Note: Descriptions are shown in the official language in which they were submitted.
CA 02253409 2002-08-22
METHOD AND DEVICE FOR MANUFACTURING INK JET PR1NTHEAD
FIELD OF THE INVENTION
The present invention is related to a method for manufacturing an ink jet
printhead,
and more particularly to a device for manufacturing an ink jet printhead.
BACKGROUND OF THE INVENTION
Ink jet printers play an important role in printing field. Although they are
put into
application before laser jet printers, the use of laser jet printers does not
supersede ink jet
printers because of their increasingly high resolution and potential in color
printing. The
ink jet printhead is the most important part in an ink jet printer because it
is crucial to
printing performance and quality.
Please refer to Fig. 1 which is a schematic diagram showing a typical ink jet
printhead. The main part of the printhead is a chip 1 including circuits which
are used for
receiving signals generated from the computer through the software program
operation,
and controlling the ink-ejecting operation in accordance with the received
signals. In the
center of the chip 1 is a through hole 2 for storing the ink 21. There are
many ink-
containing holes 3 provided around through hole 2. The plurality of ink-
containing holes
3 are communicated with the through hole 2 so ink 21 contained in through hole
2 can
flow into the ink-containing holes 3. A nozzle plate 4 having many nozzles 41
therethrough covers ink-containing holes 3 wherein the plurality of nozzles 41
respectively
correspond to the plurality of ink-containing holes 3.
Please refer to Fig. 2 which is a sectional diagram showing an ink-containing
hole
and its peripheral structure. The ink-containing hole 3 is formed by
photolithographing a
photoresist 31. The chip 1 has a heating element. When a printing instruction
is given,
the circuits of chip 1 control the heating element to heat ink 21 restrained
in ink-containing
hole 3, and then ink 21 will be ejected through the nozzle 41 of the nozzle
plate 4. Thus, it
can be seen that the nozzle 41 must be small enough so that the amount of
ejected ink 21
can be controlled well and high resolution of the ink jet printer can be
anticipated.
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Please refer to Figs. 3(a)-(d) which are schematic diagrams showing a
conventional
process for manufacturing an ink jet printhead. Fig. 3(a) shows the first step
of forming a
photoresist 31 on the chip 1 followed by the next step of forming a plurality
of ink-
containing holes 3 on the chip 1 by photolithographing the photoresist 31 as
shown in
Fig. 3(b). Then, a hard baking step is executed in order to reduce the solvent
in the
photoresist 31. For bonding the nozzle plate 4 and the chip 1, the adhesive 5
is coated
right above the photoresist 31 as shown in Fig. 3(c). Fig. 3(d) shows that the
nozzle plate
4 is placed on the adhesive 5. It must be noted that the plurality of nozzles
41 are in
vertical alignment with the plurality of ink-containing holes 3 respectively
so the ink can
be ejected smoothly through the nozzle 41. At last, the chip 1 accompanied
with the
nozzle plate 4 is transferred to a heating chamber to be heated to bond the
chip 1 and the
nozzle plate 4 together firmly. It is difficult to operate this prior method
because such a
tiny element requires an extremely small amount of adhesive 5. The small
amount of
adhesive is not easily controllable. Too much adhesive chokes the small nozzle
and the
ink cannot be ejected. On the other hand, too less adhesive cannot bond the
chip and the
nozzle plate properly so the nozzle plate will fall down or the ink will leak
out. Moreover,
the adhesive-coating instrument is very expensive, but the rejection rate is
as high as fifty
percent. It really wastes too much production cost.
Before the chip and the nozzle plate are moved to the heating chamber, the
fixing
step is also important because a careless fixing will cause a relative
displacement between
the chip and the nozzle plate. When the semiconductor manufacturing process is
progressed into the sub-micron field, such a careless mistake is not allowable
because it
results in failure of the element. Sometimes, a simple clip is used for fixing
the chip and
the nozzle plate, but the force exerted by the clip can not be controlled.
Usually, a press
gripper is used in fixing wafers. Please refer to Fig. 4 which is a schematic
diagram of a
conventional fixing facility. The nozzle plate 4 is placed on the chip 1 and
is fixed by a
press gripper 6. The press gripper 6 includes a bottom 61, contact mediums 62,
a cylinder
63, and an air-supplying pipe 64. The air-supplying pipe 64 supplies a
controlled amount
of air into the cylinder 63, and the upper contact medium 62 presses down to
fix the nozzle
plate 4 on the chip 1. This kind of fixing device can control the exerted
force on the
nozzle plate 4 by controlling the flow rate of the supplied air. Different
forces are exerted
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in view of different strengths of the chip 1 and the nozzle plate 4. But, it
is possible that
the introduced force on the nozzle plate 4 is not a normal force. It will thus
cause a
relative displacement between the chip 1 and the nozzle plate 4. Besides, if
the exerted
forces on the two sides of the nozzle plate 4 are not balanced, these elements
still cannot
be fixed well due to the resulting inclination of these elements.
SUMMARY OF THE INVENTION
An objective of the present invention is to provide a method for manufacturing
an
ink jet printhead with high yield rate.
Another objective of the present invention is to provide a device for
manufacturing
an ink jet printhead with high yield rate.
In accordance with the objective of the present invention, a method for
manufacturing an ink jet printhead which includes a plurality of ink-
containing holes for
containing therein an ink, a nozzle plate having therethrough a plurality of
nozzles
corresponding to the plurality of ink-containing holes for ejecting
therethrough the ink,
and a chip for controlling the ejection of the ink, includes steps of (a)
forming a photo-
sensitive layer on the chip, (b) forming the plurality of ink-containing holes
on the photo-
sensitive layer, (c) placing the nozzle plate on the photo-sensitive layer,
and (d) heating the
photo-sensitive layer to bond the chip and the nozzle plate.
In accordance with another aspect of the present invention, the photo-
sensitive layer
is a photoresist.
In accordance with another aspect of the present invention, the photoresist is
a dry
photoresist. The thickness of the formed photoresist is preferably from 50 ~m
to
1000 ~tm.
In accordance with another aspect of the present invention, the photoresist is
a wet
photoresist. The thickness of the formed photoresist is preferably from 0.1 ~m
to 50 pm.
In accordance with another aspect of the present invention, the plurality of
ink
containing holes are formed by photolithography.
In accordance with another aspect of the present invention, the photo-
sensitive layer
is heated by a hot plate at a temperature from 100°C to 250°C
for a period from 1 minute
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to 10 hours.
In accordance with another aspect of the present invention, the heating step
(d)
further comprises exerting a pressure from 0.01 kg/cmz to 1 kg/cm2 on the
nozzle plate to
prompt the bonding of the chip and the nozzle plate.
In accordance with another aspect of the present invention, the plurality of
nozzles
are respectively in vertical alignment with the corresponding ink-containing
holes.
In accordance with another aspect of the present invention, the step (c)
further
comprises fixing the nozzle plate on the chip.
In accordance with another aspect of the present invention, the nozzle plate
is fixed
on the chip by a clip.
In accordance with another aspect of the present invention, the fixing
step(cl)
further comprises placing the nozzle plate and the chip on a base wherein a
through hole in
the chip is immediately above a vacuum aperture on the base, and applying
vacuum to the
aperture for fixing the nozzle plate by sucking the nozzle plate against the
chip.
In accordance with another aspect of the present invention, the vacuum applied
to
the aperture is preferably less than ambient pressure by 50 mmHg to 200 mmHg.
In accordance with another aspect of the present invention, the nozzle plate
is a
metal plate such as a nickel plate.
In accordance with the objective of the present invention, a method for
manufacturing an ink jet printhead which includes a plurality of ink-
containing holes for
containing therein an ink, a nozzle plate having thereon a plurality of
nozzles for ejecting
therethrough the ink, and a chip for controlling the ejection of the ink,
includes the steps of
placing the chip on a base wherein a through hole in the chip is immediately
above an
aperture on the base, coating an adhesive on the chip, placing the nozzle
plate on the chip,
applying vacuum to the aperture for fixing the nozzle plate by a sucking
force, and heating
the adhesive to bond the chip and the nozzle plate.
In accordance with another aspect of the present invention, the base further
includes
a plurality of independent flutes which have different vacuum pressures.
In accordance with another aspect of the present invention, the method further
comprises, after the heating step, removing the vacuum applied to the aperture
for
removing the sucking force.
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In accordance with another objective of the present invention, a device for
manufacturing an ink jet printhead which includes a nozzle plate for ejecting
therethrough
an ink, and a chip mounted below the nozzle plate for controlling the ejection
of the ink
and having therein a through hole, includes a base and an aperture provided on
the base
having an opening communicating with the aperture, and a vacuum apparatus
communicating with the opening. The base is used for supporting thereon the
chip
wherein the through hole is right above the aperture. The vacuum apparatus is
used for
applying vacuum to the aperture to fix the nozzle plate to the chip by a
sucking force.
In accordance with another aspect of the present invention, the aperture can
be
straight or annular.
In accordance with another aspect of the present invention, the vacuum
apparatus is
preferably a rotary vacuum pump.
In accordance with another aspect of the present invention, the device further
includes a three-way valve mounted between the vacuum apparatus and the
opening for
controlling the sucking force. The valve communicates the aperture with the
vacuum
apparatus for applying vacuum to the aperture to exert the sucking force in a
first instance.
And the valve communicates the aperture with the ambient for removing vacuum
from the
aperture to remove the sucking force in a second instance.
The present invention may best be understood through the following description
with reference to the accompanying drawings, in which:
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic diagram showing a typical ink jet printhead;
Fig. 2 is a sectional diagram showing an ink-containing hole and its
peripheral structure;
Figs. 3(a)-(d) are schematic diagrams showing a conventional process for
manufacturing
an ink j et printhead;
Fig. 4 is a schematic diagram of a conventional fixing medium;
Figs. 5(a)-(c) are schematic diagrams showing a preferred embodiment of a
method for
manufacturing an ink jet printhead according to the present invention;
Fig. 6 is a schematic diagram showing another preferred embodiment of the
printhead-
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manufacturing method according to the present invention; and
Fig. 7 is a schematic diagram showing a preferred embodiment of a fixing
device
according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention will now be described more specifically with reference
to the
following embodiments. It is to be noted that the following descriptions of
preferred
embodiments of this invention are presented herein for the purpose of
illustration and
description only; it is not intended to be exhaustive or to be limited to the
precise form
disclosed.
The present invention provides a method for manufacturing an ink j et
printhead
more rapidly. Please refer to Fig. 5 which is a schematic diagram showing a
preferred
embodiment of a method for manufacturing the ink jet printhead according to
the present
invention. At first, coat a photoresist 31 on the chip 1 as shown in Fig.
5(a). The
photoresist 31 is made from a known photo-sensitive material and has no other
limitations.
The photoresist is typically classified into dry photoresist or wet
photoresist according to
the amount of solvent in the photoresist. The dry tape is applicable to
thicker photoresist
with thickness from 50 pm to 1000 pm while the other type is applicable to
thinner
photoresist with thickness from 0.1 pm to 50 Vim. The dry type is the most
often used one
because the thickness range is suitable for containing the ink. The coating
step is executed
by spin-coating because the obtained photoresist is especially smooth by this
method.
Please refer to Fig. 5(b). The next step is to photolithograph the photoresist
31 to
form the ink-containing hole 3. The steps including soft baking, exposure, and
development are executed in sequence to form a plurality of holes, so-called
ink-
containing holes 3, on the photoresist 31. According to the prior art, the
next step should
be hard baking step for evaporating the solvent in the photoresist 31 in order
to adhere the
photoresist 31 to the chip 1 more firmly. But the photoresist 31 is not gluey
after it is
dried so another adhesive is needed for bonding the nozzle plate 4 to the chip
1. Please
refer to Fig. 5(c). According to the present invention, the conventional hard
baking step is
suspended temporarily. Before the photoresist 31 is dried, place the nozzle
plate 4 on the
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photoresist 31 wherein each nozzle 41 is in alignment with its corresponding
ink-
containing hole 3. Then, the hard baking step is resumed.
Hard baking step is used for reducing the amount of solvent in the photoresist
31.
This step can make the photoresist 31 adhere to the chip 1 and the nozzle
plate 4 properly.
The photoresist 31 is heated by conduction. In other words, a hot plate is
adopted. The
heat temperature and heat period are determined according to the material of
photoresist
31. Typically, the heating temperature is from 100°C to 250°C
while the heating period is
from 1 minute to 10 hours. Too low a heating temperature requires a longer
period of time
to evaporate the solvent. Too high a heating temperature causes a worse
adhesion of the
photoresist due to much tensile stress stored in it. It is difficult to fully
evaporate the
solvent in the photoresist if the heating period is too short. On the other
hand, the
photoresist becomes fragile if the heating period is too long. For the above
reasons, the
heating temperature and the heating period must be determined properly.
Besides, an
additional pressure from 0.01 kg/cm2 to 1 kg/cmz can be exerted on the nozzle
plate 4 to
prompt the bonding of nozzle plate 4 and chip 1.
Certainly, the production efficiency can be increased by slightly modifying
the
present technology. Heretofore, because of the limit of the adhesive-coating
step, the
manufacturers cannot manufacture many ink jet printheads at a particular
period of time.
They must bond the first nozzle plate on the first chip, then bond the second
nozzle plate
on the second chip, and so on. If a wafer has thereon one hundred chips, the
bonding step
must be repeated for one hundred times. It is impossible to coat an adhesive
on all of the
chips included in one wafer at first, and then place all the nozzle plates on
the wafer
because the adhesive-coating step is a time-consuming step. The coated
adhesive will dry
before all the nozzle plates are placed on the wafer. On the contrary, the
method according
to the present invention can manufacture many ink jet printheads at a time. A
metal plate
having hundreds of nozzle plates is placed on the photoresist above the wafer
having
hundreds of chips before the photoresist is dried. Then, the metal plate
accompanied with
the wafer is heated and all hundreds of nozzle plates and chips are bonded
together.
Apparently, this method can speed up the production efficiency.
Compared with the prior art, the present invention eliminates the adhesive-
coating
step so that the process consumes less time. Moreover, the present invention
can even
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bond hundreds of nozzle plates and chips at the same time so that the process
consumes
much less time. Besides, eliminating the adhesive-coating step also eliminates
the
troubles, such as choke of the nozzle, leakage of the ink, or falling of the
nozzle plate,
resulting from an improper amount of the adhesive occurred during the adhesive-
coating
step. The rejection rate will be reduced to zero if the nozzles of the nozzle
plates are really
in alignment of the ink-containing holes on the chips. The expensive adhesive-
coating
instrument is not needed any more so this method saves not only production
time but also
production cost.
The fixing device is also improved according to the present invention. If the
nozzle
plates are not fixed properly on the chips, the above-described efforts are in
vain because
there is a relative displacement between the nozzle plates and the chips
before we heat the
photoresist. Please refer to Fig. 6 which is a schematice diagram showing
another
preferred embodiment of the printhead-manufacturing method according to the
present
invention. The wafer 8 including many chips 1 is placed on the base 71 wherein
the
through holes 2 of the chips 1 are right above the aperture 72 of the base 71.
After the
photoresist is coated on the chips l, the metal plate 9 including many nozzle
plates 4 is
placed on the wafer 8 wherein the nozzles of the nozzle plates 4 are in
vertical alignment
with the ink-containing holes of the chips 1 as described in the prior
preferred
embodiment. Before heating the photoresist located between the metal plate 9
and the
wafer 8, the metal plate 9 and the wafer 8 must be fixed firmly so there is no
relative
displacement between them when they are translated. The vacuum apparatus 73
communicating with the opening 721 of the base 71 applies vacuum to the
aperture 72 and
a sucking force is generated to fix the metal plate 9 to the wafer 8. The
vacuum apparatus
73 is a rotary vacuum pump. A three-way valve 74 can be added to control the
sucking
force. If the sucking force is desired, the three-way valve 74 is caused to
communicate the
rotary vacuum pump 73 with the aperture 72 and the rotary vacuum pump 73
applies
vacuum to the aperture 72. After the heating step, the metal plate 9 and the
wafer 8 are
bonded together so the sucking force can be removed. Consequently, the three-
way valve
74 communicates the aperture 72 with the ambient and the whereby vacuum is
removed
from the aperture 72 so that the sucking force is removed. When the rotary
vacuum pump
73 works, the pressure difference between the aperture 72 and the surroundings
is from
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50 mmHg ~ 200 mmHg. The greater the pressure difference is, the greater the
sucking
force is. The pressure difference is determined by the vacuuming power of the
rotary
vacuum pump 73 in accordance with the strength of the metal plate 9. It is
noted that
although a great pressure difference can fix the metal plate 9 more firmly,
too great a
pressure difference will cause damage to the metal plate 9.
Certainly, it is not necessary that all the through holes 2 are right above
the aperture
72. The generation of sucking force is not affected if some through holes 2
are not right
above the aperture 72.
Certainly, the fixing method is also practicable if there are a plurality of
apertures on
the base, or the aperture is otherwise shaped. Please refer to Fig. 7 which is
a schematic
diagram showing a preferred embodiment of the fixing device according to the
present
invention. The apertures 72 are annular apertures. Each aperture 72
corresponds to a
rotary vacuum pump 73 and a three-way valve 74. Accordingly, the pressure
differences
between the apertures 72 and the surroundings may be different. For example,
if the
strength of the metal plate is not equable, the exerted sucking forces must be
different at
different points of the metal plate. Thus, proper sucking forces can be
exerted at any point
of the metal plate by respectively controlling the vacuuming powers of each
rotary vacuum
pump 73.
The present fixing method used for manufacturing the ink jet printhead is
better than
the prior art. The manufacturers need not worry about other forces which are
not normal
to the metal plate are introduced according to the prior art. The best
advantage is that the
force strength can be adjusted arbitrarily at any point. The manufacturers
also need not
worry that the metal plate is not fixed well or the metal plate is damaged
because of
improper exerted forces. Moreover, the sucking force is uniform for the whole
metal plate
according to the present invention while the sucking force is not uniform
according to the
prior art because strains are only generated at the points where the clips or
the grippers are
added. Such improper fixing will cause deformation of the metal plate and the
wafer.
Accordingly, the present method is more utilizable due to its easily
controlled
characteristics.
While the invention has been described in terms of what are presently
considered to
be the most practical and preferred embodiments, it is to be understood that
the invention
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need not be limited to the disclosed embodiment. On the contrary, it is
intended to cover
various modifications and similar arrangements included within the spirit and
scope of the
appended claims which are to be accorded with the broadest interpretation so
as to
encompass all such modifications and similar structures.
