Electric heating – Metal heating – By arc
Reexamination Certificate
2001-10-11
2003-03-11
Dunn, Tom (Department: 1725)
Electric heating
Metal heating
By arc
C219S121740
Reexamination Certificate
active
06531678
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a processing method for a ceramic green sheet and a laser beam machine, which are used when, for example, laminated ceramic electronic components are manufactured. In particular, the present invention relates to a processing method for a ceramic green sheet and a laser beam machine used therefor in order to form penetration holes (for example, holes for functioning as via holes, through holes, etc.) in a ceramic green sheet.
2. Description of the Related Art
In laminated coil components, laminated substrates, and other various laminated ceramic electronic components, electric connection between internal electrodes (interlayer) laminated or arranged with a ceramic layer therebetween is usually. performed through a via hole (penetration hole) formed in a ceramic green sheet.
Hitherto, as a processing method for forming a via hole (penetration hole) in a ceramic green sheet, a method in which the ceramic green sheet is punched using a mold and a pin has been used widely.
However, the aforementioned processing method using punching has problems in that:
(a) since dimensional accuracy of the mold and the pin affect accuracy of the penetration hole by a large degree, accuracy of the dimensions and the shape of the mold and the pin must be kept high, so that an increase in the equipment cost cannot be avoided;
(b) the mold and the pin have short life spans and must be exchanged periodically, in spite of their high costs, and the exchange operation requires time and effort;
(c) when the shape of the component to be processed is changed, the mold and the pin must be exchanged, and furthermore, precise adjustment of the mold and the pin is required after the exchange causing the expenditure of time and effort; and
(d) the accuracy of processing (accuracy of shape) is reduced with decrease in dimensions of the penetration hole.
In order to solve the aforementioned problems, a laser processing method, which can form a small penetration hole having a dimension of about 80 &mgr;m in diameter at a predetermined location of a ceramic green sheet with high accuracy of shape and location using a laser beam, has been suggested and a part thereof has been practiced.
For example, in the case where a penetration hole is formed in a ceramic green sheet primarily containing a magnetic ceramic using a CO
2
laser, the laser beam is hardly absorbed by Fe, Ni, Cu, etc., constituting the magnetic ceramic, and is absorbed by the binder, for example, vinyl acetate, and the dispersing agent, for example, ammonium polycarboxylate, and the like, which are necessary in the molding of the ceramic green sheet, so that a penetration hole is thereby formed.
Therefore, the laser energy absorption efficiency of the ceramic green sheet is usually about 30% to 40%.
In the aforementioned laser processing method, a laser beam radiated from a laser beam source is passed through a diffraction grating so as to be divided into a plurality of laser beams having a uniform shape and dimension in response to penetration holes to be formed, and the resulting uniformly divided laser beams are radiated to the ceramic green sheet so as to form a plurality of penetration holes having a uniform shape and dimension in the ceramic green sheet.
Among the laser beams divided by the diffraction grating, there are (a) a first order diffracted beam which is radiated to a predetermined location based on the design with an energy required for the processing, (b) a higher order diffracted beam which is generated outside the first order diffracted beam accompanying the diffraction and has an energy level very lower than that of the first order diffracted beam, and (c) a zero order diffracted beam which is radiated to the center of the spectral region without division and has a relatively high energy level, although the energy level is lower than that of the first order diffracted beam.
The energy level of the laser beam of the aforementioned (b) higher order diffracted beam is low, and attack thereof against the material to be processed is very weak. However, since the number of laser beams which become noise is greater than the number of,divided lights, and increases in proportion to the number of divided lights, the total amount of the energy thereof becomes not negligible.
Since the laser beam of the aforementioned (c), which passes through the diffraction grating without division, only passes through the diffraction grating, the energy level thereof is lower than that of the first order diffracted beam, but the energy level thereof becomes higher than that of the higher order diffracted beam. Therefore, when a plurality of penetration holes are simultaneously formed in the ceramic green sheet by dividing the laser beam with the diffraction grating, an undesired part of the ceramic green sheet is processed due to the laser energy (noise) which have become higher order diffracted beam and the zero order diffracted beam.
The energy that becomes noise has been suppressed by increasing accuracy of processing of the diffraction grating. However, since the energy of the zero order diffracted beam is high, it is difficult to avoid processing of undesired parts. In order to avoid the processing of undesired parts, the first order diffracted beam required for processing has been superposed on the zero order diffracted beam. Nevertheless, it is difficult to sufficiently avoid the processing of undesired parts. Furthermore, in order that the first order diffracted beam required for processing is superposed on the zero order diffracted beam, the accuracy of the laser beam machine must be increased so as to cause the problems of increase in complexity and increase in cost of equipment.
Specifically, the zero order diffracted beam, which is a noise, is usually 5% to 10% of the first order diffracted beam, and in accordance with the absorption of the laser beam, the size of the formed penetration hole becomes greater than those of other penetration holes at the part where the zero order diffracted beam is superposed on the first order diffracted beam.
FIG. 1
shows the state in which when processing is performed using laser beams divided with a common diffraction grating, the diameter of penetration hole
15
(
15
a
) formed at the central portion of the region, where a penetration hole
15
is to be formed, (that is, the penetration hole formed at the portion where the zero order diffracted beam is superposed on the first order diffracted beam) in the ceramic green sheet
10
has become greater than diameters of penetration holes
15
on the periphery portion due to laser beam of the zero order diffracted beam radiated to the central portion of the spectral region without division.
SUMMARY OF THE INVENTION
The present invention was made to solve the aforementioned problems, and it is an object of the present invention to provide a processing method for a ceramic green sheet and a laser beam machine used therefor, which can efficiently form a plurality of penetration holes having a desired shape and dimension at predetermined locations of the ceramic green sheet.
In order to achieve the aforementioned object, according to the present invention, a method for processing a ceramic green sheet is provided, which is to form a plurality of penetration holes in the ceramic green sheet, and includes the steps of shaping a laser beam radiated from a laser beam source into a predetermined shape by passing through a mask; dividing the shaped laser beam into a plurality of laser beams by passing through a diffraction grating such that the energy of an individual zero order diffracted beam becomes equivalent to, or less than, a threshold value for processing the ceramic green sheet; reflecting the laser beams divided by the diffraction grating with a galvanomirror; individually converging the laser beams reflected by the galvanomirror with a converging lens; forming a plurality of penetration holes simultaneously having a desired shape and dimension at predetermined locations of the
Dickstein Shapiro Morin & Oshinsky LLP.
Dunn Tom
Johnson Jonathan
Murata Manufacturing Co. Ltd.
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