JP2001212684A - Via-hole processing method and its apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a via-hole processing method which can process a via-hole with better accuracy and its apparatus. SOLUTION: A pulsed laser beam L1 for processing is irradiated to a first layer 5A of a complex material 5 so that a via-hole 5V is made. A laser beam L2 for a probe is also irradiated to the first layer 5A and its reflected laser beam L3 is measured by a light interferometer 8. Based on the light interferometer, a direct vibration generating on the surface at a moment when the pulse laser beam L1 is irradiated to the first layer is detected, and a reflected vibration exposed on the surface of the first layer after the direct vibration is reflected by a second layer can be also detected. A time difference detecting the two vibrations becomes smaller in proportion to a remaining thickness δof the first layer. Therefore, the time difference is measured at first when the above-described thickness becomes a predetermined thickness, and then, a via-hole processing is stopped when the time difference becomes within a predetermined value. Alternately, the time difference when a degree of a vibration exposed on the surface of the first layer becomes equal to and more than a predetermined value, a via-hole processing may be stopped.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for processing a via hole in a composite material.

[0002]

2. Description of the Related Art Conventionally, for a composite material such as a printed circuit board having an insulating resin layer as a first layer and a metal conductive layer as a second layer, a via hole having a predetermined depth is formed in the insulating resin layer. In the case, that is, when forming a via hole having a required depth without leaving the insulating resin layer of a predetermined thickness without exposing the conductive layer, a laser for processing a via hole until the above depth is obtained in advance. The number of shots and processing time by the apparatus are measured, and the processing is terminated when the shot number is obtained or when the processing time has elapsed.

[0003]

However, when processing is completed by measuring the number of shots and the processing time described above, the thickness of the remaining insulating resin layer may be reduced due to fluctuations in the output of the laser device and variations in the composite material. Had the disadvantage of becoming non-uniform. If the thickness of the remaining insulating resin layer is too thin or completely removed, the conductive layer is heated, and peeling may occur between the conductive layer and the insulating resin layer in other portions, or in the worst case. In such a case, a through-hole was formed in the conductive layer, which made the printed circuit board unsuitable. On the other hand, if the thickness of the remaining insulating resin layer is too thick, the insulating resin layer cannot be completely removed in the next etching step to expose the conductive layer. Sometimes it was appropriate. The present invention has been made in view of such circumstances, and provides a via hole processing method and apparatus capable of processing a via hole with higher accuracy.

[0004]

According to the first aspect of the present invention, the first layer of a composite material having a first layer and a second layer is irradiated with a processing pulse laser beam from a via hole processing laser device. A via hole processing method for processing a via hole having a predetermined depth in the first layer;
A direct vibration generated on the surface of the first layer by irradiating the pulse laser beam for processing onto the first layer, and the direct vibration is propagated to the second layer and reflected by the surface of the first layer. Is measured again, and when a time difference between the time when the direct vibration is obtained and the time when the reflected vibration is obtained is within a predetermined value, the first layer by the processing pulse laser beam is used. Is stopped. As the reflection vibration, any one of a first reflection vibration obtained by reflection on the front surface of the second layer and a second reflection vibration obtained by reflection on the back surface of the second layer can be used. According to a third aspect of the present invention, the first layer of the composite material having a first layer and a second layer is irradiated with a pulse laser beam for processing from a laser device for processing a via hole, and the first layer is irradiated with a predetermined laser beam. In a via hole processing method for processing a via hole having a depth, a vibration generated on a surface of the first layer is measured by irradiating the processing pulse laser beam to the first layer, and the measured value is predetermined. When the value exceeds a predetermined value, the via hole processing of the first layer by the processing pulse laser beam is stopped. The vibration to be measured is a direct vibration directly generated on the surface of the first layer by irradiating the pulse laser beam for processing onto the first layer, and the direct vibration is propagated to the second layer, and the second layer is The first reflected vibration that occurs again on the surface of the first layer by being reflected by the surface of the first layer, and the direct vibration is propagated to the second layer, and the first reflected vibration is reflected by the back surface of the second layer. Either of the second reflected vibrations that reappear on the surface of one layer can be used. Claim 9
The invention relates to a via-hole processing laser device for irradiating a composite material with a via-hole processing pulse laser beam, a probe laser device for irradiating a probe laser beam to the composite material, and a probe reflected from the composite material. Input a laser beam, and from this reflected laser beam,
An optical interferometer for measuring a vibration generated in the composite material by irradiating the composite material with the processing laser beam.

According to the first aspect of the present invention, when the first layer of the composite material is irradiated with the processing pulse laser beam from the via hole processing laser device, the irradiation causes direct vibration on the surface of the first layer. Become. Then, when the direct vibration is propagated to the second layer, the direct vibration is reflected by the surface of the second layer, and the first reflected vibration again occurs on the surface of the first layer. Further, the direct vibration propagates in the second layer and is reflected also on the back surface of the second layer,
The second reflection vibration is generated again on the surface of the first layer. Since the thickness of the first layer is large at the beginning of the processing, from the moment when the direct vibration from the first layer is obtained to the time when the reflected vibration (the first reflected vibration or the second reflected vibration) from the second layer is obtained. Is large, but when the processing of the via hole proceeds and the thickness of the first layer is reduced, the time difference between the two becomes smaller. In addition,
Since the thickness of the second layer does not change, the time difference between when the first reflected vibration is obtained and when the second reflected vibration is obtained is constant. Therefore, the time difference when the thickness of the remaining first layer reaches a predetermined thickness is measured in advance, and when the time difference falls within a predetermined value, the first layer by the via hole processing laser device is used. When the via hole processing is stopped, the thickness of the remaining first layer can always be controlled to a predetermined thickness with high precision. In addition, the oscillation is performed by irradiating the surface of the first layer with the laser beam for the probe from the laser device for the probe, and inputting the laser beam for the probe reflected from the surface of the first layer to the optical interferometer, It can be measured by the optical interferometer. According to the third aspect of the present invention, since the respective frequencies and amplitudes of the direct vibration, the first reflected vibration and the second reflected vibration described above increase as the thickness of the first layer becomes thinner, the vibrations remain in advance. What is necessary is just to measure the magnitude of the measurement value when the thickness of the first layer to be formed reaches a predetermined thickness. In this case, when the measured value becomes equal to or more than a predetermined value, the via hole processing of the first layer by the laser device for via hole processing is stopped, and the thickness of the remaining first layer is reduced to a predetermined thickness. Can be managed with high accuracy. According to the ninth aspect of the present invention, the above first aspect is provided.
And the method according to the third aspect of the present invention.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, when describing the present invention for the illustrated embodiment, in FIG. 1, the via hole processing laser device 1, for example, emits a processing pulse laser beam L ₁ having a wavelength of 10.6μm The CO ₂ pulse gas laser device 1 can be used. The laser beam L _1, the beam combiner 2, perforated reflection mirror 3 as a beam separator, and through the condenser lens 4 are irradiated to the composite material 5. As the processing pulse laser beam L ₁ is not limited to those having a wavelength of 10.6 [mu] m, may be any pulsed laser beam if it is possible to process the via holes in the composite material 5. The composite material 5 includes a first layer 5
A printed circuit board comprising A and a second layer 5B, wherein the first layer 5A is made of an insulating resin layer 5A made of, for example, polyimide, and the second layer is a metal conductive layer, more specifically, It consists of a copper layer 5B. And the above laser device 1
By irradiating the laser beam L ₁ to the insulating resin layer 5A from, and so as to form a via hole 5C until just before the copper layer 5B.

[0007] The probe laser device 6 is, for example, 0.6.
A He—Ne laser device 6 that emits a continuous laser beam L ₂ having a wavelength of 3 μm can be used. The probe laser beam L ₂ is generated by the beam combiner 2 using the pulse laser beam L ₁ from the laser device ₁ . Collected on the optical axis, the perforated reflection mirror 3 and the condenser lens 4
Is applied to the composite material 5 via the. This is not limited to those having a wavelength of 0.63μm as the laser beam L ₂ probe, it may be any laser beam as long as it is reflected by the surface of the composite material 5. Furthermore, the reflected laser beam L _{3 of} the probe laser beam L ₂ reflected from the composite material 5
Are laterally separated from the optical axes of the laser beams L ₁ and L ₂ by a perforated reflecting mirror 3, and are passed through a condenser lens 7 and a confocal Fabry-Perot optical interferometer 8 to form an avalanche photodiode or a photomultiplier. And the like. Then, the signal is further input to the oscilloscope 12 via the filter 10 and the amplifier 11, and the waveform is detected.

[0008] Figure 2 is a detection waveform displayed by the oscilloscope 12, reference numeral 14 is only the probe laser beam L ₂ is irradiated to the surface of the insulating resin layer 5A,
Reflected laser beam L ₃ reflected by the surface of the insulating resin layer 5A is a voltage value in a state being detected. In this state, the voltage detected by the photometer 9 has a small value 14. When the processing pulse laser beam L ₁ in this state is irradiated onto the surface of the insulating resin layer 5A, by the impact vibration on the surface of the insulating resin layer 5A occurs. The vibration at this time, that is, the processing pulse laser beam L
_The vibration directly generated by irradiating 1 to the surface of the insulating resin layer 5A is referred to as direct vibration. Insulating resin layer 5A
Of the said direct vibration is small in its surface caused displacement occurs on the surface, become a difference in optical path length of the reflected laser beam L ₃ reflected by the surface occurs, the optical interferometer 8 of the optical path length The vibration can be detected as the intensity of light from the difference. Then, since the light measuring device 9 converts the intensity of the light into a voltage, the voltage detected by the light measuring device 9 has a large value 15. That is, the direct vibration 15 can be measured by the optical interferometer 8. The direct vibration 15 can be detected for a very short time, and when the direct vibration on the surface of the insulating resin layer 5A stops, the voltage detected by the optical measuring device 9 becomes a small value 14 again.

When the direct vibration 15 is transmitted in the insulating resin layer 5A and propagated to the copper layer 5B, the direct vibration is reflected by the surface of the copper layer 5B and transmitted again in the insulating resin layer 5A. Vibration is caused on the surface of the insulating resin layer 5A. The vibration at this time is referred to as first reflected vibration 16. The direct vibration propagated to the copper layer 5B is not only reflected by the surface of the copper layer 5B, but also
B is transmitted inside, and is also reflected by the back surface of the copper layer 5B. The direct vibration reflected by the back surface of the copper layer 5B is transmitted through the inside of the copper layer 5B and the inside of the insulating resin layer 5A, and the first reflected vibration 1
After a delay of 6, vibration occurs on the surface of the insulating resin layer 5A. The vibration at this time is referred to as a second reflected vibration 1
No. 7. The first reflected vibration 16 and the second reflected vibration 17 generated on the surface of the insulating resin layer 5A are sequentially detected by the optical interferometer 8 with a time difference as shown in FIG. It will be converted to voltage.
At this time, the first reflected vibration 16 is attenuated and reduced while being transmitted through the insulating resin layer 5A, and thus has a smaller voltage value than the direct vibration 15. Second reflection vibration 1
7 has a voltage value smaller than that of the first reflected vibration 16 by the amount transmitted through the copper layer 5B.

In the initial stage of processing the insulating resin layer 5A, the distance between the surface of the insulating resin layer 5A and the surface of the copper layer 5B, that is, the thickness δ of the insulating resin layer 5A is large.
Time interval t ₀ from direct vibration 15 is obtained to the first reflection vibration 16 caused by reflection of the surface of the copper layer 5B is obtained on the surface of the is larger. When the processing of the via hole 5C proceeds from this state and the thickness δ of the insulating resin layer 5A becomes thinner, the distance between the surface of the insulating resin layer 5A and the surface of the copper layer 5B becomes shorter. The time interval between the direct vibration 15 on the surface of the copper layer 5B and the first reflected vibration 16 on the surface of the copper layer 5B gradually decreases (see FIG. 3). Similarly,
Direct vibration 15 and second reflected vibration 1 by the back surface of copper layer 5B
7, the time interval t between the first reflected vibration 16 and the second reflected vibration 17 is constant because there is no change in the thickness of the copper layer 5B. As shown in FIG. 3, when the required depth of the via hole 5C is obtained, that is, when the thickness δ of the insulating resin layer 5A becomes a predetermined thickness, the direct vibration 15 and the first reflected vibration 16 are obtained.
Time interval t ₁ between the Yes previously measured, its After a predetermined time interval t ₁ is obtained in the processing pulse laser beam L ₁ irradiated is stopped. Thereby, the predetermined thickness δ
Via hole 5C of required depth leaving insulating resin layer 5A
Is obtained. Thereafter, the insulating resin layer 5A at the bottom of the via hole 5C is removed by a conventionally known etching, and the surface of the copper layer 5B is exposed.

When the thickness δ of the insulating resin layer 5A becomes a predetermined thickness, the direct vibration 15 and the second reflected vibration 1
Previously measuring the time interval between 7 and also to stop the irradiation of the processing pulse laser beam L ₁ When the predetermined time interval is obtained, leaving the insulating resin layer 5A having a predetermined thinness δ It is clear that the required via hole 5C can be obtained.

[0012] Next, in the above embodiment, the predetermined time interval t ₁ is so as to terminate the process If obtained,
Instead, when the thickness δ of the insulating resin layer 5A becomes thinner, the direct vibration 15, the first reflected vibration 16 and the second
Since the frequency and amplitude of the reflected vibration 17 gradually increase, a via hole 5C having a required depth may be obtained by using this. That is, the composite material 5 is thick when the via hole 5C is not formed in the composite material 5, and becomes thinner as the via hole 5C is formed deeper. Then, the frequency of the direct vibration 15 upon irradiation of the processing pulse laser beam L ₁ in a thick composite material 5 is relatively low, the composite material 5
The frequency of the direct vibration 15 increases as the
The amplitude also increases. This is the same for the first reflected vibration 16 and the second reflected vibration 17. When the frequencies and amplitudes of the vibrations 15, 16, and 17 increase, the intensity of light measured by the optical interferometer 8 increases, so that the measurement value increases, and the voltage obtained by the optical measuring device 9 also increases. Become. Thus, for example, direct vibration 15
In the following, the magnitude of the voltage v of the insulating resin layer 5A when the thickness δ of the insulating resin layer 5A has become a predetermined thickness is measured in advance, and the voltage of the direct vibration 15 determines the predetermined magnitude. Once across, the pulse laser beam L ₁ for processing
May be stopped. As a result, a via hole 5C having a required depth is obtained while leaving the insulating resin layer 5A having a predetermined thickness δ.

Incidentally, even if the magnitudes of the first reflected vibration 16 and the second reflected vibration 17 are detected, a via hole 5C having a required depth can be obtained similarly. At this time, it is generally desirable to detect the direct vibration 15 having the largest value, but the first reflected vibration 16 or the second reflected vibration 1
7 may be detected. However, the first reflected vibration 1
6 and the second reflected vibration 17, the value of the first reflected vibration 17 is large.
It is desirable to detect the reflected vibration 16 of. Further, in the above embodiment, the light intensity measured by the optical interferometer 8 is measured by the optical measuring device 9.
Is converted to a voltage, but the present invention is not limited to this, and any voltage may be used as long as the value measured by the optical interferometer 8 can be used.

[0014]

As described above, according to the present invention, when the thickness of the first layer becomes a predetermined thickness, the via hole processing of the first layer by the via hole processing laser device can be stopped. The effect is obtained that the via hole can be processed with higher accuracy than in the past.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention.

FIG. 2 is a waveform chart obtained by the present invention.

FIG. 3 is a waveform chart in a state in which via hole processing has progressed more than in FIG. 2;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Laser device for via hole processing 2 ... Beam combiner 3 ... Perforated reflection mirror (separator) 5 ... Composite material 5A ... Insulating resin layer (1st layer) 5B ... Copper layer (2nd layer) 5C ... Via hole 6 ... For probe The laser apparatus 8 ... optical interferometer L ₁ ~L 3 _... laser beams t _1, t 2 _... time difference [delta] ... thickness

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H05K 3/46 H05K 3/46 Y // B23K 101: 42 B23K 101: 42 F term (Reference) 2F065 AA30 CC01 FF32 FF51 GG04 HH04 JJ01 LL12 LL30 QQ25 QQ29 4E068 AF01 CA17 CB09 CC00 CC01 DA11 DB14 5E346 AA12 AA15 AA32 AA38 AA43 BB01 CC08 FF01 GG01 GG15 GG34 HH33

Claims (10)

[Claims] 1. A laser beam for processing from a via-hole processing device is irradiated with a processing pulse laser beam on the first layer of a composite material having a first layer and a second layer, so that the first layer has a predetermined depth. In a via hole processing method for processing a via hole, a direct vibration generated on a surface of the first layer by irradiating the processing pulse laser beam to the first layer, and the direct vibration is transmitted to the second layer. The reflected vibration that occurs again on the surface of the first layer by being reflected is measured, and the time difference between the time when the direct vibration is obtained and the time when the reflected vibration is obtained is within a predetermined value. And stopping the via hole processing of the first layer by the processing pulse laser beam. 2. The reflection vibration is one of a first reflection vibration obtained by reflection on a surface of a second layer and a second reflection vibration obtained by reflection on a back surface of a second layer. The method for processing a via hole according to claim 1, wherein: 3. A pulse laser beam for processing from a laser device for processing a via hole is applied to the first layer of the composite material having a first layer and a second layer, and the first layer has a predetermined depth. In a via hole processing method for processing a via hole, a vibration generated on a surface of the first layer is measured by irradiating the pulse laser beam for processing to the first layer, and the measured value is equal to or more than a predetermined value. A via hole processing method comprising: stopping the via hole processing of the first layer by the processing pulse laser beam when the above becomes true. 4. The vibration to be measured is obtained by irradiating the first layer with the pulse laser beam for processing.
A direct vibration that occurs directly on the surface of the layer, a first reflected vibration that propagates to the second layer and is reflected by the surface of the second layer, and then reappears on the surface of the first layer; The direct vibration is propagated to the second layer, and the second
The via hole processing method according to claim 3, wherein the second reflection vibration is any one of a second reflection vibration generated again on the surface of the first layer by being reflected by a back surface of the layer. 5. A laser beam for a probe is emitted from a laser device for a probe to the surface of the first layer, and the laser beam for a probe reflected from the surface of the first layer is input to an optical interferometer. 5. The via hole processing method according to claim 1, wherein the vibration is measured by an optical interferometer. 6. The via hole processing apparatus according to claim 5, wherein the optical interferometer is a confocal Fabry-Perot optical interferometer. 7. The method according to claim 1, wherein the first layer is an insulating resin layer, and the second layer is a metal conductive layer. 8. The method according to claim 1, wherein after the processing of the via hole is stopped, the first layer at the bottom of the via hole is removed by etching to expose the second layer. Via hole processing method. 9. A via hole processing laser device for irradiating a pulsed laser beam for processing a via hole to a composite material,
A probe laser device for irradiating the composite material with a probe laser beam, and a probe laser beam reflected from the composite material are input, and the composite material is irradiated with the processing laser beam from the reflected laser beam. And a light interferometer for measuring a vibration generated in the composite material. 10. The via hole processing apparatus according to claim 9, wherein the optical interferometer is a confocal Fabry-Perot optical interferometer.