U.S. patent application number 09/315019 was filed with the patent office on 2001-07-19 for method for forming through holes.
Invention is credited to HASEGAWA, TOSHINORI, ISHIMATSU, SHIN, KOIDE, JUN.
Application Number | 20010008234 09/315019 |
Document ID | / |
Family ID | 27317120 |
Filed Date | 2001-07-19 |
United States Patent
Application |
20010008234 |
Kind Code |
A1 |
HASEGAWA, TOSHINORI ; et
al. |
July 19, 2001 |
METHOD FOR FORMING THROUGH HOLES
Abstract
A method for forming through holes, which has laser beam as the
light source to project the laser beam to the work object using an
optical system through a photomask for the formation of through
holes on the work object by ablation processing, comprises the
steps of increasing the concentration of the optical processing
energy contributing to the process using the reflected beam created
from the work object in the laser ablation processing; and forming
each of through holes having the configuration enabling the
narrower end to be changed to the wider end in the incident
direction of laser beam. With the structure thus arranged, it
becomes possible to increase the energy concentration that
contributes to the process as compared with the usual ablation
processing, because the reflected beam created in the ablation
processing can be utilized again for the optical processing. Then,
each of the through holes can be formed easily in the configuration
in which the narrower end changes to the wider end in the incident
direction of laser beam, which cannot be easily processed by the
application of the usual ablation processing.
Inventors: |
HASEGAWA, TOSHINORI; (TOKYO,
JP) ; ISHIMATSU, SHIN; (YOKOHAMA-SHI, JP) ;
KOIDE, JUN; (KANAGAWA-KEN, JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Family ID: |
27317120 |
Appl. No.: |
09/315019 |
Filed: |
May 20, 1999 |
Current U.S.
Class: |
219/121.71 |
Current CPC
Class: |
H05K 3/0026 20130101;
B41J 2/1634 20130101; B23K 26/384 20151001; B41J 2/162 20130101;
Y10T 29/49401 20150115; H05K 2203/0557 20130101 |
Class at
Publication: |
219/121.71 |
International
Class: |
B23K 026/38 |
Foreign Application Data
Date |
Code |
Application Number |
May 20, 1998 |
JP |
10-138653 |
Jun 15, 1998 |
JP |
10-166899 |
May 17, 1998 |
JP |
11-135658 |
Claims
What is claimed is:
1. A method for forming a through hole having laser beam as a light
source to project said laser beam to the work object using an
optical system through a photomask for the formation of a through
hole on said work object by ablation processing, comprising the
following steps of: increasing the concentration of the optical
processing energy contributing to the process using the reflected
beam created from said work object in the laser ablation
processing; and forming the through hole having the configuration
enabling the narrower end to be changed to the wider end in the
incident direction of laser beam.
2. A method for forming a through hole according to claim 1,
wherein the depth of said through hole is made as desired by
cutting said work object in the thickness direction of said work
object from the incident direction side of the laser beam
subsequent to said laser irradiation step.
3. A method for forming through holes according to claim 2, wherein
the thickness of said work object is secured by bonding the same
kind of material to said work object on the incident direction side
of the laser beam, and said bonded material is peeled off after
said laser beam irradiation step.
4. A method for forming a through hole according to either one of
claim 1 to claim 3, wherein said through hole is the one arranged
on an insulating layer portion and filled with a conductive
substance to connect electrically the conductive layers themselves
of a substrate having said conductive layers above and below
through the insulating layer.
5. A method for forming through holes according to claim 1, wherein
said laser beam is excimer laser beam.
6. A method for forming a through hole according to claim 1,
wherein said photomask comprises a light shielding portion to form
the unexposed portion in the interior of the through hole formed on
the work object, and a light transmitting portion surrounding said
light shielding portion to form each of said through hole.
7. A method for forming through holes according to claim 6, wherein
the reflected beam from said work object created in said laser
ablation processing is the reflected beam from the unprocessed
portion by the optical processing, and resides inside the
processing configuration.
8. A method for forming a through hole according to claim 6,
wherein the ratio between the outer diameter of said light
transmitting portion and the outer diameter of said light shielding
portion of said mask is 30% or more and 80% or less.
9. A method for forming through holes according to claim 6, wherein
given the distance between said light transmitting portion and
light shielding portion as WT, the thickness of said work object is
d>4.76.multidot.K.multidot.WT (where the K is the contraction
magnification of the optical system, and the WT is the distance
between the light transmitting portion and light shielding portion
of the mask).
10. A method for forming through holes according to claim 1,
wherein said thorough hole is a discharge port of an ink jet
head.
11. A method for forming a through hole according to claim 10,
wherein said laser beam is irradiated from the ink discharge side
of said ink discharge port.
12. A method for forming a through hole according to claim 11,
wherein the irradiation of said laser beam is performed in the
state of said work object being bonded to the main body of an ink
jet head.
13. A method for forming a through hole having laser beam as the
light source to project said laser beam to the work object using an
optical system through a photomask for the formation of the through
hole on said work object by ablation processing, wherein said
photomask comprises a light shielding portion to form the unexposed
portion in the interior of the through hole formed on the work
object, and a light transmitting portion surrounding said light
shielding portion to form each of said through hole.
14. A method for forming a through hole according to claim 13,
wherein said through hole is a discharge port of an ink jet head.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method for forming
through holes on a work piece by use of laser beam.
[0003] 2. Related Background Art
[0004] Conventionally, as a method for forming through holes, the
machining that uses a drill or the like has been mainly practiced.
However, with a method of the kind, it is difficult to process a
hole of a diameter as small as .phi. 100 .mu.m or less, for
example. Also, in recent years, along with the development of the
high performance electronic equipment, it has been required to
arrange its wiring in higher density. As a result, there is a need
increasingly for processing fine holes at small pitches, such as a
printed-circuit board which is a typical example of those requiring
a larger amount of drilling operation.
[0005] As one of the processing methods to meet such requirement,
there is a method for processing the sample locally by the coherent
beam irradiated onto the work piece through the mask provided with
openings which are partly arranged. For example, as disclosed in
the specification of Japanese Patent Laid-Open Application No.
60-13449, when through holes are processed on a printed-circuit
board where a metallic layer is bonded on the surface of an organic
substrate, such as polyimide, polyester, glass epoxy, it is
arranged that, at first the metallic layer on the surface is
selectively etched into the pattern to be processed. Then, with
this metallic layer as a mask, the coherent laser beam is
irradiated onto the substrate to process the through holes. Also,
as disclosed in the specification of Japanese Patent Laid- Open
Application No. 61-48582, there is a fine processing method using
the etching and the irradiation of the coherent laser beam in
combination. In this method, photoresist film is formed by the same
pattern in the same position on both faces of a work piece, and
then, the etching process is suspended before the hole is
penetrated. Then, after the resist film is removed, the total
number or a given number of bridges thus formed are removed by use
of the coherent laser beam that runs along the same locus as the
photoresist pattern.
[0006] However, when a work piece is processed by use of the
coherent laser beam by the application of this technique, there is
a problem that only the hole whose leading end may become narrower
can be formed, but no others. This is because the converged
coherent laser beam is caused to irradiate the inclined faces due
to the taper angle created when the laser process is executed.
Then, conceivably, as compared with the energy concentration of the
coherent laser beam irradiated to the flat surface, the energy of
the irradiated coherent laser beam is attenuated in this event to
be less than the limit of the energy concentration (the threshold
value).
[0007] Since each of the through holes is configured to be narrower
at its leading end (the so-called tapered configuration), the
difference becomes greater between the diameter of the opening of
the through hole on the side where the laser beam is incident upon
(the entrance side), and that of the exit side inevitably.
[0008] For example, if the printed-circuit board is provided with
conductive layers above and below the insulation layer, which are
electrically connected themselves with each other through the
conductive substance filled in the through hole formed on the
insulation layer, it is preferable to make the area larger for each
opening on the edges of the through hole. In this case, if the
difference is great between the diameters of the openings on the
edges of the through hole as described earlier, it may be difficult
to secure the sufficient diameter of the opening on the exit side
in some cases. If it should be attempted to secure the sufficient
diameter of the opening on the exit side, the diameter of the
opening on the entrance side should be made larger than actually
needed. Thus, the structure becomes improper for the formation of
the through holes which should be arranged in higher density.
[0009] Also, if through holes of the kind should be adopted for the
discharge ports of an ink jet head, the thickness of the exit edge
of each through hole (discharge port) becomes thinner locally
depending on the taper angles. Then, there is a fear that the exit
end of each through hole (discharge port) is chipped off due to the
repeated cleaning by use of a blade or the like.
SUMMARY OF THE INVENTION
[0010] The present invention is designed in consideration of the
technical problems discussed above. It is an object of the
invention to provide a method for forming through holes which makes
it easier to form each of them with a small difference between the
opening diameters by the utilization of coherent laser beam that
reflects from a work piece while in the laser ablation.
[0011] The inventors hereof have given attention to the reflected
beam created from the work object in the ablation processing when
the laser beam is projected to the work object through the
photomask for the performance of the ablation processing in order
to achieve the objectives of the present invention. Then, the
method of the invention for forming through holes, which has laser
beam as the light source to project the laser beam to the work
object using an optical system through a photomask for the
formation of through holes on the work object by ablation
processing, comprises the steps of increasing the concentration of
the optical processing energy contributing to the process using the
reflected beam created from the work object in the laser ablation
processing; and forming each of through holes having the
configuration enabling the narrower end to be changed to the wider
end in the incident direction of laser beam.
[0012] Also, the method of the invention for forming through holes
is provided with laser beam as the light source to project the
laser beam to the work object using an optical system through a
photomask for the formation of through holes on the work object by
ablation processing. For this method, it is arranged that the
photomask comprises a light shielding portion to form the unexposed
portion in the interior of the through hole formed on the work
object, and a light transmitting portion surrounding the light
shielding portion to form each of the through holes.
[0013] With the structure thus arranged, it becomes possible to
increase the energy concentration that contributes to the process
as compared with the usual ablation processing, because the
reflected beam created in the ablation processing can be utilized
again for the optical processing. As a result, each of the through
holes can be formed easily in the configuration in which the
narrower end changes to the wider end in the incident direction of
laser beam, which cannot be easily processed by the application of
the usual ablation processing. Then, in accordance with the method
of the present invention, the difference is made smaller between
the opening diameters, hence making it possible to apply the method
preferably for the formation of through holes which are arranged in
higher density. Also, the section of the edge portion formed inner
side of the end portion of the through hole does not present any
acute angle for the through holes of the minimum diameter. As a
result, if the through holes thus formed are applied to the
discharge ports of an ink jet head described earlier, it becomes
possible to reduce the chip off of the edge portion thereof
significantly.
[0014] Further, with the structure of the photomask thus arranged,
the amount of laser irradiation to the work piece becomes smaller
than the conventional method. As a result, it becomes possible to
significantly reduce the expansion of the work piece due to heat
generated in the laser processing. Also, with the unprocessed
portion that resides in the interior of each through hole, it is
possible to form each of the through holes having a lesser amount
of flash.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a view which illustrates one example of the
optical processing apparatus using the present invention.
[0016] FIG. 2 is a view which illustrates the conventional optical
processing method.
[0017] FIG. 3 is a view which illustrates the optical processing
method that utilizes the reflected beam.
[0018] FIG. 4 is a view which shows the coordinate system defined
for the geometrical illustration of the optical processing method
that utilizes the reflected beam.
[0019] FIG. 5 is a view which illustrates the through hole
formation processing by the utilization of the reflected beam
created by the taper angles in accordance with one embodiment of
the present invention.
[0020] FIG. 6 is a schematic view which shows a mask in accordance
with a second embodiment of the present invention.
[0021] FIGS. 7A and 7B are views which illustrate the state of
laser processing in accordance with the second embodiment and the
conventional example.
[0022] FIG. 8 is a view which illustrates the optical processing
method that utilizes the reflected beam in accordance with the
second embodiment.
[0023] FIG. 9 is a view which shows the coordinate system defined
for the geometrical illustration of the optical processing method
that utilizes the reflected beam in accordance with the second
embodiment.
[0024] FIGS. 10A and 10B are views which illustrate the difference
in the processed configurations of the through hole depending on
the laser powers.
[0025] FIGS. 11A, 11B and 11C are schematic views which show an ink
jet head in accordance with a third embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] Hereinafter, with reference to the accompanying drawings,
the present invention will be described.
[0027] (First Embodiment)
[0028] At first, preceding to the description of the present
invention, the conventional method of the optical processing will
be described in conjunction with the accompanying drawings.
[0029] FIG. 2 is a view which illustrates the conventional method
of the optical processing. In FIG. 2, a reference numeral 111
designates a work piece; 112, the coherent laser beam used for the
optical processing; 113, the taper angle of the process; and 114,
the reflected coherent laser beam 112 created by reflection due to
the taper of the work piece 111.
[0030] When the laser ablation process is executed by the
irradiation of the coherent laser beam 112 onto the work piece 111,
the taper angle 113 is created at first on the outer contour of the
portion (the processing shape) of the work piece upon which the
laser is irradiated. Characteristically, this taper angle 113 is
influenced by the energy of the irradiated coherent laser beam. The
higher the irradiated energy, the smaller is the taper angle 113.
The lower the energy of the irradiated coherent laser beam, the
larger is the taper angle 113. Then, once a taper angle of the kind
takes place, the coherent beam 112 is incident upon the processing
surface of the work piece 111 diagonally. As a result, the laser
beam 112 is reflected partly as at 114 in FIG. 2, making it
impossible to secure the sufficient energy concentration of the
laser beam in the direction of its incidence. The resultant process
advances almost along the taper angle 113 thus initially formed,
and the through hole having the narrower leading end is formed in
the taper configuration eventually.
[0031] In contrast, for the present invention, attention is given
to the beam reflected from the objective work piece while in
process. Then, the through hole is formed by the utilization of
this reflected beam so that its configuration changes from the
narrower leading end to the wider one.
[0032] FIG. 3 is a view which illustrates the method for forming
through holes in accordance with the present invention. In FIG. 3,
a reference numeral 111 designates a work piece; 112, the coherent
laser beam for use of the optical processing; 113, the taper angle
of the process; 114, the reflected coherent laser beam created by
the coherent laser beam 112 for use of the optical processing when
it is reflected from the taper angle portion of the work piece
111.
[0033] In accordance with the present embodiment, it is arranged
that the aspect ratio of the through hole becomes higher as
compared with the conventional example described earlier (that is,
the ratio of the depth d of the through hole is greater than the
diameter w thereof), and that the reflected coherent laser beam,
which has never contributed to the through hole processing
conventionally, is again irradiated to the work piece.
[0034] In accordance with the present embodiment, too, the through
hole 120 having the narrower leading end is being formed in the
initial stage of the ablation process as in the conventional art.
However, after the depth of the through hole almost exceeds the
distance h, the laser beam 114 reflected from the processing
surface of the work piece 111 begins to be irradiated onto the
opposite side face 116 of the through hole 120. On this side face
116, the laser beam 112 is also irradiated from above the through
hole. Therefore, the concentration of the laser energy on this
portion becomes increased to make the diameter of the through hole
gradually wider (widen toward the end) in processing.
[0035] In this respect, the side face on the opposite side of the
through hole is processed in the same manner. Therefore, the actual
configuration becomes as shown in FIG. 5 eventually.
[0036] Here, it is preferable to use the excimer laser beam as the
laser beam used for the present invention.
[0037] Now, the distance h at which the reflected beam begins to be
irradiated is determined almost by the diameter of the opening of
the through hole on the incidence side of the laser beam (the
diameter of the mask opening) w, and the taper angle .THETA. which
is made in the initial stage of the laser processing. Hereunder, in
conjunction with FIG. 4, the description will be made of the
relationship between this distance h and the w and the .THETA..
[0038] For the convenience of the description, it is defined in
FIG. 4 to set 0 at the right-side end of the incident side of the
through hole 120 for the two dimensional coordinate axis (X-Y). The
coherent laser beam 112 irradiated for the ablation processing is
reflected by the taper angle 113 in processing the work piece 111.
The reflected beam 114 advances in the direction at an angel of
-2.THETA. to the axis Y. Therefore, in the coordinate system in
FIG. 4, this reflected beam is expressed by the linear equation as
follows:
y=-x.multidot.tan(90.degree.-2.THETA.) (1)
[0039] Also, the taper, which is positioned at the distance w away
from the intersection of the axes X and Y, and angled at .THETA. to
the facing work piece 115, is expressed by the quadratic equation
as follows:
y=(x-w).multidot.tan(90.degree.-.THETA.) (2)
[0040] From them, it is possible to obtain the coordinate of the
position at 116 where the reflected beam 114 is again irradiated
onto the processing surface of the facing work piece 115 as the
intersecting point of the straight lines expressed by the equations
(1) and (2).
[0041] Now, the distance h is expressed as follows by the function
of the w and .THETA.:
h=w.multidot.tan(90.degree.-.THETA.).multidot.tan(90.degree.-2.THETA.)/{ta-
n(90.degree.-2.THETA.)+tan(90.degree.-.THETA.)} (3)
[0042] Also, the reference mark t in FIG. 4 is:
t=d-h
[0043] from the relationship between the thickness d of the work
piece 115 and the distance h. Therefore, by the application of the
expression (3), it can be expressed as follows:
t=d-w.multidot.tan(90.degree.-.THETA.).multidot.tan(90.degree.-2.THETA.)/{-
tan(90.degree.-2.THETA.)+tan(90.degree.-.THETA.)} (4)
[0044] This value t indicates the inner location away from the
bottom end (the exit side end of the through hole) of the work
piece 115, in which the reflected beam 114 causes the taper angle
to change.
[0045] In other words,
[0046] if the t.gtoreq.0, the reflected beam is again irradiated
onto the facing work piece 115.
[0047] If the t<0, the reflected beam is not irradiated again to
the facing work piece 115, and passes the work pieces.
[0048] Therefore, if the taper angle .THETA. 113 and the opening
diameter w of the through hole should satisfy the condition of the
t>0, it becomes possible to perform the optical processing
utilizing the reflected beam 114.
[0049] Then, if the reflected beam can be utilized, it is possible
to obtain the same effect as the one which may be obtainable by the
increased luminance of the irradiation.
[0050] Also, with the structure described above, it is necessary to
make the aspect ratio higher for the structure of the through hole,
but when the present invention is applied to the through hole
having the lower aspect ratio, it may be possible to obtain the
desired depth of the through hole by the arrangement of the
structure in which the work piece is cut in the thickness direction
from the incident side of the laser beam subsequent to the laser
irradiation step or by the arrangement of the structure in which
the same kind of the material as the work piece is bonded in
advance to the work piece on the incident side of the laser beam,
and then, after laser irradiation step, this bonded material is
peeled off.
[0051] In accordance with the present embodiment, the work piece is
prepared by resin in a thickness of 0.1 mm, and at the same time,
the laser power of the excimer laser is adjusted so as to make the
taper angle .THETA. 10.degree. in processing. Then, using the mask
having the patterns of different opening diameters the laser
ablation process is performed on the work piece to form the through
holes. Each configuration of the through holes is observed at that
time, and the values h and t are also measured and shown in Table
1.
1TABLE 1 Thickness 0.1 of resin (mm) Taper 10.degree. angle in the
process .theta.(.degree.) w(mm) 0.2 0.1 0.08 0.06 0.05 0.03 h(mm)
0.370 0.185 0.148 0.111 0.093 0.056 t(mm) -0.5934 -0.1467 -0.0574
0.0320 0.0766 0.1660
[0052] As shown in the table, there is no change in the taper
angles of the through hole if the opening diameter is 0.08 mm or
more thereof on the incident side of the laser beam. This is
because the aforesaid t value becomes negative, and conceivably,
the reflected beam created in the optical processing is not
irradiated onto the facing work piece. On the other hand, if the
gap in the work piece is less than 0.06 mm, the aforesaid value t
should become positive. Here, in the actual through hole, there is
also observed no portion where the taper angle changes due to the
reflected beam.
[0053] As shown in FIG. 1, the apparatus, which performs the
ablation processing by the utilization of the aforesaid reflected
beam, comprises the coherent beam oscillator 101 serving as the
light source to generate the coherent beam L; the controller 102
that changes the oscillating voltages and the oscillation
frequencies of the coherent beam irradiated from the oscillator;
the mask 103 having the opening pattern of a desired processing
configuration; the shift driving device 104 that moves the mask
freely foward and backward in the axial direction of the coherent
beam L and the controller 105 that controls this device; and the
projection optical system 106 to project the opening pattern onto
the blank 10, the rotary driving device 107 to rotate the
projection optical system 106 around the optical axis of the
coherent beam L, and the controller 108 that controls this device.
The blank 10 is positioned by the movable stage 109 controlled by
the controller 110 within the plane (Y and Z plane) perpendicular
to the optical axis (axis X) of the coherent beam L.
[0054] The shift driving device 104 is provided with a driving
mechanism using a motor (a stepping more or a servo motor, for
example), and by use of the controller 105, the mask 103 is made
movable in a precision of micron unit freely in the arbitrary
directions, such as on the optical axis of the coherent beam L, the
arrangement direction (along the axis Y in FIG. 4) of the opening
pattern for use of the groove processing, the drilling, or both, or
around the center of the optical axis of the coherent beam L. Also,
as to the movement of the mask 103 itself, it is possible to select
the continuous shift at a constant speed or the intermittent
shifts.
[0055] Also, by use of a computer or the like, it may be possible
to control the controllers 102, 105, 108, and 110 altogether to
control the coherent beam oscillator 101 and each of the driving
devices 104, 107, and 109.
[0056] (Second Embodiment)
[0057] One of the features of the structure in accordance with the
present embodiment is the mask which is preferably usable for the
laser processing that uses the aforesaid reflected beam.
[0058] FIG. 6 is a schematic view which shows the mask pattern of
the present embodiment. In FIG. 6, a reference numeral 1 designates
the mask. For this mask, the light transmitting portion 2 is
provided to enable the laser to transmit it. The outer diameter of
this light transmitting portion 2 determines the configuration of
the through hole. In FIG. 6, a reference mark a designates the
dimension of the frame portion, and .THETA., the outer
diameter.
[0059] Inside the light transmitting portion 2, the light shielding
portion 3 is arranged in such a manner to be framed by the light
transmitting portion 2. When this mask pattern (hereinafter, the
mask that has this mask pattern is referred to as the "framed
mask") is used for the laser ablation processing, there remains on
the work piece the portion yet to be processed in the through hole
corresponding to the aforesaid light shielding portion 3. This
unprocessed portion is separated from the work piece around it when
the laser processing is performed on the light transmitting portion
2. Therefore, when the through hole is penetrated, this unprocessed
portion is exhausted from the through hole by the application of
the laser energy. As a result, the through hole is formed as in the
case where the light shielding portion 3 is not provided for the
interior of the light transmitting portion 2 of the conventional
mask.
[0060] In accordance with the present invention, the laser energy
is made smaller by the presence of the aforesaid unprocessed
portion when it is irradiated to the work piece accordingly.
Therefore, as compared with the conventional method, the expansion
of the work piece is suppressed significantly, making it possible
to perform a desired processing even when the through holes should
be formed in higher density. Further, when the laser ablation
process is performed, by-product adheres to the circumference of an
opening. However, in accordance with the present invention, the
amount of such adhesive particles is significantly reduced as
compared with the conventional method. Particularly when the
discharge ports of an ink jet head is processed by means of
ablation, the adhesive particles of the kind may cause the
direction of ink discharges to be twisted. Conventionally,
therefore, it is necessary to arrange an extra step of removing
such adhesive particles. With the structure of the present
invention, this processing step of removing the adhesive particles
is omitted or simplified.
[0061] Also, in accordance with the present invention, it becomes
possible to reduce the flash that may be created in the through
hole nearby the end portion of the laser beam exit side.
[0062] Now, the description will be made of the mechanism with
which the flash of the through hole is reduced by means of the
structure of the present invention.
[0063] FIG. 7A is a view which illustrates the state of the
conventional laser processing. FIG. 7B is a view which illustrates
the state of the laser processing of the present invention.
[0064] In FIG. 7A, a reference numeral 300 designates a work piece;
303, a through hole; and 304, laser beam.
[0065] As the work piece 300 is being processed by laser ablation,
a structure is formed as if a sheet cover 301 is arranged on the
surface of the work piece immediately before the through hole is
penetrated.
[0066] Then, the laser beam 304 is further irradiated from this
state to process this cover 301 more, thus penetrating the through
hole 303. Here, if the laser beam 304 is able to process the
interior of the through hole 303 at a uniform velocity, the cover
301 is caused to fly out straightly in the processing direction. If
the processing velocity of the laser beam 304 is varied in the
interior of the through hole 303, the portion where the processing
velocity is slower becomes a hinge 302. As a result, the cover 301
moves as if opening a door. Then, by the shock exerted by this
movement of the cover 301, the hinged portion 302 is cut off. Then,
the flash is created on this portion.
[0067] In contrast, the structure arranged by the present invention
makes it possible to keep the unprocessed portion 305 still
remaining on the cover portion immediately before the through hole
is penetrated as shown in FIG. 7B. As compared with the cover, the
volume of this unprocessed portion 305 is far greater.
Consequently, the unprocessed portion 305 is not allowed to fly out
until its connecting portion 306 is completely removed by the laser
beam 304 even if the processing velocity of the laser beam 304 is
varied in the interior of the through hole 303. As a result, the
unprocessed portion 305 is not hinged to make it difficult to
create any flash on that portion.
[0068] In this respect, if the discharge ports of an ink jet head
are formed by the method described earlier, there have been created
conventionally fine flashes partly on the exit edges of through
holes (discharge ports), and there is a fear that depending on the
configurations of the flash, the direction of ink discharges is
subjected to being twisted eventually. With the structure described
above, the flashes are not easily created. Then, the ink jet heads
having excellent ink discharge direction are manufactured in a
better production yield.
[0069] In accordance with the present embodiment, 140 through holes
are formed on a work piece by the irradiation of excimer laser with
the laser power of 750 mj/cm.sup.2.multidot.pulse on a polysulfone
material of 60 .mu.m thick by use of the mask which may produce the
opening diameter (incident side) of each through hole to be 40
.mu.m, the diameter of each unprocessed portion to be 20 .mu.m, and
the arrangement density of the through holes to be 600 dpi. Also,
as a comparative example, the through holes are formed in the same
condition, but by use of a mask having the same opening diameter of
each through hole without light shielding portions: with the result
that whereas all the through holes formed by the method of the
present invention for forming through holes are smooth in its
configuration of the exit side of the laser beam, some of the
through holes of the comparative example present flash, and
by-product is caused to adhere in a large amount. Also, the work
piece of 12 mm wide is used: with the result that whereas the work
piece processed by the present embodiment presents the expansion of
2 .mu.m in its width direction, the comparative example presents
the expansion of approximately 6 .mu.m. Thus, in accordance with
the present invention, not only the through holes are formed
uniformly in its configuration, but also, the expansion of the work
piece can be suppressed significantly.
[0070] Now, the description will be made of the structure using the
framed mask described earlier, which is applied to the technique to
change the taper angles in the optical processing that utilizes the
reflected beam.
[0071] Hereinafter, in conjunction with FIG. 8, the description
will be made of a method for creating the reflected beam to change
the taper angles of a work piece by the utilization of the
aforesaid reflected beam. In FIG. 8, a reference numeral 111
designates a work piece; 112, the coherent laser beam for use of
the optical processing; 114, the reflected coherent beam created
when the coherent beam 112 for use of the optical processing is
reflected from the taper angled portion of the work piece 111; 117,
the unprocessed portion where no coherent beam is irradiated on the
work piece 111; 120, a through hole; W, the outer dimension of the
configuration formed on the work piece 111 by the application of
the optical process. This reference mark W corresponds to the
diameter of the light transmitting portion described earlier. Also,
a reference mark Wm designates the width of the unprocessed portion
117 on the side of the work piece where the beam is irradiated.
This Wm corresponds to the diameter of the light shielding portion
described earlier. A reference mark Wt designates the distance
between the unprocessed portion 117 and the work piece 111 on the
incident side of the laser beam.
[0072] When the ablation processing is performed by irradiating the
coherent laser beam 112 onto the work piece 111, the taper angle
113 appears at first on the outer contour of the portion of the
work piece where the laser is irradiated (the processed
configuration). This tape angle 113 is influenced by the energy of
the coherent laser beam 112 thus irradiated. It has the
characteristics that the higher the irradiated energy, the smaller
is the taper angle 113, and the lower the energy of the irradiated
coherent laser beam 112, the larger becomes the taper angle 113.
Then, once such taper angle takes place, the coherent laser beam
112 is incident upon the processing surface of the work piece 111
diagonally. As a result, the laser beam 112 is partly reflected at
114 in FIG. 8 to make it impossible to secure the sufficient energy
concentration in the incident direction of the laser beam 112, and
the processing advances almost along the taper angle 113 which is
initially formed.
[0073] After that, when the depth of the through hole 120 exceeds
the distance h, the laser beam 114 reflected from the processing
surface of the work piece 111 begins to be irradiated onto the
unprocessed portion 117. Likewise, the laser beam reflected from
the processing surface of the unprocessed portion 117 begins to be
irradiated onto the opposite side face 116 of the through hole 120.
On these portions, the laser beam 112 is also irradiated from above
through hole. Therefore, the concentration of the laser energy is
increased, thus processing the diameter of the through hole to be
gradually wider (widen toward the end).
[0074] Now, if it is intended to utilize the reflected beam for the
laser processing by use of the usual mask, there is a need for
making the aspect ratio of the through hole higher (that is, the
ratio of the depth d of a through hole is greater than the diameter
w thereof). In contrast, by the structure of the present
embodiment, the reflected beam takes place from the processing
surface of the unprocessed portion in addition to the one from the
processing surface of the through hole. Therefore, there is no need
for making the aspect ratio higher as compared with the case where
the reflected beam is utilized for the laser processing by use of
the usual mask.
[0075] Now, the examination is made on the condition that may allow
the utilization of the reflected beam when the framed mask is
used.
[0076] Each of the reflected beam 114 of the coherent beams 112
irradiated onto the work piece 111 and the unprocessed portion 117
is positioned away from each other by the distance Wt, and it is
shown that the reflected beam is again irradiated to the point 116
on the taper angle of the facing work piece 111 having the
thickness of d. The position where the reflected beam is again
irradiated begins with the position at the distance h from the
upper end of the work piece 111. Now, in conjunction with FIG. 9,
the description will be made of the expression of the distance h in
terms of the function of the Wt and the .THETA..
[0077] For the convenience of the description, the axis of the
two-dimensional coordinate(X-Y) is defined as shown in FIG. 9.
Here, the intersecting point of the axis X and the axis Y is set at
the upper end portion of the through hole on the left-hand side in
FIG. 9.
[0078] The coherent beam irradiated for performing the ablation
processing is reflected on the taper angled portion .THETA. of the
work piece, and the reflected beam 114 advances in the direction at
the angle 2.THETA.. Therefore, in the coordinate system in FIG. 9,
this reflected beam is expressed as follows:
y=-x.multidot.tan(90.degree.-2.THETA.) (5)
[0079] Also, being positioned away by the distance Wt, the taper
angled portion having the angle .THETA. of the facing unprocessed
portion 117 is expressed in the coordinate system in FIG. 9 as
follows:
y=(x-Wt).multidot.tan (90.degree.-2.THETA.) (6)
[0080] From them, the coordinate of the position 116 where the
reflected beam 114 is reflected at the taper angled portion of the
facing unprocessed portion 117 is obtainable as the intersecting
portion of the straight lines shown by the expressions (5) and
(6).
[0081] Now, the absolute amount h is expressed by the following
function of the Wt and the .THETA.:
h=(Wt/2).multidot.tan (90.degree.-2.THETA.) (7)
[0082] Therefore, when the depth (the thickness of the work piece)
d of the through hole is grater than the h, the reflected beam is
again irradiated. Then, the condition that may allow the reflected
beam to be irradiated is as follows:
d>(Wt/2).multidot.tan(90.degree.-2.THETA.) (8)
[0083] However, since the Wt is defined as the dimension of the
work piece, the distance WT between the light transmitting portion
and the light shielding portion on the actual mask is considered to
be:
d>(K.multidot.WT/2).multidot.tan(90.degree.-2.THETA.) (9)
[0084] where the contraction coefficient of the optical system is
given as K. Therefore, it becomes possible to perform the optical
processing by the utilization of the reflected beam 114 if the
distance WT between the light transmitting portion and the light
shielding portion satisfies the aforesaid condition.
[0085] Also, as to the taper angle .THETA., it changes depending on
the laser powers as described earlier. Usually, however, its range
is within 3.degree. to 20.degree.. As a result, if the
.THETA.=3.degree., it may become possible to utilize the reflected
beam in most cases if the following relationship is satisfied:
d>(K.multidot.WT/2).multidot.tan(90.degree.-2.3.degree.)=4.76.multidot.-
K.multidot.WT (10)
[0086] Therefore, it is clear that in accordance with the present
embodiment, if only the dimension of the distance WT between the
light transmitting portion and the light shielding portion on the
mask, and the thickness d of the work piece can satisfy the
expression (6), the taper angle is made smaller by use of the
coherent beam reflected from the taper angled portion of the facing
work piece.
[0087] Also, if the size of the unprocessed portion is made smaller
than the resolution of the irradiating coherent beam, the
unprocessed portion is eliminated as the processing advances to
obtain the desired configuration.
[0088] With the structure arranged as described above, the taper
angles are made changeable by use of the reflected beam even if the
through hole is not configured with a higher aspect. It is also
found that this structure may produce an unexpected effect. In
other words, the area of the open hole is not easily affected by
the laser power when the laser ablation process is performed by the
utilization of the reflected beam while using the aforesaid
mask.
[0089] Hereinafter, in conjunction with FIGS. 10A and 10B, this
ablation process will be described specifically.
[0090] When the usual mask is used for processing, the taper
portions (at 1103 in the lower powered processing and at 1113 in
the higher powered processing) are formed as indicated by the
broken lines in FIGS. 10A and 10B, having the taper angles in
proportion to the processing powers (at 1106 in the lower powered
processing and at 1114 in the higher powered processing).
[0091] In this case, if the framed mask 1201 is used, an
unprocessed portion is formed on the central part corresponding to
the light shielding portion 1202 on the framed mask. On the
unprocessed portion, the tapered portion (at 1103 in the lower
powered processing and at 1113 in the higher powered processing) as
indicated by the broken lines in FIGS. 10A and 10B having the taper
angles in proportion to the processing powers (at 1106 in the lower
powered processing and at 1114 in the higher powered
processing).
[0092] When the processing energy is low, the taper angle .THETA.1
1106 which is obtainable in the usual processing is great as shown
in FIG. 10A. At this juncture, the taper angle formed by use of the
framed mask 1201 on the unprocessed portion 1104 in the interior of
the processed configuration is also equal to the angle .THETA.1 at
1106. Since this angle .THETA.1 at 1106 is great, the laser beam
1105 reflected from the unprocessed portion 1104 is again
irradiated above the facing taper angle 1103 (the portion indicated
by broken line) in the process. The laser beam 1105 is also
irradiated from above again to increase the energy of the laser
irradiation on that portion. Hence, the taper angle becomes smaller
(indicated by solid lines) in the process.
[0093] When the processing energy is high, the taper angle .THETA.2
1114 which is obtainable in the usual processing is small as shown
in FIG. 10B. At this juncture, the taper angle formed by use of the
framed mask 1201 on the unprocessed portion 1104 in the interior of
the processed configuration is also equal to the angle .THETA.2 at
1114. Since this angle .THETA.2 at 1114 is small, the laser beam
1105 reflected from the unprocessed portion 1104 is again
irradiated below the facing taper angle 1113 (the portion indicated
by broken line) in the process. The laser beam 1105 is irradiated
again to increase the energy of the laser irradiation on that
portion. As a result, the taper angle is scarcely made smaller
(indicated by solid lines) in the process. Therefore, the smaller
taper angle .THETA.2 at 1114, which is created fundamentally by the
higher energy processing, becomes dominant so as to implement the
processing of the discharge ports each having larger opening
area.
[0094] Here, in accordance with the present embodiment, it is
possible to absorb the influences exerted by the changes in the
laser powers for the reasons described above. Thus, the variation
of the opening areas of the through holes can be reduced
significantly.
[0095] The inventors hereof have conducted the following
experiments in order to confirm the effects of the present
invention.
[0096] At first, polysulfone resin of 60 .mu.m thick is prepared as
the work piece. Then, with the contraction optical system, the
diameter of the light transmitting portion of the mask is defined
so that the opening area of the through hole on the incident side
becomes 1,385 .mu.m. Subsequently, by changing the size of the
light shielding portion arranged in the interior of the light
transmitting portion, the examination is made on the changing
condition of the opening area of the through hole on the exit
side.
[0097] In this respect, as to the laser powers, two kinds are
adopted, that is, 652 mj/cm.sup.2.multidot.pulse at the time of
higher power, and 895 mj/cm.sup.2.multidot.pulse at the time of
lower power. The results are shown in Table 2. Here, in the table,
the size of the light shielding portion is indicated by its ration
to the light transmitting portion (hereinafter, this ratio is
referred to as the frame rate and defined as the frame rate=the
outer diameter of the light transmitting portion/the outer diameter
of the light shielding porion (%)).
[0098] From the Table 2 it is understandable that the higher the
frame rate, the greater becomes the opening area of the through
hole on the exit side, and at the same time, the changes of the
opening area become smaller against the laser powers. However, it
becomes impossible to process the one having the frame rate of 90%
or more, because the shielding ratio becomes too high. Also, it is
clear from the graph that the effect of the frame becomes
conspicuous when the frame rate is approximately 30% or more. It
is, therefore, preferable to set the frame rate of the mask at 30
to 80%.
2TABLE 2 Frame rate (%) 100 90 80 70 60 50 40 30 20 10 0 Hole area
at -- -- 985.7 937.8 883.3 857.1 843.2 837.9 834.9 833.3 831.2 High
Power Hole area at -- -- 940 889.6 822.7 775.4 750.3 740.5 733.7
730.6 730.6 Low Power Hole area -- -- 45.7 48.2 60.6 81.7 82.9 97.4
101.2 102.7 100.6 Range
[0099] In this respect, the framed mask of the present embodiment
demonstrates excellent effect particularly when it is applied to
the method for forming through holes that utilizes the reflected
beam. However, the present invention is not necessarily limited to
this method. The invention also demonstrates the aforesaid effect
when applied to the usual laser processing which does not utilize
the reflected beam.
[0100] (Third Embodiment)
[0101] Now, the description will be made of the example in which
this method for forming through holes is applied to the formation
of the discharge ports of an ink jet head.
[0102] The print quality of an ink jet printer depends greatly on
the characteristics of ink discharged from the discharge ports
serving as the openings from which ink is discharged, respectively.
The ink discharging characteristics are determined substantially by
the configuration and diameter of each discharge port. As a method
for forming the discharge ports, there are roughly two methods.
There have been proposed the electroforming that uses metallic
plates or the formation that uses the electric discharge machining,
and a method for processing a material, such as organic polymer
resin, by sublimation (ablation) by the application of ultraviolet
laser or higher energy laser which is typically represented by the
excimer laser. At present, however, the fine processing method
using the ultraviolet laser, is generally practiced. When the
material, such as organic polymer resin, is processed by ablation
using the ultraviolet laser with the energy concentration suitable
for sublimate processing in accordance with the conventional
technique, the processing area is gradually reduced from the
incident side of the laser to the exit side thereof. The processed
configuration becomes the so-called tapered shape. Here, the
discharge port configuration, which is needed for the enhancement
of the print quality of an ink jet head, is tapered to become
narrower on the ink discharge side eventually. Therefore, the laser
processing method should be arranged so that the laser is
irradiated from the ink supply side (the ink flow path side of the
discharge port plate) as disclosed in the specification of Japanese
Patent Laid-Open Application No. 02-187346, for example.
[0103] However, in such a case of the laser processing, it has been
known that the degree of the taper is caused to change depending on
the applied laser powers. Also, since the length of the ink
discharge port is required to be approximately 10 .mu.m to 100
.mu.m in consideration of the print quality. Naturally, the same
thickness is required for the plate of the discharge ports
accordingly. As a result, when the discharge ports are formed by
the application of the method described above, the diameter of each
discharge port on the ink discharge side (the exit side of laser)
may be varied depending on each of the heads. Then, if the diameter
of each discharge port should vary, there is a need for the head to
provide the information to correct the discharge characteristics
after having conducted the discharge inspections following the
completion of each head particularly for the ink jet head which is
provided with a plurality of discharge port groups or for the ink
jet printer having a plurality of ink jet heads mounted on it.
[0104] In contrast, if the laser beam is irradiated from the ink
discharge side, the diameter of each discharge port is scarcely
influenced by the variation of the laser power. However, the
configuration of each discharge port is inevitably in such a form
that it becomes wider on the ink discharge side.
[0105] Now, therefore, if the laser processing that uses the
reflected beam is applied to the formation of the discharge ports
of an ink jet head, it becomes possible to form each discharge port
in the tapered shape which becomes narrower toward the ink
discharge side even if the laser beam is irradiated from the ink
discharge side.
[0106] Here, FIGS. 11A to 11C are views which illustrate an ink jet
head to which the aforesaid method for forming discharge ports is
applied.
[0107] In FIGS. 11A to 11C, a reference numeral 33 designates a
substrate. On this substrate, the ink discharge pressure generating
elements 34, such as electrothermal converting elements,
electromechanical converting elements, are arranged. The ink
discharge pressure generating elements 34 are arranged in the ink
flow paths 31 communicated with the discharge ports 21,
respectively. Each of the ink flow paths 31 is communicated with
the common liquid chamber 32. To the common liquid chamber 32, an
ink supply tube (not shown) is connected to supply ink from the ink
tank through this ink supply tube. Also, a reference numeral 35
designates the ceiling plate having the recessed portions that form
the ink flow paths 31 and the common liquid chamber 32. When this
ceiling plate is bonded to the substrate 33, the ink flow paths 31
and the common liquid chamber 32 are formed. Further, the discharge
port plate 20 having the discharge ports 21 arranged therefor is
provided on the end portion of the bonded body of the substrate 33
and the ceiling plate 35 on the ink flow path edge side. The ink
jet head thus structured is produced in the following manner.
[0108] In other words, at first, the substrate 33 is produced by
patterning the heaters 34, which are the heat generating resistive
elements for use of generating the ink discharge pressure, and the
integrated circuits, such as shift registers and others, as well as
the electric wiring on the silicon substrate. At the same time, the
ceiling plate 35 is produced by chemically etching the recessed
portions that become the ink flow paths 31 and the ink liquid
chamber 32, as well as the ink supply port, on the silicon plate.
After that, the substrate 33 and the ceiling plate 35 are aligned
so that the end face on the ink discharge port side and the
arrangements of the ink flow paths 31 and the heaters 34 are in
agreement with each other. Then, the discharge port plate 20 before
the formation of the discharge ports is bonded to the edge face of
the integrated body of the ceiling plate 35 and the substrate 33 on
the ink discharge port side. Here, in this state, the discharge
ports are formed by use of the laser processing equipment shown in
FIG. 1 which irradiates excimer laser to the discharge port plate
from the ink discharge side through the framed mask of the second
embodiment hereof. After that, the electric board having the
terminals for use of heat driving (not shown) is bonded, and at the
same time, the aluminum base plate is bonded to the substrate 33.
Then, the holder that supports each member and the ink tank to
supply ink are coupled to assemble an ink jet head. The ink jet
head thus obtained shows the configuration having the narrower
leading end in the incident direction of the laser beam, and there
are no flashes observed on each of opening configuration,
either.
[0109] In this respect, it may be possible to make arrangement to
align and bond the substrate 33 having the integrated circuit chip
with the patterned heaters 34 with the structure having the ceiling
plate provided with the grooves that become the ink flow paths 31,
the recessed portion that becomes the ink chamber 32, and the ink
supply port, as well as the discharge port plate 200 before the
discharge ports are integrally formed on polysulfone or some other
resin by injection molding, and then, to form the discharge ports
21 by use of the discharge port processing method described above.
After that, the electric board having the terminals for use of heat
driving (not shown) is bonded, and at the same time, the aluminum
base plate is bonded to the substrate 33. Subsequently, the holder
that supports each member and the ink tank to supply ink are
coupled to assemble an ink jet head.
[0110] Here, irrespective of the structure of an ink jet head, the
discharge port processing of the present invention should
preferably be performed in the processing step after the step in
which the discharge port plate for which discharge ports yet to be
processed is bonded to the member (head main body) that supports
this plate. With an ink jet head thus manufactured, it becomes
possible to prevent the discharge ports from being distorted in its
arrangement along with the deformation of the discharge port plate
that may take place when it is bonded to its supporting member or
to prevent the discharge ports from being deformed so as not to
allow the arrangement direction of each discharge port to become
irregular, which may otherwise result in the positional variation
of the ink thus discharged.
* * * * *