Plastic and nonmetallic article shaping or treating: processes – Laser ablative shaping or piercing
Reexamination Certificate
2000-03-31
2004-10-05
Staicovici, Stefan (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Laser ablative shaping or piercing
C264S482000, C219S121710, C219S121740, C219S121750, C219S121760
Reexamination Certificate
active
06800237
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for machining a ceramic green sheet to be used in manufacturing laminated ceramic electronic components, and an apparatus for machining the same. In more detail, the present invention relates to a method for machining a ceramic green sheet for forming a plurality of feedthrough holes (for example, the holes that serve as a via-hole and through-hole), and an apparatus for machining the same.
2. Description of the Related Art
Internal electrodes laminated and disposed via ceramic layers (interlayer electrodes) are usually put into electrical continuity through via-holes (feedthrough holes) in various laminated ceramic electronic components such as laminated coil components, laminated substrates and the like.
The via-holes (feedthrough holes) have been formed by punching the ceramic green sheet using a die and a pin.
However, the die-cut method described above involves the following problems:
1. High dimensional and configurational accuracies of the die and pin are required since they largely affect the accuracy of the feedthrough hole, thus inevitably increasing the facility cost;
2. The die and pin have short service life requiring a periodic exchange which is expensive, and takes a long time;
3. The die and pin should be exchanged in every change of the shape of a product or the machining portions. Further time consuming precise adjustment is required after exchanging the die and pin; and
4. Machining accuracy (configurational accuracy) is decreased as the size of the feedthrough hole becomes fine.
For solving the above problems, a method (a laser machining method) has been proposed and a part of the method has been practically used today, whereby fine feedthrough holes with a size as small as about 80 &mgr;m can be formed within a desired area on the ceramic green sheet with high configurational and positional accuracies.
While different sites on the ceramic green sheet have been machined (to form feedthrough holes) in a sequence by allowing a table holding a galvano-scan mirror and green sheet to travel in the conventional machining method using a laser beam, the machining rate is determined by oscillation frequency of the laser beam, scanning speed of the galvano-scan mirror and travel speed of the table all of which serve to restrict improved machining rate.
The machining rate when the laser machining method is used is considerably slow as compared with the machining rate in the method using the die and pin, the former being usually one several and often one tenth of the latter.
Although a method for simultaneously forming several feedthrough holes using YAG laser has been proposed for improving the machining rate in the laser machining method, the method also involves the following problems:
1. A large part of the laser energy is lost in a shunt for splitting the laser beam and in the laser beam transmission system after passing through the shunt. The number of the split beams can not be sufficiently increased since only 30 to 50% of the energy emitted from the laser oscillator is utilized; and
2. Expensive materials should be used for a YAG laser absorber when the ceramic green sheet has a composition with a low YAG laser absorbance.
Although other machining methods for simultaneously forming a plurality of the feedthrough holes on the ceramic green sheet, such as an image transfer method taking advantage of YAG laser and CO
2
laser, or a method using a mask having a given transmission pattern, have been proposed, these methods also involve the following problems:
1. The number of holes that are simultaneously formed cannot be sufficiently increased because only 10 to 30% of the laser energy emitted from the laser oscillator is effectively utilized; and
2. The image focusing mask and image transfer mask are so liable to be damaged with the laser beam that high precision machining is not secured.
In compliance with recent requirements of compacting and high degree of integration of electronic components, the diameter of the via-holes to be formed on the ceramic green sheet is required to be fine.
However, machining precision (configurational accuracy) in is decreased as the hole diameter (hole size) is reduced as hitherto described when the punching method is used.
Forming the feedthrough holes with high configurational and dimensional accuracies also turns out to be difficult when the hole diameter (hole size) is reduced to 50 &mgr;m or less in the laser machining method making use of YAG laser and CO
2
laser. Therefore, the minimum hole diameter available has been considered to be about 30 &mgr;m. This is because clear focusing becomes difficult when the laser wavelength approaches the minimum hole diameter in the laser machining making use of a YAG laser and a CO
2
laser.
The output energy of the laser oscillator is adjusted to be suitable for forming fine feedthrough holes in the conventional laser machining method, because the output energy of the laser oscillator is related to the laser beam width as shown in FIG.
6
. While the laser beam irradiated to the ceramic green sheet is required to have a width d when fine holes with, a diameter of d is formed, the laser beam energy at an output level of the conventional laser oscillator is so large that the laser beam width turns out to be larger than the hole diameter d of the feedthrough hole to be formed on the ceramic green sheet, failing to form the feedthrough holes having a desired hole diameter d. Focused width at the energy required for perforation is larger than the laser beam width to form the hole diameter d of the feedthrough hole. Therefore, the laser beam width should be reduced to correspond to the desired feedthrough hole diameter d by decreasing the output energy of the laser oscillator.
However, a stable laser oscillation is not possible when the output energy of the laser oscillator is lowered to reduce the laser beam width to a level corresponding to the feedthrough hole diameter d. Consequently, it is difficult to form fine feedthrough holes with high configurational and dimensional accuracies due to instability of machining qualities.
As shown in
FIG. 15
when a ceramic green sheet one face of which is supported with a carrier film is punched by the method described above, a feedthrough hole
52
a
is formed through the carrier film
52
besides forming a feedthrough hole
51
a
through the ceramic green sheet
51
. A conductive paste
54
is applied through the feedthrough hole
52
a
on the carrier film
52
as shown in FIG.
16
and adheres on a table
53
supporting the ceramic green sheet
51
, when the conductive paste is printed by a screen printing method for forming interlayer connection and wiring patterns in the post-machining process. The conductive paste
54
adhered on the table
53
is left behind on the table
53
as shown in
FIG. 17
to deteriorate the accuracy of the screen printing, or causes poor quality of the ceramic green sheet by adhesion of the paste to the succeeding green sheets. Therefore, cleaning of the table is required after screen printing each layer of the ceramic green sheet, decreasing the manufacturing efficiency of the ceramic green sheet.
As shown in
FIG. 18
peeling of internal conductors (conductive paste)
54
in the feedthrough holes
51
a
and
52
a
also causes poor quality, when the carrier film
52
is peeled off from the ceramic green sheet
51
after the ceramic green sheet
51
has been lifted up from the table
53
together with the carrier film
53
.
For solving the problems as described above, a method (a laser machining method) has been proposed and put into practical application (Japanese Unexamined Patent Application Publication No. 7-193375), by which a feedthrough hole that does not perforate through the carrier film but perforates only through the ceramic green sheet can be formed using a laser beam within a desired area on the ceramic green sheet one face of which is supported with a carrier film.
However, the conventional laser machining
Komatsu Hiroshi
Morimoto Tadashi
Shikama Takashi
Yamamoto Takahiro
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