Patent Application
20240100851
The disclosure is directed to fluid supply cartridges for fluid ejection devices and in particular to fluid supply cartridges that provide improved dimensional stability for cartridge bodies used for ejecting a variety of fluids.
A conventional fluid cartridge body is typically constructed of one or more plastic materials to which a semiconductor ejection head chip is directly attached by means of a die bond adhesive. However, the use of solvent-based fluids in fluid ejection cartridges for inks and other commercial and industrial applications can cause the plastic materials to swell. Swelling of the plastic material of the cartridge body increases mechanical stresses on the silicon of the ejection head chip causing the chip to crack. Additionally, a mismatch of the coefficient of thermal expansion (CTE) between the plastic cartridge body and the ejection head chip causes swelling of the cartridge body during heat curing of the die bond adhesive. The resin material of the cartridge body may swell from about 3 to 5% during the die bond curing step. The swelling of the resin may cause the overall ejection head chip bow in the Y direction to a range of from −5 um to >40 um over a period of 4 weeks. Any imperfection or defects in the ejection head chip generated by deep reactive ion etching (DRIE) or dicing of the ejection head chips from a silicon wafer may provide additional stress concentration areas which can lead to ejection head chip cracking when installed on a plastic cartridge body.
Accordingly, there is a need for a dimensionally stable surface for attaching and ejection head chip thereto that has a coefficient of thermal or mechanical expansion similar to that of the silicon substrate of the ejection head chip. What is also needed is an ejection head chip bonding surface that is chemically stable for use with fluids that cause plastic materials to swell.
In view of the foregoing, the disclosure provides a fluid cartridge having a plastic fluid body, a bottom wall having a fluid supply opening therein. An insert is adhesively fastened to the bottom wall. The insert has a fluid supply slot therein corresponding to the fluid supply opening in the bottom wall, a die bond surface adjacent to the fluid supply slot for adhesively fastening an ejection head chip thereto, and a plurality of air vents adjacent to the die bond surface. The insert is a material selected from an epoxy molding compound and a ceramic material. An ejection head chip is adhesively fastened to the die bond surface of the insert.
In another embodiment, there is provided a method for eliminating mechanical stresses on an ejection head chip. The method includes providing a providing a fluid cartridge having a plastic fluid body and having a bottom wall containing a fluid supply opening therein. An insert is adhesively fastened to the bottom wall, wherein the insert has a fluid supply slot therein corresponding to the fluid supply opening in the bottom wall, a die bond surface adjacent to the fluid supply slot for adhesively attaching an ejection head chip thereto, and a plurality of air vents adjacent to the die bond surface. The insert is made of a material selected from an epoxy molding compound and a ceramic material. An ejection head chip is adhesively fastened to the die bond surface of the insert. A flexible circuit is connected to the ejection head chip.
In some embodiments, the insert is selected an injection molded insert, a dry pressed insert, and an extruded insert. In other embodiments, the insert is a stamped insert.
In some embodiments, the insert is made from a ceramic material selected from alumina powder, aluminum oxide, crystalline magnesium silicate, magnesium aluminum silicate, and zirconium oxide. In other embodiments, the insert is made from aluminum oxide. In still other embodiments, the insert is coated with an inert coating to prevent flocculation of solids from fluids ejected by the ejection head chip.
In some embodiments, the insert is made from an epoxy molding compound.
In some embodiments, the insert has a stamped chip pocket in the die bond surface for adhesively fastening the ejection head chip therein. In other embodiments, the chip pocket includes a racetrack circumscribing the fluid supply slot.
In some embodiments, the insert includes a deck area between the chip pocket and the air vents for a die bond adhesive that is effective to electrically and chemically insolate a back side of the flexible circuit from the insert and from corrosive fluids.
In some embodiments, the insert has a thickness ranging from about 1.5 to about 4 millimeters.
In some embodiments, the cartridge body includes at least two guide pins extending orthogonally from the bottom wall. In other embodiments, the insert has apertures therein corresponding to the at least two guide pins for positioning the insert on the bottom wall of the cartridge body.
In some embodiments, a flexible circuit is electrically connected to the ejection head chip.
An unexpected advantage of embodiments of the disclosure is the flatness of the ejection head chip after curing the die bond adhesive when using an insert, as described herein, between the ejection head chip and the bottom wall of the cartridge body. Without the insert, the ejection head chip may bow during curing of the die bond adhesive causing inaccurate placement of fluid droplets ejected from the ejection head. Another advantage of the disclosed embodiments is that a wider variety of fluids may be used with the fluid cartridge and ejection head without causing ejection head chip cracking due to swelling of the resin of the plastic cartridge body.
With reference to the figures,
According to an embodiment of the disclosure, an insert 24, selected from an epoxy molding compound and a ceramic material is fastened by means of a first adhesive 26 to the bottom wall 14 of the cartridge body 12. A second adhesive 28 is used to bond the flexible circuit 20 to the insert 24 while also insulating the insert from lead beams on the flexible circuit 20. The insert 24 has an overall thickness ranging from about 1.5 to about 4 mm in thickness and will typically have a thickness ranging from about 1.75 to about 2.5 mm. The length L of the insert 24 may range from about 18 to about 25 mm and the width W of the insert 24 may range from about 12 to about 14 mm A particularly suitable insert 24 is a material selected from an epoxy molding compound, such as available from Kyocera Corporation under the trade name KE-4700, and from Henkel IP & Holding GmbH under the trade name LOCTITE HYSOL GR 510, and a ceramic material selected from alumina powder, aluminum oxide, crystalline magnesium silicate, magnesium aluminum silicate, and zirconium oxide. The insert may be made by injection molding, dry pressing, or extrusion to form the insert 24. In some embodiments, the insert 24 may include an inert coating to prevent flocculation of solids from fluids ejected by the ejection head chip 18. Suitable inserts made from epoxy molding compounds preferably have a coefficient of thermal expansion (CTE) ranging from about 7 to about 9 ppm/° C. Suitable inserts made from ceramic materials may have a coefficient of thermal expansion (CTE) ranging from about 2.6 to about 10.5 ppm/° C. depending on the particular ceramic material selected.
The bottom wall 14 of the cartridge body 12 also includes at least two guide pins 30A and 30B for guiding the insert 24 into place on the bottom wall 14 of the cartridge body 12. As shown in
Another feature of the bottom wall 14 of the cartridge body 12 is the planarization pads 34A-34C that provide a substantially planar surface for the attachment of the insert 24 to the bottom wall 14 of the cartridge body 12. The planarization pads 34A-34C may be raised pads molded into the bottom wall 14 of the cartridge body 12 or machined to provide a planar surface to which the insert 24 is adhesively attached.
The first adhesive 26 used to attach the insert 24 to the bottom wall 14 of the cartridge body 12, may be a heat curable epoxy adhesive that is compatible with the resin used to make the cartridge body 12. In order to enhance adhesion between the insert 24 made of a ceramic material and the bottom wall 14, the underside 36 of the insert 24 may be cleaned and treated with water, isopropyl alcohol, or silane. The underside 36 of the insert made from ceramic may also be blasted with a high pressure stream of air or aluminum oxide to enhance adhesion. Likewise, the bottom wall 14 of the cartridge body may be coated with an adhesion enhancing coating such as a silane coating.
Once the insert 24 is adhesively attached to the bottom wall 14 of the cartridge body, the ejection head chip 18 may be adhesively attached to the insert 24 using a die bond adhesive. A conventional ejection head chip 18 is illustrated in
The flexible circuit 20, which is used to connect fluid ejectors 50 on the ejection head chip 18 with a control activation device for the fluid ejectors 50, surrounds the ejection head chip 18 and is fastened to the insert 24 using the second adhesive 28, also known as a pre-form pressure sensitive adhesive. The flexible circuit 20 includes a plurality of beams which extend therefrom and electrically connect with bond pads (not shown) on the semiconductor substrate 40 of the ejection head chip 18. After the ejection head chip 18 is placed within the chip pocket 42 and the flexible circuit 20 is attached to the ejection head chip 18, an ultraviolet (UV) photosensitive adhesive is applied along the sides of the ejection head chip 18, over the beams, as an encapsulant and protectant to prevent shorting and corrosion from fluid ejected by the ejection head chip 18. A light source is applied to the UV adhesive to cure the same. However, a portion of the UV adhesive which flows around and behind the beams is not exposed to the applied UV light source, and therefore is not cured thereby.
Once the fluid cartridge 10 is fully assembled, the fluid cartridge 10 is placed within an oven and the die bond adhesive is cured at an elevated temperature to permanently affix the ejection head chip 18 to the insert 24. During the curing process, the adhesive may produce gas which forms gas bubbles in the adhesive. Some of the gas may remain entrapped within the adhesive as residual gas bubbles after the curing process is finished. Such gas bubbles, because of the void left in the adhesive, may affect the bond strength between the ejection head chip 18 and the insert 24. Moreover, other gas bubbles may expand at the elevated cure temperature and/or join with adjacent gas bubbles to form passageways or channels within the adhesive. Such a phenomenon, known as “die bond channeling,” may result in channels which extend from the fluid supply slot 56 within the insert 24 to the ambient environment, thereby allowing fluid to leak from the fluid cartridge assembly to the ambient environment. Alternatively, in the case of a multi-fluid cartridge assembly, the channels formed in the adhesive may allow cross-contamination between the different fluids within the cartridge body 12.
Additionally, the uncured UV or thermally cured epoxy adhesive is subsequently cured and/or volatilized by the heating process used to cure the die bond adhesive. During the heat curing process, the UV and/or thermally cured epoxy adhesive may also produce gas. Because the UV and/or thermally cured epoxy adhesive placed over the beams on each side of the ejection head chip 18 has previously been cured, and the flexible circuit 20 is affixed to the insert 24 and surrounds the ejection head chip 18, gas which is produced during the heat curing process may expand (because of the increased temperature) and flow through the die bond adhesive and UV adhesive toward and into the fluid supply slot 56 within the insert 24 creating channels for leaking of fluid from the fluid supply cartridge out to the ambient environment.
Accordingly, the insert 24 is configured with at least one air vent, and preferably, a plurality of air vents adjacent to the chip pocket 58 to enable air to escape from the die bond adhesive and/or UV adhesive during the curing process. With reference again to
The grooves have dimensions corresponding to the dimensions represented by the reference letters W1, S and L1. The dimension W1 is preferably between 0.15 and 0.75 mm, and more preferably between 0.2 and 0.3 mm. The dimension S is preferably between 0.75 and 2.5 mm, and more preferably between 1 and 2 mm. The dimension L1 is preferably between 1.0 and 4.0 mm, and more preferably between 1.5 and 2.5 mm. Further, grooves 60 and 62 have a depth (substantially perpendicular to the drawing in
During the heat curing process for the die bond adhesive and/or the UV adhesive, any gas generated will flow from the lateral grooves 62 to the longitudinal grooves 60 and 72 and out to the ambient atmosphere at the edges 66 and 68 of the insert rather than flowing inward toward the fluid supply slot 56. Accordingly, air channels in the adhesive are avoided by use of the insert 24 containing the grooves 60, 62, and 72.
An advantage of having the ejection head chip 18 bonded to the insert 24 rather than to the plastic cartridge body 12 is that the insert 24 provides a mechanically stable surface for the ejection head chip 18 so that any swelling or distortion of the plastic cartridge body 12 is isolated from the ejection head chip 18. Accordingly, a wider variety of fluids may be ejected with a fluid cartridge 10 have the insert 24 as described above, including organic fluids that may cause the resin of the cartridge body 12 to swell. In some embodiments, when using an insert 24 made of a ceramic material, the insert 24 may also provide a heat sink for cooling the ejection head chip 18 during fluid ejection.
While the foregoing embodiments are directed specifically to inserts made of ceramic and epoxy molding compounds, other dimensionally stable materials, such as metals and carbon fiber reinforced polymers may be used as an insert. Such alternative materials may also be formed with vents as described above to prevent air channels from forming in the bonding adhesives during heat curing cycles.
It is noted that, as used in this specification and the appended claims, the singular forms “a,” “an,” and “the,” include plural referents unless expressly and unequivocally limited to one referent. As used herein, the term “include” and its grammatical variants are intended to be non-limiting, such that recitation of items in a list is not to the exclusion of other like items that can be substituted or added to the listed items
For the purposes of this specification and appended claims, unless otherwise indicated, all numbers expressing quantities, percentages or proportions, and other numerical values used in the specification and claims, are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by the present disclosure. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
While particular embodiments have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are or can be presently unforeseen can arise to applicants or others skilled in the art. Accordingly, the appended claims as filed and as they can be amended are intended to embrace all such alternatives, modifications variations, improvements, and substantial equivalents.
This application is a continuation-in-part of application Ser. No. 17/454,130, filed Nov. 9, 2021, now allowed.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 17454130 | Nov 2021 | US |
| Child | 18526147 | US |
