Ink jet printhead

Details Ink jet printhead Ink jet printhead

2000-12-29

2002-07-02

Barlow, John (Department: 2853)

Incremental printing of symbolic information

Ink jet

Ejector mechanism

C347S043000

Reexamination Certificate

active

06412921

ABSTRACT:

TECHNOLOGICAL AREA OF THE INVENTION
This invention relates generically to ink jet printheads and, in particular but not exclusively, to the thin-film heads employing the thermal ink jet printing technology, called “top-shooters”, i.e. those in which the drop of ink is emitted in a direction perpendicular to the emission chamber, which accommodates the resistor that, when heated, generates the vapor bubble that ultimately results in emission of the drop.
THE PRIOR ART
Ink jet printheads of the type described above, both monochromatic and colour, are widely known in the sector art and comprise an actuator assembly, typically consisting of:
a silicon chip or die, on the upper face of which various layers are deposited using known technologies to form the emission resistors and the interconnections, and upon which active electronic components, the MOS transistors driving the emission resistors, for example, are made;
a layer of a photopolymer, overlaid on the upper face of the silicon die, in which the emission chambers disposed in correspondence with the emission resistors and the ink ducts are made using known photolithographic technologies; and
a nozzles plate, overlaid on the layer of photopolymer, in which the nozzles through which the ink drops are emitted are made in correspondence with the emission chambers, using known technologies.
It is equally widely known that the ink jet printheads of the type described above comprise an ink tank, attached to the lower face of the silicon die, and that the feeding of the ink from the tank to the above-mentioned ducts and emission chambers is effected through a pass-through slot, made in the center of the silicon die, for example by way of a sandblasted cut. Typically the silicon die is rectangular shape, and the emission resistors, the emission chambers and the nozzles are arranged in two rows parallel to the greater side of the rectangle and on two opposite sides of the central slot. The slot is typically oblong shape and of an overall length slightly less than that of the greater side of the rectangle, in order to be able to feed the ink uniformly to all the emission chambers.
The fact of having the slot means that the silicon die is mechanically weaker, and this increased fragility is the cause of breaks both during the cutting of the slot itself and during the subsequent steps in manufacturing the heads, all the more so the greater the number of nozzles in the head and, consequently, the longer the greater side of the silicon die. Unfortunately, today's technology tends to produce heads with an ever greater number of nozzles, as this enables printing times to be reduced and the printer's throughput to be accordingly enhanced.
One way of solving the problem of satisfying these contrasting requirements is that illustrated in the U.S. Pat. No. 5,317,346, wherein the pass-through slot for feeding of the ink is divided into a certain number of shorter pass-through slots, all in a line parallel to the greater side of the silicon die and in the center thereof, and finishing in a single trench made in the upper face of the silicon die itself The shape of the trench is symmetrically mirrored in an analogous cavity formed in the photopolymer, from which the channels conveying the ink and the emission chambers depart.
Accordingly the feeding of the ink from the tank to the emission chambers is effected through a duct consisting of the combination of a slot made in the silicon die (for example, by means of cut performed by sandblasting) starting from the latter's lower face, and a trench, again in the silicon die, made by means of a chemical etching process starting from the upper face of the die. The latter process is, for example, described in a second U.S. Pat. No. 5,387,314, granted to the same assignee as the previous one and related thereto, wherein the process is specified to be a dry etching process, known to those acquainted with the sector art and based on the use of CF
4
+O
2
, SF
6
or a mixture of noble gases and fluorocarbon compounds.
In practice, however, it has been verified that the methodology illustrated, though valid from a strictly theoretical viewpoint, cannot be used for the production on an industrial scale (i.e. with low times and costs) of a trench on the upper face of the silicon die having the required depth, i.e. 25÷100 &mgr;m.
There is also a second problem, in addition to that of the fragility of the silicon die, that is not solved in the patents cited but which is very much present in the sector art: this problem is that of succeeding in using optimally the surface area of the upper face of the die in the case of a colour printhead, or at any rate of a non-monochromatic one.
It is well-known, in fact, that colour heads typically comprise three distinct groups of nozzles, each connected to and fed from a tank containing a different colour ink (generally cyan, magenta and yellow) through a separate pass-through slot made in the usual silicon die; the three groups of nozzles are reciprocally aligned in a direction parallel to the greater side of the rectangle of the silicon die and, in turn, the nozzles of each group are arranged in two rows, each parallel to the greater side of the rectangular silicon die, as in the case of the monochromatic heads.
In order to prevent adjacent nozzles belonging to different colour groups reciprocally “polluting” each other and also to permit a suitable physical separation between the different tanks of ink, the three groups of nozzles are set apart by a distance typically equal to approximately 30 elementary steps of {fraction (1/600)}
th
of an inch (=1.27 mm; the 300
th
and the 600
th
of an inch are units of measure widely used throughout this sector of the art), with the result that a non negligible area of the silicon die remains unused and the cost of the actuator assembly is increased.
Whereas the problem of the reciprocal “pollution” between adjacent nozzles belonging to different colour groups could be resolved by setting the three groups of nozzles apart by only 10÷15 elementary steps of {fraction (1/600)}
th
of an inch (≈0.4÷0.6 mm), the tolerances on positional precision of the sealing elements between the tanks, however, mean that a physical separation must be maintained between the different ink tanks, such that the distance between adjacent groups of nozzles cannot be less than the value cited above of approximately 30 elementary steps of {fraction (1/600)}
th
of an inch, leaving unresolved the problem of optimal use of the die surface area.
SUMMARY OF THE INVENTION
The object of this invention is to define an ink jet printhead that enables optimal use to be made of the surface area of the upper face of the silicon die, including in the case of a non-monochromatic head having numerous different ink tanks. For each tank of ink, the head according to the invention has one pass-through slot that departs from the lower face of the silicon die and finishes in a wider trench made in the upper face, made using a chemical etching type incision technique known as ICP (Inductively Coupled Plasma), thereby maximizing the distance between the tanks of the different inks and, at the same time, maximizing the distance between the different groups of nozzles on the upper face of the die. An additional advantage is that the head according to this invention considerably lowers the risk of the silicon substrate breaking during the various stages of manufacture.
A further object of the invention is that of defining an ink jet printhead manufacturing process that enables the cost of the actuator assembly to be reduced, optimizing utilization of the surface area on the upper face of the silicon die, including in the case of color printheads with tanks of different colored inks, and cutting down on the number of manufacturing rejects due to breaks in the silicon substrates through the production of a pass-through slot starting from the lower face of the die and flowing into a wider trench made in the upper face using an ICP chemic

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