FR2549627A1 - Connecting device for a display screen and a display screen comprising such a device. - Google Patents

Abstract

The device relates to flat-type display screens comprising two transparent sheets, more particularly those with smectic liquid crystals. It permits remote connection to a flat screen. It comprises conducting microballs 13 and insulating microballs 37 in suspension in a polymerisable resin 36 arranged between the two sheets 31, 32. Application to display of images for television and display peripherals, for remote transmission.

Description

DEVICE FOR CONNECTING A VISUALIZATION SCREEN
METHOD AND VISUALIZATION SCREEN COMPRISING SUCH A DEVICE PROCEDE.

 The invention relates to a device for connecting a display screen.

 The invention applies more particularly to liquid crystal display devices with a matrix access screen. Such screens include conductive tracks placed horizontally called rows and conductive tracks placed vertically called columns. The number of intersection points between the rows and the columns determines the maximum resolution of the image that can be obtained. The constant increase in this resolution leads to an ever increasing number of rows and columns for the same screen surface. To fix an order of magnitude, the conductive tracks can have a width of 250 μm and be separated by a distance of the same order, their thickness being less than 1 μm. These conductive tracks are connected to their control circuits by means of a bundle of conductive wires arranged in a sheet.

Known solutions for connecting networks of parallel conductive tracks on an insulating support are:
- The use of conventional connectors:
Connectors requiring glass drilling operations cannot be used. Glass slides must therefore be inserted into a connector for printed circuits (a clamp and friction type). None of these connectors has not less than 1.27 mm, which leads to the flowering of the etched glass networks. This development will disrupt the heating network technology either, If we remain in a thin layer, by modifying the resistances to be taken into account, or if we pass in a thick layer, by a range of additional complex operations. The dimensional increase of the glass slides caused by the blooming also causes problems of mechanical resistance. In addition, the thin layers used to make the networks do not have mechanical resistance to friction.
o sufficient (3000 A thickness) to avoid the thickening operation.

- Ultra-sound microwelding:
This technique only provides electrical continuity and has the main disadvantages:
the need to thicken the welding zones on the network when there is compatibility between network metal and wire (thickening from 300 A to 1 / μm) or production of a multilayer to ensure this compatibility.

 the manual microwelding is long and very painful visually for the operator, the automation does not eliminate mechanical fragility.

 the need to ensure redundancy of the contacts by a second wire, which leads to 2 wires and 4 solders per connected track.

Fuse alloy microwelding:
In this technique, conventional alloys are used where the tin-lead eutectic dominates (SnPb 63-37).

 It can be a wire-to-wire technique which presents difficulties of the same order as for ultrasonic microwelding.

 It can also be a block welding technique: globally the fusion of a calibrated wire is then made, placed perpendicularly and between the two networks to be connected. During the liquid phase, the capillarity causes the displacement of the alloy along the tracks of the networks, the liquid phase must "wet" the materials of the tracks and not "wet" the substrates carrying the tracks. If the volume of fusible alloy is not too large, the phenomena of capillarity and wettability play to the full and cause between contiguous tracks on the substrates the rupture of the continuity of the "wire" of soldering. of this type of wire, other problems related to the necessary material exist, in particular the thermal problems caused by the large dimension of the heating breakdown (greater than 100 mm to avoid successive "passes").

 Finally, it can be a reflow technique. But there are no preforms to sizes and no contact points. In addition, the liquid crystal screen being filled before welding, there would be in this technology a very great risk of destruction caused by the differential expansion between liquid and envelope (thermometer effect).

- Connection by elastomers:
Currently, there are three types of elastomers on the market.

 The loaded elastomers are constituted by the stack of slices of elastomers whose conduction is ensured by a load of graphite or silver and slices of insulating elastomers. These "connectors" have parasitic contact resistances greater than 1000 Q systematically and require significant crushing (10 to 15%) which results in the application of crushing forces of at least several kilograms (2 to 6 kg for 10 cm for most of these connectors).

 Elastomers with embedded wires have wires which provide connection at their ends. Apart from the difficulties due to the pitch of the wires which is not compatible with current networks, one can note an annoying evolution of the disturbing resistance during tests on the heating networks. The contact resistance is close to Ohm if the crushing force of the elastomer is sufficient. The risk of scratching and "cutting" the tracks is not negligible. Here too, the crushing force is important. The irregularity of its application over the length of the connector results in the absence of numerous contacts.

 The elastomers with surface threads have a general U-shape which makes it possible to reduce the crushing forces between the two branches.

The use of golden wires however requires a significant effort to try to obtain stable parasitic resistances less than ten Ohms.

To overcome the drawbacks of the known art which have just been recalled, the present invention comprises conductive microbeads and insulating microbeads suspended in a polymerizable resin, it ensures:
A parasitic electrical resistance between the networks to be connected, lower than the Ohm;
An electrical insulation resistance between contiguous tracks of the same very high network;
. Good sealing of the contact points;
Significant redundancy of the connection (several dozen contact points between the tracks to be connected);
. A good mechanical connection between the networks to be connected;
Regular spacing between the two networks constituting the cell;
. Easy and global implementation (screen printing);
An absence of specific surface treatment for:
- avoid abrasion on thin layers
- avoid oxidation of the areas in contact;
- facilitate welding.

 The device of the invention allows a definitive connection between a flat liquid crystal screen and its printed control circuit and the transfer, on one of the two substrates constituting the matrix screen, of all of the conductive tracks so as to ensure on the same side of the plane the connection to the control electronics.

 This device performs a low electrical resistance interconnection of networks of conductive lines with fine pitch from one plane to another plane.

 The subject of the invention is a device for connecting a display screen reproducing the images analyzed in the form of a grid of rows and columns, this screen comprising a layer of material which can be written down by a mixed thermal and electrical effect. , comprised between two transparent blades in which the transparent and parallel electrode plies are deposited on these two blades, this connection device being characterized in that it comprises conductive microbeads, insulating microbeads, of dimension smaller than that of microbeads conductive and playing the role of shims between the two glass slides, suspended in a polymerizable resin, these conductive microbeads having mechanical resistance allowing creep during the crushing of the layer of writable material between the two slides, for making the connection, the insulating microbeads having a higher crushing resistance than those of microb conductive girls.

 The invention will be better understood and other advantages will become apparent from the following description, with reference to the appended figures.

- Figure 1 shows a connection device of the prior art;
- Figure 2 shows the connection areas of a device of the prior art;
- Figure 3 shows the connection areas of the device of the invention;
- Figure 4 illustrates a flat matrix screen with smectic liquid crystal;
- Figure 5 illustrates a diagram of the control of a network as illustrated in Figure 4
- Figure 6 illustrates a section of the device of the invention along the axis of the conductive lines
- Figure 7 illustrates a section of the device of the invention in a direction perpendicular to the axis of the conductive lines.

 Figures 8 to 10 illustrate a display screen comprising the device of the invention.

 Among the different possible display devices, the invention applies more particularly to high definition liquid crystal display screens, of the matrix type.

 The invention applies in particular to display screens comprising liquid crystals in the smectic phase, which are current controlled.

 It is known that when a thin layer of a material having a smectic phase is cooled starting from the liquid phase, the optical appearance of the thin layer strongly depends on the cooling rate. If the cooling takes place under an electric field, the material is oriented uniformly and the layer appears to be perfectly transparent. If on the other hand, the transition from the liquid phase to the smectic phase takes place naturally in the absence of an electric field, it forms in the layer of domains having different relative to each other and resulting in a strong diffusion of transmitted or reflected light. This effect can be used to record an image on a liquid crystal film having a smectic phase. The material, placed between two transparent slides, is kept at a temperature such that it is in its smectic phase, the inscription of a image point is obtained by heating the liquid layer followed by the application of the electric field. The quantity of heat necessary for melting the layer of liquid crystals can be provided by infrared radiation or by laser radiation. But it is possible to increase the speed of writing of the image in a layer of material having such a thermoelectric effect by using members which are heating resistors making it possible to write an image line by line, which then allows have the duration of a line to simultaneously write all the points on this line. This method of writing and erasing is faster than optical methods and allows you to get closer to writing on a display screen d 'video images.

 FIG. 1 represents a device for connecting conductors arranged on two elements, according to the prior art. We have chosen to represent the connection system of a glass substrate 1 which can be one of the plates supporting pun networks of electrodes of a matrix access display screen. The element 10 symbolizes the rest of the display screen comprising, for example, a layer of liquid crystal inserted between the blade 1 and another blade 11 supporting the other array of electrodes of the screen. Conductors 2 are etched on the substrate 1 on the side of the element 10. They are arranged parallel to each other and are regularly spaced.

In order for a light ray incident to the substrate 1 to be able to access the liquid crystal layer of the screen, the conductors 2 must be transparent. They can consist of a layer of indium oxide. A printed circuit 3 is placed under the element 10 and supports elements 4 forming part of the screen's electronic control circuits. It is understood that the electrical contacts between the internal face of the printed circuit 3 and the conductors supported by the blade 11 are easily achievable. On the other hand, the connections between the conductors 2 of the substrate 1 and the conductors 5 which correspond to them on the printed circuit must be provided by means of a connector 6. The ends of the conductors 5 are etched at the same pitch as the conductors 2 and are located opposite these conductors. The connector 6 is generally constituted by an elastomer body 7 which is encircled according to its largest dimension of conductive tracks 8 isolated from each other and parallel to the conductors 2 and 5. The space separating the tracks 8 between them is of the same order of magnitude as the width of these tracks. The pitch of the connection tracks is generally chosen to be less than that of the conductors to be connected. This has several advantages: the positioning of the connector relative to the conductors to be connected does not need to be rigorous and the risks of short circuits between conductors are thus avoided. A second connector 9 playing the same role as the connector 6 can be provided at the other end of the conductors 2. A slight tightening exerted on the assembly, as indicated by the arrows, ensures the electrical contact of the different parts. connectors being made of elastomer slightly deform under the effect of tightening ensuring the effectiveness of the contact. However, it is imperative to align the conductors of the substrate with those of the printed circuit. This operation is quite delicate, especially if the substrate is not transparent and therefore does not allow visual alignment.

 FIG. 2 schematically represents the connection zones of a device of the prior art.

 FIG. 3 schematically represents the connection zones of the device of the invention.

 The device of the invention makes it possible to ensure the transfer, on one of the two substrates constituting the matrix screen, of all of the conductive tracks so as to associate on the same face of the plane the connection to the control electronics. .

 In these two figures, the arrows indicate the connection zones of the electrodes deposited on the two transparent blades 12 and 13 enclosing the liquid crystal layer of a display screen with matrix access, as well as their orientation relating to the technology of flat matrix screens. with smectic liquid crystals on which information display is obtained by thermo-optical effect which makes it possible to pass from an isotropic state of the crystal, when the latter is heated, to a diffusing state if the cooling of the crystal is spontaneous, or to a transparent state if this cooling takes place under an electric field.

 FIG. 4 represents a flat matrix screen with smectic liquid crystal.

 The two layers 20 and 21 are for example made of glass the network 22 is that which makes it possible to impose the electric field E. The network 23 provides the heating power. Zone 24 represents the space filled by the liquid crystal.

 To make a connection ensuring the transfer of heating power, we can consider the diagram of the heating control shown in Figure 5.

Indeed, it is necessary to take into account the related imperatives:
to control circuit technologies (maximum output voltage and maximum power that can be output: #M = U2 / R (R being the output resistance of the circuits).

a to the technology for producing the heating network R = P
p resistivity of the material constituting the heating electrode.

 1 length of the heating electrode.

 e width of heating electrode.

 thickness of the heating electrode.

 Also it is imperative to make connections introducing parasitic series resistances as low as possible. (r = R / 10 being a minimum).

 Parasitic resistances are considered whose values do not exceed the fraction of Ohm. The mismatching of the impedances is then minimal and the power lost at the connection level is negligible.

 In FIG. 5, there is the control circuit support 26, the connectors 27 and the liquid crystal cell 28.

The heating power is P = Ri2 with R ~ 15 to 30 r for example
u
1 = z Ri by construction R3, R'3 <<R
R, R'1 <<OulQ
with i = 1 to 2 Amps (Pulses)
and R2 + R'2 <1 Q
R2, R'2 being the parasitic connection resistances.

In such a cell, the electrode networks face each other in the cell, which results in the production of the supports for the control circuits:
. either the use of two support families t
or an inversion operation dependent on flexible circuits.

 The device of the invention makes it possible to carry out this transfer during the sealing operation of the cell.

 Depending on the type of layers used to make the networks, we can transfer the video network (indium tin oxide (ITO) Semitransparent) on the heating network (aluminum) or transfer the heating network (Aluminum ) in terms of the Video network (indium tin oxide (ITO) Copper). Here too, the imperative condition is that the disturbing resistance is much lower than the resistance of the heating line.

 In the device of the invention, the low resistance electrical contact is ensured only by a deformation of metallic elements, in contact with the tracks. The insulation and the mechanical resistance are ensured by an adhesive or a polymerizable resin which can ensure the sealing of the contact zones. The role of shims is held by insulating balls (glass balls) whose crush resistance is much higher than that of metallic elements. These balls limit the possibility of short circuits in the event of excessive crushing.

 The various elements of the device of the invention are shown in Figures 6 and 7 which are sectional views of the device of the invention respectively along the axis of the conductive lines and in a direction perpendicular to this axis.

 - The conductive elements 35 are micrograins or microbeads of calibrated dimensions, conductive of a metallic nature. The quantity and the.

dimensions of these are linked to the type of connection to be made (no tracks, width of the insulators, distance between the networks to be connected and implementation).

 - The shims of thickness 37 are micrograins or microbeads of glass (or other hard material and electrical insulator) of calibrated dimension. The quantity and dimensions of these must meet the same criteria as the conductive elements. But their dimensions are smaller than those of the metallic elements.

 - The adhesive or resin 36 are used together, and they include the conductive elements and the thickness shims in suspension. This resin must be: compatible with suspended materials; compatible with the metals constituting the tracks; adhere and be compatible with the substrates carrying the tracks. It can be polymerized in situ by any of the conventional methods.

The device of the invention therefore comprises:
the substrate 31 from which the line network is to be transferred.

- the transfer substrate 32
- the conductive line 33 to be transferred
- the transfer conductor 34
conductive metal microbeads 35
- the bonding resin 36
- the insulating microbeads 37.

These metallic conductive elements can be: in mental or soft alloys which have a low resistance to crushing such as Aluminum, Indium, Copper, and their alloys, for example. These metallic elements have the following characteristics: low electrical resistivities; average mechanical resistance to crushing in order to be able to creep properly during the placement crushing; sizes can range from 5 to 25 / µm. Depending on the application, one selects, for example, a slice of 5 / μm in width, which depends above all on the thickness setting between the networks (for example 15 to 20 / μm for a setting at 10
15 jum) which have a low crush resistance
The quantity of suspension is determined according to the volume, from the dimensions of the zones to be connected, the number of contact points desired, as well as the width of the isolation zones on each network. For a quantity greater than one maximum we obtain the known phenomenon of percolation (agglomerate) of grains which leads to short circuits between contiguous tracks. As regards the shape of the grains, it is desirable that the shape coefficient (i.e. the ratio
larger dimension
smallest dimension for the same grain) does not exceed 1.5 to 2.

 The shims may be insulating microbeads made of glass or any other hard insulating material. The so-called "microbeads" can be replaced by segments of fibers (glass for example). They have the following characteristics: good electrical insulation; high crush resistance; homogeneity of dimension. This benefits glass fibers over microbeads; the quantity put in suspension depends on the importance of the setting problem and makes it possible to control the viscosity of the adhesive of the resin which it makes it possible to adapt to the method of implementation.

 With regard to the adhesive or resin apart from the problem of compatibility with the materials present, it is necessary to use a rapidly polymerizable material to obtain a final bond. The polymerization technique can be the following ultra violet radiation + pressure; or temperature- (application time) + pressure couple which can only be critical if the temperature-time couple is high and not damped before any disturbance of the liquid crystal when it is in the cell.

 Figures 8, 9, 10 illustrate a display screen comprising the device of the invention; Figures 9 and 10 being two sectional views, Figure 9 along the cutting plane BB 'and Figure 10 along the cutting plane AA'.

 As shown in FIGS. 6 and 7, the two transparent blades 31 and 32 have, on their opposite faces, sheets of transparent electrodes which are parallel to each other and which make it possible to address all points of the liquid crystal which is located between these two blades 31 and 32.

 A net of resin is deposited between these two blades all along the surface of the blade 31. The sheet of electrodes 45 is disposed over the entire length of the blade 32. On the other hand, the sheet of electrodes 44 and the sheet of electrodes 43 are not interconnected. They are connected by means of the resin 36 and the electrode sheet 46 deposited on the blade 31; zone 47 being that of the active substance which may comprise, for example, liquid crystals.

As a nonlimiting example, we can consider the following values:
- sheets of electrodes with a pitch of 700 μm, the width of the electrodes being approximately 350 μm;
- the two networks being of 100 tracks each, one being an aluminum deposit on a glass support, and the other a copper deposit on a flexible support;
- the conductive microbeads forming 7 to 10% of the volume of resin;
- conductive microbeads in cuproplomb from 15 to 35 / µm, having a shape coefficient of 1.5;
- the insulating microbeads of 17 to 20 μm forming 5% of the volume of resin;
the resin being of raraldite which can be polymerized using the temperature-time pair, the thread of adhesive deposited having a width of approximately 1 mm.

The device which is the subject of the invention ensures:
parasitic electrical resistance between the networks to be connected, lower than the Ohm
an electrical resistance of insulation between contiguous tracks of the same very high network;
good sealing of the contact points;
. significant redundancy of the connection (several dozen contact points between the tracks to be connected);
. a good mechanical connection between the networks to be connected;
. regular spacing between the two networks constituting the cell;
. easy and global implementation (screen printing);
. an absence of specific surface treatment for:
- avoid abrasion on thin layers;
- avoid oxidation of the areas in contact;
- facilitate welding.

Thus the device of the invention finds its application in:
. a sealing bead for matrix access liquid crystal flat screens;
a low resistance connection (lower than the Ohm) for flat screens;
. all connections in thin and large dimensions of a large number of points in a plane.

Claims (10)

 1. Device for connecting a display screen reproducing analyzed images in the form of a grid of rows and columns, this screen comprising a layer of material which can be written by a mixed thermal and electrical effect, between two plates transparent (31, 32) in which the transparent and parallel electrode plies are deposited on these two blades (31, 32), this connection device being characterized in that it comprises conductive microbeads (35), insulating microbeads (37) of dimension smaller than that of the conductive microbeads, and playing the role of shims between the two glass slides (31, 32), suspended in a polymerizable resin (36); these conductive microbeads (35) having a mechanical resistance allowing creep during the crushing of the layer of writable material between the two blades for making the connection, the insulating microbeads (37) having a higher crushing resistance than that of the conductive microbeads (35).  2. Device according to claim 1, characterized in that the conductive microbeads (35) have a diameter in the range 5 to 50 micrometers.  3. Device according to claim 1, characterized in that the conductive microbeads (35) are made of metal.  4. Device according to claim 3, characterized in that the conductive microbeads (35) are made of copper, aluminum or indium.  5. Device according to claim 1, characterized in that the conductive microbeads (35) are made of alloy.  6. Device according to claim 5, characterized in that the conductive microbeads (35) are made of aluminum alloy, indium or copper.  7. Device according to claim 1, characterized in that the insulating microbeads (37) are made of glass.  8. Device according to claim 1, characterized in that the insulating microbeads (37) are segments of glass fibers.  9. Device according to claim 1, characterized in that the conductive microbeads (35) have a form coefficient less than 2.  10. Display screen comprising the device of claim 1, characterized in that the writable material is of the liquid crystal type in the smectic phase.