Method for opening holes in a printed substrate using a carbon dioxide laser

Abstract

A method for opening holes to form blind vias or through vias in a printed substrate using a carbon dioxide laser. The multiple laser irradiations performed to form blind vias in the printed substrate are carried out by combining a continuous pulse irradiation mode and an intermittent pulse irradiation mode. Therefore, a large amount of processing can be carried out using the continuous pulse irradiation mode, and then accurate processing can be carried out using the shooting of the intermittent pulse irradiation mode. In this way, less heat is generated during processing, and heat conduction can be used to dissipate heat at a low power value so that the insulating layer can be sufficiently cooled. Therefore, the operation efficiency can be improved, the operation cost can be reduced, high processing accuracy can be achieved, and damage to the internal copper foil layer serving as the internal conductor layer in the insulating layer can be prevented.

Description

Technical Field

[0001] The present invention relates to a method for processing a printed circuit board, and more particularly to a method for forming holes in a printed circuit board using a carbon dioxide laser. The printed circuit board has an insulating layer composed of a glass fiber cloth woven from resin and glass fiber, an external conductor layer composed of copper foil or the like provided on at least one surface of the insulating layer, and an internal conductor layer composed of copper foil or the like provided in the insulating layer. The hole-forming method is used to form a blind hole (hereinafter referred to as "BH") that exposes the copper foil in the insulating layer at the bottom of the printed circuit board, or a through hole (hereinafter referred to as "TH") that penetrates the printed circuit board. Background Art

[0002] Conventionally, in order to form holes such as BH or TH in the above-mentioned printed circuit board, a carbon dioxide laser (hereinafter simply referred to as "laser") is used to improve the working efficiency of hole forming and reduce the working cost of the hole forming.

[0003] In recent years, there has been a demand for thinning of printed circuit boards and miniaturization of hole forming in hole forming of the above-mentioned printed circuit boards using lasers. Therefore, high processing accuracy is required for hole forming of BH or TH in printed circuit boards.

[0004] Moreover, as the internal conductor layer provided in the insulating layer of the printed circuit board becomes thinner, particularly during BH processing, it is necessary to prevent damage such as discoloration, melting, penetration, or peeling of the internal conductor layer.

[0005] However, the laser used in the above-mentioned conventional hole forming for forming BH or TH is a continuous oscillation type, and the power of this laser is relatively large. Therefore, when forming holes in the printed circuit board, heat energy is generated due to the decomposition of the insulating layer by the laser, and this heat energy remains in the insulating layer, resulting in deformation such as internal expansion, or damage such as discoloration, melting, penetration, or peeling of the internal conductor layer.

[0006] Therefore, it is possible to consider reducing the power of the laser during the above-mentioned BH processing or TH processing to prevent the occurrence of deformation such as internal expansion or damage to the internal conductor layer. However, this will prolong the time required for hole forming, and the bottom diameter necessary for the BH processing cannot be obtained, resulting in the processing hole size of the BH on the printed circuit board exceeding the allowable range, and high processing accuracy cannot be achieved in the hole forming of printed circuit boards that require miniaturization.

[0007] In addition, in the case of TH in which a laser is irradiated onto both sides of a printed circuit board to form a through hole, even when using a laser with the same power, the processing amount will still vary depending on the density of the glass fibers that make up the glass fiber cloth in the insulating layer. That is to say, if the laser is irradiated onto a part of the glass fiber cloth that makes up the insulating layer where the glass fibers are relatively loose, the degree of decomposition of the insulating layer by the laser is relatively high, resulting in a wider bottom diameter of the hole formed on one side of the printed circuit board. On the contrary, if the laser is irradiated onto a part of the glass fiber cloth that makes up the insulating layer where the glass fibers are relatively dense, the degree of decomposition of the insulating layer by the laser is relatively low, resulting in a narrower bottom diameter of the hole formed on one side of the printed circuit board. Therefore, when performing through-hole opening processing for forming TH on a printed circuit board, a large difference in width will occur at the center diameter (that is, the hole diameter at the middle position in the depth direction of TH). In particular, when opening holes in a printed circuit board that requires miniaturization, it is difficult to ensure a high enough processing accuracy to maintain the reliability of plating materials such as copper foil provided on the inner wall of TH.

[0008] In response to this, for example, in a carbon dioxide laser processing method for removing a first conductor layer and an insulating layer from a laminated material to form a blind hole or a groove reaching a second conductor layer, the energy density of the aforementioned laser is set to 25 J / cm 2 or more, and in a beam start time ranging from 1 μs to 10 μs, a method of performing pulsed irradiation on the part to be processed (please refer to Patent Document 1: International Patent Publication No. WO 2002 / 081141).

[0009] In this way, compared with the situation where carbon dioxide laser irradiation is performed with a beam start time shorter than 1 μs or longer than 10 μs under the same area and the same energy density, the energy of the carbon dioxide laser is efficiently absorbed and consumed when removing the conductor layer (Patent Document 1), and the excess carbon dioxide laser will not cause unnecessary extended processing to the insulating layer (Patent Document 1). Therefore, it is possible to prevent a single pulse from causing the glass fiber cloth (Patent Document 1) to protrude into the hole or the hole to have a condition of intermediate expansion. That is to say, by implementing the above-mentioned carbon dioxide laser processing method for laminated materials, the operation efficiency of through-hole opening processing can be improved, the operation cost of through-hole opening processing can be reduced, and deformation such as intermediate expansion shape can be prevented, and high processing accuracy can be obtained.

[0010] However, especially when the insulating layer is pulse-irradiated with a carbon dioxide laser in the range where the beam start time is from 1 μs to 10 μs, because this beam start time is long, and the energy density is 25 J / cm 2As described above, the irradiated carbon dioxide laser is of high power. Therefore, when decomposing and removing the insulating layer, a large amount of heat is generated, and the generated heat gradually stays in the insulating layer. Therefore, it is impossible to completely stop deformation such as central expansion shape occurring in the blind hole. In addition, there is a possibility of causing damage such as discoloration, melting, penetration, or peeling to the conductor layer exposed at the bottom in the blind hole.

[0011] The problem to be solved by the present invention is, in a method for forming openings of BH or TH in a printed circuit board using a laser, to improve the working efficiency and reduce the working cost during the processing of BH or TH, and at the same time improve the processing accuracy so that the bottom diameter of the BH or the central diameter of the TH formed in the printed circuit board can fall within the allowable range of the design value. In particular, it is possible to prevent damage to the internal conductor layer provided in the insulating layer during BH processing. Summary of the Invention

[0012] An object of the present invention is to provide a method for forming an opening in a printed circuit board using a carbon dioxide laser that can solve the above problems.

[0013] The first feature of the present invention is a method for forming a blind hole (hereinafter simply referred to as "BH") in a printed circuit board using a carbon dioxide laser (hereinafter simply referred to as "laser"). The printed circuit board has an insulating layer composed of a resin and a glass fiber cloth of glass fiber, an external conductor layer provided on at least one surface of the insulating layer, and an internal conductor layer provided inside the insulating layer. The opening processing method is to perform multiple laser irradiations (hereinafter, each irradiation in this laser irradiation is simply referred to as "shot") to perform opening processing on the printed circuit board, and includes the following steps:

[0014] (1) At least during the first shot, irradiate the external conductor layer of the printed circuit board in a continuous pulse irradiation mode to decompose and remove the external conductor layer or a part of the external conductor layer and the insulating layer. The continuous pulse irradiation mode (hereinafter simply referred to as "continuous pulse irradiation", refer to Figure 5 (A)) is that, during the time of a single shot, the peak power of the pulse oscillation of the laser irradiation is fixed and continuous.

[0015] (2) In subsequent shots, perform the continuous pulse irradiation mode or the intermittent pulse irradiation mode until the depth of decomposition and removal of the insulating layer is about to reach the depth of the internal conductor layer in the insulating layer. The intermittent pulse irradiation mode (hereinafter simply referred to as "intermittent pulse irradiation", refer to Figure 5 (B)) is that, during the time of a single shot, the peak power of the pulse oscillation of the laser irradiation is fixed, and the output power alternates between the peak power and the power bottom value of zero power, and the laser irradiation is intermittent.

[0016] (3) At least after reaching the depth of the inner conductor layer within the insulating layer, irradiate in the intermittent pulse irradiation mode to decompose and remove the remaining insulating layer.

[0017] Therefore, for the opening processing of forming BH on the printed circuit board, a combination of continuous pulse irradiation and intermittent pulse irradiation with a carbon dioxide laser is used, which can shorten the operation time of the opening processing, improve the operation efficiency, and reduce the operation cost of the opening processing.

[0018] That is, for the opening processing of the outer conductor layer of the printed circuit board, high-energy continuous pulse irradiation is performed, so that the outer conductor layer absorbs a large amount of heat and can be easily decomposed.

[0019] Here, the continuous pulse irradiation for the first shot to decompose and remove the outer conductor layer or a part of the outer conductor layer and the insulating layer corresponds to the thickness of the outer conductor layer that is surface-treated and easily absorbs CO 2 laser. Generally, the energy density is 50 - 100 J / cm 2 , and the pulse width is 12 μs (the same below).

[0020] Moreover, for the insulating layer exposed by the laser of the above continuous pulse irradiation or intermittent pulse irradiation on the printed circuit board, the final opening processing is performed by intermittent pulse irradiation. Therefore, at the power bottom value in the intermittent pulse irradiation of repeatedly shooting the insulating layer, the heat energy generated and staying in the insulating layer will be dissipated through the insulating layer due to the heat conduction of the insulating layer, so it can be fully cooled.

[0021] Moreover, because the power of the laser in the above intermittent pulse irradiation is low, the insulating layer can be processed correctly.

[0022] In this way, high processing accuracy can be ensured in the opening processing of BH (hereinafter simply referred to as "BH processing"), damage such as discoloration, melting, penetration, or peeling of the inner conductor layer exposed at the bottom of BH can be prevented, and the bottom diameter at the bottom of BH can fall within the allowable range of the design value.

[0023] The second feature of the present invention is an opening processing method for forming a via hole (hereinafter simply referred to as "TH") on a printed circuit board with a carbon dioxide laser. The printed circuit board has an insulating layer composed of a resin and a glass fiber cloth of glass fiber, two outer conductor layers respectively provided on both sides of the insulating layer, and an inner conductor layer provided inside the insulating layer. The opening processing method performs multiple laser irradiations to perform opening processing on the printed circuit board, including the following steps:

[0024] (1) At least during the first shot, irradiate the outer conductor layer on one side of the printed circuit board in a continuous pulse irradiation manner to decompose and remove the outer conductor layer or a part of the outer conductor layer and the insulating layer to form a hole. The continuous pulse irradiation manner is such that during the time of a single shot, the peak power of the laser irradiation pulse oscillation is fixed and continuous.

[0025] (2) In subsequent shots, perform the continuous pulse irradiation manner or the intermittent pulse irradiation manner until the depth of decomposition and removal of the insulating layer is about to reach half of the thickness of the printed circuit board. The intermittent pulse irradiation manner is such that during the time of a single shot, the peak power of the laser irradiation pulse oscillation is fixed, and the output power alternates between the peak power and the power bottom value of zero power, resulting in intermittent laser irradiation.

[0026] (3) At least after reaching about half of the thickness of the printed circuit board, perform the intermittent pulse irradiation manner to decompose and remove the remaining insulating layer until reaching the position of half of the thickness of the printed circuit board.

[0027] (4) After that, on the other side of the printed circuit board, also perform the processing in the above (1) to (3) to form a hole, so that the holes formed on both sides penetrate.

[0028] Therefore, in the printed circuit board, TH opening processing (hereinafter referred to as "TH processing") can be performed, which can shorten the operation time and reduce the operation cost of the opening processing.

[0029] Moreover, in TH processing, it is processed from both sides of the printed circuit board to penetrate and form TH. Since the opening processing after reaching about half of the thickness of the printed circuit board is performed by intermittent pulse irradiation, when the power bottom value in the intermittent pulse irradiation of repeatedly shooting the insulating layer occurs, the heat generated and staying in the insulating layer will be dissipated through the insulating layer due to the heat conduction of the insulating layer, so it can be fully cooled.

[0030] In this way, the holes formed in the insulating layer from both sides of the printed circuit board can be processed with high precision. Therefore, for TH composed of the holes, it can also achieve high processing precision with the central diameter of TH falling within the allowable range of the design value.

[0031] The beneficial effects of the present invention are as follows: When the present invention performs opening processing of forming BH or TH on the printed circuit board with a carbon dioxide laser, by combining continuous pulse irradiation and intermittent pulse irradiation, the opening processing of the outer conductor layer and the insulating layer of the printed circuit board can be efficiently performed, which can shorten the operation time and improve the operation efficiency, and has the excellent effect of reducing the operation cost.

[0032] Moreover, the intermittent pulse irradiation on the insulating layer is of low power and can dissipate the heat energy generated and remaining during the opening process through heat conduction via the insulating layer at the bottom value of the power of the intermittent pulse irradiation, enabling sufficient cooling.

[0033] In this way, if intermittent pulse irradiation is also used in the intermediate shooting, it is possible to prevent deformation such as intermediate swelling of BH or TH formation, and to finely adjust the processing amount of the laser irradiation, enabling correct processing and achieving high processing accuracy.

[0034] In particular, when processing BH to expose the internal conductor layer in the insulating layer of the printed circuit board, at least the last shooting of the opening process of the insulating layer will be intermittent pulse irradiation. Therefore, the heat energy generated and remaining during the opening process will be sufficiently cooled by heat conduction at the bottom value of the power of the intermittent pulse irradiation. Therefore, it also has an excellent effect of preventing damage such as discoloration, melting, penetration, or peeling of the internal conductor layer exposed at the bottom of BH.

[0035] In addition, in the TH processing that penetrates the printed circuit board, the bottom diameter of the holes formed on both sides of the printed circuit board can be correctly processed. Therefore, even if the holes penetrate to become TH, the central diameter of the TH will fall within the allowable range of the design value, and it has an excellent effect of achieving high processing accuracy that can maintain the reliability of the inner wall plating of TH. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic diagram showing an opening processing device for a printed circuit board for implementing the method of opening a printed circuit board with a carbon dioxide laser according to the present invention;

[0037] Figure 2 It is a flowchart showing the steps of forming BH by the method of opening a printed circuit board with a carbon dioxide laser according to the present invention;

[0038] Figure 3 It is a schematic diagram showing the operation status of laser irradiation when forming multiple BHs or THs on a printed circuit board by applying the method of opening a printed circuit board with a carbon dioxide laser according to the present invention;

[0039] Figure 4 It is a flowchart showing the steps of forming TH by the method of opening a printed circuit board with a carbon dioxide laser according to the present invention;

[0040] Figure 5 It is a schematic diagram showing (A) continuous pulse irradiation and (B) intermittent pulse irradiation used in the method of opening a printed circuit board with a carbon dioxide laser according to the present invention;

[0041] Figure 6 It is a cross-sectional schematic view showing the step of forming a BH on the printed substrate by the method of opening holes in the printed substrate with a carbon dioxide laser according to the present invention; and

[0042] Figure 7 It is a cross-sectional schematic view showing the step of forming a TH on the printed substrate by the method of opening holes in the printed substrate with a carbon dioxide laser according to the present invention. Detailed implementation mode

[0043] Modes for implementing the present invention:

[0044] Continuous pulse irradiation is performed on an external conductor layer of a printed substrate to decompose and remove the external conductor layer or a part of the external conductor layer and an insulating layer, and then continuous pulse irradiation or intermittent pulse irradiation is performed on the insulating layer, and finally intermittent pulse irradiation is performed to complete the hole opening process.

[0045] In this way, the operation time required for the hole opening process of forming a BH or a TH on the printed substrate can be shortened, the operation efficiency can be improved, and the operation cost can be reduced. In particular, during the intermittent pulse irradiation for opening holes in the insulating layer, the heat energy generated and staying in the BH or TH will dissipate due to heat conduction at the low power value, and can be sufficiently cooled to achieve high processing accuracy. Moreover, especially during BH processing, the bottom diameter of the bottom of the BH can fall within the allowable range of the design value, and at the same time, damage such as peeling of an internal conductor layer can be prevented. In addition, during TH processing, for the TH formed by penetrating two holes formed on both sides of the printed substrate, the central diameter can also fall within the allowable range of the design value.

[0046] Moreover, during the hole opening process, it is preferable that the pulse width of the continuous pulse irradiation for the first irradiation of the printed substrate is 1 μs or more. The heat energy generated by the laser irradiated in this way on the external conductor layer of the printed substrate is relatively large, and the heat storage effect necessary for removing the external conductor layer can be fully exerted. In this way, the external conductor layer of the printed substrate can be more easily decomposed and removed.

[0047] Relatively, in the intermittent pulse irradiation performed in the final shot, it is better that the pulse width is less than 1 μs. Therefore, in a certain pulse cycle, the time of the power bottom value is longer, so the thermal energy generated along with the laser irradiation is smaller. At this time, although the processing amount is also less, the processing amount can be adjusted to perform processing correctly. Moreover, the thermal energy generated during the above processing will be quickly diffused by heat conduction at the power bottom value and cooled sufficiently. Therefore, for BH, damage to the internal conductor layer can be suppressed, and high processing accuracy can be achieved such that the bottom diameter of the bottom easily falls within the allowable range of the design value. Also, high processing accuracy can be achieved such that the central diameter of TH easily falls within the allowable range of the design value.

[0048] Example 1:

[0049] Refer to Figure 1 、 Figure 6 and Figure 7 , Figure 1 discloses a printed circuit board via hole machining device A for implementing the method of machining a via hole in a printed circuit board using a carbon dioxide laser according to the present invention. The printed circuit board via hole machining device A uses a carbon dioxide laser to remove a surface copper foil layer 3 as an outer conductor layer constituting a printed circuit board 1 to form a blind hole B, so that an inner copper foil layer 4 as an inner conductor layer provided in an insulating layer 2 of the printed circuit board 1 is exposed, or removes two surface copper foil layers 3' as outer conductor layers on both sides of the printed circuit board 1 to machine and form a through hole C.

[0050] Here, the printed circuit board via hole machining device A is composed of the following structure: an oscillator a that generates a laser h; a zoom module b that condenses the optical path of the laser h generated by the oscillator a using a plurality of lenses b'; an aperture c that reduces the optical path of the laser h whose optical path is condensed by the zoom module b to a predetermined optical path; a galvanometer mirror e that is controlled by a galvanometer scanner d to irradiate the target position on the irradiation surface of a predetermined area on the printed circuit board 1 with the laser h passing through the aperture c; an FΘ lens f that irradiates the laser h perpendicularly to the irradiation surface of the printed circuit board 1; a processing table g that mounts the printed circuit board 1 to be processed by the laser h passing through the FΘ lens f and can move horizontally and vertically in the plane direction when necessary to set the printed circuit board 1 in an appropriate position; a plurality of mirrors i that reflect and guide the laser h to form an optical path from the oscillator a through the zoom module b, the aperture c, the galvanometer mirror e, the FΘ lens f, and reaching the printed circuit board 1, and an NC device j that integrally controls the oscillator a, the galvanometer scanner d, and the processing table g.

[0051] Here, the laser h irradiated by the oscillator a is positioned by the galvanometer scanner d and focused on the printed circuit board 1 by the FΘ lens f for perforation processing, and the oscillator a, the galvanometer scanner d, and the processing table g are controlled according to the instructions of the NC device j.

[0052] However, when performing perforation processing on the printed circuit board 1, the processing area of the galvanometer scanner d is limited to the area of the FΘ lens f. Therefore, when the processing area of the galvanometer scanner d is outside the area of the FΘ lens f, the position of the printed circuit board 1 is adjusted by moving the processing table g in the planar direction to perform perforation processing.

[0053] Refer to Figure 1 and Figure 5 In addition, in the above-mentioned perforation processing device A for a printed circuit board, the oscillator a is controlled by the programming provided in the NC device j to change whether the laser h irradiated on the printed circuit board 1 is continuous pulse irradiation La or intermittent pulse irradiation Lb.

[0054] In addition, the processing part programming of the NC device j for integrally controlling the oscillator a, the galvanometer scanner d, and the processing table g is composed of a processing condition selection instruction (hereinafter simply referred to as "T instruction") and a processing position instruction.

[0055] Therefore, in the NC device j, corresponding to the T instruction, processing conditions such as laser oscillation conditions and processing modes are set, these conditions are read simultaneously with the above-mentioned processing part programming, and according to the instruction information, the processing area of the printed circuit board 1 is moved to below the FΘ lens f by the processing table g, the processing position of the printed circuit board 1 is positioned by the galvanometer scanner d, and perforation processing is performed by continuous pulse irradiation La or intermittent pulse irradiation Lb oscillated by the oscillator a.

[0056] Here, the selection item of the processing mode of the processing conditions of the T instruction is set as the method for perforating a printed circuit board with a carbon dioxide laser according to the present invention, and for example, in the multiple laser irradiations on the printed circuit board 1 during perforation processing, the T instruction can specifically set either continuous pulse irradiation La or intermittent pulse irradiation Lb for individual shots.

[0057] Moreover, the perforation processing device A for a printed circuit board that implements the above-mentioned method for perforating a printed circuit board with a carbon dioxide laser can also be used for the processing method of TH described in Example 2.

[0058] Refer to Figure 2 andFigure 6 , herein, by the method of opening holes in a printed substrate using a carbon dioxide laser according to the present invention, in accordance with Figure 2 the steps S21 to S23 shown, the operation process of forming BH(B) on the printed substrate 1 as shown Figure 6 will be described.

[0059] Herein, the printed substrate 1 is composed of the following structure: the insulating layer 2 composed of the resin 2a and the glass fiber cloth 2b of glass fiber, the surface copper foil layer 3 as an external conductor layer on at least one surface of the insulating layer 2, and the internal copper foil layer 4 provided in the insulating layer 2 as an internal conductor layer.

[0060] Therefore, when forming BH(B) on the above-mentioned printed substrate 1, the following steps are carried out:

[0061] (1) As in Figure 2 the step S21 shown, first, for the surface copper foil layer 3 as an external conductor layer on the printed substrate 1, during the first shot, continuous pulse irradiation La is carried out to decompose and remove the surface copper foil layer 3 as an external conductor layer, or a part of the surface copper foil layer 3 as an external conductor layer and the insulating layer 2 (see Figure 6 (A) to (B)).

[0062] In addition, at this stage, if the internal copper foil layer 4 as an internal conductor layer in the insulating layer 2 has been substantially exposed, the intermittent pulse irradiation Lb described in the following step (3) is directly carried out.

[0063] (2) As in Figure 2 the step S22 shown, and during subsequent shots, continuous pulse irradiation La or intermittent pulse irradiation Lb is properly combined to decompose and remove the insulating layer 2 until it is about to reach the internal copper foil layer 4 as an internal conductor layer in the insulating layer 2 (see Figure 6 (B) to (C)).

[0064] (3) As in Figure 2 the step S23 shown, and moreover, at least during the last shot, intermittent pulse irradiation Lb is carried out to decompose and remove the insulating layer 2 until the internal conductor layer 4 in the insulating layer 2 is completely exposed (see Figure 6 (C) to (E)).

[0065] (4) In this way, a BH(B) with a predetermined bottom diameter can be finally formed (see Figure 6 (E)).

[0066] See Figure 3 and Figure 6, in addition, the processing method for forming BH(B) on the above-mentioned printed circuit board 1 targets a single BH(B). However, when forming multiple (N) BH(B)s with the same width and depth on one printed circuit board 1, the processing is carried out as shown in Figure 3 as follows.

[0067] For example, when drilling a single BH, if the processing condition for completion is a total of 4 shots with continuous pulse irradiation La plus intermittent pulse irradiation Lb, for each processing position (holes 1 to N) of all BH(B)s on the printed circuit board 1, first, move and shoot in sequence (holes 1 to N) with the continuous pulse irradiation La of the first shot (see Figure 3 (A)), then return to the original position and shoot at the same processing position for the second shot (see Figure 3 (B)), and move from hole 1 to hole N in sequence for continuous pulse irradiation La. After that, since the processing depth has reached near the internal copper foil layer 4 which is the internal conductor layer in the insulating layer 2, the third shot (see Figure 3 (C)) moves from hole 1 to hole N in sequence for intermittent pulse irradiation, and the fourth shot is to perform intermittent pulse irradiation on holes 1 to N in sequence (see Figure 3 (D)), so that the internal conductor layer in the insulating layer 2 is completely exposed without causing damage such as discoloration, melting, penetration, or peeling. In this way, N BH(B)s with the same width and depth can be formed simultaneously on one printed circuit board 1. In addition, in Example 2, holes 5 equivalent to multiple TH(C)s can also be formed on one printed circuit board 1 in the same way (see Figure 7 ).

[0068] By using the method described above to form BH(B) on the printed circuit board 1, the operation time for drilling BH(B) on the printed circuit board 1 can be shortened, and the operation cost can be reduced.

[0069] Moreover, since the internal copper foil layer 4 which is the internal conductor layer in the insulating layer 2 is completely exposed by intermittent pulse irradiation Lb, its power is relatively weak, the processing amount of its laser irradiation is less and it is easy to adjust the processing amount, so BH(B) formed on the insulating layer can be processed correctly.

[0070] Furthermore, less heat is generated and remains in BH(B), and it will dissipate and cool through heat conduction at the power bottom value. Therefore, damage such as discoloration, melting, penetration, or peeling to the internal copper foil layer 4 which is the internal conductor layer exposed at the bottom of the BH(B) can be prevented.

[0071] Here, the effects that can be achieved when forming BH(B) by using the method of the present invention for performing opening processing on a printed substrate with a carbon dioxide laser are discussed.

[0072] Assume that for the printed substrate 1 with a thickness of 5 μm for the surface copper foil layer 3 as the external conductor layer, a thickness of 60 μm for the insulating layer 2, and a thickness of 9 μm for the internal copper foil layer 4 as the internal conductor layer, a specification with a top diameter The bottom diameter is 75% or more of the top diameter, and BH(B) is formed on the premise of not damaging the internal copper foil layer 4. At this time, the conditions of the intermittent pulse irradiation Lb are changed, that is, the processing quality of the combination of continuous pulse irradiation La and intermittent pulse irradiation Lb with various pulse widths (conditions 5 - 9 in Table 1 below) is compared, and the processing quality under various conditions (conditions 1 - 4 in Table 1 below) where all shootings use continuous pulse irradiation La is compared. The results are shown in Table 1.

[0073] In addition, the purpose of the continuous pulse irradiation La for the first shooting is to remove the surface copper foil layer 3 of the printed substrate 1 as the external conductor layer, and its energy density is 53 J / cm 2 And the pulse width is 10 μs. Since this parameter is common to all conditions 1 - 9 in Table 1, it is omitted from the description.

[0074]

[0075] Table 1

[0076] As described above, first, in order to ensure that the bottom diameter of the bottom of BH(B) is 75% or more of the top diameter, an energy density of 9 J / cm 2 or more is required. However, if only continuous pulse irradiation La is used, the internal copper foil layer 4 as the internal conductor layer will be damaged (in Table 1, "×" represents damaged, and "○" represents not damaged). In contrast, if, after the aforementioned first continuous pulse irradiation La, intermittent pulse irradiation Lb with an energy density of 9 J / cm 2 or more is performed, and the pulse width of the intermittent pulse irradiation Lb is less than 1 μs. When it is 0.6 μs or less, the power is obviously insufficient. Therefore, by setting the pulse width to be 0.7 μs or more and 0.8 μs or less, the result that the bottom diameter of BH(B) is 75% or more of the top diameter and damage to the internal copper foil layer 4 in the insulating layer 2 can be prevented is obtained, thus confirming the effects of the present invention.

[0077] Example 2:

[0078] Next, according to Figure 4 the steps S41 - S44 shown, as Figure 7As shown, it illustrates the operation process of forming TH on a printed circuit board 1' by the method of opening holes in the printed circuit board with a carbon dioxide laser according to the present invention.

[0079] Here, the printed circuit board 1' is composed of an insulating layer 2' and two surface copper foil layers 3' as external conductor layers on both sides of the insulating layer 2'. The insulating layer 2' is composed of a resin 2a' and a glass fiber cloth 2b' of glass fiber.

[0080] Here, when forming TH(C) on the above-mentioned printed circuit board 1', the following steps are performed:

[0081] (1) As shown in step S41, first, in the first shot, continuous pulse irradiation La is performed on one surface 1a' of the two surfaces of the surface copper foil layer 3' as the external conductor layer of the printed circuit board 1' to decompose and remove the surface copper foil layer 3' as the external conductor layer, or a part of the surface copper foil layer 3' as the external conductor layer and the insulating layer 2' (refer to Figure 4 (A) - (B)). Figure 7 (A) - (B)).

[0082] In addition, at this stage, if the depth of a hole 5 formed in the insulating layer 2' is about to reach half of the thickness of the printed circuit board 1', the intermittent pulse irradiation described in the following step (3) S43 is directly performed.

[0083] (2) As shown in step S42, in subsequent shots, continuous pulse irradiation La or intermittent pulse irradiation Lb is appropriately combined to decompose and remove the insulating layer 2' until the depth of the hole 5 is about to reach half of the thickness of the printed circuit board 1' (refer to Figure 4 (B)). Figure 7 (B)).

[0084] (3) As shown in step S43, and at least in the last shot, intermittent pulse irradiation Lb is performed to decompose and remove the insulating layer 2' until the depth of the hole 5 reaches half of the thickness position of the printed circuit board 1' (refer to Figure 4 (C)). Figure 7 (C)).

[0085] (4) As shown in step S44, afterwards, the processing of steps S41 - S43 of the above (1) - (3) is also performed on the other side of the printed circuit board 1' (refer to Figure 4 (D) - (E)). In this way, the two holes 5, 5 can be finally penetrated to form TH(C) (refer to Figure 7 (D) - (E)). In this way, the two holes 5, 5 can be finally penetrated to form TH(C) (refer to Figure 7 (F)).

[0086] In the manner described above, forming TH(C) on the printed circuit board 1' can shorten the operation time for opening holes for TH(C) in the printed circuit board 1' and reduce the operation cost.

[0087] Moreover, when performing hole opening processing on one side and the other side of the printed circuit board 1', at least during the final hole opening processing for each side, intermittent pulse irradiation Lb is performed. Since its power is weak, the processing amount is small and it is easy to adjust the processing amount. Therefore, for the TH(C) formed by penetrating through the holes 5, 5 formed on both sides of the printed circuit board 1', the center diameter can be precisely processed and can fall within the allowable range of the design value.

[0088] In this way, the reliability of the plating layer provided on the wall surface of TH(C) can be maintained.

[0089] Here, the effects that can be achieved when forming TH(C) by using the method of opening holes in a printed circuit board with a carbon dioxide laser according to the present invention are studied.

[0090] Assume that for the printed circuit board 1' with a thickness of 2 μm for the surface copper foil layer 3' as the external conductor layer on both sides of the insulating layer 2' and a thickness of 60 μm for the insulating layer 2', the specification is such that the opening diameter on the surface copper foil layer 3' as the external conductor layer of the printed circuit board 1' is The center diameter is of TH(C). At this time, the conditions of the intermittent pulse irradiation Lb are changed, that is, the processing quality of the combination of continuous pulse irradiation La and intermittent pulse irradiation Lb with various pulse widths (conditions 5 to 9 in Table 2 below) is compared, and the processing quality under various conditions (conditions 1 to 4 in Table 2 below) where all shootings use continuous pulse irradiation La is compared. The results are shown in Table 2.

[0091] In addition, the purpose of the continuous pulse irradiation La for the first shooting is to remove the surface copper foil layer 3' of the printed circuit board 1' as the surface conductor layer. Its energy density is 52 J / cm 2 and the pulse width is 8 μs. Since this parameter is common to all of conditions 1 to 9 in Table 2, it is omitted from the description.

[0092]

[0093] Table 2

[0094] As described above, first, in order to make the center diameter of TH fall between an energy density of about 18 J / cm 2 is required. However, if only continuous pulse irradiation La is used, it is impossible to make the center diameter of TH fall within the allowable range of the design value ( That is, it is within a range of more than 30 μm and less than 50 μm. In contrast, if after the aforementioned first continuous pulse irradiation of La, intermittent pulse irradiation Lb with an energy density of 18 J / cm 2 or more is performed, and the pulse width of the intermittent pulse irradiation Lb is less than 1 μs. At 0.4 μs, the power is obviously insufficient. Therefore, by setting the pulse width to be 0.5 μs or more and 0.7 μs or less, the center diameter of TH can be obtained as The result is thus, confirming the effect of the present invention.

[0095] Industrial applicability:

[0096] For a printed circuit board, in multiple laser irradiations performed to form BH or TH, by combining continuous pulse irradiation and intermittent pulse irradiation, the working efficiency of laser processing can be improved, the working cost can be reduced, the processing accuracy can be improved, and damage to the internal conductor layer provided in the insulating layer of the printed circuit board during processing can be avoided. Therefore, it can be applied not only to printed circuit boards, but also to the processing of various substrates that are thinned and miniaturized.

[0097] The above are only embodiments of the present invention, and the scope of implementation of the present invention cannot be limited thereby. That is, all simple equivalent changes and modifications made according to the claims and the content of the specification of the present invention still fall within the scope of the present invention.

Claims

1. A method for opening holes by using a carbon dioxide laser to form blind holes in a printed substrate, the printed substrate having an insulating layer composed of a resin and a glass fiber cloth of glass fiber, an external conductor layer provided on at least one surface of the insulating layer, and an internal conductor layer provided inside the insulating layer, the hole opening method being to perform multiple laser irradiations to perform hole opening processing on the printed substrate. Characterized in that, the hole opening method comprises the following steps: (1) At least during the first laser irradiation, irradiate the external conductor layer of the printed substrate in a continuous pulse irradiation mode to decompose and remove the external conductor layer or a part of the external conductor layer and the insulating layer. The continuous pulse irradiation mode is that during the time of a single laser irradiation, the peak power of the pulse oscillation of the laser irradiation is fixed and continuous. (2) In subsequent laser irradiations, perform the continuous pulse irradiation mode or the intermittent pulse irradiation mode until the depth of decomposition and removal of the insulating layer is about to reach the depth of the internal conductor layer in the insulating layer. The intermittent pulse irradiation mode is that during the time of a single laser irradiation, the peak power of the pulse oscillation of the laser irradiation is fixed, and the output power alternates between the peak power and the power bottom value of zero power, and the laser irradiation is intermittent. And (3) At least after reaching the depth of the internal conductor layer in the insulating layer, irradiate in the intermittent pulse irradiation mode to decompose and remove the remaining insulating layer.

2. A method for opening holes by using a carbon dioxide laser to form through holes in a printed substrate, the printed substrate having an insulating layer composed of a resin and a glass fiber cloth of glass fiber, two external conductor layers respectively provided on two surfaces of the insulating layer, and an internal conductor layer provided inside the insulating layer, the hole opening method being to perform multiple laser irradiations to perform hole opening processing on the printed substrate. Characterized in that, the hole opening method comprises the following steps: (1) At least during the first laser irradiation, irradiate the external conductor layer on one surface of the printed substrate in a continuous pulse irradiation mode to decompose and remove the external conductor layer or a part of the external conductor layer and the insulating layer to form a hole. The continuous pulse irradiation mode is that during the time of a single laser irradiation, the peak power of the pulse oscillation of the laser irradiation is fixed and continuous. (2) In subsequent laser irradiations, perform the continuous pulse irradiation mode or the intermittent pulse irradiation mode until the depth of decomposition and removal of the insulating layer is about to reach half of the thickness of the printed substrate. The intermittent pulse irradiation mode is that during the time of a single laser irradiation, the peak power of the pulse oscillation of the laser irradiation is fixed, and the output power alternates between the peak power and the power bottom value of zero power, and the laser irradiation is intermittent. (3) At least after reaching about half of the thickness of the printed substrate, perform the intermittent pulse irradiation mode to decompose and remove the remaining insulating layer until reaching the position of half of the thickness of the printed substrate. And (4) After that, on the other side of the printed circuit board, the processing of the above (1) to (3) is also carried out to form holes, so that the holes formed on both sides thereof are penetrated.

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