JP2007029990A - Laser beam machining apparatus, and laser beam machining method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser beam machining apparatus and a laser beam machining method capable of improving the numerical aperture of a hole in a printed circuit board. <P>SOLUTION: An intermediate optical system is arranged between a laser light source and a workpiece held by a stage. The intermediate optical system comprises two conical prisms arranged in such a manner that the central axes are made coincident, and, in such a manner that, regarding the beam profile in the surface of the workpiece, the circumferential part of a beam spot has a raised part more raised than the center, shapes the beam profile of the laser beam. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a laser processing apparatus and a laser processing method, and more particularly to a laser processing apparatus and a laser processing method for forming a hole in a workpiece.

  There is known a method of forming a hole by irradiating a laser beam to a resin layer of a printed wiring board in which resin layers and metal wirings are alternately laminated. A normal laser beam has a profile in which the light intensity is high at the center of the beam spot and the light intensity decreases as the distance from the center increases.

  When this laser beam is incident on the resin layer, the processing speed of the portion having a high light intensity at the center of the beam spot is high, and the processing speed decreases as the distance from the center increases. For this reason, a hole whose side surface is inclined is formed. When the diameter of the opening of the hole is Dt and the diameter of the bottom is Db, the aperture ratio defined by Db / Dt is small. Since the contact resistance of the wiring on the printed wiring board increases as the aperture ratio decreases, it is desired to increase the aperture ratio.

  Patent Document 1 below discloses a laser processing apparatus and a processing method in which a beam profile shaping unit is disposed between a laser light source and a scanning optical system to improve an aperture ratio. In the apparatus disclosed in Patent Document 1, a laser beam having a beam profile in which the intensity at the periphery of the beam spot is stronger than the intensity at the center is used.

JP 2003-236690 A

  In the method disclosed in Patent Document 1, the aperture ratio is improved, but it is not sufficient.

  An object of the present invention is to provide a laser processing apparatus and a processing method capable of improving the aperture ratio of a hole to be processed.

  According to one aspect of the present invention, an intermediate optical system disposed between a laser light source that emits a laser beam, a stage that holds a workpiece, the laser light source, and a workpiece that is held by the stage. And including two conical prisms arranged so that the central axes thereof coincide with each other, and the beam profile on the surface of the object to be processed has a raised portion raised from the center at the periphery of the beam spot. A laser processing apparatus having an intermediate optical system for shaping the beam profile of the laser beam is provided.

  According to another aspect of the present invention, a step of emitting a laser beam from a laser light source, and a laser beam emitted from the laser light source, the beam profile on the surface of the workpiece is raised at the periphery of the beam spot from the center. The beam profile is shaped so that the minimum light intensity inside the rising portion of the beam profile is 80% or less of the maximum light intensity of the rising portion. And a step of forming a hole in the object to be processed.

  By using an intermediate optical system including two conical prisms, the light intensity in the peripheral portion can be made stronger than the central portion of the beam spot. By drilling with a laser beam having such a beam profile, a hole with a high aperture ratio can be formed.

  When heat generated in a portion with high light intensity around the beam spot is transmitted to the central portion, excessive heat generation occurs in the central portion, and the bottom surface of the hole to be formed may be damaged. In the present invention, since two conical prisms are used, the light intensity at the center of the beam spot can be sufficiently reduced. Thereby, excessive heat generation in the center portion can be prevented, and occurrence of damage in the center portion of the bottom surface of the hole can be suppressed.

  The occurrence of this damage can be suppressed by setting the light intensity at the center of the beam spot to 80% or less of the light intensity at the peripheral part.

  FIG. 1 shows a schematic diagram of a laser processing apparatus in an embodiment of the present application.

The laser light source 1 emits a pulse laser beam. The laser light source 1 is a CO ₂ gas laser and emits an infrared laser beam.

  The laser beam emitted from the laser light source 1 enters the first conical prism 3 via the relay lens 2 and then enters the second conical prism 4. The conical prisms 3 and 4 are arranged so that the central axes coincide with each other. In addition, the distance between the two conical prisms can be changed by the moving mechanism 9.

  The laser beam emitted from the laser light source 1 and the laser beam that has passed through the relay lens 2 are usually Gaussian beams. The light intensity is large at the center of the beam spot, and the light intensity decreases as the distance from the center increases. The conical prisms 3 and 4 shape the profile of the laser beam so as to have a profile having a shoulder that is raised at the periphery rather than the center of the beam spot.

  The laser beam that has passed through the conical prisms 3 and 4 enters the mask 5. The laser beam that has passed through the through-hole provided in the mask 5 enters the folding mirror 6.

  The laser beam reflected by the folding mirror 6 enters the galvano scanner 7. The galvano scanner 7 includes a pair of swingable reflecting mirrors and scans the laser beam in a two-dimensional direction. The laser beam scanned by the galvano scanner 7 is converged by the fθ lens 8 and enters the workpiece 30 held on the XY stage 11. The fθ lens 8 forms an image of the through hole of the mask 5 on the surface of the workpiece 30.

  The conical prisms 3 and 4, the mask 5, the folding mirror 6, the galvano scanner 7, and the fθ lens 8 are collectively referred to as an intermediate optical system 10.

  FIG. 2 shows the profile of the laser beam that has passed through the conical prisms 3 and 4. A swelled portion that is raised from the central portion is formed at the periphery of the beam spot. The maximum value of the light intensity at the rising portion is Ip, and the minimum value of the light intensity inside the rising portion is Ic. By adjusting the distance between the two conical prisms 3 and 4, the ratio between the minimum value Ic and the maximum value Ip can be brought close to a desired value. For example, Ic / Ip can be set to 80% or less, and Ic can be set to 0.

  When the points where the light intensity is maximum in the radial direction are connected, the circumference shares the center with the beam spot. The radius of this circumference is Rp, and the radius of the beam spot is Rt. By adjusting the distance between the two conical prisms 3 and 4, Rp / Rt can be changed. Here, the radius Rt of the beam spot can be defined, for example, as a radius of a circle defined by connecting points where the light intensity is 10% of the maximum value of the light intensity in the beam spot.

  With reference to FIG. 3 (A) and FIG. 3 (B), the method to form a hole using the laser processing apparatus by an Example is demonstrated.

  As shown in FIG. 3A, an inner layer wiring pattern 32 made of copper is formed on the surface of a core substrate 31 made of an epoxy resin. A resin layer 33 made of an epoxy resin is formed on the core substrate 31 so as to cover the inner layer wiring pattern 32. The workpiece 30 on which the core substrate 31, the inner layer wiring pattern 32, and the resin layer 33 are stacked is placed on the XY stage 11 of the laser processing apparatus shown in FIG.

  A pulse laser beam is emitted from the laser light source 1, and the pulse laser beam 50 is incident on the workpiece 30. As described with reference to FIG. 2, the beam profile (light intensity distribution) 51 of the pulse laser beam 50 on the surface of the workpiece 30 has a raised portion having a light intensity stronger than that of the central portion at the peripheral portion.

  In the region where the swelled portion is incident, the amount of heat generation increases, and the amount of heat generation decreases as the distance from the swelled portion increases toward the center and toward the outside. Since heat flows from the high temperature portion to the low temperature portion, the heat generated in the region where the rising portion is incident flows toward the center portion and the outer peripheral portion. Since heat flows into the central part from all directions, the central part is heated to the same extent as the region where the rising part is incident.

  In the region where the swelled portion is incident, the resin layer 33 is removed by being directly heated by the incidence of the pulse laser beam. In the central portion of the beam spot, the heating due to the incidence of the pulse laser beam is superimposed on the heating due to the heat conduction from the surroundings, and the resin layer 33 is removed.

  Since heat transmitted from the rising portion to the outside gradually dissipates, the region outside the rising portion has a smaller temperature rise due to heat conduction than the central portion. For this reason, almost the processing based on the beam profile is performed in the vicinity of the outer periphery of the beam spot.

  As shown in FIG. 3B, a hole 34 penetrating the resin layer 33 is formed. The outer periphery of the beam spot is steeper than the beam profile of the Gaussian beam. For this reason, compared with the case where it processes with a Gaussian beam, the inclination angle of the side surface of the hole 34 becomes large, and the hole 34 with a large aperture ratio can be formed.

  As a reference example, consider a case where processing is performed with a laser beam having a top flat profile. When the flat portion of the profile is incident, sufficient heating is performed to remove the resin layer. At the center of the beam spot, direct heating due to the incidence of the laser beam and heating due to heat conduction from the surroundings are superimposed, resulting in an excessive temperature rise. An excessive increase in temperature may damage the inner layer wiring pattern 32 exposed on the bottom surface of the hole 34.

  In the case of the present embodiment, the amount of heat directly input from the pulse laser beam at the center of the beam spot is smaller than that in the case of the reference example. For this reason, an excessive temperature rise is prevented, and damage to the inner layer wiring pattern 32 can be prevented. Further, since excessive heating is not performed, the energy of the pulse laser beam can be used effectively.

  In the beam profile shown in FIG. 2, if the radius Rp is too small compared to the radius Rt of the beam spot, or if the difference between the light intensity Ic and the maximum value Ip of the light intensity at the center of the beam spot is too small, it will be excessive. It is not possible to expect a sufficient effect to suppress the temperature rise. In order to obtain a sufficient effect, the radius Rp is preferably set to 45% or more of the radius Rt of the beam spot. Furthermore, it is preferable that the light intensity Ic at the center of the beam spot is 80% or less of the maximum value Ip of the light intensity.

  If the resin layer can be removed only by heating by heat conduction from the periphery at the center of the beam spot, the light intensity Ic at the center may be set to zero. In general, the light intensity Ic is preferably 50% or more of the maximum value Ip of the light intensity.

  Next, the effect when the mask 5 is used will be described. FIG. 4A shows the relationship between the size and position of the beam profile of the laser beam that has passed through the conical prisms 3 and 4 and the through hole 5 </ b> A of the mask 5. The size of the through-hole 5A of the mask 5 is such that when the laser beam is transmitted through the through-hole 5A, a portion outside the position where the light intensity of the laser beam takes the maximum value is shielded by the mask 5. is there. FIG. 4B shows a beam profile on the surface of the workpiece with and without the mask 5 on the path of the laser beam. The beam profile of the laser beam when the mask 5 is present is steeper at the outer peripheral portion than the beam profile of the laser beam when the mask 5 is not present. For this reason, a hole whose side surface is more perpendicular to the surface of the workpiece is formed, and the aperture ratio is increased.

  FIG. 5A shows another example of the processing object. An inner layer wiring pattern 32 is formed on the surface of the core substrate 31. A resin layer 33 is formed on the core substrate 31 so as to cover the inner layer wiring pattern 32. It has a laminated structure in which a metal layer 40 is further formed on the surface of the resin layer 33. The inner wiring pattern 32 and the metal layer 40 are made of, for example, copper, and the core substrate 31 and the resin layer 33 are made of, for example, an epoxy resin. First, a laser beam having a fluence equal to or higher than the fluence threshold per pulse required for forming a hole in copper is incident on the metal layer 40 to form a hole penetrating the metal layer 40. A part of the resin layer 33 on the bottom surface of the hole formed in the metal layer 40 is also etched at the same time. Thereafter, the fluence per pulse is made smaller than the threshold value for etching copper, and a hole is formed in the resin layer 33. By reducing the fluence, the embedded inner layer wiring pattern 32 can be prevented from being damaged. The beam profile of the laser beam that forms holes in the metal layer 40 and the resin layer 33 has a raised portion in the vicinity of the outer periphery of the beam spot, similar to the beam profile of the laser beam used in the present embodiment. . For this reason, a hole with a large aperture ratio can be formed in the metal layer 40 and the resin layer 33.

  FIG. 5B shows still another example of the workpiece. An inner layer wiring pattern 32 is formed on the surface of the core substrate 31. A resin layer 33 is formed on the core substrate 31 so as to cover the inner layer wiring pattern 32. It has a laminated structure in which a metal layer 40 is further formed on the surface of the resin layer 33. The inner layer wiring pattern 32 and the metal layer 40 are made of, for example, copper, and the resin layer 33 is made of, for example, an epoxy resin. First, a hole is formed in the metal layer 40 by chemical etching or the like. Next, when a laser beam is irradiated toward the hole formed in the metal layer 40, the resin layer 33 on the bottom surface of the hole formed in the metal layer 40 is etched, and the hole 34 is formed. The beam profile of the laser beam to be used has a raised portion in the vicinity of the outer peripheral portion of the beam spot, like the beam profile of the laser beam used in the embodiment of the present application. Thereby, a hole with a large aperture ratio can be formed in the resin layer 33.

  The object to be processed shown in FIG. 5C is a tape automated bonding (TAB) film in which the metal layers 40 and 41 are in close contact with both surfaces of the resin layer 42. A hole penetrating these three layers can be formed by making a laser beam having a fluence equal to or higher than a threshold value for forming a hole in copper. The beam profile of the laser beam used has a raised portion near the outer periphery of the beam spot, similar to the beam profile of the laser beam used in the present embodiment. Thereby, the difference in the size of the hole formed in the metal layer 40 on the front side and the metal layer 41 on the back side of the resin layer 42 can be reduced.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

It is the schematic of the laser processing apparatus used in the Example of this application. It is a diagram which shows the beam profile in the surface of the workpiece of the laser beam used in the Example of this application. (A) is the diagram which shows the beam profile in the surface of the processing target object of the laser beam used by the Example of this application, and sectional drawing of the processing target object in the process in which a hole is formed in a processing target object, (B ) Is a cross-sectional view of an object to be processed after forming a hole by the method according to the embodiment of the present application. (A) is a figure which shows the relationship between the magnitude | size and position of the beam profile in the Example of this application, and the through-hole of a mask, (B) shows the beam profile with the case where it does not arrange | position with the mask arrangement | positioning. FIG. It is sectional drawing of the processing target object which has another laminated structure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser light source 2 Relay lens 3, 4 Conical prism 5 Mask 5A Through-hole 6 Folding mirror 7 Galvano scanner 8 f (theta) lens 9 Moving mechanism 10 Intermediate optical system 11 XY stage 30 Process target 31 Underlayer substrate 32 Inner layer wiring pattern 33, 42 Resin Layer 34 Hole 40, 41 Metal layer

Claims (6)

A laser light source for emitting a laser beam;
A stage for holding the workpiece,
An intermediate optical system disposed between the laser light source and a workpiece to be processed held by the stage, including two conical prisms arranged so that central axes coincide with each other, and the workpiece And an intermediate optical system for shaping the beam profile of the laser beam so that the beam profile on the surface of the laser beam has a raised portion that is raised from the center at the periphery of the beam spot.   The laser processing apparatus according to claim 1, wherein the intermediate optical system further includes a moving mechanism that changes a distance between the two conical prisms.   The intermediate optical system has a laser beam so that the minimum light intensity inside the raised portion of the beam profile on the surface of the workpiece is 80% or less of the maximum light intensity of the raised portion. The laser processing apparatus according to claim 1, wherein the profile is shaped.   The laser processing apparatus according to claim 1, wherein the laser light source emits a laser beam in an infrared region. Emitting a laser beam from a laser light source;
The laser beam emitted from the laser light source is such that the beam profile on the surface of the object to be processed has a raised portion that is raised from the center at the periphery of the beam spot, and is the smallest inside the raised portion of the beam profile. Forming a hole in the processing object by shaping the beam profile so that the light intensity is 80% or less of the maximum light intensity of the raised portion, and forming the hole in the processing object. Method.   The laser processing method according to claim 5, wherein a wavelength of the laser beam is in an infrared region.

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