Laser processing method and laser processing apparatus

Abstract

The present invention addresses the problem of providing a laser processing method in which a through-hole without welding residue can be formed in a low-dielectric tangent ceramic substrate only by a laser processing step using a carbon dioxide laser. The solution of the present invention is a laser processing method for forming a through-hole using a laser processing device provided with: an oscillator that oscillates a carbon dioxide laser pulse; a modulator that further modulates the laser pulse oscillated from the oscillator into a processing laser pulse having a predetermined pulse energy; a condenser lens that condenses the processing laser pulse on a workpiece; a table on which the workpiece is placed; a beam diameter adjustment optical system for adjusting a beam diameter at a processing point of the processing laser pulse; and an overall control unit for controlling the overall operation of the device, the workpiece being a low-temperature sintered glass ceramic substrate, and the pulse energy of the laser pulse for processing being 6.7 mJ or more.

Description

Technical Field

[0001] The invention relates to a laser processing method and a laser processing device for forming a through hole in a ceramic substrate by using a carbon dioxide laser. Background Art

[0002] Conventionally, the materials used for semiconductor package substrates (interposers) and core layers of printed wiring boards have mainly been organic materials, and from the perspective of production efficiency, through holes for forming through electrodes have been mainly formed using laser processing equipment.

[0003] In recent years, in order to cope with the next generation communication speeds of 5G and 6G, research is being conducted on using materials with low dielectric tangent as substrates and other materials to improve frequency characteristics, and sintered low dielectric tangent ceramics are candidates. However, it is known that if a through hole is formed in a sintered ceramic by a laser processing device, molten residue will adhere to its inner wall. Then, if the molten residue adheres to the inner wall of the through hole, there is a problem that it is difficult to form electroplating for making the through hole conductor. In addition, the generation of molten residue when forming a through hole in laser processing is a phenomenon that occurs to the entire sintered ceramic substrate.

[0004] Therefore, as described in Patent Document 1, for example, a method has been proposed in which an alumina ceramic substrate, which is generally known as a ceramic with a low dielectric tangent, is laser processed in a chamber in an inert gas environment containing hydrogen chloride gas, and then a removal liquid such as a sodium hydroxide solution is used to remove the molten residue on the inner wall of the through hole.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2013-180938 Summary of the invention

[0008] Problems to be solved by the invention

[0009] However, in the method described in Patent Document 1, since another process for removing the molten residue on the inner wall is required after the drilling process using laser, the production efficiency is reduced. Therefore, a method for forming a through hole without molten residue only by a laser processing process is desired. In addition, it is known that if a laser with a wavelength region of UV is used, a through hole without molten residue on the inner wall of a ceramic substrate can be formed only by a laser processing process, but the through hole formation speed using UV laser is slow and the productivity is poor. In contrast, if a carbon dioxide laser can be used, high productivity can be expected because the through hole formation speed is fast.

[0010] Therefore, in order to solve the above problems, the present invention aims to find processing conditions that can form through holes without molten residue on the inner wall only by laser processing steps using carbon dioxide lasers, which were previously considered impossible, and types of ceramics with low dielectric tangent that can be processed.

[0011] Technical solutions to problems

[0012] In order to solve the above-mentioned problems, the inventors have conducted various studies and experiments and found that, for a low-temperature sintered ceramic substrate, which is a type of low dielectric tangent ceramic, it is possible to process it using a predetermined pulse energy without generating molten residue on the inner wall of the through hole, thereby completing the present invention.

[0013] That is, in order to solve the above-mentioned problems, the present invention is characterized by a laser processing method for forming a through hole using a laser processing device, wherein the laser processing device comprises: an oscillator, which oscillates carbon dioxide laser pulses; a modulator, which further modulates the laser pulses oscillated by the oscillator into processing laser pulses with a predetermined pulse energy; a focusing lens, which focuses the processing laser pulses on a workpiece; a workbench, which carries the workpiece; a beam diameter adjustment optical system, which is used to adjust the beam diameter at the processing point of the processing laser pulse; and an overall control unit, which controls the overall operation of the device, wherein the workpiece is a low-temperature sintered glass ceramic substrate, so that the pulse energy of the processing laser pulse is 6.7 mJ or more.

[0014] Effects of the Invention

[0015] According to the present invention, a through hole having no molten residue on the inner wall can be formed in a low-temperature sintered glass ceramic substrate, which is a type of ceramic substrate with a low dielectric tangent, only by a laser processing step using a carbon dioxide laser. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the overall structure of a laser processing device suitable for implementing the present invention;

[0017] Figure 2 is a photograph in lieu of a drawing showing a cross section of a through hole processed in an embodiment;

[0018] Figure 3 is a photograph in lieu of a drawing showing a cross section of a through hole processed in an embodiment;

[0019] Figure 4 is a photograph in lieu of a drawing showing a cross section of a through hole processed in an embodiment;

[0020] Figure 5 It is a drawing-substitute photograph which shows the cross section of the through hole processed in the comparative example.

[0021] Description of Reference Numerals

[0022] 1: Laser oscillator (carbon dioxide laser pulse oscillator)

[0023] 2: Acousto-optic modulator (AOM)

[0024] 3: Electrical deflection unit

[0025] 4: Condenser lens (fθ lens)

[0026] 5: Workpiece (low temperature sintered glass ceramic substrate)

[0027] 51: Melt residue

[0028] 6: Mobile workbench

[0029] 7: Damper

[0030] 11: Laser oscillation control unit

[0031] 12: AOM control unit

[0032] 13: Electric control unit

[0033] 14: Overall Control Department

[0034] 151: Melt residue DETAILED DESCRIPTION

[0035] Hereinafter, embodiments of the laser processing method of the present invention will be described with reference to the drawings. Figure 1 This is a schematic diagram of the overall structure of a laser processing device suitable for the implementation of the present invention. In addition, in the drawings, each component and connecting line mainly represents the part that is considered necessary for explaining this embodiment, and does not represent all the parts required as a laser processing device. The laser processing device includes: a laser oscillator 1, which oscillates a carbon dioxide laser pulse with a wavelength of 9.4μm; an acousto-optic modulator (AOM) 2, which modulates the laser pulse oscillated from the laser oscillator 1 in accordance with the processing conditions, and branches the laser with a predetermined pulse width and a predetermined pulse energy as a processing laser pulse to the optical axis for processing; an electrical deflection unit 3, which deflects the processing laser pulse branched by the AOM2 to the direction of the processing position on the low-temperature sintered ceramic substrate 5 (hereinafter, also referred to as "substrate 5") as the workpiece; a focusing lens (fθ lens) 4, which focuses the processing laser pulse deflected by the electrical deflection unit 3 on the substrate 5; and a damper 7, which absorbs non-processing laser light that is not branched by the AOM2. Furthermore, a movable stage 6 is provided on which the substrate 5 is mounted and fixed and can be moved in the X direction and the Y direction.

[0036] In addition, although not shown in the figure, a dust collecting mechanism is provided between the substrate 5 and the movable workbench 6. The dust collecting mechanism is composed of a top plate and a dust collecting base, wherein the top plate is provided with a hole (discharge hole) having a diameter larger than the processing diameter at the same position as the processing target position of the substrate 5, and the dust collecting base holds the top plate and has a dust collecting space inside. When the recess formed by laser irradiation penetrates the substrate 5, the molten material scatters upward, and scatters through the discharge hole of the top plate to the dust collecting space, and is discharged from the through hole.

[0037] Although not shown in the figure, a conduit is provided between the condenser lens 4 and the substrate 5, and the conduit attracts the molten scattered matter generated by the laser irradiation on the substrate 5. Although not shown in the figure, a beam diameter adjustment optical system such as an aperture and a lens for adjusting the beam diameter (beam waist) at the processing point is provided between the laser oscillator 1 and the AOM 2.

[0038] The low temperature sintered ceramic substrate 5 as the workpiece is also called LTCC (Low Temperature Co-fired Ceramics), which is made by sintering a green sheet of a ceramic material such as alumina to which a low melting point glass material is added. The sintering temperature is about 1000° or less, and is sintered at a lower temperature than alumina ceramics, which are generally known as a type of low dielectric tangent ceramics (the sintering temperature of alumina ceramics is about 1500°). In addition, since a low melting point glass material is added, the low temperature sintered ceramic substrate 5 has a lower melting point than the generally known alumina ceramics.

[0039] Return to Figure 1 The laser processing device further includes: a laser oscillation control unit 11, which controls the oscillation of the laser pulse performed by the laser oscillator 1; an AOM control unit 12, which controls the operation of the AOM 2; an electrical control unit 13, which controls the operation of the electrical deflection unit 3; and an overall control unit 14, which is used to control the operation of these control units and the device as a whole. In addition, the overall control unit 14 is realized by a processing device such as a program control, and has a storage unit for storing various information inside. The overall control unit 14 has a control function other than that described here, and is also connected to blocks not shown in the figure.

[0040] The processing method of the present invention is performed as follows using, for example, the above-mentioned laser processing device. A processing program indicating the processing position is input in advance into the overall control unit 14, and processing conditions such as the pulse width and pulse energy of the processing laser pulse are further input. In addition, the beam diameter adjustment optical system is adjusted so that the beam diameter at the processing point becomes the desired value, and the low-temperature sintered glass ceramic substrate 5 is placed on the movable workbench 6. In addition, as the processing pulse energy, it is pre-set to a value above 6.7mJ. Then, when the overall control unit 14 is instructed to start processing, the overall control unit 14 controls each part so that the processing device operates as follows. First, the electrical deflection unit 3 is operated so that the laser optical axis is located at the processing position indicated by the processing program. Then, the laser pulse is oscillated from the laser oscillator 1, and the laser pulse is incident on the AOM2. The AOM2 modulates the incident laser pulse to become the pulse width and pulse energy input as the processing conditions, and branches it toward the electrical deflection unit 3 as a processing laser pulse. In this way, the processing laser pulse incident on the electrical deflection unit 3 is deflected and is incident on the processing position of the substrate 5 via the condenser lens 4 .

[0041] When the laser is incident on the processing position of the substrate 5, the surface of the position is instantly melted, scattered, and evaporated due to the heat of the laser irradiation, and a concave portion is formed. Each time the processing laser pulse is repeatedly irradiated, the concave portion becomes deeper, and a through hole is formed by reaching the back side of the substrate 5 through the concave portion.

[0042] [Example]

[0043] The following is a description of a specific embodiment of the present invention. The inventor used the above-mentioned laser processing device to perform processing to form through holes on a low-temperature sintered ceramic substrate under the condition of changing the pulse energy of various processing laser pulses. Specifically, the processing was performed by changing the pulse energy of the processing laser pulse by 10% (0.95mJ) in the range of ±40% (5.7mJ~13.3mJ) based on 9.5mJ. In addition, the thickness of the low-temperature sintered ceramic substrate used for processing is 0.4mm. In addition, the pulse width of the processing laser pulse branched by AOM2 is set to 20μs, and the beam diameter (beam waist) at the processing point is set to 120μm.

[0044] In addition, in each embodiment, the formation is performed by so-called cyclic processing, which is to irradiate a plurality of predetermined processing positions with one pulse, then irradiate all processing positions with one pulse again, and repeat the processing until the substrate is penetrated. In each embodiment, the irradiation interval of the pulse laser to the same processing position is about 3s.

[0045] Then, the results of the investigation on whether or not there is molten residue on the inner wall of the through hole processed according to each embodiment are summarized in Table 1. Table 1 also records the energy density. Figure 2 to Figure 4 It is a photograph in lieu of a drawing showing a cross section of a through hole processed in each example.

[0046] [Table 1]

[0047]

[0048] As can be seen from Table 1, when the pulse energy is 5.7 mJ (Example 1), Figure 2 As shown in (A), molten residue 51 is observed on the inner wall of the through hole. On the other hand, when the pulse energy is 6.7 mJ or more (Examples 2 to 9), as shown in Figure 2 (B)~ Figure 4 As shown in (C), no molten residue was observed on the inner walls of all the through holes.

[0049] This is believed to be because when the pulse energy is 6.7 mJ or more, the surface at the laser irradiation point instantly reaches a high temperature and melts, and the viscosity is low and it quickly disperses, so there is no residual molten material on the inner wall. On the other hand, when it is 5.7 mJ, it is believed that even if the temperature at the irradiation point rises instantly, it will not reach a very high temperature. Although it will melt, it has a high viscosity and therefore cannot quickly disperse and remains on the inner wall.

[0050] In addition, when the surface of the recessed portion during the formation of the through hole (a state where a recessed portion is formed at the processing point but has not yet penetrated to the back side) is also observed, molten residues are observed on the surface of the recessed portion when the pulse energy is 5.7 mJ (Example 1), but no molten residues are observed when the pulse energy is 6.7 mJ or more (Examples 2 to 9). Therefore, it can also be said that in the case where the pulse energy is 6.7 mJ or more, a recessed portion without molten residues can be formed by laser pulse irradiation. Therefore, although a substrate with a thickness of 0.4 mm is processed in each embodiment, in the case where the pulse energy is 6.7 mJ or more, a through hole with no molten residues on the inner wall can be formed even for a substrate thicker than this. In other words, if the pulse energy is 6.7 mJ or more, not to mention a substrate with a thickness of less than 0.4 mm, a through hole with no molten residues on the inner wall can be formed even for a substrate thicker than this. Therefore, for example, even for a substrate (interposer) having a thickness of about 50 μm (0.05 mm) to 1500 μm (1.5 mm) which is generally assumed as a semiconductor package substrate, by setting the pulse energy to 6.7 mJ or more, a through hole without the adhesion of molten residue can be processed.

[0051] Furthermore, in any embodiment, the pulse width is set to 20μs, but the length of the pulse width is a factor that affects the depth of the recess formed by one pulse laser irradiation, and in order not to affect the adhesion of the molten residue to the inner wall, the pulse width is not limited to 20μs. However, if the pulse width is shortened, a larger number of irradiations will be required to penetrate the substrate, so the processing time becomes longer and the production efficiency is reduced. On the other hand, if the pulse width is increased, the number of irradiations used for penetration will be reduced, but the amount of molten flying materials generated by one irradiation will increase, and the dust collection mechanism needs to be cleaned frequently, resulting in reduced production efficiency. Therefore, for example, if the pulse width is set in the range of 5μs to 30μs, processing can be performed with good production efficiency.

[0052] It can be seen from the above embodiments that for a low temperature sintered glass ceramic substrate, by setting the pulse energy to 6.7 mJ or more for processing, a through hole without molten residue on the inner wall can be formed using a carbon dioxide pulse laser.

[0053] [Comparative Example]

[0054] As a comparative example, an alumina ceramic substrate, which is widely known as a ceramic substrate with a low dielectric tangent, was processed by changing the pulse energy to 9.5 mJ (Comparative Example 1) and 13.3 mJ (Comparative Example 2). In either comparative example, the pulse width was 20 μs, and the beam diameter at the processing point was 120 μm. In addition, the pulse energy density in the case of comparative example 1 was 840.4 mJ / mm 2 The pulse energy of Comparative Example 2 is 1176.6 mJ / mm 2 . Figure 5 The drawings are photographs showing cross sections of through holes processed in Comparative Examples 1 and 2. As shown in the drawings, in any of the comparative examples, molten residues adhere to the inner wall.

[0055] As described above, according to the present invention, a through hole having no molten residue attached to the inner wall can be formed only by the laser processing step using a carbon dioxide laser in a low temperature sintered ceramic substrate which is a kind of low dielectric tangent ceramic.

[0056] Furthermore, in the above description, the through hole for forming the substrate through-electrode is processed, but the present invention is not limited thereto, and can also be used to form a through hole for cutting a substrate.

Claims

1. A laser processing method for forming a through hole using a laser processing device, characterized in that: The laser processing device comprises: an oscillator that oscillates a carbon dioxide laser pulse; a modulator that further modulates the laser pulse oscillated by the oscillator into a processing laser pulse of a predetermined pulse energy; a focusing lens that focuses the processing laser pulse on a workpiece; a worktable that places the workpiece; a beam diameter adjustment optical system for adjusting the beam diameter of the processing laser pulse at a processing point; and an overall control unit that controls the overall operation of the device. The workpiece is a low-temperature sintered glass ceramic substrate. The pulse energy of the processing laser pulse is set to 6.7 mJ or more.

2. The laser processing method according to claim 1, characterized in that: The energy density of the processing laser pulse at the processing point is 592.7 mJ / mm 2 above.

3. A laser processing device for forming through holes in a low temperature sintered glass ceramic substrate, characterized in that: have: an oscillator that oscillates the CO2 laser pulses; a modulator that further modulates the laser pulse oscillated from the oscillator into a processing laser pulse of a predetermined pulse energy; A focusing lens that focuses the processing laser pulse on the workpiece; A workbench on which the workpiece is placed; a beam diameter adjustment optical system for adjusting the beam diameter of the processing laser pulse at a processing point; and The overall control unit controls the overall operation of the device. The modulator modulates the pulse energy of the processing laser pulse to 6.7 mJ or more.

4. The laser processing device according to claim 3, characterized in that: The beam diameter of the processing laser pulse at the processing point is adjusted by the beam diameter adjustment optical system so that the energy density of the processing laser pulse at the processing point is 592.7 mJ / mm 2 above.

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