Patent Application
20080079779
Further advantages of exemplary embodiments disclosed herein may become apparent by reference to the detailed description of exemplary embodiments when considered in conjunction with the drawings, which are not to scale, wherein like reference characters designate like or similar elements throughout the several drawings as follows:
According to exemplary embodiments disclosed herein, there is provided methods for modifying low thermal conductivity substrates to yield substrates having improved thermal conductivity properties. With reference to
In a manner well known in the art, thermal fluid ejection actuators, such as heater resistors, are formed adjacent to a device surface of the modified substrate 12 in an actuator region 14 of the substrate 12. Upon activation of a thermal fluid ejection actuator in the actuator region 14, fluid supplied through a fluid path(s) in an associated fluid reservoir and corresponding fluid flow slot(s) in the substrate 12 is caused to be ejected toward a media through a nozzle in a nozzle plate associated with the substrate 12.
Substrate 12 represents a base substrate material which has been modified by adding a thermal bus 16 including a thermally conductive material 18. The thermal bus 16 is configured to dissipate heat associated with the operation of the ejection actuators and improve the overall thermal conductivity of the head 10 as compared to a corresponding head devoid of the thermal bus 16.
The base material used to provide the substrate 12 may be selected from materials having a thermal conductivity ranging from the thermal conductivity of glass (1.4 W/m-° C.) to a thermal conductivity less than that of silicon (148 W/m-° C.), and in some embodiments, also less than the thermal conductivity of alumina (30 W/m-° C.). For example, suitable materials include glass and ceramic substrates, such as, low temperature co-fired ceramic (LTCC) substrates which have a thermal conductivity generally in the range of from about 2 to about 4 W/m-° C.
For example, suitable substrates have a thermal conductivity ranging from about 1.4 W/m-° C. to about 148 W/m-° C., in some cases desireably from about 1.4 W/m-° C. to about 30 W/m-° C., and, in some cases, more desirably from about 1.4 W/m-° C. to about 4 W/m-° C.
The thermal bus 16 may be provided for by forming one or more trenches 20 in the substrate 12, such as by a variety of methods including, laser, diamond saw, abrasive water jet, water-laser-jet, sandblasting, and the like. The trench may also be formed by, for example, stacking pre-punched layers of LTCC in such a way as to form the trench for the thermal bus. Next, the thermally conductive material 18, such as metal may be introduced into the trenches 20.
The trenches 20 for the thermal bus 16 may run substantially the length of the actuator region 14, and may be located under the actuator region 14. Although not necessarily preferred, it is functionally possible to have a thin layer separating the actuator from the thermal bus, depending on the heat dissipation requirements. The application of the thermally conductive material 18 may be accomplished as by depositing the thermally conductive material 18 in each trench 20 by screen printing, plating, or spray deposition. With screen printing and spray deposition, the deposited metal or other material 18 may be heated such as to drive off solvents and other volatiles. The thermally conductive trenches may also be provided as by the so-called Damascene metallization process. If the thermally conductive material 18 is screen printed or spray deposited, the deposited material may sit flush or just under flush to the top edge of the trench 20. If the deposited material 18 sits above the edge of the trench 20, it may be ground, polished, or otherwise removed until it is flush with the trench 20.
Materials suitable for use as the thermally conductive material 18 may include materials having a thermal conductivity of at least about 200 W/m-° C. Particularly suitable materials may include metals such as silver (thermal conductivity ranging from about 406 to about 429 W/m-° C.) and copper (thermal conductivity ranging from about 385 to about 429 W/m-° C.) and mixtures thereof. The trenches 20 (and hence the material 18 therein) may have a thickness or depth (D) of, for example, at least about 40 μm, a length (L) of, for example, at least about 150 μm, and a width (W) of, for example, at least substantially corresponding to a length of the actuator region 14 (typically greater than about 25 millimeters).
In addition to providing heat dissipation properties it has also been observed that the thermal bus 16 may function as an embedded power/ground bus. For example, to maintain the electrical isolation properties of the substrate 12, a material with high thermal and electrical insulation properties may be deposited between the trench and the actuator region 14. Materials that are appropriate for this layer may include, glass borophosphosilicate glass (BPSG), spin-on-glass (SOG), and the like. In constructing the thermal/electrical insulation layer, it may be necessary to bring it up to a suitable reflow temperature. In this regard, the melting temperature of the metal or other thermally conductive material 18 in the trench 20 may be above that of the reflow temperature of the electrical/thermal insulation material.
The thermal bus 16 may alternatively be provided as a blanket of the thermally conductive material 18 deposited as a layer adjacent to substantially the whole of the substrate 12. This embodiment advantageously facilitates any subsequent polishing steps.
Modification of relatively low thermal conductivity substrates 12 in accordance with the disclosed exemplary embodiments are believed to improve heat dissipation properties. Furthermore, it is believed that such modified substrates should have heat dissipation characteristics so as to be usable in place of conventional substrates made of silicon and alumina for micro-fluid ejection applications such as inkjet printheads.
For example, with reference to
As will be noted, the head having the silicon substrate (
In
To the contrary, the LTCC substrate modified in accordance with the disclosed exemplary embodiments has a modeled thermal profile which closely resembles that of the silicon substrate illustrated in
The micro-fluid ejection heads modeled in the temperature profiles of
The structures associated with the graphs for
To provide the results depicted in the graphs of
It is contemplated, and will be apparent to those skilled in the art from the preceding description and the accompanying drawings that modifications and/or changes may be made in the embodiments of the disclosure. Accordingly, it is expressly intended that the foregoing description and the accompanying drawings are illustrative of exemplary embodiments only, not limiting thereto, and that the true spirit and scope of the present invention(s) be determined by reference to the appended claims.
