Patent Application
20080158298
This invention relates generally to the field of digitally controlled printing devices, and more particularly to encapsulation of electrical connections associated with these devices.
Encapsulation of printhead electrical connections is known, see, for example, U.S. Pat. No. 5,953,032 to Haarz et al., issued Sep. 14, 1999, entitled “Method for forming and inspecting a barrier layer of an ink jet print cartridge,” and U.S. Pat. No. 6,099,109 to Komuro, issued Aug. 8, 2000, entitled “Liquid-ejecting head and method of manufacturing the same.” However, when the encapsulation process is not performed with a sufficient degree of precision, the encapsulating material can migrate to regions of the printhead that include liquid ejection nozzles and drop forming mechanisms, for example, thermal resistor elements, resulting in reduced printhead performance and even printhead operational failure.
In attempt to control migration of the encapsulating material, U.S. Pat. No. 6,099,109 to Komuro discloses including a depression region on an orifice plate of a printhead that defines an area of encapsulation on the printhead. However, forming the depression region in the orifice plate may involve additional manufacturing steps and/or processes resulting in increased printhead fabrication costs.
U.S. Pat. No. 5,953,032 to Haarz et al. discloses a process for forming a barrier layer over one or more extending sections of a flexible circuit and one or more bond pads of a print cartridge printhead using an encapsulant material and subsequently inspecting the print cartridge to determine if the encapsulant material has been properly placed on the print cartridge. The process involves providing an inspection mark on an orifice plate of the printhead before the barrier layer is formed. After the barrier layer has been formed, an inspection is made to determine if the barrier layer extends beyond the inspection mark and contacts a second portion of the print cartridge. If it does, then the print cartridge is unacceptable. If not, then the print cartridge is acceptable. Alternatively, the location of the barrier layer may be considered unacceptable if it contacts any portion of the inspection mark even though it may not contact the second portion of the print cartridge. However, the inclusion of an inspection mark on the printhead may increase printhead fabrication costs and necessitates that each printhead be inspected to determine whether each printhead meets acceptable quality standards.
Encapsulation of electronic device components is also known. For example, U.S. Pat. No. 6,573,328 to Kropp et al., issued Jun. 3, 2003, entitled “Low temperature, fast curing silicone compositions,” discloses two methods of encapsulating a semi-conductor chip that is electrically connected to a circuit board. These methods are commonly referred to as a “glob top” application and a “dam and fill” application.
However, there is still a need to encapsulate printhead electrical connections using a technique that does not require the formation of inspection marks or depressions in the printhead or necessitate inspection of each printhead after the electrical connections of the printhead have been encapsulated.
According to one feature of the present invention, a printhead includes a printhead die and an interconnect substrate. The printhead die includes a surface. The interconnect substrate includes electrical circuitry and a surface. The electrical circuitry is in electrical communication with the printhead die through a plurality of electrical connections. An encapsulant structure is positioned to encapsulate the plurality of electrical connections, and includes a barrier portion and a filler portion. The barrier portion includes a first wall and a second wall. The first wall is in contact with the surface of the printhead die and the second wall is in contact with the surface of the interconnect substrate. The filler portion is in contact with the plurality of electrical connections and positioned between the first wall of the barrier portion and the second wall of the barrier portion.
According to another feature of the present invention, a method of manufacturing a printhead includes providing a printhead die including a surface; providing an interconnect substrate including electrical circuitry, the interconnect substrate including a surface, the electrical circuitry being in electrical communication with the printhead die through a plurality of electrical connections; and forming an encapsulant structure positioned to encapsulate the plurality of electrical connections, the encapsulant structure including a barrier portion and a filler portion, the barrier portion including a first wall and a second wall by: positioning the first wall of the barrier portion in contact with the surface of the printhead die; positioning the second wall of the barrier portion in contact with the surface of the interconnect substrate; and positioning the filler portion between the first wall of the barrier portion and the second wall of the barrier portion and in contact with the plurality of electrical connections.
In the detailed description of the preferred embodiments of the invention presented below, reference is made to the accompanying drawings, in which:
The present description will be directed in particular to elements forming part of, or cooperating more directly with, apparatus in accordance with the present invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art.
Referring to
Typically, printhead die 12 is made from a silicon material although printhead die 12 can be made from other materials. Interconnect substrate 14 can be of the type commonly referred to as “a flex circuit,” “flex tape,” or “flex,” however, other types of interconnect substrates can be used with the present invention.
An encapsulant structure 24 is positioned to encapsulate the plurality of electrical connections 22. Encapsulant structure 24 includes a barrier portion 26 and a filler portion 28. Barrier portion 26 includes a first wall 30 and a second wall 32. First wall 30 contacts surface 18 of printhead die 12 while second wall 32 contacts surface 20 of interconnect substrate 14. Filler portion 28 contacts the plurality of electrical connections 22 and is positioned between first wall 30 of barrier portion 26 and second wall 32 of barrier portion 26.
As shown in
The viscosity of the barrier portion polymer material is greater (or higher) than the viscosity of the filler portion material in the present invention. The higher viscosity barrier portion 26 material helps to prevent excessive or nonuniform flow of the material onto printhead die 12 and/or interconnect substrate 14. This is significant because excessive flow of the material onto printhead die 12 can lead to the nozzles of the printhead becoming plugged by the material. When too many nozzles become plugged, the printhead is considered defective and unusable.
The lower viscosity filler portion 28 polymer material provides acceptable penetration into and around electrical connections 22 without creating material voids or pockets of air in filler portion 28. Material voids and/or air pockets can cause excessive stress on electrical connections 22 leading to premature failure of electrical connections 22 causing the printhead to become defective and unusable.
Curing of the barrier portion and the filler portion of the encapsulant takes place at elevated temperature. As the temperature is raised, and prior to crosslinking of the two materials, both portions become somewhat more flowable. As a result, the overall shape of the encapsulant structure 24 becomes smoother with a more gradual curvature as shown in the perspective view of
By contrast,
Referring to
Circuitry 42 can include electrical leads from the region pads to which interconnections 22 are bonded to a second region (not shown) where connection pads from the printhead to the printer are located. However, other types of circuitry 42 can be encapsulated using the present invention. In the nozzle configuration shown in
Referring to
In another example embodiment of barrier portion 26, barrier portion 26 can be a prefabricated frame including, for example, first wall 30, second wall 32, and two additional walls 36 that is affixed to surface 18 of printhead die 12 and surface 20 of interconnect substrate 14. The prefabricated frame of barrier portion 26 can be affixed using conventional adhesive or after the material forming the prefabricated frame has been partially cured. Filler portion 28 is added after barrier portion 26 has been affixed to surfaces 18 and 20.
Regardless of the specific configuration of barrier portion 26, one wall, for example, first wall 30, is positioned between the plurality of electrical connections 22 and nozzles 38 arranged along an array direction 40 on printhead die 12. This helps to control the position of lower viscosity filler portion 28 material and reduce the likelihood of lower viscosity filler portion 28 material migrating toward nozzles 38. As shown in
As the edge 21 of encapsulant structure 24 of the present structure is substantially straight and has a low entry angle with respect to surface 18, the blade is able to deform uniformly in passing over the encapsulant structure, so that a good seal remains between the tip of blade 44 and the surface of the printhead 10. As a result, blade 44 is in substantially continuous contact with the printhead surface (until it leaves the printhead for the scraper) and is able to push substantially the entire puddle of ink 50 over the encapsulant structure 24 as shown in
By contrast,
Encapsulating the plurality of electrical connections 22 can be accomplished using the following manufacturing method. Printhead die 12 including surface 18 is provided. Interconnect substrate 14 including electrical circuitry 42 and surface 20 is provided. Electrical circuitry is connected in electrical communication with the printhead die through a plurality of electrical connections 22. Electrical connections 22 can be formed, for example, using a wire bonding process.
Encapsulant structure 24, positioned to encapsulate the plurality of electrical connections 22, is then formed. Encapsulant structure 24 includes a barrier portion 26 and a filler portion 28. Barrier portion 26 includes a first wall 30 and a second wall 32. First wall 30 is positioned in contact with surface 18 of printhead die 12. Second wall 32 is positioned in contact with surface 20 of interconnect substrate 14. Filler portion 28 is positioned between first wall 30 and second wall 32 in contact with the plurality of electrical connections 22. First wall 30 and second wall 32 can be formed by applying a material having a first viscosity to surface 18 of printhead die 12 and surface 20 of interconnect substrate 14. Filler portion 28 can be formed by applying a material having a second viscosity between first wall 30 and second wall 32 of barrier portion 26 and in contact with the plurality of electrical connections 22. The first viscosity material used for barrier portion 26 is greater than the second viscosity material used for filler portion 28. The second viscosity material is applied after the first viscosity material. After both materials have been applied to printhead 10, the materials are cured using a conventional curing process. Curing of the material can be accomplished by, but is not limited to, the following methods: a) thermally using ovens of various configurations and types; b) ultraviolet and/or visible light emitted from sources of various configurations and types; c) any combination of a) and b); or d) microwave radiation. Examples of material that are suitable for use in barrier portion 26 include reactive polymer systems such as epoxies, urethanes, silicones, and acrylics, plus particulate filler additives such as silica, silicates metal oxides and polymers. The purpose of the particulate fillers is to modify the viscosity and rheology of the uncured resin, as well as to modify the hardness, thermal conductivity and thermal expansion of the cured material.
Examples of material that are suitable for use in filler portion 28 include similar types of materials as are listed above for use in barrier portion 26. The difference is that a lower viscosity material is used for filler portion 28. This maybe accomplished by using different polymers (either dissimilar chemically or similar chemically but with different molecular weights), or by adding diluents, and/or by using different amounts of particulate filler additives.
Typically, barrier and filler materials are dispensed using automated dispensing systems including a reservoir to hold the material, a dispensing pump to control the flow of the material and/or extrude the material and a mechanism to move the pump over the substrate target area, although other processes can be used.
The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention.
