JP2002273590A - Method and apparatus for laser beam machining - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for a laser beam machining by which a machining quality is improved while increase in a machining time is suppressed. SOLUTION: An object to be machined, on which a plurality of machining points at which the drilling is performed are demacated, is prepared. The drilling is performed by sequentially making a pulse laser beam incident on a plurality of machining spots under a condition that at least two shots are successively made incident on one machining spot. Thereafter, the drilling is performed by sequentially making the pulse laser beam incident, under a condition that only one shot is made incident on every machining spot, on a plurality of machining spots on which the pulse laser beam is made incident in the first irradiation process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser processing apparatus and a processing method, and more particularly, to a laser processing apparatus and a processing method for performing a drilling process by irradiating a laser beam to a processing object.

[0002]

2. Description of the Related Art Attention has been focused on a laser processing technique for forming a hole reaching a surface of a copper layer by irradiating a pulsed laser beam to a resin layer of a multilayer wiring board in which a resin layer and a copper wiring layer are laminated. A hole can be formed at a desired position by changing the traveling direction of the laser beam with a galvano scanner and moving the position of the beam spot on the surface of the object to be processed. Normally, a hole that penetrates the resin layer cannot be formed by only one shot irradiation, so that a single location is irradiated with a plurality of shots of a pulse laser beam. As a method of irradiating a plurality of shots to one location, a burst method and a cycle method are known.

[0003] The burst method is a method in which a required number of shots of a pulse laser beam are continuously incident on one location. When a hole penetrating the resin layer is formed, the laser spot is moved to the next position where the hole is to be formed, and the pulsed laser beam is continuously incident on that position.

In the cycle method, when one shot is irradiated at one location, the beam spot is moved to the next position where a hole is to be formed, and the next one shot is irradiated. After irradiating one shot at a time to all positions where holes are to be formed, the process returns to the first irradiated position, and irradiates the next one shot. By repeating this, irradiation of the required number of shots is finally performed on all holes.

[0005]

In the burst method, a pulse laser beam is irradiated at an extremely short interval, so that it is easily affected by heat during processing. Due to this heat, the processing quality may be degraded. In contrast, in the cycle method, 1
Focusing on one hole, the time interval from one shot to the next shot is long. Therefore, it is hardly affected by heat. However, in the cycle method, the galvanomirror must be moved while one shot is completed and the next shot is performed. The time required to move the galvanomirror
It is longer than the pulse repetition cycle of the pulsed laser beam. This increases the processing time to complete all drilling.

An object of the present invention is to provide a laser processing apparatus and a processing method capable of improving processing quality while suppressing an increase in processing time.

[0007]

According to one aspect of the present invention, there is provided a process for preparing a workpiece in which a plurality of processing points to be drilled are defined, and at least two shots are continuously incident per processing point. A first irradiation step in which a pulsed laser beam is sequentially incident on the plurality of processing points to perform drilling, and a condition in which only one shot per one processing point is incident on the first irradiation step. And a second irradiation step of performing a drilling process by sequentially irradiating the pulse laser beam to a plurality of processing points where the pulse laser beam has entered.

According to another aspect of the present invention, there is provided a laser light source for emitting a pulsed laser beam, a stage for holding a processing object on a surface of which a plurality of processing points to be drilled are defined, and the laser light source. The pulsed laser beam emitted from the laser beam is made incident on the object held by the stage, and the traveling direction of the pulsed laser beam is changed by a position control signal given from the outside, so that the position of the beam spot on the surface of the object is A scanning optical system for moving the laser beam, and a pulse laser beam is sequentially incident on the plurality of processing points under the condition that at least two shots are continuously incident on one processing point, and thereafter, a plurality of processing points on which the pulse laser beam has already been incident Drilling by sequentially applying a pulsed laser beam under the condition that only one shot per processing point The laser processing apparatus is provided with a control device for controlling the scanning optical system to take place.

According to yet another aspect of the present invention, there is provided a step of preparing a workpiece in which a plurality of processing points to be drilled are determined, and continuously projecting at least two shots at the first processing point. A first drilling step of making a hole, and a second drilling step of making at least two shots continuously incident on at least one second processing point different from the first processing point to form a hole; Thereafter, a step of making only one shot incident on the first processing point to deepen the hole is provided.

Focusing on one processing point, the time until the first irradiation of a plurality of shots is performed and the second irradiation of only one shot is performed is shorter than the case where a plurality of shots are continuously incident. become longer. Therefore, the influence of heat can be reduced, and the processing quality can be improved. Also, 1
The processing time can be reduced as compared with the cycle method in which the incident point of the pulse laser beam is moved while only one shot is incident per processing point.

[0011]

FIG. 1 is a schematic view of a laser processing apparatus according to an embodiment of the present invention. The laser light source 1 emits a pulse laser beam. As the laser light source 1, for example, a CO ₂ gas laser oscillator having an oscillation wavelength of 9.3 to 9.4 μm can be used. The pulsed laser beam emitted from the laser light source 1 is incident on the through hole of the mask 8, and the beam cross section is shaped. The pulsed laser beam transmitted through the through hole of the mask 8 is reflected by the turning mirror 9 and enters the galvano scanner 10. The controller 13 controls the laser light source 1
Transmits the oscillation start signal sig _1, the oscillation start signal sig ₁
In synchronization with the position control signal s
and it sends the ig _2.

The pulse laser beam whose traveling direction is changed by the galvano scanner 10 is converged by the fθ lens 11,
Workpiece 2 held on movable surface of XY stage 12
Incident at 0. lens 11 forms an image of the through-hole of mask 8 on the surface of workpiece 20.

FIG. 2A is a plan view of the object 20 to be processed. A copper wiring pattern 33 is formed on the surface of the processing object 20.
Are formed, and a plurality of processing points P _{1 to} P _N where holes are to be formed are defined at positions overlapping the wiring pattern 33. The galvano scanner 10 can move the beam spot to an arbitrary position within a square area 21 of, for example, 50 mm × 50 mm. For example, M processing points P _{1 to} P _M are arranged in an area 21 that can be scanned by the galvano scanner 10. By driving the XY stage 12, the operable area 21 can be moved within the surface of the processing target 20.

FIG. 2B is a sectional view of one processing point P. A lower wiring pattern 31 of copper having a thickness of 35 μm is formed on a base substrate 30, a resin layer 32 having a thickness of 45 μm is formed thereon, and an upper wiring pattern 33 of copper having a thickness of 18 μm is formed thereon. Have been. An opening 33 a having a diameter of 135 μm is formed in the upper wiring pattern 33. The processing point P is defined by the opening 33a.

A laser beam 40 is incident on a processing point P.
The diameter of the through hole of the mask 8 shown in FIG. 1 is 3.6 mm, and the reduction magnification of the fθ lens 11 is 15 times. At this time, the diameter of the beam spot on the surface of the processing object 20 is about 240 μm. The pulse energy of the pulse laser beam 40 is 5.9 mJ / pulse, the energy density on the surface of the resin layer 32 is 5.1 mJ / cm ² , and the full width at half maximum of the pulse waveform is 14 μs. Upper layer wiring pattern 3
3 functions as a mask, and a hole aligned with the opening 33a is formed. As described above, a method of forming a hole aligned with an opening provided in a mask on a resin layer on which a hole is to be formed is as follows.
It is generally called a conformal mask processing method.

FIG. 2C is a timing chart of the pulse laser beam during processing. First, add 2 to machining point P ₁
The shot is irradiated with a pulsed laser beam. The time A from the rise of the first shot pulse to the rise of the second shot pulse depends on the repetition frequency of the pulse of the laser light source 1, and its length is 0.5 ms.

Next, by operating the galvanometer scanner 10, performs irradiation of 2 shots machining point P _2. 1 from the rise of the second shot pulse of the machining point P ₁ of the machining point P ₂
The time B until the pulse of the shot pulse rises is determined by the operation time of the galvano scanner 10, and its length is about 2 ms. Thus, while the incident by two shots into one processing point to move the point of incidence of the sequentially pulsed laser beam from all of the machining point P ₁ in the irradiation region 21 to P _M. By this irradiation, a hole is formed at each processing point, but the hole does not reach the upper surface of the lower wiring pattern 31.

The laser irradiation so far is referred to as a first irradiation step. In the first irradiation step, irradiation with a pulsed laser beam is performed in the same manner as in the conventional burst method.

[0019] The first irradiation step is completed, the process returns to the first processing point P _1, to irradiate only one shot.
While irradiation of one shot to one processing point, to move the point of incidence of the sequentially pulsed laser beam from the processing point P ₁ to P _M. This step will be referred to as a second irradiation step.

As shown in FIG. 3A, when the second irradiation step is completed, the lower wiring pattern 31 is provided at each processing point.
Is formed to reach the upper surface of the substrate. The side surface of the hole 35 has a tapered shape in which the lower wiring pattern 31 side is narrowed, and a hole having a shape close to a hole formed by a conventional cycle method can be formed. On the other hand, the same pulse laser beam as the pulse laser beam used in the above embodiment was used.
When processing was performed by a burst method in which three shots were continuously incident on one processing point, a barrel-shaped hole 36 was formed as shown in FIG. 3B.

In the case of this embodiment, since the hole 35 having a tapered side surface is formed, copper is plated on the side surface of the hole 35 to make the upper wiring pattern 33 and the lower wiring pattern 31 conductive. The occurrence of conduction failure can be prevented.

When drilling is performed by the conventional cycle method, irradiation for each shot must be repeated three cycles. At this time, the processing time Ts is

[0023]

Ts = (B × M) × 3 = (6 × M) [ms] On the other hand, when the method (combination method) according to the above embodiment is employed, the processing time Tc is:

[0024]

Tc = (A + B) × M + B × M = (4.5 ×
M) [ms]. Thus, by employing the method according to the embodiment, the processing time can be shortened as compared with the case of processing by the cycle method.

In the above embodiment, in the first irradiation step,
Irradiation of two shots per processing point is performed sequentially,
In the second irradiation step, irradiation of only one shot per processing point was sequentially performed. The number of shots to be irradiated to one processing point in the first irradiation step is not limited to two. However, the number of shots to be irradiated on one processing point in the second irradiation step needs to be one. The number of shots per processing point in the first irradiation step is such that the holes formed in the first irradiation step do not reach the upper surface of the lower wiring pattern, and the number of shots in the second irradiation step is one shot. What is necessary is just to select so that the hole which reaches to the upper surface of a pattern may be formed.

[0026] In the above embodiment, in the first irradiation step, was irradiated one by two shots in all the machining point P ₁ to P _M of irradiation-enabled area 21 shown in FIG. 2 (A) rear,
Although the process has proceeded to the second irradiation process, the process may proceed to the second irradiation process after irradiating only a part of the processing points in the first irradiation process. Focusing on one processing point, after irradiating two shots in the first irradiation step,
10m time to one shot in the second irradiation step
If it is not less than s, a high quality hole can be formed.

[0027] Since FIG. 2 (C) in time comprises the operating time of the galvano scanner shown B is about 2 ms, after irradiating up to 5 th machining point P ₅ in the first irradiation step, the first processing point Referring back to P _1, time of 10ms is ensured. When the operation time of the galvano scanner is long, after processing to the second processing point P ₂ by the first irradiation step, there will be cases where it may return to the first processing point P _1. As described above, first, the first processing point is irradiated with a plurality of shots, then, at least one other processing point is irradiated with the plurality of shots, and then the process returns to the first processing point to irradiate only one shot. May be performed.

In the above embodiment, the case where the hole formed in the first irradiation step does not reach the upper surface of the lower wiring pattern has been described. However, the hole reaches the upper surface of the lower wiring pattern, and a part thereof is exposed. Even in this case, if the area of the exposed portion is sufficiently small, the same effect as in the above embodiment will be obtained. That is, after the first irradiation step,
What is necessary is that it does not become a barrel shape as shown in FIG. In this case, in the second irradiation step, a high-quality hole can be formed by increasing the area of the exposed portion of the lower wiring pattern to a desired size.

In the case of the direct processing method in which a laser beam is condensed on the surface of the resin layer whose entire surface is exposed to form a hole, a relatively high-quality hole can be formed even by using a burst method. it can. Therefore, the combination method according to the above embodiment has a particularly large effect when the conformal mask processing method is employed.

In the case of the direct processing method, the effect of the combination method is small in optimizing the sectional shape of the hole. However, the combination method is superior to the burst method in reducing the residual resin film (desmear) remaining on the bottom of the hole.

The present invention has been described in connection with the preferred embodiments.
The present invention is not limited to these. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0032]

As described above, according to the present invention,
The first irradiation step is performed by the burst method, and then the second irradiation step is performed.
In the second irradiation step, irradiation of only one shot per one processing point is performed. Thereby, holes of higher quality than holes formed by the conventional burst method can be formed.
Further, the processing time can be reduced as compared with the case where the holes are formed by the conventional cycle method.

[Brief description of the drawings]

FIG. 1 is a schematic view of a laser processing apparatus according to an embodiment of the present invention.

FIG. 2 is a plan view of a processing object, a cross-sectional view of a processing point, and a timing chart of pulse laser irradiation in a processing method according to an embodiment.

3 (A) and 3 (B) are cross-sectional views of holes formed by a method according to an embodiment and a conventional burst method, respectively.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 laser light source 8 mask 9 folding mirror 10 galvano scanner 11 fθ lens 12 XY stage 13 control device 20 processing object 21 irradiable area 30 base substrate 31 lower wiring pattern 32 resin layer 33 upper wiring pattern 33a openings 35, 36 holes 40 pulses Laser beam

Claims (8)

[Claims] 1. A step of preparing a processing object in which a plurality of processing points to be drilled are defined; and sequentially applying pulses to the plurality of processing points under a condition that at least two shots are continuously incident per processing point. In a first irradiation step in which a laser beam is incident to perform drilling, and under a condition that only one shot is incident per one processing point,
A second irradiation step in which a pulsed laser beam is sequentially incident on a plurality of processing points where the pulsed laser beam is incident in the first irradiation step to perform drilling. 2. The processing object is a laminated substrate in which a resin layer is formed on a base metal layer, and a hole formed in the first irradiation step does not penetrate the resin layer. The laser processing method according to claim 1, wherein a hole penetrating the resin layer is formed in the second irradiation step. 3. The object to be processed is a laminated substrate having a resin layer formed on an underlying metal layer, wherein a hole formed in the first irradiation step penetrates the resin layer, and The area of the surface of the metal layer appearing on the bottom surface of the hole is a first area, and the area of the surface of the metal layer appearing on the bottom surface of the hole in the second irradiation step is smaller than the first area. The laser processing method according to claim 1, wherein the value is also increased. 4. The processing object is a laminated substrate having a metal mask layer formed on a resin layer, and an opening provided in the metal mask layer is arranged at the position of the processing point. Item 4. The laser processing method according to any one of Items 1 to 3. 5. A laser light source for emitting a pulsed laser beam, a stage for holding a workpiece on which a plurality of processing points to be drilled are defined, and a pulsed laser beam emitted from the laser light source. A scanning optical system for causing the pulse laser beam to travel in the direction of movement of the pulse laser beam by a position control signal given from the outside while being incident on the object held by the stage, and moving the position of a beam spot on the surface of the object to be processed. Under the condition that at least two shots are continuously incident on one processing point, a pulse laser beam is sequentially incident on the plurality of processing points, and thereafter, a plurality of processing points on which the pulse laser beam has already been incident are processed per one processing point. Under the condition that only one shot is incident, the scanning is performed so that a pulsed laser beam is sequentially incident and drilling is performed. A laser processing apparatus having a control device for controlling an optical system. 6. A step of preparing a processing object in which a plurality of processing points to be drilled are determined, and a first drilling step of continuously irradiating at least two shots to the first processing point. A second drilling step of continuously piercing at least two shots into at least one second processing point different from the first processing point to form a hole; and thereafter, the first processing point A step of making only one shot incident on the substrate and making the hole deeper. 7. The object to be processed is a laminated substrate having a resin layer formed on an underlying metal layer, and a hole formed in the first drilling step does not penetrate the resin layer. 7. The laser processing method according to claim 6, wherein a hole penetrating the resin layer is formed in the step of deepening the hole. 8. A resin layer is formed on an underlying metal layer,
A step of preparing a processing object in which a plurality of processing points to be drilled are determined; and a step of continuously irradiating at least two shots to the first processing point to form a hole penetrating the resin layer. A second drilling step of continuously piercing at least two shots into at least one second processing point different from the first processing point to form a hole; Irradiating only one shot to the processing point to increase the area of the portion of the surface of the metal layer that appears at the bottom of the hole.