Patent Grant
9242460
1. Field of the Invention
The present invention relates to a liquid-discharge-head substrate, a method of manufacturing the liquid-discharge-head substrate, and a liquid discharge head.
2. Description of the Related Art
A typical thermal type liquid discharge head (hereinafter, also referred to as head) includes a liquid-discharge-head substrate (hereinafter, also referred to as head substrate) having a liquid discharge heater and a conductive layer for electrical connection, and a member having a discharge port which corresponds to the heater and discharges liquid.
In recent years, functions for stabilizing discharge of liquid are added to a head substrate. One of the functions is obtained by a technique of pre-heating the head substrate by a heating member (hereinafter, also referred to as sub-heater) provided at the substrate, in addition to a heating element for liquid discharge (hereinafter, also referred to as heater).
As such a sub-heater, for example, Japanese Patent Laid-Open No. 3-005151 discloses a structure in which a heater and a sub-heater are formed of a conductive layer. The sub-heater heats a head substrate to prevent a discharge characteristic from being degraded at a low temperature.
Meanwhile, a head substrate increases in size as the number of heating elements increases. Also, when the number of colors of inks increases, the number of supply ports increases, resulting in the size of the head substrate increasing. Hence, in related art, variation in temperature distribution may likely appear in the head substrate when the head substrate is pre-heated.
When the variation in temperature distribution in the head substrate increases, discharge characteristics such as a discharge amount and a discharge speed of ink droplets may vary among a plurality of nozzles. This may cause density unevenness and disorder of landing points of the ink droplets. Recording quality may be degraded.
In particular, when pre-heating is performed before a recording operation, the temperature of the head substrate has to be quickly increased to a predetermined temperature. Owing to this, power to be applied to the sub-heater is increased. A large temperature gradient may appear in the head substrate between a position close to the sub-heater and a position far from the sub-heater.
In addition, when pre-heating is performed to keep the temperature of the head at a predetermined temperature during a recording operation, a temperature gradient may increase as the temperature of the head substrate is set high. This may degrade recording quality.
Accordingly, the present invention provides a head substrate and a head capable of decreasing variation in temperature distribution in the head substrate, and increasing recording quality with a simple structure.
Also, the present invention provides a method of easily manufacturing such a head substrate with a reduced process load.
According to an aspect of the present invention, a method of manufacturing a liquid-discharge-head substrate is provided. The substrate has an element, the element being configured to generate thermal energy for discharging liquid. The method includes the steps of preparing a substrate having an insulating layer on or above a surface of the substrate, the insulating layer being made of an insulating material; providing a conductive layer on or above the insulating layer, the conductive layer made of a conductive material; and, forming a conductive line and a heating member by using the conductive layer, the conductive line being configured to supply current for driving the element, and the heating member being electrically separated from the conductive line and configured to generate heat for heating the liquid-discharge-head substrate.
With the aspect, a head substrate is provided, which can decrease the variation in temperature distribution in the head substrate and increase the recording quality. In addition, a manufacturing method is provided, which easily provides the above-mentioned head substrate.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
First, a liquid discharge (inkjet) device will be briefly described.
A sheet pressure plate 5002 presses a recording sheet P against a platen 5000 over a moving direction of the carriage HC. Photosensors 5007 and 5008 are home position detecting elements which detect a lever 5006 of the carriage HC in a detection area and changes a rotating direction of the drive motor 5013. A cap 5022 covers a front surface of the head unit 400 in an airtight manner. The cap 5022 is supported by a support member 5016. A sucking member 5015 sucks the cap 5022 for a sucking and recovery operation of the head unit 400 through a cap opening 5023. A cleaning blade 5017 and a member 5019 are supported by a body support plate 5018. The member 5019 allows the cleaning blade 5017 to move in a front-rear direction. The cleaning blade 5017 is not limited to one described above. Any of typical cleaning blades can be applied to this embodiment. A lever 5021 starts sucking of the sucking and recovery operation. The lever 5021 is moved when a cam 5020 engaging with the carriage HC moves. The lever 5021 is moved by the driving force from the drive motor and controlled through a transmission mechanism such as a clutch.
The operations of capping, cleaning, and sucking and recovery are performed at corresponding positions when the carriage HC is moved to an area at a home position by the lead screw 5004. As long as desired operations are performed at proper timings, this embodiment can be applied to any configuration.
Next, a control circuit section for controlling a recording operation of the liquid discharge device will be described with reference to a block diagram of
The control circuit section is electrically connected to a carrier motor 1710 which carries the head unit 1708, and to a convey motor 1709 which conveys a recording sheet. The control circuit section drives the convey motor 1709 and the carrier motor 1710 through motor drivers 1706 and 1707. A head 1705 is provided at the head unit 1708. The head 1705 has a discharge heater (hereinafter, also referred to as heater) serving as an element for generating thermal energy to discharge liquid, and a drive circuit for driving the heater.
An operation of the above-mentioned control configuration is described. When a recording signal is input to the interface 1700, the recording signal is converted into recording data for printing through the GA 1704 and the MPU 1701. Then, the motor drivers 1706 and 1707 are driven, and the heater is driven in accordance with the recording data sent to the head 1705 of the head unit 1708. Hence, recording is performed.
Next, the head unit 400 will be described with reference to
Referring to
Referring to
The head 50 is bonded to the support body 301 by die bonding, the TAB line 401 is bonded on the second support body 302, and the inner lead of the TAB line 401 is connected to the pads of the head 50. Then, the support body 301 is jointed to the sub-tank 403, to connect the TAB line 401 to the printed wiring board 402. The printed wiring board 402 is fixed to the sub-tank 403 by caulking. Thusly, the head unit 400 is completed.
The head 50 includes a liquid-discharge-head substrate (hereinafter, also referred to as head substrate) 100 having supply ports 101 which are long through holes and heaters 501, and a member 56 to provide a wall for forming an ink path. The supply ports 101, or the long through holes, are formed in a silicon substrate. An array of the heaters 501 are provided on either side of each supply port 101. The heaters 501 generate energy for liquid discharge. Further, each heater 501 is connected to an electric line for power supply. The electric line is electrically connected to the outside through external connection pads 110 provided at the head substrate 100. The member 56 having discharge port arrays 210 is provided on the head substrate 100. Each discharge port array 210 has a plurality of discharge ports 200. The member 56 has the discharge ports 200 at positions facing the heaters 501.
Referring to
A conductive line for connecting elements of the drive circuits, and the drive circuit line 103 are formed of the first conductive layer made of, for example, aluminium. The first conductive layer is provided above a surface of the head substrate 100 in a direction perpendicular to the surface, at which the driver section and the elements (e.g., AND circuit) used for the drive circuits are provided. A part of the first conductive layer functions as sub-heaters 512, which are formed of the first conductive layer. The sub-heaters 512 are arranged in a direction orthogonal to the discharge heater array 102.
A wiring line formed of the second conductive layer is provided above the surface of the head substrate 100 formed of the first conductive layer in the direction perpendicular to the surface, with an insulating layer interposed therebetween. VH power lines 120 and GNDH power lines 121 are provided above the driver section in the direction perpendicular to the surface of the head substrate 100. The VH power lines 120 and the GNDH power lines 121 are formed of the second conductive layer and supply power to the plurality of heaters. In addition, referring to
Referring to
Next, a method of driving the discharge heater will be described.
Referring to
Next, reliability of the sub-heater is described.
When a part of a wiring line is used as a sub-heater by supplying high current to aluminium, which is typically used for a conductive layer, electromigration resistance has to be considered.
Electromigration (hereinafter, also referred to as EM) is a phenomenon in which atoms of aluminium of the wiring line move in a flow direction of electrons when current is supplied to the wiring line. As a result, voids may be generated and surface defects, such as hillocks and whiskers, may appear.
A mean time to failure of the head substrate due to EM relies on Black's empirical equation. Referring to Black's empirical equation, the mean time to failure is generally inversely proportional to a current density to the n-th power (n is normally 2). That is, when the wiring line is used as the sub-heater, the current density has to be a predetermined value or lower for the head substrate to have a sufficiently long life regarding EM. Black's Empirical Equation (1) is as follows:
MTTF=A×J−n×eEa/kT (1),
where MTTF is a mean time to failure (hours), A is a constant determined depending on a structure and a material of a wiring line, J is a current density (A/cm2), n is a constant representing a dependency of current density, normally 2, depending on a temperature gradient, an acceleration condition, etc., Ea is an activation energy (eV), normally ranging from 0.4 to 0.7 eV, depending on an orientation, a particle diameter, a protection film, etc., k is Boltzmann constant, i.e., 8.616×10−5 eV/K, and T is an absolute temperature (K) of the wiring line.
To use the wiring line as the sub-heater, power consumption of a certain value or higher is necessary. To secure a longer life regarding EM while heat is generated with a necessary power consumption, in particular to decrease the current density while keeping a constant voltage-current, both the length and cross-sectional area of the wiring line have to be increased. For example, when the length of the wiring line is doubled and the cross-sectional area of the wiring line is doubled, a resistance of the wiring line for forming the sub-heater is not changed, and hence, the power consumption is not changed. The current density, however, can be halved. Regarding Black's empirical equation, a mean time to failure due to EM can be substantially quadrupled.
As described above, to secure a reasonable life regarding EM, the sub-heater has to have a suitable length of the wiring line and a suitable cross-sectional area of the wiring line. In addition, to perform pre-heating with an even temperature distribution, the wiring line for the sub-heater should be arranged as evenly as possible within a plane of the head substrate.
To secure the proper length of the wiring line for the sub-heater and to arrange the wiring line substantially evenly in the head substrate, the sub-heater can be formed of a plurality of conductive layers. For example, when a head substrate is a thermal type, the head substrate typically includes a heater line for power supply to a heater, and a logic line used for a drive circuit for driving the heater. In such a head substrate, a second conductive layer for the heater line and a first conductive layer for the logic line are used. Hence, the sub-heater is efficiently arranged to extend continuously through an area not occupied by the two supply ports as shown in
Now, an example method of manufacturing the head substrate according to the embodiment will be described with reference to
A substrate 600 made of silicon and having a driver section and elements for drive circuits including an AND circuit is prepared. A material, for example, aluminium is provided on the substrate by sputtering or the like, so that a first conductive layer 112 is made by a conductive material, for example, Al—Cu (
Next, a structure of sub-heaters shown in
In the embodiment, the resistance layer 114 is arranged between the insulating layer 115 and the individual line 504 formed of the second conductive layer 123. However, the resistance layer 114 may be provided on a wiring line as shown in
When a substrate temperature is a predetermined temperature or lower, a voltage is applied from the external connection pad 110 through the inner lead of the TAB line 401 and hence current is supplied. The current flows to the sub-heater 511, the connection portion, the sub-heater 512, the connection portion, and the sub-heater 511, . . . , in that order, and flows to another external connection pad 110. As a result, the sub-heaters generate heat, and increase the substrate temperature to a predetermined temperature. After the substrate temperature is increased, application of the voltage to the sub-heaters is decreased, and is controlled to keep the substrate temperature constant.
As described above, in this embodiment, the sub-heaters are provided in the area between the two adjacent supply ports 101 and areas between the supply ports 101 and the edges of the head substrate 100. With this configuration, the head substrate 100 can be evenly pre-heated in the array direction of the heaters formed by the discharge heater array 102. Further, with this configuration, the proper width and length of the wiring line can be easily provided to decrease the current density of the sub-heaters. Hence, reliability of the sub-heaters can be increased.
With the sub-heaters as described above, the temperature distribution in the substrate can be evenly kept in the array direction of the heaters. Thus, discharge characteristic of liquid (ink) can be equalized, and recording quality can be increased.
The inventors studied a case where high durability is demanded because of pre-heating with further high current and because of long-term use of a head.
In a typical head substrate, a heater conductive layer and a resistance layer are stacked. An area contacting the resistance layer and not occupied by the heater conductive layer is used as a heater.
The heater may employ a configuration in which the second conductive layer 111 in
In the configuration of
EM endurance testing was performed for the sub-heater shown in
Arrows in
Here, the connection portion (
A typical semiconductor element is sealed with resin. Hence, although a slight crack appears at the protective layer, the crack does not cause a serious damage. However, in the case of the head substrate, liquid is present on the surface of the substrate. Hence, if a crack appears at a protective layer, the liquid may enter the crack, resulting in the wiring line being corroded, or disconnected.
In contrast, in the connection portion in
At the connection portion where electrons flow from the first conductive layer 112 to the second conductive layer 111, the electrons flow from four sides to the center portion of the connection portion, and hence, Al atoms of the first conductive layer 112 attempt to move toward the center portion of the connection portion. However, since the resistance layer 114 is provided, the Al atoms cannot move or be dispersed to the upper side. The Al atoms are collected at the center portion of the connection portion, and a hillock appears.
In contrast, at the connection portion where electrons flow from the second conductive layer 111 through the resistance layer 114 to the first conductive layer 112, the current density becomes highest at a step portion of the second conductive layer 111. Owing to this, the second conductive layer 111 is deformed at a portion close to the four sides of the connection portion. However, electrons are less likely to flow toward the center portion of the connection portion. Hence, a large hillock tends not to appear at the center portion of the connection portion.
As mentioned above, the sub-heater formed of the first conductive layer, the resistance layer, and the second conductive layer has a bottleneck of having a lower EM durability at the connection portion between the conductive layers as compared with an EM durability of the line portion. In particular, the EM durability of the connection portion where electrons flow from the first conductive layer through the resistance layer to the second conductive layer may be lower than the EM durability of the connection portion where electrons flow from the second conductive layer through the resistance layer to the first conductive layer.
Regarding Black's empirical equation, the mean time to failure due to EM is inversely proportional to a current density to the 2nd power. Hence, to increase the EM durability at the connection portion, the area of the connection portion has to be increased. However, the increase in area of the connection portion may cause an increase in size of the head substrate.
In a head substrate 100 of this embodiment, sub-heaters 511 are formed by using the second conductive layer 111 in a manner similar to the VH power lines 120 and GNDH power lines 121. A plurality of the sub-heaters are separately arranged at positions on the head substrate 100. In addition, external connection pads 110 serving as external connection electrodes are provided at the head substrate 100. Each sub-heater is electrically connected to two external connection pads 110 at both ends of the sub-heater.
When a substrate temperature is a predetermined temperature or lower, an electric potential is applied to the external connection pad 110 through an inner lead of a TAB line 401 and hence current flows from the external connection pad 110. Referring to
As described above, in this embodiment, a connection portion for connecting the first conductive layer 112 and the second conductive layer 111 is not provided. Hence, electromigration can be avoided. Accordingly, even when a head is used with high current for a long period, a damage of the sub-heater because of electromigration can be prevented, and reliability can be increased. In some cases, a head for industrial use is used constantly at a high temperature depending on the characteristic of liquid. Also, the head for industrial use has to operate for a long period. For such a head for industrial use, the configuration of this embodiment is effective.
In this embodiment, the length of the sub-heater is increased by folding the sub-heater one time within the head substrate. However, the sub-heater may be desirably arranged depending on necessary power and life of the sub-heater. As long as only the second conductive layer is used, a straight line may be provided to extend from one end to the other end of the head substrate. Also, the number of folding times of the sub-heater is not limited to one, and the sub-heater may be folded a plurality of times.
To further increase the EM durability, using the head substrate shown in
This head substrate 100 has line sections respectively extending from external connection pads 110 of second conductive layers 111 of three independent sub-heaters, through a TAB line 401, to a printed wiring board 402 located outside the head substrate 100. The line sections extending from the external connection pads 110 of the second conductive layers 111 are electrically connected to the printed wiring board 402 such that the three sub-heaters are arranged in series.
As described above, by using only the second conductive layer for the sub-heater and folding the sub-heater, a long length of the wiring line can be provided, and the current density can be decreased. Thus, the sub-heater with a reduced EM durability can be provided on the substrate.
Further, the long sub-heater is provided along the supply port in an area between the adjacent supply ports and areas between the supply ports and the edges of the substrate. With the sub-heater as described above, the temperature distribution in the substrate can be evenly kept in the array direction of the heaters. Thus, discharge characteristic of liquid (ink) can be equalized, and recording quality can be increased.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2008-221494 filed Aug. 29, 2008, which is hereby incorporated by reference herein in its entirety.
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