Note: Descriptions are shown in the official language in which they were submitted.
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ELECTRICAL INDICIA DISPLAY D~VICE
AND METHOD FOR MAKING SAME
The present invention relates to an electrical indicia
display device and method for making same. Specifically,
the invention relates to a new arrangement of anodes and
cathodes in a gas discharge digital display unit.
Conventional gas discharge digital display units -
generally include a substrate having an upper surface
which is enclosed within a sealed envelope having a viewing
10 window on the upper portion thereof. Cathode segments and
anodes are placed within the envelope together with an
ionizable gas. Whenever an electric potential is imposed
between the cathode segments and the anodes, a cathode glow
occurs in the ionizable gas adjacent the cathode segments.
The cathode segMents are usually arranged in patterns
which permit them to be activated selectively so as to form
glow patterns which correspond to various indicia.
The positioning of the cathodes with respect to the
anodes is important in order to obtain the proper glow
20 characteristics. It is important that the glow be isolated
to a confined area adjacent each cathode segment. Improper
positioning of the cathode segments or the anodes causes
"cross talk"-or unwanted "blue glow" inside the unit.
Cross talk is a term describing the phenomenoll of glow
occurring near a cathode segment which is not actuated,
but which is adjacent an actuated cathode segment. Blue
glow is a phenomenon whereby a bluish glow occurs over the
surace of the anode in such a generalized form as to
prevent the clear definition of the indicia desired. Also,
30 the positioning of the anodes with respect to the cathodes
is important to determine the starting voltage required to
induce glow adjacent each cathode segrnent. The closer the
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cathode segment is with respect to the anode, the less
voltage is re~uired to initiate cathode glow. Variations
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in the distances o:E the various cathode segments with
respect to the anodes results in variation in the starting
voltage required to initiate each of the respective
cathode segments. -
Presently the arrangemen~ of the cathodes to the anodes
ls done in one of two ways. One commonly used method is
to place the cathode segments on a substrate within the
10 sealed envelope. The anodes are then mounted on the
under surface of the glass window in spaced relation above
the cathode segments. The anodes are translucent so that
whenever a glow occurs adjacent a cathode segment, that
glow is visible from outside the window.
Several disadvantages are encountered with the above
arrangement. Even though the anode is translucent, it causes
reflections from outside the window, and therefore makes
it more difficult for the viewer to see the indicia being
displayed. Furthermore, the manufacturer of such units `~
20 requires two technologies for placing the cathodes and the
anodes in the unit. One technology is utilized for placing
the translucent ànode on the under surface of the glass
window, and another technology is used for placing the
cathode segments on the upper surface of the substrate ;
within the compartment.
Other arrangements of anodes and cathodes within
the envelope have been utilized. For example, the anodes
and cathodes have been placed in side by side relations~ip
on the upper surface of the substrate. This arrangement
30 also has disadvantages. With this side by side arrangement,
it is difficult to space the cathode segments equidistantly
from all the anodes. ~ccordingly, there is often variation
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in the starting voltage required for each of the separatecathode segments. Also, the distance between the anodes
and the cathodes must be relatively large, and this results
in requiring a higher starting voltage than with the units
having the anode on the under surface of the window. Also,
cross talk and unwanted blue glow often occur in these
side by side units.
The present invention contemplates placing both the
anodes and the cathodes on the substrate. However, the
10 cathodes are placed over the anode and separated therefrom
by a layer of dielectric material. This technology permits
a series of printed layers to be formed on the substrate,
forming first the anodes, second, the dielectric layer, and
third, the cathode se~ments. The same technology is
utilized for both the imprinting of the anodes and the
imprinting of the cathodes. The distance between the anodes
and the cathodes is determined by the thickness of the
dielectric layer therebetween. Thus it is possible to make
this distance small so as to minimize the starting voltage l ;
20 re~uired to induce cathode glow. Furthermore, because this
distance is consistent from one cathode segment to another,
there is greater consistency in the starting voltage requirèd `
to actuate the various cathode segments.
It has also been determined that the spacing of the ;
window above the substrate affects the performance of the
cathode segments. In the configuration with a transparent
anode on the front glass cover, it has be`en known that the ; ~-
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spacing between the glass cover and the substrate is
important, and this spaciny has been maintained at a `
30 distance of from .020 to .015 inches. However, when the
anodes and cathodes have been placed on the same substrate,
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little importance has been attached to the distance betweenthe glass cover and the substrate.
This distance is i~portant to the present invention,
for it has been found that as the spacing between the glass
cover and the substrate increases, the starting voltage ;~
goes down, the cross tal]~ problem increases, and the tendency
for blue glow to form between adjacent digits increases.
As the spacing decreases, the starting voltage goes up,
the cross talk problem diminishes and the tendency for blue
glow to form between digits decreases while the tendency
for blue glow to form between anodes and cathodes of the ~-
same digit increases. The present invention contemplates
a distance of .035 inches to .045 inches to produce the
best results.
Therefore, a primary object of the present invention
is the provision of an electrical indicia display device
and method for making same.
A further object of the present invention is the
provision of a method and means which produces greater
consistency in starting voltage re~uired to induce cathode
glow adjacent each of the various cathode segments.
A further object of the present invention is the
provision of a method and means which results in a low
starting voltage which is comparable in rnagnitude to the
starting voltage required for devices having a transparent ~ -
anode on the front glass cover.
A further object o the present invention is the
provision of a method and means which results in a greater
electrical field being produced between the anode and
cathode segments than has been obtained in previous side by
side cathode-anode arrangements
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A further object of the present invention is the
provision of a method and means which permits easier
control of the distance between the anode and the cathode.
A further object of the present invention is the
provision of a method and means which permits the use of
identical technolo~y for placing both the anodes and the
ca-thodes in the unit.
A further object of the present invention is the
provision of a method and means which chooses the spacing
between the glass cover and the substrate so as to provide
the most advantageous combination of factors relating to
starting voltage, cross talk, and a blue glow.
A further object o the present invention is the
provision of a method and means which i6 econornical and ;;;
simpler than previous electrical indicia display devices
and methods for rnaking same.
BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS
This invention consists in the construction,
arrangements and combination of the various parts of the
device, whereby the objects contemplated are attained as
hereinafter more fully set forth, specifically pointed
out in the claims, and illustrated in the accompanying
drawings in which:
Figure 1 is a perspective view of the present
invention.
Figures 2A, 2B, 2C and 2D are plan views showing the
substrate having the first, second, third, and fourth
printing thereon respectively.
Figures 3 and 4 are sectional views taken along
lines 3-3 and 4-4 of Figure 1.
Figure 5 is a view similar to Figure 3, showing an
enlarged view of the cathode segment, dielectric layer~ and
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anode, and illustrating the lines of force which resul-t
from imposing a potential difference on the anode and
cathode.
DETAILED DESCRIPTION
Referring to the drawings, the numeral 10 refers to
the indicia display device of the present invention.
Device 10 comprises a housing formed by a substrate 12 and
a glass window 14 which are joined in spaced parallel
relationship by a glass solder material 16 so as to form
10 a sealed compartment 18 therebetween. Substrate 12 ~ -
includes an aperture 20 therein which provides communica-
tion into the interior of compartment 18. A glass tube
22 is secured over aperture 20 by means of glass solder
23. Glass tube 22 has been melted to close off its end
24 and thereby her~etically seal compartment 18 from the
atmosphere.
The first steps in the fabrication of device 10 ;~
involve screen printing. Various dielectric materials may
be utilized for the substrate including aluminum oxide or
glass or other materials.
The first pattern is a conductor layer which is
printed on the substrate as shown in Figure 2A. The layer
includes a plurality of anodes 26 which may hàve varying
shapes, but which are shown in Figure 2A to be shaped in
parallelograms (for numerals) and small circles ~for -
decimal points). This first conductor pattern also includes
a plurality of elongated conductors 28 which are in -
electrical connection with a plurality of leads 30
positioned adjacent the edge oE substrate 12.
The conductor material is an ink manufactured by
DuPont Company under the product designation #8730 PD-AG.
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The ink is then electroplated with nickel. Alternatively,
there are low firing nickel pastes commercially available
which could be used.
Figure 2B illustrates the second pattern which is
printed on the substrates. This pattern is a dielectric
layer 32 which is preferably printed twice to insure good
insulation characteristics. The pattern includes a
rectangular sheet having a predetermined pattern of vias
or holes 34 therein. Also, the dielectric layer 32 has a
plurality of anode openings 36 therein positioned in
registered alignment over anodes 26.
The location of vias 34 is arranged so as to be in
registered alignment with various conductors 28 shown in
Figure 2A. The relationship of anode openings 36 to
anodes 26 i9 shown in Figures 3-S. The margins of anode
openings 36 overlap slightly around the edyes of anodes
26, and these overlapping portions are designated by the
numeral 38.
The third printing step is shown in Figure 2C and
20 comprises printing a conductor ink in the form of cathode ;
segments 40. Also connected to each cathode segment 40
is a conductor 42 which leads to a via 34 where it is in
electrical contact through via 34 to conductors 28 of the
~irst printing shown in Figure 2A. A plurality of anode
conductors 43 are each connected at one end through a via ;~
34 to an anode 2'6 and at the opposite end through a via 34 to `~
a lead 30. Segments 40 are arranged in Figure 8 pattern
in a conventional manner presently known in the art. By
inducing cathode glow adjacent various combinations of the ;~
segments 40 within each Figure 8 pattern, it is possible to
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produce various digits which are visible through window 14.
Each seyment 40 of each diyit is connected through a via to
the conductor pattern below shown in Figure 2A.
The last pattern is another dielectric layer 44 shown
in Figure 2D. This layer covers all portions of the seg- -,
ments which are not supposed to show. It also provides
contrasting backgrou,nd so the display will be easier to
read. ~
After each of the above prints has been made, the unit ~ ,,,
10 is fired in a belt kiln at the appropriate temperature and ' -, ~
time for the various materials used. This fires each layer ;~
of paste into a permanent rigid conductor or insulator. The ,
resulting component is an electrical circuit. , '
Of particular importance is the arrangement of cathode
segments 40 with respect to anode 26 and dielectric layers ~'
36. Cathode segments 40 overlie the overlapping portions
38 of dielectric layer 32 so that the overlapping portions
38 separate cathode segments 40 from anode 26. The inner
margins of anode openings 36 in dielectric layer 32 are
20 exposed to the atmosphere within compartment 18. ',
Figure 5 illustrates the electrical field which is
produced whenever a potential difference is imposed between ,
cathode segments 40'and anode 26. The letters X designate
the lines of equal potential which emanate adjacent the ,' '
exposed inner Inargins of anode openings 36 in Figure 5. ,
It can be seen that the distance between cathode segments
40 and anode 26 is determined by the thickness of dielectric
layer 32. The electric field intensity is dependent upon 3'
the thickness of the dielectric and is not greatly affected
by the distance designated "a" in Figure 5. Thus, it is
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possible for a small manufacturing error to occur in the
placement of cathode segments 40 with respect to the edges
of anode opening 36. Slight variations will not result in
appreciable differences in the intensity of the electric
field designated by lines X. Because the field intensity
is great, it i5 possible to induce a cathode glow with a
smaller starting voltage in the present invention than in
previous devices which placed cathodes and anodes on the
substrate in side by side relationship.
10After the final printing shown in Figure 2D has
occurred, glass window 14 is sealed over substrate 12 by
means of ~lass solder 16. Conventional glass solders ;
manufactured on the market have been found to be satisfac-tory
for this purpose.
After assembly of the display unit is attached to a high ~ ~
vacuum pump by means of glass tube 22 (which at this point - --
in the assembly has not yet been sealed off). Compartment
18 is then exhausted and the display unit is baked at
300C. to 400C. The pressure within compartment 18 is
20 held below 10 7torr. ;~
After baking the display is then ready to be filled.
The proper mixture of neon plus another gas (usually argon)
is introduced together with mercury and the exhaust tube
is cut off with a torch, sealing the proper atmosphere `
inside the display. The display is then hea~ed to the
proper temperature to vaporize the mercury inside. This
temperature depends upon the pressure sealed inside the
display. After the mercury is vaporized the remainder of
the exhaust tube is cut o-ff as near to the substrate as -
possible, making a short stub which is closed at tube end
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Several advantages are obtained by the present inven-
tion. A greater consistency is obtained in the starting
voltage Erom one cathode segment to another. The starting
voltage is kept low due to the small distance between the
cathodes and the anodes, and therefore, it is possible to
maintain starting voltages at least as low as is obtained
in units having the anode placed on the under surface of
the glass window. The present arrangement creates a
greater electrical field between the cathodes and the ;
anodes in response to a given potential difference than
is obtained with the side by side arrangement previo~sly
known. Furthermore it is easier~to control the thickness
of the dielectric layer in the present invention than the
lateral distance of the anodes to the cathodes in the
previous side by side arrangements. Since the intensity
of the electric field depends upon the distances of the
cathodes from the anodes, greater consistency is obtained
by the present invention and also a smaller starting -
voltage is required to produce a given electric field.
The present method also utilizes the same technology -
for both anodes and cathodes, and therefore, simplifies
the manufacturing process. Furthermore, the present inven-
tion eliminates the necessity for using a transparent or
translucen-t anode on the under surface of the viewing
window. Thus the present invention produces a device
which permits easier viewing of the cathode glow from
outside the unit and minimizes the reflection which `
occurs from the viewing window.
Another important aspect of the present invention is
the spacing between the glass cover and the substrate. In
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the usual prior art configuration with the transparent
anode on the front glass cover, the spacing is approxi-
mately .020 inches to .015 inches, and must be held there
to maintain the correct starting voltage. Where the anodes
and cathodes are on the same substrate, the spacing
between the glass cover and the substrate has not been
recognized as being important. However, this distance is
important in the present invention. As the spacing
increases, the starting voltage goes down, the cross talk
10 problem increases, and the tendenc~ Eor blue glow to form ~ -
between adjacent digits increases. As the spacing
decreases, the starting voltage goes up~ the cross talk
problem diminishes and the tendency for blue glow to form
between digits de~reases while the tendency for blue
glow to form between anodes and cathodes of the same
digit increases. It has been found that a distance of
.035 inches to .045 inches produces the best results.
In view of the foregoing, it can be seen that the
device accomplishes at least all of its stated objectives. `~
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