Thermal ink jet printhead and fabrication method therefor

A plurality of thermal ink jet printheads are fabricated from two substrates, at least one of which is a (100) silcon wafer. A plurality of sets of heating element arrays are formed on one substrate, together with addressing electrodes for each heating element. A thick film insulative layer is placed over the heating elements and addressing electrodes which is patterned to remove the thick film from over the individual heating elements, placing them each in a recess, and the thermal end portions of the electrodes including the contact pads therefor. A plurality of ink supplying manifold recesses are anisotropically etched in the silicon wafer and a plurality of sets of channel grooves are formed, each set of which communicate with an associated manifold. The silicon wafer and heating element substrates are aligned and bonded together, so that each channel groove contains a heating element. The individual printheads are formed by first removing unwanted silicon above each set of end portions of electrodes by a dicing operation and then dicing the heating element substrate to obtain the individual printheads. The patterned trough in the thick film insulative layer above the electrode end portions provides the spacing between the two substrates to enable removal of the unwanted silicon without the need of etched relief recesses as used in the prior art.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to thermal ink jet printing, and more particularly 
to an improved fabrication process for a thermal ink jet printhead. 
2. Description of the Prior Art 
Thermal ink jet printing systems use thermal energy to produce a vapor 
bubble in an ink filled channel to expel an ink droplet on demand. 
Generally, thermal ink jet printing is accomplished by the use of a 
printhead comprising one or more ink filled channels which communicate 
with a relatively small supply chamber at one end and have an opening at 
the opposite end such as disclosed in U.S. Pat. No. 4,463,359 to Ayata et 
al. A resistor is located in each of the channels a predetermined distance 
upstream from the channel orifice. The resistors are individually 
addressed with a current pulse to momentarily vaporize the ink and form a 
bubble which expels an ink droplet. 
U.S. Pat. No. 4,601,777 to Hawkins et al discloses a thermal ink jet 
printhead and method of fabrication. A plurality of printheads are 
concurrently fabricated by forming a plurality of sets of heating elements 
with their individual addressing electrodes on one substrate surface and 
etching corresponding sets of grooves which may serve as ink channels with 
a common reservoir in the surface of a silicon wafer. The wafer and 
substrate are aligned and bonded together so that each channel has a 
heating element. The individual printheads are obtained by milling away 
the unwanted silicon material in the etched wafer to expose the addressing 
electrode terminals on the substrate and then the bonded structure is 
diced into a plurality of separate printheads. 
U.S. Pat. No. 4,532,530 to Hawkins discloses a carriage type thermal ink 
jet printing system having improved bubble generating resistors formed 
from doped polycrystalline. Glass mesas thermally isolate the active 
portion of the resistor from the silicon supporting substrate and from the 
electrode connecting points so that the electrode connection points are 
maintained relatively cool during operation. A thermally grown dielectric 
layer permits a thinner electrical isolation layer between the resistor 
and a protective ink interfacing tantalum layer, thus increasing the 
thermal energy transfer to the ink. 
U.S. Pat. No. 4,571,599 to Rezanka discloses a plurality of disposable 
individually replaceable ink supply cartridges mountable on the carriage 
of an ink jet printer. Each cartridge has a thermal ink jet printhead 
fixedly attached thereto. A constant, slightly negative pressure is 
maintained at the nozzles of the printhead by means of a secondary 
reservoir with a level of ink maintained below the ink supply. The 
majority of the ink is stored in a hermetically sealed main reservoir in 
the cartridge which contains the ink supply at the negative pressure. A 
passageway provides ink from the main reservoir to the printhead nozzles. 
A secondary reservoir within the cartridge holds an air pocket at 
atmospheric pressure and releases air into the main reservoir as required 
to maintain the desired negative pressure constant as the ink supply is 
depleted. 
U.S. Pat. No. 4,612,554 to Poleshuk discloses an ink jet printhead composed 
of substantially two identical parts and method of batch fabricating the 
parts. Each part has V-grooves anisotropically etched between a linear 
array of heating elements having selectively addressable electrodes which 
are parallel to each other. The groove structures of the parts permit them 
to be mated face to face, so that they may be automatically self-aligned 
by the intermeshing of the lands containing the heating elements on one 
part with the grooves of the other part. A pair of parts may be used as a 
printhead for a carriage-type ink jet printer or a plurality of parts may 
be assembled for a pagewidth printer. 
U.S. Pat. No. 4,639,748 to Drake et al discloses an ink jet printhead 
having an integral integrated filtering system and fabricating process 
therefor. Each printhead is composed of two parts aligned and bonded 
together. One part is substantially flat substrate which contains on the 
surface thereof a linear array of heating elements and addressing 
electrodes. The other part is a flat substrate having a set of 
concurrently etched recesses in one surface. The set of recesses include a 
parallel array of elongated recesses for use as capillary filled ink 
channels having ink droplet emitting nozzles at one end and having 
interconnection with a common ink supply manifold recess at the other end. 
The manifold recess contains an internal closed wall defining a chamber 
with an ink fill hole. Small passageways are formed in the internal 
chamber walls to permit the passage of the ink therefrom into the 
manifold. Each of the passageways have smaller cross sectional flow areas 
than the nozzles to filter the ink, while the total cross sectional flow 
area of the passageways is larger than the total cross sectional flow area 
of the nozzles. 
U.S. Pat. No. 4,678,529 to Drake et al discloses a method of bonding ink 
jet printhead components together by coating a flexible substrate with a 
relatively thin uniform layer of an adhesive having an intermediate 
non-tacky curing stage with a shelf life around one month for ease of 
alignment of the parts and ease of storage of the components having the 
adhesive thereon. About half of the adhesive layer on the flexible 
substrate is transferred to the high points or lands of the printhead 
components within a predetermined time of the coating of the flexible 
substrate by placing it in contact therewith and then peeling it away from 
the printhead component. The transferred adhesive layer remaining on the 
printhead component enters an intermediate non-tacky curing stage to 
assist in subsequent alignment for the printhead components. The printhead 
components are then aligned and the adhesive layer cured to complete the 
fabrication of the printhead. 
U.S. Pat. No. 4,412,224 to Sugitani discloses a method of forming an ink 
jet printhead. The ink jet printhead comprises an ink flow path and an ink 
ejecting nozzle for discharging ink at one end of the ink flow path. The 
ink flow path is formed by a groove produced at the surface of a substrate 
by a photoforming technique. 
U.S. Pat. No. 4,577,202 to Hara discloses an ink jet printhead for a 
recording apparatus. A heat generating section is located between at least 
one pair of confronting electrodes with at least one of the electrodes 
having a portion lying under an ink storage chamber. The heating 
generating section comprises a first layer of an inorganic dielectric 
material, a second layer of an organic material, and a third layer of an 
inorganic material. 
U.S. Pat. No. 4,611,219 to Sugitani et al discloses a thermal ink jet 
printhead comprising a flat substrate with an array of orifices therein 
and a base structure on which the flat substrate with the orifices is 
mounted. The base structure includes a plurality of chambers for receiving 
the ink and each chamber is exclusively associated with a set of orifices. 
Each chamber has a number of separate branch paths for conveying the ink 
to its associated set of orifices in a direction generally parallel to the 
plane of the flat substrate. Each branch path of the ink has a pressure 
generating transducer, such as a bubble generating resistor, to eject ink 
from a corresponding orifice in a direction transverse to the flow 
direction of the ink in the branch path. 
U.S. Pat. No. 4,638,337 to Torpey et al discloses a thermal ink jet 
printhead having a plurality of capillary filled ink channels each having 
a droplet emitting nozzle at one end and coupled to an ink supply manifold 
at the other end. Each channel has a heating element upstream from the 
nozzle that is located in a recess. The recess walls containing the 
heating elements prevent the lateral movement of the bubbles through the 
nozzles and therefore prevent the sudden release of vaporized ink to the 
atmosphere. 
As taught by at least some of the above-mentioned patents, thermal ink jet 
printheads may be batched produced by placing a plurality of sets of 
heating elements on one substrate and anisotropically etching plurality of 
sets of channel grooves and associated manifolds in a second silicon 
wafer. These were aligned and bonded together and then diced into a 
plurality of individual printheads. In order to make electrical 
interconnection to the printhead, such as by wire bonding, to an electrode 
board commonly referred to as a daughter board, relief grooves had to also 
be etched in the silicon wafer around each set of ink channels and 
manifolds, so that when bonded to the heating element substrate, a dicing 
element could remove the silicon directly above the addressing electrode 
terminals without contact and damage thereto. The relief groove also 
prevented contamination of these terminals or contact pads by preventing 
the application of adhesive thereover during the bonding of the silicon 
wafer and the heating element substrate. 
As discussed later with respect to FIG. 4, flat dicing blades may be used 
to remove the unwanted silicon material from around the addressing 
electrode contact pads. However, the anisotropically etched relief 
grooves, though successful, provide a wafer which relatively fragile 
before being bonded to the heating element substrate. Thus, the prior art 
devices encountered a significant problem of channel wafers being broken 
during handling prior to successful alignment and bonding to the heating 
element plate. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an improved ink jet 
printhead having more rigid components and being more cost effective to 
fabricate than prior art devices. 
It is another object of this invention to provide a channel wafer which 
does not have or require silicon relief grooves that permit removal of the 
silicon therefrom in areas over the wire bonding pads on an associated 
substrate without damage thereto, after the wafer and substrate are 
aligned and bonded together to form a plurality of attached printheads 
awaiting separation. 
In the present invention, a plurality of ink jet printheads are fabricated 
from two substrates, at least one of which is a (100) silicon wafer. The 
surfaces of the silicon wafer are coated with an etched resistant 
material, each side is patterned to produce a plurality of vias on each 
side thereof for orientation dependent etching of a plurality of recesses 
on opposite sides that are abounded by {111} planes, the etching being 
timed so that one recess is formed which will later serve as the ink 
manifold and the other recess opens into the floor of the manifold recess 
and serves as the fill hole. The surface having the manifold recess has 
formed therein a plurality of grooves which may be produced by etching or 
by dicing. Alternatively, the silicon wafer may be etched from one side 
only to form the reservoir with fill hole by etching a slot completely 
through the wafer. A plurality of linear arrays of resistant material is 
formed on one surface of the other substrate for use as heating elements, 
and a pattern of addressing electrodes is formed on the same substrate 
surface for enabling individual addressing of each of the heating elements 
with current pulses. A passivation layer is placed over the addressing 
electrodes and heating elements. The passivation layer is removed from the 
terminal ends of the electrodes to enable electrical connection thereto 
such as by wire bonding. A thick film insulative layer having a 
predetermined thickness is formed over the passivation layer, the thick 
film layer is photolithographically patterned so that the thick film 
material is removed from over each heating element and a plurality of 
troughs are formed in the thick film substrate to expose the terminal ends 
of each of the addressing electrodes and common return. The plurality of 
ink jet printheads are simultaneously made by first aligning the heating 
elements with the grooves in the silicon wafer and bonding the two 
surfaces together, and the unwanted silicon material above the electrode 
terminals may be removed by a low tolerance dicing blade, because the 
terminals are recessed in the troughs formed in the thick film layer. Next 
the two bonded substrates are diced into individual printheads.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In FIGS. 1A-1C, a typical prior art silicon wafer having at least two 
alignment apertures and a plurality of manifold recesses and other 
recesses and grooves for subsequent clearance of electrode terminals are 
shown with one manifold recess and one alignment opening shown enlarged. 
The manifold recess and the other recesses and grooves for electrode 
terminal clearance were formed by anisotropic etching as disclosed in the 
above identified patents, such as, for example, U.S. Pat. No. 4,638,337. A 
two side polished, (100) silicon wafer 39 may be used, for example, to 
produce a plurality of upper substrates 31 for the printhead. After the 
wafer is chemically cleaned, a pyrolytic CVD silicon nitrite layer 47 (see 
FIG. 3) is deposited on both sides. Using conventional photolithography, a 
via for fill hole 25 for each of the plurality of upper substrates 31 and, 
at least two vias for alignment openings 40 at predetermined locations are 
printed on one wafer side 42 opposite the side shown in FIGS. 1A and 1C. 
The silicon nitride is plasma etched off of the patterned vias 
representing the fill holes in alignment openings. As in the printhead 
fabrication process discussed in U.S. Pat. No. 4,601,777 to Hawkins et al, 
referred to earlier in the Background section, a potassium hydroxide (KOH) 
anisotropic etch may be used to etch the fill holes and alignment 
openings. In this case, the {111} planes of the (100) wafer make an angle 
of 54.7.degree. with the surface of the wafer. The fill holes are small 
square surface patterns of about 20 mils (0.5millimeters) per side and the 
alignment openings are about 60 to 80 mils (1.5 to 2.0 millimeters) 
square. Thus, the alignment openings are etched entirely through the 20 
mil (0.5 mm) thick wafer, while the fill holes are etched to a terminating 
apex 43 at about half way to three-quarters through the wafer (see FIG. 
3). The relatively small square fill hole is invariant to further size 
increase with continued etching, so that the etching of the alignment 
openings and fill holes are not significantly time constrained. This 
etching takes about two hours and many wafers can be simultaneously 
processed. 
Next, the opposite side 44 of the wafer 39 is photolithographically 
patterned, using the previously etched alignment holes as a reference, to 
form the relatively large rectangular recesses 45 that will eventually 
become the ink manifold of the printheads. Also patterned are two recesses 
46 between the manifolds in each substrate 31 and adjacent each of the 
shorter walls 51 of the manifold recesses. Parallel elongated grooves 53, 
which are parallel and adjacent each longer manifold recess wall 52, 
extend entirely across the wafer suface 44 and between the manifold 
recesses of adjacent substrate 31. The elongated grooves do not extend to 
the edge of the wafer as explained in the prior art patents. The tops 47a 
of the walls defining the manifold recesses are portions of the original 
wafer surface 44 that still contain the silicon nitride layer and forms 
the streets 47 on which the adhesive will be applied later for bonding the 
wafer 39 and substrate 36 together. The elongated grooves 53 and recesses 
46 provide clearance for the printhead electrode terminals during the 
bonding process discussed in the prior art. One of the manifold recess 
walls 52 of each manifold will later contain channel grooves 48 which will 
serve as ink channels as discussed with referenced to FIG. 8. At this 
stage in the process, the grooves 48 have not yet been formed, so that 
they are shown in dashed line FIG. 1C on top of one of the longer manifold 
recess walls 52 to assist in understanding where the future channels will 
be produced. The clearance grooves and clearance recesses required to 
provide electrode terminal clearance produces a relatively fragile wafer 
prior to alignment and bonding to the heating element substrate. This 
invention, discussed later, not only provides a simpler etching pattern 
for the manifold recesses, but also produces a more rugged etched wafer 
39, thus improving the yield and improving the cost effectiveness of the 
fabricating process for the ink jet printheads. 
It is disclosed in the prior art, a KOH solution anisotropic etch is used 
to produce the recesses but, because of the size of the surface pattern, 
the etching process must be timed to stop the depth of the manifold 
recesses. Otherwise, the pattern size is so large that the etchant would 
etch entirely through the wafer. The floor 45a of the manifold recess is 
determined at a depth where the etching process is stopped. This floor 45a 
is low enough to meet or slightly surpass the depth of the fill hole apex 
43, so that the opening is produced that is suitable for use as the fill 
hole 25. After the channel wafer 39 has been etched, parallel grooves 48 
are milled into a predetermined recess wall 52 of each upper substrate 31 
by any dicing machine as is well known in the art. Each groove 48, as 
shown in FIG. 8, is about 20 mils (0.5 mm) long and has a depth and width 
of about 1 mil (0.25 microns). The lineal spacing between the axial center 
lines of the grooves are about 3 mils (0.75 microns). The silicon nitride 
layer 47 on wafer side 44 forms the bonding surfaces and a coating of an 
adhesive, such as a thermal setting epoxy, is applied in a manner such 
that it does not run or spread into the grooves 48 or other recesses as 
disclosed in U.S. Pat. No. 4,678,529 to Drake et al. 
In accordance with U.S. Pat. No. 4,638,337, the alignment openings 40 are 
used, for example, with a vacuum chuck mask aligner to align the channel 
wafer 39 via the alignment marks on a heating element and addressing 
electrode substrate (not shown). The wafer and substrate are accurately 
mated and tacked together by partial curing of the adhesive. The grooves 
48 automatically are positioned, so that each one has a heating element 
therein located a predetermined distance from the nozzles 27 or groove 48 
open ends at the channel plate edge 29 (see FIGS. 8 and 9). The wafer and 
substrate are cured in an oven or laminator to permanently bond them 
together, and the channel wafers milled to produce individual upper 
substrates. 
Referring to FIG. 4, an enlarged cross sectional view of wafer 39, after 
etching to produce the plurality of individual channel plates 31, is shown 
aligned with and bonded to substrate 28 which contains the plurality of 
sets of heating elements and addressing electrodes. The cross sectional 
view is depicted as viewed along view line 4--4 in FIG. 1C. Thick film 
layer 58 is shown as disclosed in U.S. Pat. No. 4,638,337, but this layer 
is optional if lower droplet velocity is acceptable. Recess 46 provides 
relief above the contact pads or terminal ends 32 of the addressing 
electrodes 33. The ink manifolds 45, fill holes 25, and nozzle 27, are 
shown in dashed line, since they are not otherwise visible in this view. 
Dicing blade 50 is also shown in dashed line to show how the unwanted 
silicon material is removed from the wafer 39 prior to dicing the 
substrate 28 into individual printheads as depicted by the dicing blade 54 
shown in dashed line. This unwanted silicon is shown removed at one side 
location 23. A dicing cut made perpendicular to each set of channels 48 in 
each row of channels 31 in the wafer produces the edge face 29 shown in 
FIGS. 8 and 9. In FIGS. 1 and 2, the plane 49 is shown in dashed line to 
indicate where the dicing machine cuts to produce the nozzles bearing face 
29. The dicing cuts by dicing blade 50 produces parallel side walls 55 
with sloping surface portions 56 at the interfaces with the heater plates 
28. The sloping surfaces were formed along the {111} planes of the silicon 
wafer, so that they have an angle of 54.7.degree. with the wafer surfaces 
42,44. 
FIGS. 5A-5C are similar to FIGS. 1A-1C, showing a plurality of channel 
plates 21 with a simpler, more rigid channel plate having only recess 45 
and intersecting recess 25, which serve as the ink manifold and fill hole 
respectively. Each recess has end walls 51 and elongated side walls 52 
intersecting floor 45a, which contains the fill hole 25. The channel 
grooves 48 may be formed by a dicing operation in a subsequent operation 
and are shown in dashed line. Plane 29 is shown in dashed line to show 
where a subsequent dicing operation will form in face 29 to provide 
channels of the appropriate length and contain nozzles 27. 
A fabricating process for the present invention is clearly shown in FIGS. 6 
and 7. Etched channel wafer 39 is shown aligned and bonded with the heater 
substrate 28 with a thick film layer 58 therebetween which is 
photolithographically patterned to remove that portion (not shown) of the 
thick film layer over the heating elements and that portion 60 over the 
addressing electrodes and common return terminals. The etched manifolds 
and intersecting fill holes, as well as the nozzles 27, are shown in 
dashed line, to illustrate that a space is formed between the channel 
wafer and the heater substrate where the electrode terminals 32 are 
located. FIG. 7 shows the dicing blade 50 in place to remove the unwanted 
silicon material above the electrode terminals. The channel plates 21 
formed by the dicing operation have vertical walls 57, and the dicing 
blades remove a portion of the corner edges of the thick film layer 58 to 
assure complete removal of the silicon. This causes a step 59 to be formed 
in the edge of the thick film layer as more clearly shown in FIG. 9. 
In the preferred embodiment, a two side polished, (100) silicon wafer 39 is 
used to produce the plurality of channel plates 21 for the printhead of 
the present invention. After the wafer is chemically cleaned, a pyrolytic 
CVD silicon nitride layer (not shown) is deposited on both sides. Vias for 
fill hole 25 for each of the plurality of channel plates 21 are 
photolithographically produced. At least two vias for alignment openings 
40 at a predetermined locations are printed on the wafer side 42, which is 
opposite to side 44 shown in FIGS. 5A-5C. The silicon nitride is plasma 
etched off of the patterned vias representing the fill holes and alignment 
openings. As in the prior art printhead fabrication process discussed 
above in conjunction with FIGS. 1-3, a potassium hydroxide anisotropic 
etch is used to etch the fill holes and alignment openings. The fill holes 
and alignment openings are about the same size as that of the prior art. 
Thus, the fill holes are etched to a terminating apex at about half-way to 
three quarters through the wafer while the alignment openings are etched 
entirely through the 20 mil thick wafer. The opposite side 44 of wafer 39 
is photolithographically patterned, using the previously etched alignment 
holes as a reference to form the relatively large rectangular recesses 45 
that will eventually become the ink manifolds of the printheads. The 
substrate 28, which may optionally be a silicon wafer, has a plurality of 
sets of bubble generating, heating elements 34 and their addressing 
electrodes 33 patterned on one surface thereof as disclosed in the prior 
art discussed above. A thick film type insulative layer 58, such as, for 
example, Riston.RTM., Vacrel.RTM., Probimer 52.RTM., or polyimide, is 
formed on the passivation layer of the heating element wafer having a 
thickness of between 5 and 100 microns and preferably in the range of 15 
to 50 microns. The insulative layer 58 is photolithographically processed 
to enable etching and removal of those portions of the layer 58 over each 
heating element and over a predetermined area covering the electrode 
terminals 32, 37. After the silicon material above the electrode terminals 
is removed by dicing blade 50 as shown in FIG. 7, the heating element 
substrate 28 is cut into individual printheads as shown by dicing blade 54 
shown in dashed line. 
FIG. 9 is an enlarged, schematic, isometric view of the front face of 
printhead 10 showing the array of droplet emitting nozzles 27. The heating 
element plate 28 has heating elements (not shown) and addressing 
electrodes 33 patterned on the surface 30 thereof, while the channel plate 
21 has parallel grooves which extend in one direction and penetrate 
through the channel plate front face 29. The other end of the grooves 
communicate with a common internal recess 45 shown in dashed line in FIGS. 
6 and 7, and in FIG. 5C. The floor 45a of the internal recess 45 has an 
opening therethrough for use as an ink fill hole 25. The surface of the 
upper substrate 21 with the grooves are aligned and bonded to the lower 
substrate 28, as described above, so that a respective one of the 
plurality of heating elements is positioned in each channel, formed by the 
grooves and the lower substrate. Ink enters the manifold formed by the 
recess 45 and the lower substrate 28 through the fill hole 25 and by 
capillary action fills the channels. The ink at each nozzle forms a 
meniscus, the surface tension of which prevents the ink from weeping 
therefrom. Addressing electrodes 33 on the lower substrate 28 terminate at 
terminals or contact pads 32 and the common electrode return 35 terminates 
at contact pads 37. The channel plate 21 is smaller than that of the lower 
substrate in order that the electrode terminals 32, 37 are exposed and 
available for wire bonding to the electrodes of the daughter board 19 on 
which the printhead 10 is permanently mounted. Layer 58 is a thick film 
passivation layer, discussed above, which is sandwiched between the 
channel plate and the lower substrate or heater plate. This layer is 
etched to expose the heating elements, thus placing them in a recess or 
pit as disclosed in U.S. Pat. No. 4,638,337. This layer is also etched, as 
discussed in connection with FIGS. 6 and 7, to permit removal of the 
unwanted silicon material between channel plates by a dicing blade 50 to 
form parallel sidewalls 57. By using the thickness of the thick film layer 
58 to space the channel plate above the heating element plate 28, no 
anisotropically etched relief recesses or grooves are required thus 
providing a more rigid etched channel wafer. The printhead fabrication 
methods disclosed in the prior art provided a serious yield problem 
because the etched channel wafers were very fragile and a significant 
percentage broke during handling. With this clearance being provided by 
the thick film layer 58, a simpler, more rigid channel wafer is possible. 
In the preferred alternate fabrication embodiment of FIGS. 10A-10C, all of 
the etching is done from one side of the wafer 63. Therefore, only a 
single-side-polished, (100) wafer 63 is required, as disclosed in the 
abovementioned U.S. Pat. No. 4,601,777 to Hawkins et al and incorporated 
herein by reference. On the chemically cleaned, single-polished surface of 
the wafer, a layer 47 of pyrolytic CVD silicon nitride is deposited. A 
mask for the plurality of the manifolds and alignment openings are printed 
on the silicon nitride layer using conventional photolithography. The 
silicon nitride 47 is plasma etched from the printed areas of the mask on 
the surface of the wafer. Next, a KOH anisotropic etch is used to etch 
completely, the wafer. This takes about two hours and many wafers can be 
simultaneously processed. The etching depth depends upon the surface area 
of the wafer exposed to the etchant. The recesses for the alignment 
opening 40 and the manifold 65 are sized so that the etchant etches 
through the wafer. The channel grooves 48 shown in dashed line may be 
either diced in later or currently etched as also disclosed in U.S. Pat. 
No. 4,601,777. The manifold recess is bounded by walls 51 and 52 which lie 
along {111} planes. The fill hole is now the open bottom of the manifold 
recess 65. In all the other respects, this alternrate fabrication method 
is the same as the one for the two-sided wafer embodiment discussed above 
with respect to FIGS. 5 through 7. 
The original surface of the wafer 63 with silicon nitride layer 47 serves 
as the bonding area for bonding the wafer to the heating element substrate 
28, the wafer having the plurality of sets of channels with associated 
manifolds and the substrate 28, which may also be a silicon wafer, having 
the plurality of sets of heating elements and addressing electrodes. The 
bonding area is coated with a thermosetting epoxy resin and then the two 
structures are aligned together by using an infrared aligner-bonder which 
holds the channel wafer and aligns the channel wafer with the heating 
element substrate. Instead of using alignment holes 40 in the wafer 63, 
alignment marks (not shown) on this wafer can be used which are opaque to 
an infrared microscope. The alignment marks (not shown) on the substrate 
having the plurality of sets of heating elements 34 can be aluminum 
patterns, for example, which are also infrared opaque. Therefore, use of 
an infrared microscope with infrared opaque markings on each structure to 
be aligned is yet another alternative technique to align the wafer and 
heating element substrate together. 
Prior to the alignment, the top 47 of the wafer is coated with a layer of 
adhesive, with care being taken not to permit the adhesive to run or weep 
into the channels 48. 
The wafer 63 and substrate 28 are tacked together and cured permanently in 
a laminator. The printhead electrode terminals are cleared by milling the 
wafer portions as shown in FIGS. 6 and 7. Next, the heating element 
substrate is diced into a plurality of individual printheads, forming the 
nozzles 27 in the freshly cut face 29. FIG. 9 is an enlarged, isometric 
view of the finished printhead, but, in this embodiment, would have an 
elongated slot (not shown) for a fill hole, since the manifold 65 was 
etched through the channel plate 61. Note channel plate 21 in Figure 9 
shows the fill hole 25 formed by the two step etching progress of Figure 
5. Each printhead is permanently mounted on a daughter board 19 and the 
respective electrodes are wire-bonded together. The wire bonds (not shown) 
and pads or terminals 32, 37 are coated with a passivation layer of 
silicone encapsulation compound, such as Dow Corning 3-6550 RTV.TM.. This 
layer electrically isolates the electrodes and wire bonds. 
Many modifications and variations are apparent from the foregoing 
description of the invention and all such modifications and variations are 
intended to be within the scope of the present invention.