JP3738539B2 - Laser processing method for laminated member - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a processing method using a laser such as blind via hole processing and groove processing on a multilayer wiring board called a so-called printed circuit board, particularly a processing method capable of forming a fine conduction hole quickly and with high quality, and this processing. The present invention relates to a laser processing apparatus that generates a pulsed laser beam optimal for the above.
[0002]
[Prior art]
With recent improvements in performance of electronic devices, higher wiring density is required, and in order to satisfy this requirement, multilayered and miniaturized printed circuit boards are required. In order to realize such multilayering and miniaturization, it is indispensable to form fine blind holes for interlayer conduction connection having a hole diameter of about 150 μm, called blind via holes (BVH). However, drilling of φ0.2 mm or less is difficult with the current drilling process. In addition, the insulating layer thickness of a high-density printed circuit board is 100 μm or less, and it is difficult to control the depth with this accuracy. Fine BVH cannot be formed by processing.
[0003]
As an alternative to this drilling, BVH formation methods include IBM Journal of Research and Development (IBM J. Res. Development) Vol. 26, No. 3, pages 306-317 (1982) and Japanese Patent Publication No. 4-3676. A method of applying a laser beam such as a carbon dioxide laser shown in the drawing has attracted attention and has been partially put into practical use. These laser beam processing methods utilize the difference in the absorption rate of light energy of a carbon dioxide laser with respect to resin or glass fiber as an insulating base material constituting a printed circuit board and copper as a conductor layer.
[0004]
18A and 18B are diagrams for explaining a conventional laser processing method. FIG. 18A shows a printed circuit board during laser processing, and FIG. 18B shows a printed circuit board after laser processing. In the figure, 101 is a printed circuit board, 102 is a copper foil provided on the surface of the printed circuit board 101 and from which the removing portion 102a is removed, and 103 is laser light emitted from a carbon dioxide laser processing apparatus.
[0005]
As shown in FIG. 18A, a copper foil removing portion 102a having a necessary hole diameter is formed in the copper foil 102 on the surface of the printed circuit board 101 by etching or the like, and the laser beam 103 is irradiated through the removing portion 102a. As a result, the resin and glass in the printed circuit board 101 are selectively decomposed and removed to form fine processed holes 104 in the printed circuit board 101. Here, since copper has a characteristic of almost reflecting the carbon dioxide laser, only the portion where the copper foil 102 is removed is processed, and the portion where the copper foil 102 exists is not processed, and FIG. A processed hole 104 as shown in FIG.
[0006]
In addition, as shown in FIG. 19, if the inner layer copper foil 102b is laminated in advance inside the processing portion, the decomposition / removal of the insulating base material stops at the inner layer copper foil 102b, so that the inner layer copper foil 102b stops reliably. A blind hole 104 can be formed.
[0007]
However, as shown in FIG. 19, when the stop hole is processed by a carbon dioxide gas laser when it is stopped by a copper foil, even if the laser beam is sufficiently irradiated, the resin which is an insulating substrate having a thickness of 1 μm or less is the inner layer copper foil. It will remain on top. For this reason, after the laser processing, it is necessary to completely remove the residual resin by etching the residual resin with permanganic acid or the like.
[0008]
[Problems to be solved by the invention]
Since the conventional laser processing method is performed as described above, when forming a perforated hole, if the processed hole is reduced to about 100 μm, the etching solution becomes difficult to reach the inside of the hole, and there is a hole that cannot completely remove the residual resin. It tends to occur. Then, when plating is performed in this state to form BVH, a part of the resin remains between the plating film and the inner layer copper foil. When stress is applied due to a thermal cycle or the like, the plating film is formed from this as a starting point. It will come off.
[0009]
This is because the heat generated inside the resin is taken away by heat conduction in the copper foil, where the temperature hardly rises even when laser is irradiated. To prevent this, the heat generated in the resin is taken away by the heat conduction to the copper foil. It is necessary to input energy necessary for removal before it is released. That is, it is necessary to shorten the beam ON time of the laser light and increase the peak power.
[0010]
  The present invention has been made to solve the above-described problems, and an object thereof is to provide a laser processing method capable of achieving complete removal of a resin, that is, having high reliability.
  Another object of the present invention is to provide a laser processing method capable of achieving complete removal of the resin without reducing the processing speed, that is, capable of achieving both high reliability and high efficiency..
[0011]
[Means for Solving the Problems]
  The laser processing method according to the present invention includes a hole forming step of forming a hole by irradiating a laminated member in which a resin layer is formed on a conductor layer to form a hole, and a laser beam ON time is short and a peak power is low. highCO2 laserA residual resin removing step of irradiating the hole with laser light to remove the residual resin.
[0012]
  Also,The laser processing method according to the present invention includes a hole forming step of forming a hole in a laminated member in which a resin layer is formed on a conductor layer, and removing the residual resin by irradiating the hole with a laser beam of a carbon dioxide gas laser. A residual resin removal step..
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1 FIG.
The laser processing apparatus according to the present embodiment is not limited to a normal laser beam having a long laser beam ON time and a low peak power, but also a laser extracted by Q-switch oscillation with a short laser beam ON time and a high peak power. The light can also be extracted by one laser processing apparatus.
[0016]
FIG. 1 is a diagram showing a carbon dioxide laser processing apparatus according to the first embodiment.
In the figure, 1 is a concave-shaped total reflection mirror made of copper, and 2 is a concave-shaped partial reflection mirror made of ZnSe arranged opposite to the total reflection mirror 1, and the partial reflection mirror 2 and the total reflection mirror 1 are A stable laser resonator is formed.
[0017]
3 is a laser beam generated in the laser resonator, 4a and 4b are Brewster windows for transmitting only the P-polarized component of the laser beam 3 and reflecting the S-polarized component, 5 is a quarter-wave plate, and 6 is a discharge tube. , 7 is an electro-optic amplitude modulator made of CdTe and changing the polarization state according to an externally applied voltage, 8 is a pulse generator for generating a voltage to be applied to the electro-optic amplitude modulator 7, and 9 is a pulse current in the discharge tube 6. 10 is a synchronous controller that gives a trigger pulse to the pulse generator 8 and the pulse laser power source 9, and 10a is a laser beam extracted from the partial reflection mirror 2 to the outside of the oscillator.
[0018]
Next, the operation of the carbon dioxide laser processing apparatus of this embodiment will be described.
First, an operation when a pulse current is supplied from the pulse laser power source 9 shown in FIG. 1 to the discharge tube 6 and no voltage is applied from the pulse generator 8 to the electro-optic amplitude modulator 7 will be described.
FIG. 2 is a diagram for explaining the operation at this time. In order to simplify the description in the figure, the pulse generator 8, the pulse laser power source 9, and the synchronization controller 10 are not shown, and the other parts are the same as the laser processing apparatus shown in FIG.
[0019]
When a pulse current is applied from the pulse laser power source 9 to the discharge tube 6, the laser beam 3 passes through the Brewster window 4 a and the quarter-wave plate 5 and reaches the electro-optic amplitude modulator 7. At this time, since the laser beam 3 passing through the discharge tube 6 surrounded by the Brewster windows 4a and 4b is only linearly polarized light of only the P-polarized component, the laser beam 3 passing through the quarter-wave plate 5 is on the right side. Around circularly polarized light.
[0020]
Since no voltage is applied to the electro-optic amplitude modulator 7, the laser beam 3 that has reached the electro-optic amplitude modulator 7 passes through the electro-optic modulator 7 in the form of clockwise circular polarization and is reflected by the total reflection mirror 1. reflect. The laser beam 3 becomes counterclockwise circularly polarized light by total reflection at this time. Then, the laser beam 3 that has passed through the electro-optic amplitude modulator 7 again while being left-handed circularly polarized light becomes linearly polarized light of an S-polarized component when passing through the quarter-wave plate 5 again. However, since the laser beam 3 at this time is not a P-polarized component, it cannot pass through the discharge tube 6 surrounded by the Brewster windows 4a and 4b, and in this case, laser oscillation does not occur.
[0021]
Next, the operation when a quarter-wave voltage is applied from the pulse generator 8 to the electro-optic amplitude modulator 7 while the pulse current is being supplied from the pulse laser power source 9 to the discharge tube 6 will be described. .
FIG. 3 is a diagram for explaining the operation at this time. In order to simplify the description in the figure, the pulse generator 8, the pulse laser power source 9, and the synchronization controller 10 are not shown, and the other parts are the same as the laser processing apparatus shown in FIG.
[0022]
As in the case where no voltage is applied to the electro-optic amplitude modulator 7, the laser beam 3 that has passed through the quarter-wave plate 5 from the Brewster window 4a becomes clockwise circularly polarized light. Next, since a voltage is applied to the electro-optic amplitude modulator 7, the laser beam 3 reaching the electro-optic amplitude modulator 7 passes through the electro-optic amplitude modulator 7. As a result, the S-polarized light component becomes linearly polarized light.
[0023]
Then, the laser beam 3 is reflected by the total reflection mirror 1, and the laser beam 3 that has passed through the electro-optic amplitude modulator 7 again becomes counterclockwise circularly polarized light by the electro-optic amplitude modulator 7, and is again a quarter. When passing through the wave plate 5, it becomes linearly polarized light of a P-polarized component. Since this laser beam 3 is a P-polarized component, it can pass through the discharge tube 6 surrounded by the Brewster windows 4a and 4b, and the laser beam 3 can reach the partial reflection mirror 2 through the discharge tube 8, so that the laser Oscillation occurs.
[0024]
Further, the operation in the case where the voltage is repeatedly applied from the pulse generator 8 to the electro-optic amplitude modulator 7 while the pulse current is supplied from the pulse laser power source 9 to the discharge tube 6 will be described.
First, the synchronous controller 10 gives a trigger pulse to the pulse generator 8 and the pulse laser power source 9. The pulse laser power source 9 applies a pulse current to the discharge tube 6 so that a pulse of a pulse current input from the time when the trigger pulse is applied rises. The pulse generator 8 also applies a plurality of pulses having a small pulse width to the electro-optic amplitude modulator 7 by repeating ON / OFF from the time when the trigger pulse is given.
[0025]
FIG. 4 is a diagram showing the relationship between the pulse current input from the pulse laser power source and the pulse voltage applied from the pulse generator.
As shown in FIG. 4, the pulse generator 8 is repeatedly turned on and off while the pulse current is being supplied from the pulse laser power source 9 to the discharge tube 6, so that the pulse generator 8 causes the electro-optic amplitude modulator. A plurality of pulses having a small pulse width can be applied to 7, and a laser beam having a high peak intensity and a short pulse width as shown in FIG. 5 can be extracted. Such a method is called Q-switching, and a laser beam extracted by such a method is called a Q-switched laser beam.
[0026]
In this embodiment, the frequency of the Q-switched laser beam extracted by repeatedly performing Q switching is 10 kHz, the peak power is 1.8 MW, the full width at half maximum is 30 ns, and the laser energy extracted per cycle is about 50 mJ. It was.
[0027]
In addition, when a quarter wavelength voltage is applied from the pulse generator to the electro-optic amplitude modulator while a current is being supplied from the pulse laser power source to the discharge tube, the pulse is longer than the Q switch pulse. A normal laser beam with a low width and low peak power is extracted. In the present embodiment, the pulse frequency of the laser beam is 200 Hz, the peak power is 3 kW, the full width at half maximum is 48 μs, and the laser energy extracted per pulse is about 150 mJ.
[0028]
In the laser processing apparatus of this embodiment, a synchronous controller is provided, and the synchronous controller controls the synchronization of the pulse laser power source and the pulse generator, so that the Q-switched laser extracted by the pulse generated by the Q-switch oscillation. A single laser processing device can realize a beam and a normal laser beam having a pulse width longer than that of the Q-switched laser beam and a low peak power, so that various processing can be performed and the device can be made simple and inexpensive. .
[0029]
Embodiment 2. FIG.
FIG. 6 is a schematic diagram showing a configuration of a laser processing apparatus for processing the laminated member in the second embodiment. In the figure, reference numeral 11 denotes a carbon dioxide laser processing apparatus (hereinafter referred to as a carbon dioxide oscillator) described in the first embodiment, which can output normal laser light and laser light extracted by Q-switch oscillation.
Reference numeral 12 denotes a transfer mask, reference numerals 13a and 13b denote positioning mirrors that position the laser beam emitted from the carbon dioxide oscillator 11 at a predetermined position, and reference numeral 14 denotes a transfer lens that images the laser beam on the object. , 15 is a processing table on which an object to be processed that can move in the vertical and horizontal directions, 16 is a printed circuit board that is an object of laser processing, and 17 is a laser beam.
[0030]
Next, the operation will be described.
A part of the laser beam 17 emitted from the pulse carbon dioxide laser oscillator 11 passes through the transfer mask 12 and is set on the processing table 15 by the transfer lens 14 through two positioning mirrors 13a and 13b controlled by a control device (not shown). An image of the transfer mask 12 is formed on the printed board 16.
In the present embodiment, a printed board 16 having a glass epoxy layer having a thickness of 100 μm formed on the front and back surfaces of a double-sided copper-clad glass epoxy board having a thickness of 0.8 mm is used, and an image of φ100 μm is formed on the substrate surface. Imaged.
[0031]
Next, a processing method for processing a perforated hole will be described.
FIG. 7 is a schematic view showing a part of the steps of the laser processing method of the laminated member according to the second embodiment. In the figure, 11 is a pulse carbon dioxide laser oscillator, 16 is a printed circuit board which is an object of laser processing, 17 is a laser beam emitted from the pulse carbon dioxide laser oscillator 11, 18 is an inner layer copper foil provided inside the processing part, 19 is a processed hole of the printed circuit board 16, and 20 is a residual resin.
[0032]
First, a trigger pulse is sent from the synchronous controller 10 only to the pulsed laser power source 9, and the laser beam 17 is normally oscillated to form the machining hole 19. At this time, the laser beam has a peak power of 3 kW and a full width at half maximum of 48 μs at the exit of the oscillator, and the laser energy extracted per cycle is about 150 mJ. In order to form the processed hole 19, 5 pulses were irradiated per processed hole. At this time, a residual resin film 20 made of an epoxy resin having a thickness of 0.7 μm was present on the copper foil 18 on the bottom surface of the processed hole 19.
[0033]
A mechanism for generating residual resin will be described below.
FIG. 8 is a diagram showing the relationship between the depth from the processed surface and the transmitted energy when the epoxy resin is irradiated with a carbon dioxide laser. The transmission energy on the processed surface was 1.
As shown in FIG. 8, the laser light penetrates from the surface of the resin to a certain depth and is absorbed. For example, when an epoxy resin is irradiated with a carbon dioxide gas laser, the transmitted energy that is transmitted while traveling from the surface to a depth of 40 μm is 45%, so that 55 of the energy absorbed by the surface while traveling from the surface to a depth of 40 μm. % Is absorbed by the resin material. Therefore, when the depth from the surface is shallow, the epoxy resin cannot sufficiently absorb the energy of the laser beam irradiated from the carbon dioxide laser.
[0034]
Therefore, when the blind hole is shallow from the processed surface when it is formed, that is, when laser light is applied to the resin having a small thickness on the copper foil 18 shown in FIG. 7, a part of the laser light is obtained as shown in FIG. While the energy is absorbed by the resin, it reaches the bottom copper foil. The laser light that reaches the copper foil is reflected by the copper foil, but since the reflectance of the copper foil to the carbon dioxide laser is as high as 95%, the laser light that has passed through the resin is hardly absorbed by the copper foil and the resin again. Reflected inside. Thereafter, the reflected laser light is partially absorbed by the resin and passes through the resin.
Therefore, only a part of the energy of the laser beam is absorbed by the resin, and the other part is completely transmitted. In addition, the energy absorbed by the resin is also taken away by heat conduction to the copper foil whose temperature hardly rises even when irradiated with a laser.
[0035]
In consideration of the above, FIG. 10 shows the distribution of the maximum temperature of the copper foil and the resin when a 1 μm thick polyimide resin on the copper foil is irradiated with a carbon dioxide laser having a power density of 5 MW per square centimeter for 10 μs. Is shown. From the figure, it can be seen that about 0.2 μm (the distance from the surface is about 0.8 μm) from the interface between the copper foil and the polyimide does not reach the decomposition temperature of the polyimide. This is because the heat generated inside the polyimide is taken away by heat conduction in the copper foil whose temperature hardly increases even when the laser is irradiated.
[0036]
In order to prevent this, it is necessary to input energy necessary for removal before the heat generated in the polyimide is taken away by the copper foil by heat conduction. That is, it is necessary to shorten the beam ON time of the laser light and increase the peak power.
Therefore, in this embodiment, in order to remove such residual resin, the residual resin is removed by irradiation with a Q-switched laser beam. Hereinafter, the residual resin removing step will be described.
[0037]
As shown in FIG. 11, the synchronous controller applies a pulse voltage that is turned on and off in binary to the electro-optic amplitude modulator while the pulse that is normally oscillated is ON, to the pulse laser power source and the pulse generator. A trigger pulse is sent to irradiate the machining hole with a Q-switched laser beam. At this time, the frequency of the pulse voltage applied to the electro-optic amplitude modulator of the Q-switched laser beam is 10 kHz, the peak power of 1.8 MW and the full width at half maximum are 30 ns at the exit of the oscillator, and the laser energy extracted per pulse is about 50 mJ. Met. This Q-switched laser beam pulse was irradiated with 2 pulses per processing hole. Thereby, the epoxy resin on the copper foil on the bottom surface of the processed hole could be completely removed.
[0038]
Ten printed boards with 2000 holes processed per sheet were prepared by the above method. At this time, by controlling the two positioning mirrors so as to be positioned at 200 positions per second, it took about 2 minutes to process each sheet. After this substrate was desmeared, plating and pattern formation were performed to create a reliability evaluation substrate. When a heat cycle test at −65 ° C. (30 minutes) and 125 ° C. (30 minutes) was performed on this substrate, high reliability was obtained with a resistance change rate of 1% at 650 cycles for any substrate.
[0039]
Comparative form 1.
In addition, for comparison with the conventional method, 10 substrates processed with only a normal oscillation laser beam and not irradiated with a Q-switched laser beam were prepared, and a similar heat cycle test was performed. As for the substrate, the rate of change of resistance exceeded 10% in 100 cycles, and a substrate in which wiring was disconnected in 350 cycles was generated. This is because, as described above, residual resin remains in the processing hole in processing using only a normal laser beam, and therefore, when stress is applied by a thermal cycle, the plating film is peeled off starting from this.
As described above, according to the present invention, the conduction reliability is remarkably improved as compared with the conventional method.
[0040]
Comparative form 2.
Furthermore, when 10 substrates processed with only a Q-switched laser beam without irradiation with normal oscillation pulses were prepared and subjected to the same heat cycle test, 200 pulses per hole were formed to form processed holes. Was necessary. For this reason, the processing time required about 40 minutes per sheet. In the heat cycle test, all the substrates obtained high conduction reliability with a resistance change rate of 1% at 650 cycles.
As described above, the temperature of the substance to be removed generally increases as the laser beam is shortened to a high peak, so that the removal depth per unit energy decreases, resulting in longer processing time and efficiency. Decreases.
[0041]
In the present embodiment, the processing hole is formed by laser light, but this is not particularly limited, and the processing hole is formed by drilling or the like, and then laser light having a short pulse high peak is applied to the processing hole. You may make it irradiate. However, drilling is not suitable for forming fine holes.
[0042]
As described above, in the second embodiment, after the hole is formed by the normal laser beam, the residual resin remaining in the hole is removed by the short pulse high peak laser beam. Processing can be performed in a shorter time than the conventional method while maintaining the properties, and the efficiency is remarkably improved.
[0043]
Embodiment 3 FIG.
FIG. 12 is a diagram showing a change in conduction reliability when the pulse ON time of the Q-switched laser beam of this embodiment is changed. During processing, the pulse ON time of the Q-switched laser beam was changed from 30 ns to 1 μs, and 10 substrates were produced at each pulse ON time. The vertical axis represents the number of substrates whose resistance change rate became 10% or more after 1000 cycles in the heat cycle test.
From the figure, it can be seen that when the pulse ON time of the laser beam of the Q switch is 500 ns or less, the resistance change rate after 1000 cycles does not become 10% or more, and high conduction reliability is obtained.
[0044]
FIG. 13 shows the relationship between the pulse ON time of the laser beam used for processing and the time required to process 2000 holes of 100 μm deep holes on the surface of the printed circuit board used in the second embodiment. FIG. Here, the irradiation energy of one pulse at each pulse ON time was made substantially constant, and the processing time was set to the time until the remaining film on the bottom copper foil became 1 μm or less.
From the figure, it can be seen that when the pulse width is 1 μs or less, the processing time becomes remarkably long and the efficiency is poor.
From the above, by performing processing until the remaining film on the bottom copper foil becomes 1 μm or less with a pulse with a pulse ON time of 1 μs or more, and then removing the residual film with a pulse with a pulse ON time of 100 ns or less. As a result, it is possible to efficiently achieve both reliability of conduction and high efficiency.
[0045]
Embodiment 4 FIG.
FIG. 14 is a schematic view of an apparatus used in the laser processing method for a laminated member according to the fourth embodiment. In the figure, 11 is a normal pulse carbon dioxide laser oscillator, and 21 is a Q switch pulse YAG laser oscillator that oscillates a second harmonic of a wavelength of 532 nm. Others are the same as those described in the second embodiment, and a description thereof will be omitted.
[0046]
Next, the operation will be described.
In the figure, a part of the pulse carbon dioxide laser beam 17 emitted from the pulse carbon dioxide laser oscillator 11 passes through the transfer mask 12, passes through two positioning mirrors 13a, b controlled by a control device (not shown), and is transferred by the transfer lens 14. An image of the transfer mask 12 is formed on the printed circuit board 16 placed on the processing table 15. In this embodiment, a printed circuit board is used in which a glass epoxy layer having a thickness of 100 μm is formed on the front and back surfaces of a double-sided copper-clad glass epoxy substrate having a thickness of 0.8 mm, and an image of φ100 μm is formed on the substrate surface. It was.
[0047]
The Q switch pulse second harmonic YAG laser beam 22 emitted from the Q switch pulse YAG laser oscillator 21 is condensed by the condenser lens 14 through two positioning mirrors 13c and 13d controlled by a control device (not shown). Then, by the positioning by the processing table 15 and the two positioning mirrors 13c and 13d, the processing holes on the printed circuit board 16 where the drilling with the pulse carbon dioxide laser beam 17 has been completed are irradiated.
[0048]
FIG. 15 is a schematic diagram showing the steps of the laser processing method for a laminated member according to the third embodiment. In the figure, 16 is a printed circuit board which is an object of laser processing, 17 is a laser beam emitted from the pulse carbon dioxide laser oscillator 11, 18 is an inner layer copper foil provided inside the processing portion, and 19 is processing of the printed circuit board 16. Hole 20, residual resin 20, and 22 a laser beam emitted from the Q-switch pulse second harmonic YAG laser oscillator 21.
[0049]
First, the processing hole 19 is formed by irradiating the printed circuit board 16 with the pulse carbon dioxide laser beam 17 emitted from the pulse carbon dioxide laser oscillator 11. At this time, the laser beam has a peak power of 3 kW and a full width at half maximum of 48 μs at the exit of the oscillator, the laser energy extracted per cycle is about 150 mJ, and 5 pulses are irradiated per processing hole to form the processing hole 19. did. At this time, a residual resin film 20 made of an epoxy resin having a thickness of 0.7 μm remained on the copper foil 18 on the bottom surface of the processed hole 19.
[0050]
After the machining hole 19 is formed by the pulse carbon dioxide laser beam 17 in this way, the machining hole 19 is irradiated with the Q-switched YAG laser beam 22 oscillated from the Q-switch pulse YAG laser 21. At this time, the Q-switch pulse second harmonic YAG laser beam 22 had a frequency of 10 kHz, a peak power of 0.1 MW and a full width at half maximum of 10 ns at the exit of the oscillator, and the laser energy extracted per pulse was about 1 mJ. This Q-switched laser beam pulse was irradiated with 4 pulses per processing hole. Thereby, the epoxy resin 20 on the copper foil 18 on the bottom surface of the processed hole 19 could be completely removed.
[0051]
Ten printed boards with 2000 holes processed per sheet were prepared by the above method. At this time, by controlling each of the two sets of two positioning mirrors so as to be positioned at 200 positions per second, it took about 4 minutes to process each sheet. After this substrate was desmeared, plating and pattern formation were performed to create a reliability evaluation substrate. When a heat cycle test at −65 ° C. (30 minutes) and 125 ° C. (30 minutes) was performed on this substrate, high reliability was obtained with a resistance change rate of 1% at 650 cycles for any substrate.
[0052]
Comparative form 3.
In addition, for comparison with the conventional method, 10 substrates processed without using a Q-switched YAG laser beam only with a pulsed carbon dioxide laser beam were prepared, and a similar heat cycle test was performed. As for the substrate, the rate of change of resistance exceeded 10% in 100 cycles, and a substrate in which wiring was disconnected in 350 cycles was generated.
As described above, according to the present invention, the conduction reliability is remarkably improved as compared with the conventional method.
[0053]
Comparative form 4.
Furthermore, when 10 substrates processed with only a Q-switched YAG laser beam without irradiation with a pulsed carbon dioxide laser beam were prepared and subjected to the same heat cycle test, 500 pulses per hole were formed in order to form processed holes. Was necessary. For this reason, the processing time required about 100 minutes per sheet. In the heat cycle test, all substrates had a high reliability with a resistance change rate of 1% after 650 cycles.
As described above, according to the present invention, processing can be performed in a shorter time than the conventional method while maintaining high reliability, and the efficiency is remarkably improved.
[0054]
Embodiment 5. FIG.
FIG. 16 is a diagram showing a Q-switched carbon dioxide laser device used in the laser processing method for laminated members according to the fifth embodiment.
In the figure, 1 is a concave-shaped total reflection mirror made of copper, and 2 is a concave-shaped partial reflection mirror made of ZnSe arranged opposite to the total reflection mirror 1, and the partial reflection mirror 2 and the total reflection mirror 1 are stable. A type of laser resonator is formed.
[0055]
3 is a laser beam generated in the laser resonator, 4a and 4b are Brewster windows for transmitting only the P-polarized component of the laser beam 3 and reflecting the S-polarized component, 5 is a quarter-wave plate, and 6 is a discharge tube. , 7 is an electro-optic amplitude modulator that is made of CdTe and changes a change state according to an externally applied voltage, 8 is a pulse generator that generates a voltage to be applied to the electro-optic amplitude modulator 7, and 10 is triggered by the pulse generator 8 A control device 10 for applying a pulse 19 is a laser beam extracted from the partial reflection mirror 2 to the outside of the oscillator, and 23 is a continuous laser power source for supplying current to the discharge tube 6.
[0056]
FIG. 17 is a schematic diagram showing the form of pulses used for laser processing of the laminated member according to the fifth embodiment using the laser apparatus shown in FIG. The apparatus configuration and workpiece used for processing were the same as in the case of FIG. 6 of the second embodiment.
First, the pulse generator 8 was controlled, and a pulse train 24 in which a Q switch pulse having a pulse width of 500 ns was oscillated 100 pulses at 100 kHz was oscillated at 200 Hz, and 6 pulses were irradiated per machining hole. At this time, the laser beam had a peak power of 3 kW at the exit of the oscillator, the laser energy extracted per cycle of the pulse train was about 150 mJ, and 5 pulses were irradiated per processed hole to form a processed hole. At this time, an epoxy resin having a thickness of 0.7 μm remained on the copper foil at the bottom of the processed hole.
[0057]
Next, the pulse generator 8 was controlled to oscillate a Q switch pulse 25 having a pulse width of 30 ns at 10 kHz, and irradiate the processed hole processed with the Q switch pulse train. At this time, the laser energy of the Q-switched laser beam extracted per pulse with a peak power of 1.8 MW at the exit of the oscillator was about 50 mJ. This Q-switched laser beam pulse was irradiated with 2 pulses per processing hole. Thereby, the epoxy resin on the copper foil on the bottom surface of the processed hole could be completely removed.
[0058]
Ten printed boards with 2000 holes processed per sheet were prepared by the above method. At this time, by controlling the two positioning mirrors so as to be positioned at 200 positions per second, it took about 2 minutes to process each sheet. After this substrate was desmeared, plating and pattern formation were performed to create a reliability evaluation substrate. When a heat cycle test at −65 ° C. (30 minutes) and 125 ° C. (30 minutes) was performed on this substrate, high reliability was obtained with a resistance change rate of 1% at 650 cycles for any substrate.
[0059]
As described above, according to the present invention, since an inexpensive continuous output power source can be used as a laser power source, it is possible to achieve both ensuring of conduction reliability and high efficiency with an inexpensive device.
[0060]
【The invention's effect】
  The laser processing method according to the present invention includes a hole forming step of forming a hole by irradiating a laminated member in which a resin layer is formed on a conductor layer to form a hole, and a laser beam ON time is short and a peak power is reduced. highCO2 laserA residual resin removing step of removing the residual resin by irradiating the hole with laser light, so that the residual resin remaining in the hole is removed by the laser light having a short beam ON time and high peak power. And a processing method with high conduction reliability can be realized.
[0061]
  Further, the laser processing method according to the present invention includes a hole forming step of forming a hole in a laminated member in which a resin layer is formed on a conductor layer, and a residual resin by irradiating the hole with a laser beam of a carbon dioxide laser. Since the residual resin removing step to be removed is included, the residual resin remaining in the hole can be removed by the laser beam, and a processing method with high conduction reliability can be realized.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a carbon dioxide gas laser device according to a first embodiment of the present invention.
FIG. 2 is a diagram for explaining the operation of the carbon dioxide laser device shown in FIG.
FIG. 3 is a diagram for explaining the operation of the carbon dioxide laser device shown in FIG. 1;
FIG. 4 is a diagram showing a relationship between a pulse current and a pulse voltage.
5 is a diagram showing a pulse waveform of the carbon dioxide laser device shown in FIG. 1. FIG.
FIG. 6 is a schematic diagram of a laser processing apparatus according to a second embodiment of the present invention.
FIG. 7 is a diagram showing a process of a laser processing method according to a second embodiment of the present invention.
FIG. 8 is a schematic diagram showing a transmission energy distribution in a workpiece.
FIG. 9 is a schematic diagram showing a propagation path of a laser beam.
FIG. 10 is a schematic view showing a temperature distribution of a workpiece.
FIG. 11 is a diagram showing a relationship between a pulse current and a pulse voltage.
FIG. 12 is a diagram showing the relationship between the beam ON time and the number of defective substrates in Embodiment 3 of the present invention.
FIG. 13 is a diagram showing a relationship between a beam ON time and a rough machining time according to the third embodiment of the present invention.
FIG. 14 is a schematic diagram of a laser processing apparatus according to a fourth embodiment of the present invention.
FIG. 15 is a diagram showing a process of a laser processing method according to a fourth embodiment of the present invention.
FIG. 16 is a sectional view of a laser device according to a fifth embodiment of the present invention.
FIG. 17 is a schematic diagram showing a pulse form according to the fifth embodiment of the present invention.
FIG. 18 is a schematic view showing a conventional method for drilling a printed circuit board of a laser.
FIG. 19 is a schematic view showing a conventional method for drilling a printed circuit board of a laser.
[Explanation of symbols]
1 Total reflection mirror 2 Partial reflection mirror
3 Laser beam in the resonator 4 Brewster window
5 1/4 wave plate 6 discharge tube
7 Electro-optic amplitude modulator 8 Pulse generator
9 Pulse laser power supply 10 Synchronous controller
10a Laser beam
11 Carbon dioxide generator 12 Transfer mask
13 Positioning mirror 14 Transfer lens
15 Processing table 16 Printed circuit board
17 Pulsed carbon dioxide laser beam 18 Inner layer copper foil
19 Processing hole 20 Residual resin
21 Q-switch pulse second harmonic YAG laser oscillator
22 Q-switch pulse second harmonic YAG laser oscillation beam
23 Continuous laser power supply 24 Q switch pulse train
25 Q switch pulse
101 Printed circuit board 102 Copper foil
102a removal part 102b inner layer copper foil
103 Laser light 104 Processing hole

Claims (5)

A hole forming step of forming a hole by irradiating a carbon dioxide gas laser to a laminated member in which a resin layer is formed on a conductor layer;
And a residual resin removing step of removing residual resin by irradiating the hole with a laser beam of a carbon dioxide laser having a short beam ON time and a high peak power. A hole forming step of forming a hole in a laminated member in which a resin layer is formed on the conductor layer;
And a residual resin removal step of removing residual resin by irradiating the hole with a laser beam of a carbon dioxide laser. Wherein after the residual resin removing step, the laser processing method according to claim 1 or claim 2, characterized by performing desmear processing. The residue after resin removal step, plating, laser processing method according to any one of claims 1-3, characterized in that performing pattern formation. The laminated member, a laser processing method according to claim 1 or claim 2, characterized in that a glass epoxy substrate having a conductive portion.

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