US3923566A

US3923566A - Method of fabricating an apertured mask for a cathode-ray tube

Info

Publication number: US3923566A
Application number: US264833A
Authority: US
Inventors: Harold Bell Law
Original assignee: RCA Corp
Current assignee: RCA Licensing Corp
Priority date: 1972-06-21
Filing date: 1972-06-21
Publication date: 1975-12-02
Anticipated expiration: 1992-12-02
Also published as: IT984035B; JPS4958747A; GB1419010A; BR7304582D0; CA979967A; FR2189861B1; FR2189861A1; ES415914A1; AR196135A1; ES200005U; ES200005Y; DE2331535A1; BE801147A; NL7308567A; USB264833I5; AU5678273A

Abstract

A metal sheet is embossed by a special embossing tool to provide regions in the sheet of minimum thickness at the intended aperture locations thereon. Following embossing, the sheet is shaped into a desired mask contour and the embossed side of the sheet is coated with a stop-off substance to prevent subsequent removal of material from that side. The regions of minimum thickness are then removed, such as by etching the uncoated side of the sheet, to provide the apertures.

Description

ilnited States Patent [191 Law 1 Dec.2, 1975 1 1 METHOD OF FABRICATING AN APERTURED MASK FOR A CATHODE-RAY TUBE [44] Published under the Trial Voluntary Protest Program on January 28, 1975 as document no.

[52] US. Cl. 156/3; 156/6; 156/8 [51] Int. C1. v 4 C23F 1/02 [58] Field of Search 156/3, 6, 7, 8, 11. 16, 156/18; 96/361; 101/32; 161/109. 116; 313/92 B [561 References Cited UNITED STATES PATENTS 2,565,623 8/1951 Parker 156/7 3,148,098 9/1964 Beste 156/6 3.666462 5/1972 Kaplan 96/361 3666.579 5/1972 156/16 3.679500 7/1972 Kubo et a1, 156/11 FOREIGN PATENTS OR APPLICATIONS 598,994 3/1948 L'nited Kingdom Primary E.\'uminerWi11iam A. Powell Attorney, Age/1!, 0r FirmG1enn H. Bruestle; Dennis H. lrlbeck [57] ABSTRACT A metal sheet is embossed by a special embossing tool to provide regions in the sheet of minimum thickness at the intended aperture locations thereon. Following embossing. the sheet is shaped into a desired mask contour and the embossed side of the sheet is coated with a stop-off substance to prevent subsequent removal of material from that side, The regions of minimum thickness are then removed. such as by etching the uncoated side of the sheet. to provide the apertures.

14 Claims, 51 Drawing Figures US. Patent Dec. 2, 1975 Sheetlo f8 3,923,566

US. Patent Dec. 2, 1975 Sheet 2 of 8 3,923,566

US. Patent Dec. 2, 1975 Sheet 3 of8 3,923,566

US. Patent Dec. 2, 1975 Sheet 4 of8 3,923,566

US. Patent Dec. 2, 1975 Sheet 5 of8 3 ,923,566

Fig. 27.

a US. Patent Dec. 2, 1975 shw 6 0f 8, 3,923,566

US. Patent Dec.2, 1975 Sheet7of8 3,923,566

US. Patent Dec.2, 1975 Sheet80f 8 3,923,566

208 Fig. 50.

Fig. 5'].

AFTER ETCHING Fig: 46. A

METHOD OF FABRICATING AN APERTURED MASK FOR A CATI-IODE-RAY TUBE BACKGROUND OF THE INVENTION This invention relates to apertured mask-type cathode-ray tubes. More particularly, it relates to a method of fabricating an apertured mask fora cathode-ray tube.

Cathode-ray tubes for use in color television usually include a screen of red, green and blue emitting phosphor lines or dots, electron gun means for exciting the screen, and an apertured mask interposed between the gun means and the screen. The apertured mask is a thin metal sheet precisely disposed adjacent to the screen so that the mask apertures are systematically related to the phosphor lines or dots.

Much of the previous development of color television cathode-ray tubes has centered around the improvement of a tube having a mask with round apertures and a screen with phosphor dots. As such development progressed, various limits were approached as this type of tube was improved. For example, once the size of the round apertures in the masks were optimized to obtain a desired tube brightness-screen tolerance trade-off, thereby fixing the mask electron beam transmission factor, further improvements in tube brightness became possible only with further improvements of the phosphor, electron guns, deflection yoke, and screen printing optics.

Recently, interest has been shown in line-screen, slitmask type tubes. Such tubes provide the possibility for an increased electron beam transmission factor and, therefore, greater brightness than is now possible with masks having round apertures. However, when a slit mask is constructed in the same manner as is now used to construct masks with round apertures, various problems, which are acceptable in the masks with round apertures, become magnified to an extent where they can not be tolerated. For example, the edges of each slit opening must be much sharper than is required for a round aperture opening. This requirement is necessary to suppress electron scattering developed at the edges of the apertures since the periphery-toarea ratio of a slit is higher than that of a round aperture. Because of the difference of this ratio, a tube employing a slit mask is much more vulnerable to contrast degradation caused by poor edges that is a tube having a mask with round apertures. Therefore, to minimize electron scattering and thereby increase contrast in tubes having slit masks, it is important to utilize a mask fabrication method that provides apertures having sharp knife edges and highly accurate dimensions.

In a slit mask, the slits usually are oriented longitudi nally and are disposed in rows or columns. Longitudinally adjacent slits are separated by laterally extending cross ties that hold the mask together. In order to attain the maximum benefit possible with a slit mask, it is nec essary to minimize the area of these cross ties so that the percentage of the electron beams intercepted by the cross ties is reduced. For normal tube operation, the cross ties need only be strong enough to make the mask self-supporting. However, it is common in the prior art to shape the mask into its final configuration after the slits on the apertures are formed. Therefore, the cross ties in the prior art masks had to be made thick enough to withstand the stresses encountered during the shaping procedure. The thick cross ties of 2 the prior art significantly affected tube brightness and caused visible shadows on the viewing screen.

SUMMARY OF THE INVENTION The present invention provides a method of fabricating an apertured mask for a cathode-ray tube. A metal sheet is embossed to provide regions of reduced thickness at intended aperture locations. These regions are then removed to provide the apertures.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of a color television picture tube.

FIG. 2 is a cross-sectional view taken on line 22 of FIGURE 1 showing, partly broken away, an apertured mask assembly.

FIGS. 3 through 9 are cross-sectional views illustrating the step-by-step fabrication of an apertured mask in accordance with the instant invention.

FIG. 10 is an enlarged partial vertical view of a first embossing tool.

FIG. 11 is a front view of the tool of FIG. 10.

FIG. 12 is an enlarged partial vertical view of an apertured mask formed with the tool of FIGS. 10 and 11.

FIG. 13 is a front view of the mask of FIG. 12.

FIG. 14 is an enlarged vertical view of a second embossing tool.

FIG. 15 is a front view of the tool of FIG. 14.

FIG. 16 is an enlarged partial vertical view of an apertured mask formed with the: tool of FIGS. 14 and 15.

FIG. 17 is a front view of the mask of FIG. 16.

FIG. 18 is an enlarged partial view of a third embossing tool.

FIG. 19 is a front view of the tool of FIG. 18.

FIG. 20 is an enlarged partial view of an apertured mask formed with the tool of FIGS. 18 and 19.

FIG. 21 is a front view of the mask of FIG. 20.

FIG. 22 is an enlarged partial view of a fourth embossing tool.

FIG. 23 is a front view of the tool of FIG. 22.

FIG. 24 is an enlarged partial view of an apertured mask formed with the tool of FIGS. 22 and 23.

FIG. 25 is a front view of the mask of FIG. 24.

FIG. 26 is an enlarged partial view of a fifth embossing tool.

FIG. 27 is a front view of the tool of FIG. 26.

FIG 28 is an enlarged partial view of an apertured mask formed with the tool of FIGS. 26 and 27.

FIG. 29 is a front view of the mask of FIG. 28.

FIG. 30 is an exploded perspective view of a metal sheet used in mask fabrication.

FIG. 31 is a perspective view of the sheet of FIG. 30 assembled.

FIGS. 32 and 33 are side and front views of the metal sheet of FIGS. 30 and 31 during embossing.

FIG. 34 is an enlarged vertical view of an apertured mask formed from the metal sheet of FIGS. 30 and 31.

FIGS. 35 through 39 are cross-sectional views illustrating the step-by-step fabrication of an apertured mask.

FIG. 40 is a perspective view of the mask fabricated as illustrated in FIGS. 35 through 39.

FIGS. 41 through 46 are enlarged partial surface and side views illustrating the step-by-step fabrication of an embossing tool.

FIGS. 47 through 51 are enlarged partial surface and side views illustrating an alternate step-by-step fabrication of an embossing tool.

DETAILED DESCRIPTION FIG. 1 depicts a color television cathode-ray picture tube 40. The tube 40 is comprised of an evacuated envclope 42 having three sections: a funnel portion 44, a neck portion 46 and an end cap 48. The end cap 48 includes a viewing faceplate 50 that is interiorly coated with a color phosphor screen 52. An electron gun 54, positioned within the neck portion 46, is adapted to project at least one. but preferably three. electron beams through a magnetic deflection yoke 56 toward the screen 52. When suitably energized, the yoke 56 causes the beams to scan the screen 52 in a rectangular raster.

The screen 52, shown in greater detail in FIG. 2, is composed of a plurality of parallel phosphor strips or lines 58. These lines 58 can comprise cylically successive strips of red-emitting. green-emitting and blueemitting phosphors. Although the preferred embodiments of the present invention are described with respect to this line screen. it should be noted that the scope of the present invention also includes embodiments that use dot-like screens.

To produce color selection. an apertured mask 60 is mounted within the end cap 48 adjacent to the screen 52 and is thereby interposed in the path of the electron beams from the gun 54. Only the portions of the electron beams that pass through the apertures of the mask 60 strike the screen 52. Dashed lines 62 outline the maximum vertical deflection of the electron beams for the 90v. rectangular tube of FIG. 1.

Generally. in accordance with the present invention, the apertured mask 60 is constructed by embossing a metal sheet with a relief pattern to provide regions of reduced or minimum thickness therein at intended aperture locations. Thereafter the metal sheet is treated. such as by etching. to remove portions of the sheet including the regions of minimum thickness thus forming apertures in the sheet. One of the advantages of the foregoing method is that the metal sheet can be bent or shaped into a contoured mask configuration prior to removal of the portions of the metal sheet that include the regions of minimum thickness. This is possible because shaping of the mask prior to removal of the regions of minimum thickness utilizes these regions of minimum thickness to provide mechanical strength during shaping. Because the cross ties are not subjected to the entire shaping forces. the cross ties can be formed with reduced thickness thereby permitting maximum tube brightness.

One method of fabricating an apertured mask is illustrated in FIGS. 3-9. In FIG. 3, a thin metal sheet 70 is positioned on the flat surface 72 of an anvil 74. An embossing tool 76 is shown directly above the metal sheet 70. The embossing tool 76 has a plurality of raised portions 78 at the intended locations of apertures. The areas 80 between the raised portion 78 are grooved to minimize compression of the metal sheet 70 in these areas and to permit flow of the sheet metal from the regions compressed by the portion 78. Each raised portion 78 is separated longitudinally from adjacent portions by small grooves 81. These grooves 81 provide for formation of cross ties in the mask that make the mask self supporting.

FIG. 4 illustrates the embossing step wherein the embossing tool 76 has moved downward to impress its pattern into the metal sheet 70. After completion of the embossing step, the tool 76 is raised and the embossed 4 metal sheet is removed. As shown in FIG. 5, each raised portion 78 of the embossing tool 76 forms a depression 82 in the metal sheet 70. Beneath these depressions 82 are regions 84 of minimum thickness in the sheet 70. The embossed sheet is then trimmed to leave a border around the pattern and the metal sheet 70 is curved into the desired apertured mask configuration as shown in FIG. 6. Once the sheet 70 has been curved. the embossed side of the sheet can be completely coated with a material. such as a layer 86 of a stop-off lacquer. a properly treated fish glue. as shown in FIG. 7. to protect it during subsequent etching steps. Next. the uncoated side 88 of the sheet 70 is uniformly etched until the regions 84 of minimum thickness 84 are completely removed. as shown in FIG. 8. Thereafter, the coating or stop-off lacquer 86 is removed thereby leaving the completed apertured mask 70' wherein the depressions 82 have become the apertures of the mask separated longitudinally by cross ties 83.

FIGS. 10 and 11 show a bottom and a side view, respectively, of a portion of one type of embossing tool 90. As shown in the side view of FIG. 11. the embossing tool pattern looks something like a chopped sawtooth wave. The flat wave crests are raised portions 92 which form the depressions or grooves that become apertures. At intervals along each raised portion 92 are slots 94 that provide areas in the embossing pattern that provide for the cross ties.

A mask 96 formed by the tool of FIGS. 10 and 11, utilizing the previously described method, is shown in top view in FIG. 12 and in side view in FIG. 13. The mask contains apertures 98 which are formed at locations corresponding to the locations of the raised portions 92 of the embossing tool 90, and webs or cross ties 100 which are formed by the slots 94.

Another embossing tool 102 is shown in FIGS. 14 and 15. In this tool 102, the raised portions 104 that are used to form the aperture grooves are positioned on pedestals 106 that provide shoulders 108 about the raised portions 104. The apertured mask 110 formed with this tool 102, utilizing the previously described method, is shown in FIGS. 16 and 17. As illustrated, the shoulders 108 of the embossing tool form a thin section 112 of material around the apertures 114 in the shadow mask 110. In this particular mask embodiment, the apertures are formed with straight vertical sides. Therefore, ethcing time for this mask 110 is much less critical than for the mask 96 of FIGS. 12 and 13 since aperture width in the mask 110 remains constant for a certain etching period after the apertures 114 are opened.

A modification of the embossing tool of FIGS. 14 and 15 is shown in FIGS. 18 and 19. The embossing tool 116 of FIGS. 18 and 19 includes pedestals 118 having two steps or

shoulders

120 and 124. This tool pattern is especially applicable to the known type of color tube fabrication technique in which a partially completed mask having a first or small width slit is used to define and print the screen of the tube, and upon completion of the screen, a second, larger width slit is provided for the mask which is incorporated in the finished cathode ray tube. FIGS. 20 and 21 show the apertured mask 128 produced by the embossing tool 116 of FIGS. 18 and 19. The A side of FIGS. 20 and 21 depicts the apertured mask 128 after a first etching step to form the narrowslits 130 that are used in fabricating the cathode-ray tube screen, and the side B depicts the same mask after a second etching step to form the slits 132 that are used in the mask used in the operational tube.

It can be seen that the first etch uniformly removes the metal from the uncoated side of the mask and can be terminated at any time after opening of the narrow slits 130 but before the grooves that are to form the wide slits 132 are reached. The stop-off lacquer is then removed from the mask and the mask is inserted in a cathode-ray tube face plate. Thereafter, utilizing known lighthouse exposure techniques, the phosphor screen of the cathoderay tube is defined. When the screen is completed the embossed side of the mask is again coated with a stop-off lacquer and the mask is subjected to a second etch. The second etch can be terminated at any time after the wide slits 132 have been reached but before the etch reaches the slit shoulders. preferably, for maximum mask strength, the second etch should be terminated shortly after the wide slits are opened.

Another embossing tool 134 is illustrated in the bot tom and side views of FIGS. 22 and 23, respectively. This tool 134 provides a mask having polygonal shaped apertures for use in a cathode-ray tube having a dot screen. The pattern of tool 134 has a plurality of hexagonal pedestals 136 each having a hexagonal raised portion 138 thereon. The mask 140 formed with the embossing tool 134 is shown in FIGS. 24 and 25. Side A of FIGS. 24 and 25 depicts the apertured mask after a first etching step to form the apertures 142 that are used in forming the cathode-ray tube screen, and side B depicts the same mask after a second etching step to form the apertures 144 that are used in the operational tube.

An embodiment of the invention for use with cathode-ray tubes having screens with round phosphor dots is illustrated in FIGS. 26-29. The pattern of tool 145 has a plurality of cylindrical pedestals 146 with each pedestal having a smaller raised cylindrical portion 147 thereon. The mask 148 formed with the embossing tool 145 is shown in FIGS. 28 and 29. Side A of FIGS. 28 and 29 depicts the apertured mask after a first etching step to form small apertures 149. The mask in the small aperture configuration is then inserted into a faceplate of a cathode-ray tube and is used in establishing a dot screen. Thereafter, the mask is removed from the faceplate and is etched a second time to form the large apertures 149a depicted at side B in FIGS. 28 and 29. The mask in its large aperture configuration is then reinserted into the faceplate and is used in the operational cathode-ray tube.

Another embodiment of the invention is illustrated in FIGS. 30-34. FIGS. 30 and 31, respectively, depict an exploded view and an assembled view of a laminated panel 150 comprising two

metal sheets

152 and 154 having a plurality of parallel wires 156 therebetween. Fabrication of the panel 150 can be made in a rolling operation by inserting appropriate diameter wires 156 between the two

metal sheets

152 and 154 and laminating the sheets together so that the wires are compressed and embedded between the sheets, as the laminate panel 150 is rolled thinner.

The fabricated panel 150 is next embossed by a tool 158 having a pattern of raised elongated portions 160 thereon separated by grooves 161. Each of these portions 160 forms a groove in the panel 150 that eventually becomes a slit in the resultant mask. FIG. 31 shows the embossing tool 158 in a raised position above the panel 150 and FIGS. 32 and 33 show two views of the tool 158 and panel 150 during the embossing step. Each raised elongated portion 160 is intersected by 6 cut-outs or grooves 159 that prevent distortion of the embedded wires during embossing.

During the embossing step, the raised portions 160 of tool 158 press against the metal between wires 156. Thus a portion of the metal directly beneath the raised portions 160 is compressed and the remaining metal is forced to flow into the recessed longitudinal areas 161 of the tool. At this point, the panel 150 has a plurality of elongated portions of reduced thickness, each por tion separated longitudinally lby wires 156. Laterally, the rows or columns of reduced thickness portions are separated by longitudinally extending strips that are to form the body of the mask.

After the panel 150 has been embossed, the entire panel is shaped and etched until the regions of minimum thickness in the panel formed during the embossing step are removed. The material of the wires 156 is such as not to be affected by the etchant used. The completed mask 162 is shown in FIG. 34. The mask consists of parallel strips of metal 164 held together by the parallel cross tie wires 156.. In this embodiment, the cross tie wires 156 can be significantly thinner than the cross ties provided in the previously described embodiments if the wire 156 consists of a suitably strong material.

Another variation in mask construction is shown in FIGS. 35-40. FIG. 35 depicts a metal sheet which has been embossed to include a plurality of triangular shaped elongated portions 174 that are connected together by regions 176 of reduced sheet thickness. The sheet 170 is then shaped, i.e., arched, into a mask configuration, as shown in FIG. 36', and a plurality of wires 178 are welded to the apex of each triangular shaped portion 174, as shown in FIG. 37. Thereafter, a stop-off material 180 is coated over the wires 178 and the embossed side of the sheet 170, as depicted in FIG. 38, and the sheet regions 176 of minimum thickness are etched away, as shown in FIG. 39. The resulting mask 182, shown in FIG. 40, comprises a plurality of parallel triangular strips 184 held together by a plurality of wires 178 welded to each strip 184.

Many variations in mask design are made possible by the foregoing method, some of which are described hereinafter. An important piece of equipment required in the fabrication of all the mask designs is the embossing tool, which can be in the form of any embossing roll used in opposition with a smooth roll on a rolling mill.

A preferred method for forming the embossing tool 102 of FIGS. 14 and 15 is illustrated in FIGS. 41 through 46. FIGS. 41 and 42 show top and side views, respectively, of a steel plate having a plurality of parallel photoresist strips 192 thereon. The center of each strip 192 is positioned so as to coincide with the intended location of a raised portion of the tool. The regions 194 between the photoresist strips 192 are then etched away, as shown in FIG. 43, to form a plurality of parallel ridges 196. The photoresist pattern 192 is removed and another pattern of photoresist strips 198 (FIGS. 44 and 45) is printed on top of the ridges 196. As shown, each of the photoresist strips 198 covers only a central portion of the ridges, and each strip 198 has a series of gaps 199 therein. A second etch of the plate 190 produces the embossing contour shown by the dashed lines in FIG. 46. The tool 102 is now completed by removing the photoresist pattern 198.

Another method for forming the embossing tool 102 of FIGS. 14 and 15 is illustrated in FIGS. 47 through 51. This method is simply the reverse process of the previously described preferred method. FIGS. 47 and 48 show a top and side view, respectively, of a steel plate 200 having a first photoresist pattern 202 thereon. The pattern 202 covers those portions 104 of the steel plate that are to become the ridges 104 of the embossing tool 102. After the pattern 202 is established, the surface of the plate 200 is lightly etched to form a plurality of pedestals 204 and shallow recesses 206 as shown in FIG. 49. Following the first etch, the first photoresist pattern 202 is removed and the surface of the plate 200 is covered with a plurality of parallel photoresist strips 208. Each strip 208 completely covers a pedestal 204 and extends slightly beyond the sides thereof. Thereafter, the surface of the plate 200 is subjected to a second etch to form a plurality of grooves 210 between the pedestals 204. This second method for forming the embossing tool 102 is then completed by removing the second photoresist pattern of strips 208.

In constructing the embossing tool by etching, it is important that the photoresist be completely free of defects. For example, a pinhole in the resist can result in the tool being etched at undesirable locations. Repair of such damage caused by pinholes is difficult and it is probable that the repaired area will not stand up under use nearly as well as the original steel used to construct the tool. This problem of repair durability is particularly bad if a pinhole is located at the edge of a pedestal. Therefore, an additional step to check the soundness of the resist pattern is preferably used. For example, the soundness of the resist pattern can be tested by attempting to plate a metal of contrasting color, such as copper, onto the workpiece covered with the resist. If any pinholes through the resist are present, thus exposing areas of the underlying metal, the contrasting color metal will plate onto these exposed areas, thereby providing a visual indicator for locating the pinholes. The pinholes so located can be then repaired prior to further processing.

The embossing tools of the present invention can also be made by highly accurate machining techniques. Each tool can be either in the form of a flat, uniform thickness plate or a cylindrical roll.

EXAMPLE I A first mask fabrication process is begun by pressing a sheet of metal, e.g., 6 mil thick, etc., between a smooth roll ofa rolling mill and a special embossing roll having a relief pattern thereon. For example, the relief pattern can be that shown in FIGS. 18 and 19, thereby resulting in the sheet being embossed with a pattern of longitudinal grooves. The bottom of the grooves are quite thin, about 1.5 mils thick, as a result of flow of metal in the embossing operation.

The embossed sheet is then annealed, and the annealed sheet is shaped into a spherical configuration. Preferably, to provide maximum strength, to resist subsequent changes in shape of the spherically shaped sheet, a minimal amount of annealing, just sufficient to prevent tearing of the sheet during the shaping operation, is done.

After the shaping operation, the entire embossed side of the sheet is covered with a coating of stop-off lacquer and the uncoated side of the sheet is uniformly etched with a suitable etchant such as ferric chloride. At least 1.5 mils of this uncoated side is removed to completely remove the thinned regions of the steel sheet. After etching, the stop-offlacquer is removed, as by peeling or washing with a suitable solvent, thereby 8 leaving the finished mask. Further operations, such as blackening of the mask and welding the mask to a frame, can then be done in accordance with known techniques. If a second etch is required, as previously discussed, the mask is recoated with stop-offlacquer on the convex embossed side of the mask after the mask has been used, etc., and a second etching step is performed. This second etching step is preferably performed with the mask attached to the frame in order to ensure proper alignment between the mask and screen.

EXAMPLE II In a second mask fabrication process, a plurality of wires are disposed between two sheets of metal, e.g., 3 mils thick, and the two sheets are laminated together by a rolling operation to establish a good bond. The wires can be as small as from 2 to 4 mils in diameter and are ofa material resistant to the etchant used in subsequent processing steps. Wires formed from titanium or titanium alloys are preferable when an etchant such as ferric chloride is used. The laminated sheets are then embossed with an embossing tool such as that shown in FIGS. 28 and 29 to form grooves perpendicular to the embedded wires. Next, the embossed sheets are shaped to a spherical form and then annealed. Thereafter, the formed embossed sheets are etched with a suitable etchant such as ferric chloride to produce the final mask.

By utilizing an embossing step in the fabrication of an apertured mask, apertures are formed having knife edges and accurate dimensions. The cross ties that are formed are of uniform area and can be made as thin as possible consistent with operational strength requirements. Since aperture location is established in the embossing step, the mask may be shaped to its final configuration prior to removal of the regions of minimum thickness, when the embossed metal sheet is its strongest, thereby permitting much thinner cross ties than when the cross ties are subjected to the entire formation stress.

The foregoing apertured mask embodiments have other advantages in addition to increased transmission factors and reduced electron scattering. For example, minimization of cross tie thickness also aids in reducing moir. Moire appears on a viewing screen as alternating light and dark bands, often resembling a wood grain. This phenomenon is caused by the variations in the amount of the electron beams intercepted by the mask as the scan line spacing and phase changes. Minimizing the thickness of the horizontal portions or cross ties of a mask, therefore, minimizes the visible moir pattern.

It is noted that in each of the mask embodiments the portions of the masks located between rows of apertures are recessed or sloped away from the edges of the apertures. This ensures that at any angle of deflection, the electron beams will not deflect off the mask after they have passed through the mask apertures.

I claim:

1. A method of fabricating an apertured mask for a cathode-ray tube comprising:

embossing a relief pattern on one side of a flat metal sheet with an embossing tool, said relief pattern providing regions of minimum thickness relative to the remaining regions thereof at intended aperture location and straight vertical sides perpendicular to the flat dimension of said sheet surrounding the intended aperture locations;

shaping said metal sheet into a desired mask contour;

masking the pattern side of said metal sheet with an etch-resistant material; and

etching the opposite side of said metal sheet until said regions of minimum thickness are etched through to provide apertures.

2. The method as defined in claim 1, including mounting said metal sheet in a frame prior to etching.

3. The method as defined in claim 1 wherein said relief pattern comprises an array of substantially round depressions forming said regions of minimum thickness.

4. The method as defined in claim 1, wherein said relief pattern comprises an array of polygonal depressions forming said regions of minimum thickness.

5. The method as defined in claim 1, wherein said etching step is performed after said shaping step.

6. The method as defined in claim 5, wherein said relief pattern comprises an array of parallel elongated depressions forming said regions of minimum thickness.

7. The method as defined in claim 1, wherein said relief pattern comprises an array of elongated depressions disposed in parallel rows, each depression being elongated in the direction of said rows and separated from adjacent depressions in each row by raised web portions of said relief pattern, said depressing forming said regions of minimum reduced thickness.

8. The method as defined in claim 7, wherein said relief pattern includes shoulders parallel with and adjacent to each elongated side of each depression, said shoulders being substantially level with said raised web portions.

9. The method as defined in claim 1, wherein said relief pattern comprises:

a first array of depressions forming said regions of minimum thickness, said first array including paral lel rows of said first depressions, each of said first depressions being elongated in the direction of said rows,

a second array of elongated second depressions superimposed on said first depressions, said second depressions being of substantially identical length as said first depressions and having greater width than said first depressions, said second depressions forming regions of intermediate thickness in said metal sheet, said first depressions and said second depressions being separated from adjacent depres- 10 sions in each row by common raised web portions of said metal sheet.

10. The method as defined in claim 9 wherein said relief pattern includes shoulders parallel with and adjacent to each elongated side of each second depression, said shoulders being substantially level with said raised web portions.

11. The method as defined in'claim 9, including the step of reetching said second side of said metal sheet at least until said regions of intermediate thickness are removed to provide enlarged apertures in said metal sheet.

12. A method of fabricating an apertured mask for a cathode-ray tube comprising;

embossing a relief pattern on one side of a metal sheet comprising two laminated metal layers having a plurality of spaced parallel wires therebetween, said relief pattern providing regions of minimum thickness relative to the remaining regions thereof at intended aperture locations;

shaping said metal sheet into a desired mask contour;

and

etching the opposite side of said metal sheet until said regions of minimum thickness are etched through to provide apertures. 13. The method as defined in claim 12, wherein said relief pattern comprises an array of elongated depressions forming said regions of minimum thickness, said array including parallel rows of said depressions, each depression being elongated in the direction of said rows perpendicular to said wires and separated from adjacent depressions in each row by web portions of said metal sheet including said wires.

14. A method of fabricating an apertured mask for a cathode-ray tube comprising:

embossing a relief pattern on one side of a metal sheet, said relief pattern comprising an array of parallel elongated depressions forming regions of minimum thickness relative to the remaining regions thereof at intended aperture locations shaping said metal sheet into a desired mask contour; and attaching a plurality of wires to a pattern side of said metal sheet perpendicular to the direction of said elongated depressions;

etching the opposite side of said metal sheet after said shaping until said regions of minimum thickness are etched through to provide apertures.

Claims

1. A METHOD OF FABRICATING AN APERTURED MASK FOR A CATHODERAY TUBE COMPRISING: EMBOSSING A RELIEF PATTERN ON ONE SIDE OF A FLAT METAL SHEET WITH AN EMBOSSING TOOL, SAID RELIEF PATTERN PROVIDING REGIONS OF MINIMUM THICKENSS RELATIVE TO THE REMAINING REGIONS THEREOF AT INTENDED APERTURE LOCATION AND STRAIGHT VERTICAL SIDES PERPENDICULAR TO THE FLAT DIMENSION OF SAID SHEET SURROUNDING THE INTENDED APERTURE LOCATION; SHAPING SAID METAL SHEET INTO A DESIRED MASK CONTOUR, MASKING THE PATTERN SIDE OF SAID METAL SHEET WITH AN ETCHRESISTANT MATERIAL, AND ETCHING THE OPPOSITE SIDE OF SAID METAL SHEET UNTIL SAID REGIONS OF MINIMUM THICKNESS AE ETCHED THROUGH TO PROVIDE APERTURES.

9. The method as defined in claim 1, wherein said relief pattern comprises: a first array of depressions forming said regions of minimum thickness, said first array including parallel rows of said first depressions, each of said first depressions being elongated in the direction of said rows, a second array of elongated second depressions superimposed on said first depressions, said second depressions being of substantially identical length as said first depressions and having greater width than said first depressions, said second depressions forming regions of intermediate thickness in said metal sheet, said first depressions and said second depressions being separated from adjacent depressions in each row by common raised web portions of said metal sheet.

11. The method as defined in claim 9, including the step of reetching said second side of said metal sheet at least until said regions of intermediate thickness are removed to provide enlarged apertures in said metal sheet.

12. A METHOD OF FABRICATING AN APERTURED MASK FOR A CATHODE-RAY TUBE COMPRISING, EMBOSSING A RELIF PATTERN ON ONE SIDE OF A METAL SHEET COMPRISING TWO LAMINATED METAL LAYERS HAVING A PLURALITY OF SPACED PARALLEL WIRES THEREBETWEEN, SAID RELIEF PATTERN PROVIDING REGIONS OF MINIMUMM THICKNESS RELATIVE TO THE REMAINING REGIONS THEREOF AT INTENDED APERTURE LOCATIONS, SHAPING SAID METAL SHEET INTO A DESIRED MASK CONTOUR, AND ETCHING THE OPPOSITE SIDE OF SAID METAL SHEET UNTIL SAID REGIONS OF MINIMUM THICKNESS ARE ETCHED THROUGH TO PROVIDE APERTURES.

13. The method as defined in claim 12, wherein said relief pattern comprises an array of elongated depressions forming said regions of minimum thickness, said array including parallel rows of said depressions, each depression being elongated in the direction of said rows perpendicular to said wires and separated from adjacent depressions in each row by web portions of said metal sheet including said wires.

14. A method of fabricating an apertured mask for a cathode-ray tube comprising: embossing a relief pattern on one side of a metal sheet, said relief pattern comprising an array of parallel elongated depressions forming regions of minimum thickness relative to the remaining regions thereof at intended aperture locations shaping said metal sheet into a desired mask contour; and attaching a plurality of wires to a pattern side of said metal sheet perpendicular to the direction of said elongated depressions; etching the opposite side of said metal sheet after said shaping until said regions of minimum thickness are etched through to provide apertures.