Note: Descriptions are shown in the official language in which they were submitted.
1 ~ 7B'34~
THERMAL INK JET PRINT HEAD ASSEMBLY INCLUDING COMMON
SLOTTED INK FEED THROUGH AND NETHOD OF MANUFACTURE
Technical Field
This invention relates generally to thermal
ink jet printing and more particularly to a new and
improved thermal ink jet printhead assembly.
Backqround Art
Thermal ink jet printing has been described in
many technical publications, and one such publication
relevant to this invention is the Hewlett Packard
Journal, Volume 36, Number 5, May 1985.
In the art of thermal ink jet printing, it is
known to provide a plurality of electrically resistive
elements on a common thin film substrate for the
purpose of heating a corresponding plurality of
adjacent ink reservoirs during the ink ejection and
printing process. Using such an arrangement, the
adjacent ink reservoirs are typically provided as
cavities in a barrier layer above the substrate for
properly concentrating thermal energy emanating from the
resistive elements to predefined volumes of ink. Also, a
plurality of ink ejection orifices are provided above these
cavities and provide exit paths for ink during the printing
process .
In constructing the above type of printhead
assembly, one practice has been to drill vertical holes in a
common substrate in order to provide ink flow paths from a
common ink reservoir to the individual reservoir cavitles
within the barrier layer. However, the use of multiple
holes (vertical cylindrical channels) in a single substrate
possesses several disadvantages. One of these disadvantages
is that the boring bit used for drilling holes in the sub-
strate places a substantial pressure on the substrate
material and thus can cause fracturing of this material. On
the other hand, if laser drilling is utilized, the laser
beam will leave channels with fratured side walls as a
result of heating, and thus produce a weakened substrate
structure.
The per se creation of mulitiple vertical channels
in the silicon substrate weakens the printhead structure,
and with some types of prior art printhead structures, these
channels are used to provide ink flow to a plurality of
resistive heater elements located at different distances
from the channels. In such a structure, these varying ink-
flow distances produce corresponding different pressure
~ ~t7~
drops in the ink flow paths. That is, the pressure drop
along a liquid ink flow path i~ proportional to the cube of
the distance of the path. Thi~ fact has sometimes resulted
in pressure drops over large ink flow distances sufficiently
great as to prevent adequate vaporization during ink jet
propulsion from the ink ~et ori~ice.
Another disadvantage of u~ing small diameter ver-
tical channels to supply ink to the ink reservoirs is that
these channels simply do not have the capacity to adequately
respond to certain ink volume demands at the required
increasingly higher frequencies of operation.
A further disadvantage of using a plurality~of ink
flow channels in a common substrate is that they normally
require a special routing of conductive leads on the sub-
strate surface. In addition to the added costs associated
with this special rout~ng, this requirement also greatly
reduce-~ the achievable pacXing density because of the sur-
face area required to accomodate such special routing
schemes.
Disclosure of Invention
The general purpose of this invention is to pro-
vide a new and improved ink jet printhead assembly which
eliminates tha above problems associated with the use of
drilled holes through a common printhead substrate member.
In this new assembly, a single elongated slot is cut in the
~ ~7~3~34~
substrate and provides ink flow to a plurality of ink reser-
voirs associated with reslstiva heater elements formed above
the top surface of the substrate. These heater elements are
spaced around the periphery of the slot at predetermined
distances therefrom. Conductive leads are provided on the
substrate between each resistive heater element and external
electrical connections, and a barrier layer and oriPice
plate member covers all of the resistive heater elements and
defines a plurality of individual ink reservoirs repectively
above each of the reci~tive heater elements.
The above described slotted geometry structure
greatly increases the packing density of heater resistors on
the common printhead substrate. This increase in packing
density is partially a result of the fact that, in the prior
art multiple hole printhead structures, the conductive
traces to the individual resistor elements had to be routed
around the holes, thu~ increasing the required substrate
area. Thus, by using the elongated slot arrangement of this
invention instead of vertical holes in the prior art struc-
tures, a pacXing density increase of 8:1 to 10:1 may be
achieved.
After the orifice plate and associated barrier
layer member are secured to the thin film substrate, the
substrate is die bonded to a header manifold member. This
manifold member has an elongated slot therein for passing
8~
ink from a well section of the header manifold and
through the substrate slot to the individual reservoirs
of the barrier layer and orifice plate member.
Accordingly, it is an object of an aspect o~ the
present invention ~o provid~ a new and improved thermal
ink jet printhead assembly having an improved packing
density for the heater resistors and their associated
ink jet orifices and reservoirs.
An object of an aspect of this invention is to
provide a new and improved manufacturing process for
realizing this assembly using latest state-of-the-art
semiconductor processing techniques.
A novel feature of this invention is the provision
of improved control of ink flow pressures from a common
ink supply source and through a single slot in a thin
film resistor structure and then through a common ink
flow path simultaneously to a plurality of ink
reservoirs in the printhead assembly.
Various aspects of this invention are as follows:
A process for fabricating a thermal ink jet
printhead assembly which includes the steps of:
(a) providing a thin film resistor structure
having a common ink feed opening therein and a plurality
of resistive heater elements spaced around the periphery
of said opening,
(b) bonding a plurality of conductive leads into
electrical contact with said resistive heater elements
at the surface of said thin film resistor structure,
(c) affixing an orifice plate to the surface of
said thin film resistor structure, and
(d) bonding said thin film resistor structure to
an insulating header having an ink feed opening therein
of dimensions corresponding to the dimensions of
949
said ink feed opening in said thin film resistor
structure, whereby ink may be fed through both of said
openings in said header and said thin film resistor
structure, respectively and into reservoir cavities in
said orifice plate, and ink in said reservoir cavities
may be heated from energy from said resistive heater
elements and caused to expand through openings in said
orifice plate during an ink jet printing operation.
A process for maximizing packing density of
resistor heater elements and associated ink jet orifices
in thermal ink jet printheads which includes:
(a) providing a thin film resistor structure
having an ink feed opening therein around which resistor
heater elemenks are spaced at predetermined distances,
(b) making electrical contacts to said
resistor heater elements,
(c) mounting an orifice plate member atop
said thin film resistor structure for ejecting ink
therefrom upon receiving thermal energy from said
resistor heater elements, and
(d) affixing said thin film resistor
structure to an insulating header having a matching ink
feed opening therein for providing ink to said ink feed
opening in said thin film resistor structure.
A thermal ink jet printhead assembly
including in combination:
(a) a thin film resistor structure having an
elongated slot therein extending from one major surface
to another and having a plurality of resistive heater
elements spaced uniformly around the periphery of said
slot,
(b) a conductive lead frame member uniformly
wire bonded to said thin film resistor structure to make
electrical connections to said resistive heater elements
and extending laterally away from said resistive heater
elements in the plane thereof,
5a
~i9 ~
(c) an orifice plate affixed atop said thin
film resistor structure and having ink reservoirs and
output orifices aligned with said resistive heater
elements for receiving thermal energy therefrom during
an ink jet printing operation, and
(d) an insulating header member having an
elongated slot therein of width and length dimensions
equal to the width and length dimensions of said
elongated slot in said thin film resistor structure and
bonded thereto so that said elongated slots in said thin
film resistor structure and in said header are aligned
and provide an ink flow pa~h from a common source of ink
to said reservoirs in said orifice plate, and the
conductive leads of said conductive lead frame may be
contoured to the shape of the surface of said header
member, whereby the packing density of said resistive
heater elements on said thin film resistor structure is
maximized.
A thermal ink jet printhead assembly
including, in combination:
(a) a thin film resistor structure having an
ink feed opening therein extending from one major
surface to another and having a plurality of resistive
heater elements,
(b) a conductive lead frame member uniformly
wire bonded to said thin film resistor structure to make
electrical connections to said resistive heater elements
and extending laterally away from said resistive heater
elements,
(c) an orifice plate affixed atop said thin
film resistor structure and having ink reservoirs and
output orifices aligned with respect to said resistive
heater elements for receiving thermal energy therefrom
during an ink jet printing operation, and
(d) an insulating header member having an
opening therein of dimensions corresponding to the
5b
A
1~789~
dimensions of said ink feed opening so that said header
may contain a source of ink to said reservoirs, and the
conductive leads of said conductive lead frame may be
contoured to the shape of the surface of said header
member, whereby the packing density of said resistive
heater elements on said thin film resistor stxucture is
maximized and the ink pressure drops between said ink
flow opening and said reservoirs are equalized.
A thermal ink jet printhead assembly
including:
(a) a substrate member having an elongated
slot therein for receiving ink from a common reservoir,
said substrate mounted on a header for providing a
supply of ink and further having an ink feed slot which
is aligned with said elongated slot on said substrate
for providing ink flow to said elongated slot,
(b) a plurality of resistive heater elements
spaced around the periphery of said slot at
predetermined distances therefrom and connected to a
corresponding plurality of conductors atop the surface
of said substrate member, and
(c) a barrier layer and orifice plate member
mounted atop said conductors and including a
corresponding plurality of ink jet reservoirs for
receiving ink from said elongated slot, said reservoirs
aligned with said resistive heater elements and with a
plurality of exit orifices for receiving thermal energy
from said heater elements and ejecting ink onto a
selected print medium, said reservoirs all being at
predetermined ink flow path distancss from said
elongated slot, whereby the liquid pressure flow loss
between said reservoirs and said slot is equalized.
A thermal ink jet printhead assembly
including:
(a) a substrate member having a vertical ink
feed opening therein for receiving ink from a common
5c
8':34~
reservoir, said substrate mounted on a header for
providing a supply of ink to said in~ feed opening;
(b~ a plurality of resistive heater elements
spaced around the periphery of said ink feed opening at
predetermined distances therefrom and connected to a
corresponding plurality o~ conductors atop the surface
of said substrate member; and
(c) a barrier layer and orifice plate member
mounted atop said conductors and including a
corresponding plurality of ink jet reservoirs for
raceiving ink from said ink feed opening, said
reservoirs aligned with respect to said resistive heater
elements and with respect to a plurality of exit
orifices and operative to receive thermal energy from
said heater elements and ejecting ink onto a selected
print medium, said reservoirs all being at predetermined
ink flow path distances from said ink feed opening,
whereby the liquid pressure flow loss between said
reservoirs and said ink feed opening is equalized.
These and other objects and features of this
invention will become more readily apparent from the
following description of the accompanying drawing.
Brief Descri~tion of Drawinqs
Figure 1 is an isometric view of the slotted thin
film resistor die (substrate) used in a preferred
embodiment of the invention.
Figure 2 is an exploded view showing the die
5d
~.~78'~4~
placement, the external lead attachment, and the orifice
plate attachment step~ used in fabricating the complete
thermal ink jet printhead assembly in a preferred
embodiment of the invention.
Figures 3A and 3B are fragmented and greatly
enlarged plan and cross section views respectively, of
the novel slot and lateral ink feed sections of the
above printhead structure.
Best Mode for Carryinq Out the Invention
Referring now to Figure 1, there is shown a thin
film resistor substrate 10 for a thermal ink jet printer
and including a metal orifice plate 12 thereon. The
orifice plate 12 is typically constructed of nickel and
includes a plurality of ink ejection openings or nozzles
14 spaced uniformly around the edges of an ink feed slot
16 indicated by the dotted lines in Figure 1. Slot 16
may be formed by cutting a silicon substrate with a
diamond saw blade.
Referring now Figure 2, the thin film resistor
substrate 10 will be mounted on the top, I-beam shaped
surface 18 of a header manifold 20. The header manifold
20 will include an ink reservoir (not shown) within the
confines thereof which communicates with an ink feed
slot 22. The slot 22 is aligned with the ink feed slot
16 in the thin film resistor substrate 10. The header
manifold 20 further includes contoured walls 24 which
ha~e been shaped to match corresponding contoured walls
of an ink jet printer
~ ;~'78~:3~
carriage assembly (not shown) for receiving the
printhead structure of Figure 2 when completely
assembled.
When this printhead structure is completed and
all the piece parts shown in Figure 2 brought together,
the thin film resistor substrate 10 is positioned
directly on the upper surface 18 of the header 20, and a
flexible, tape automated bond (TAB) circuit 26 is
brought into electrical contact with conductive traces
on the top surface of the thin film resistor substrate
10. A plurality of thin conductive leads 28 overlie the
contoured side walls 24 of the header 20, and the
interior leads 30 of the tab bond flex circuit 26 are
thermocompression bonded to conductive traces on the
thin film resistor substrate 10 by a process disclosad
and claimed in U.S. Patent 4,635,073, issued January 6,
1987, Gary E. Hanson and assigned to the present
assignee. In addition, the orifice plate 12 will be
brought into alignment with the thin film resistor
substrate 10 by means of an orifice plate and barrier
layer manu~acturing process disclosed and claimed in
U.S. Patents 4,716,423 and 4,694,3~8, issued December
29, 1987 and September 15, 1987 respectively, C.S. Chan
et al., also assigned to the present assignee.
Referring now to Figures 3A and 3B, the thin
film resistor substrate 10 will typically include a
silicon substrate 32 upon which is deposited a thin
layer 34 of silicon dioxide for passivating and
insulating the surface of the silicon substrate 32. A
plurality of heater resistors 36
~ 7~ ~4~
and 38 are formed on the upper surface of the silicon
dioxide layer 34 and will typically be either tantalum
aluminum or tantalum pentoxide and fabricated using known
photolithographic masking and etching techniques. Aluminum
trace conductors 40 make electrical contact to the heater
resistors 36 and 38 for providing electrical pulses thereto
during an inX jet printing operation, and these conductors
are formed from a layer of aluminum previously evaporated on
the upper urface of tha silicon layer 34 using conventional
metal evaporation processes.
After the formation of the aluminum conductors 40
is completed, a surface barrier layer 42, typically of
silicon carbide or silicon nitride, is deposited over the
upper surfaces of the conductors 40 and the heater resistors
36 and 38 to protect these members from cavitation wear and
the ink corrosion which would otherwise be caused by the
highly corrosive ink located in the reservoirs directly
above these heater resistors. The silicon carbide layer 42,
as well as the previously identified SiO2 surface layer 34,
resistors 36 and 38 and aluminum conductors 40 are all
formed using semiconductor processes well known to those
skilled in thermal ink jet and semiconductor processing arts
and for that reason are not described in detail herein.
However, for a further detailed discussion of such
processes, reference may be made to the above Hewlett
ar9
Packard Journal, Volume 36, Number 5, ~ay 1985.
A nickel orifice plate 44 is positioned as
shown on top of the silicon carbide layer 42 and
includes ink reservoir areas 46 and 48 located directly
above the heater resistors 36 and 38 for receiving ink
therein by way of the horizontal slot 16. These ink
reservoirs 46 and 48 extend vertically upward of the
substrate 10 as shown and merge into the output ink
ejection orifices defined by the convergent contoured
10 walls 50 and 52. These contoured walls 50 and 52 have
been designed to reduce cavitational wear and prevent
"gulping" during an ink jet printing operation as
described in more detail in U.S. Patents 4,716,423 and
4,694,308, issued December 29, 1987 and September 15,
1987 respectively, Chan et al.
During an ink jet printing operation, ink will
flow along the path indicated by the arrow 54 and
laterally along the path 56 and into the ink flow ports
58, 60, 62, 64, 66 and 68 as identified on the left-hand
portion of the structure of Figures 3A and 3B.
Likewise, ink will enter the ink flow ports 70, 72, 74,
76, 78 and 80 on the right-hand portion of the structure
of Figure 3B. By flowing ink from a common ink
reservoir into the plurality of flow ports identified
above, the pressure drops in the ink from the ink feed
slot 16 to the individual heater resistors, such as 36
and 38, will be equal and thus insure proper ink bubble
evaporation and firing during an ink jet printing operation.
The advantages of this feature of the invention in contrast
"r`,
to the prior art have been previously discussed above.
