JP2004074253A - Laser beam machining method and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser beam machining method and device that reduce damage to an inner layer copper foil and that enable highly reliable via hole to be machined. <P>SOLUTION: The amount of energy required for completing machining of a workpiece from its arbitrary machined state is preliminarily determined, collected in a data table and stored in a storage section 23. At the time of machining, a machined state of the workpiece 14 is determined from the intensity of a beam 15 reflected on the machining zone, so that the energy of a laser beam 3 to be emitted next is controlled by referring to the data table. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laser processing method and a laser processing apparatus for processing or cutting holes using laser light, and more particularly to a laser processing method and a laser processing apparatus suitable for processing a via hole in a printed wiring board.
[0002]
[Prior art]
Hereinafter, a conventional laser processing apparatus will be described.
[0003]
Along with the downsizing and high-density mounting of electronic devices, multilayer wiring boards in which a plurality of boards are stacked as a printed wiring board have become mainstream. In a multilayer wiring board, it is necessary to electrically connect conductive layers between substrates stacked one above the other. Therefore, a via hole (hole) reaching the lower conductive layer is formed in the insulating layer of the multilayer wiring board, and conductive plating is applied to the inside of the via hole to electrically connect the conductive layers between the substrates stacked vertically. doing.
[0004]
For the formation of the via hole, a high-power CO2 laser or a UV laser using a harmonic of YAG is used with the miniaturization of the via hole. Further, high-speed processing is realized by scanning a laser beam using a beam scanning optical system in which a galvanometer mirror and an fθ lens are combined. Furthermore, in order to select the hole diameter to be processed, an aperture is used as a mask, a transfer optical system is used to transfer the aperture image onto the substrate using an imaging lens, and a plurality of laser beams are emitted to one via hole. By irradiating in divided times, the shape accuracy of the via hole is improved.
[0005]
By the way, even if it is one printed wiring board, the thickness of an insulating layer varies with places. Furthermore, when the glass cloth is contained in the insulating layer, the glass cloth is sparse and dense. Therefore, in general, the energy of the laser beam is set to the most necessary size, and the via hole is reliably formed.
[0006]
However, when processing is completed with energy lower than the input energy, the energy is excessive and the target conductor layer (hereinafter referred to as “inner layer copper foil”) may be damaged.
[0007]
Therefore, in Japanese Patent Application Laid-Open No. 2000-202668, the peak power of the laser light is gradually reduced by changing the frequency of the Q switch oscillation using a laser capable of Q switch oscillation and reducing the peak power and pulse energy of the Q switch. To make it smaller.
[0008]
In Japanese Patent No. 3011183, a means for detecting the intensity of the laser beam reflected by the substrate is provided, and the number of times of laser irradiation is controlled by judging the processing state from the difference in the amount of reflected light between the resin layer of the substrate and the inner layer copper foil. I am doing so.
[0009]
[Problems to be solved by the invention]
FIG. 9 is a diagram schematically showing a so-called glass-containing substrate, in which (a) is a plan view, (b) is a cross-sectional view taken along line AA in (a), and (c) is a cross-sectional view taken along line BB in (a). FIG. The insulating layer of the substrate is composed of a resin 55 and glass fibers 56 woven in a lattice shape, and the surface to the inner layer copper foil 54 are filled with the resin 55 alone as in the first hole position 57. Some places, like the second hole positions 58, are places where the glass fibers 56 are dense.
[0010]
By the way, in order to process the glass fiber 56, the energy of several hundred times is required compared with the case where the resin 55 is processed. For this reason, there are cases where the desired processing cannot be performed even if the processing is repeated under the same conditions as in the former case of the prior art. On the other hand, although the latter of the prior art controls the number of times of laser irradiation, since the energy to be irradiated is determined in advance, depending on the amount of resin remaining in the processed part, the energy is excessively supplied and damages the inner layer copper foil There is a case.
[0011]
The objective of this invention is providing the laser processing method and laser processing apparatus which can process the above-mentioned subject, can reduce the damage of an inner layer copper foil, and can process a highly reliable via hole. .
[0012]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the first means of the present invention is necessary for completing the processing from an arbitrary processing state of the processing object in the laser processing method for processing by irradiating pulsed laser light. The present invention is characterized in that a predetermined energy is obtained in advance, the current machining state is monitored at the time of machining, and the energy of the laser beam to be irradiated next is controlled according to the obtained result.
[0013]
The second means of the present invention comprises means for controlling the energy of the laser light output from the laser oscillator, and light detection means for detecting the intensity of the light, and the workpiece is processed by the light detection means. In a laser processing apparatus that performs processing while detecting the intensity of the reflected light reflected at, processing data storage means is provided, and this storage means is necessary from the arbitrary processing state of the processing object to completion of the processing In this case, the energy of the laser beam to be irradiated next is controlled in accordance with the intensity of the reflected light detected by the light detection means during processing.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described based on the illustrated embodiments. FIG. 1 is a configuration diagram of a laser processing apparatus according to the present invention.
[0015]
First, the optical path of laser light will be described.
[0016]
On the optical path of the laser oscillator 2, a pulse width adjuster 100, a zoom unit 7, a mask 5, a beam splitter 8, a biaxial scanner 11, an fθ lens 12, and a substrate 14 are arranged.
[0017]
The laser oscillator 2 emits a laser beam 3 having a substantially constant peak energy based on a command from the processing machine control unit 1. The pulse width adjuster 100 controls the pulse width of the laser light 3 based on a command from the processing machine control unit 1. The drive mechanism 6 operates the zoom unit 7 based on a command from the processing machine control unit 1 to control the beam diameter of the incident laser light 3. The mask 5 is formed with a plurality of apertures 5a. The mask switching drive mechanism 4 arranges a desired aperture 5 a on the optical path of the laser beam 3 based on a command from the processing machine control unit 1.
[0018]
The beam splitter 8 is disposed at 45 degrees with respect to the optical path of the laser light 3, reflects most of the laser light 3 as the processing beam 9, and transmits (goes straight) the remaining laser light 3 as the monitor beam 10. On the optical path of the monitor beam 10, a light attenuating means 21, a condensing lens 19, and a photodetector 17 are arranged.
[0019]
Further, on the extended line of the processing beam 9 on the back side of the beam splitter 8 (on the monitor beam 10 side), a light attenuating means 20, a condensing lens 18, and a photodetector 16 are arranged.
[0020]
The biaxial scanner 11 includes galvanometer mirrors 25 and 26, and controls the rotation angle of the galvanometer mirrors 25 and 26 based on a command from the processing machine control unit 1. The XY stage 13 places the multilayer wiring board 14, and positions the multilayer wiring board 14 with respect to the fθ lens 12 based on a command from the processing machine control unit 1.
[0021]
The photodetectors 16 and 17 output the detection result to the machining state diagnosis unit 22. The machining state diagnosis unit 22 outputs the diagnosis result to the processing machine control unit 1. The processing machine control unit 1 is connected to a storage unit 23 that stores a data table, which will be described later, and stores a diagnosis result output from the processing state diagnosis unit 22, and a display unit 24 that displays the processing state.
[0022]
Next, the data table stored in the storage unit 23 will be described.
[0023]
FIG. 3 is a diagram showing the relationship between the hole bottom area S on the surface of the inner layer copper foil 54 and the intensity R of the reflected beam 15 (which is a part of the processed beam 9 reflected by the multilayer wiring board 14). (A) The upper stage is a plan view of the hole, the lower stage is a sectional view of the hole, and (b) shows the relationship between the hole bottom area S and the intensity R of the reflected beam 15.
[0024]
As shown in FIG. 5B, the intensity R of the reflected beam 15 increases almost in proportion to the hole bottom area S. Therefore, the hole bottom area S can be estimated from the intensity R of the reflected beam 15. Further, after the hole bottom is exposed, the amount of resin to be processed is small, so that the energy supplied to the processed portion may be less than the energy set initially. Therefore, the test is performed in advance by changing the processing conditions for each material of the substrate and the hole diameter to be processed, and the relationship between the intensity R of the reflected beam 15, that is, the processing state of the processing portion and the hole bottom area S is grasped. Then, the energy required until the processing is completed is obtained from each processing state, and the energy (in this case, the pulse width) of the laser beam irradiated in the next shot is determined for each arbitrary processing state. Then, the result is stored in the storage unit 23 as a data table.
[0025]
FIG. 4 is a diagram showing an example of an irradiation pattern of laser light in the present invention. FIG. 4A shows a pulse of laser light to be irradiated next when the intensity R of the reflected beam 15 is R2 or less shown in FIG. In this example, the width is t, the pulse width is 0.5 t when the intensity R of the reflected beam 15 exceeds R2 and is equal to or less than R4, and the pulse width is 0.1 t when the intensity R of the reflected beam 15 exceeds R4. is there. If the pulse width of the laser beam is t, the hole can be surely processed even in the second hole position 58 in FIG. 9 where the glass fiber 56 is dense.
[0026]
FIG. 4B shows that the pulse width is t when the intensity R of the reflected beam 15 is R1 or less, and the pulse width is 0.75 t when the intensity R of the reflected beam 15 is more than R1 and less than R2, and the reflected beam 15 When the intensity R of the reflected beam 15 is greater than R2 and less than or equal to R3, the pulse width is 0.5 t. When the intensity R of the reflected beam 15 is greater than R3 and less than or equal to R4, the pulse width is 0.25 t, and the intensity R of the reflected beam 15 is R4. In the case of exceeding, the pulse width is 0.1t.
[0027]
FIG. 5C shows an example in which the pulse width is t when the intensity R of the reflected beam 15 is R4 or less, and the pulse width is 0.1 t when the intensity R of the reflected beam 15 exceeds R4.
[0028]
Note that the laser light irradiation pattern may be set according to the material of the substrate, the hole diameter to be processed, and the like.
[0029]
In the above description, the energy of the laser light to be irradiated next is set to 100% or less of the first energy, but may be a value exceeding 100%.
[0030]
Next, the pattern shown in FIG. 4A is adopted as the irradiation pattern, and the case of processing the hole with three shots (that is, by irradiating the laser beam 3 three times) is shown in FIG. A case where the substrate is processed will be described.
[0031]
FIG. 5 and FIG. 6 are diagrams showing the relationship between the intensity and the processing shape of the monitor beam 10 and the reflected beam 15 when processing the first hole position 57 and the second hole position 58 in FIG. a) shows the intensity of the monitor beam (output signal of the photodetector 17) and the intensity of the reflected beam (output signal of the photodetector 16), and (b) shows the cross-sectional shape of the processed portion.
[0032]
In the case of the first hole position 58 shown in FIG. 5, since the glass fibers 56 are dense, the internal copper foil 54 finally begins to be exposed by the laser light of the third shot, and the exposed area is substantially processed after the middle stage of the pulse. Equal to 9 diameters. As the hole bottom area does not change, the intensity signal of the reflected beam 15 becomes constant beyond the reference 2 (R4). In this state, it can be determined that the processing has been completed.
[0033]
On the other hand, in the case of the second hole position 57 without the glass fiber 56 shown in FIG. 6, a hole reaching the internal copper foil 54 is formed by the first shot of laser light, and the internal copper foil 54 begins to be exposed, and the reflected beam Since the intensity of 15 exceeds the reference 1 (R2), the pulse width of the laser light for the second shot is set to 0.5 t. From the middle stage of the second shot, the hole bottom area S of the internal copper foil 54 becomes substantially equal to the diameter of the machining beam 9, and the hole bottom area does not change. Is constant. In this state, it can be determined that the processing is completed, but here, the pulse width of the third shot is controlled to 0.1 t, and extremely weak energy that does not damage the inner layer copper foil 54 is irradiated. In this way, the insulator remaining at the hole bottom can be reliably removed.
[0034]
As described above, in the present invention, since only the energy required for processing is supplied to the processing portion, it is possible to prevent the inner layer copper foil 54 from being damaged.
[0035]
Next, the operation of this embodiment will be described.
[0036]
FIG. 2 is a flowchart showing a processing procedure when processing one via hole according to the present invention.
[0037]
Prior to processing, processing conditions are input to the processing machine control unit 1 in advance. As the processing conditions, the type of the substrate, the diameter of the hole to be processed, the pulse width and pulse interval of the laser beam, the peak energy, the number of times of irradiation, etc. are input.
[0038]
When the machining start button (not shown) is turned on, the processing machine control unit 1 sets the number of irradiations n1 to 0 (S10), then performs the n1th irradiation (S20), and sets the number of irradiations n1 to n1 + 1 (S30). ). The laser beam 3 emitted from the laser oscillator 2 is shaped into a predetermined diameter by the zoom unit 7 and then enters the mask 5. Most of the laser light 3 transmitted through the aperture 5a is reflected by the beam splitter 8, and enters the processing portion of the substrate 14 defined by the biaxial scanner 11 and the fθ lens 12 as the processing beam 9, and processes the portion. .
[0039]
The reflected beam 15 enters the beam splitter 8 via the fθ lens 12 and the biaxial scanner 11. Then, the reflected beam 15 transmitted through the beam splitter 8 is attenuated in energy by the light attenuating means 20, enters the condenser lens 18, and is collected at the center of the photodetector 16.
[0040]
The photodetector 16 outputs the detected light amount of the reflected beam 15 to the machining state diagnosis unit 22. The machining state diagnosing unit 22 evaluates the current machining state by comparing the output signal of the photodetector 16 with an evaluation criterion inputted in advance, and outputs the result to the machine control unit 1. The processing machine control unit 1 refers to the data table in the storage unit 23 based on the result output from the processing state diagnosis unit 22, selects an appropriate pulse width, and outputs the value to the pulse width adjuster 100. . Further, the result obtained by the machining state diagnosis unit 22 is integrated with information on the machining position and the number of laser shots and stored in the storage unit 23 and displayed on the display unit 24. The data stored in the storage unit 23 is used for subsequent processes such as processing and inspection.
[0041]
Since the intensity of the monitor beam 10 is proportional to the intensity of the laser beam 3, the intensity of the monitor beam 10 that has passed through the beam splitter 8 is evaluated by the processing state diagnostic unit 22 as in the case of the reflected beam 15 (S40). ). If the intensity of the monitor beam 10 satisfies the evaluation criteria input in advance, the process of S50 is performed, and otherwise the process of S80 is performed. In S50, the intensity of the reflected beam 15 is compared with an evaluation criterion inputted in advance. If the intensity of the reflected beam 15 satisfies the evaluation criterion, the processing of this hole is finished, and in other cases, the processing of S60 is performed. Do.
[0042]
In S60, the number of times of irradiation n1 and n are compared. If n1 <n, the process of S70 is performed, and if n1 = n, the process of S80 is performed.
[0043]
In S70, referring to the data table based on the intensity of the reflected beam 15, the pulse width of the laser light irradiated for the (n1 + 1) th time is set. In S80, the machining position is stored as a machining defect location, a machining error is displayed (S90), and the process ends.
[0044]
As described above, the processing threshold (in the required energy) varies by obtaining the processing energy necessary for completing the processing in advance and preventing the laser beam from being excessively irradiated. But high quality processing is possible.
[0045]
In the above, the processing state is evaluated every time the laser beam is irradiated, and when it is evaluated that the processing is completed, the processing is ended even if the number of irradiation is less than the set number of times. As shown in FIG. 7, the processing state may be evaluated after the steps S50 and S60 are interchanged and the laser beam is irradiated a predetermined number of times.
[0046]
Note that the measurement result of the monitor beam 10 may be stored in the storage unit 23.
[0047]
In the above description, a CO ₂ laser is used as a laser source. However, a Q-switched laser can be used as a laser source.
[0048]
FIG. 8 is an explanatory diagram of another energy control method according to the present invention.
[0049]
In the case of a Q switch laser, the relationship between the oscillation frequency f and the peak power is such that the peak power decreases as the oscillation frequency f increases, as shown in FIG. Therefore, when the processing state is monitored, for example, when the energy of the laser beam to be irradiated next can be reduced, the laser beam irradiated to the processing portion by increasing the oscillation frequency as shown in FIG. If the energy of is reduced, the energy supplied to the processing portion can be controlled as in the case of the CO ₂ laser.
[0050]
【The invention's effect】
As described above, according to the present invention, the prescribed number of times of laser beam irradiation is determined in advance, the bottom state of the hole is monitored during processing, and the processing energy to be irradiated next is controlled according to the bottom state of the hole. High quality holes can be machined even on substrates with varying processing thresholds.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a laser processing apparatus according to the present invention.
FIG. 2 is a flowchart showing a processing procedure of the present invention.
FIG. 3 is a diagram showing the relationship between the hole bottom area on the surface of the inner layer copper foil and the intensity of the reflected beam.
FIG. 4 is a diagram showing an example of an irradiation pattern of laser light in the present invention.
FIG. 5 is a diagram showing a relationship between intensity signals of a monitor beam and a reflected beam and a machining shape.
FIG. 6 is a diagram showing a relationship between intensity signals of a monitor beam and a reflected beam and a machining shape.
FIG. 7 is another flowchart showing the processing procedure of the present invention.
FIG. 8 is an explanatory diagram of another energy control method according to the present invention.
FIG. 9 is a diagram schematically showing a so-called glass-containing substrate.
[Explanation of symbols]
3 Laser beam 14 Object 15 Reflected beam 23 Storage unit

Claims (4)

In a laser processing method for processing by irradiating pulsed laser light,
Obtain in advance the energy required to complete the processing from any processing state of the processing object,
A laser processing method characterized by monitoring a current processing state at the time of processing and controlling energy of laser light to be irradiated next according to the obtained result. 2. The laser processing method according to claim 1, wherein when the obtained result matches a predetermined result, the processing is terminated. A means for controlling the energy of the laser light output from the laser oscillator; and a light detecting means for detecting the intensity of the light. The light detecting means detects the intensity of the reflected light reflected from the workpiece. In laser processing equipment that performs processing while
A storage unit for processing data is provided, and energy necessary for the processing to be completed from an arbitrary processing state of the processing object is stored in the storage unit,
A laser processing apparatus for controlling the energy of laser light to be irradiated next in accordance with the intensity of reflected light detected by the light detection means during processing. 4. The laser processing apparatus according to claim 3, wherein the laser oscillator is a laser oscillator capable of Q-switch oscillation, and the energy of the laser beam is controlled by controlling an oscillation frequency of the Q switch.

Images