonic.
When Nd: YAG is used as the laser medium, the third
The harmonic wavelength is 351 nm. In addition, the laser medium
In addition to Nd: YAG, Nd: YLF and Nd: YVO
_FourMay be used. As a wavelength conversion element, BBO or KD
P optical crystals can be used. In addition, the third harmonic and above
It is also possible to use harmonics in the outer ultraviolet region.

The laser beam emitted from the laser light source 1 enters the electro-optical element 2. A voltage is applied from the driver 9 to the electro-optical element 2, and the polarization direction of the incident laser beam is rotated. The turning angle depends on the applied voltage. The laser light source 1 and the driver 9 are controlled by the control device 10.

The pulsed laser beam that has passed through the electro-optical element 2 enters the mask 3. The laser beam transmitted through the beam transmitting hole provided in the mask 3 enters the polarizing plate 4. The polarizing plate 4 has an incident angle of 45 degrees for the incident laser beam.
The polarization component (P component) parallel to the incidence plane is transmitted and the polarization component (S component perpendicular to the incidence plane (S
Component) is reflected. The P component pulsed laser beam that has passed through the polarizing plate 4 enters the damper 8.

The S component pulsed laser beam reflected by the polarizing plate 4 enters the galvano scanner 5. The galvano scanner 5 includes a pair of swingable reflecting mirrors, and scans a laser beam in a two-dimensional direction. The laser beam scanned by the galvano scanner 5 is focused by the fθ lens 6 and is incident on the processing object 10 held by the XY stage 7. The fθ lens 6 forms an image of the beam transmission hole of the mask 3 on the surface of the processing target object 20.

When the polarization direction of the pulsed laser beam is swung by the electro-optical element 2, the intensity ratio of the P component and the S component changes. This makes it possible to change the pulse energy of the pulse laser beam incident on the processing target 20. That is, the polarizing plate 4 functions as an attenuator capable of changing the attenuation rate depending on the polarization direction of the incident pulsed laser beam.

A laser processing method according to an embodiment of the present invention will be described with reference to FIG. Note that FIG. 1 is referred to when necessary. FIG. 2A shows a cross-sectional view of the printed wiring board which is the processing target 20. The inner layer wiring 31 made of copper is formed on the surface of the support substrate 30 made of glass epoxy. Support substrate 3 so as to cover inner layer wiring 31
An insulating layer 32 made of polyimide is formed on the surface of the insulating film 0. An upper layer 33 made of copper is formed on the surface of the insulating layer 32. For example, consider a case where the insulating layer 32 has a thickness of 25 μm and the upper layer 33 has a thickness of 12 μm, and a hole having a diameter of 75 μm is formed in these two layers.

First, the electro-optical element 2 is arranged so that the pulsed laser beam that has passed through the electro-optical element 2 has all S components.
To control. At this time, almost all components of the pulsed laser beam emitted from the laser light source 1 enter the object to be processed 20. The laser light source 1 is operated at the pulse frequency at which the pulse energy density on the surface of the processing target 20 becomes 20 J / cm ² . For example, the pulse frequency is 3 kHz,
The output is 6W. A pulse laser beam is incident on the upper layer 33, and a hole 34 penetrating the upper layer 33 in about 10 shots.
Is formed.

The electro-optical element 2 is controlled so that the pulse energy density on the surface of the workpiece 20 is ² J / cm ² without changing the pulse frequency of the laser light source 1. More specifically, the electro-optical element 2 is controlled so that the intensity of the S component of the pulse laser beam that has passed through the electro-optical element 2 is 10% of the intensity of the pulse laser beam emitted from the laser light source 1.

As shown in FIG. 2B, the hole 3 penetrating the insulating layer 32 exposed on the bottom surface of the hole 34 in about 30 shots.
5 is formed. The pulse energy density at this time is 2J
/ Cm ² , the inner layer wiring 31 exposed on the bottom surface of the hole 35 is hardly damaged.

Since the response characteristic of the electro-optical element 2 is on the order of MHz and the pulse frequency of the pulsed laser beam is on the order of kHz, the pulse energy reaching the object to be processed 20 can be switched in pulse units.

In the above embodiment, the pulse frequency of the laser light source does not change during the drilling process. Therefore, the quality of the pulsed laser beam is stable, and high-quality holes can be formed. Further, by adjusting the output characteristic at the pulse frequency to be used, it is possible to perform processing using only the pulse frequency whose output characteristic is adjusted in advance. This makes it possible to perform processing that does not depend on variations in output characteristics between laser oscillators.

In the above embodiment, the inner layer wiring 31, the insulating layer 3
2, and a hole was formed in the processing target object 20 in which the upper layer 33 was laminated in this order. More generally, at least the first
Layer, the second layer and the third layer are laminated in this order, and the second layer is more easily etched by the laser beam than the materials of the first layer and the third layer. Holes can be formed through the third and second layers of the workpiece formed of the material. At this time, the first layer exposed on the bottom surface of the hole is hardly damaged.

The present invention has been described above with reference to the embodiments.
The present invention is not limited to these. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0023]

As described above, according to the present invention,
By controlling the amount of attenuation of the pulsed laser beam, it is possible to perform drilling on a plurality of layers of different materials with pulse energy suitable for the material of each layer. Since it is not necessary to change the pulse frequency, the quality of the pulsed laser beam is stable and high quality holes can be formed.

[Brief description of drawings]

FIG. 1 is a schematic view of a laser processing apparatus according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of an object to be processed and a processed object to be processed by the laser processing method according to the embodiment of the present invention.

[Explanation of symbols]

1 laser light source 2 Electro-optical element 3 masks 4 Polarizer 5 galvano scanner 6 fθ lens 7 XY stage 8 damper 10 Control device 20 Object to be processed 30 support substrate 31 Inner layer wiring 32 insulating layer 33 Upper layer 34, 35 holes

Claims (3)

[Claims] 1. A laser light source that emits a linearly polarized pulse laser beam, and a polarized light that is incident with the pulse laser beam emitted from the laser light source and that can change the polarization direction of the pulse laser beam by external control. A direction control element, an attenuation element that attenuates the intensity of a pulse laser beam whose polarization direction is controlled by the polarization direction control element depending on the polarization direction, a holding unit that holds a workpiece, and an attenuation element that attenuates the attenuation element. And a condenser lens for condensing the pulsed laser beam thus generated onto the object to be processed held by the holding means. 2. The attenuating element is a polarizing plate arranged obliquely with respect to a traveling direction of the pulse laser beam whose polarization direction is controlled, and the pulse laser beam reflected by the polarizing plate and the polarizing plate. The laser processing apparatus according to claim 1, wherein one of the pulsed laser beams that has passed through the laser beam is focused on the processing target held by the holding means by the condenser lens. 3. At least a first layer, a second layer and a third layer.
A workpiece having a laminated structure in which the layers are laminated in this order, and the second layer is formed of a material that is more easily etched by a laser beam than the materials of the first layer and the third layer. And a linearly polarized pulsed laser beam is made incident on an attenuating element whose attenuation amount changes depending on the polarization direction, and the attenuated pulsed laser beam is made incident on the third layer of the object to be processed. A step of forming a hole penetrating the third layer, the polarization direction of the pulse laser beam incident on the attenuation element is changed to increase the attenuation amount of the pulse laser beam, and the attenuated pulse laser beam is The second layer on the bottom surface of the hole formed in the third layer of the processing object is made to enter the second layer.
Forming a hole that penetrates through the layer and exposes a part of the first layer.