JPH11342484A - Device and method for detecting reflection light from processing face in laser processing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflection light detecting device for automatically detecting the completion of piercing with a laser light. SOLUTION: A detector 12 is provided to directly detect a reflection light from a workpiece 11 held by a laser processing device. It is detected that a hole is formed on an insulation layer from the difference of the reflectance of a insulation layer 13 and that of a conductive layer 14. Since an optical system does not exist between the workpiece and the detector, the light other than the reflection light is not erroneously detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for detecting reflected light from a processing surface in laser processing.

[0002]

2. Description of the Related Art In the manufacture of high-density multilayer printed circuit boards, holes (vias) such as inner vias and blind vias are formed in insulating resin disposed between wiring patterns in order to make interlayer connections between laminated wiring patterns. hole)
Need to be formed.

[0003] In the past, via holes were formed by a mechanical drill or an exposure method (photolithography technology), but recently, in order to meet the demand for higher density, a via hole having a smaller diameter can be formed. Techniques using laser light have been used.

In drilling using a laser, a workpiece (multilayer printed circuit board) on a processing table is irradiated with a laser beam from a laser oscillator via an optical system to partially evaporate the workpiece. (Laser ablation). In other words, by irradiating the workpiece with pulsed laser light several times,
A hole having a predetermined depth is formed in the workpiece. Usually, the hole is formed by a copper land (conductive layer) embedded in the insulating resin.
This is done to expose a part of.

[0005]

In a conventional laser drilling apparatus, laser light is appropriately focused by an optical system, and the light intensity (power) per unit area varies depending on the light focusing rate. Further, the depth of the hole to be formed also varies depending on the diameter of the laser beam applied to the workpiece. Further, the depth of the hole formed by one shot of laser light also differs depending on the material of the workpiece. Therefore, the number of shots of the laser beam applied to the workpiece is determined based on the material of the workpiece, the diameter and depth of the hole to be formed, and the like. For example, when the diameter of a laser beam is about 100 μm, it is assumed that a hole having a depth of 20 to 30 μm can be formed per shot by irradiating an insulating resin which is a workpiece. In this case, laser light irradiation of about 2 to 5 shots is required to form a hole reaching the lower wiring pattern in the insulating resin having a thickness of 60 to 100 μm.

As described above, in the conventional laser drilling apparatus, a sample of the same material as the workpiece is irradiated with laser light in advance, and the processing depth per shot is measured.
The number of laser light irradiation shots required for processing the workpiece is calculated. Then, the workpiece is processed based on the calculation result.

However, according to this method, the laser oscillator becomes unstable for some reason, the light intensity of the laser beam fluctuates, or the laser does not oscillate (misshot), or the thickness of the insulating layer is increased. If the number of shots is not uniform, there is a problem that the lower conductive layer is not exposed with a predetermined number of shots.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a reflected light detecting device which automatically detects that drilling has been completed by detecting that a lower conductive layer is exposed in a hole.

[0009]

According to the present invention, a laser beam is applied to a workpiece to be used in laser processing for making a hole in the workpiece, and is reflected by the workpiece. An apparatus for detecting reflected light of a processed surface in laser processing, comprising a photodetector for directly detecting the laser light, is obtained.

According to the present invention, a laser beam is irradiated on a workpiece to detect a laser beam reflected by the workpiece during laser processing for making a hole in the workpiece. In the method of detecting reflected light of a processing surface in laser processing, a method of detecting reflected light of a processed surface in laser processing, wherein reflected light from the workpiece is directly detected by a photodetector, is obtained.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1A and 1B show an embodiment of the present invention. This reflected light detection device is used together with a laser processing device (not shown), and has a detector 12 that detects reflected light (scattered light) from a processing point on a workpiece 11 held by the laser processing device. I have. No optical system is arranged between the workpiece 11 and the detector 12, and the reflected light from the workpiece 11 is directly incident on the detector 12. As described above, by making the reflected light from the workpiece directly enter the detector 12, the possibility of detecting light other than the reflected light can be eliminated. That is, erroneous detection can be prevented.

The laser beam emitted from the laser oscillator of the laser processing apparatus is irradiated on the workpiece 11 through the optical system. The workpiece 11 has a conductive layer below the insulating layer 13. Then, by laser irradiation, ablation occurs in the insulating layer 13 and holes are formed from FIG. 1A to FIG. 1B. At this time, the laser beam applied to the workpiece is reflected on the surface of the workpiece 11. The detector 12 detects the laser light reflected on the surface of the workpiece.

The insulating layer 13 has a low reflectance (high absorptance) with respect to laser light. On the other hand, the conductive layer 14 has a high reflectance to laser light. Therefore, by detecting this difference by the detector 12, it is possible to detect the completion of the drilling by the laser beam. That is, as shown in FIG. 1B, when the insulating layer 13 is partially completely removed (a hole is formed) and the underlying conductive layer 14 is exposed, the light intensity of the reflected light sharply increases. Increase. By detecting this with the detector, the completion of the laser processing can be determined.

The detector 12 may output a signal indicating the intensity of the detected light, or may output an output signal only when light having a predetermined level or more is detected. Is also good. In any case, detector 1
The output of 2 is input to the control device of the laser processing device and used for controlling the laser oscillator.

As described above, the reflected light detecting device according to the present embodiment can detect completion of hole formation by laser processing.

In the above embodiment, the case where holes are formed in the insulating layer formed on the conductive layer has been described. However, the present invention can also be used in the case where through holes are formed in the insulating layer.

[0018]

According to the present invention, the end of laser processing can be accurately detected without erroneous detection by using a detector that directly detects reflected light from the surface of a workpiece processed by a laser processing apparatus. A reflected light detection device that can be obtained can be obtained.

[Brief description of the drawings]

FIGS. 1A and 1B are diagrams showing an embodiment of the present invention. FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Workpiece 12 Detector 13 Insulating layer 14 Conductive layer

Claims (2)

[Claims] 1. A photodetector for irradiating a laser beam to a workpiece to make a hole in the workpiece and directly detecting the laser beam reflected by the workpiece. A reflected light detection device for a processed surface in laser processing, comprising: 2. A laser processing method comprising: irradiating a laser beam on a workpiece to form a hole in the workpiece; and detecting a laser beam reflected by the workpiece during laser processing. In the reflected light detection method, the reflected light from the workpiece is directly detected by a photodetector, and the reflected light is detected on a processed surface in laser processing.