Abstract:
A fluid ejection head assembly having improved assembly characteristics and methods of manufacturing a fluid ejection head assembly. The fluid ejection head includes a fluid supply body having at least one fluid supply port in a recessed area therein and a semiconductor chip attached in the recessed area of the fluid supply body adjacent the fluid supply port using a thermal cure adhesive. A compression prevention body having a coefficient of thermal expansion ranging from about 1.0 to less than about 30 microns/meter per ° C. disposed adjacent to the fluid supply port of the fluid supply body and the semiconductor chip.

Description:
TECHNICAL FIELD 
     The disclosure relates to fluid ejection head structures and in particular to an apparatus and method that are effective for improving the manufacture of fluid ejection devices. 
     BACKGROUND AND SUMMARY 
     Fluid ejection heads for fluid ejection devices such as ink jet printers, vapor evaporation devices, and the like continue to be improved as the technology for making the ejection heads continues to advance. New techniques are constantly being developed to provide low cost, highly reliable fluid ejection head structures that can be manufactured in high volume with high yield having relatively low amount of spoilage or ejection head damage. 
     In order to increase ejection head speed and volume output, larger ejection heads having an increased number of ejection actuators are being developed. However, as the ejection head size and number of ejection actuators increases, manufacturing apparatus and techniques are required to meet increased tolerance demands for such ejection heads. Slight variations in tolerances of parts may have a significant impact on the operation and yield of suitable ejection head products. 
     The primary components of the fluid ejection head are a substrate or chip containing fluid ejector actuators, and a nozzle plate attached to the chip. The chip is typically made of silicon and contains various passivation layers, conductive metal layers, resistive layers, insulative layers and protective layers deposited on a device surface thereof. For thermal fluid ejection heads, individual heaters are defined in the resistive layers and each heater resistor corresponds to a nozzle hole in the nozzle plate for heating and ejecting fluid from the ejection head toward a target media. Fluid ejection heads may also include bubble pump type ejection head. In a top-shooter type ejection head, nozzle plates are attached to the chips and there are fluid chambers and fluid feed channels for directing fluid to each of the heaters or bubble pumps on the chip either formed in the nozzle plate material or in a separate thick film layer. In a center feed design for a top-shooter type ejection head, fluid is supplied to the channels and chambers from a slot or via that is conventionally formed by chemically etching or grit blasting through the thickness of the chip. The chip containing the nozzle plate is typically bonded to a thermoplastic body using a heat curable adhesive to provide a fluid ejection head structure. 
     The thermal cure process locks the components together at an elevated temperature. The heater chip has a relatively low CTE (coefficient of thermal expansion) while the plastic body has a relatively high CTE. Heating the components causes each one to expand according to their respective CTEs. As the parts cool and shrink, the higher CTE plastic body shrinks more than the lower CTE silicon heater chip resulting in thermal stresses on the chip. The force-deflection (spring rate) characteristics of the chip and body determine the equilibrium deflection of each part. In many cases the plastic body spring rate dominates the chip spring rate causing via compression and nozzle plate bowing. Nozzle plate bowing may result in poor drop placement or nozzle plate structural failure. 
     In order to address the issues related to thermal compression of the chip as the chip and plastic body cool, ceramic substrates have been attached to the chip. However, ceramic substrates substantially increase the cost of the ejection head. Silicon bridges in a via area of the chip have also been used, but such silicon bridges result in fluid flow problems in the chip via area. 
     It is believed that a predominant contributor of chip distortion, cracking, and nozzle plate damage is the coefficient of thermal expansion mismatch between the chip and the thermoplastic body. During manufacturing, when the chip and body go through the adhesive cure cycle, chip distortion is introduced as the components cool. Accordingly, there continues to be a need for improved manufacturing processes and techniques which provide improved ejection head components and structures without product loss due to chip cracking or nozzle plate damage. 
     With regard to the above, there is provided a fluid ejection head assembly having improved assembly characteristics and methods of manufacturing a fluid ejection head assembly. The fluid ejection head includes a fluid supply body having at least one fluid supply port in a recessed area therein and a semiconductor chip attached in the recessed area of the fluid supply body adjacent the fluid supply port using a thermal cure adhesive. A compression prevention body having a coefficient of thermal expansion ranging from about 1.0 to less than about 30 microns/meter per ° C. disposed adjacent to the fluid supply port of the fluid supply body and the semiconductor chip. 
     In another embodiment, there is provided a method for reducing compressive forces on a semiconductor chip of a fluid ejection head during a thermal cure process for attaching the semiconductor chip to a fluid supply body. The method includes providing a fluid supply port in a recessed area of the fluid supply body. A compression prevention body is disposed adjacent to the fluid supply port of the fluid supply body and the semiconductor chip, wherein the compression prevention body has a coefficient of thermal expansion ranging from about 1.0 to less than about 30 microns/meter per ° C. A semiconductor chip is attached in the recessed area of the fluid supply body adjacent the fluid supply port using a thermal cure adhesive. The adhesive is thermally cured to fixedly attach the semiconductor chip in the recessed area of the fluid supply body. 
     In a further embodiment, there is provided a method for reducing via distortion in a semiconductor chip of a fluid ejection head during a thermal cure process for attaching the semiconductor chip to a fluid supply body. The method includes providing a fluid supply port in a recessed area of the fluid supply body. A spherical body is disposed adjacent to the fluid supply port of the fluid supply body and the semiconductor chip, wherein the spherical body has a coefficient of thermal expansion ranging from about 1.0 to less than about 30 microns/meter per ° C. A semiconductor chip is attached in the recessed area of the fluid supply body adjacent the fluid supply port using a thermal cure adhesive. The adhesive is thermally cured to fixedly attach the semiconductor chip in the recessed area of the fluid supply body. 
     In some embodiments, the compression prevention body has a shape selected from a sphere, a rectangular cube, and a cylinder. In one embodiment, the compression prevention body is a spherical body having a diameter ranging from about 2.0 to about 3.5 millimeters. 
     In some embodiments, the compression prevention body is made of a material selected from silicon, glass, alumina, stainless steel, or a low CTE polymeric material. 
     In some embodiments, the compression prevention body has a coefficient of thermal expansion of less than about half a coefficient of thermal expansion of the fluid supply body. 
     In some embodiments, the fluid ejection head assembly is a micro-fluid ejection head attached to a fluid supply body wherein the fluid ejection head assembly further includes a compression prevention body. 
     For the purposes of this disclosure, the term “fluid ejection head assembly” means, at least, a combination of cartridge body, compression prevention body, and semiconductor chip. 
     An advantage of the foregoing structures and methods is that after the adhesive is cured and the parts have cooled, the fluid supply body compresses on the compression prevention body and the chip simultaneously rather than only on the chip. Since the compression prevention body has a spring rate much greater than that of the semiconductor chip in the areas where the chip may be deflected, the deflection of the chip is significantly reduced so that compression of the via in the chip is reduced. Likewise, the compression of the nozzle plate attached to the chip will also be significantly reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages of the disclosure may be apparent by reference to the detailed description of preferred embodiments when considered in conjunction with the following drawings, in which like reference numbers denote like elements throughout the several views, wherein features have been exaggerated for ease of understanding and are not intended to be illustrative of relative thicknesses of the features, and wherein: 
         FIG. 1  is a perspective view, not to scale, of prior art fluid supply cartridge containing a fluid ejection head. 
         FIG. 2A  is a bottom view, not to scale, of a nose section of the prior art fluid supply cartridge of  FIG. 1  showing a semiconductor chip and nozzle plate attached thereto. 
         FIG. 2B  is a partial cross-sectional view, not to scale, of the nose section of  FIG. 2A  showing a fluid supply via in the cartridge body and fluid via in the semiconductor chip. 
         FIG. 2C  is a partial top view, not to scale, of the nose section of the prior art fluid supply cartridge of  FIG. 2A  showing a fluid supply side of the chip. 
         FIG. 2D  is a partial lengthwise sectional view, not to scale, of the nose section of the prior art fluid supply cartridge of  FIG. 2A  with the chip removed. 
         FIG. 2E  is a partial bottom view, not to scale, of the nose section of the prior art fluid supply cartridge of  FIG. 2A  with the semiconductor chip attached to the nose section. 
         FIG. 3A  is a schematic illustration of the total compressive forces on a semiconductor chip attached to the nose section of the prior art fluid supply cartridge of  FIG. 2A . 
         FIG. 3B  is a schematic illustration of a total force P over a length l for use in determining a maximum deflection for a via in a semiconductor chip according to a beam equation with fixed ends. 
         FIG. 4A  is a partial top view, not to scale, of the nose section of a fluid supply cartridge according to an embodiment of the disclosure. 
         FIG. 4B  is a partial lengthwise sectional view, not to scale, of the nose section of the fluid supply cartridge of  FIG. 4A . 
         FIG. 4C  is a partial bottom view, not to scale, of the nose section of the fluid supply cartridge of  FIG. 4A  with the semiconductor chip removed. 
         FIG. 4D  is a partial cross-sectional view, not to scale, of the nose section of  FIG. 4A  showing a fluid supply via in the cartridge body and fluid via in the semiconductor chip and a compression prevention body disposed adjacent the fluid supply via of the cartridge body. 
         FIG. 5A  is a partial top view, not to scale, of the nose section of a fluid supply cartridge according to another embodiment of the disclosure. 
         FIG. 5B  is a partial lengthwise sectional view, not to scale, of the nose section of the fluid supply cartridge of  FIG. 5A . 
         FIG. 5C  is a partial bottom view, not to scale, of the nose section of the fluid supply cartridge of  FIG. 5A  with the semiconductor chip removed. 
         FIG. 5D  is a partial cross-sectional view, not to scale, of the nose section of  FIG. 5A  showing a fluid supply via in the cartridge body and fluid via in the semiconductor chip. 
         FIG. 6  is a schematic illustration of the compressive forces on a semiconductor chip attached to the nose section of a fluid supply cartridge of when a compression prevention body is used. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A prior art fluid ejection cartridge  10  is illustrated in  FIGS. 1 and 2 . The fluid ejection cartridge  10  includes a thermoplastic body  12  having a nose section  14  that contains a fluid ejection head  16 . The fluid ejection head  16  includes a nozzle plate  18  attached to a semiconductor chip  20 . Details of the fluid ejection head  16  components are well known in the art and thus are not reproduced here. A flexible circuit  22  is attached to the semiconductor chip  20  and body  12  to provide power and control of fluid ejection from the ejection head  16 . 
     The body  12  may be made of a polymeric material, such as amorphous thermoplastic polyetherimide materials, glass filled thermoplastic polyethylene terephthalate resin materials, glass-filled polyamide, syndiotactic polystyrene containing glass fiber, polyphenylene ether/polystyrene alloy resins, and polyamide/polyphenylene ether alloy resins. A particularly suitable material for making the body  10  is glass-filled polyphenylene ether/polystyrene alloy resins and polyamide/polyphenylene ether alloy resins. A body  12  made from the foregoing polyphenylene ether resins has a coefficient of thermal expansion (CTE) ranging from about 30 to 75 microns/meter per ° C. as determined by ASTM E-831. By contrast, the substrate  12  may have a CTE of about 2 to about 3 microns/meter per ° C. as determined by ASTM C-372. 
     A bottom plan view of the nose section  14  of the fluid ejection cartridge  10  is shown in  FIG. 2A . An enlarged, partial cross sectional view of a fluid flow area of the body  12  is shown in  FIG. 2B . The body  12  includes a fluid supply port  24  in the nose section  14  thereof for providing fluid from a fluid reservoir in the body  12  to the ejection head  16 . 
     An inside view of the nose section  14  of the ejection fluid cartridge  10  is shown in  FIG. 2C  and an outside view of the nose section  14  with the ejection head  16  removed is shown in  FIG. 2D . A lengthwise, partial cross-section view of the nose section  14  is shown in  FIG. 2E . The foregoing views show the amount of body material surrounding the ejection head  16 . 
     As described above, the ejection head  16  includes a nozzle plate  18  attached to a semiconductor chip  20 . The semiconductor chip  20  portion of the fluid ejection head  16  may be made of semiconductor or ceramic materials and are fragile compared to the material of the body  12 . Accordingly, care must be taken to assure that the semiconductor chips  20  and nozzle plates  18  are not damaged during assembly of the fluid ejection heads  16 . The semiconductor chip  20  of the fluid ejection head  16  is relatively small and may have a length (L) of from about 7 to about 100 millimeters by from about 2.5 to about 10 millimeters in width (W) by from about 200 to about 800 microns in thickness (T). The semiconductor chip  20  includes one or more fluid feed vias  26  therein defined by etching through the thickness T of the semiconductor chip  20 , for supplying fluid from the body  12  to ejection actuators on a device surface of the semiconductor chip  20 . 
     The ejection head  16  is attached using a thermally curable adhesive (not shown) in a chip pocket area  28  of the nose section  14  of the fluid ejection cartridge  10 . The adhesive fixedly attaches the ejection head  16  in the chip pocket area  28  of the nose section  14 . The adhesive may be a thermally curable die bond adhesive such as an epoxy adhesive. The thickness of adhesive bond line in the chip pocket  28  between the semiconductor chip  20  and the body  12  may range from about 25 microns to about 150 microns. Heat is typically required to cure the adhesive and fixedly attach the ejection head  16  to the body  12  in the chip pocket  28 . The adhesive provides a complete seal between the fluid supply side of the semiconductor chip  20  and the body  12  and is dispensed in the chip pocket  28  prior to attaching the chip  20  in the chip pocket  28 . During chip placement, the adhesive will be displaced along the sides of the chip  20  and may protect electrical leads from corrosion from the fluid supply side of the chip  20 . An end cap adhesive is dispensed after the chip  20  is in place to complete the encapsulation of the electrical contacts and leads in order to protect the leads from corrosion. 
     During a procedure for attaching the ejection head  16  to the body  12 , there may be a cure cycle temperature change of approximately 60° C. Such a temperature change may cause thermal expansion of the ejection head  16  and the body  12 , and the expanded head  16  and body  12  are locked in place by the adhesive. Since the body  12  has an order of magnitude higher thermal expansion coefficient than the ejection head  16 , shrinkage in the body  12  during a cooling cycle may be substantially greater than shrinkage of the ejection head  16  causing thermal stresses as the body and head attempt to return to their original unexpanded state. The higher shrinkage of the body  12  causes a compressive force on the semiconductor chip  20  of the ejection head  16  as shown schematically in  FIG. 3A . The compressive forces (CF) may cause chip bowing and compression of the fluid feed via  26  along the length of the chip  20 . Beam geometry for compressive forces acting on the chip  20  during the cooling cycle is shown schematically in  FIG. 3B . 
     A beam equation for beam geometry having fixed ends and uniform loading as illustrated in  FIG. 3B  is as follows: 
               Max   ⁢           ⁢   y     =         -   P     ×     l   3         384   ×   E   ×   I             
wherein y is the maximum single side deflection of the fluid feed via  26  in chip  20 , E is a modulus of elasticity for a silicon chip, l is the via length, b the thickness of the silicon chip, h is a width of the area from a side edge of the chip to the via, P is a compressive load over the length l resulting from CTE mismatch, and I=(b×h 3 )/12 is the area moment of inertia.
 
     In one embodiment of the disclosure, shown in  FIGS. 4A to 4D , a compression prevention body  30  in the shape of a sphere is adhesively attached or press fit to the body  12  in the fluid supply port  24  thereof. A partial top view of the cartridge body  12  is shown in  FIG. 4A  and a partial lengthwise view of a portion of the cartridge body  12  is shown in  FIG. 4B  showing the placement of the compression prevention body  30  within a filter tower riser  32  of the cartridge body. A partial body view of the cartridge body  12  with the ejection head  16  removed is shown in  FIG. 4C  showing placement of the compression prevention body  30  therein. As shown in  FIG. 4D , the compression prevention body  30  has a size that is effective to reduce compression of the cartridge body  12  on the fluid ejection head  16  as the cartridge body  12  cools. In that regard, the compression prevention body  30  may have a dimension that is substantially the same as an overall width of the semiconductor chip  20 . In the case of a spherical compression prevention body  30 , the diameter of the body  30  may range from about 1.5 to about 5 millimeters, such as from about 2.5 to about 3.5 millimeters in diameter. 
     In  FIGS. 4A to 4D , the compression prevention body  30  is inserted into the cartridge body  12  from the fluid fed side or inside of the cartridge body  12 . In an embodiment illustrated in  FIGS. 5A-5D , a compression prevention body  34  that has a diameter smaller than the width (W) of the semiconductor chip  20  may be inserted into the fluid flow path  24  of the cartridge body  12  through the chip pocket  28  before the ejection head  16  is attached to the cartridge body  12 . 
     In other embodiments, the compression prevention body may have a cylindrical shape or a rectangular cubical shape. However, a spherical shape may be the most cost effective since the orientation of the compression prevention body in the cartridge body  12  is unimportant when the compression prevention body has a spherical shape. For example, a cubical compression prevention body may provide a greater area for resisting compressive forces against the chip, however, it may be difficult to properly orient a cubical compression prevention body within the fluid supply port  24 . 
     Regardless of the shape of the compression prevention body  30  or  34 , it is highly desirable that the compression prevention body  30  or  34  have a coefficient of thermal expansion similar to a coefficient of thermal expansion of semiconductor chip  20 . Accordingly, materials that may be used for the compression prevention body  30  or  34  may be selected from but are not limited to silicon, glass such as borosilicate glass and soda-lime glass, alumina, stainless steel, and a low CTE polymeric material. The coefficient of thermal expansion of the compression prevention body  30  or  34  may range from about 1.0 to less than about 30 microns/meter per ° C., such from about 1.5 to less than about 25 microns/meter per ° C. or from about 2.0 to less than about 18 microns/meter per ° C. 
     Another important characteristic of the compression prevention body  30  or  34  is that the compression prevention body has a spring rate that is based on the modulus of the material and the geometry of the compression prevention body. The spring rate of the compression prevention body is substantially greater than the spring rate of the semiconductor chip  20  in the areas where the chip  20  may be deflected. While not desiring to be bound by theoretical considerations, it is believed that the spring rate of the compression prevention body must also be much stiffer than spring rate of the cartridge body  12  at the point of placement of the compression prevention body in the cartridge body  12 . 
     As shown in  FIGS. 4D and 5D  the ejection head  16  is adhesively attached to the cartridge body  12  and thus any compression of the body  12  during a cooling cycle will tend to compress the fluid feed via  26  in the semiconductor chip  20 . However, with the compression prevention body  30  or  34  in place in the fluid supply port  24 , the compression of the body  12  on the semiconductor chip  20  is substantially reduced according to the above beam equation. Since the coefficient of thermal expansion of the body  12  is much greater than that of the compression prevention body  30  or  34  and the semiconductor chip  20 , the body compresses on both the chip  20  and the compression prevention body  30  or  34 . The spring rate of the compression prevention body  30  is much greater than that of the chip  20  providing a modified beam geometry structure of the combination of body  30  or  34  and chip  20  as illustrated in  FIG. 6  according to  FIG. 3B . 
     As shown in  FIG. 6 , the beam length l and P are reduced by about 50% thereby reducing the maximum deflection in the fluid feed via  26  by about 1/16th according to the above beam equation assuming the body  30  or  34  and chip  20  have the same coefficient of thermal expansion. However, even if the body  30  or  34  and chip  20  have slightly dissimilar coefficients of thermal expansion, the two parts will pick up the compression load on the fluid feed via  26  in parallel. Thus the compression of the fluid feed via  26  is minimized by use of the compression prevention body  30  or  34 . In practice, the deflection reduction of the fluid feed via  26  may be less due to part tolerances, surrounding part geometry, and material properties variations of the parts. Also, the fluid feed via  26  between the compression prevention body  30  or  34  and the end of the chip  20  will have some via compression. Accordingly, more than one compression prevention body  30  or  34  may be used along the length of the fluid feed via  26  to support the compression forces and thereby further reduce compression of the via  26 . 
     While the disclosure has been described in terms of exemplary embodiments, those skilled in the art will recognize that the disclosure can be practiced with modifications in the spirit and scope of the appended claims. The examples are merely illustrative and are not meant to be an exhaustive list of all possible designs, embodiments, applications or modifications of the disclosure. 
     The patentees do not intend to dedicate any disclosed embodiments to the public, and to the extent any disclosed modifications or alterations may not literally fall within the scope of the claims, they are considered to be part hereof under the doctrine of equivalents.