Screen contact means for a cathode ray tube

A cathode ray tube comprises an envelope having a funnel portion with an electrical terminal extending through a wall surface thereof. A faceplate is sealed to the funnel portion and a screen contact assembly provides electrical contact between the electrical terminal and an aluminum coating on an inside surface of the faceplate. The screen contact assembly includes a conductive strip attached at one end to the electrical terminal. At the other end of the strip and attached thereto is a relatively flexible first contact member which is in pressured electrical contact with the aluminum layer on the faceplate. Disposed between the flexible first contact member and the aluminum layer on the faceplate is an oxidized, silver plated NICHROME foil member of high electrical conductivity. Transverse support and lateral stability is provided by a relatively flexible second contact member attached to and forming a part of the screen contact assembly.

BACKGROUND OF THE INVENTION 
The invention relates to a screen contact assembly for a cathode ray tube 
and particularly to a structure for bridging a frit seal joining a 
faceplate to a funnel portion of such a tube. 
One piece envelopes for cathode ray tubes are well known in the art; 
however, such envelopes pose problems that are not present in envelope 
assemblies comprising a funnel portion and a separate faceplate. For 
example, when an aluminum layer is evaporated on a phosphor screen of a 
one piece envelope it is necessary to position the aluminum evaporators a 
few inches from the phosphor screen in order to direct the aluminum onto 
the screen surface. At such a close distance the aluminum evaporation 
tends to be nonuniform thus providing a much thicker aluminum coating on 
the central portion of the screen, which is close to the evaporators, than 
at the edge of the screen. This aluminum nonuniformity decreases the 
effective phosphor efficiency of the central portion of the screen by 
absorbing energy from the incident electron beam. Furthermore, at the 
close evaporation distance described above, aluminum particles are 
sputtered from the evaporators and cling to the surface of the screen thus 
causing spot rejects. 
It is therefore desirable to fabricate and inspect the faceplate of the 
cathode ray tube, including deposition of the aluminum layer onto the 
phosphor screen, before sealing the faceplate to the funnel portion of the 
envelope assembly. This can be done only if the phosphor screening and 
aluminizing operations are performed on a faceplate which is separate from 
the funnel and which is then sealed, for example, by frit sealing, to the 
funnel portion of the envelope. However, frit sealed structures pose 
problems in that it is necessary to electrically connect the aluminum 
layer which overlies the phosphor screen to a source of electrical 
potential. 
It is known in the art to connect the aluminum layer on the phosphor screen 
to the conductive coating on the inside of the funnel, for example, by 
painting a conductive stripe or evaporating a conductive material over the 
frit seal; however, such structures are unreliable especially where the 
frit seal is reentrant causing the conductive striping or coating to 
become discontinuous. In applications where peak electrical currents in 
the 2 to 3 milliampere range are experienced, it is also necessary to have 
an electrical connecting structure which can withstand such high currents. 
U.S. Pat. No. 3,432,803 to Nice, issued Mar. 11, 1969, shows a "through the 
frit" structure providing electrical contact between an external high 
voltage lead and the aluminum layer on the phosphor screen of the cathode 
ray tube. U.S. Pat. No. 3,898,501 to Davis et al. issued Aug. 5, 1975, 
also shows a "through the frit" type of connection. Both the Nice and the 
Davis et al. structures introduce mechanical stresses in the frit seal 
area and thus are unreliable structures for providing the proper voltage 
to the screen of the cathode ray tube. 
U.S. Pat. No. 3,876,899 to Davis et al. issued Apr. 8, 1975, discloses an 
electrical connective member which bridges the frit seal of the cathode 
ray tube and contacts the aluminum layer that extends along a longitudinal 
portion of the sidewall of the faceplate assembly. The connective member 
is disclosed to have a forward contact area formed to have a substantially 
reverse-turned leading edge or turned-under rounded terminal end having a 
thickness of about twice the thickness of the body of the conductive 
member. The rounded turned-under terminal end is located to effect 
slidable pressured contact to the aluminum layer which forms a tab 
extending along the sidewall of the faceplate assembly. 
The connective member of the Davis et al. U.S. Pat. No. 3,876,899 must be 
carefully formed to insure that it does not contact the viewing portion of 
the faceplate since the rounded turned-under terminal end of the 
connective member is non yielding in the longitudinal direction and would 
rupture the aluminum layer on the viewing surface of the phosphor screen. 
In cathode ray tubes such as projection tubes, the faceplate is sealed 
directly to the funnel portion of the envelope. In such tubes there is no 
longitudinally extending sidewall portion of the faceplate and thus the 
aluminum layer on the screen terminates adjacent to the sealing edge of 
the faceplate. The Davis et al. connective structure cannot be used in 
such a tube since the rounded terminal end of the connective member would 
rupture the aluminum screen coating and break the electrical connection to 
the screen. 
SUMMARY OF THE INVENTION 
Screen contact assembly means for a cathode ray tube comprises a conductive 
strip having attached thereto a relatively flexible first contact member. 
The screen contact assembly means extends between an electrical terminal 
within a funnel portion of the tube and an aluminum conductive layer 
disposed on a faceplate of the tube. A relatively flexible second contact 
member provides lateral support for the relatively flexible first contact 
member. A conductive foil member is attached to the screen contact 
assembly means and is disposed between the relatively flexible first 
contact member and the aluminum conductive layer.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1 there is shown a cathode ray tube such as a projection 
tube, comprising an evacuated envelope designated generally by the numeral 
10, which includes a funnel portion 12 having a seal land 13 at one end 
and a neck portion 14 at the other end. An outwardly curved faceplate 16 
is joined to the funnel by a seal 18, preferably of devitrified glass. A 
luminescent layer 20 of phosphor material is disposed on a portion of an 
interior surface of the faceplate 16. The composition of the luminescent 
layer 20 may be any type of phosphor structure well known in the art; 
however, in a projection tube the phosphor material should emit one of the 
basic colors, i.e., either red, blue or green. A light reflecting metal 
coating 22 of aluminum is evaporated onto the luminescent layer 20 and on 
at least a portion of the remaining area of the faceplate not covered by 
the layer 20. The layer 20 when scanned by an electron beam from a gun in 
a mount assembly 24 located in the neck 14, is capable of producing an 
illuminated image. The layer 20 and the light reflecting metal coating 22 
constitute the screen of the tube. 
An electrically-conductive coating 26, such as iron oxide, is disposed on a 
portion of the interior surface of the funnel 12 between the mount 
assembly 24 and the seal land 13. A plurality of metal fingers 28 (only 
one is shown) space the mount assembly 24 from neck 14 and connect the 
forward portion of the mount assembly 24 with the internal coating 26. 
An anode button 30 provides an electrical terminal which extends through a 
wall surface of the funnel 12 adjacent to but spaced from the seal 18. A 
stud 32 projects inwardly from the anode button 30. A screen contact 
assembly 34 bridges the seal 18 and extends from the anode button to the 
aluminum coating 22 on the faceplate 16. A proximal end of the screen 
contact assembly 34 is attached, for example, by a locking nut 36 to the 
stud 32 in the anode button 30. In the fabrication of the envelope 
assembly the aforementioned screen contact assembly 34 is attached as 
described above before the frit seal 18 is made. This permits the 
faceplate 16 to be screened, aluminized, and inspected prior to the 
assembly of the faceplate to the funnel. 
As shown in FIGS. 1 and 2 the screen contact assembly 34 contacts the 
aluminum layer 22 in an area of the faceplate 16 where there is no 
phosphor screen 20. The absence of the phosphor screen in the contact area 
designated 38 in FIG. 1 and 2 provides a hard, positive electrical contact 
which is capable of carrying high anode currents which normally average 
500 microamperes but which may approach 2 to 3 milliamperes of peak 
current. To improve the electrical contact between the screen contact 
assembly 34 and the contact area 38 of the screen, a foil member 40 made 
from an alloy consisting of 80% nickel and 20% chromium sold under the 
trademark NICHROME and having an oxidized silver plated coating thereon, 
the foil member having a thickness of about 0.001 inches (0.0254 mm), is 
attached to the screen contact assembly 34 and extends between the screen 
contact assembly 34 and the contact area 38. 
As shown in FIG. 3, the faceplate 16 comprises a viewing portion 42, the 
electrical contact portion or area 38, and a sealing surface 44. While the 
contact area 38 is shown as a segment of the circular faceplate 16, it 
should be clear to one skilled in the art that the contact area 38 may 
take any shape, for example, rectangular, square, triangular, or circular. 
As shown in detail in FIG. 4, the novel screen contact assembly 34 of the 
present invention comprises a relatively stiff conductive strip 50 of 
stainless steel having a thickness of about 0.020 inches (0.508 mm). A 
relatively flexible contact member 52 also made of stainless steel and 
having a thickness of about 0.005 inches (0.127 mm) is fixedly attached at 
one end thereof to a distal end of the conductive strip 50. The flexible 
contact member 52 extends across the seal 18. A distal end 54 of the 
contact member 52 is bifurcated so as to form a pair of contact surfaces 
which are embossed in such a manner as to upturn and inwardly direct the 
contact surfaces to permit sealing of the outwardly curved faceplate 16 to 
the funnel 12 without damage to the aluminum layer on the contact areas 38 
of the faceplate. A relatively flexible transverse member 56 is disposed 
orthogonal to and attached at its midpoint to the stainless steel strip 
member 50. The transverse member 56 is an elongated element which provides 
lateral stability to the conductive strip 50 and is formed in a manner 
similar to that described for the distal end 54 of the flexible member 52. 
The transverse member 56 contacts the conductive coating 26 on the funnel 
12. The transverse member 56 is shown as having embossed, inwardly 
directed and upturned contact surfaces formed in a pair of bifurcated 
distal ends 58 and 60; however, any similar type of structure including 
dimpling or embossing of the ends 58 and 60 may also be used to provide a 
spring pressure contact to the conductive coating 26. 
The NICHROME foil member 40 is shown in FIG. 4 to be attached to the screen 
contact 34 so that when the foil member 40 is disposed in the tube 10 it 
will be located between the layer of aluminum 22 on the contact area 38 
and the contact surfaces formed in the bifurcated distal end 54 of the 
flexible member 52. While the highly conductive, oxidized, silver plated 
NICHROME foil member 40 is shown to be located only between the flexible 
contact member 52 and the aluminum screen, similar silver plated NICHROME 
foil members (not shown) may also be located on the distal ends 58 and 60 
of the transverse member 56 to improve the electrical contact between the 
ends of the transverse member 56 and the conductive coating 26 on the 
funnel 12.