JP3667705B2 - Laser processing apparatus and processing method - Google Patents

Description

[0001]
BACKGROUND 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 pulse laser beam incident on a processing target.
[0002]
[Prior art]
A laser beam is incident on a printed wiring board having an inner layer wiring, a resin layer, and an upper layer film formed on the surface of the support substrate to form a hole that penetrates the upper layer film and the resin layer and exposes part of the inner layer wiring. be able to. The inner layer wiring and the upper layer film are usually made 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 pulse laser beam in the ultraviolet region with a wavelength of 351 nm, 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. The pulse energy is about ² J / cm ² .
[0003]
When the hole is formed in the upper layer film, the pulse energy of the laser beam is set to 20 J / cm ² or more. When a hole penetrating the upper layer film is formed, the pulse energy is reduced to about ² J / cm ² and the resin layer is processed. Since the inner layer wiring is not etched with a pulse energy of ² J / cm ² , a hole penetrating the resin layer can be formed without damaging the inner layer wiring.
[0004]
[Problems to be solved by the invention]
Adjustment of the pulse energy of the solid-state laser is usually performed by changing the pulse frequency. For example, when the pulse frequency is increased, the pulse energy decreases. Therefore, when a hole penetrating the upper layer film is formed, the pulse frequency is increased and the resin layer is processed. However, when the pulse frequency is changed, the quality of the laser beam, for example, the stability of the pulse energy, the divergence angle, the beam profile, and the like also change.
[0005]
In general, the output of the solid-state laser oscillator is adjusted at a specific pulse frequency. Therefore, the output at a pulse frequency other than the adjusted pulse frequency of the output varies between laser oscillators. For example, when the output is adjusted at the pulse frequency when forming the upper layer film, the output when forming the resin layer varies between apparatuses.
[0006]
An object of the present invention is to provide a laser processing apparatus and a processing method capable of drilling a plurality of layers of different materials without changing the pulse frequency.
[0007]
[Means for Solving the Problems]
According to one aspect of the present invention, a laser light source that emits a linearly polarized pulsed laser beam, a pulsed laser beam emitted from the laser light source is incident, and the polarization direction of the pulsed laser beam is changed by external control. Polarization direction control element capable of absorbing, attenuating element for attenuating the intensity of the pulsed laser beam whose polarization direction is controlled by the polarization direction controlling element depending on the polarization direction, and the attenuating element for attenuating the intensity of the pulsed laser beam As described above, the driver for controlling the polarization direction control element, the holding means for holding the object to be processed, and the pulse laser beam attenuated by the attenuation element are condensed on the object to be processed held by the holding means. A laser processing apparatus having a condensing lens to be provided is provided.
[0008]
According to another aspect of the present invention, at least the first layer, the second layer, and the third layer have a stacked structure in which the layers are stacked in this order, and the second layer includes the first layer and the third layer. Prepare a workpiece formed of a material that is easier to etch with a laser beam than the material of the layer of the laser beam, and enter a linearly polarized pulsed laser beam into an attenuation element whose attenuation changes depending on the polarization direction And a step of causing the attenuated pulsed laser beam to enter the third layer of the workpiece, forming a hole penetrating the third layer, and a polarization direction of the pulsed laser beam incident on the attenuation element And the attenuation amount of the pulse laser beam is increased to cause the attenuated pulse laser beam to enter the second layer on the bottom surface of the hole formed in the third layer of the workpiece, Penetrates the layer and exposes a portion of the first layer. Laser processing method and a step of forming a hole is provided.
[0009]
By adjusting the attenuation amount of the pulse laser beam, the pulse energy density of the laser beam on the surface of the workpiece can be changed without changing the output of the laser light source. Thereby, it can process with the laser beam which has a pulse energy density suitable for the material which should form a hole.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic view of a laser processing apparatus according to an embodiment of the present invention. The laser light source 1 emits a pulse laser beam for processing. The laser light source 1 includes a solid-state laser using a solid dielectric containing ions as a laser medium and a wavelength conversion element, and an emitted pulse laser beam is a third-harmonic wave that is linearly polarized. When Nd: YAG is used as the laser medium, the wavelength of the third harmonic is 351 nm. In addition to Nd: YAG, Nd: YLF or Nd: YVO ₄ may be used as the laser medium. As the wavelength conversion element, BBO or KDP optical crystal can be used. It is also possible to use harmonics in the ultraviolet region other than the third harmonic.
[0011]
A laser beam emitted from the laser light source 1 enters the electro-optical element 2. The electro-optic element 2 is applied with a voltage from the driver 9 and rotates the polarization direction of the incident laser beam. The swivel angle depends on the applied voltage. The laser light source 1 and the driver 9 are controlled by the control device 10.
[0012]
The pulse laser beam that has passed through the electro-optic element 2 enters the mask 3. The laser beam that has passed through the beam transmission hole provided in the mask 3 enters the polarizing plate 4. The polarizing plate 4 is arranged so that the incident angle of the incident laser beam is 45 °, transmits a polarized component (P component) parallel to the incident surface, and is polarized perpendicular to the incident surface (S component). To reflect. The P component pulse laser beam transmitted through the polarizing plate 4 enters the damper 8.
[0013]
The S component pulse 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 the laser beam in a two-dimensional direction. The laser beam scanned by the galvano scanner 5 is focused by the fθ lens 6 and enters the workpiece 10 held on the XY stage 7. The fθ lens 6 images the beam transmission hole of the mask 3 on the surface of the workpiece 20.
[0014]
When the polarization direction of the pulse laser beam is rotated by the electro-optical element 2, the intensity ratio between the P component and the S component changes. Thereby, the pulse energy of the pulse laser beam incident on the workpiece 20 can be changed. That is, the polarizing plate 4 functions as an attenuator that can change the attenuation rate depending on the polarization direction of the incident pulse laser beam.
[0015]
A laser processing method according to an embodiment of the present invention will be described with reference to FIG. In addition, FIG. 1 is referred as needed.
FIG. 2A shows a cross-sectional view of a printed wiring board that is the workpiece 20. An inner layer wiring 31 made of copper is formed on the surface of the support substrate 30 made of glass epoxy. An insulating layer 32 made of polyimide is formed on the support substrate 30 so as to cover the inner layer wiring 31. An upper layer 33 made of copper is formed on the surface of the insulating layer 32. For example, consider the case where the thickness of the insulating layer 32 is 25 μm, the thickness of the upper layer 33 is 12 μm, and a hole having a diameter of 75 μm is formed in these two layers.
[0016]
First, the electro-optical element 2 is controlled so that the pulse laser beam that has passed through the electro-optical element 2 becomes an S component. At this time, almost all components of the pulse laser beam emitted from the laser light source 1 enter the workpiece 20. The laser light source 1 is operated at a pulse frequency at which the pulse energy density on the surface of the workpiece 20 is 20 J / cm ² . For example, the pulse frequency is 3 kHz and the output is 6 W. The pulse laser beam is incident on the upper layer 33, and a hole 34 penetrating the upper layer 33 is formed in about 10 shots.
[0017]
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-optic element 2 is controlled so that the intensity of the S component of the pulse laser beam that has passed through the electro-optic element 2 becomes 10% of the intensity of the pulse laser beam emitted from the laser light source 1.
[0018]
As shown in FIG. 2B, a hole 35 penetrating the insulating layer 32 exposed on the bottom surface of the hole 34 is formed in about 30 shots. Since the pulse energy density at this time is ² J / cm ² , the inner layer wiring 31 exposed on the bottom surface of the hole 35 is hardly damaged.
[0019]
Since the response characteristics of the electro-optic element 2 are on the order of MHz and the pulse frequency of the pulse laser beam is on the order of kHz, the pulse energy that reaches the workpiece 20 can be switched in units of pulses.
[0020]
In the above embodiment, the pulse frequency of the laser light source does not change during the drilling process. For this reason, the quality of the pulse laser beam is stabilized, and a high-quality hole can be formed. Further, by adjusting the output characteristics at the pulse frequency to be used, it is possible to perform processing using only the pulse frequency whose output characteristics have been adjusted in advance. This makes it possible to perform processing that does not depend on variations in output characteristics between laser oscillators.
[0021]
In the said Example, the hole was formed in the workpiece 20 by which the inner layer wiring 31, the insulating layer 32, and the upper layer 33 were laminated | stacked in this order. More generally, at least the first layer, the second layer, and the third layer have a stacked structure in which the layers are stacked in this order, and the second layer includes the first layer and the third layer. A hole penetrating the third layer and the second layer of the workpiece formed of a material that is more easily etched by a laser beam than the material can be formed. At this time, the first layer exposed on the bottom surface of the hole is hardly damaged.
[0022]
Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.
[0023]
【The invention's effect】
As described above, according to the present invention, by controlling the attenuation amount of the pulse laser beam, it is possible to perform drilling in a plurality of layers having different materials with pulse energy suitable for the material of each layer. Since there is no need to change the pulse frequency, the quality of the pulse laser beam is stabilized, and a high-quality hole can be formed.
[Brief description of the 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]
DESCRIPTION OF SYMBOLS 1 Laser light source 2 Electro-optical element 3 Mask 4 Polarizing plate 5 Galvano scanner 6 f (theta) lens 7 XY stage 8 Damper 10 Control apparatus 20 Process target 30 Support substrate 31 Inner layer wiring 32 Insulating layer 33 Upper layers 34, 35 Hole

Claims (3)

A laser light source that emits a linearly polarized pulsed laser beam;
A polarization direction control element that receives a pulse laser beam emitted from the laser light source and can change a polarization direction of the pulse laser beam by external control;
An attenuation 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;
A driver for controlling the polarization direction control element so that the attenuation element attenuates the intensity of the pulsed laser beam;
Holding means for holding the workpiece;
A laser processing apparatus comprising: a condensing lens that condenses the pulsed laser beam attenuated by the attenuating element onto the object to be processed held by the holding means.   The attenuating element is a polarizing plate disposed obliquely with respect to the traveling direction of the pulse laser beam whose polarization direction is controlled, and the pulse laser beam reflected by the polarizing plate and the pulse laser transmitted through the polarizing plate The laser processing apparatus according to claim 1, wherein one of the beams is condensed on the object to be processed held by the holding unit by the condenser lens. At least the first layer, the second layer, and the third layer have a stacked structure in which the layers are stacked in this order, and the second layer is irradiated with a laser beam more than the material of the first layer and the third layer. Preparing a workpiece formed of a material that is easily etched;
The linearly polarized pulsed laser beam is incident on an attenuating element whose amount of attenuation varies depending on the polarization direction, and the attenuated pulsed laser beam is incident on the third layer of the workpiece, Forming a hole penetrating through the layer;
The amount of attenuation of the pulse laser beam is increased by changing the polarization direction of the pulse laser beam incident on the attenuation element, and the attenuated pulse laser beam is applied to the bottom surface of the hole formed in the third layer of the workpiece. Forming a hole that is incident on the second layer, penetrates the second layer, and exposes a part of the first layer.

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