WO2004011264A1

WO2004011264A1 - High-density print head

Info

Publication number: WO2004011264A1
Application number: PCT/CH2003/000476
Authority: WO
Inventors: Francis Cardot
Original assignee: Csem Centre Suisse D'electronique Et De Microtechnique Sa
Priority date: 2002-07-26
Filing date: 2003-07-16
Publication date: 2004-02-05
Also published as: FR2842759A1; AU2003245793A1; FR2842759B1

Abstract

The invention relates to a print head using ink electrocoagulation. The inventive print head is characterised in that it consists of a rectilinear frame (10) comprising two sets of identical modules (12) which are mounted alternately thereto along two close parallel axes. The aforementioned modules are equipped with at least one chip (18), the front face thereof comprising at least one line of regularly-spaced diamond microelectrodes (30). Moreover, each module (12) comprises a support plate (14) which is fixed to the above-mentioned frame (10) and a printed circuit (20) which is disposed on said plate and which is equipped with bonding pads. The rear face of the chip comprises contact zones which are connected respectively to the microelectrodes (30) and which are fixed to said pads.

Description

HIGH DENSITY PRINTER HEAD

The present invention relates to print heads with high writing density. It relates, more particularly, to a printer head operating on the principle called Elcography® which was invented in 1973 by the creator of the company Technologie Elcorsy Inc. The invention also relates to a module intended to equip such a printer head .

Elcography® is based on electrocoagulation of ink on a drum. The print head is made up of a line of individually addressable metal micro-electrodes. This head faces a drum whose axis is parallel to it. When a current flows between selected micro-electrodes (cathodes) and the drum (anode) through an aqueous ink, the latter coagulates on the drum, forming there a set of points which define an image. Due to the rotation of the drum, this image is transferred by contact to a sheet of paper. A color image with a high printing density (400 dpi) can thus be reproduced by successively bringing the sheet into contact with several drums associated with inks of different colors.

The print head described above has two main drawbacks. On the one hand, the fact that it is composed of the discrete elements that are the metal wires makes its manufacture difficult and limits the possibilities of working with more miniaturized components to obtain a higher writing density. On the other hand, the nature of the wires, made of stainless steel, makes this head sensitive to chemical and electrochemical wear. The object of the present invention is to provide a printing head by electrocoagulation, the micro-electrodes of which are free from the above-mentioned drawbacks and whose modular structure simplifies and rationalizes its manufacture and its interfacing to the control electronics.

More specifically, the invention relates to a printer head by electrocoagulation of ink, characterized in that it comprises a rectilinear frame and, mounted thereon alternately along two parallel axes nearby, two series of identical modules equipped with at least one chip comprising, on its front face, at least one line of diamond micro-electrodes regularly spaced from each other.

The printer head according to the invention also has all or some of the main characteristics set out below:

each module comprises a support plate fixed to the chassis and a printed circuit bonded to said plate and provided with contact pads, said chip comprising, on its rear face, contact zones respectively connected to said micro-electrodes and fixed to said pads;

each chip includes a wafer-substrate of conductive silicon in which circular trenches have been made, making it possible to isolate at least one line of cylindrical pads, and a diamond disc made of conductor, formed on the front face of each pad and forming one of said micro-electrodes, the rear face of the stud constituting said contact zone;

- said trenches are filled with an insulating material;

- The front face of the silicon wafer is covered, with the exception of micro-electrodes, with at least one layer of insulating material; - the rear face of the studs is covered with a metallic layer;

- The chips have n lines of micro-electrodes, the space between the micro-electrodes of a line being n times the elementary pitch between two successive printing dots;

- the space between two neighboring lines is a multiple of the elementary step; - the micro-electrodes of two neighboring lines are horizontally offset by the elementary pitch;

the spacing between the micro-electrode situated at the end of a chip of one series and the micro-electrode situated at the opposite end of the chip adjacent to the other series is equal to the elementary pitch; - Each module is equipped with two chips which are arranged parallel to each other and offset horizontally by half of the elementary pitch;

- the printed circuit of each module is linked to multiplex addressing electronics.

The present invention also relates to a module for a printer head by electrocoagulation of ink, characterized in that it comprises at least one chip provided, on its front face, with a plurality of micro-electrodes, a printed circuit on which said chip is fixed by its rear face so that each micro-electrode is in connection with one of its tracks and an electronic multiplex addressing circuit connected to said tracks.

In a particularly advantageous manner, each chip of the module defined above comprises a wafer-substrate of conductive silicon in which circular trenches have been made making it possible to isolate a plurality of cylindrical pads, and a diamond disc made of conductive formed on the face. before each pad and constituting a micro-electrode, the rear face of the pad ensuring electrical contact with the printed circuit.

Other characteristics of the invention will emerge from the description which follows, given with reference to the appended drawing, in which: - Figures 1 and 2 are views from above and side respectively of a printer head according to the 'invention;

- Figures 3 and 4 are views in enlarged scales respectively from above and in section of a chip; and

- Figure 5 illustrates an alternative embodiment with two chips per module. Reference is made, first of all, to FIGS. 1 and 2 which show at 10 an elongated rectilinear chassis with a U-shaped section having, typically, a length of 45 cm and a width of 8 cm. The ends of the branches of the U respectively serve as the basis for two series of nine identical modules 12 mounted in cantilever alternately on either side of the longitudinal axis XX of the chassis and extending towards the interior of this one. Each module 12 comprises a support plate 14 fixed, at one end, to the chassis 10 by means of screws 16 and carrying, at the other end, a chip 18 whose rear face is provided, as will appear below, with contact areas. The latter are electrically and mechanically linked to the contact pads of a flexible printed circuit 20 bonded to the plate 14 and having, at its opposite end, a connector 22 used to connect the chip to its electronic control card (not shown) which includes a multiplex addressing circuit. The connection of the chip 18 to the printed circuit 20 is ensured using conductive adhesive deposited on the contact pads by screen printing or an anisotropic conductive adhesive film.

Before specifying the manner in which the two series of modules 12 are arranged relative to each other, reference will be made to FIGS. 3 and 4 which represent a chip 18 on very enlarged scales.

In these figures, there is shown at 24 a wafer-conductive silicon substrate in which have been practiced, advantageously by chemical etching, circular trenches making it possible to isolate a network of cylindrical studs 26 arranged in several parallel lines. These lines are three in number on the drawing but, according to the invention, their number n can be between 1 and 6. In this example, the pads 26 of the same line are spaced by three elementary steps p of 63.5 μm, or 190.5 μm, this step of 63.5 μm corresponding to 1/400 ^th of an inch. More generally, for an n-line chip structure, the spacing between the pads 26 is nx 63.5 μm.

The space between two neighboring lines is also a multiple of the elementary step p of 63.5 mm. Typically, this multiple can be between 0 and 8, the value 0 corresponding to a configuration comprising a single row of studs 26. In the example shown, the space between rows is 2p.

It will be noted above all that, regardless of the number of lines, the studs 26 of two neighboring lines are horizontally offset by the elementary step p of 63.5 μm. As shown in Figure 4, the trenches surrounding the studs 26 are filled with an insulating material 28 which strengthens the mechanical strength of the structure. This material can be a resin curable under the effect of heat or light. The front face of each pad 26 receives, by any method known to those skilled in the art, a micro-electrode 30 in the form of a diamond disc made conductive by doping. The rest of the front face of the pad is covered with a layer of SiO ₂ 32, itself covered with a layer of S1 ₃ N ₄ 34, which both provide electrical insulation of the pad and contribute to its mechanical strength . The layer 34 covers the periphery of the electrode 30 of which it thus defines the active surface. According to the example described, this surface corresponds to an electrode diameter of 20 to 30 μm.

The rear face of the studs 26 is covered with a metal layer 36, for example aluminum, to form the contact pads with the printed circuit 20. In the embodiment described, each chip 18 typically has a length of 26 mm and a width of 4 mm.

Returning to FIG. 1, it can be seen that the two series of modules 12 are arranged alternately on either side of the longitudinal axis XX of the chassis 10 and parallel to it, so that the spacing between the electrode located at the end of a chip of one series and the electrode located at the opposite end of the chip adjacent to the other series corresponds to the elementary pitch p of 63.5 μm. According to the embodiment described, the difference between the two chip lines is approximately 2 to 8 mm.

Thus, a printer head with 400 electrodes per inch in length (400 dpi) is produced which, thanks to the use of diamond micro-electrodes, does not suffer from parasitic coagulation of the ink. In addition, its modular structure makes it possible to simplify and rationalize its manufacture and its interfacing with the control electronics. It should be noted that, in a known manner, all or part of this control electronics (for example, addressing circuits) can be integrated on the chips 18. Finally, reference is made to FIG. 5 which schematically shows the manner in which the above-described printer head structure, offering a writing density of 400 dpi, can be easily adapted to obtain a density of 800 dpi. It suffices, in this case, without touching anything to the silicon substrate 24 or to the array of pads 26, to reduce the active surface of the micro-electrodes 30 by covering their periphery more by the insulating layer 34. Typically, the electrode diameter is then lowered from 20 to 10 μm.

As shown in FIG. 5, each support plate then receives two chips 38 with micro-electrodes 40 of reduced diameter, which are arranged parallel to one another and offset horizontally by half of the elementary pitch p of 63.5 μm and vertically about 6350 μm.

Thus, using 400 dpi chips, an 800 dpi printer head in interlaced mode is produced which requires neither technological development nor particular manufacturing. Furthermore, the control electronics need not be modified. It is enough to double the number of cards which goes from 18 for a 400 dpi head to 36 for the 800 dpi head.

Claims

1. Printer head by electrocoagulation of ink, characterized in that it comprises a rectilinear chassis (10) and, mounted thereon alternately along two close parallel axes, two series of identical modules (12) equipped with 'at least one chip (18) comprising, on its front face, at least one line of diamond micro-electrodes (30) regularly spaced from each other.

2. Printer head according to claim 1, characterized in that each module (12) comprises a support plate (14) fixed to the chassis (10) and a printed circuit (20) disposed on said plate and provided with contact pads , said chip comprising, on its rear face, contact zones (36) respectively connected to said micro-electrodes (30) and fixed on said pads.

3. Printer head according to claim 2, characterized in that each chip (18) comprises a wafer-substrate of conductive silicon (24) in which have been formed circular trenches making it possible to isolate at least one line of cylindrical pads (26), and a diamond disc made conductive, formed on the front face of each pad and forming a micro-electrode (30), the rear face of the pad constituting said contact area.

4. Printer head according to claim 3, characterized in that said trenches are filled with an insulating material (28).

5. Printer head according to one of claims 3 and 4, characterized in that the front face of the silicon wafer (24) is covered, with the exception of at least part of the micro-electrodes (30 ), at least one layer of insulating material (32, 34).

6. Printer head according to one of claims 3 to 5, characterized in that the rear face of the pads (26) is covered with a metallic layer.

7. Printer head according to one of claims 1 to 6, characterized in that the chips have n rows of micro-electrodes (30) and in that the space between the micro-electrodes of a line is n times the elementary step between two successive printing points.

8. Printer head according to claim 7, characterized in that the space between two neighboring lines of micro-electrodes (30) is a multiple of the elementary pitch.

9. Printer head according to one of claims 7 and 8, characterized in that the micro-electrodes (30) of two neighboring lines are horizontally offset by the elementary pitch.

10. Printer head according to one of claims 7 to 9, characterized in that the spacing between the micro-electrode (30) located at the end of a chip (18) of a series and the micro -electrode located at the opposite end of the chip adjacent to the other series is equal to the elementary pitch.

11. Printer head according to one of claims 7 to 10, characterized in that each module is equipped with two chips (38) which are arranged parallel to each other and offset horizontally by half of the elementary pitch .

12. Printer head according to one of claims 2 to 1 1, characterized in that said printed circuit (20) is linked to a multiplex addressing electronics.

13. Module for a printer head by electrocoagulation of ink, characterized in that it comprises at least one chip (18) provided, on its front face, with a plurality of micro-electrodes (30), a printed circuit (20) on which said chip is fixed by its rear face so that each micro-electrode is in connection with one of its tracks and an electronic multiplex addressing circuit connected to said tracks.

14. Module according to claim 13, characterized in that each chip (18) comprises a wafer-substrate of conductive silicon (24) in which circular trenches have been made making it possible to isolate a plurality of cylindrical pads (26), and a diamond disc made conductive formed on the front face of each stud and constituting a micro-electrode (30), the rear face of the stud ensuring electrical contact with the printed circuit (20).