Information
-
Patent Grant
-
6663232
-
Patent Number
6,663,232
-
Date Filed
Wednesday, March 13, 200222 years ago
-
Date Issued
Tuesday, December 16, 200320 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
- Whitham, Curtis & Christofferson, P.C.
-
CPC
-
US Classifications
-
International Classifications
-
Abstract
An ink jet print head 1 includes a laminated piezoelectric element 31. The piezoelectric element 31 is fixedly attached to electrodes 33 by electrically conductive adhesive 32. A flexible printed cable 16 is electrically connected to electrodes 35 by soldering. The stationary plate 15 is formed with through holes 36, which are filled with an electrically conductive filler 34. The filler 34 and the electrodes 33, 35 are formed of tungsten, and the electrodes 33, 35 are plated with gold.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink jet print head, and more specifically to a continuity configuration of a laminated piezoelectric element of the head.
2. Related Art
A conventional ink jet print head includes a ceramic plate serving as a stationary plate, individual front electrodes mounted on a front surface of the ceramic plate, laminated piezoelectric elements electrically connected to the corresponding front electrodes by an electrically conductive adhesive, individual rear electrodes mounted on a rear surface of the ceramic plate, and flexible printed cable (FPC) electrically connected to the corresponding rear electrodes by soldering. The ceramic plate is formed from alumina with a plurality of through holes having a diameter of 0.25 mm. The through holes are filled with silver paste as filler, which electrically connecting the front electrode with the corresponding rear electrode. That is, the laminated piezoelectric element is electrically connected to the flexible printed cable via the front and rear electrodes and the filler.
This type of ink jet print head is formed in the following process. A green sheet is prepared and subject to calcinations to provide the ceramic plate. The plurality of through holes are formed in the ceramic plate by laser beam technique. The silver paste is applied into the through holes and also over the entire front surface of the ceramic plate, and is subject to sintering. The electrically conductive adhesive is coated over the front surface, and a block of piezoelectric element is placed thereon. The resultant product is subject to a dicing process to cut the block into the plurality of piezoelectric elements. At the same time, the silver paste on the ceramic sheet is also cut into a plurality of pieces, thereby providing the plurality of individual front electrodes.
However, the conventional ceramic plate with the above configuration has the following problems.
Firstly, when the above ceramic plate is placed in a high-temperature high-humid environment or get wet with ink, migration occurs in the front and rear electrodes. This results in continuity failure.
Secondly, a heat cycle that repeats between a room temperature and a higher temperature of 130° C. weakens the strength of the solder joint between the flexible printed cable and the rear electrodes, thereby causing disconnection.
SUMMARY OF THE INVENTION
It is an objective of the present invention to overcome the above problems and also to provide an ink jet print head in which continuity failure is effectively prevented and a method for producing the same.
In order to achieve the above and other objects, there is provided an ink jet print head including a stationary plate having a first surface and a second surface, a first electrode provided on the first surface, and a laminated piezoelectric element mounted on the first surface. The laminated piezoelectric element is electrically connected to the first electrode via an electrically conductive adhesive. The first electrode is formed of one of tungsten and molybdenum-manganese alloy.
There is also provided a producing method of producing an ink jet print head. The method includes the steps of a) forming a plurality of through holes in a green sheet, the through holes having first ends opened to a first surface of the green sheet and second ends opened to a second surface of the green sheet, b) filling in the through holes with filler, wherein the filler is one of tungsten and molybdenum-manganese alloy, c) forming a plurality of first electrodes from one of tungsten and molybdenum-manganese alloy on the first ends, d) forming a plurality of second electrodes from one of tungsten and molybdenum-manganese alloy on the second ends, e) plating the first and second electrodes with gold, f) placing a laminated-piezoelectric block on the first surface, g) applying an electrically conductive adhesive over the first surface and the first electrodes, and h) dicing the laminated-piezoelectric block into a plurality of laminated piezoelectric elements.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1
is a cross-sectional view of an ink jet print head according to an embodiment of the present invention;
FIG. 2
is an enlarged partial view of
FIG. 1
;
FIG.
3
(
a
) is a plan view of a stationary plate with electrodes formed thereon in a manufacturing process of the head;
FIG.
3
(
b
) is a plan view of the stationary plate in a manufacturing process of the head, where piezoelectric-element blocks are placed on the stationary plate;
FIG.
3
(
c
) is a plan view of the stationary plate in the manufacturing process of the head, where an electrically conductive adhesive is coated over the stationary plate; and
FIG.
3
(
d
) is a plan view of the stationary plate after a dicing process is performed to cut the piezoelectric-element blocks into a plurality of piezoelectric elements in the manufacturing process of the head.
PREFERRED EMBODIMENT OF THE PRESENT INVENTION
Next, an ink jet print head
1
according to an embodiment of the present invention will be described while referring to the attached drawings.
As shown in
FIG. 1
, an ink jet print head
1
of the present embodiment includes an orifice plate
11
, a chamber plate
12
, a restrictor plate
13
, a diaphragm plate
19
, a support plate
14
, and a stationary ceramic plate
15
. All are attached one on the other in this order to form a print head unit. The stationary plate
15
is formed from alumina (A1203) with high rigidity.
The orifice plate
11
is formed with an orifice
21
, and the chamber plate
12
is formed with an ink chamber
22
. The restrictor plate
13
is formed with a pressure chamber
23
. The orifice
21
, the ink chamber
22
, and the pressure chamber
23
together define a nozzle.
The ink jet print head
1
further includes a laminated piezoelectric element
31
and a flexible printed cable
16
. One end of the piezoelectric element
31
is attached to the diaphragm plate
19
, and the other end is fixedly attached to a front surface
15
a
of the stationary plate
15
by epoxy adhesive (not shown). The flexible printed cable
16
is provided to a rear surface
15
b
of the stationary plate
15
for transmitting electrical signal to the piezoelectric element
31
. The stationary plate
15
is formed with through holes
36
, which are filled with an electrically conductive filler
34
.
As shown in
FIGS. 2 and 3
, electrodes
33
,
35
are formed on the front and rear surfaces
15
a,
15
b
at positions corresponding to the through holes
36
. The flexible printed cable
16
is connected to the electrode
35
by soldering.
Although not shown in the drawings, the piezoelectric element
31
is provided with a pair of side electrodes, one on a side of the piezoelectric element
31
for positive polarity and the other on opposite side for negative polarity. The electrode
33
is coated with the electrically conductive adhesive
32
for the continuity with the side electrodes of the piezoelectric element
31
.
The electrodes
33
,
35
are both plated with gold. It has been confirmed through an experiment that if the electrode
33
is not plated with gold, the contact resistance between the electrode
33
made from the tungsten and the electrically conductive adhesive
32
will be undesirably large. Plating the electrode
33
with gold solves this problem.
Also, plating the electrode
35
with gold well secures the solder joint between the flexible printed cable
16
and the electrode
35
. In addition, a high-ink-resistant solder joint is provided.
Next, the method for providing the stationary plate
15
attached with the piezoelectric element
31
will be described. First, a green sheet, which will be the stationary plate
15
, is prepared, and the plurality of through holes
36
are formed thereto. In the present embodiment, a diameter d
2
of the through holes
36
is set to 0.2 mm. Then, tungsten is filled as the filler
34
in the through holes
36
and is also applied on the front and rear surfaces
15
a,
15
b
over the through holes
36
for the electrodes
33
,
35
. The resultant product is subject to calcinations at a temperature of about 2000° C. Because the tungsten has a melting point of 3387° C., the tungsten will not be melted down during the calcinations at the temperature of about 2000° C. As a result, the stationary plate
15
with the electrodes
33
,
35
formed thereon is provided (
FIG. 3
(
a
)). In this embodiment, the stationary plate
15
has a thickness of 1 mm. A diameter d
1
of the electrodes
33
is preferably 0.20 mm to 0.45 mm, and is set to 0.45 mm in this embodiment. Then, the surface of the electrodes
33
and
35
is plated with gold, and a pair of piezoelectric-element blocks
31
a
are placed and fixed by an epoxy adhesive (not shown) on the stationary plate
15
at predetermined positions and orientation as shown in FIG.
3
(
b
).
Next, as shown in FIG.
3
(
c
), the adhesive
32
are coated on the front surface
15
a
and on the electrodes
33
, but not on the piezoelectric-element block
31
a.
Then, as shown in FIG.
3
(
d
), the piezoelectric-element blocks
31
a
are cut into a plurality of piezoelectric elements
31
with dicing process. As shown, a dicing width is H
2
, and the resultant piezoelectric element
31
has a width of H
1
. In this embodiment, the dicing width H
2
=0.18 mm, and the element width H
1
=0.33 mm. Because the element width H
1
is smaller than the diameter d
1
of the electrode
33
, the dicing process cuts away portions of the electrodes
33
, resulting in oval-shaped electrodes
33
. Finally, the electrode
35
is soldered with the flexible printed cable
16
.
As described above, according to the present embodiment, the diameter d
1
of the electrode
33
is set to 0.45 mm. This dimension of the electrode
33
is small enough for providing a sufficient adhering area between the adhesive
32
and the stationary plate
15
, and is large enough for securing sufficient conductivity. That is, the adhering strength between the adhesive
32
and gold plated on the electrodes
33
is relatively weak, and so there is a danger that the adhesive
32
is peeled off the stationary plate
15
during the dicing process. However, because the adhesive
32
is securely adhered to the stationary plate
15
with relatively large area, the peelings will be avoided during the dicing process and even in the heat cycle. At the same time, the electrode
33
has the sufficient dimension to secure the conductivity between the adhesive
32
.
Although the diameter d
2
of the through holes
36
could be as large as 0.51 mm, within which the interference between the neighboring electrodes
33
would be theoretically prevented, the diameter d
2
is set to equal to or less than the dicing width H
1
(d
2
≦H
1
) in the present embodiment. This is because that if the diameter d
2
is set greater than the dicing width H
1
, the dicing process will whittle a portion of the filler
34
. This is a waste of the filler
34
, and there is no reason for setting the diameter d
2
greater than the dicing width H
1
.
As described above, because the tungsten is used as the filler
34
rather than the conventional silver paste, the filler
34
can be filled into the through holes
36
before the green sheet is subject to calcinations. Therefore, the sintering process for the tungsten is unnecessary after the calcinations. Accordingly, compared with the conventional process where the filler is sintered after the calcinations, the process of the present embodiment is simplified and economical.
Further, when the filler is sintered after the calcinations, the volume of the filler will be reduced at the time of sintering, resulting in air bubbles generated within the filler. Such air bubbles weaken the strength of the filler and causes breakage of the filler in the worse case. However, the calcinations for the stationary plate
15
and the sintering for the filler are performed at the same time, air bubbles will be not generated within the filler because the shrinkage percentage of the green sheet is larger than that of the filler. Accordingly, such problems can be avoided.
Because the individual electrodes
33
are formed on the stationary plate
15
before the dicing process, the adhesive
32
is not peeled off the electrode
33
during the dicing process, so the continuity can be well maintained. That is, if the tungsten plated with gold is first coated all over the front surface
15
a
and then cut into individual electrodes
33
by the dicing process as in the conventional manner, the conductive adhesive
32
would be easily peeled off the electrode
33
. This results in undesirable electrical disconnection between the piezoelectric element and the front electrodes. However, the present embodiment prevents such problems.
Moreover, migration has not occurred with the tungsten electrodes
33
,
35
even when the resultant product has been placed in high-temperature high-humidity environment. Accordingly, the continuity failure can be avoided, and the head
1
will less likely have continuity failure. This contrast to the conventional head with electrodes formed of silver.
Because electrode
35
is formed of tungsten plated with gold, the electrode
35
is easily soldered with the flexible printed cable
16
with a soldering temperature, which is nearly 30° C. lower than a soldering temperature for a conventional silver electrode. Also, the soldering strength between the gold-plated electrode
35
and the flexible printed cable
16
is sufficiently strong even under the heat cycle.
It is easier to form the through holes
36
as small as 0.2 mm before the calcinations compared with after the calcinations. This further improves integration of nozzles.
It should be noted that although the tungsten is used as the filler
34
in the above described embodiment, molybdenum-manganese alloy can be used instead. In this case also, the head
1
can be formed in the same manner, and the above effects can be obtained.
While some exemplary embodiments of this invention have been described in detail, those skilled in the art will recognize that there are many possible modifications and variations which may be made in these exemplary embodiments while yet retaining many of the novel features and advantages of the invention.
Claims
- 1. An ink jet print head comprising:a stationary plate having a first surface and a second surface opposite to the first surface, a first electrode provided on the first surface; and a laminated piezoelectric element mounted on the first surface, the laminated piezoelectric element being electrically connected to the first electrode via an electrically conductive adhesive, wherein the first electrode is formed of one of tungsten and molybdenum-manganese alloy.
- 2. The ink jet print head according to claim 1, further comprising:a second electrode provided on the second surface; and a flexible printed cable mounted on the second surface, the flexible printed cable being in electrical connection with the second electrode, wherein the second electrode is formed of one of tungsten and molybdenum-manganese alloy.
- 3. The ink jet print head according to claim 2, wherein the first electrode and the second electrode are both plated with gold.
- 4. The ink jet print head according to claim 2, wherein:the stationary plate is formed with a through hole having first end opened at the first surface and a second end opened at the second surface, the through hole being filled with a filler that is electrically conductive, wherein the filler is one of tungsten and molybdenum-manganese alloy; the first electrode is provided on the first end in electrical connection with the filler; the second electrode is provided on the second end in electrical connection with the filler; and the stationary plate is a ceramic plate.
- 5. A producing method of producing an ink jet print head, comprising the steps of:a) forming a plurality of through holes in a green sheet, the through holes having first ends opened to a first surface of the green sheet and second ends opened to a second surface of the green sheet; b) filling in the through holes with filler, wherein the filler is one of tungsten and molybdenum-manganese alloy; c) forming a plurality of first electrodes on the first ends from one of tungsten and molybdenum-manganese alloy; d) forming a plurality of second electrodes on the second ends from one of tungsten and molybdenum-manganese alloy; e) plating the first and second electrodes with gold; f) placing a laminated-piezoelectric block on the first surface; g) applying an electrically conductive adhesive over the first surface and the first electrodes; and h) dicing the laminated-piezoelectric block into a plurality of laminated piezoelectric elements.
- 6. The producing method according to claim 5, further comprising the steps of i) attaching a flexible printed cable to the corresponding second electrode by soldering.
- 7. The producing method according to claim 5, further comprising the steps of j) calcinating the green sheet after the step d).
Priority Claims (1)
Number |
Date |
Country |
Kind |
P2001-075178 |
Mar 2001 |
JP |
|
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A |
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Apr 2000 |
A |
6186612 |
Maeda et al. |
Feb 2001 |
B1 |
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Oct 2002 |
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