Electric heating – Metal heating – By arc
Reexamination Certificate
2001-06-04
2003-04-29
Elve, M. Alexandra (Department: 1725)
Electric heating
Metal heating
By arc
C219S121700, C219S121830
Reexamination Certificate
active
06555782
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a laser machining apparatus, and more particularly to a laser machining apparatus and its control method suitable for drilling holes in a circuit board formed by laminating an insulating layer and a conductive layer.
BACKGROUND OF THE INVENTION
Generally, circuit boards include the type called multilayer circuit board formed by laminating an insulating layer and a conductive layer alternately, and such multilayer circuit board is effective for enhancing the mounting density, and has come to be used widely.
Specifically, in the multilayer circuit board, holes are drilled in the insulating layer, and the holes are filled with solder or conductive paste to achieve conduction between adjacent conductive layers.
As the processing technology for drilling holes in such insulating layer, laser machining is widely employed.
The wavelength of the laser beam to be used is selected at a wavelength easy to be absorbed in the insulating layer and easy to be reflected in the conductive layer. For example, if the insulating layer is a glass epoxy resin and the conductive layer is a copper foil, carbon dioxide laser beam is used, so that the insulating layer only can be removed selectively.
It is important to drill holes so as to achieve conduction securely between adjacent conductive layers.
A prior art is disclosed, for example, in Japanese Laid-open patent No. 2-92482. According to this publication, when drilling holes in the workpiece by irradiating laser beam, the direct outputted beam from the laser output unit and the reflected beam from the workpiece are detected by individual sensors, and the reflected beam quantity ratio is calculated from the both beam quantities, then the laser beam is controlled by comparison with the reference value.
More specifically, when the reflected beam quantity ratio becomes larger than a predetermined reference value, the output unit is stopped.
By such operation, damage of conductive layer by laser beam is prevented, and the processing time is shortened at the same time.
The prior art, however, had the following problems.
That is, in the conventional machining method, only the reflected beam from the workpiece was detected. If the surface of the conductive layer for reflecting the laser beam of the workpiece is contaminated to absorb the laser beam due to some cause, the level of the reflected beam may not reach the specified level. As a result, excessive machining or abnormal heating may occur. When machining the workpiece, therefore, holes may not be drilled to a desired shape. This is one of the problems of the prior art.
Moreover, when the laser beam passes a focusing lens for machining, in the case of machining the center portion of the processing area by the scanning mirror, the laser beam is irradiated vertically to the object of machining. In the case of machining of peripheral portion, however, the laser beam is not irradiated vertically to the object of machining, and the laser beam reflected from the workpiece may be dislocated from the intermediate optical system parts, or may be irradiated to the optical parts holding portion, and the laser beam reflected from the workpiece may be diffused on the way, and part of the reflected beam may not reach the reflected beam detector. As a result, detection of reflected beam is imperfect, thereby lowering the precision of judgement of machining state of drilled holes.
Or, if the table on which the workpiece is mounted is inclined, similarly, part of the laser beam reflected from the workpiece may not return to the detector of laser beam. As a result, the reflected beam is not detected accurately, and the precision of judgement of machining sate of drilled holes is lowered. The prior art involved also such problems.
SUMMARY OF THE INVENTION
In the beam of the above background, it is a first object of the invention to set the condition and maximum number of outputs in every one pulse output of laser capable of machining the workpiece securely. That is, if reaching the specified level by comparison with the reference value before reaching the preset number of outputs, it is controlled to stop the laser output unit. As a result, laser machining is increased in speed. Setting of the maximum number of outputs prevents excessive machining. Therefore, high quality hole drilling is realized at high yield of machining.
It is a second object to detect the laser beam reflected from the workpiece by a detector, and correct the intensity signal of the detected laser beam. That is, the laser beam reflected from the workpiece is detected by a detector, the intensity signal of the detected laser beam is corrected, and the intensity of the laser beam reflected from the workpiece is calculated accurately. As a result, the machining state of drilled holes is detected accurately, and holes are drilled at high quality.
It is hence an object of the invention to present a laser machining apparatus and its control method capable of increasing the laser machining speed, enhancing the machining yield, and realizing high quality hole drilling.
A first aspect of the invention to achieve the objects is described. A first step is for executing laser machining after setting the number of laser outputs as the laser output condition for drilling holes in the workpiece by plural times of laser pulse outputs. A second step is for detecting the machining state of the workpiece in the process of execution of laser machining, and judging if reaching the desired machining state or not by laser machining. A next step is for finishing the laser machining when judging the workpiece has reached the desired machining state, if not reaching the set number of laser outputs, and otherwise continuing the laser machining up to the set number of laser outputs. In this way, laser machining is done in three steps.
A second aspect of the invention is described. A first step is for executing laser machining after setting the number of laser outputs as the laser output condition for drilling holes in the workpiece by plural times of laser pulse outputs. A second step is for detecting the machining state of the workpiece in the process of execution of laser machining, and judging if reaching the desired machining state or not by laser machining. A third step is for finishing the laser machining when judging the workpiece has reached the desired machining state, if not reaching the set number of laser outputs, and otherwise continuing the laser machining up to the set number of laser outputs. A next step is for processing error when judging the workpiece has not reached the desired machining state in the case of executing laser machining up to the set number of laser outputs. In this way, laser machining is done in four steps.
A third aspect of the invention is described. A first step is for executing laser machining after setting the number of laser outputs as the laser output condition for drilling holes in the workpiece by plural times of laser pulse outputs. A second step is for detecting the machining state of the workpiece in the process of execution of laser machining, and judging if reaching the desired machining state or not by laser machining. A third step is for finishing the laser machining when judging the workpiece has reached a first desired machining state, if not reaching the set number of laser outputs, and otherwise continuing the laser machining up to the set number of laser outputs. A fourth step is for detecting the machining state of the workpiece when laser machining is executed up to the set number of laser outputs, and judging if reaching a second desired machining state or not by laser machining. In this way, laser machining is done in four steps.
A fourth aspect of the invention is described. A first step is for executing laser machining after setting the number of laser outputs as the laser output condition for drilling holes in the workpiece by plural times of laser pulse outputs. A second step is for detecting the machining state of the workpiece in the process of executio
Isaji Kazuhide
Karasaki Hidehiko
Kato Makoto
Kinoshita Hisashi
Elve M. Alexandra
Matsushita Electric - Industrial Co., Ltd.
RatnerPrestia
LandOfFree
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