Hole processing method using a carbon dioxide gas laser on a printed circuit board

Abstract

To improve work efficiency, to reduce cost, further to realize higher machining precision and to prevent an inner conductor layer of a printed circuit board from being damaged in hole machining with a carbon oxide laser on the printed circuit board.SOLUTION: A plurality of times of shots to be performed in forming a BH(B) on a printed circuit board 1 is performed by combining continuous pulse irradiation La with intermittent pulse irradiation Lb, such that a hole is machined large by the continuous pulse irradiation and further machined precisely by shots of the intermittent pulse irradiation, moreover, heat to be generated is reduced and an insulation layer can be cooled sufficiently by dissipating heat through heat conduction at the time of output bottom. Thus, work efficiency is improved, work cost is reduced, further, high machining precision can be realized, and an inner copper foil layer which is an inner conductor layer in the insulation layer can be prevented from being damaged.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a hole processing method for forming through holes (hereinafter referred to as "TH") penetrating a printed circuit board using a carbon dioxide laser in a printed circuit board that includes an insulating layer made of glass cloth formed by weaving resin and glass fiber, an external conductor layer made of copper foil or the like provided on at least one surface of the insulating layer, and an internal conductor layer made of copper foil or the like provided within the insulating layer. [Background technology]

[0002] Conventionally, a carbon dioxide laser (hereinafter referred to as "laser") has been used for hole processing to form THs in the above-mentioned printed circuit boards in order to improve the efficiency of the hole processing work and reduce the work costs of the hole processing work. In recent years, in the laser hole processing of the above-mentioned printed circuit boards, as the printed circuit boards have become thinner, there has been a demand for finer hole processing, and as a result, high processing accuracy is required in the hole processing to form THs in the printed circuit boards.

[0003] However, the laser used in the conventional hole processing for forming the TH is a continuous wave laser, and has a large output. Therefore, when processing holes in a printed circuit board, heat is generated within the insulating layer as the insulating layer is decomposed by the laser, and the heat remains inside the insulating layer, causing deformation such as a bulge in the middle, and may also cause damage to the internal conductor layer such as discoloration, melting, penetration, or peeling.

[0004] Therefore, in order to prevent deformation such as bulging and damage to the internal conductor layer during the TH processing, it is conceivable to reduce the laser output, but this would require a long time for hole processing.

[0005] andIn a TH formed by piercing holes formed by laser irradiation from both sides of a printed circuit board, differences in the amount of processing can occur depending on the density of the glass fibers that make up the glass cloth in the insulating layer, even when using a laser with the same power. That is, when a laser is irradiated on a part of the glass cloth that makes up the insulating layer where the glass fibers are sparse, the decomposition of the insulating layer by the laser progresses, and the bottom diameter of the hole formed from one side of the printed circuit board becomes wider. On the other hand, when a laser is irradiated on a part of the glass cloth that makes up the insulating layer where the glass fibers are dense, the decomposition by the laser does not progress, and the bottom diameter of the hole formed from one side of the printed circuit board becomes narrower. Therefore, when processing holes to form THs in printed circuit boards, a large difference in the center diameter (i.e., the diameter at the midpoint in the depth direction of the TH) occurs, and particularly when processing holes in printed circuit boards where fineness is required, it is not possible to ensure high processing precision that can maintain the reliability of plating such as copper foil applied to the inner walls of the TH.

[0006] Therefore, for example, in a carbon dioxide laser processing method for laminated materials in which a first conductive layer and an insulating layer are removed to form blind holes or grooves that reach the second conductive layer, a method has been proposed in which the laser light is irradiated in pulses onto the processing area with an energy density of 25 J / cm2 or more and a beam ON time in the range of 1 μs to 10 μs (see Patent Document 1).

[0007] As a result, compared with the case where the same area is irradiated with carbon dioxide laser light having a beam-on time shorter than 1 μs or longer than 10 μs at the same energy density, the energy of the carbon dioxide laser light is efficiently absorbed and consumed in removing the conductor layer 4, and the excess carbon dioxide laser light does not unnecessarily process the insulating layer 1 to a large extent, making it possible to prevent the glass cloth 2b from protruding into the hole with one pulse or the hole from becoming bulged. In other words, by implementing the above carbon dioxide laser processing method for laminated material, the efficiency of hole processing can be improved, the cost of hole processing can be reduced, and deformation such as bulging can be prevented, resulting in high processing accuracy.

[0008] However, the carbon dioxide laser that is irradiated onto the insulating layer is irradiated in pulses with a beam ON time in the range of 1 μs to 10 μs, but since the beam ON time is long and the energy density is 25 J / cm2 or more, the output of the carbon dioxide laser that is irradiated is high. Therefore, a large amount of heat is generated when the insulating layer is decomposed and removed, and the generated heat gradually accumulates within the insulating layer, making it impossible to completely prevent deformation such as a bulging shape in the blind hole.Furthermore, there is a risk of damage such as discoloration, melting, penetration, or peeling to the conductor layer exposed at the bottom of the blind hole. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Republished Patent Publication No. WO2002 / 081141 Summary of the Invention [Problem to be solved by the invention]

[0010] The problem to be solved is to achieve high processing accuracy in a hole processing method for forming a TH using a laser in a printed circuit board, while improving the work efficiency of processing the TH and reducing the work cost, so that the center diameter of the TH formed in the printed circuit board is within the allowable range of the design value. [Means for solving the problem]

[0011] The first feature is, A hole processing method for forming through holes (hereinafter referred to as "TH") using a laser in a printed circuit board that is composed of an insulating layer made of resin and glass fiber glass cloth, external conductor layers provided on both sides of the insulating layer, and an internal conductor layer provided inside the insulating layer, comprising: A plurality of shots are performed to process holes in the printed circuit board, (1) In at least the first shot, a continuous pulse is irradiated onto an outer conductor layer on one side of a printed circuit board to decompose and remove the outer conductor layer or a part of the outer conductor layer and the insulating layer; (2) In subsequent shots, continuous pulse irradiation is performed. stomach is an intermittent pulse irradiation, and the point just before the position where it is half the thickness of the printed circuit board is (That is, "up to the point where the hole depth reaches half the thickness of the printed circuit board after at least the last shot of intermittent pulse irradiation." The same applies below.) Decompose and remove the insulating layer to a depth of (3) Furthermore, at least immediately before the position where the thickness of the printed circuit board is halfway through, shots of intermittent pulse irradiation are performed to decompose and remove the insulating layer remaining up to the position where the thickness of the printed circuit board is halfway through; (4) Then, the other surface of the printed circuit board is processed in the same manner as in (1) to (3) above, and holes are made to penetrate from both sides.

[0012] Therefore, in hole processing for TH in a printed circuit board (hereinafter referred to as "TH processing"), the processing time can be shortened and the processing cost can be reduced. Furthermore, in TH processing, the printed circuit board is processed from both sides and penetrated to form the TH, and hole processing from just before the position where it is half the thickness of the printed circuit board is performed by intermittent pulse irradiation.Therefore, when the output of the intermittent pulse irradiation reaches its bottom, the heat that is generated and remains within the insulating layer is dissipated through the insulating layer by the thermal conduction of the insulating layer and is sufficiently cooled. As a result, holes formed in the insulating layer from both sides of the printed circuit board can be processed with high processing accuracy, so even when these holes are combined to form a TH, high processing accuracy can be achieved to keep the center diameter of the TH within the allowable range of the design value. [Effects of the Invention]

[0013] The present invention combines continuous pulse irradiation and intermittent pulse irradiation in hole processing to form THs in printed circuit boards using a carbon dioxide laser, so that hole processing can be performed efficiently in the external conductor layer and insulating layer of the printed circuit board, thereby having the excellent effect of shortening work time, improving work efficiency, and reducing work costs.

[0014] Furthermore, when intermittent pulse irradiation is performed on an insulating layer, the output is small, and the heat that is generated and accumulates during hole processing is dissipated by thermal conduction through the insulating layer when the output of the intermittent pulse irradiation is at its lowest, and is sufficiently cooled. As a result, when intermittent pulses are used for the intermediate shots as well, deformations such as bulging can be prevented in the TH while the amount of processing by laser irradiation can be finely adjusted to achieve accurate processing, thereby achieving high processing accuracy.

[0015] In particular, when processing a TH that penetrates a printed circuit board, the bottom diameter of the hole formed from both sides of the printed circuit board is processed accurately, so even if these holes are penetrated to form a TH, the center diameter of the TH will be within the allowable range of the design value, which has the excellent effect of achieving high processing precision that is sufficient to maintain the reliability of the plating on the inner wall of the TH. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic diagram of a hole drilling device for a printed circuit board that implements the hole drilling method for a printed circuit board using a carbon dioxide gas laser according to the present invention. [Figure 2] FIG. 2 is a diagram showing the movement of laser irradiation when a hole processing method for a printed circuit board using a carbon dioxide gas laser according to the present invention is applied to form a plurality of THs on the printed circuit board. [Figure 3] FIG. 3 is a diagram showing a process for forming a TH by a hole processing method using a carbon dioxide gas laser in a printed circuit board according to the present invention. [Figure 4] FIG. 4 is a conceptual diagram of (A) continuous pulse irradiation and (B) intermittent pulse irradiation used in the hole processing method for a printed circuit board by a carbon dioxide gas laser according to the present invention. [Figure 5] FIG. 5 is a cross-sectional view showing a process of forming a TH in a printed circuit board by the hole processing method for a printed circuit board using a carbon dioxide gas laser according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] The outer conductor layer of the printed circuit board is subjected to continuous pulse irradiation to decompose and remove the outer conductor layer or a part of the outer conductor layer and the insulating layer, and then the insulating layer is subjected to continuous pulse irradiation or stomach The first involves intermittent pulse irradiation, followed by final finishing of the hole processing by intermittent pulse irradiation. As a result, the working time for hole processing of TH in printed circuit boards is shortened, improving working efficiency and reducing working costs. In particular, in the case of intermittent pulse irradiation for hole processing in insulating layers, the heat generated and accumulated in the TH at the bottom of the output is dissipated by thermal conduction, and sufficient cooling achieves high processing accuracy. In addition, even if the TH is formed by penetrating both holes formed from both sides of the printed circuit board in TH processing, its center diameter is within the allowable range of the design value.

[0018] It is desirable to set the pulse width of the initial continuous pulse irradiation to 1 μs or more during hole drilling, so that the heat applied to the external conductor layer of the printed circuit board irradiated with the laser is increased, and the heat storage effect required for removing the external conductor layer is fully exerted, which makes it possible to easily decompose and remove the external conductor layer on the printed circuit board.

[0019] On the other hand, it is desirable to set the pulse width of the intermittent pulse irradiation performed in the last shot to less than 1 μs. This increases the output bottom time in a certain pulse cycle, so the heat generated by laser irradiation decreases and the processing volume also decreases, but the processing volume can be adjusted to perform processing accurately, and the heat generated during the processing is quickly diffused and sufficiently cooled by thermal conduction at the output bottom, achieving high processing accuracy that keeps the center diameter of the TH within the allowable range of the design value. [Example]

[0020] FIG. 1 shows a printed circuit board hole drilling device A for carrying out the method of drilling holes in a printed circuit board by using a carbon dioxide gas laser according to the present invention. The hole processing device A for the printed circuit board processes through holes TH by removing the surface copper foil layer 3', which is the external conductor layer on both sides of the printed circuit board 1, using a carbon dioxide laser to expose the internal copper foil layer 4, which is the internal conductor layer provided within the insulating layer 2 that constitutes the printed circuit board 1.

[0021] Therefore, the hole processing device A for the above-mentioned printed circuit board is composed of an oscillator a that generates a laser beam h, a zoom b that uses multiple lenses b' to converge the beam diameter of the laser beam h generated from the oscillator a, an aperture c that narrows the laser beam h, whose beam diameter has been converged by the zoom b, to a predetermined beam diameter, a galvanometer mirror e that is controlled by a galvanometer scanner d so that the laser beam h that has passed through the aperture c is directed at a targeted position on the irradiation surface of a certain section of the printed circuit board, an Fθ lens f that irradiates the laser beam h perpendicularly to the irradiation surface of the printed circuit board 1, a processing table g that places the printed circuit board 1 to be processed by the laser beam h that has passed through the Fθ lens f and that can move vertically and horizontally in a planar direction to set the printed circuit board 1 to an appropriate position if necessary, multiple mirrors i that form an optical path that reflects and guides the laser beam h from the oscillator a to the zoom b, aperture c, galvanometer mirror e, and Fθ lens f to the printed circuit board 1, and an NC device j that comprehensively controls the oscillator a, galvanometer scanner d, and processing table g.

[0022] Here, the laser h emitted from the oscillator a is positioned by the galvanometer scanner d and focused on the printed circuit board 1 by the Fθ lens f to perform hole processing, and the oscillator a, the galvanometer scanner d, and the processing table g are controlled by instructions from the NC device j. Incidentally, in hole drilling on the printed circuit board 1, the processing area of the galvano scanner d is limited to the area of the Fθ lens f. Therefore, when the processing area of the galvano scanner d is outside the area of the Fθ lens f, the processing table g is made movable in the plane direction to adjust the position of the printed circuit board 1 and perform hole drilling. In the hole processing device A for the printed circuit board, the change of the continuous pulse irradiation La or the intermittent pulse irradiation Lb of the laser h irradiated to the printed circuit board 1 is performed by controlling the oscillator a by a program built into the NC device j.

[0023] The machining part program of the NC device j, which controls the oscillator a, galvano scanner d, and machining table g in an integrated manner, is composed of a machining condition selection command (hereinafter referred to as a "T command") and a machining position command. Therefore, the NC device j sets processing conditions such as laser oscillation conditions and processing mode corresponding to the T command, reads them together with the processing part program, and according to the instruction data, moves the processing area of the printed circuit board 1 by the processing table g so that it is under the Fθ lens f, positions the processing position of the printed circuit board 1 by the galvano scanner d, and performs hole processing by continuous pulse irradiation La or intermittent pulse irradiation Lb oscillated from the oscillator a.

[0024] Here, the processing mode selection items for the processing conditions of the T command include a method of hole processing using a carbon dioxide laser in the printed circuit board of the present invention, and as a processing condition of the T command, for example, in multiple laser irradiations irradiated onto the printed circuit board 1 for hole processing, it is possible to set each shot individually and specifically to either continuous pulse oscillation La or intermittent pulse oscillation Lb.

[0025] Next, by the hole processing method for a printed circuit board using a carbon dioxide gas laser according to the present invention, 3 According to the schedule shown in Figure 5 As shown in the figure, the process for forming a TH on a printed circuit board will be described. Here, the printed circuit board 1' is composed of an insulating layer 2' and surface copper foil layers 3' which are external conductor layers on both sides of the insulating layer 2'. Therefore, the TH(C) is formed on the printed circuit board 1' as follows. (1) First, of both sides of the printed circuit board 1' having the surface copper foil layer 3' as the external conductor layer, one side 1a' is subjected to continuous pulse irradiation La in the first shot to decompose and remove the surface copper foil layer 3' as the external conductor layer, or the surface copper foil layer 3' as the external conductor layer and part of the insulating layer 2' [Fig. 5 See (a) to (b). At this stage, if the depth of the hole 5 formed in the insulating layer 2' reaches just before half the thickness of the printed circuit board 1', the process moves to intermittent pulse irradiation (3). (2) Then, in subsequent shots, continuous pulse irradiation La or intermittent pulse irradiation Lb is appropriately combined until the depth of the hole 5 reaches just before half the thickness of the printed circuit board 1', thereby decomposing and removing the insulating layer 2' (see Figure 1 (b)). (3) Furthermore, 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 the thickness of the printed circuit board 1' (see Figure (c)). (4) Then, the other surface of the printed circuit board 1' is subjected to the processes (1) to (3) above (see (d) to (e) in the same figure). (5) As a result, the two holes 5, 5 are finally penetrated to form TH(C) (see FIG. 1(f)).

[0026] As described above, the TH(C) is formed on the printed circuit board 1', so that the time required for processing holes for the TH(C) on the printed circuit board 1' can be shortened, and the work cost can be reduced. When processing each hole from one side and the other side of the printed circuit board 1', at least the last hole is processed by intermittent pulse irradiation Lb, so although the output is weak, the processing amount is small and easy to adjust, so that the center diameter of TH(C) formed by the holes 5, 5 formed on both sides of the printed circuit board 1' can be accurately processed so that it is within the allowable range of the design value. As a result, it is possible to maintain the reliability of the plating on the wall surface of the TH(C).

[0027] Therefore, the effects of the present invention were examined when forming TH(C) by the hole processing method using a carbon dioxide gas laser in a printed circuit board according to the present invention. For a printed circuit board 1' having a surface copper foil layer 3', which is an external conductor layer on both sides of an insulating layer 2', and a thickness of 2 μm and an insulating layer 2' thickness of 60 μm, an opening diameter in the surface copper foil layer 3', which is an external conductor layer of the printed circuit board 1', of φ60 μm and a center diameter of φ40±10 μm was formed. The conditions for intermittent pulse irradiation Lb were varied in various ways, that is, the processing quality of a combination of continuous pulse irradiation La and intermittent pulse irradiation Lb of various pulse widths (conditions 5 to 9) was compared with the processing quality of a combination of continuous pulse irradiation La for all shots (conditions 1 to 4). The results are shown in Table 2. The first shot of continuous pulse irradiation La has an energy density of 52 J / cm2 and a pulse width of 8 μs, with the aim of removing the surface copper foil layer 3', which is the surface conductor layer of the printed circuit board 1'. This is common to conditions 1 to 9 in Table 2, so it will be omitted here.

[0028] [Table 1]

[0029] As described above, an energy density of approximately 18 J / cm² is required to achieve a center diameter of 30 to 50 μm. However, continuous pulse irradiation La alone was unable to achieve a center diameter of 40 ± 10 μm, within the design tolerance range, i.e., 30 μm or more and 50 μm or less. In contrast, when the energy density was set to 18 J / cm² or more and intermittent pulse irradiation Lb was performed following the continuous pulse irradiation La, the pulse width of the intermittent pulse irradiation Lb was clearly insufficient, even if it was less than 1 μs, particularly 0.4 μs. Therefore, by setting the pulse width to 0.5 μs or more and 0.7 μs or less, the center diameter of the TH was achieved to 30 to 50 μm, confirming the effectiveness of the present invention. [Industrial Applicability]

[0030] In the multiple laser irradiations performed to form THs in printed circuit boards, a combination of continuous pulse irradiation and intermittent pulse irradiation improves the efficiency of laser processing, reduces operating costs, and achieves high processing accuracy. In addition, since the internal conductor layer provided within the insulating layer of the printed circuit board is not damaged during processing, the method can be applied to processing not only printed circuit boards but also any thin-walled and miniaturized boards. [Explanation of symbols]

[0031] 1' Printed circuit board 1a' one side 2' Insulating layer 2a' resin 2b' Glass cloth 3' (surface conductor layer) surface copper foil layer 5 holes A. Hole processing equipment for printed circuit boards a. Oscillator b Zoom b' lens c Aperture d Galvanometer scanner e Galvanometer mirror f Fθ lens g Processing table h laser iMirror j NC device C Through hole (TH)

Claims

1. A hole processing method for forming through holes (hereinafter referred to as "TH") using a laser in a printed circuit board that is composed of an insulating layer made of resin and glass fiber glass cloth, external conductor layers provided on both sides of the insulating layer, and an internal conductor layer provided within the insulating layer, comprising: A plurality of shots are performed to process holes in the printed circuit board, (1) In at least the first shot, continuous pulse irradiation is performed on an outer conductor layer on one surface of a printed circuit board to decompose and remove the outer conductor layer or a part of the outer conductor layer and the insulating layer; (2) In subsequent shots, continuous or intermittent pulse irradiation is performed to decompose and remove the insulating layer to a depth just before the position where the thickness of the printed circuit board is half (i.e., "at least the last shot of intermittent pulse irradiation is performed until the depth of the hole reaches the position where the thickness of the printed circuit board is half"; the same applies below), (3) Furthermore, at least immediately before the position where the thickness of the printed circuit board is halfway through, shots of intermittent pulse irradiation are performed to decompose and remove the insulating layer remaining up to the position where the thickness of the printed circuit board is halfway through; (4) Then, the other side of the printed circuit board is also processed in the same way as in (1) to (3), and holes are drilled from both sides.

2. A method for drilling holes in a printed circuit board using a carbon dioxide gas laser.

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