Method for laser processing of printed circuit boards and laser processing device for printed circuit boards

Abstract

A laser processing method and apparatus for printed circuit boards are provided, which effectively utilize a laser oscillator to optimize processing efficiency and quality. The laser processing method uses a laser oscillator to perform laser processing by applying RF pulses to oscillate the laser. During laser output after the application of the RF pulse ends, the RF pulse is applied again to continue laser oscillation, and a desired duration of laser light is extracted from the continuously oscillating laser for laser processing of the printed circuit board.

Description

Technical Field

[0001] This invention relates to a method and apparatus for processing circuit boards, and more particularly to a laser processing method and apparatus for printed circuit boards, which are suitable for forming blind vias (non-perforated vias, hereinafter simply referred to as holes or BHs) on an insulating layer during the manufacturing process of a packaging substrate. The insulating layer is composed of ABF material bonded to a copper layer or ABF coated with PET. Background Technology

[0002] Existing composite printed circuit boards have an insulating layer (hereinafter referred to as "insulating layer") made of resin containing glass fiber or filler sandwiched between the copper layer and the copper layer to form an integral whole. Holes of 40~120μm are laser-processed to serve as interlayer connections. These holes are then plated to connect the surface copper layer and the underlying copper layer.

[0003] First, let's explain the structure of existing laser processing equipment.

[0004] Figure 9 This is a structural diagram of an existing two-headed laser processing device.

[0005] A carbon dioxide laser oscillator 1 (hereinafter referred to as laser oscillator 1) outputs a pulsed, linearly polarized laser 2. A beam diameter adjustment device 3, disposed between the laser oscillator 1 and the beam splitter 4, is used to adjust the energy density of the laser 2, and the energy density of the laser 2 is adjusted by changing the outer diameter of the laser 2 output from the laser oscillator 1. That is, the energy of the laser 2 before and after the beam diameter adjustment device 3 does not change. Therefore, since the laser 2 emitted from the beam diameter adjustment device 3 can be considered as the laser 2 output from the laser oscillator 1, the laser oscillator 1 and the beam diameter adjustment device 3 are collectively referred to as laser output device 1A below. Alternatively, there are cases where the beam diameter adjustment device 3 is not used.

[0006] A beam splitter 4 is disposed between the beam diameter adjustment device 3 and the polarization conversion device 5A. The beam splitter 4 splits the laser 2 into lasers 2A and 2B, which are perpendicular to each other. Laser 2A is supplied to a first processing head (not shown in the figure); and laser 2B is supplied to a second processing head (not shown in the figure). Here, since the first and second processing heads have the same structure, objects with the same structure (marked 5 to 12) are marked with the prefixes A and B to distinguish them. That is, those marked 5A, 6A, 7A, 8A, 9A, 10Aa, 10Ab, 11A, and 12A are the structures applied to the first processing head, and those marked 5B, 6B, 7B, 8B, 9B, 10Ba, 10Bb, 11B, and 12B are the structures applied to the second processing head, and the objects corresponding to the symbols have the same structure. Hereinafter, only the case of the first processing head will be described.

[0007] The polarization conversion device 5A converts linearly polarized laser 2A into circularly polarized laser 6A. Furthermore, the polarization conversion device 5A includes a reflection light blocking mechanism (details omitted), which blocks the laser 6A reflected by the processed part during processing and prevents damage to the laser oscillator 1 caused by the laser 6A reflected by the processed part. The plate 7A, positioned between the polarization conversion device 5A and the galvanometer reflector 10Aa, is made of a material that prevents the laser 6A from passing through (e.g., copper), and can selectively form multiple apertures 8A (windows, in this case, circular through-holes) at designated positions. The plate 7A is driven by a drive device (not shown) and the axis of the selected aperture 8A is coaxially positioned with the axis of the laser 6A. The galvanometer device 9A consists of a pair of galvanometer reflectors 10Aa and 10Ab, which can rotate freely around the rotation axis as shown by the arrows in the figure, and the reflecting surface can be positioned at any angle. An fθ lens (condenser lens) 11A is disposed on the first processing head (not shown). A galvanometer reflector 10Aa, 10Ab and the fθ lens 11A constitute an optical axis positioning device, which positions the optical axis of the laser 6A at the desired position 12A on the printed circuit board. The scanning area (i.e., the processing area) 12A, defined by the rotation angles of the galvanometer reflectors 10Aa, 10Ab and the diameter of the fθ lens 11A, is approximately 50mm × 50mm. The printed circuit board 13, which is a processed component and is composed of a copper layer and an insulating layer, is fixed to the XY stage 14. Furthermore, the first processing head and the second processing head can process printed circuit boards 13 with the same pattern or with different patterns. The control device 20 controls the laser oscillator 1, the beam diameter adjustment device 3, the driving devices of the flat plates 7A and 7B, the galvanometer reflectors 10Aa, 10Ab, 10Ba, 10Bb, and the XY stage 14 (or, depending on the situation, the first processing head and the second processing head each correspond to one XY stage).

[0008] Then, when machining holes, the XY stage 14 is moved so that the designated machining areas 12A and 12B are facing the fθ lenses 11A and 11B respectively. First, the holes are machined by irradiating all the copper layers in the machining areas 12A and 12B with a single beam (i.e., a single pulse irradiation). Then, the insulating layer is machined by irradiating with one or more pulses to complete the machining of holes in the machining areas 12A and 12B.

[0009] See Figure 9 and Figure 10 , Figure 10 The attached diagram shows the setting time of the galvanometer reflector and the laser irradiation time, with the horizontal axis representing time.

[0010] Figure 9In the first processing head, the time during which the positioning time at a certain processing point becomes longer between the galvanometer reflector 10Aa and the galvanometer reflector 10Ab is called the galvanometer detection time GA of the first processing head. Figure 10 The reference galvanometer mirrors 10Ba and 10Bb of the second processing head, the time during which the positioning time at a certain processing point becomes longer, is called the galvanometer detection time GB of the second processing head. Figure 10 The standard designation is GB1 or GB2). L1 represents the duration of one laser irradiation session.

[0011] As attached Figure 10 As shown in (a), when the printed circuit board 13 processed by the first processing head and the second processing head (or each processing head corresponds to one printed circuit board) has the same processing content and the same detection time, laser 2 can be supplied to both processing heads simultaneously. However, as shown in the attached diagram... Figure 10 As shown in (a) and (b), when the processing contents of the first and second processing heads are different, or when the current checking times GA and GB are different, a longer current checking time is required to simultaneously supply laser 2 to both the first and second processing heads. That is, when GA1...<GB1、GA2> When processing GB2, there is a waiting time of (GB1-GA1) in the first processing head and a waiting time of (GA2-GB2) in the second processing head. Therefore, the overall processing efficiency will decrease.

[0012] The problem that the invention aims to solve:

[0013] In recent years, with the advancement of substrate thinning, holes have been fabricated in insulating layers without copper layers on the surface to create substrates for packaging. In this case, when the diameter of the fabricated holes is less than 60 μm, the required output for processing is approximately 20 W. Next, a practical processing example will be described.

[0014] Figure 11 The example of laser irradiation is shown, with the vertical axis representing the output of the oscillating laser and the horizontal axis representing time. The upper section also shows the switching of the RF pulse (hereinafter referred to as RF) that excites the oscillation medium of the laser oscillator 1.

[0015] For example, when machining a 60μm hole in an insulating layer, following the output curve A1 with the output adjusted to 20W, the laser is irradiated for 20μs with an RF time, and then irradiated again with the same pulse period. That is, the machining time at this point is 180μs, calculated by adding the laser pulse period of the first pulse (100μs) after the galvanometer reflector is positioned, and the subsequent 80μs (including the 60μs time from RF termination to laser extinction) within the second 100μs pulse period after the first pulse. Here, unlike machining copper layers with high machining thresholds or insulating layers with a thickness exceeding 60μm after copper machining, this is machining an insulating layer with a low machining threshold and a thickness of only about 30μm. Therefore, the heat accumulated in the machining area is smaller, allowing for two consecutive laser irradiations.

[0016] In addition, as Figure 11 As shown, output curve A1 exhibits a first peak output immediately after RF application (the output duration is short). This first peak output is approximately half the second peak output during a standard RF application time (20 μs). Furthermore, after RF application ceases, the energy accumulated in the oscillation medium within the laser oscillator is converted into laser light. In the illustrated case, the duration of the laser light emitted due to the oscillation medium within the laser oscillator is approximately 60 μs.

[0017] However, the above processing may result in the following adverse conditions.

[0018] (1) The diameter of the entrance of the processed hole may increase by 2 to 3 μm due to the influence of the first peak output.

[0019] (2) Due to the variation in laser output, the diameter of the processed holes is uneven.

[0020] The output variation of the laser described above is illustrated here.

[0021] Figure 12 To show the output variation for the second peak output, Figure 12 (a) shows the pulse frequency as 1–5 kHz. Figure 12 (b) shows the pulse frequency range of 1–10 kHz. For example, when the spacing of the processed holes is approximately the same, the second peak output remains almost unchanged. However, since the spacing of the processed holes is determined by the spacing of the mounts on the printed circuit board or the position of the holes connected to the underlying copper layer, it will not be consistent. As a result, the gain accumulated in the excitation medium will change due to the variation in the laser excitation interval (i.e., the duty cycle), and thus… Figure 12As shown in (a), the output varies by approximately ±3% when the frequency is between 1 and 5 kHz, and as... Figure 12 As shown in (b), the output varies by about ±5% at frequencies ranging from 1 to 10 kHz. Therefore, the diameter of the machined holes will vary.

[0022] (3) During the RF stop period after the RF application time of 20 μs, the energy accumulated in the laser medium will irradiate the processing part for about 60 μs from the start of the RF stop, causing the temperature of the processing part to rise. Even if the temperature rise of the processing part is lower than the processing threshold of the insulating layer, if this period lasts for more than 10 μs, the insulating layer at the bottom of the hole and the hole wall will be easily carbonized, thus reducing the processing quality of the hole.

[0023] As explained above, the industry expects that uniform hole diameters during processing can prevent a reduction in the quality of the insulation layer.

[0024] The purpose of this invention is to provide a laser processing method and apparatus for printed circuit boards that achieves excellent processing efficiency and high quality by effectively utilizing a laser oscillator. Summary of the Invention

[0025] The purpose of this invention is to provide a laser processing method and apparatus for printed circuit boards, which effectively utilizes a laser oscillator to optimize processing efficiency and quality.

[0026] To solve the above-mentioned problems, the first means of the present invention is:

[0027] A laser processing method for printed circuit boards uses a carbon dioxide laser oscillator to perform laser processing. The carbon dioxide laser oscillator oscillates the laser by applying RF pulses. During the laser output period after the application of the RF pulses ends, the laser oscillation is continued by applying the RF pulses again. A laser of a desired duration is extracted from the continuously oscillating laser to perform laser processing on the printed circuit board.

[0028] The second aspect of the present invention is the aforementioned laser processing method for printed circuit boards, wherein a sawtooth pulse is generated by controlling the application time and the stop time of the RF pulse, and processing is performed using the generated sawtooth pulse.

[0029] The third aspect of the present invention is the aforementioned laser processing method for printed circuit boards, wherein at least one of the following is controlled: the sum of the application time of the RF pulse and the stop time of the RF pulse, or the ratio of the application time of the RF pulse to the stop time of the RF pulse.

[0030] The fourth means of the present invention is:

[0031] A laser processing apparatus for printed circuit boards uses a carbon dioxide laser oscillator to perform laser processing, the carbon dioxide laser oscillator oscillating the laser by applying RF pulses, and the laser processing apparatus includes a control device.

[0032] The control device performs the following control: during the laser output period after the application of the RF pulse ends, the RF pulse is applied again to continue laser oscillation, and a laser of the desired duration is extracted from the continuously oscillating laser and supplied to the processing unit.

[0033] The fifth aspect of the present invention is that the aforementioned laser processing apparatus for printed circuit boards further includes multiple processing heads, forming an architecture for distributing laser from the carbon dioxide laser oscillator to each of the processing heads. When the positioning of any one of the processing heads is completed, the control device supplies laser to the processing head without considering the positioning status of the other processing heads.

[0034] The beneficial effects of this invention are as follows: Through the above-described method and apparatus, not only can the diameter of the processed holes and the quality of the hole walls be improved, but processing efficiency can also be increased. Furthermore, because of the continuously oscillating and stable laser, when supplying laser to multiple processing heads, the necessary laser can be supplied to any one processing head without affecting other processing heads, thus improving the processing efficiency of the laser processing apparatus. In this way, the diameter of the processed holes can be made uniform, while the quality of the hole walls is improved, and processing efficiency is also increased. Moreover, because the laser can oscillate continuously and stably, and because the necessary laser can be supplied to multiple processing heads without affecting other processing heads, the processing efficiency of the laser processing machine can be improved. Attached Figure Description

[0035] Figure 1 The accompanying drawing illustrates the essential elements of the sawtooth wave of the present invention.

[0036] Figure 2 Here is an example of the output waveform;

[0037] Figure 3 The accompanying drawing illustrates the steps for generating the sawtooth wave according to the present invention.

[0038] Figure 4 This is a diagram illustrating the energy required when the hole is opened;

[0039] Figure 5 (a) and (b) in the figure are attached diagrams illustrating the spatial distribution of the output energy;

[0040] Figure 6 This is a structural diagram of an embodiment of the laser processing apparatus for printed circuit boards of the present invention (two-head laser processing apparatus);

[0041] Figure 7(a) and (b) in the figure are attached diagrams showing the setting time of the galvanometer reflector and the laser irradiation time;

[0042] Figure 8 (a), (b), (c), and (d) in the figure are illustrations of rectangular pulses during the processing of an insulating layer containing filler;

[0043] Figure 9 This is a structural diagram of an existing two-headed laser processing device;

[0044] Figure 10 (a) and (b) in the figure are attached diagrams showing the setting time of the galvanometer reflector and the laser irradiation time;

[0045] Figure 11 The accompanying diagram illustrates an example of laser irradiation; and

[0046] Figure 12 (a) and (b) in the figure are the output changes of the second peak output. Detailed Implementation

[0047] Figure 1 This is a drawing illustrating the constituent elements of the sawtooth wave of the present invention.

[0048] again, Figure 1 The output curve C (basic pulse waveform) is the output curve for 60% of the rated duty cycle (i.e., RF application time / pulse period. Hereinafter, "Dty" represents "rated duty cycle"), with a frequency of 10KHz and a maximum output of 250W.

[0049] First, let's explain the output curve C. If the RF is activated at time T0, the laser will be explosively output at time T1. After reaching the first peak output at time Tj, it weakens until time Td, then increases again, reaching the second peak output of 250W at time T2, 60 μs after the RF application time from time T0. Here, the output shown as a solid line during the RF application time is the sum of the output transferred from the N2 gas to the CO2 gas via the excitation medium (time T2, shown as a dashed line around 60 μs), and the output of the CO2 gas directly excited by the RF (i.e., the output shown as a dashed line and the output shown as a solid line). If the RF application is stopped, the output of the CO2 gas directly excited by the RF becomes 0, and the laser output is the energy accumulated in the excitation medium (N2 gas) within the laser oscillator after time T2. Furthermore, the energy accumulated in the excitation medium is output approximately 60 μs after time T2.

[0050] The inventors first confirmed the following requirements through experiments and simulations:

[0051] 1.Requirement 1

[0052] For example, when oscillation is performed with an RF applied at 10 kHz and a Dty of 60% (pulse width 60 μs), as shown in output curve C, the oscillating laser output gradually increases and reaches its maximum at the 60 μs pulse width. Furthermore, the output decays after the RF application stops. Also, when oscillating within the Dty (RF application time / RF period) range of the laser oscillator, even if the RF application time changes, the output will still follow the same output curve (…). Figure 1 The output curve C rises. That is, when oscillating at Dty 40% (pulse width 40μs) and 10kHz, the output rises along the output curve C, reaching its maximum at a pulse width of 40μs, and then decays in the same manner as described above. Furthermore, when oscillating at Dty 20% (pulse width 20μs) and 10kHz, the output rises along the output curve C, reaching its maximum at a pulse width of 20μs, and then decays in the same manner as described above. Figure 1 The part marked P1 is the output rising section, and the part marked P2 is the output switching section.

[0053] 2. Requirement 2

[0054] When using a carbon dioxide laser, if RF is applied at time T0, the laser will start to oscillate at time T1 due to the excitation output accumulated in the excitation medium. The output increases rapidly and becomes the first peak output Wj at time Tj. After a period of decay (at time Td), the output increases again and becomes the second peak output when the RF application stops.

[0055] At this time, time Td is between 0.4 and 0.5 μs from time T0. Even if Dty and pulse width change, it can still be seen that the output response (output change per unit time) Ws is roughly fixed in time Td.

[0056] 3. Requirement 3

[0057] Furthermore, after the RF application is stopped, the laser output switches from 250W to output based on the residual energy accumulated in the laser medium. The switching time is 0.4~0.5μs, with the output initially decreasing, then increasing slightly, and then decreasing again. Hereinafter, the output response during the output switching, when the output decreases, is called the output response Wc, and the output response during the slight increase is called the output response Wd. This output response Wc is a value that remains almost unchanged even if Dty and pulse width change. Also, although the output response Wc and the aforementioned output response Ws have different output directions, the magnitudes of their output components are almost the same.

[0058] 4.Requirement 4

[0059] Figure 2This is an example of an output waveform, specifically the output waveform when the energy accumulated in the waveform excitation medium is reapplied at the end of the pulse period and RF is applied again. For example... Figure 2 As shown, if there is a cumulative residual output in the excitation medium at the start of RF application (i.e., ... Figure 2 The Δz shown by the slash is Δw, while the output at the start of RF application is Δw. Here, Δw > 0. Therefore, at the start of the next (second) pulse cycle, the excited output will overlap with the residual output, as shown by the slash. After 0.4–0.5 μs, the output response Ws will increase. At this point, the first peak output Wj will not occur. Furthermore, this description refers to the situation between the first and second pulse cycles. However, if repeated to the nth pulse cycle, the output intensity of the output response Ws will gradually increase, relatively causing the second peak output to gradually decrease, but it will stabilize after about 1 second.

[0060] Here, the above Figure 11 Under these conditions, since the remaining energy accumulated in the excitation medium before the start of the second pulse cycle becomes 0, the output curve of the second pulse cycle is the same as that of the first pulse cycle.

[0061] See Figure 1 Here, the average output Wav is defined as the integral value of the output curve C that oscillates continuously at Dty 60% (i.e., the total energy output during the pulse period of 0–100 μs) divided by the pulse period of 100 μs. Furthermore, when Dty is fixed and the pulse period is within the range of 20–200 kHz... Figure 1 The average output Wav shown remains almost constant. On the other hand, when the pulse period is fixed, the average output Wav increases proportionally to Dty. Furthermore, the output response Wr in the tangent direction of output curve C (see...) Figure 3 ) and output response Wf (see Figure 3 ) is the value inherent to the pre-set average output.

[0062] Also, at Figure 1 The records include sawtooth waves at 100kHz and 200kHz, among which, Figure 1 The label P3 indicates the output rise section, P4 indicates the output switching section, and P5 indicates the continuation of the next output rise section. Detailed information is available using... Figure 3 To explain.

[0063] Figure 3 The accompanying drawing illustrates the steps for generating the sawtooth wave according to the present invention.

[0064] For the output curve C (see) Figure 1By setting Dty = trf1 / tm (where tm is the pulse period, composed of the RF application time trf1 and the RF application stop time trf0) in the formula, the average output Wav is determined. Even if the pulse period tm is shortened, if the ratio of the RF application time trf1 to the RF application stop time trf0 remains the same, Dty will remain the same, and the average output Wav will not change. Here, the sawtooth wave of the present invention is generated based on the basic wave pulse waveform (the output curve C mentioned above) and the above-mentioned requirements 1 to 4.

[0065] The generation method of the sawtooth wave is described below. The sawtooth pulse of the present invention is generated based on the basic wave pulse waveform (output curve C above) through the following steps.

[0066] Step 1: Using the vertical axis as the output axis, set Dty, pulse period tm, average output Wav, and upper limit output Wp. Here, the upper limit output Wp is the output (J / s) sufficient to achieve the target aperture with the irradiation pulse, and is set to the value corresponding to the material threshold. The lower limit output Wv is an output larger than the processing critical value Wm of the insulating layer.

[0067] Step 2: Using the horizontal axis as the time axis, designate the point on the lower limit output Wv at time t0 as Q1, and the point on the lower limit output Wv at time t2 (which is the pulse period) as Q6. Then, mark the output response Ws starting from point Q1, and mark the end point of the output response Ws as point Q2.

[0068] Step 3: Connect point Q2 to point Q3 on the upper limit output Wp at time t1 using the output response Wr. Also, time t1 is the end point of trf1 (the starting point of trf0).

[0069] Step 4: Take point Q3 as the starting point and mark the output response Wc, and take the end point of the output response Wc as point Q4.

[0070] Step 5: Mark the small output response Wd on the extension line connecting point Q1 and point Q4, and take the endpoint as point Q5.

[0071] Step 6: Connect point Q5 and point Q6 with the output line segment Wf. That is, point Q5 is the intersection of the extension of the line connecting points Q1 and Q4 and the output response Wf with point Q6 as the starting point.

[0072] By following the steps above, the sawtooth wave applied to the lower limit output Wv is completed.

[0073] Hereinafter, the polygon formed by the above steps, which overlaps with the sawtooth pulse of the lower limit output Wv, will be referred to as the "sawtooth pulse".

[0074] Furthermore, as explained below (when changing the pulse period tm under a fixed Dty... referred to as "sawtooth n rectangular pulse"), the output of the laser oscillator will become stable after more than 1 second. As long as the laser oscillator remains in operation, the variation range between the average output Wav and the upper limit output Wp is approximately ±1%.

[0075] Figure 1 The diagram shows a 100kHz sawtooth pulse and a 200kHz sawtooth pulse generated through the steps described above.

[0076] Also, such as Figure 3 As shown, points Q1 and Q4 are connected by a dashed line. The output enclosed by the quadrilateral Q1Q2Q3Q4 is as described above. Figure 1 The accompanying drawing illustrates the constituent elements of the sawtooth wave of the present invention… The energy accumulated in the excitation medium is output approximately 60 μs after time T2, which is equivalent to the output of CO2 gas directly excited by RF.

[0077] Furthermore, when the pulse period tm is changed under a fixed Dty, the output responses Ws and Wc do not change. On the other hand, although the output responses Wr, Wd, and Wf change with the pulse period tm, the average output does not change.

[0078] Furthermore, when Dty is changed within a fixed pulse period tm, the output responses Ws and Wc remain almost unchanged, and the changes in output responses Wr, Wd, and Wf are relatively small. Also, although the average output changes according to Dty, each remains a fixed value.

[0079] Therefore, by setting the pulse period tm, RF application time trf1, and RF application stop time trf0 within the Dty range, the waveform and output of the sawtooth pulse can be controlled.

[0080] In actual processing, the aforementioned waveform generation steps are performed continuously to generate n sawtooth pulses (n is an integer greater than or equal to 1, hereinafter referred to as "sawtooth n rectangular pulses").

[0081] Figure 4 This is an attached diagram illustrating the energy generated when the hole is opened; the vertical axis represents the output, and the horizontal axis represents time.

[0082] Here, it is assumed that the machined hole is the same as described above. Figure 11 If the hole described is the same, then the prior art uses two pulses with a pulse frequency of 10kHz for processing, with two laser irradiation times of 20μs each. The processing time is the sum of the pulse period of the first pulse (100μs), the RF application time of the second pulse (20μs), and the non-excitation time (60μs), which is 180μs. On the other hand, in the case of the present invention, as... Figure 4As shown, processing with two rectangular pulses of 100kHz for the sawtooth 2 achieves the same pulse energy as existing methods, without being affected by the pulse period. Therefore, the interval between the two rectangular pulses can be arbitrarily set. Even if the interval between the two sawtooth rectangular pulses is set to 60μs (the existing pulse interval is 20μs), the processing time is 100μs. Therefore, according to the present invention, the processing time can be shortened by 80μs compared to existing methods.

[0083] Next, the case and the prior art will be explained with reference to the shape of the machined hole.

[0084] Figure 5 This is a diagram illustrating the spatial distribution of the output energy. Figure 5 (a) in the text describes the situation in this case. Figure 5 (b) in the diagram represents the current state of the technology. The vertical axis represents the standardized energy level and processing depth, and the horizontal axis represents the radial direction of the hole. Here, Ds represents the spot diameter of the processing section, DR represents the target hole diameter, DR1 and DR' represent hole diameters smaller than DR, and DB and DB' represent the bottom diameter of the hole. Furthermore, Lv0 represents the position of energy level 0, Lv1 represents the surface position of the insulating layer, Lv2 represents the bottom position of the insulating layer, and k represents the processing threshold of the insulating layer. Also, ep represents the energy distribution when outputting Wp, ev represents the energy distribution when outputting Wv, eav represents the energy distribution when the average output Wav is reached, 1e represents the energy distribution of the first pulse, and 2e represents the energy distribution of the second pulse. In addition, the outputs Wp, Wv, and average output Wav are as follows: Figure 3 As shown.

[0085] See Figure 3 and Figure 5 The following will explain the machining steps corresponding to the radial direction of the machined hole. Furthermore, the energy distribution during the RF application time trf1 when the machining diameter increases is called the diameter increase energy distribution, and the energy distribution during the RF application stop time trf0 when the machining diameter decreases is called the diameter decrease energy distribution. Machining begins with an output response Ws that is superimposed on the output Wv at the same time as the RF application, resulting in an output increase of approximately 0.4 μs. Machining is then performed based on the machining diameter increase energy distribution of the output response Wr. After time trf1, the entrance diameter of the target hole is formed. When the RF application stops, machining is performed again based on the output response Wc of the machining diameter decrease energy distribution, the output response Wd of the machining diameter slight increase, and the output response Wf of the machining diameter decrease energy distribution.

[0086] In the above processing steps, processing is performed using alternating beam diameters DR and DB, and DR' and DB'. The output rise at the start of processing is steeper and the irradiation time is shorter than existing pulses. Furthermore, since the energy distribution diameter decreases and moves away from the hole entrance and sidewalls after RF application stops, heat conduction at the hole entrance and sidewalls during insulating layer processing is reduced, thus mitigating the thermal impact of the insulating layer on the hole walls and improving hole quality. Also, because sawtooth pulse processing is performed continuously, laser irradiation unrelated to processing, as in existing techniques, is avoided. Therefore, the quality of the hole entrance and hole walls is not reduced. Moreover, since it is not affected by the first peak output, the hole entrance diameter does not increase.

[0087] Figure 6 This is a structural diagram of an embodiment of the laser processing apparatus for printed circuit boards of the present invention (a two-headed laser processing apparatus), and... Figure 9 Use the same symbol for objects that are identical or have the same function, and omit detailed descriptions.

[0088] By setting the application and stopping times of the high-frequency RF driving the laser oscillation, a laser oscillator 1 outputs a continuously linearly polarized sawtooth laser 2 with a frequency of 50 kHz or higher. A beam diameter adjustment device 3, disposed between the laser oscillator 1 and a beam splitter 4, is a device for adjusting the energy density of the laser 2. It adjusts the energy density of the laser 2 by changing the outer diameter of the laser 2 output from the laser oscillator 1. That is, the energy of the laser 2 before and after the beam diameter adjustment device 3 does not change. Therefore, since the laser 2 emitted from the beam diameter adjustment device 3 can be regarded as the laser 2 output from the laser oscillator 1, the laser oscillator 1 and the beam diameter adjustment device 3 are combined into a single laser output device 1A. Alternatively, the beam diameter adjustment device 3 may not be used.

[0089] An AOM 50A (driven by a driver 61B, which drives an AOM 50B) is disposed between the beam splitter 4 and a polarization conversion device 5A. The AOM 50A splits a laser 2A into a first-order laser 2A1K and a second-order laser 2A0 (the AOM 50B splits a laser 2B into a first-order laser 2B1K and a second-order laser 2B0). By changing the distribution ratio (aperture), the output of the laser 2A1K used for processing is adjusted. Unused laser 2A0 is disposed of in a buffer (not shown) to minimize its diffusion to the surrounding area.

[0090] This laser processing apparatus is configured to position a second processing head relative to a fixed first processing head in the X direction via a second processing head moving device (not shown). The apparatus is also configured to extend the position of the second processing head relative to the first processing head by a maximum distance *s*. A mirror 31 and a mirror 34 are fixed in predetermined positions, and two mirrors 32 and 33 are supported by a mirror moving device (not shown) and can be freely positioned in the X direction. Furthermore, the mirrors 31-34 are configured such that, regardless of the position of the mirrors 32 and 33 in the X direction, the axis of an aperture 8B coincides with the center of a current detector 10Ba. A control device 20 controls the laser oscillator 1, the beam path adjustment device 3, the drive components 61A and 61B of the AOM, the drive devices of multiple plates 7A and 7B, the galvanometer reflectors 10Aa, 10Ab, 10Ba, and 10Bb, and an XY stage 14 (which may also be a first processing head and a second processing head, each corresponding to an XY stage, depending on the situation); a moving device for a second processing head (not shown in the figure) and a mirror moving device.

[0091] The processing steps are described below. Furthermore, the processing content may vary depending on the processing head, but since the operation is essentially the same, the process will be described using the first processing head as an example.

[0092] After the processing is initiated, the control device 20 drives the moving device of the second processing head and moves the second processing head to the designated position. Next, the XY stage 14 is controlled to position the first processing head in the processing position, and the galvanometer reflectors 10Aa and 10Ab are positioned at the starting processing position and placed in standby mode. Additionally, the moving device of the second processing head (not shown) is activated to move the second processing head a distance s relative to the first processing head. Then, the mirror moving device (not shown) is operated to move the position of the mirror 32 a distance s / 2 in the direction of movement of the second processing head. Thus, since the distance between the aperture 8B and the galvanometer reflector 10Ba becomes constant, the size of the image of the aperture 8B remains constant regardless of the position of the second processing head.

[0093] Then, the laser oscillator 1 is activated first, and after a predetermined waiting time, the processing programming is initiated to begin processing. The reason for setting the waiting time is that the output of the laser oscillator 1 is unstable until it reaches thermal equilibrium, which takes approximately 1 to 2 seconds.

[0094] Then, after a waiting period, the control device 20 outputs the serrated laser 2 (hereinafter simply referred to as laser 2) from the laser oscillator 1 according to the pre-input processing program. The laser 2 changes its diameter through the beam diameter adjustment device 3 and is split into laser 2A by the beam splitter 4, and then incident on the AOM 50A. The AOM 50A discards the laser 2A in the buffer until it receives an action command from the control device 20. After receiving a positioning completion signal from the galvanometer reflector 10Aa and 10Ab, which is the one that completed positioning later, the control device 20 actuates the AOM 50A through the drive unit 61A to output the laser 2A as a rectangular pulse 2A1K (i.e., the first-order laser 2A1K mentioned above), which consists of n serrated pulses attenuated to a predetermined output. The rectangular pulse 2A1K is positioned by the galvanometer reflectors 10Aa and 10Ab and incident on a designated location on the printed circuit board 13 to form a hole in the printed circuit board 13. Hereinafter, as in the existing process, the above-described hole-forming operation is repeated until the specified processing is completed. Furthermore, during the above processing, the laser oscillator 1 continuously outputs the laser 2 from the start to the end of the processing by switching the RF on and off at a predetermined period and pulse period.

[0095] Figure 7 The accompanying drawing shows the setting time of the galvanometer reflector and the laser irradiation time in this invention. Figure 7 (a) shows the case where the first processing head is used. Figure 7 (b) shows the case where the second processing head is used, and Figure 7 The horizontal axis represents time. For example... Figure 7 As shown, the lasers 2A and 2B, composed of sawtooth pulses, are normally output during processing. In the case of the first processing head, after the current checking times GA1 and GA2 are completed, the rectangular pulse 2A1K, consisting of the necessary n sawtooth pulses, is irradiated onto the processing section via the AOM50A to form a hole. At this time, the first processing head can continue operating without considering the current checking times GB1 and GB2 of the second processing head. Similarly, the second processing head can also continue operating without considering the current checking times GA1 and GA2 of the first processing head. Thus, since each processing head does not require waiting time, the processing efficiency can be improved by 20-30% compared to the prior art. Furthermore, according to the control clock signal of the device omitted in the figure, after the positioning of the galvanometer reflector is completed, the AOM50 is controlled to apply the RF start time in conjunction with the initial sawtooth pulse, ensuring that the rectangular pulses supplied to the processing section are not missing or interrupted.

[0096] Next, the structure of the saw teeth of the present invention will be described in detail.

[0097] Figure 8 This diagram illustrates the rectangular pulses generated during the processing of an insulating layer containing filler (reinforcing material). The horizontal axis represents time, and t is the time referenced to t0.

[0098] exist Figure 8 The upper section displays the AOM's operation, where A represents the AOM's opening degree of 100% and mA represents the AOM's opening degree of m%. The middle section displays the RF's on or off status, where tm is the pulse period, trf1 is the RF's on period, and trf0 is the RF's off period. The lower section displays the outputs, where Wpf is the upper limit output for processing the filler in the insulating layer, and Wpr is the upper limit output for processing the resin in the insulating layer.

[0099] Figure 8 In (a) of the diagram, the laser beam path is expanded during RF startup, primarily for processing the filler material. During RF shutdown, the laser beam path is narrowed to rapidly remove gas or machining debris generated during processing from the machining area, thus improving the machining quality of the hole walls and bottom. Furthermore, Figure 8 (b) Figure 8 (d) in the middle is also related to Figure 8 Similarly, in (a), it can quickly remove gas or machining chips generated during machining from the machining section, thus improving the machining quality of the hole walls and the bottom of the hole.

[0100] also, Figure 8 (c) in the middle is Figure 8 Examples of changes to the portion enclosed by the dashed line in (a) are shown below. Figure 8 Example of waveform control in (a) during the output rise phase of RF startup (starting from time td1 in the figure, AOM is only started at time ta). In this way, processing with the average output Wavh at the high point of the output rise phase can make the hole entrance step and hole wall uniform, thereby improving the hole quality. In addition, tg is the time when AOM is turned off, and tp is the time point when AOM is first started.

[0101] For example, when you want to tilt the hole towards its depth, you can use... Figure 8 (d) in the middle.

[0102] Next, we will explain the processing example.

[0103] use Figure 8 The rectangular pulses with sawtooth n in (a), (b), and (c) are either Figure 11 The results of processing an insulating layer (ABF material manufactured by Ajinomoto Co., Ltd., approximately 30 μm thick) containing encapsulation filler with the same 60 μm aperture are as follows. Additionally, Figure 8It displays the shape of the sawtooth pulses, rather than the rectangular pulses of the sawtooth n used for machining.

[0104] exist Figure 8 Under condition (a) in the above, the machining is performed with two rectangular pulses of sawtooth 3 at a frequency of 100KHz, Dty 60% (trf1=6μs, trf0=4μs), and AOM opening of 100%. The hole inlet diameter is about 62μm and the hole (bottom diameter / inlet diameter) ratio is about 80%.

[0105] exist Figure 8 Under condition (b) in the above, the machining is carried out with two rectangular pulses of sawtooth 3 with a frequency of 100KHz, Dty 60% (trf1=6μs, trf0=4μs), and AOM opening of 0%. The hole inlet diameter is about 60μm and the hole (bottom diameter / inlet diameter) ratio is about 80%.

[0106] exist Figure 8 In condition (c), machining is performed with two rectangular pulses of sawtooth 3 at a frequency of 100KHz, Dty 60%, td1=6μs, under the condition of 0% AOM opening, or ta=4μs, under the condition of 100% AOM opening. The hole inlet diameter is about 60μm and the hole (bottom diameter / inlet diameter) ratio is about 81%.

[0107] And in Figure 8 In cases (a), (b), and (c), almost no resin carbonization was found on the copper layer surface at the bottom of the hole.

[0108] Furthermore, if in Figure 11 Under the existing pulse conditions shown, processing was performed with a pulse width of 20 μs, a pulse frequency of 10 kHz, and a pulse number of 4. The hole entrance diameter was approximately 65 μm, and the hole (bottom diameter / entrance diameter) ratio was approximately 77%. Furthermore, resin carbonization was observed on the copper surface at the bottom of the hole. Additionally, when the first peak output Wj of the pulse was higher than the second peak output Wp, the increased output during processing caused refracted light from the higher first peak output Wj, resulting in ring-shaped damage around the hole entrance.

[0109] Also, please see Figure 3 The optimal output response values ​​Ws, Wc, Wr, Wd, and Wf will vary depending on the material of the workpiece. Therefore, setting the output response values ​​Ws, Wc, Wr, Wd, and Wf to the most appropriate values ​​according to the material of the workpiece can improve processing quality and speed.

[0110] Incidentally, in actual processing, the values ​​of the output energy levels Wp and Wv, and the output responses Ws, Wc, Wr, Wd, and Wf for each workpiece can be known in advance. Furthermore, the maximum output of the laser oscillator can be known in advance when determining the rated working cycle and pulse period. Moreover, the appropriate aperture diameter corresponding to the machining aperture is also known.

[0111] Here, if processing is being done on a first-time material, the values ​​of energy levels Wp and Wv are tentatively determined by referring to existing data. The output energy level Wp is then adjusted by comparing the hole diameter obtained through experiments with the desired hole diameter. Next, processing is performed using sawtooth pulses n, with the value of n determined based on the depth of the processed hole. However, increasing n will cause quality degradation due to heat in the insulating layer. Therefore, if the value of n is large, a rectangular pulse with multiple sawtooth pulses m should be used, and a cooling time for the processing unit should be provided between each rectangular pulse.

[0112] In addition, such as Figure 6 In the dual-head laser processing machine shown, if the output of laser oscillator 1 is 250W, the average output is 125W. Therefore, it is divided using beam splitter 4, and each processing head is supplied with an output of 62.5W. Thus, as explained above (followed by a processing example… causing annular damage around the hole entrance), when Wpf = 20W, both the first and second processing heads can be used for processing. However, for example, when processing resin with a PET carrier film, Wpf = 70W is required. Here, if Wpf = 70W is required, then… Figure 6 The output of oscillator 1 needs to be, for example, 500W.

[0113] Furthermore, the laser oscillator illustrated in the above examples has a basic pulse waveform whose output characteristics are such that the first peak output immediately after RF application is smaller than the second peak output when RF application stops. Figure 1 Output curve C Figure 11 The output curve A1) can be applied to laser oscillators whose output characteristics are such that the first peak output immediately after RF application is larger than the second peak output when RF application stops, which is the basic wave pulse waveform.

[0114] In summary, the laser processing method and apparatus for printed circuit boards of the present invention can indeed achieve the objectives of the present invention.

[0115] The above description is merely an embodiment of the present invention and should not be construed as limiting the scope of the present invention. Any simple equivalent changes and modifications made in accordance with the claims and description of the present invention shall still fall within the scope of the present invention.

Claims

1. A laser processing method for a printed circuit board, using a carbon dioxide laser oscillator to perform laser processing by applying an RF pulse to oscillate laser light, characterized by: during a laser output period after the application of the RF pulse is completed, continuing laser oscillation by applying the RF pulse again, generating a sawtooth pulse by controlling the ratio of the application time and the stop time of the RF pulse in a pulse period so that the energy of the pulse in a single pulse period changes in a sawtooth shape, and extracting the sawtooth pulse for a desired time from the continuous sawtooth pulses to perform laser processing for a printed circuit board; setting a duty cycle Dty = trfl / tm, tm being a pulse period, and being constituted by an RF application time trfl and an RF application stop time trfo, the sawtooth pulse being generated in the following manner: Step 1: setting a duty cycle Dty, a pulse period tm, an average output Wav, an upper limit output Wp, and a lower limit output Wv, the upper limit output Wp being an output calculated so as to be sufficient to obtain a target aperture for an irradiation pulse, the lower limit output Wv being an output larger than a processing threshold value Wm of an insulating layer; Step 2: setting a time axis as a horizontal axis, setting a point on the lower limit output Wv at time t0 as Ql, and setting a point on the lower limit output Wv at time t2 which is a pulse period as Q6, indicating an output response Ws with the point Ql as a starting point, and setting the end point of the output response Ws as a point Q2; Step 3: connecting the point Q2 and a point Q3 on the upper limit output Wp at time tl with an output response Wr, time tl being the end point of trfl; Step 4: setting the point Q3 as a starting point and indicating an output response Wc, and setting the end point of the output response Wc as a point Q4; Step 5: indicating a small output response Wd on an extension line connecting the point Ql and the point Q4, and setting the end point as a point Q5; Step 6: connecting the point Q5 and the point Q6 with an output line segment Wf; by the above steps, the sawtooth pulse applied to the lower limit output Wv is completed; the output enclosed by a quadrangle QlQ2Q3Q4 corresponds to the output of the carbon dioxide gas directly excited by the RF pulse. Further, a plurality of processing heads are used, and an architecture in which laser light is distributed from the carbon dioxide laser oscillator to each of the processing heads is constituted, and when the positioning of any one of the processing heads is completed, laser light is supplied to the processing head regardless of the positioning state of the other processing heads.

3. A laser processing apparatus for a printed circuit board, using a carbon dioxide laser oscillator to perform laser processing by applying an RF pulse to oscillate laser light, the laser processing apparatus including a control device, characterized by: ​ ​ ​ ​ ​ ​ ​ ​ ​ 2. The laser processing method of a printed circuit board according to claim 1, characterized by: ​ ​ The control device controls to generate a sawtooth pulse by controlling a ratio of an application time and a stop time of the RF pulse in a pulse period so that an energy of a pulse of a single pulse period is varied in a sawtooth shape to continue laser oscillation by re-applying the RF pulse during a laser output period after the application of the RF pulse ends, and to take out the sawtooth pulse of a desired time from the continuous sawtooth pulses to perform laser processing of a printed circuit board. A duty cycle Dty=trf1 / tm is set, tm is a pulse period, and is constituted by an RF application time trf1 and an RF application stop time trf0, The sawtooth pulse is generated in the following manner: Step 1: Set a vertical axis as an output axis, a duty cycle Dty, a pulse period tm, an average output Wav, an upper limit output Wp, and a lower limit output Wv, the upper limit output Wp is an output obtained by irradiating a pulse enough to obtain a target aperture, and the lower limit output Wv is an output larger than a processing critical value Wm of an insulating layer; Step 2: Set a horizontal axis as a time axis, set a point on the lower limit output Wv at time t0 as Q1, and set a point on the lower limit output Wv at time t2 which is a pulse period as Q6, indicate an output response Ws with the point Q1 as a starting point, and set an end point of the output response Ws as a point Q2; Step 3: Connect the point Q2 and a point Q3 on the upper limit output Wp at time t1 with an output response Wr, time t1 is an end point of trf1; Step 4: Set the point Q3 as a starting point and indicate an output response Wc, and set an end point of the output response Wc as a point Q4; Step 5: Indicate a small output response Wd on an extension line connecting the point Q1 and the point Q4, and set an end point as a point Q5; Step 6: Connect the point Q5 and the point Q6 with an output line segment Wf; By the above steps, the sawtooth pulse applied to the lower limit output Wv is completed; An output enclosed by a quadrangle Q1Q2Q3Q4 corresponds to an output obtained by directly exciting carbon dioxide gas by the RF pulse.

4. The laser processing apparatus of the printed circuit board according to claim 3, characterized by: A plurality of processing heads are further included, a configuration for distributing laser light from the carbon dioxide laser oscillator to each of the processing heads is constituted, and when positioning of any one of the processing heads is completed, the control device supplies laser light to the processing head regardless of a positioning state of the other processing heads.

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