Spacers for flat display screens

A method for assembling a spaced flat panel display screen having a first plate and second plate, each with an internal facing surface that are opposing comprises the steps of positioning spacers on the internal facing surface of the first plate, positioning the second plate so that the internal facing surface of the second plate contacts the spacers, heating the spacers to a temperature causing soldering of the spacers to the plates, pulling the first and second plates apart to stretch the spacers to a predetermined distance, and cooling the spacers.

The present invention relates to spacers used in flat display screens as 
well as processes for implementing these spacers. 
The invention more particularly relates to the industrial manufacturing of 
display screens, such as micropoints, plasma, liquid crystal, etc., 
screens, formed by two adjacent plates made of glass, quartz or silicon 
and forming a flat airtight chamber that is subjected to a vacuum. 
Flat display screens require the use of spacers for maintaining a 
predetermined distance between the two support plates. To maintain a 
predetermined distance between the electrodes raises problems as regards 
the spacer's size (spacers must be invisible) and its implementation. 
In the prior art processes, the distance to be kept between the two plates 
is generally provided by balls that are distributed over one of the plates 
and glued before the second plate is mounted. The distribution of the 
balls is controlled with a frame or an analogous device. Such a technique 
has many drawbacks: 
The balls are inaccurately positioned which may cause some active portions 
of the electrodes disposed over the plates to be crushed. 
It is difficult to control the final distance between the two plates due to 
the pressure applied by the plates onto the balls once vacuum is 
established. 
The width of the balls cannot be smaller than their height. 
The balls are subject to electrostatic charging that may cause destroying 
breakdowns. 
An object of the present invention is to avoid the above-mentioned 
drawbacks. Indeed, the invention allows both to accurately control the 
distance between the plates and the position of the spacers and to 
decrease the lateral size of the spacers. 
The invention uses continuous or discontinuous spacers formed by circular, 
polygonal or other threads or pads that are preferably made of glass or 
quartz. The spacers are made of fibers, pads or piles of various shapes 
that are glued, welded or sealed, either on one plate (their height being 
equal to the desired distance) or on both plates so as to be interleaved, 
each series of spacers providing a portion of the distance between the two 
plates once the process is completed.

The device of FIGS. 1-6 is constituted by a flat display screen, such as a 
micropoint, plasma or analogous screen, that is formed by two plates 1, 2 
made of glass, quartz or silicon. Plates 1, 2 are associated with spacers 
3, 4 formed by fibers preferably made of glass or quartz. 
These circular, rectangular or polygonal fibers 3 can be threads or pads 
that are stretched and fixed by glueing, laser welding or by any other 
suitable means, onto one of the two plates 1, 2 (FIGS. 1, 2, 3, 4) or on 
both plates (FIGS. 2, 5) in one or two parallel element arrays. 
When fibers 3 are disposed over only one plate, their height must be chosen 
to be equal to the desired distance. 
In contrast, if the spacers are fixed onto the two plates, the distance 
must be equal to the sum of the heights or thicknesses of the fibers of 
the two networks, these heights being not necessarily identical. In the 
latter case, the two arrays are mounted in dissimilar directions, 
generally perpendicular, so as to interleave each other (FIG. 2). 
According to an alternative embodiment, the spacers 3 are formed by one 
fiber 5 or by a few fibers stretched between plates 1, 2 by means of clips 
6 and thread-guide rollers 7 (FIG. 6). 
When the total length of the fibers is important, due to the large 
supporting surface area thus obtained (with respect to the balls), spacers 
3 are not liable to be crushed, despite the vacuum existing between the 
plates. Accordingly, the final distance obtained is substantially equal to 
the thickness of the fibers disposed alone or superposed. 
However, for short fibers, or for pads or piles disposed perpendicularly to 
the surface of plates 1, 2, the final distance will be advantageously 
accurately determined by a process including the following steps: 
1. Treatment of the plates. The inner surfaces of plates 1, 2 are 
chemically etched by using a resist mask 8, for example, or mechanically 
etched or equivalent, to provide satisfactory bonding of the fusible glass 
spacers 3 onto the etched area 9 (FIG. 7). 
2. Positioning of the spacers. Spacers 3, that may be glued or laser 
welded, are disposed over a plate 1, (that will be the lower plate during 
the process), on the etched areas 9. The size of the spacers is calculated 
as a function of their maximum width after stretching and as a function of 
the desired final distance between the two plates. 
3. Cleaning/Outgassing. Plates 1, 2 are conventionally cleaned, and are 
then outgassed in a vacuum chamber while a distance sufficient to obtain 
the desired value is maintained between them. 
4. Assembling of the plates. Both plates are brought nearer until they 
mechanically contact spacers 3 (FIG. 8). 
5. Soldering of spacers. A heating step adapted to the mass of glass or 
quartz of plates 1, 2 and of spacers 3 rises the temperature of the 
assembly up to a value slightly higher than the melting temperature of the 
fusible glass constituting the spacers. The distance between the plates is 
controlled by mechanical wedges that limit the flattening of the spacers. 
The fusible glass of the spacers partially melts and "wets" the plates 
over the etched areas 9, thus causing soldering of the spacers over these 
areas (FIG. 9). 
6. Stretching. Plates 1, 2 are set apart one from the other until the 
desired distance is obtained. Spacers 3 are thus stretched and their width 
is accordingly reduced (FIG. 10). 
7. Cooling. The assembly is let to cool or is cooled down until spacers 3 
are solidified. The process is completed. 
Remarks 
1. From step 3, the process is carried out in the same airtight chamber in 
order not to "break" the vacuum chain. 
2. The external airtightness of the flat chamber can be simultaneously 
carried out by means of a string of peripheral fusible glass. 
According to an alternative embodiment of the invention, the spacers are 
constituted by pads 10 made of fusible glass disposed over the lower plate 
1 by means of a cooled nozzle 11 and welded through fusion with a welding 
torch 12 for melting the base of the pads (FIG. 11). The pads can also be 
sealed in holes 13 previously pierced in the support plate 1 by any 
suitable means. Pads 10 may also be welded (FIG. 12). 
The positioning of the various constitutive elements confers to the 
invention many advantages that have not yet been obtained with similar 
devices or processes.