JP2004223533A - Laser beam machining method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser beam machining method capable of opening a hole of a large area and cleaning a bottom surface of the hole with pulse laser beams of small shot number. <P>SOLUTION: A work with a covering layer 11 of a material different from that of a surface layer part of a base member formed thereon is prepared on a surface of the base member 13. Pulse laser beams having properties of transmitting through the covering layer, being reflected by a boundary between the covering layer and the base member, and peeling the covering layer at the reflection position from the base member are incident on the work from the surface of the covering layer to peel a part of the covering layer from the base member, and form a peeling portion to expose the surface of the base member to a bottom surface. Pulse laser beams of the wavelength equal to that when the peeling portion is formed are incident on a bottom surface of the peeling portion, and the remaining covering layer is removed if a part of the covering layer remains on the bottom surface of the peeling portion. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laser processing method for irradiating a processing object having a coating layer with a laser beam to open a hole in the coating layer.
[0002]
[Prior art]
FIGS. 6A to 6D are schematic cross-sectional views of a processing object for explaining a conventional laser processing method of irradiating a pulse laser beam to make a hole in the processing object.
[0003]
As shown in FIG. 6A, the object to be processed includes a copper layer (first copper layer 51a and second copper layer 51b) and an epoxy resin layer (first epoxy resin layer 52a and second epoxy resin). A multilayer printed circuit board in which the layers 52b) are arranged alternately. The second epoxy resin layer 52b, the second copper layer 51b, the first epoxy resin layer 52a, and the first copper layer 51a are laminated in this order from the bottom. A hole penetrating the first copper layer 51a and the first epoxy resin layer 51b is formed in the printed multilayer board.
[0004]
Reference is made to FIG. First, the hole 53 which penetrates the 1st copper layer 51a of a multilayer printed circuit board is formed using a drill.
[0005]
Reference is made to FIG. For example, a processing laser pulse having a relatively long oscillation time (for example, pulse width of 0.45 to 0.55 ms) is irradiated through the window hole 53, the first epoxy resin layer 52a is removed, and the copper layer 51b is formed on the bottom surface. Is formed. At this time, the epoxy residual resin 55 remains on the bottom surface of the hole 54.
[0006]
Reference is made to FIG. The hole 54 is irradiated with a cleaning laser pulse having a relatively short oscillation time (for example, pulse width 0.2 to 0.3 ms) to remove the residual resin 55 remaining on the bottom surface of the second hole 54.
[0007]
As described above, after forming a hole in the resin layer by irradiating the pulsed laser beam, a laser beam having a different oscillation time can be incident on the bottom surface of the formed hole to expose a clean copper layer. . (For example, see Patent Document 1.)
Further, a pulse laser beam having a pulse width of 100 ns or less is irradiated on the entire surface of the printed circuit board in which holes are formed in the resin layer under the condition that the pulse energy density on the irradiated surface is 1 J / cm ² or less, and the bottom surface of the holes There has also been proposed a method for removing film-like processing residues remaining on the substrate. (For example, see Patent Document 2.)
Furthermore, recently, a laser processing method different from the conventional ablation processing has been invented and published by the present inventors. For example, one shot of a pulsed laser beam, for example, a fundamental wave (wavelength 1047 nm) of an Nd: YLF laser is incident on a resin coating layer laminated on a metal layer. The resin coating layer is formed of a resin material that is substantially transparent to the fundamental wave of the Nd: YLF laser, and the metal layer is formed of a metal material that reflects most of the fundamental wave of the Nd: YLF laser. Most of the laser beams are transmitted through the resin coating layer and reflected at the interface between the resin coating layer and the metal layer. Of the resin coating layer, the portion where the laser beam is incident peels from the metal layer, and a hole is opened in the resin coating layer.
[0008]
The holes formed in the resin coating layer with a single shot pulse laser beam by this laser processing method are compared with the holes formed by making a plurality of shot pulse laser beams incident on the same part of the resin coating layer by conventional ablation processing. The hole diameter is large. (For example, see Patent Document 3)
[0009]
[Patent Document 1]
Japanese Patent No. 28724453 [Patent Document 2]
JP 2000-197987 A [Patent Document 3]
Japanese Patent Laid-Open No. 2002-044970
[Problems to be solved by the invention]
In the laser processing method described in Patent Document 3, it is necessary to make a laser beam having sufficient intensity reach the interface between the resin coating layer and the metal layer. However, for example, when a short-pulse laser beam having a pulse width of about 10 ps or less is used, multiphoton absorption occurs near the surface of the resin coating layer, which is necessary for processing up to the interface between the resin coating layer and the metal layer. The intense beam may not reach and processing may not be performed satisfactorily.
[0011]
Further, when the laser processing method described in Patent Document 3 is used to penetrate the resin coating layer and open a through hole reaching the metal layer, depending on the material for forming the resin coating layer and the metal layer, The film remains on the bottom of the hole (the surface of the metal layer).
[0012]
The object of the present invention is to irradiate a coating layer formed on the surface of the base member with a pulsed laser beam to open a large-area hole. If a part of the coating layer remains on the bottom surface of the drilled hole, the remaining coating layer should be removed by irradiating with a laser beam having the same wavelength as in the drilling process. It is to provide a laser processing method that enables the above.
[0013]
[Means for Solving the Problems]
According to one aspect of the present invention, a step of preparing a processing object in which a coating layer made of a material different from a material of a surface layer portion of the foundation member is formed on the surface of the foundation member; Then, a pulsed laser beam reflected at the interface between the coating layer and the base member and having the property of peeling the coating layer at the reflection position from the base member is incident on the workpiece from the surface of the coating layer. A step of peeling a part of the coating layer from the base member to form a peeled portion exposing the surface of the base member to the bottom surface, and a pulse having the same wavelength as the pulse laser beam on the bottom surface of the peeled portion. And a step of removing the remaining coating layer when a part of the coating layer remains on the bottom surface of the peeled portion.
[0014]
It is considered that the peeled portion was formed as a result of inducing peeling of the coating layer by heating the base member with a pulsed laser beam. The peeled portion formed by this laser processing method is formed, for example, by irradiation with one shot of a pulsed laser beam. In addition, in conventional ablation processing, the pulse energy of the laser beam is increased and can be opened unless a large number of shots are added. It has an area that can not be. In addition, according to this laser processing method, the coating layer can be peeled off with little influence on the base member.
[0015]
Further, a pulse laser beam having the same wavelength as that at the time of forming the peeled portion can be incident on the bottom of the peeled portion by a small number of shots, and a part of the coating layer remaining on the bottom of the peeled portion can be removed.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic view of a laser processing apparatus used in the laser processing method according to the first embodiment of the present invention. A fundamental wave (wavelength 1047 nm) of an Nd: YLF laser is emitted from a laser light source 1, for example, an Nd: YLF laser oscillator, with a pulse width on the order of picoseconds. The repetition frequency of the pulse laser beam is, for example, 10 Hz. The laser beam is, for example, a mask 2 having a circular through-hole 2a, the shape of the beam cross-section is shaped into a circle, and a plano-convex lens 3 that forms an image of the through-hole 2a on the multilayer substrate 6 that is an object to be processed. Then, the light enters the multi-layer substrate 6 held on the stage 5 through the reflecting mirror 4 arranged in the above manner. The stage 5 is a movable stage and can change the incident position of the laser beam incident on the multilayer substrate 6.
[0017]
FIG. 2A is a schematic cross-sectional view of the multilayer substrate 6. For example, a resin base layer 13 that is an epoxy resin layer reinforced with glass fibers, a metal layer 12 formed of a metal material such as copper, and a resin coating layer 11 that is a cyanate resin layer, for example, are arranged in this order from the bottom. Are stacked. The thickness of the resin coating layer 11 is, for example, 35 μm.
[0018]
A laser processing method according to the first embodiment will be described. A laser beam, for example, a fundamental wave of an Nd: YLF laser is incident on the upper surface of the resin coating layer 11. The resin coating layer 11 transmits most of the fundamental wave of the Nd: YLF laser, and the metal layer 12 reflects most of it. A hole is opened in the resin coating layer 11 by the irradiated laser beam.
[0019]
FIG. 2B is a schematic cross-sectional view of the multilayer substrate 6 in which holes are formed in the resin coating layer 11. A hole 11 a penetrating the resin coating layer 11 is formed by one shot of the laser beam incident on the upper surface of the resin coating layer 11.
[0020]
It is considered that the hole 11a was formed as a result of the metal layer 12 being heated by the laser beam to induce the peeling of the resin coating layer 11. Such a phenomenon is referred to as a “lifting phenomenon”. Further, the processing using the “lifting phenomenon” is referred to as “lifting processing”.
[0021]
Unlike the ablation process, the lifting process is performed with a small number of shots, so that the metal layer 12 is hardly affected. In addition, the hole formed in the resin coating layer by irradiation with one shot of the pulse laser beam is a conventional ablation process, in which multiple shot pulse laser beams are incident on the same portion of the resin coating layer, and compared to the hole to be formed, The hole diameter is large. In the lifting process, a hole 11a having a required opening shape can be formed by shaping a laser beam cross-section into a different shape using a mask having a different through-hole shape.
[0022]
When the hole 11a is opened in the resin coating layer 11 by lifting, the coating film of the coating layer may remain thinly on the bottom surface of the hole depending on the substrate. For example, a laser beam is applied to a multilayer substrate 6 having a structure in which a resin coating layer 11 which is a cyanate resin layer having a thickness of 35 μm is laminated on the surface of a metal layer 12 made of copper, and the resin coating is performed by lifting processing. When a hole penetrating the layer 11 is formed, a thin cyanate resin film 11b remains on the bottom surface of the hole (the surface of the metal layer 12).
[0023]
Therefore, when processing the object to be processed as described above, a pulse laser beam having the same wavelength as that used when drilling using the lifting phenomenon, here, a fundamental wave of an Nd: YLF laser, a plurality of shots, By irradiating the bottom surface of the hole 11a, the remaining film 11b is removed. In the first embodiment, the laser beam is incident on the resin coating layer 11, and the pulse width of the pulse laser beam used for drilling by the lifting phenomenon, the fluence per pulse on the resin coating layer 11, the hole, The light is incident on the bottom surface of 11a, and the pulse width of the pulse laser beam used to remove the coating 11b and the fluence per pulse on the bottom surface of the hole 11a are made equal. At this time, the surface layer portion of the metal layer 12 located on the bottom surface of the hole 11a is also ablated and removed. The film 11b is removed together with the surface layer portion of the metal layer 12, and the clean metal layer 12 is exposed on the bottom surface of the hole 11a.
[0024]
Next, the multilayer substrate 6 is moved by the stage 5. From the next pulse of the laser beam, it enters the resin coating layer 11 at a position separated by the amount of movement.
[0025]
FIG. 2C is a schematic cross-sectional view of the multilayer substrate 6 in which new holes are formed by a plurality of shot pulse laser beams irradiated after the movement of the multilayer substrate 6 by the stage 5. Similarly to the case described with reference to FIG. 2B, the resin coating layer 11 is penetrated to a position different from the position where the hole 11a is formed by irradiation with a plurality of shot pulse laser beams, and the bottom surface is clean. A hole 11c exposing the metal layer 12 is formed. By repeating the movement of the multilayer substrate 6 by the stage 5, a plurality of holes that expose the clean metal layer 12 to the bottom surface can be formed in the resin coating layer 11 at a desired position.
[0026]
Next, suitable conditions for the pulse laser beam to be irradiated will be described.
[0027]
FIG. 3 is a graph showing the relationship between the fluence per one pulse of the laser beam for removing the remaining film incident on the bottom surface (surface of the metal layer) of the hole formed by lifting and the etching rate of the metal layer. The horizontal axis of the graph represents the fluence per pulse of the laser beam at the bottom of the hole (the surface of the metal layer) in units of “J / cm ² ”, and the vertical axis represents the etching rate in units of “nm / pulse”. . The metal layer was made of copper. The irradiated laser beam was a second harmonic (wavelength 523 nm) of the Nd: YLF laser, and the pulse width was 10 ps.
[0028]
When the fluence is smaller than 0.5 J / cm ² , the etching of the metal layer hardly proceeds. In the region where the fluence is 0.5 J / cm ² or more, the etching rate gradually increases as the fluence increases. In order to remove the surface layer portion of the metal layer appearing at the bottom of the hole with the second harmonic (wavelength 523 nm) of the Nd: YLF laser, the fluence per pulse at the bottom surface of the hole (the surface of the metal layer) is 0. 0.5 J / cm ² or more is preferable.
[0029]
The fundamental wave (wavelength 1047 nm) of the Nd: YLF laser has the property that it is hard to be absorbed by copper several times the second harmonic (wavelength 523 nm). Therefore, in order to remove the surface layer portion of the metal layer that appeared at the bottom of the hole with the fundamental wave (wavelength 1047 nm) of the Nd: YLF laser, the fluence per pulse on the bottom surface of the hole (surface of the metal layer) is several. J / cm ² or more is preferable.
[0030]
As described above, in the lifting process, it is necessary to reach the interface between the resin coating layer and the metal layer with a laser beam having an intensity necessary for peeling the resin coating layer from the metal layer. However, for example, when processing is performed using a laser beam with a pulse width of the order of picoseconds or less, depending on the processing conditions, multiphoton absorption occurs near the surface of the resin coating layer, and it reaches the interface between the resin coating layer and the metal layer. In some cases, the beam having the intensity required for processing may not reach.
[0031]
It is known that the occurrence of multiphoton absorption in the resin coating layer is related to the pulse width of the pulse laser beam incident on the resin coating layer and the fluence of the incident beam on the surface of the resin coating layer. When the pulse width is short, multiphoton absorption occurs even at a low fluence, and when the pulse width is long, a high fluence is required to generate multiphoton absorption.
[0032]
Therefore, when laser processing according to the first embodiment is performed using a pulsed laser beam having a pulse width on the order of picoseconds, in order to form a hole in the resin coating layer by lifting processing, the laser beam is incident on the processing object. The pulse width of the pulse laser beam and the fluence per pulse on the surface of the resin coating layer are such that no multiphoton absorption occurs in the resin coating layer, or even when multiphoton absorption occurs, the resin coating layer is removed from the metal layer. It is necessary to set the value to be equal to or higher than the value necessary for peeling. In addition, in order to remove the film (processing residue) remaining on the formed hole bottom, the pulse width of the pulse laser beam incident on the bottom surface of the hole and the fluence per pulse on the bottom surface of the hole are determined by the surface layer portion of the metal layer. It must be set to a value that can be ablated.
[0033]
A suitable pulse width of the laser beam to be irradiated will be described. During the duration τ of one pulse of the pulsed laser beam, the thermal diffusion distance δ is
δ = (12aτ) ^1/2
It is expressed. Here, a is the thermal diffusivity of the material irradiated with the laser beam. For example, the thermal diffusivity a of copper is 1.12 × 10 ⁻⁴ m ² / s.
[0034]
The thermal diffusion distances δ when the pulse width τ is 1 ps, 10 ps, 100 ps, 1 ns, and 10 nm are 37 nm, 116 nm, 367 nm, 1.16 μm, and 3.67 μm, respectively. When removing the remaining film, it is preferable to thinly remove only the surface layer portion of the metal layer on the bottom surface of the hole. In order to make the surface layer portion to be removed thinner, it is not preferable that the thermal diffusion distance δ is in the order of microns. For this reason, it is preferable that the pulse width of the laser beam to be irradiated is 1 ps or more and less than 1 ns, particularly 1 ps or more and 100 ps or less.
[0035]
As described above, when the pulse width is shortened, the laser irradiation is completed before the heat supplied by the laser irradiation is diffused by heat conduction. That is, it is considered that all laser energy is input to the metal layer before heat loss due to heat conduction occurs. For this reason, the surface layer part of a metal layer can be removed efficiently.
[0036]
FIG. 4 is a graph showing a temperature rise distribution at a depth of 20 nm immediately after the fall of the pulse of the laser beam applied to the metal layer formed of copper. The horizontal axis represents the depth from the surface of the metal layer in the unit “nm”, and the vertical axis represents the temperature in the unit “K”. Curves a, b, c, d, and e in the figure show temperature rises when a pulse laser beam having a pulse width of 2 ps, 20 ps, 200 ps, 2 ns, and 20 ns is incident, respectively. The pulse energy density of the pulse laser beam was selected so that the temperature at a depth of 20 nm was a boiling point of copper of 2630 ° C. Since the room temperature is 20 ° C. and the boiling point of copper is 2630 ° C., the temperature increase width at a position of 20 nm depth is 2610K.
[0037]
The pulse energy densities when the pulse width is 2 ps, 20 ps, 200 ps, 2 ns, and 20 ns are 0.040 J / cm ² , 0.045 J / cm ² , 0.109 J / cm ² , 0.318 J / cm ² , respectively. And 0.98 J / cm ² . The reflectance of the laser beam was 80%. This is substantially equal to the reflectance of copper in the fundamental wavelength region of the Nd: YLF laser.
[0038]
In order to efficiently remove the surface layer portion of the metal layer, it is ideal that the temperature does not rise in a region deeper than 20 nm. However, since heat conduction actually occurs, in all of the curves a, b, c, d, and e in FIG. 4, a temperature rise is seen in a region deeper than 20 nm. As shown in curves a and b, it can be seen that the temperature rise when the pulse width is 2 ps and 20 ps is significantly smaller than the temperature rise shown in curves c, d, and e.
[0039]
That is, when the pulse width is longer than 20 ps, the amount of heat that diffuses into a region deeper than 20 nm deep is large, so it is necessary to input energy corresponding thereto. Pulse width 200 ps, 2 ns, with increasing long as ^{20ns, 0.109J / cm 2, 0.318J} / cm 2, is required large fluence and so 0.98J / cm ^2. When a laser beam having such a pulse width is irradiated, the time during which the metal melts is long and the melting region becomes thick in the temperature rising process in which the metal melts and vaporizes. For this reason, the resin film (processing residue) on the surface of the metal layer is caught up to a deep region of the metal layer.
[0040]
On the other hand, when the pulse width is 20 ps or less, the region shallower than 20 nm is locally heated, so that the required fluences such as 0.040 J / cm ² and 0.045 J / cm ² are small. The required fluence is almost equal between the case where the pulse width is 20 ps and the case where the pulse width is 2 ps. In this case, since the melting time of the metal is short and the melting region is also local, the resin coating layer film (processing residue) on the surface of the metal layer is difficult to be caught inside the metal layer. Therefore, the pulse width is preferably 20 ps or less.
[0041]
By the way, it is said that a photon is absorbed by electrons in the object to be heated, and about several ps is required for it to be converted into heat. In order to effectively convert the energy of the laser beam into thermal energy, the pulse width is preferably set to 5 ps or more.
[0042]
The processing conditions for removing the resin film (processing residue) remaining on the metal layer formed of copper have been discussed above. This is also applied when the metal layer is formed of an alloy mainly composed of copper. Further, for example, considering that the thermal diffusion distances δ of gold, silver, and aluminum are 531 nm, 640 nm, and 448 nm, respectively, which are similar to the thermal diffusion distance of copper, they are formed of gold, silver, aluminum, or the like. In the case of removing the resin film (processing residue) remaining on the metal layer, the above preferable processing conditions may be applied.
[0043]
FIG. 5 is a schematic view of a laser processing apparatus used in the laser processing method according to the second embodiment of the present invention. A variable attenuator 7 is added to the optical path of the laser beam between the laser light source 1 and the mask 2 in the laser processing apparatus shown in FIG. The variable attenuator 7 can change the energy attenuation rate of the emitted laser beam. Other configurations are the same as those of the laser processing apparatus shown in FIG. Similar to the laser processing method according to the first embodiment, after opening the hole 11a penetrating the resin coating layer 11 of the multilayer substrate 6 shown in FIG. 2B, the coating 11b remaining on the bottom surface of the hole 11a The metal layer 12 is removed together with the surface layer portion.
[0044]
In the first embodiment, in the step of forming the hole 11a in the resin coating layer 11 using the lifting phenomenon, the fluence per pulse of the pulse laser beam incident on the surface of the resin coating layer 11 and the remaining coating 11b are obtained. In the removing step, the fluence per pulse of the pulse laser beam incident on the bottom surface of the hole 11a was made equal. In the laser processing method according to the second embodiment, the latter is made larger than the former.
[0045]
After the pulse laser beam emitted from the laser light source 1 is attenuated in pulse energy by the variable attenuator 7, it follows the same transmission path as that described in the first embodiment, and the multilayer substrate 6 that is the object to be processed is Incident on the resin coating layer 11. A hole 11a penetrating the resin coating layer 11 is formed at the beam incident position of the resin coating layer 11 by the lifting phenomenon by one shot of laser beam irradiation.
[0046]
Next, the variable attenuator 7 reduces the energy attenuation rate of the pulse laser beam. A pulse laser beam whose energy decay rate is adjusted to be small is incident on the bottom surface of the hole 11a. The pulse laser beam incident on the bottom surface of the hole 11a has a larger pulse energy than the pulse laser beam in which the hole 11a is formed by lifting processing. Therefore, if the area of the beam spot on the irradiated surface is substantially equal, the fluence of the pulse laser beam incident on the bottom surface of the hole 11a at the bottom surface of the hole 11a is the surface of the resin coating layer 11 of the pulse laser beam in which the hole 11a is formed by lifting processing. Greater than the fluence at. A plurality of shot pulse laser beams are incident on the bottom surface of the hole 11 a, and the coating 11 b of the resin coating layer 11 remaining on the bottom surface of the hole 11 a is removed together with the surface layer portion of the metal layer 12.
[0047]
By increasing the fluence of the pulse laser beam incident on the bottom surface of the hole 11a, effective processing can be performed using a pulse laser beam with a wider range of pulse width and wider wavelength range. For example, when laser processing according to the first embodiment is performed using a laser beam having a certain pulse width, depending on the pulse width, a metal layer may be used in a fluence that allows the resin coating layer 11 to be drilled by lifting processing. The 12 surface layers may not be effectively ablated. In such a case, by using the laser processing method according to the second embodiment and increasing the fluence of the pulse laser beam for removing the film 11b, it is possible to make a hole with that pulse width and to remove the remaining film. .
[0048]
In addition, when processing is performed with a constant fluence, it is possible to achieve both lifting drilling of the resin coating layer 11 and effective ablation processing of the surface portion of the metal layer 12 regardless of the pulse width of the laser beam. There may be cases where it is not. Even in such a case, the laser processing method according to the second embodiment is effective. By changing the fluence between the lifting process and the residual film removal process, both processes can be performed with a laser beam having the same pulse width.
[0049]
It may be determined as appropriate from among the laser processing methods according to the first and second embodiments, depending on the pulse width and wavelength of the laser beam, the processing material, and the like.
[0050]
In the first and second embodiments, an Nd: YLF laser oscillator is used. However, a laser oscillator capable of emitting a pulse laser beam having a pulse width on the order of picoseconds, such as an Nd: YAG laser oscillator or a Ti: sapphire laser oscillator. Can be used. If the pulse laser beam has a wavelength of 700 nm or more and 1500 nm or less, similar results can be obtained.
[0051]
Further, the metal layer 12 may be formed of an alloy containing copper as a main component or a metal other than copper.
[0052]
As mentioned above, although this invention was demonstrated along the Example, this invention is not limited to these. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.
[0053]
【The invention's effect】
As described above, according to the present invention, a process of irradiating a coating layer formed on the surface of a base member with a pulsed laser beam to form a large-area hole can be performed by irradiating a beam with a small number of shots. This can be done with little effect on the underlying member. Furthermore, when a part of the coating layer remains on the bottom surface of the drilled hole, it is possible to remove the remaining coating layer by irradiating a laser beam having the same wavelength as that used in the drilling process.
[Brief description of the drawings]
FIG. 1 is a schematic view of a laser processing apparatus used in a laser processing method according to a first embodiment.
2A is a schematic cross-sectional view of a multilayer substrate, and FIG. 2B and FIG. 2C are schematic cross-sectional views of the multilayer substrate in which holes are formed in the resin coating layer.
FIG. 3 is a graph showing a relationship between a fluence per one pulse of a laser beam for removing a remaining film incident on a bottom surface of a hole formed by lifting and an etching rate of a metal layer formed of copper.
FIG. 4 is a graph showing a temperature rise distribution at a depth of 20 nm immediately after the fall of a pulse of a laser beam applied to a metal layer formed of copper.
FIG. 5 is a schematic view of a laser processing apparatus used in a laser processing method according to a second embodiment.
6A to 6D are schematic cross-sectional views of an object to be processed for explaining a conventional laser processing method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Laser light source 2 Mask 2a Through-hole 3 Plano-convex lens 4 Reflective mirror 5 Stage 6 Multilayer substrate 7 Variable attenuator 11 Resin coating layer 11a Hole 11b Film 11c Hole 12 Metal layer 13 Resin ground layer 51a First copper layer 51b Second copper Layer 52a First epoxy resin layer 52b Second epoxy resin layer 53 Window hole 54 Hole 55 Residual resin

Claims (9)

(A) preparing a workpiece on which a coating layer made of a material different from the material of the surface layer portion of the base member is formed on the surface of the base member;
(B) A surface of the coating layer is irradiated with a pulsed laser beam having a property of passing through the coating layer, reflecting at the interface between the coating layer and the base member, and peeling the coating layer at a reflection position from the base member. Forming a peeled portion that causes the surface of the base member to be exposed on the bottom surface, by causing the workpiece to be incident on the workpiece, causing a part of the covering layer to peel from the base member, and
(C) When a pulse laser beam having the same wavelength as that of the pulse laser beam is incident on the bottom surface of the peeling portion and a part of the coating layer remains on the bottom surface of the peeling portion, the remaining coating And a step of removing the layer. In the step (b), the pulse width of the pulse laser beam incident on the object to be processed and the fluence per pulse on the surface of the coating layer are set so that multi-photon absorption does not occur in the coating layer, or multi-photon Even when absorption occurs, the coating layer is set to be equal to or greater than the value necessary for peeling from the base member,
In the step (c), the pulse width of the pulse laser beam incident on the bottom surface of the peeling portion and the fluence per pulse on the bottom surface of the peeling portion are set to values that can ablate the surface layer portion of the base member. The laser processing method according to claim 1. 3. The laser according to claim 1, wherein in the step (c), a part of the coating layer remaining on the bottom surface of the peeling portion is removed together with a surface layer portion of the base member positioned on the bottom surface of the peeling portion. Processing method. In the step (b), the pulse width of the pulse laser beam incident on the workpiece and the fluence per pulse on the surface of the coating layer, and the pulse incident on the bottom surface of the peeled portion in the step (c) The laser processing method according to claim 1, wherein the pulse width of the laser beam and the fluence per pulse at the bottom surface of the peeled portion are equal. In the step (b), the fluence per pulse of the pulse laser beam incident on the object to be processed on the surface of the coating layer is the pulse laser beam incident on the bottom surface of the peeling portion in the step (c). The laser processing method according to claim 1, wherein the laser processing method is smaller than a fluence per pulse on the bottom surface of the peeled portion. The laser processing method according to claim 1, wherein a pulse width of the pulse laser beam is 1 ps or more and less than 1 ns. The laser processing method according to claim 1, wherein a pulse width of the pulse laser beam is 1 ps or more and 100 ps or less. The laser processing method according to claim 1, wherein a wavelength of the pulse laser beam is 700 nm or more and 1500 nm or less. The laser processing method according to claim 1, wherein a surface layer portion of the base member is formed of copper or an alloy containing copper as a main component.

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