MULTIBEAM ELECTRON GUN AND METHOD OF ASSEMBLY

Abstract: An electron gun (10) comprises, as in prior guns, a plurality of cathode assemblies (16) and at least two spaced successive electrodes (18,20) having aligned apertures (60, 64) therethrough for passage of a plurality of electron beams. The cathode assemblies and the electrodes are individually held in position from a common ceramic member (50) The ceramic member has a first major surface (52) and an oppositely disposed second major surface (54), with a metallized pattern (56a, 56b; 56c) formed on at least a portion of each major surface. The electrodes are attached to the first major surface, and the cathode assemblies are attached to the second major surface. Unlike prior guns, a first transition member (74/78) is attached to the metallized pattern (65a, 56b) on the first major surface. At least one of the electrodes is attached to the first transition member. A second transition member (68, 94) may also be disposed on the second major surface for the attachment of the cathode assemblies.

Description: The present invention relates to a multibeam electron gun and a method for assembling that gun. The gun and method can provide better alignment of successive grid apertures, better control of spacing between successive grid electrodes and a reduction in electron gun distortion, as compared with prior gun designs. U.S. Patent 4,298,818, issued to McCandless on November 3, 1981, describes an electron gun for use in a multibeam cathode-ray tube. The gun includes at least two spaced successive electrodes brazed directly to metallized patterns on one surface of a ceramic support, and a plurality of cathode support assemblies brazed directly to metallized patterns on the opposite surface of the ceramic support. Each electrode comprises a single metal plate having three beam-defining apertures therethrough, which apertures are so aligned as to permit the passage of three electron beams. The sizes and shapes of the electron beams are determined, in part, by the sizes, shapes and alignments of the apertures. Apertures that are misaligned by as little as 0.0125 mm (0.5 mil) can cause distorted beam shapes and degrade the performance of the tube. U.S. Patent 4,500,808, issued to McCandless on February 19, 1985, describes an improved electron gun similar to that of U.S. Patent 4,298,818 above, except that the second electrode comprises a composite structure having a metal support plate brazed directly to a metallized pattern on one surface of a ceramic support. The metal support plate has a window therein opposite each of the apertures in a first electrode which is also brazed directly to a separate metallized pattern on the same surface of the ceramic support. Separate metal plates are brazed to the metal support plate and close the windows therein. Each of the metal plates has a single electron beam-defining aperture therein which is separately aligned with one of the apertures in the first electrode. This structure provides more accurate alignment of successive grid apertures than previous structures. In each of the above-described electron guns, the successive electrodes and the cathode support assemblies are simultaneously brazed directly to metallized patterns formed on the ceramic support. This simultaneous brazing process has several drawbacks, some of which include: the difficulty of adjusting the spacing between successive electrodes; the difficulty of removing the completed assembly from the brazing fixture; dirt in the brazing fixture can effect alignment of the apertures; forming the electrode contact leads can change the spacing between the electrodes; and, most importantly, the brazing operation frequently distorts the metal parts and imparts stress into the ceramic support which can crack the ceramic support. As a result, a structure and assembly process are required which reduce or eliminate the drawbacks of the prior art. In accordance with the present invention, there is provided a multibeam electron gun for a cathode-ray tube according to claim 1 and a method for assembling a multibeam electron gun for a cathode-ray tube according to claim 11. In the drawings: FIGURE 1 is a partially cut-away, side elevational view of a preferred embodiment of the inventive electron gun. FIGURE 2 is an enlarged side elevational view of a cathode-grid subassembly of the electron gun of FIGURE 1. FIGURES 3 and 4 are an enlarged plan view and an enlarged side sectional view, respectively, of a portion of the cathode-grid subassembly during its manufacture. FIGURE 5 is an enlarged view of the portion of the cathode-grid subassembly shown within the circle 5 of FIGURE 4. FIGURES 6 and 7 are an enlarged plan view and a side sectional view, respectively, of a transition member according to the present invention. FIGURE 8 is an enlarged front sectional view of a portion of the cathode-grid subassembly during its manufacture. As shown in FIGURE 1, an improved electron gun 10 includes a cathode-grid subassembly 12. The improved gun 10 is similar to the gun disclosed in the above-identified U.S. Patent 4,500,808, except for the cathode-grid subassembly 12 and the method of fabricating the subassembly with these electrodes. The gun 10 comprises two glass support rods 14, also called beads, upon which various electrodes of the gun are mounted. These electrodes include three equally-spaced inline cathode assemblies 16, one for each electron beam (only one of which is shown in the view in FIGURE 1), a control grid electrode 18, a screen grid electrode 20, a first focusing electrode 22, a second focusing electrode 24 and a shield cup 26, spaced from the cathode assemblies in the order named. The first focusing electrode 22 comprises a substantially rectangularly cup-shaped lower first member 28 and a similarly shaped upper first member 30, joined together at their open ends. The closed ends of the members 28 and 30 have three apertures therethrough, although only the center apertures are shown in FIGURE 1. The apertures in the first focusing electrode 22 are aligned with the apertures in the control and screen grid electrodes 18 and 20. The second focusing electrode 24 also comprises two rectangularly cup-shaped members, including a lower second member 32 and an upper second member 34, joined together at their open ends. Three inline apertures also are formed in the closed ends of the upper and lower second members 32 and 34, respectively. The center apertures in the upper and lower second members 32 and 34 are aligned with the center apertures in the other electrodes; however, the two outer apertures (not shown) in the second focusing electrode 24 are slightly offset outwardly with respect to the two outer apertures in the first focusing electrode 22, to aid in convergence of the outer beams with the center beam. The shield cup 26, located at the output end of the gun 10, has appropriate coma correction members 36 located on its base around or near the electron beam paths, as is known in the art. Each of the cathode assemblies 16 comprises a substantially cylindrical cathode sleeve 38 closed at the forward end and having an electron emissive coating (not shown) thereon. The cathode sleeve 38 is supported at its open end within a cathode eyelet 40. A heater coil 42 is positioned within the sleeve 38, in order to indirectly heat the electron emissive coating. The heater coil 42 has a pair of legs 44 which are welded to heater straps 46 which, in turn, are welded to support studs 48 that are embedded in the glass support rods 14. The cathode-grid subassembly 12, shown in detail in FIGURE 2, includes a ceramic member 50, having an alumina content of about 99%, to which the cathode assemblies 16 and the control grid and screen grid electrodes 18 and 20, respectively, are attached. The ceramic member 50 includes a first major surface 52 and an oppositely-disposed, substantially-parallel second major surface 54. The ceramic member has a thickness of about 1.5 mm (0.060 inch). At least a portion of the first major surface 52 has metallizing patterns 56a and 56b formed thereon, to permit attachment thereto of the electrodes 18 and 20, respectively. A plurality of electrically isolated metallizing patterns (only one of which, 56c, is shown) are provided on the second major surface 54, to permit attachment of the cathode assemblies 16 thereto. The metallizing of a ceramic member is well known in the art and needs no further explanation. The major surfaces 52 and 54 may include lands, as shown in FIGURE 2, which facilitate application of the metallizing patterns thereto. The control grid electrode 18 is essentially a flat plate having two parallel flanges 58 on opposite sides of the three inline, precisely-spaced, beam-defining first apertures 60, only one of which is shown. The screen grid electrode 20 is also essentially a single flat metal plate, having two parallel flanges 62 on opposite sides of three inline, precisely-spaced, beam-defining second apertures 64, only one of which is shown. Alternatively, the screen grid electrode may comprise a composite structure, as described in the above-identified U.S. Patent 4,500,808. In U.S. Patent 4,500,808 above, and in US-A-4605880 (published on August 12, 1986) and US-A-4607187 (published on August 19, 1986), control and screen grid electrodes and portions of the cathode assemblies are brazed directly to the metallized patterns on the ceramic surfaces. The brazing of a plurality of formed metal parts tends to distort at least some of the parts and introduce stress into the ceramic member. If the stress is sufficiently great, the ceramic member will crack, rendering the cathode-grid subassembly unusable. In the present structure, the distortion of the formed metal parts, including the control grid 18 and the screen grid 20, is reduced by providing, as shown in FIGURES 2-5, a substantially flat first bimetal transition member 66 which is brazed to the first major surface 52 of the ceramic member 50. A substantially flat second bimetal transition member 68, shown in FIGURES 6 and 7, is brazed to the second major surface 54 of the ceramic member 50. With reference to FIGURES 2-5, the first bimetal transition member 66 is shown disposed on the first major surface 52 of the ceramic member 50. The transition member 66 includes two layers of metal bonded face-to-face to form a bimetal. The first metal layer 70 is preferably formed from a nickel-iron alloy of 42% nickel and 58% iron, having a thickness of about 0.2 mm (0.008 inch), which is not greater than about 20% of the thickness of the ceramic member 50; and the second metal layer 72 is preferably formed of copper, having a thickness of about 0.025 mm (0.001 inch). The melting point of the copper layer 72 is about 1083°C, and the melting point of the nickel-iron alloy layer 70 is about 1427°C, which is substantially higher than that of the copper. The first transition member is stamped or photo-etched, and thereby configured to conform to the shape of the metallizing patterns 56a and 56b on the first major surface 52 of the ceramic 50. The second metal layer 72 is disposed on the first major surface 52. As shown in FIGURE 3, the first transition member 66 includes first electrode contact portions 74 disposed above and below a trio of large inline apertures 76 in the ceramic member 50, and second electrode contact portions 78 spaced from the first electrode contact portions 74. A pair of oppositely disposed removable frame portions 80 are connected to the electrode contact portions 74 and 78 by weakened bridge regions 82, which comprise oppositely disposed notches 84 formed in the first metal layer 70. A pair of oppositely disposed, arcuately shaped alignment channels 86 are formed in the bridge regions 82. The alignment channels are aligned, in a manner to be described below, with corresponding alignment apertures 88 in the ceramic member 50, to register the first electrode contact portions 74 and the second electrode contact portions 78 with the first and second major surface metallizing patterns 56a and 56b, respectively. The second bimetal transition member 68, shown in FIGURES 2, 6 and 7, also includes two layers of metal bonded face-to-face to form a bimetal. The first metal layer 90 is preferably formed of the above-described nickel-iron alloy and has a thickness of about 0.2 mm (0.008 inch), and the second metal layer 92 is preferably formed of copper and has a thickness of about 0.025 mm (0.001 inch). The second transition member 68 is stamped or photo-etched to conform to the shape of the metallizing patterns 56c on the second major surface 54 of the ceramic member 50. During fabrication of the cathode-grid subassembly 12, the second metal layer 92, comprising copper, is disposed on the second major surface 54. The second transition member includes three pairs of cathode assembly contact portions 94, and a pair of removable frame portions 96 which are connected to the cathode assembly contact portions 94 by weakened bridge regions 98. The bridge regions are configured to provide integral cathode contact leads 100 on one side of the cathode assembly contact portions 94. A pair of oppositely disposed, arcuately shaped second transition member alignment channels 102 are formed in the removable frame portions 96, to facilitate alignment of the channels 102 with the alignment apertures 88 in the ceramic member 50, to register the cathode assembly contact portions 94 with the metallizing patterns 56c formed on the second major surface 54 of the ceramic member 50. With reference to FIGURE 8, a brazing jig 104 comprises lower and upper jig members 106 and 108, respectively. The second bimetal transition member 68 is positioned on the lower jig member 106, with the first metal layer 90, comprising nickel-iron, in contact with the lower jig member. The ceramic member 50 is disposed on the second bimetal transition member 68 so that the second metallized patterns 56c on portions of the second major surface 54 of the ceramic member are in contact with the second metal layer 92 of the cathode assembly contact portions (not shown) of the second bimetal transition member. The first bimetal transition member 66 is disposed on the first major surface 52 of the ceramic member 50 so that the second metal layer 72 of the first and second contact portions 74 and 78 (only 74 being shown) is in contact with the metallizing patterns 56a and 56b, respectively (only pattern 56a being shown). Brazing alignment pins 110 are fitted in the lower jig member 106 to align the alignment channels 86 and 102 (shown in FIGURES 3 and 6, respectively) in the first and second bimetal transition members 66 and 68, with the alignment apertures 88 in the ceramic member 50. The upper jig member 108 is placed in contact with the first metal layer 70 of the first bimetal transition member 66. A pair of reference apertures 112 in the upper jig member 108 enclose the alignment pins 110. The jig 104, loaded in the manner described herein, is then heated in a wet hydrogen atmosphere in a BTU three-zone belt furnace (not shown), at tempertures of 1105°C, 1120°C and 1105°C, to melt the copper layers 72 and 92. The belt speed through the furnace is about 100 mm (4 inches) per minute. Since the transition members 66 and 68 comprise substantially flat members having nickel-iron layers 70 and 90, each with a thickness not more than about 20% the thickness of the ceramic member 50, little or no stress is introduced into the ceramic member during the brazing operation. The fabrication of the cathode-grid subassembly 12 proceeds as follows. After the brazing of the first and second bimetal transition members 66 and 68 to the ceramic member 50, the removable frame portions 80 and 96, respectively, are removed at the weakened bridge regions 82 and 98. The removal of the frame portions 80 from the first transition member 66 electrically isolates the first electrode contact portions 74 from the second electrode contact portions 78. As shown in FIGURE 5, the metallized pattern 56b, underlying the second electrode contact portion 78, terminates at the lower notch 84 of the weakened bridge portion 82. Thus, only the copper layer 72 to the left of the lower notch 84 in FIGURE 5 is brazed to the metallized pattern 56b. Since there is no metallizing to the right of the lower notch 84, the copper layer 72 will not adhere to the ceramic member 50, and the frame portion 80 can be broken away readily. The frame portions 96 of the second bimetal transition member 68 are also broken away, along the weakened bridge regions 98, thereby electrically isolating each of the cathode assembly contact portions 94 attached to the metallized patterns 56c on the second surface 54 of the ceramic member 50. The cathode contact leads 100, extending from selected ones of the portions 94, are bent at about a 90° angle, as shown in FIGURE 2, to facilitate attachment thereto of stem leads (not shown). The cathode eyelets 40 are welded, e.g., by laser welding, to oppositely disposed pairs of the cathode assembly contact portions 94. The control grid electrode 18 is then disposed upon the first electrode contact portions 74 and aligned by means of secondary apertures (not shown) with the alignment apertures 88 in the ceramic member 50. Such a method of alignment is described in the above-identified U.S.-A-4605880. The flanges 58 of control grid electrode 18 are welded, e.g., by laser welding, to the first electrode contact portions 74. Next, the second apertures 64 of the screen grid electrode 20 are aligned, either directly or indirectly, with the first apertures 60 in the control grid electrode 18. The parallel flanges 62 of the screen grid electrode 20 are welded, e.g., by laser welding, to the second electrode contact portions 78. The cathode sleeves 38 are inserted into the eyelets 40 and welded thereto. The heater coils 42 are located within the sleeves 38, and the heater legs 44 are welded to the heater straps 46. Preferably, the cathode assembly welds also are made by laser welding. Laser welding is preferred since no pressure is applied to physically distort the parts, and the welding parameters can be precisely controlled. While the cathode-grid subassembly 12 described herein only has the control grid electrode 18 and the screen grid electrode 20 attached to electrical contact portions 74 and 78 of the transition member 66, it should be clear to one skilled in the art that the size of the ceramic member and the transition member brazed thereto can be increased to permit attachment thereto, e.g., of the first focusing electrode. Correspondingly, the transition member brazed to the second surface 54 of the ceramic may also be provided with tabs, in addition to the cathode contact leads 100 to which heater supports for the heater straps 46 are attached. The fabrication method here is preferable to previous fabrication methods, for the following reasons: precise alignment is not required to braze the transition members 66 and 68 to the metallized patterns; the control grid 18 and the screen grid 20 are laser welded to the electrical contact portions 74 and 78 without the distortion that occurs during high temperature brazing; the grids 18 and 20 can be individually aligned and spaced to provide greater alignment accuracy; the subassembly 12 can be inspected after each step to minimize the expense of manufacturing defective structures; and the use of the transition members with removable frame portions simplifies the manufacturing process, since it is easier to align unitized members than to separately align a plurality of discrete components.

Claims: A multibeam electron gun (10) for a cathode-ray tube, comprising a plurality of cathode assemblies (16) and at least two spaced successive electrodes (18,20) having aligned apertures (60,64) therethrough for passage of a plurality of electron beams, said cathode assemblies and said electrodes being individually held in position from a common ceramic member (50), said ceramic member having a first major surface (52) and an oppositely disposed second major surface (54), with a metallized pattern (56a,56b;56c) formed on at least a portion of each major surface, said electrodes being attached to said first major surface, and said cathode assemblies being attached to said second major surface; characterized in that a first transition member (66) is attached to said metallized pattern (56a,56b) on said first major surface of said ceramic member, said first transition member including stress reducing means (70), and at least one of said electrodes is attached to said transition member. The gun (10) according to Claim 1, characterized in that said first transition member (66) includes at least one electrode contact portion (74,78), to which a removable frame portion (80) was connected by at least one weakened bridge region (82). The gun (10) according to Claim 2, characterized in that said first transition member (66) is disposed between said metallized pattern (56a,56b) on said first major surface (52) and two of said electrodes (18,20), whereby said electrodes are connected to the electrode contact portions (74,78) of said transition member and electrically isolated from one another by the removal of said frame portion (80) at said weakened bridge region (82). The gun (10) according to Claim 1, characterized in that a second transition member (68) is attached to said metallized pattern (56c) on said second major surface (54), said second transition member including stress reducing means (90), said second transition member being disposed between said metallized pattern and said cathode assemblies (16). The gun (10) according to Claim 4, characterized in that said second transition member (68) includes a plurality of cathode assembly contact portions (94), to which a removable frame portion (96)was connected by a plurality of weakened bridge regions (98), said cathode assemblies being connected to different ones of said cathode assembly contact portions and electrically isolated from one another by the removal of said frame portion at said plurality of weakened bridge regions. The gun (10) according to Claim 4, characterized in that the stress reducing means for said first transition member (66) and said second transition member (68) comprise substantially flat plates (70;90) configured to conform to the metallized patterns (56a,56b;56c) formed on said first (52) and said second (54) major surfaces. The gun (10) according to Claim 6, characterized in that said first transition member (66) and said second transition member (68) comprise two layers (70,72; 90,92) of metal bonded face-to-face to form a bimetal, one layer (72;92) of metal having a melting point lower than the other layer (70;90) of metal. The gun (10) according to Claim 7, characterized in that said layer (72;92) of metal having the lower melting point comprises copper. The gun (10) according to Claim 8, characterized in that the other layer (70;90) of metal comprises a nickel-iron alloy of 42% nickel and 58% iron. The gun (10) according to Claim 9, characterized in that the stress reducing means further comprises the layer (70;90) of nickel-iron alloy having a thickness of not more than about 20% of the thickness of said ceramic member (50). A method for assembling a multibeam electron gun (10) for a cathode-ray tube, said gun including a plurality of cathode assemblies (16) and at least one spaced electrode (18,20) held in position from a ceramic member (50) having a metallized pattern (56a,56b;56c) thereon; characterized by the steps of: (a) disposing a transition member (66;68) on a major surface (52;54) of said ceramic member, said transition member comprising two metal layers (70,72;90,92) bonded face-to-face, one layer of metal (72;92) having a melting point lower than the other metal layer (70;90), said layer of metal having the lower melting point being adjacent to the major surface; (b) aligning said transition member with said metallized pattern; (c) heating said ceramic member and said aligned transition member to a temperature sufficient to melt said layer of metal having the lower melting point, to attach said transition member to said major surface of said ceramic member; (d) cooling said ceramic member with said transition member attached thereto to room temperature; and (e) removing portions of said transition member at weakened bridge regions (82;98), thereby providing a plurality of electrically isolated electrical contact portions (74,78;94). A method for assembling a multibeam electron gun (10) for a cathode-ray tube, said gun comprising a plurality of cathode assemblies (16) and at least two spaced successive electrodes (18,20) individually held in position from a common ceramic member (50), each of said cathode assemblies including a cathode eyelet (40), a cathode sleeve (38) disposed within said eyelet, said sleeve being closed at the forward end by a cap, a cathode heater (42) within said cathode sleeve and a pair of heater straps (46) attached to said heater, said electrodes including a control grid (18) and a screen grid (20), each of said grids having a plurality of beam forming apertures (60,64) therethrough, said ceramic member having a first major surface (52) and an oppositely disposed second major surface (54), with a metallized pattern (56a,56b;56c) formed on at least a portion of each major surface; characterized by the steps of: (a) disposing a first transition member (66) configured to conform to said metallized pattern (56a,56b) on said first major surface, said first transition member including a plurality of electrode contact portions (74,78) and a removable frame portion (80) connected to said electrode contact portions by at least one weakened bridge region (82), and disposing a second transition member (68) configured to conform to said metallized pattern (56c) on said second major surface, said second transition member including a plurality of pairs of cathode assembly contact portions (94) and a removable frame portion (96) connected to said cathode assembly contact portions by a plurality of weakened bridge regions (98), said first and second transition members comprising two layers of metal (70,72;90,92) bonded face-to-face to form a bimetal, one layer of metal (72;92) having a melting point lower than the other layer of metal (70;90), and said transition members being disposed so that said layers thereof of metal having the lower melting point are adjacent to their respective major surfaces; (b) aligning said electrode contact portions of said first transition member with said metallized pattern on said first surface; (c) aligning said cathode assembly contact portions of said second transition member with said metallized pattern on said second major surface; (d) heating said ceramic member and said aligned first and second transition members to a temperature sufficient to melt said layers of metal having the lower melting point so as to attach said first and second transition members to said first and second major surfaces, respectively, of said ceramic member; (e) cooling said ceramic member with said first and second transition members attached thereto to room temperature; (f) removing said frame portions from said first and second transition members at the weakened bridge regions, thereby providing a plurality of electrically isolated electrode contact portions and cathode assembly contact portions; (g) aligning the cathode eyelet of each of said cathode assemblies with a different pair of said cathode assembly contact portions attached to said second major surface of said ceramic member; (h) welding each of the cathode eyelets to its respective pair of cathode assembly contact portions; (i) aligning said control grid with two of said plurality of electrode contact portions attached to said first major surface of ceramic member; (j) welding said control grid to said electrode contact portions (56a); (k) aligning the beam forming apertures in said screen grid with the beam forming apertures in said control grid; and (l) welding said screen grid to two different electrode contact portions (56b) attached to said first surface of said ceramic member so that said screen grid is electrically isolated from said control grid. The method according to Claim 12, characterized in that said welding steps comprise laser welding to prevent distorting said grids (18,20).

Inventors: MCCANDLESS, HARRY EDWIN
Applicants: RCA LICENSING CORPORATION
Application year: 1986
Main classification: H01J29
IPC codes: H01J29, H01J9