Note: Descriptions are shown in the official language in which they were submitted.
WO91/18757 PCT/US9l/03706
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METHOD FOR APPLYING ELECTRICAL
BUS BARS TO A SUBSTRATE
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates generally to electrical
bus bars on transparent or non-transparent substrates, and
more particularly, to a method of applying the bus bars to
substrates using vapor deposition processes such as
sputtering, cathodic arc process, ion plating process and
vacuum evaporation.
;~ Electrical bus bars applied to glass for automobile-
windshields for e~ample, is well known in the art. Typically
electric current is passed through a transparent electro-
conductive coating or film via the bus bars to heat the
coating to de-ice, defog, or defrost a glass surface.
For esample, U.S. Patent No. 4,743,741 to Ramus
,
discloses an electrically heated windshield having a pair of
` electrically conductive bus bars applied to one of the
' surfaces of the windshield. The '741 Patent is incorporated
by reference herein.
Another example of electrically heated windows is found
~~ in U.S. Patent No. 4,778,732 to Hasegawa, et al. Hasegawa
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discIoses an electrically conductive glass sheet used as a
fog resistant automotive window. The glass sheet comprises a
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~ pair of bus bars and an electrically conductive, transparent
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thin film. The '732 patent is also incorporated by reference
herein.
Ramus ànd Hasegawa as well as others (see also, U.S.
Patent No. 4,847,472 to Koontz) have applied their
electrically conductive bus bars to the glass substrates
using a silver ceramic material which is silk screen printed
on the selected surface of the glass and then heated to a
temperature as high as 600DF or more to bond the silver
ceramic material to the glass. This is disclosed in Column
4, Lines 10-15 in Ramus. In Column 2, Lines 18-30 of
Hasegawa, it states that the bus bars are formed on the glass
by printing electrically conductive paste by the silk screen
~ printing process, and baking the paste. It goes on to say
; that the paste may be of a needed mixture of glass powder
(frit) of a low melting point containing metal particles such
~! as Ag, Cu, or Pd, for example, and an organic solvent or a
binder. Others have used inks, lacquers, or W paint for the
bus bars (see U.S. Patent No. 4,830,876 to Dietrich, et al.)
.~1 There are many disadvantages to the above methods for
~` applying the bus bars. For one, they use volatile solvents
with various pigments. Secondly, the result is a relatively
thick coating of silver from 0.001 to 0.002 inches. Since
, ~ bus bars are usually at or near the edges of the glass, thick
bus bars between laminated panes of glass will cause the
panes of glass to have less intimate contact over their
entire surfaces lnducing stresses in the glass. Third, high
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temperature firing or baking causes excessive thermal stress
and weakness in the glass. Fourth, the material cost of
silver is high.
The present invention has many advantages over the above
described methods. With the present invention, very thin,
durable and reliable bus bars which require no firing or
baking process are provided. Therefore, the glass is not
stressed as much as with previous methods. The bus bars may
be thinner resulting in close and intimate contact over the
entire mating surfaces of glass panes laminated together. In
addition, using the present invention, the material cost of
the bus bars is lower and they are applied with greater ease
in conjunction with current window fabrication processes and
techniques.
Although the example thus far has concerned automobile
` windshields, there are many other applications for the
present invention. The present invention will be useful in
~ automotive vehicle windows, including rooftop windows,
~ airçraft windows, marine craft windows, architectural
windows, mirrors, various electronic applications including
computer screens and display panels, food hea-ting or warming
devices, cerami~s, metal substrates, silicon substrates,
.
electrochromic devices, as well as many other glass, plastic,
and other transparent substrates, and non-transparent
substrate applications.
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WO91/18757 PCT/US91/~3706
In the present invention, the bus bars are conductivepaths for applying electrical energy, either AC or DC to the
extent that a uniform flow of current takes place between the
bus bars through a conductive medium. The medium could be a
transparent or non-transparent coating or film, many
electro-conductive materlals such as wires (currently used in
automobile rear window defoggers), and other metal or even
non-metal conductive devices. A uniformally developed
heating pattern may be established between the bus bar system
through the conductive coating or other conductive material.
The bus bars of the present invention may also be used in an
electrochromic device to distribute electrical power over a
large surface area. Flat or bent substrates can be used.
The bus bars of the present invention are applied by any one
of the vapor deposition processes mentioned above. Various
layers of metals (for example Cr-Cu-Cr) form the bus bar and
are applied on the substrate to arrange a bus bar system for
carrying electrical heating currents through the transparent
conductive coating or other conductiva material.
The bus bars may be applied to a window pane border
portion after-a dark coating has been applied to the window
border portion. This may be done to conceal the bus bars
f rom view.
The foregoing and other objects and advantages will
become more apparent when viewed in light of the accompanying
drawings and following detailed description.
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~ BRIEF DESCRIPTION OF THE DRAWINGS
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FIGURE l is an elevational view of an automobile
.: windshield having the bus bars of the present invention;
FIGURE 2 is a cross sectional view of the windshield of
. FIGURE l;
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FIGURE 3 is a cross section of a bus bar of the present
invention in use on a single pane of glass, plastic, or other
transparent substrate and in contact with a transparent
` electro-conduct1ve coating; ~ .
FIGURE 4 is a cross section of another embodiment of a
bus bar of the present invention having two layers on a
substrate;
i
.FIGURE 5 is a cross section of a bus bar of the present
.. invention applied to a substrate without a transparent
coating;
~: FIGURE 6 is a cross section of a bus bar of the present
~'
: invention applied to a non-transparent substrate;
FIGURE 7 is a cross section of a bus bar of the present
invention applied to a~substrate and in contact with a
; non-transparent electro-conductive heating element;
FIGURE 8 is a cross sect1on of a bus bar of the present -
invention for use in another application involving two panes
of glass with an air or gas filled space between them;
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FIGURE 9 is a cross section of a bus bar of the present
invention applied to a dark coating that has been applied to
a transparent substrate;
FIGURE l0 is a cross section of another embodiment of a
bus bar of the present invention having four layers applied
to a substrate; and
FIGURE ll is a cross section of yet another embodiment
of a bus bar of the present invention having five layers
-~ applied to a substrate.
. DETAILED DESCRIPTION OF THE PREFERRED EMBODIME~TtS)
,. . .
~ Referring to FIGURE l, there is shown a typical
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automobile windshield 20. The windshield 20 is comprised of
a glass substrate 22. Also shown are a pair of electrically
conductive bus bars 24, 26 applied to one of the surfaces of
the substrate 22.
Typically, a windshield 20 will be made of a laminated
construction in which two sheets of glass 22, 28 are used to
form the windshield 20. The two sheets of glass 22, 28 may
be ùnitod by an inner layer of plastic (polyvinyl butyral) 30
in a manner known to those skilled in the art. As shown for
e~ample in FIGURE 2, there may be si~ different surfaces 32,
34, 36, 38, 40, 42 upon which the bus bars 24, 26 could be
applied but usually the bus bars 24, 26 are applied to the
inner surface 34 of the outside sheet 22 or the outer surface
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40 of the inside sheet 28. The shape and configuration of
the bus bars in FIGURE l is just one way of arranging the bus
bars 24, 26. Many other shapes and arrangements could also
be used effectively.
In other applications, a single substrate sheet 44 may,
be desired and the bus bars 24, 26 could be applied to either
surface 46, 48 of the substrate 44 as shown in FIGURE 3. The
significance of FIGURE 3 is that the bus bars may be applied
to many other substrates besides automobile windshields.
~ The bus bars 24, 26 may ba positioned on the substrate
22 in order to achieve generally equal distance between the
bus bars 24, 26. Generally, the bus bars 24, 26 are applied
near the top 50 and bottom 52 edges of the substrate 22 but
other arrangements could be employed to achieve the same
results in an appropriate application. After the bus bars
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24, 26 are applied, a transparent conductive coating 54 may
be applied to the substrate 22 between the bus bars 24, 26.
Using vapor deposition processes for applying the conductive
coating 54 is well known in the art.- However, us.ing vapor
deposition processes to apply the bus bars 24, 26 to a
substrate 22 has heretofore never been successfully
accomplished to the knowledge of the present inventors.
To apply the bus bars 24,'26 to a substrate 22 using a
vapor deposition process at least one problem must be
vercome. The bus bars 24, 26 should adhere to the substrate
22 so that they will be durable and will not tend to peel off
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(for example, when electrical wires are soldered onto the bus
bars 29, 26). For durability of the bus bars 24, 26, the
substrate 22 should first be thoroughly cleaned. This may be
done by washing the substrate 22 with water and detergent
then rinsing the detergent off. Another rinse with deionized
water should follow. Then, warm blown filtered air directed
at the substrate 22 will dry it. The substrate 2Z may then
- ~ be placed in a vacuum chamber (not shown) and glow discharge
`~ cleaned using a wet gas technique as is known in the glass
cleaning art.
The substrate 22 may be left in the same vacuum chamber
for the vapor deposition of the bus bars 24, 26 if the
particular vacuum chamber in use is suited for this. An
initial metal layer may be deposited onto the substrate 22 as
the first layer or bond layer 58 of the bus bars 24, 26. The
ne~t layer deposited onto the bond layer 58 is a conductive
metal layer 60.
In FIGURE 2 a cross section~of the windshield 20 of
FIGURE l- is shown. In FIGURES 2-ll only a single bus bar
cross section is shown for clarity but it should be
recognized that in most applications two or more bus bars
applied at separate locat1ons on a substrate, would be
needed. The bond layer 58 of the bus bar 24 may be deposited
directly to the inner surface 34 of the outside glass sheet
22 or the outer surface 40 of the inside glass sheet 28. The
conductive layer 60 of the bus bar 24 is deposited onto the
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WO91/18757 PCT/US91/03706
208~0~8
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bond layer 58. A protective layer 62 may then be deposited
onto the conductive layer 60 to form a three layer bus bar
~ 24. In the e~ample as shown in FIGURE 2 a transparent
`~ ~ electro-conductive coating 54 1S deposited onto the
protective layer 62 and the coating 54 will substantially
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; cover the windshield 20. various coatings may exhibit the
combination of transparency and electroconductivity to serve
as the heating element for a windshield 20 or the like, which
is known to those skilled in the art. Continuing in
reference to FIGU~E 2, a plastic (polyvinyl butyral) layer 30
and an inside glass sheet 28 are added and the entire
assembly 64 is laminated together.
Referring again to FIGURE l, electrical connections 66,
68 to the windshield bus bars 24, 26-may be made at the lower
edge 70, center portion 72 thereof. But, the connections 66,
68 could be placed elsewhere along the bus bars 24, 26 and
function effectively. In the embodiment described above, a
small portion of the protective layer 62 of the bus bars 24,
26 should be removed, by acid etching for e~ample, so that an
electrical connection 66, 68 can be made directly to the
conductive metal layer 60 of the bus-bars 24, 26. For the
electrical connection, wire leads (not shown) may be bonded
- to the conductive layer 60 by, for e~ample, soldering,
welding, brazing, diffusion bonding, physically clamping, or
other like methods.
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FIGURE 5 is an example of a bus bar 74 arrangement
without a transparent electro-conductive coating which may
not be necessary in some applications. Most any conductive
material (not shown) could be applied to the substrate 76 to
contact the bus bar 74. FIGURE 4 shows another embodiment 78
of the bus bars of the present invention in two layer form.
In this embodiment 78 a bond layer 80 is deposited onto the
, . . .
transparent substrate 82 in the same manner as described
above for a windshield. A conductive layer 84 is next
deposited onto the bond layer ~0. In some situations this
two layer bus bar 78 may be sufficient.
FIGURE 6 is an example of another embodiment 86 of the
bus bars of the present i~vention applied to a
non-transparent substrate 8B such as ceramics, plastics,
metal oxides, silicon, etc. In this embodiment 86 the
conductive layer 90 may be a heating layer. The heating
layer 90 has a resistor material, for e~ample nichrome (NiCr)
in place of a conductor. In this e~ample, the bus bars could
be used for heating mirrors, food trays or other containers,
heating elements in heaters for buildings, and many other
e~amples too numerous to mention wherein a substrate would be
heated.
FIGURE 7 is yet another e~ample wherein the bus bar 92
.
is deposited on a substrate 94 and in this case a non-
transparent electro-conductive heating element 96 is in
cortact with the bus bar.
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W09t/t8757 PCT/US91/0370~
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FIGURE 8 is another application for the bus bars 97 of
the present invention. Insulated windows for architectural
use and freeæer or refrigerator door windows, for e~ample,
typically have two transparent substrates 98, 100 (usually
glass) separated by a dead air or gas filled space 102. The
; layers 104, 106, 108 of the bus bar 97 could be deposited
onto a portion of the inner surface 110 oE one of the
substrates 98 usin~ the method of the present invention. A
transparent electro-conductive coating 112 may then be
applied over the substrate 98 and in contact with the bus bar
97 so that the substrate 98 c~an be heated to defrost, defog
or de-ice it, for example.
FIGURE 9 shows a laminated window assembly 114 much like
that shown in FIGURE 2 e~cept the bond layer 116 of the bus
bar 118 is deposited onto a dark or opaque border 120. The
dark border 120 may be applied to the substrate 122 to
conceal the bus bar 118.
FIGURE 10 is a view of another embodiment of the present
invention in which a four layer bus bar 124 is deposited onto
a substrate 126. In this bus bar 124, a bond layer 128 is
first applied. Then a first conductive layer 130 is-
deposited onto the bond layer I28. This first conductive
~; layer 130 could be a metal such as copper. A second
conductive layer 132 is deposited over the first conductive
layer 130. This second conductive layer 132 couid be a
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; different metal such as aluminum. Finally, a protective
layer 134 is deposited onto the second conductive layer 132.
~ FIGURE 11 is a view of yet another embodiment of the
:; . present invention in which a five layer bus bar 136 is
deposited onto a substrate 138. In this embodiment, a bond
layer 140 is deposited onto a surface 142 of the substrate
138. Then a first conductive layer 144 is deposited onto the
bond layer 140. An intermediate layer 146 is next applied to
act as a stress reliever for differences in thermal expansion
between the conductive layers 144, 148 and the substrate 138
or as an adhesive layer for the second conductive layer 148.
A second conductive layer 148 is then deposited onto the
intermediat~ layer 146 and finally a protective layer 150 is
applied. A second conductive layer 148 offers extra power
capacity in an appropriate application.
It should be recognized that many other embodiments and
examples could have been shown. Si~ or more layer bus bars
may be needed in a given application. Countless uses for the
bus bars of the present invention could be shown. However,
for the sake of demonstrating the many variations of the bus
bars of the present invention-it is believed the FIGURES
above will cover the basic embodiments. Particular
; embodiments and uses not shown should be evident from reading
; this specification.
The protective metal layer and the bond layer may be the
same metal or different metals. The protective metal
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2~8~063
composition and bond metal composition will come from the
group chromium, tungsten, titanium, molybdenum, nickel,
tantalum, stainless steel, zirconium, hafnium, aluminum, and
mi~tures and alloys of any of these metals. The conductive
metal layer composition will come from the group copper,
silver, gold, alumi~um, and mi~tures and alloys of these
metals. The conductive layer should be a good electrical
conductor having low resistance. The layer in contact with a
transparent conductive coating in the application such as an
electrically heated windshield or an electrochromic device
should be chemically and metallurgically compatible with the
coating.
Each layer may be sequentially applied by sputtering in
a vacuum system without e~posing the substrate to the
atmosphere between application of layers. Using this
process, bus bars can be applied to flat or bent/curved
surfaces. The sputtering process of the present invention
uses argon gas under a process pressure of preferrably 1-50
millitorr (3-lO millitorr may be most preferred) and a
maximum temperature need not exceed 250F. Electrical
` conductivity laws dictate the minimum th-ickness of a bus bar-
depending upon the electric current carried by the bus bar
plus its length and width. Total bus bar thickness may be as
;~ low as lO00 Angstroms in a particular application.
` As mentioned above, other vapor deposition processes can
be used besides sputtering. The fact that a vapor deposition
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WO91/18757 q PCT/US91/03706
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process of any kind can be used to apply bus bars to a
substrate resulting in a durable bus bar is a surprising
achievement. Furthermore, making an electrical connection to
vapor deposited bus bars by soldering, for example, is also
surprising. Previousiy, it was believed that this would not
be feasible, because the bus bars would peel off once they
were soldered to. The novel method of applying bus bars of
the present invention provides a durable bus bar and
overcomes many disadvantages of pre~iously used methods for
applying bus bars.
It is thought that the method and improved bus bars of
the present invention and many of its attendant advantages
wlll be understood from the foregoing description and it will
be apparent that various changes can be made in the form and
construction of the components thereof without departing from
the spirit and scope of the invention or sacrificing all of
its matesial advantages, the form hereinbefore described
being merely preferred or e~emplary embodiments thereof.
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