JP2002103079A - Laser beam machining device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser beam machining device by which increase in the manufacturing cost can be suppressed. SOLUTION: Laser light sources 1, 2 emit laser beams pl1, pl2 having a wavelength in the ultraviolet region, while a holding base 12 holds a workpiece 20. A condensing lens 11 converges the laser beams pl1, pl2 emitted from the laser light sources 1, 2 on the surface of the workpiece 20 held on the holding base 12. A lens protecting member 15 is arranged between the condensing lens 11 and the holding base 12. This lens protecting member 15 transmits the light having a wavelength of the ultraviolet region, and prevents scattering materials from the workpiece from reaching the condensing lens 11.

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, more particularly, to a laser processing apparatus that performs laser drilling by converging a laser beam having a wavelength in an ultraviolet region on the surface of a processing object.

[0002]

2. Description of the Related Art A method of piercing a copper wiring layer of a multilayer wiring board having a resin layer and a copper wiring layer by irradiating an ultraviolet laser beam has attracted attention. In this method, for example, the optical axis of a pulsed laser beam having a wavelength in the ultraviolet region is swung by a galvano scanner or the like, and focused on the surface of the processing object by an fθ lens. When an ultraviolet laser beam is used, fine holes can be formed as compared with the case where an infrared laser beam is used.

[0003]

When drilling is performed by irradiating a copper wiring layer with an ultraviolet laser beam, scattered copper particles are generated.
Attaches to the θ lens. The scattered matter attached to the fθ lens is
Since the transmittance of the laser beam is reduced, it causes processing defects. It is not easy to remove flying copper particles attached to the fθ lens. Replacing the expensive fθ lens also increases the manufacturing cost.

[0004] An object of the present invention is to provide a laser processing apparatus capable of suppressing an increase in manufacturing cost.

[0005]

According to one aspect of the present invention, a laser light source for emitting a laser beam having a wavelength in the ultraviolet region, a holding table for holding a workpiece, and a laser emitted from the laser light source A lens that focuses the beam on the surface of the processing object held by the holding table, and is disposed between the lens and the holding table, transmits light having a wavelength in an ultraviolet region, and transmits the light from the processing object. And a lens protection member for preventing the scattered matter from reaching the lens.

[0006] Scattered matter from the processing object adheres to the lens protection member. When the transmittance of the laser beam decreases due to the scattered matter attached to the lens protection member, the desired transmittance can be maintained by replacing the lens protection member with a new one. Since a quartz glass flat plate or the like can be used as the lens protection member, the lens protection member is generally less expensive than the lens. Therefore, the maintenance cost can be reduced as compared with the case where the lens is replaced.

[0007]

FIG. 1 is a block diagram showing a laser processing apparatus according to an embodiment of the present invention. First laser light source 1
And the second laser light source 2 respectively generate the trigger signal sig ₁
And sig ₂ , and emits pulsed laser beams pl ₁ and pl ₂ having a wavelength in the ultraviolet region. The first and second laser light sources 1 and 2 are configured to include, for example, an Nd: YAG laser oscillator and a nonlinear optical element. The pulse laser beams pl ₁ and pl ₂ are, for example, Nd: YAG
Third of pulse laser beam emitted from laser oscillator
It is a harmonic (wavelength: 355 nm), and is linearly polarized vertically and horizontally, respectively.

The pulse laser beam pl ₁ emitted from the first laser light source 1 is reflected by the turning mirror 5 and is incident on the front surface of the polarizing plate 6 at an incident angle of 45 °. The pulse laser beam pl ₂ emitted from the second laser light source 2 is incident on the rear surface of the polarizing plate 6 at an incident angle of 45 °. Polarizing plate 6
Is a pulse laser beam pl linearly polarized in the vertical direction.
₁ reflects, and transmits the pulse laser beam pl ₂ which is linearly polarized in the horizontal direction.

[0009] The pulse laser beam pl
₁ and pl ₂ are superimposed on the same optical axis, and a pulse laser beam pl ₃ is obtained. The pulse laser beam pl ₃ is reflected by the return mirror 9. The reflected pulse laser beam pl ₄ enters the galvano scanner 10. Gas server Roh scanner 10, in accordance with an instruction of the control signal sig _0, shake the optical axis of the pulsed laser beam in a two-dimensional direction.

[0010] The pulse laser beam passed through the galvano scanner 10, the condenser lens 11 is condensed, a pulse laser beam pl ₅ is obtained. The condenser lens 11 is, for example, f
It is composed of a θ lens and is supported by the lens holder 14. Holder 12 holds the workpiece 20 in the focusing position of the pulsed laser beam pl _5.

A lens protection member 15 is disposed between the condenser lens 11 and the holding table 12. Lens protection member 1
Reference numeral 5 includes a quartz glass 15B having a thickness of 1 to 2 mm and a support frame 15A for physically supporting the quartz glass 15B. The support frame 15A is detachably attached to the lens holder 14. The laser beam transmitted through the condenser lens 11 passes through the quartz glass 15B and reaches the workpiece 20. The transmittance of the quartz glass 15B to the ultraviolet laser beam (355 nm in wavelength) is approximately 90%.

The control means 13 sends trigger signals sig ₁ and sig ₂ having a periodic waveform to the first laser light source 1 and the second laser light source 2, respectively. Control means 13
Can be the first control mode and selects one mode from the second control mode, it sends a trigger signal sig ₁ and sig ₂ with a phase difference which is determined for each control mode. Further, the control unit 13 controls the galvano scanner 10
In, and sends a control signal sig _0.

Next, the timing of the pulse laser beam of the laser processing apparatus shown in FIG. 1 will be described with reference to FIGS.

FIG. 2 shows a timing chart in the first control mode. Trigger signal sig ₁ and sig ₂ is equal frequency, an electrical pulse signal synchronized with each other.
Phase of the trigger signal sig ₂ is delayed by 180 degrees than the trigger signal sig ₁ phase. Pulse laser beam pl ₁ is synchronized with the trigger signal sig _1, the pulse laser beam pl ₂ is
Synchronized with the trigger signal sig _2. Therefore, the pulse laser beam pl _2, the phase is delayed 180 ° than the pulse laser beam pl _1. The pulse repetition frequency of the pulse laser beam pl ₃ through PL ₅ which the pulse laser beam pl ₁ and pl ₂ are superimposed is twice the frequency of the trigger signal sig ₁ and sig _2.

FIG. 4 shows an example of the output characteristics of the third harmonic of the laser light sources 1 and 2 using the Nd: YAG laser oscillator. The horizontal axis is the pulse repetition frequency in the unit "kHz".
, And the vertical axis represents the laser output in the unit “W”. When the repetition frequency is about 5 kHz, the laser output shows the maximum value. When the repetition frequency is 5 kHz or more, the laser output gradually decreases as the repetition frequency increases. This tendency is not limited to the Nd: YAG laser oscillator, but is substantially the same when other solid-state lasers are used.

Generally, when a hole is formed in a resin film, the energy density per pulse of a pulsed laser beam to be irradiated must be equal to or higher than a certain threshold. For example, when making a hole in an epoxy resin, the energy density per pulse needs to be about 1 J / cm ² or more. The required energy per pulse is determined from the area of the hole to be machined. Assuming that the output of the pulse laser beam is P [W] and the pulse repetition frequency is f [Hz], the energy per pulse is given by P / f [J]. From the output characteristics shown in FIG. 4, it is possible to obtain a region where the energy P / f per pulse is equal to or higher than a required threshold. By operating the laser light sources 1 and 2 in this region, a hole can be formed in the resin film.

The repetition frequency of the pulse laser beam pl ₅ irradiated to the workpiece 20 is twice the 10kHz frequency trigger signals sig ₁ and sig _2. For this reason, the drilling time can be reduced to about 比 べ compared to the case where one laser oscillator is used.

FIG. 3 shows a timing chart in the second control mode. First the control mode shown in FIG. 2, the phase of the trigger signal sig ₂ was delayed 180 ° from the phase of the trigger signal sig _1, the second control mode,
The amount of phase delay is small. Therefore, the pulse laser beam p
pulsed laser beams pl ₃ to l ₁ and pl ₂ superimposed on each other
In pl _5, and pulsed pulsed laser beam pl ₁ pulse and the pulse laser beam pl ₂ is partially overlap. Therefore, the pulse width is widened and the energy per pulse is doubled. The trigger signal sig ₁
And sig ₂ in phase, and the pulsed laser beam p
The pulse of l _{1 and} the pulse of the pulse laser beam pl ₂ may be completely overlapped. In this case, the pulse width is not widened, and the peak power is approximately doubled.

Generally, in order to drill holes in the copper layer, the energy density per pulse must be about 10 J / cm ² or more. If the diameter of the hole is 100 μm,
The energy per pulse must be about 7.9 × 10 ⁻⁴ J or more. However, it is difficult to increase the energy per pulse to about 7.9 × 10 ⁻⁴ J or more in the first control mode shown in FIG. FIG.
As shown in (1), by partially overlapping the pulses of the two pulsed laser beams, it is possible to obtain the energy per pulse required for drilling a hole in the copper layer.

If the energy per pulse is not sufficient, it is possible to secure the required energy density per pulse by converging the laser beam and reducing the beam diameter. However, since the beam diameter is small, it is necessary to move the laser beam irradiation site in order to form a hole of a desired size. For example, it is necessary to perform trepanning processing or spiral processing. By increasing the energy per pulse as in the present embodiment, a hole having a diameter of about 100 μm can be formed without performing trepanning or the like.

For example, operation at a repetition frequency of 10 kHz
FIG. 4 shows that the output of one laser light source is about 4
W is obtained. Therefore, the pulsed laser beam shown in FIG.
pl _Three~ Pl_FivePower becomes 8W. At this time, one pal
The energy per unit is 8 × 10^-FourBecome J One unit
With a laser light source, it is difficult to make holes in the copper layer,
Using two laser light sources, overlapping pulses
Energy per pulse to make holes in the copper layer
It can be large enough to remove.

The pulse laser beam pl shown in FIG._Three~
pl_FiveThe pulse width and peak intensity of the
Mu pl₁And pl_TwoAnd the phase shift amount. Trigger signal
sig ₁Trigger signal sig for_TwoAdjust the amount of phase delay
By doing so, the pulsed laser beam pl_Three~ Pl_FiveNo pa
Loose width and peak intensity can be easily controlled.

FIG. 5 is a sectional view of a multilayer wiring board. A package board 22 is mounted on the surface of the motherboard 21. A semiconductor integrated circuit chip 23 is mounted on a package board 22. The motherboard 21 and the package board 22 are formed of epoxy resin containing glass cloth.

A copper wiring layer 25 is embedded in the motherboard 21. Via hole 26 extends from the surface of motherboard 21 to copper wiring 25. Also, through hole 2
7 penetrates the motherboard 21. Copper is buried in the via hole 26 and the through hole 27. Similarly, a copper wiring 28 and a via hole 29 are formed in the package board 22. The via holes 26 and 29 and the through hole 27 are formed by the laser processing apparatus shown in FIG. The laser processing is performed on the single motherboard 21 or the package board 22 before the package board 22 is mounted on the motherboard 21.

The formation of the via holes 26 and 29 is performed in the first control mode shown in FIG. Energy per one pulse of the pulse laser beam pl ₅ at this time is large enough to pierce the resin. However, since it is not enough to make a hole in the copper layer, the copper wiring 25 can be left on the bottom surface of the via hole.

In forming the through hole 27, a hole penetrating the resin layer is formed in the first control mode, and then a hole is formed in the copper wiring in the second control mode shown in FIG.
Energy per one pulse of the pulse laser beam pl ₅ at this time is large enough to puncture the copper layer. By alternately and repeatedly performing the laser processing in the first control mode and the laser processing in the second control mode, the through hole 27 can be formed.

When a hole is formed in a resin substrate having a copper layer formed on the surface by penetrating the copper layer, the hole is first formed in the copper layer in the second control mode. If the number of pulses to be irradiated is set in advance in accordance with the thickness of the copper layer, the processing can be stopped at the point when the copper layer has penetrated. When a hole penetrating the copper layer is opened, the mode is switched to the first control mode, and a hole is opened in the resin portion. The number of pulses applied during laser processing in the first control mode is also set in advance.

When holes are formed in the copper layer, scattered copper adheres to the quartz glass 15B. The surface of the quartz glass 15B is observed, and if it is considered that the transmittance of the laser beam has been reduced by the attached matter, the lens protection member 15 is replaced with a new one. Thereby, it is possible to prevent the power of the laser beam from becoming insufficient due to the decrease in the transmittance.
Since the lens protection member 15 is less expensive than an fθ lens or the like, maintenance costs can be reduced as compared with the case where the fθ lens is replaced.

Instead of observing the surface of the quartz glass 15B with the naked eye, the power of the laser beam transmitted through the quartz glass 15B may be periodically measured by a power meter. When the measured power is lower than the reference value, the lens protection member 15 may be replaced.

In the above embodiment, the third harmonic of the Nd: YAG laser is used as the pulse laser beam having a wavelength in the ultraviolet region, but another laser may be used.
For example, the fourth or fifth harmonic of an Nd: YAG laser may be used, or YL may be used instead of the Nd: YAG laser.
An F laser or a YVO ₄ laser may be used. Also, Kr
A fundamental wave of an F excimer laser or a XeCl excimer laser may be used.

In the above embodiment, the pulse laser beam pl ₁ emitted from the first laser light source 1 and the pulse laser beam pl 2 emitted from the second laser light source _{2 are used.}
Are propagated along the same optical axis, and are condensed at the processing position of the object to be processed. However, it is not always necessary that both optical axes are the same. For example, a pulsed laser beam pl ₁ and pl ₂ is propagated along different optical axes, may be both optical axes intersect at the work location.

In the above embodiment, the lens protection member 1
Although the quartz glass 15B is used for the beam transmitting portion of No. 5, other materials that transmit light having a wavelength in the ultraviolet region may be used instead of the quartz glass. For example, CaF2, M
gF2 or the like can be used.

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.

[0034]

As described above, according to the present invention,
Since the lens protection member protects the lens, it is possible to prevent flying objects from the processing target from adhering to the lens.
If the scattered matter adheres to the lens protection member and the desired transmittance cannot be obtained, the lens protection member may be replaced with a new one.

[Brief description of the drawings]

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

FIG. 2 is a graph showing a timing chart in a first control mode of the laser processing apparatus according to the embodiment.

FIG. 3 is a graph showing a timing chart in a second control mode of the laser processing apparatus according to the embodiment.

FIG. 4 is a graph showing an example of an output characteristic of a third harmonic of an Nd: YAG laser.

FIG. 5 is a sectional view of a multilayer wiring board.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 2 Laser light source 5, 9 Folding mirror 6 Polarizing plate 10 Galvano scanner 11 Condensing lens 12 Holder 13 Control means 14 Lens holder 15 Lens protection member 15A Support frame 15B Quartz glass 20 Workpiece 21 Motherboard 22 Package board 23 Semiconductor Integrated circuit device 25, 28 Copper wiring 26, 29 Via hole 27 Through hole

Claims (2)

[Claims] 1. A laser light source for emitting a laser beam having a wavelength in an ultraviolet region, a holding table for holding an object to be processed, and a laser beam emitted from the laser light source for processing the object held by the holding table. A lens that focuses light on the surface of the object, and is disposed between the lens and the holding table, transmits light having a wavelength in an ultraviolet region, and prevents scattered objects from the processing object from reaching the lens. Laser processing device having a lens protection member. 2. The laser processing apparatus according to claim 1, further comprising a lens holder for supporting the lens, wherein the lens protection member is detachably attached to the lens holder.