Ink jet printhead with large size silicon wafer and relative...

Details Ink jet printhead with large size silicon wafer and relative... Ink jet printhead with large size silicon wafer and relative...

2002-05-06

2002-12-24

Barlow, John (Department: 2853)

Incremental printing of symbolic information

Ink jet

Ejector mechanism

C347S017000, C029S890100

Reexamination Certificate

active

06497470

ABSTRACT:

TEXT OF THE DESCRIPTION
1. Background of the Invention
This invention relates to a printhead used in equipment for forming black and colour images, by way of successive scanning passes, on a print medium, normally though not exclusively a sheet of paper, using the thermal type ink jet technology, and more particularly to the actuator assembly of the head, and to the relative manufacturing process.
2. Prior Art
The composition and general mode of operation of a printhead according to the thermal type technology, and of the “top-shooter” type in particular, i.e. those that emit the ink droplets in a director perpendicular to the actuator assembly, are already widely known in the sector art, and will not therefore be discussed in detail herein, this description instead dwelling more fully on only some of the features of the heads and their manufacturing process, or relevance for the purposes of understanding this invention.
FIG. 1
shows an enlarged perspective view of an actuator assembly
80
of a monochromatic ink jet printhead, consisting of a die
51
of a semiconductor material (usually Silicon) on the upper face of which resistors
52
have been made for the emission of the ink droplets, driving circuits
53
for controlling the resistors
52
, pads
54
for connecting the head to an electronic controller, not depicted in the figures, a resistive temperature sensor
65
, reference marks
69
, and which has a pass-through slot
55
along which the ink flows from a tank not shown in the figure. Attached to the upper face of the die is a layer
60
of photopolymer having a thickness less than or equal to 25 mm wherein are made, using known photolithographic techniques, a plurality of ducts
57
and a plurality of chambers
64
positioned in correspondence with the resistors
52
.
Stuck above the photopolymer
60
is a nozzles plate
61
, usually made from a sheet of gold-plated Nickel or of Kapton, of thickness 50 &mgr;m or less, bearing a plurality of nozzles
62
, each nozzle
62
being in correspondence with a chamber
64
. In the current art, diameter of the nozzles is usually between 10 and 60 &mgr;m, while their centers are usually set apart by a step A of {fraction (1/150)} or {fraction (1/300)} of an inch (169 &mgr;m or 84.5 &mgr;m). Usually, though not always, the nozzles
62
are disposed in two parallel rows, staggered by a distance B=A/2, in order to double the resolution of the image in the head scanning direction, which accordingly becomes {fraction (1/300)} or {fraction (1/600)} or an inch.
Also in
FIG. 1
the axes x, y and z giving the three-dimensional references of the die
51
are defined.
The traditional process for manufacture of the actuator assembly will now be described below in brief, with reference to the flow diagram of
FIG. 3
, starting from a first step
70
in which a wafer
66
is made available whereupon the dice
51
are made (FIG.
2
). In a subsequent step
71
, the wafer
66
is tested. In a step
72
, the wafer
66
is coated with a layer of photopolymer, generally of the dry film type.
In a step
73
the photopolymer is exposed and, in a subsequent step
74
, the chambers
64
, in line with the resistors
52
, and the ducts
57
are made in the layer of photopolymer
60
(FIG.
1
), through development using known techniques.
In a step
75
a protection is applied to the entire wafer and, in a subsequent step
76
, the slots
55
, which bring the ink to the ducts
57
, are cut by way of a sandblasting operation. In a step
77
, the protection is washed off and a sight check is made that the component is still whole.
In a subsequent step
100
, the nozzles plates
61
are positioned in such a way that the nozzles
62
are aligned with the chambers
64
, and stuck on the dice
51
belonging to the wafer
66
. Subsequently (step
101
) the wafer
66
is applied to an adhesive tape
113
(FIG.
4
), mounted on a frame
114
. The individual dice
51
are separated in a step
102
by cutting with a diamond wheel
115
, 50÷100 mm thick (FIG.
5
), but are kept fast in their original positions by way of the adhesive tape
113
to which they adhere. Washing and drying are then performed (step
103
), using an Ultratech machine for example.
In a step
105
, a pick and place device of known technology, picks each die
51
off the adhesive tape
113
and places it with precision (error less than ±10 &mgr;m on the x axis) on an alignment base. In a step
104
, in the form of a continuous reel, a multiplicity of flat cables
117
(
FIG. 1
) is supplied separately, each having a window
122
with fingers
123
that will be soldered to the connecting pads
54
of the dice
51
, machine contacts pads
121
and interconnecting tracks
120
which connect the pads
121
to the fingers
123
. IN a step
107
the flat cable
117
is aligned with the die
51
, with a tolerance of ±5 &mgr;m on the x and y axes. In a step
110
an ultrasound soldering head comes into position above the connecting pads
54
of the die
51
, whereto it solders one by one all the fingers
123
of the flat cable
117
(point-to-point TAB). The operations involved in the steps
105
,
107
and
110
are effected using the technique known as Tape Automatic TAB).
In a subsequent step
111
the individual flat cables
117
are separated into distinct actuator assemblies
80
.
A variant of the known art consists in making the nozzles directly on the flat cable (U.S. Pat. No. 5,278,584), which accordingly also has the function of nozzles plate, and is illustrated in FIG.
6
. The flat cable
180
with nozzles is applied on a die
183
in which the feeding of the ink is effected from both sides. As a result, the windows
181
containing the fingers
123
are disposed perpendicularly to the ends of the rows of nozzles.
As the technology evolves, so the demand grows for heads with an ever greater number of nozzles, in order to reduce the number of scanning passes the head needs to complete a page and improve the printer's productivity. To increase the number of nozzles, dice must be produced that are longer and longer and have the minimum possible width (4÷5 mm, where the mechanical requirements permit) so as to better exploit the wafer
66
.
Accordingly the slots
55
are particularly long (typically though not exclusively greater than 12.5 mm) and are an open invitation for the dice
51
to break. When the nozzles plates (step
100
) are assembled conventionally, the risk of the entire wafer
66
breaking when under pressure during soldering is high, with considerable economic damage.
Even when the step
100
is completed without damage, there is still a high risk of the individual dice
51
breaking in the subsequent machining operations, with serious economic damage on account of the notable dimensions of the dice
51
themselves. With a step A (see
FIG. 1
) of less than {fraction (1/300)} of an inch, in practice the nozzles plate have to be produced in kapton. This further increases the risk of the dice
51
breaking.
SUMMARY OF THE INVENTION
The object of this invention is to solve the problem represented by the risk of the dice breaking during the different machining stages of the nozzles assembly of an ink jet printhead, whether monochromatic or colour, by sticking the wafer on a rigid substrate and, instead of cutting the slot in a sandblasting operation, by effecting instead a through cut over the entire length of the dice.
Another object is to handle the individual dice, rendered fragile by the slot, with safety and not expose them to the risks of breaking, keeping them stuck upon a portion of the said base.
A further object is to make resistors underneath said substrate such that the operation of soldering the nozzles plates on the dice may be effected more rapidly, with local heating and a soldering temperature controlled by a sensor.
A further object is to improve the thermal dissipation of said actuator, by using the contribution to heat conduction made by said substrate.
A further object is to lower the time to refill the chamber fo

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