JP2002126886A - Laser perforating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the working speed of a perforating device perforating against a print circuit substrate, etc., using an ultra violet ray pulse. SOLUTION: As a laser beam generating means in the laser perforating device, a means of generating a higher harmanic of Nd; YLF pulse laser or Nd; YAG pulse laser is provided, and the pulse width of the pulse laser is set at 100-300 (nsec).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser drilling apparatus for drilling a resin layer such as a printed circuit board using a laser beam.

[0002]

2. Description of the Related Art In response to the demand for higher density of printed circuit boards in accordance with the miniaturization and high-density mounting of electronic devices, recently, multilayer printed circuit boards in which a plurality of printed circuit boards are stacked have appeared. In such a multilayer printed circuit board, it is necessary to electrically connect conductive layers (typically, copper patterns) between printed circuit boards stacked one above another. Such a connection forms a hole called a via hole that reaches the underlying conductive layer in the insulating resin layer (polymer such as polyimide or epoxy resin) of the printed circuit board,
This is realized by plating the inside of the hole.

Recently, laser light has begun to be used for such drilling. A laser drilling apparatus using a laser beam is superior to a mechanical processing using a mechanical fine drill in that the processing speed and the diameter of a hole can be reduced. As the laser light, excimer laser,
CO ₂ laser, YAG (yttrium aluminum
Garnet) lasers and the like are generally used.

[0004]

The excimer laser is mainly used as a light source for ultraviolet light, and the gas species is KrF, ArF, XeF, XeC.
By changing to l, the oscillation wavelength can be changed.
However, these lasers are gas lasers, and their oscillation time, that is, the pulse width is generally 10 to 20 (ns).
ec), which is extremely short. Therefore, when a laser beam is applied to a workpiece, the laser beam is absorbed in the vicinity of the surface of the workpiece. For a material having a depth, the drilling ability is smaller than that of a CO ₂ laser or a YAG laser which is thermal processing. descend. Basically, the processing depth per pulse is limited because the absorption coefficient of the material differs depending on the wavelength. In other words, the processing depth decreases as the wavelength becomes shorter.

Accordingly, as compared with the CO ₂ laser and the Nd; YAG laser, the excimer laser and the Nd;
d: YAG laser, Nd: 3rd harmonic of YVO ₄ laser, 4
5th harmonic (3rd harmonic, 4th harmonic, 5th harmonic)
, The machining speed (perforation speed) per pulse becomes lower. For this reason, when a drilling apparatus for a printed circuit board or the like using these ultraviolet lasers as a light source is configured, there is a disadvantage that the processing ability, particularly the processing speed, is reduced in a form depending on the wavelength.

SUMMARY OF THE INVENTION It is an object of the present invention to improve the processing speed of a drilling apparatus for drilling a printed circuit board or the like using an ultraviolet pulse laser.

[0007]

According to the present invention, there is provided a drilling apparatus for piercing a resin substrate by irradiating a laser beam with a laser beam, wherein the laser beam generating means comprises a Nd; YLF pulse laser or a harmonic of an Nd; YAG pulse laser. Means for generating a wave, wherein the pulse width of the pulse laser is 100
３００300 (nsec).

In this laser drilling apparatus, a mask is arranged in the optical path of the laser beam, and fθ for reducing and projecting the image of the mask on the resin substrate is provided in the optical path between the mask and the resin substrate. A lens is arranged.

[0009]

Embodiments of the present invention will be described below. The present invention focuses on the pulse width due to the configuration of the laser oscillator for the purpose of improving the processing speed of the ultraviolet laser. That is, in the laser oscillator, the pulse width can be adjusted by adjusting the interval between the pair of mirrors forming the resonator.

Here, lasers having different pulse widths, that is, XeF lasers (wavelengths of 351 n
m), a drilling machine (comparative example), and Nd; YL
The drilling performance of the drilling apparatus (the present invention) using the third harmonic (wavelength 351 nm) of the F pulse laser was compared.

The pulse width of both is about 20 for the XeF laser.
(Nsec) and the third of the Nd; YLF pulse laser.
The harmonic was set to about 170 (nsec).

FIG. 1 schematically shows a system configuration of a drilling apparatus according to the present invention. The laser oscillator 11 has N
d; a YLF pulse laser is used, especially its third harmonic. The laser beam is applied to the mask 15 via the mirror 12, the attenuator 13, and the mirror 14. The image of this mask is reduced and projected on a processing object 18 via a mirror 16 by a processing lens 17 called an fθ lens. The processing target 18 is arranged on an XY stage 19, and can pierce an arbitrary position of the processing target 18.

[0013] When a drilling apparatus as a comparative example is configured, the configuration is the same as that of FIG. 1, but an XeF laser is used as a laser oscillator. In particular, the attenuator 13 is provided for adjusting the energy of the XeF laser having a large output, and the Nd;
In the case of the F pulse laser, it may be removed.

As described above, the fluence (energy density) of the laser beam on the object 18 is adjusted to be substantially the same.

As the processing object 18, a polyimide film (Kapton film thickness 100 μm ⁺ ) was used. There is no difference in wavelength between the two lasers, and the only difference between them is the pulse width. Using the third harmonic of the XeF laser and the Nd; YLF pulse laser, both were 10 (J /
Processing was attempted with irradiation energy of ² cm ² ). as a result,
The processing depth per pulse was about 2 (μm) for the former (comparative example).
m) and about 7 (μm) in the case of the latter (the present invention).

From the above results, it can be understood that the drilling apparatus using the third harmonic of the Nd; YLF pulse laser has higher drilling ability. The reason is that when the pulse width is shortened, laser irradiation is completed in a short time, light energy is accumulated near the surface of the object to be processed, and the amount of heat absorbed into the material is low. On the other hand, when the pulse width is long, thermal diffusion into the material is large, so that the ablation reaction due to heat or thermal deterioration of the irradiated portion is accelerated, and as a result, it is presumed that the drilling speed is improved. These also apply to the second to fifth harmonics of the Nd; YLF pulse laser or the Nd; YAG pulse laser. For example, the drilling speed increased even when the pulse width was 150 (nsec) at the third harmonic of the Nd; YAG pulse laser. It has been confirmed that a preferable range of the pulse width is 100 to 300 (nsec).

The present invention is not limited to drilling,
Applications to perforation of organic materials such as polymers, surface debonding treatment, surface modification treatment, and the like can be considered.

[0018]

As described above, according to the present invention, a hole is drilled in a printed circuit board or the like by using an ultraviolet pulse laser, particularly a harmonic of an Nd; YLF pulse laser or a Nd; YAG pulse laser. At this time, the processing speed (perforation speed) can be improved by setting the pulse width of the pulse laser to 100 to 300 (nsec).

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a system configuration of a laser drilling apparatus according to the present invention.

[Explanation of symbols]

 Reference Signs List 11 laser oscillator 12, 14, 16 mirror 13 attenuator 15 mask 17 processing lens 18 processing object 19 XY stage

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) H05K 3/00 H05K 3/00 N // H05K 3/46 H05K 3/46 N X B23K 101: 42 B23K 101 : 42

Claims (2)

[Claims] 1. A drilling apparatus for irradiating a resin substrate with laser light to perform drilling, comprising: means for generating a harmonic of Nd; YLF pulse laser or Nd; YAG pulse laser as a means for generating the laser light; The pulse width of the pulse laser is 100 to 300 (nse
c) a laser drilling apparatus set in c). 2. A laser drilling apparatus according to claim 1, wherein a mask is arranged in an optical path of said laser beam, and an image of said mask is reduced to said resin substrate in an optical path between said mask and said resin substrate. A laser drilling apparatus, wherein an fθ lens for projection is arranged.