Method for aligning a substrate with respect to orifices in an inkjet printhead

In a printhead according to the preferred embodiment of the invention, a polymer tape having orifices formed therein and containing conductive traces is provided with one or more windows exposing ends of the conductive traces. A separate substrate contains heating elements and electrodes. A conventional, commercially available automatic inner lead bonder is then used to automatically align the orifices to the heating elements. The automatic alignment of the orifices and heating elements also inherently aligns the electrodes on the substrate with the exposed ends of the traces. The wire bonder is then used to bond the traces to the associated substrate electrodes through the window.

CROSS-REFERENCE TO RELATED APPLICATIONS 
This application relates to the subject matter disclosed in the following 
U.S. Pat. and co-pending U.S. applications: 
U.S. Pat. No. 4,926,197 to Childers, entitled "Plastic Substrate for 
Thermal Ink Jet Printer;" 
U.S. application Ser. No. 07/568,000, filed Aug. 16, 1990, entitled 
"Photo-Ablated Components for Inkjet Printheads;" 
U.S. application Ser. No. 07,862,668, filed herewith, entitled "Integrated 
Nozzle Member and TAB Circuit for Inkjet Printhead;" 
U.S. application Ser. No. 07/862,669, filed herewith, entitled "Nozzle 
Member Including Ink Flow Channels;" 
U.S. application Ser. No. 07/864,889, filed herewith, entitled "Laser 
Ablated Nozzle Member for Inkjet Printhead;" 
U.S. application Ser. No. 07/862,086, filed herewith, entitled "Improved 
Ink Delivery System for an Inkjet Printhead;" 
U.S. application Ser. No. 07/864,822, filed herewith, entitled "Improved 
Inkjet Printhead;" 
U.S. application Ser. No. 07/864,896, filed herewith, entitled "Adhesive 
Seal for an Inkjet Printhead;" 
U.S. application Ser. No. 07/862,667, filed herewith, entitled "Efficient 
Conductor Routing for an Inkjet Printhead;" 
U.S. application Ser. No. 07/864,890, filed herewith, entitled "Wide Inkjet 
Printhead." 
The above patent and co-pending applications are assigned to the present 
assignee and are incorporated herein by reference. 
1. Field of the Invention 
The present invention generally relates to inkjet and other types of 
printers and, more particularly, to the printhead portion of an ink 
cartridge used in such printers. 
2. Background of the Invention 
Thermal inkjet print cartridges operate by rapidly heating a small volume 
of ink to cause the ink to vaporize and be ejected through one of a 
plurality of orifices so as to print a dot of ink on a recording medium, 
such as a sheet of paper. Typically, the orifices are arranged in one or 
more linear arrays in a nozzle member. The properly sequenced ejection of 
ink from each orifice causes characters or other images to be printed upon 
the paper as the printhead is moved relative to the paper. The paper is 
typically shifted each time the printhead has moved across the paper. The 
thermal inkjet printer is fast and quiet, as only the ink strikes the 
paper. These printers produce high quality printing and can be made both 
compact and affordable. 
In one prior art design, the inkjet printhead generally includes: (1) ink 
channels to supply ink from an ink reservoir to each vaporization chamber 
proximate to an orifice; (2) a metal orifice plate or nozzle member in 
which the orifices are formed in the required pattern; and (3) a silicon 
substrate containing a series of thin film resistors, one resistor per 
vaporization chamber. 
To print a single dot of ink, an electrical current from an external power 
supply is passed through a selected thin film resistor. The resistor is 
then heated, in turn superheating a thin layer of the adjacent ink within 
a vaporization chamber, causing explosive vaporization, and, consequently, 
causing a droplet of ink to be ejected through an associated orifice onto 
the paper. 
One prior art print cartridge is disclosed in U.S. Pat. No. 4,500,895 to 
Buck et al., entitled "Disposable Inkjet Head," issued Feb. 19, 1985 and 
assigned to the present assignee. 
The prior art inkjet print cartridges include a number of drawbacks: (1) 
the metal orifice plate is expensive, difficult to form, and subject to 
corrosion; (2) the metal orifice plate is difficult to align with the 
heaters on the substrate and is difficult to affix to the substrate using 
conventional techniques; (3) the supply of ink to the vaporization 
chambers is sometimes routed through a center slot formed in the substrate 
itself, causing added manufacturing complexity and cost and increasing the 
size of the substrate; and (4) the ink seal between the back of the 
substrate and a print cartridge body is time-consuming to form. 
SUMMARY OF THE INVENTION 
The present invention is an improved inkjet printhead structure and method 
for forming the printhead which enables simple and reliable alignment of 
ink orifices in a nozzle member with the heating elements on the 
substrate, wherein this alignment also inherently aligns the external 
conductors with the electrodes on a substrate. This single alignment step 
is followed by a simple and reliable bonding step, where the substrate 
electrodes are bonded to the external conductors through a window formed 
in the nozzle member. 
In a printhead according to the preferred embodiment of the invention, a 
polymer tape having orifices formed therein and containing conductive 
traces is provided with one or more windows exposing ends of the 
conductive traces. A conventional, commercially available automatic inner 
lead bonder may then be used to automatically align the orifices in the 
nozzle member with the heating elements on a substrate. Since the orifices 
are already aligned with the conductive traces on the nozzle member, and 
the substrate electrodes are aligned with the heating elements, the 
automatic aligning of the orifices and heating elements also inherently 
aligns the electrodes on the substrate with the exposed ends of the 
traces. The inner lead bonder then uses gang bonding to bond the traces to 
the associated substrate electrodes through the windows formed in the 
tape. Thus, a very efficient alignment process is disclosed which performs 
two alignments in a single step.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, reference numeral 10 generally indicates an inkjet 
print cartridge incorporating a printhead according to one embodiment of 
the present invention. The inkjet print cartridge 10 includes an ink 
reservoir 12 and a printhead 14, where the printhead 14 is formed using 
Tape Automated Bonding (TAB). The printhead 14 (hereinafter "TAB head 
assembly 14") includes a nozzle member 16 comprising two parallel columns 
of offset holes or orifices 17 formed in a flexible polymer tape 18 by, 
for example, laser ablation. The tape 18 may be purchased commercially as 
Kapton.TM. tape, available from 3M Corporation. Other suitable tape may be 
formed of Upilex.TM. or its equivalent. 
A back surface of the tape 18 includes conductive traces 36 (shown in FIG. 
3) formed thereon using a conventional photolithographic etching and/or 
plating process. These conductive traces are terminated by large contact 
pads 20 designed to interconnect with a printer. The print cartridge 10 is 
designed to be installed in a printer so that the contact pads 20, on the 
front surface of the tape 18, contact printer electrodes providing 
externally generated energization signals to the printhead. 
In the various embodiments shown, the traces are formed on the back surface 
of the tape 18 (opposite the surface which faces the recording medium). To 
access these traces from the front surface of the tape 18, holes (vias) 
must be formed through the front surface of the tape 18 to expose the ends 
of the traces. The exposed ends of the traces are then plated with, for 
example, gold to form the contact pads 20 shown on the front surface of 
the tape 18. 
Windows 22 and 24 extend through the tape 18 and are used to facilitate 
bonding of the other ends of the conductive traces to electrodes on a 
silicon substrate containing heater resistors. The windows 22 and 24 are 
filled with an encapsulant to protect any underlying portion of the traces 
and substrate. 
In the print cartridge 10 of FIG. 1, the tape 18 is bent over the back edge 
of the print cartridge "snout" and extends approximately one half the 
length of the back wall 25 of the snout. This flap portion of the tape 18 
is needed for the routing of conductive traces which are connected to the 
substrate electrodes through the far end window 22. 
FIG. 2 shows a front view of the TAB head assembly 14 of FIG. 1 removed 
from the print cartridge 10 and prior to windows 22 and 24 in the TAB head 
assembly 14 being filled with an encapsulant. 
Affixed to the back of the TAB head assembly 14 is a silicon substrate 28 
(shown in FIG. 3) containing a plurality of individually energizable thin 
film resistors. Each resistor is located generally behind a single orifice 
17 and acts as an ohmic heater when selectively energized by one or more 
pulses applied sequentially or simultaneously to one or more of the 
contact pads 20. 
The orifices 17 and conductive traces may be of any size, number, and 
pattern, and the various figures are designed to simply and clearly show 
the features of the invention. The relative dimensions of the various 
features have been greatly adjusted for the sake of clarity. 
The orifice pattern on the tape 18 shown in FIG. 2 may be formed by a 
masking process in combination with a laser or other etching means in a 
step-and-repeat process, which would be readily understood by one of 
ordinary skilled in the art after reading this disclosure. 
FIG. 10, to be described in detail later, provides additional detail of 
this process. 
FIG. 3 shows a back surface of the TAB head assembly 14 of FIG. 2 showing 
the silicon die or substrate 28 mounted to the back of the tape 18 and 
also showing one edge of a barrier layer 30 formed on the substrate 28 
containing ink channels and vaporization chambers. FIG. 7 shows greater 
detail of this barrier layer 30 and will be discussed later. Shown along 
the edge of the barrier layer 30 are the entrances of the ink channels 32 
which receive ink from the ink reservoir 12 (FIG. 1). 
The conductive traces 36 formed on the back of the tape 18 are also shown 
in FIG. 3, where the traces 36 terminate in contact pads 20 (FIG. 2) on 
the opposite side of the tape 18. 
The windows 22 and 24 allow access to the ends of the traces 36 and the 
substrate electrodes from the other side of the tape 18 to facilitate 
bonding. 
FIG. 4 shows a side view cross-section taken along line A--A in FIG. 3 
illustrating the connection of the ends of the conductive traces 36 to the 
electrodes 40 formed on the substrate 28. As seen in FIG. 4, a portion 42 
of the barrier layer 30 is used to insulate the ends of the conductive 
traces 36 from the substrate 28. 
Also shown in FIG. 4 is a side view of the tape 18, the barrier layer 30, 
the windows 22 and 24, and the entrances of the various ink channels 32. 
Droplets 46 of ink are shown being ejected from orifice holes associated 
with each of the ink channels 32. 
FIG. 5 shows the print cartridge 10 of FIG. 1 with the TAB head assembly 14 
removed to reveal the headland pattern 50 used in providing a seal between 
the TAB head assembly 14 and the printhead body. The headland 
characteristics are exaggerated for clarity. Also shown in FIG. 5 is a 
central slot 52 in the print cartridge 10 for allowing ink from the ink 
reservoir 12 to flow to the back surface of the TAB head assembly 14. 
The headland pattern 50 formed on the print cartridge 10 is configured so 
that a bead of epoxy adhesive dispensed on the inner raised walls 54 and 
across the wall openings 55 and 56 (so as to circumscribe the substrate 
when the TAB head assembly 14 is in place) will form an ink seal between 
the body of the print cartridge 10 and the back of the TAB head assembly 
14 when the TAB head assembly 14 is pressed into place against the 
headland pattern 50. Other adhesives which may be used include hot-melt, 
silicone, UV curable adhesive, and mixtures thereof. Further, a patterned 
adhesive film may be positioned on the headland, as opposed to dispensing 
a bead of adhesive. 
When the TAB head assembly 14 of FIG. 3 is properly positioned and pressed 
down on the headland pattern 50 in FIG. 5 after the adhesive is dispensed, 
the two short ends of the substrate 28 will be supported by the surface 
portions 57 and 58 within the wall openings 55 and 56. The configuration 
of the headland pattern 50 is such that, when the substrate 28 is 
supported by the surface portions 57 and 58, the back surface of the tape 
18 will be slightly above the top of the raised walls 54 and approximately 
flush with the flat top surface 59 of the print cartridge 10. As the TAB 
head assembly 14 is pressed down onto the headland 50, the adhesive is 
squished down. From the top of the inner raised walls 54, the adhesive 
overspills into the gutter between the inner raised walls 54 and the outer 
raised wall 60 and overspills somewhat toward the slot 52. From the wall 
openings 55 and 56, the adhesive squishes inwardly in the direction of 
slot 52 and squishes outwardly toward the outer raised wall 60, which 
blocks further outward displacement of the adhesive. The outward 
displacement of the adhesive not only serves as an ink seal, but 
encapsulates the conductive traces in the vicinity of the headland 50 from 
underneath to protect the traces from ink. 
This seal formed by the adhesive circumscribing the substrate 28 will allow 
ink to flow from slot 52 and around the sides of the substrate to the 
vaporization chambers formed in the barrier layer 30, but will prevent ink 
from seeping out from under the TAB head assembly 14. Thus, this adhesive 
seal provides a strong mechanical coupling of the TAB head assembly 14 to 
the print cartridge 10, provides a fluidic seal, and provides trace 
encapsulation. The adhesive seal is also easier to cure than prior art 
seals, and it is much easier to detect leaks between the print cartridge 
body and the printhead, since the sealant line is readily observable. 
The edge feed feature, where ink flows around the sides of the substrate 
and directly into ink channels, has a number of advantages over prior art 
printhead designs which form an elongated hole or slot running lengthwise 
in the substrate to allow ink to flow into a central manifold and 
ultimately to the entrances of ink channels. One advantage is that the 
substrate can be made smaller, since a slot is not required in the 
substrate. Not only can the substrate be made narrower due to the absence 
of any elongated central hole in the substrate, but the length of the 
substrate can be shortened due to the substrate structure now being less 
prone to cracking or breaking without the central hole. This shortening of 
the substrate enables a shorter headland 50 in FIG. 5 and, hence, a 
shorter print cartridge snout. This is important when the print cartridge 
is installed in a printer which uses one or more pinch rollers below the 
snout's transport path across the paper to press the paper against the 
rotatable platen and which also uses one or more rollers (also called star 
wheels) above the transport path to maintain the paper contact around the 
platen. With a shorter print cartridge snout, the star wheels can be 
located closer to the pinch rollers to ensure better paper/roller contact 
along the transport path of the print cartridge snout. 
Additionally, by making the substrate smaller, more substrates can be 
formed per wafer, thus lowering the material cost per substrate. 
Other advantages of the edge feed feature are that manufacturing time is 
saved by not having to etch a slot in the substrate, and the substrate is 
less prone to breakage during handling. Further, the substrate is able to 
dissipate more heat, since the ink flowing across the back of the 
substrate and around the edges of the substrate acts to draw heat away 
from the back of the substrate. 
There are also a number of performance advantages to the edge feed design. 
Be eliminating the manifold as well as the slot in the substrate, the ink 
is able to flow more rapidly into the vaporization chambers, since there 
is less restriction on the ink flow. This more rapid ink flow improves the 
frequency response of the printhead, allowing higher printing rates from a 
given number of orifices. Further, the more rapid ink flow reduces 
crosstalk between nearby vaporization chambers caused by variations in ink 
flow as the heater elements in the vaporization chambers are fired. 
FIG. 6 shows a portion of the completed print cartridge 10 illustrating, by 
cross-hatching, the location of the underlying adhesive which forms the 
seal between the TAB head assembly 14 and the body of the print cartridge 
10. In FIG. 6 the adhesive is located generally between the dashed lines 
surrounding the array of orifices 17, where the outer dashed line 62 is 
slightly within the boundaries of the outer raised wall 60 in FIG. 5, and 
the inner dashed line 64 is slightly within the boundaries of the inner 
raised walls 54 in FIG. 5. The adhesive is also shown being squished 
through the wall openings 55 and 56 (FIG. 5) to encapsulate the traces 
leading to electrodes on the substrate. 
A cross-section of this seal taken along line B--B in FIG. 6 is also shown 
in FIG. 9, to be discussed later. 
FIG. 7 is a front perspective view of the silicon substrate 28 which is 
affixed to the back of the tape 18 in FIG. 2 to form the TAB head assembly 
14. 
Silicon substrate 28 has formed on it, using conventional photolithographic 
techniques, two rows of offset thin film resistors 70, shown in FIG. 7 
exposed through the vaporization chambers 72 formed in the barrier layer 
30. 
In one embodiment, the substrate 28 is approximately one-half inch long and 
contains 300 heater resistors 70, thus enabling a resolution of 600 dots 
per inch. 
Also formed on the substrate 28 are electrodes 74 for connection to the 
conductive traces 36 (shown by dashed lines) formed on the back of the 
tape 18 in FIG. 2. 
A demultiplexer 78, shown by a dashed outline in FIG. 7, is also formed on 
the substrate 28 for demultiplexing the incoming multiplexed signals 
applied to the electrodes 74 and distributing the signals to the various 
thin film resistors 70. The demultiplexer 78 enables the use of much fewer 
electrodes 74 than thin film resistors 70. Having fewer electrodes allows 
all connections to the substrate to be made from the short end portions of 
the substrate, as shown in FIG. 4, so that these connections will not 
interfere with the ink flow around the long sides of the substrate. The 
demultiplexer 78 may be any decoder for decoding encoded signals applied 
to the electrodes 74. The demultiplexer has input leads (not shown for 
simplicity) connected to the electrodes 74 and has output leads (not 
shown) connected to the various resistors 70. 
Also formed on the surface of the substrate 28 using conventional 
photolithographic techniques is the barrier layer 30, which may be a layer 
of photoresist or some other polymer, in which is formed the vaporization 
chambers 72 and ink channels 80. 
A portion 42 of the barrier layer 30 insulates the conductive traces 36 
from the underlying substrate 28, as previously discussed with respect to 
FIG. 4. 
In order to adhesively affix the top surface of the barrier layer 30 to the 
back surface of the tape 18 shown in FIG. 3, a thin adhesive layer 84, 
such as an uncured layer of poly-isoprene photoresist, is applied to the 
top surface of the barrier layer 30. A separate adhesive layer may not be 
necessary if the top of the barrier layer 30 can be otherwise made 
adhesive. The resulting substrate structure is then positioned with 
respect to the back surface of the tape 18 so as to align the resistors 70 
with the orifices formed in the tape 18. This alignment step also 
inherently aligns the electrodes 74 with the ends of the conductive traces 
36. The traces 36 are then bonded to the electrodes 74. This alignment and 
bonding process is described in more detail later with respect to FIG. 10. 
The aligned and bonded substrate/tape structure is then heated while 
applying pressure to cure the adhesive layer 84 and firmly affix the 
substrate structure to the back surface of the tape 18. 
FIG. 8 is an enlarged view of a single vaporization chamber 72, thin film 
resistor 70, and frustum shaped orifice 17 after the substrate structure 
of FIG. 7 is secured to the back of the tape 18 via the thin adhesive 
layer 84. A side edge of the substrate 28 is shown as edge 86. In 
operation, ink flows from the ink reservoir 12 in FIG. 1, around the side 
edge 86 of the substrate 28, and into the ink channel 80 and associated 
vaporization chamber 72, as shown by the arrow 88. Upon energization of 
the thin film resistor 70, a thin layer of the adjacent ink is 
superheated, causing explosive vaporization and, consequently, causing a 
droplet of ink to be ejected through the orifice 17. The vaporization 
chamber 72 is then refilled by capillary action. 
In a preferred embodiment, the barrier layer 30 is approximately 1 mils 
thick, the substrate 28 is approximately 20 mils thick, and the tape 18 is 
approximately 2 mils thick. 
Shown in FIG. 9 is a side elevational view cross-section taken along line 
B--B in FIG. 6 showing a portion of the adhesive seal 90 surrounding the 
substrate 28 and showing the substrate 28 being adhesively secured to a 
central portion of the tape 18 by the thin adhesive layer 84 on the top 
surface of the barrier layer 30 containing the ink channels and 
vaporization chambers 92 and 94. A portion of the plastic body of the 
printhead cartridge 10, including raised walls 54 shown in FIG. 5, is also 
shown. Thin film resistors 96 and 98 are shown within the vaporization 
chambers 92 and 94, respectively. 
FIG. 9 also illustrates how ink 99 from the ink reservoir 1 flows through 
the central slot 52 formed in the print cartridge 10 and flows around the 
edges of the substrate 28 into the vaporization chambers 92 and 94. When 
the resistors 96 and 98 are energized, the ink within the vaporization 
chambers 92 and 94 are ejected, as illustrated by the emitted drops of ink 
101 and 102. 
In another embodiment, the ink reservoir contains two separate ink sources, 
each containing a different color of ink. In this alternative embodiment, 
the central slot 52 in FIG. 9 is bisected, as shown by the dashed line 
103, so that each side of the central slot 52 communicates with a separate 
ink source. Therefore, the left linear array of vaporization chambers can 
be made to eject one color of ink, while the right linear array of 
vaporization chambers can be made to eject a different color of ink. This 
concept can even be used to create a four color printhead, where a 
different ink reservoir feeds ink to ink channels along each of the four 
sides of the substrate. Thus, instead of the two-edge feed design 
discussed above, a four-edge design would be used, preferably using a 
square substrate for symmetry. 
FIG. 10 illustrates one method for forming the preferred embodiment of the 
TAB head assembly 14 in FIG. 3. 
The starting material is a Kapton.TM. or Upilex.TM.-type polymer tape 104, 
although the tape 104 can be any suitable polymer film which is acceptable 
for use in the below-described procedure. Some such films may comprise 
teflon, polyimide, polymethylmethacrylate, polycarbonate, polyester, 
polyamide polyethylene-terephthalate or mixtures thereof. 
The tape 104 is typically provided in long strips on a reel 105. Sprocket 
holes 106 along the sides of the tape 104 are used to accurately and 
securely transport the tape 104. Alternately, the sprocket holes 106 may 
be omitted and the tape may be transported with other types of fixtures. 
In the preferred embodiment, the tape 104 is already provided with 
conductive copper traces 36, such as shown in FIG. 3, formed thereon using 
conventional metal deposition and photolithographic processes. The 
particular pattern of conductive traces depends on the manner in which it 
is desired to distribute electrical signals to the electrodes formed on 
silicon dies, which are subsequently mounted on the tape 104. 
In the preferred process, the tape 104 is transported to a laser processing 
chamber and laser-ablated in a pattern defined by one or more masks 108 
using laser radiation, such as that generated by an Excimer laser 112 of 
the F.sub.2, ArF, KrCl, KrF, or XeCl type. The masked laser radiation is 
designated by arrows 114. 
In a preferred embodiment, such masks 108 define all of the ablated 
features for an extended area of the tape 104, for example encompassing 
multiple orifices in the case of an orifice pattern mask 108, and multiple 
vaporization chambers in the case of a vaporization chamber pattern mask 
108. Alternatively, patterns such as the orifice pattern, the vaporization 
chamber pattern, or other patterns may be placed side by side on a common 
mask substrate which is substantially larger than the laser beam. Then 
such patterns may be moved sequentially into the beam. The masking 
material used in such masks will preferably be highly reflecting at the 
laser wavelength, consisting of, for example, a multilayer dielectric or a 
metal such as aluminum. 
The orifice pattern defined by the one or more masks 108 may be that 
generally shown in FIG. 2. Multiple masks 108 may be used to form a 
stepped orifice taper as shown in FIG. 8. 
In one embodiment, a separate mask 108 defines the pattern of windows 22 
and 24 shown in FIGS. 2 and 3; however, in the preferred embodiment, the 
windows 22 and 24 are formed using conventional photolithographic methods 
prior to the tape 104 being subjected to the processes shown in FIG. 10. 
In an alternative embodiment of a nozzle member, where the nozzle member 
also includes vaporization chambers, one or more masks 108 would be used 
to form the orifices and another mask 108 and laser energy level (and/or 
number of laser shots) would be used to define the vaporization chambers, 
ink channels, and manifolds which are formed through a portion of the 
thickness of the tape 104. 
The laser system for this process generally includes beam delivery optics, 
alignment optics, a high precision and high speed mask shuttle system, and 
a processing chamber including a mechanism for handling and positioning 
the tape 104. In the preferred embodiment, the laser system uses a 
projection mask configuration wherein a precision lens 115 interposed 
between the mask 108 and the tape 104 projects the Excimer laser light 
onto the tape 104 in the image of the pattern defined on the mask 108. 
The masked laser radiation exiting from lens 115 is represented by arrows 
116. 
Such a projection mask configuration is advantageous for high precision 
orifice dimensions, because the mask is physically remote from the nozzle 
member. Soot is naturally formed and ejected in the ablation process, 
traveling distances of about one centimeter from the nozzle member being 
ablated. If the mask were in contact with the nozzle member, or in 
proximity to it, soot buildup on the mask would tend to distort ablated 
features and reduce their dimensional accuracy. In the preferred 
embodiment, the projection lens is more than two centimeters from the 
nozzle member being ablated, thereby avoiding the buildup of any soot on 
it or on the mask. 
Ablation is well known to produce features with tapered walls, tapered so 
that the diameter of an orifice is larger at the surface onto which the 
laser is incident, and smaller at the exit surface. The taper angle varies 
significantly with variations in the optical energy density incident on 
the nozzle member for energy densities less than about two joules per 
square centimeter. If the energy density were uncontrolled, the orifices 
produced would vary significantly in taper angle, resulting in substantial 
variations in exit orifice diameter. Such variations would produce 
deleterious variations in ejected ink drop volume and velocity, reducing 
print quality. In the preferred embodiment, the optical energy of the 
ablating laser beam is precisely monitored and controlled to achieve a 
consistent taper angle, and thereby a reproducible exit diameter. In 
addition to the print quality benefits resulting from the constant orifice 
exit diameter, a taper is beneficial to the operation of the orifices, 
since the taper acts to increase the discharge speed and provide a more 
focused ejection of ink, as well as provide other advantages. The taper 
may be in the range of 5 to 15 degrees relative to the axis of the 
orifice. The preferred embodiment process described herein allows rapid 
and precise fabrication without a need to rock the laser beam relative to 
the nozzle member. It produces accurate exit diameters even though the 
laser beam is incident on the entrance surface rather than the exit 
surface of the nozzle member. 
After the step of laser-ablation, the polymer tape 104 is stepped, and the 
process is repeated. This is referred to as a step-and-repeat process. The 
total processing time required for forming a single pattern on the tape 
104 may be on the order of a few seconds. As mentioned above, a single 
mask pattern may encompass an extended group of ablated features to reduce 
the processing time per nozzle member. 
Laser ablation processes have distinct advantages over other forms of laser 
drilling for the formation of precision orifices, vaporization chambers, 
and ink channels. In laser ablation, short pulses of intense ultraviolet 
light are absorbed in a thin surface layer of material within about 1 
micrometer or less of the surface. Preferred pulse energies are greater 
than about 100 millijoules per square centimeter and pulse durations are 
shorter than about 1 microsecond. Under these conditions, the intense 
ultraviolet light photodissociates the chemical bonds in the material. 
Furthermore, the absorbed ultraviolet energy is concentrated in such a 
small volume of material that it rapidly heats the dissociated fragments 
and ejects them away from the surface of the material. Because these 
processes occur so quickly, there is no time for heat to propagate to the 
surrounding material. As a result, the surrounding region is not melted or 
otherwise damaged, and the perimeter of ablated features can replicate the 
shape of the incident optical beam with precision on the scale of about 
one micrometer. In addition, laser ablation can also form chambers with 
substantially flat bottom surfaces which form a plane recessed into the 
layer, provided the optical energy density is constant across the region 
being ablated. The depth of such chambers is determined by the number of 
laser shots, and the power density of each. 
Laser-ablation processes also have numerous advantages as compared to 
conventional lithographic electroforming processes for forming nozzle 
members for inkjet printheads. For example, laser-ablation processes 
generally are less expensive and simpler than conventional lithographic 
electroforming processes. In addition, by using laser-ablations processes, 
polymer nozzle members can be fabricated in substantially larger sizes 
(i.e., having greater surface areas) and with nozzle geometries that are 
not practical with conventional electroforming processes. In particular, 
unique nozzle shapes can be produced by controlling exposure intensity or 
making multiple exposures with a laser beam being reoriented between each 
exposure. Examples of a variety of nozzle shapes are described in 
copending application Ser. No. 07/658726, entitled "A Process of 
Photo-Ablating at Least One Stepped Opening Extending Through a Polymer 
Material, and a Nozzle Plate Having Stepped Openings," assigned to the 
present assignee and incorporated herein by reference. Also, precise 
nozzle geometries can be formed without process controls as strict as 
those required for electroforming processes. 
Another advantage of forming nozzle members by laser-ablating a polymer 
material is that the orifices or nozzles can be easily fabricated with 
various ratios of nozzle length (L) to nozzle diameter (D). In the 
preferred embodiment, the L/D ratio exceeds unity. One advantage of 
extending a nozzle's length relative to its diameter is that 
orifice-resistor positioning in a vaporization chamber becomes less 
critical. 
In use, laser-ablated polymer nozzle members for inkjet printers have 
characteristics that are superior to conventional electroformed orifice 
plates. For example, laser-ablated polymer nozzle members are highly 
resistant to corrosion by water-based printing inks and are generally 
hydrophobic. Further, laser-ablated polymer nozzle members have a 
relatively low elastic modulus, so built-in stress between the nozzle 
member and an underlying substrate or barrier layer has less of a tendency 
to cause nozzle member-to-barrier layer delamination. Still further, 
laser-ablated polymer nozzle members can be readily fixed to, or formed 
with, a polymer substrate. 
Although an Excimer laser is used in the preferred embodiments, other 
ultraviolet light sources with substantially the same optical wavelength 
and energy density may be used to accomplish the ablation process. 
Preferably, the wavelength of such an ultraviolet light source will lie in 
the 150 nm to 400 nm range to allow high absorption in the tape to be 
ablated. Furthermore, the energy density should be greater than about 100 
millijoules per square centimeter with a pulse length shorter than about 1 
microsecond to achieve rapid ejection of ablated material with essentially 
no heating of the surrounding remaining material. 
As will be understood by those of ordinary skill in the art, numerous other 
processes for forming a pattern on the tape 104 may also be used. Other 
such processes include chemical etching, stamping, reactive ion etching, 
ion beam milling, and molding or casting on a photodefined pattern. 
A next step in the process is a cleaning step wherein the laser ablated 
portion of the tape 104 is positioned under a cleaning station 117. At the 
cleaning station 117, debris from the laser ablation is removed according 
to standard industry practice. 
The tape 104 is then stepped to the next station, which is an optical 
alignment station 118 incorporated in a conventional automatic TAB bonder, 
such as an inner lead bonder commercially available from Shinkawa 
Corporation, model number IL-20. The bonder is preprogrammed with an 
alignment (target) pattern on the nozzle member, created in the same 
manner and/or step as used to create the orifices, and a target pattern on 
the substrate, created in the same manner and/or step used to create the 
resistors. In the preferred embodiment, the nozzle member material is 
semi-transparent so that the target pattern on the substrate may be viewed 
through the nozzle member. The bonder then automatically positions the 
silicon dies 120 with respect to the nozzle members so as to align the two 
target patterns. Such an alignment feature exists in the Shinkawa TAB 
bonder. This automatic alignment of the nozzle member target pattern with 
the substrate target pattern not only precisely aligns the orifices with 
the resistors but also inherently aligns the electrodes on the dies 120 
with the ends of the conductive traces formed in the tape 104, since the 
traces and the orifices are aligned in the tape 104, and the substrate 
electrodes and the heating resistors are aligned on the substrate. 
Therefore, all patterns on the tape 104 and on the silicon dies 120 will 
be aligned with respect to one another once the two target patterns are 
aligned. 
Thus, the alignment of the silicon dies 120 with respect to the tape 104 is 
performed automatically using only commercially available equipment. By 
integrating the conductive traces with the nozzle member, such an 
alignment feature is possible. Such integration not only reduces the 
assembly cost of the printhead but reduces the printhead material cost as 
well. 
The automatic TAB bonder then uses a gang bonding method to press the ends 
of the conductive traces down onto the associated substrate electrodes 
through the windows formed in the tape 104. The bonder then applies heat, 
such as by using thermocompression bonding, to weld the ends of the traces 
to the associated electrodes. A side view of one embodiment of the 
resulting structure is shown in FIG. 4. Other types of bonding can also be 
used, such as ultrasonic bonding, conductive epoxy, solder paste, or other 
well-known means. 
The tape 104 is then stepped to a heat and pressure station 122. As 
previously discussed with respect to FIG. 7, an adhesive layer 84 exists 
on the top surface of the barrier layer 30 formed on the silicon 
substrate. After the above-described bonding step, the silicon dies 120 
are then pressed down against the tape 104, and heat is applied to cure 
the adhesive layer 84 and physically bond the dies 120 to the tape 104. 
Thereafter the tape 104 steps and is optionally taken up on the take-up 
reel 124. The tape 104 may then later be cut to separate the individual 
TAB head assemblies from one another. 
The resulting TAB head assembly is then positioned on the print cartridge 
10, and the previously described adhesive seal 90 in FIG. 9 is formed to 
firmly secure the nozzle member to the print cartridge, provide an 
ink-proof seal around the substrate between the nozzle member and the ink 
reservoir, and encapsulate the traces in the vicinity of the headland so 
as to isolate the traces from the ink. 
Peripheral points on the flexible TAB head assembly are then secured to the 
plastic print cartridge 10 by a conventional melt-through type bonding 
process to cause the polymer tape 18 to remain relatively flush with the 
surface of the print cartridge 10, as shown in FIG. 1. 
The foregoing has described the principles, preferred embodiments and modes 
of operation of the present invention. However, the invention should not 
be construed as being limited to the particular embodiments discussed. As 
an example, the above-described inventions can be used in conjunction with 
inkjet printers that are not of the thermal type, as well as inkjet 
printers that are of the thermal type. Thus, the above-described 
embodiments should be regarded as illustrative rather than restrictive, 
and it should be appreciated that variations may be made in those 
embodiments by workers skilled in the art without departing from the scope 
of the present invention as defined by the following claims.