US 3889329 A
A process for making color television shadow masks and panel assemblies wherein the panels are interchangeable with masks that are made in separate operations. The openings in the shadow masks and the phosphor dots on the screen are located with sufficient precision to insure interchangeability in production.
Claims available in
Description (OCR text may contain errors)
United States Patent 1191 Fazlin 1 PROCESS FOR MAKING COLOR TELEVISION MASKS  lnventor: Paul A. Fazlin, 902 W. County Rd.,
Apt. 1 16, New Brighton, Minn. 551 10  Filed: May 16, 1973  Appl. No.: 360,643
 US. Cl. 29/25.; 96/36; 354/1  Int. Cl. H0lj 9/00  Field of Search 29/2513, 25.14, 25.15,
 References Cited UNITED STATES PATENTS 3,537,161 11/1970 Kautz 29/2515 1 June 17, 1975 3,564,195 2/1971 29/2515 3,676,914 7/1972 Fiore..... 29/2514 X 3,701,185 10/1972 Renssen 29/25.15
Primary ExaminerRoy Lake Assistant Examiner.lames W. Davie Attorney, Agent, or Firm-Bugger, Johnson & Westman  ABSTRACT A process for making color television shadow masks and panel assemblies wherein the panels are interchangeable with masks that are made in separate operations. The openings in the shadow masks and the phosphor dots on the screen are located with sufficient precision to insure interchangeability in production.
8 Claims, 17 Drawing Figures VICUl/M PATENTEDJUN 17 m5 Hill. H|||||h I FORM PANEL USE MASTER AND EXPOSE BETWEEN EACH OF THREE COLORS TO FORM TRUXD PHOSPHOR DOTS FILMING sTmP ANNEALED AND smzess H51. .2
REUEV ED PUNCH OUT MASK BLANK FRPME.
FORWNG FORMlNG SPR1NG ATTACHlNG MASK BLANK AND FRBME.
A5$EMBUNG PHOTO ETcH RESlST Ex Posme IN DlE STRNHNG AND ETCHING MASK INSERTING \N PANE L PATENTEDJUN 17 I975 SHEET l/AcuuM Vacuum /67 HLIIIH FILE. 1.2
PATENTEDJUN 11 1915 a a 89.329
PROCESS FOR MAKING COLOR TELEVISION MASKS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to methods and apparatus for manufacturing shadow masks and panel assemblies for color television picture tubes.
2. Prior Art U.S. Pat. No. 3,676,914, issued July 18, 1972 to .loseph P. Fiore, sets forth the problems involved in making shadow masks for color television tubes, and describes one method of attempting to accomplish interchangeability of the mask and frame assemblies, with face panels or screens, without pairing a mask and frame assembly with a particular panel. Pairing is a term meaning an assignment of a particular shadow mask and frame assembly to a particular face panel for a color TV tube.
However, in the actual construction of shadow masks and panels in accordance with the method set forth in U.S. Pat. No. 3,676,914 it could be argued that the individual unit is still not made with enough reliability to permit complete interchangeability of the mask and frame assembly with separately made panels, while keeping the rejection or scrap rate low.
SUMMARY OF THE INVENTION The present invention relates to manufacturing of shadow mask and panel assemblies for color picture tubes in a process which insures exact positioning of the apertures or openings in the shadow mask with respect to the supports of the shadow mask frame, and also very precise positioning of the phosphor dots required for color reproduction on the panel of the color picture tube in relation to the supporting members on the panel, so that the mask and frame assemblies are interchangeable in panels that are manufactured separately from the mask and frame assemblies.
In some prior art devices the exposure of the photo resist coatings on the shadow masks prior to etching or chemical milling of the openings through the shadow masks was done using a flat master pattern for exposing the aperture areas on the curved mask and any shift or slight irregularity in contour of the mask relative to the master could result in exaggerated errors in the shape, size and position of the subsequently formed holes. Likewise, in the screening process for placing the phosphor dots on the face panels, if pairing techniques were not used, a flat master was used for screening the curved panel, as shown in U.S. Pat. No. 3,676,914 and any slight shift of the flat master relative to the curved panel caused a great shift in the phosphor dots on the panel in relation to the desired position. When separately made masks and frame assemblies are placed into the panels any slight errors in position between the apertures in the mask or the dots on the panel were greatly magnified.
The apparatus and method disclosed includes a step of checking the curvature of the formed shadow mask blank before placing the photosensitive resist coating on the shadow mask, and while the shadow mask is being assembled to its frame. The curvature of the shadow mask then is as desired, and after the mask has been coated with photosensitive resist coating on both sides, it is placed into a die which has a matching curvature and which has precisely positioned apertures therethrough which are used when the photosensitive resist coating on the panel is exposed to form latent images prior to etching the holes through the mask. The die surfaces have the exact configuration of the desired shadow mask curvature, so that during exposure of the photosensitive coating the shadow mask is physically held across a majority of its curved surface. The apertures in the die through which the light passes during exposure are precisely placed in relation to each other, and also in relation to the mounting members used for supporting the frame that is attached to and supports the shadow mask. Thus, because the openings on the shadow mask and frame assembly can be precisely placed in relation to each other on opposite sides of the mask, and also in relation to the mask and frame assembly supports, the openings are identically positioned on each mask within the tolerances necessary.
In forming the screen on the panel, the support studs, which are used to support a mask and frame assembly, are placed on the edge walls of the panel in a known manner. A curved master mask is used for the screening process to form the phosphor dots on the panel. The master mask is fixed on the light house and is supported in the same relationship to the panel being screened as a production mask. Thus while the screening process for forming the phosphor dots on the panel is conventional, the use of a curved master (made to conform to desired standards) mounted in a precise position while exposing the phosphor dots insures that the dots are precisely placed on the panel with respect to the provided mask and frame mounting studs so that when a production run mask and frame assembly is put into position on studs of the panel during assembly for production, the apertures in the production mask are precisely positioned with respect to the phosphor dots on the production panel.
In this manner the process for producing shadow masks for color television tubes, and the face panels to which the masks are assembled is precise, repeatable, and greatly reduces rejection and therefore lowers the cost of manufacture of such color television picture tubes.
The forming die for forming or deep drawing the flat mask blank into the curved shape is of the same configuration as the die used for exposing the mask prior to etching.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a process diagram showing the manufacturing steps of making shadow mask and frame assemblies and face panels for color television tubes in accordance with the present invention;
FIG. 2 is a plan view of a typical formed shadow mask blank used in the manufacturing process prior to forming apertures through the mask;
FIG. 3 is a sectional view taken as on line 3-3 in FIG. 2',
FIG. 4 is a top plan view of a typical frame and spring assembly to which the shadow masks are assembled;
FIG. 5 is a sectional view taken as on line 5-5 showing the details of a mounting spring for mounting the frame and mask assembly;
FIG. 6 is an exploded side elevational view of the frame of FIG. 4 showing a shadow mask adjacent to the frame prior to assembly of the mask blank onto the frame;
FIG. 7 is a side elevational view of an assembly and checking fixture used for assembling the mask blanks and frames;
FIG. 8 is a top plan view of the fixture of FIG. 7;
FIG. 9 is a schematic sectional view of a die used in connection with exposing portions of the photosensitive resist coatings on the shadow masks prior to etching apertures through the shadow mask;
FIG. 10 is an enlarged vertical sectional view of the die and mask of FIG. 9 in exposing position, and showing in dotted lines the form of the apertures that are etched through the shadow mask in the etching process;
FIG. 11 is a fragmentary top plan view of a typical support used for supporting the shadow mask and frame assembly during the exposing in the die of FIG.
FIG. 12 is an enlarged fragmentary sectional view of an edge portion of the frame and shadow mask assembly showing the mask apertures after the etching process;
FIG. 13 is a part schematic sectional view showing one step in a typical process for screening the phosphor dots onto a screen or panel that is used in the manufacture of color television tubes;
FIG. 14 is a top plan view of a production shadow mask and frame assembly mounted in a production panel;
FIG. 15 is a sectional view taken as on line 15-15 in FIG. 14;
FIG. 16 is a sectional view taken as on line l6 16 in FIG. 15; and
FIG. 17 is a fragmentary top plan view of a mounting stud attached to a typical panel, and a mounting spring from a typical mask and frame assembly shown positioned in the stud.
DESCRIPTION OF THE PREFERRED EMBODIMENT The shadow masks used in color tubes are made in a variety of sizes but only one typical configuration is shown. The present process relates to procedure of forming mask and frame assemblies and making panels. Once the shadow mask is joined with a particular face panel, the subsequent manufacture of the complete color television tube takes place in a normal sequence.
The masks are usually formed with either a round or a rectangular periphery, and are made to mount on the face panel in a definite relationship. The term mask is used herein and means the thin metal sheet which is positioned behind the face panel of a color television tube and through which the electron gun is projected onto phosphor dots which are positioned on the inside surface of the panel. The phosphor material on the inside of the panel is arranged in triad dots, generally an interlace of similar deposits of green, blue and red phosphor materials. In the manufacture of a color television tube, usually there are three electron guns at the neck of the tube which are projected through the openings in the mask, so that each of the guns will light only one of the phosphor dots in order to make the color configuration on the television screen. The term mask also is used interchangeably with the term shadow mask.
The term mask and frame assembly is used to mean a mask that has been welded or otherwise fixedly attached to its supporting frame, which is in turn used for supporting and mounting the mask in a panel. The supporting frame is a rectangular or round (depending on the panel shape) open center frame that has sufficient stifi'ness to support the mask. The support members extending between the frame and the panel must be made to precisely and repeatably position the mask in relation to the panel. As shown, three springs on the frame which clip onto three studs on the panel provide a three point support.
The term panel or face panel as used herein means the face screen member that has a flange around the outside with suitable mounting studs for receiving the mounting means for the mask and frame assembly. The inside surface of the panel is provided with the phosphor dots used for reproducing color in a color television tube.
The term identical" is also used to describe the masks which are formed. This term means that the distance from the center of one hole to the center of another corresponding hole on two masks is the same, but the hole sizes can vary. The position of the hole centers is very important.
Many of the particular steps in this method employ known procedures, such as the use of photosensitive resist coatings on the mask, the exposing of the photosensitive resist coatings to light, and the etching of the mask to chemically mill the apertures through the mask subsequent to the exposure of the mask. The photosensitive resist may be applied to the masks in a variety of ways, such as flow coating, spraying or dipping.
Likewise, the screening of the panels for placing of the phosphor dots is a generally known process. The screening takes place three times for defining the three phosphor deposits that constitute the triad dots on the screen. In the present process in each of three separate screenings a mask which is configured like a finished mask and frame assembly is used as a master for exposing the phosphor surface of the panel to insure accurate positioning of the phosphor dots or deposits that constitute the image screen, but the panel is not paired with the mask used as a master.
The coupling or attaching system used in the present invention between the mask and frame assemblies and the panels is a three point coupling wherein sharp or pointed pins formed on the ends of the attaching springs are mounted in conical holes or openings in studs on the panel. Thus the locating spring and pin concept is used, but only three point attachment is necessary.
In FIG. 1 a flow chart is shown which describes in general terms the steps of the present invention, many of which are conventional and normally done. The unique portions of the steps of the manufacture of television tubes will be more fully described. However, a strip of material from which a mask is to be formed in annealed and stress relieved in the conventional man ner, and the mask blanks are then punched out. The mask blanks are formed in the desired configuration, which in the form as shown will be a rectangular mask for a rectangular picture tube with the front surface a section of a sphere, in the normal manner. The thickness of the mask can be any desired thickness, and normally is in the range of 5-6 mils.
Separately, the frames for supporting the mask are formed from suitable thickness of metal, and the springs that will form the kinematic support between the mask and the panel are attached to the frames independently, before the masks are put into place. Then,
a mask blank and a frame will be assembled, and the assembly procedure will include checking for accuracy of the formation of the curvature of the mask blank. The support members which are used for holding the mask and frame with respect to a panel are also used as the support for the frame during assembly of the frame to the mask blank to obtain an exact reference for the supports with regard to the spherical or curved face of the mask.
It should also be noted that a mask and mounting rame can be integrally formed initially, and the process described will also be advantageous with such units.
The mask is coated with suitable photosensitive resist coating, on both surfaces, as shown, in a conventional manner normally done in the trade. Then the mask of each mask and frame assembly is exposed in a die that holds the face of the mask in its desired configuration while the coating on the mask is being exposed so that the exposed areas, which will subsequently be etched or milled to form openings or apertures are precisely positioned with respect to each other, and with respect to the supporting springs for the mask and frame assembly. The coating on both sides of the mask is exposed at the same time for precise positioning of the exposed areas. Then, the mask and frame is developed and stripped so that the coating is removed in the exposed areas. The mask is etched or chemically milled in a normal manner, or in any desired manner to form the desired apertures through the mask. The exposing step can be carried out using any desired form of light suitable to sensitize the areas to be etched.
In a separate operation, the panel blank is formed in a conventional manner, and a master mask which may be formed in the same manner as a production mask, is used as a pattern for the screening process of placing phosphor dots onto the interior of the panel or screen. The master mask is supported in a known relationship to the panel to properly position the finished dots. The phosphor coating on the panel is exposed through the apertures of a master pattern and this screening process is repeated for each color of the triad dots. The triad dots are formed in a known screening manner but the use of the curved master for exposing the phosphor coating on the curved panel insures precise positioning of the phosphor dots. The panel is supported by the studs during screening, and the studs later support a mask and frame assembly. The panel then may be subject to a filming operation or can be further processed as desired. A mask and frame assembly is inserted into the panel and supported by the support springs on the frame engaging and studs on the panel as will be further described. The color tube manufacture is completed in a known manner.
Referring to FIG. 2, the mask illustrated generally at is shown in its formed shape, and it has a spherical face or body wall portion 11, and a peripheral flange 12 that is used for attaching the mask to a support frame. The mask 10 is made out of suitable material, and is formed into the shown shape prior to having any apertures therethrough. It is in its imperforate condition, and it can be formed or drawn in any desired manner usually in a precise forming die. The mask can be stressed relieved if desired, and the material used for the mask is selected to have the properties necessary for the manufacture of suitable shadow masks. The mask is formed after the flat blank has been punched out.
A frame that will be used for supporting the mask, and providing the necessary connection between the panel or screen and the mask is also formed. As shown in FIG. 4, this is an open rectangular frame 13 which has a peripheral inwardly turned flange member I4, that extends around a central opening 15. A wall 16 of the frame surrounds the opening 15. Suitable spring steel flat springs 17, which can be made of any desired material, are attached to the flange 16 in three locations as shown with by spot welding or in some suitable manner. The spring attachment is well known, although the configuration of the springs are shown is different than that previously done. The springs 17, as shown are flat pieces of spring steel that have a base portion 18 that is spot welded to the wall 16 of the frame 14, and include an outwardly extending panel attaching portion 21 that as shown has an end formed into a sharp point 22 along the lower edge thereof. A recess 23 is provided for mounting clearance purposes. The points 21 of the three springs 17 form a triangle as shown by dashed lines in FIG. 4.
As shown, there are three springs 17 mounted on the frame 13. The spring points 22 are referenced to the plane of flanges 14 of the frame when they are attached to the frame, as shown by reference lines indicated at 24. The springs are held in a fixture, and the plane of outer surface of the flanges 14 is a reference that will not shift easily. When the springs 17 are spot welded in place to walls 16 there is a reference dimension within required tolerances between the reference plane and the points 22 of the springs.
As can be seen in FIG. 6 a mask 10 is about to be mounted over the outer surfaces of the walls 16 of a frame 13. The two parts are slipped together and they are placed onto an inspection-holding jig or fixture illustrated at 26 in FIGS. 7 and 8. This jig or fixture 26 is important in the overall process because it has gage members 27 positioned on a base 29 of the fixture to check the curvature of the convex surface of the wall portion 11 of the mask 10 to make sure that the mask has the desired configuration. Support members 28 are fixed to the base 29 of the fixture in position to receive the points 22 of the springs and to hold the frame in its proper relationship with respect to a reference plane lying along the top surface of the base 29. When the frame 13 is held in this proper relationship through the points 22 of the spring and supports 28, then the positioning of the face surface of the mask, which is located by the locating members 27, is accurate with respect to the supporting points for the frame. The supports 28 as shown are provided with holes or opening to receive the points 22. If desired, these can be formed as conical holes which will be shown in connection with the studs on the panels.
Then, suitable spot welding guns indicated schematically at 30, which are positioned on the frame or base 29 in the desired location all the way around the mask 10 as it is positioned in the frame, are operated to spot weld the flange 12 of the mask to the walls 16 of the frame 13 as shown with suitable spot welds arranged to hold the unit in precise position. The spot welding guns are shown only schematically and in a representative number for illustrative purposes. Spot welding guns which move from a retracted position to a welding position are well known in the art.
The mask and frame are thus held together in a reference position with respect to the locating and checking gages 27 for the mask, and the points 22 of the springs 17 through the supports 28. It should be noted that the supports 28 are upright columns that have an outwardly extending portion 28A with an opening 288 of size to receive the points 22 of the springs on the frame so that the frame is supported through the springs 17 which will support the assembly when it is placed in a finished panel.
Further, the gage members 27 can be replaced with a suitable concave fixture that will check the configuration and forming of the curved center portions 11 of the mask at the same time that the frame is attached.
When the mask and frame have been welded together, as shown in FIG. 7, with the spot welding mechanisms 30, the mask-frame assembly 31 then is a rigid unit and it is removed from the fixture and is ready for further processing in order to properly locate, and form, the apertures or openings through the mask. In order to obtain precise relationships of the openings with respect to the support members of the mask and frame assembly 3], namely the three points 22 on the springs 17 that support the frame and mask assembly, the device shown in FIG. 9 has been advanced. This is shown schematically, and includes a main support table 35 that has upright support members 36 attached thereto, and the upright support members have outwardly extending flanges 37 that are provided with openings 38 (see FIG. 11) into which the points 22 of the springs 17 will extend. The main table or support 35 also has a center opening 39 defined therethrough and the support members 36 are positioned adjacent the sides of the opening 39 with the flanges 37 extending to overlie the opening 39. The support members 36, and the openings 38 in the flanges 37 are positioned to receive the spring ends 22 of the mounting springs 17 on a mask and frame assembly. The mask and frame assembly 31 includes the structure previously described after it has been spot welded into place with a mask attached to a frame 13, and the center portion 11 of the mask checked and found to be in the desired spherical shape. The center portions 11 of the mask are coated with a suitable photosensitive resist coating as shown in FIG. 10 at 40 and 41, on opposite sides or surfaces of the mask.
The photosensitive resist coating is exposed through suitable light means in the areas where an opening is to be formed through the mask. These openings in the mask have to be precisely located on the mask with relation to the triad dots formed on a panel in the screening process. The openings also have to be precisely located with respect to the electron guns that are mounted in the neck of a finished tube. When the masks are formed it is desirable to have the holes in the mask formed with a larger diameter on the outer or convex surface of the mask than the holes on the concave side of the mask. The direction of entry of the electron beam from the different guns (three are normally used) requires this larger opening on the convex or outer side of the mask. The form of opening is shown in US. Pat. No. 3,676,914. The addition of the photosensitive resist coating to the mask is also discussed therein. However, the structure of FIG. 9 is utilized for obtaining exact registry of the exposed areas of the photo resist coatings on the opposite sides of the mask, and also insuring that the center lines of the openings are in the proper position with respect to the center of the spherical wall portion 11 in the center portions of the mask.
As shown, a first die member 45 is mounted with respect to the table 35 in suitable sliding guides 46 which are attached to supports fixed to the table 35, and which positively guide the die member 45 in movement toward and away from the table in the directions as indicated by the arrow 47. The die member is shown as a hollow compartment having an upper wall 48 with an attaching bracket 49 connected to the rod 50 of a cylinder 51 which can be hydraulic or pneumatic and which is supported on a base 52 that is fixed with respect to the table 35. The cylinder 51, or other suitable power means, can be actuated to move the die 45 back and forth in directions as indicated by the arrow 47 between two positions under suitable controls. The interior of the die member 45 is provided with a suitable light source 53 that is used for exposing the photosensitive resist coatings 40 on the concave surface of the mask being processed.
The die wall 54 as shown has a plurality of apertures 55 therethrough which are of size to provide an exposed area on the photosensitive resist coating 40 (see FIG. 10) that is the desired size for the purposes. These apertures 55 are positioned so that the axis of the openings or apertures 55 coincide at the center of the part spherical wall 54. The wall 54 is formed as a spherical wall segment concentric with the desired wall shape of the center wall portion 11 of the mask. The axes of the apertures 55 then intersect the center of the sphere which would normally be adjacent to the light source 53.
The die 45 and interior chamber 56 are made so that a vacuum can be created therein from a vacuum source 57 if desired through suitable controls.
A lower die 60 is constructed in the same manner as the upper die, and includes a housing that has suitable guides 61 for guiding it in its movement in directions as indicated by the arrow 62. The lower die is attached to a cylinder 63 in the same manner as the upper die, and a light source 64 is also provided. The wall 65 of the die as shown is conformed to fit against the outer or convex surface of the center wall 11 of the mask being processed and therefore the wall 65 is shown as being concave, and having a plurality of apertures 66 or larger size than the apertures 55 in the wall 54 (see FIG. 10). A vacuum source 67 is also provided for die 60.
When the cylinders 51 and 63 are actuated, they are actuated simultaneously, and the die units are guided toward the mask. It can be seen that the die 45 will fit within the interior of the frame-mask assembly 31, and the outer surface of the wall 54 will engage the concave surface of wall 11 of the mask, and the outer surface of the wall 65 will engage the convex surface of the wall 11 of the mask to hold the mask in its desired spherical configuration. The unit is designed so that the force with which the dies engage the mask is not great but the mask is primarily held with respect to its support springs in a desired location with respect to the points 22 of the support springs.
During this time when the lights 53 and 64 are on, the mask center wall portions 11 are in contact with the die walls 54 and 65, as shown in FIG. 10, and the mask is held exactly spherical or in the desired configuration by these die walls. The guides 46 and 61 insure that the openings in the die walls are properly positioned with respect to each other so that the axes of the apertures or openings 55 and 66 are directly aligned where these axis intersect the surfaces of the center portions 11 of the mask.
After the exposing lights 53 and 64 have been turned on for the desired time and the photosensitive resist coatings 40 and 41 have been exposed, the dies can be moved away from the mask by actuating the cylinders 51 and 63. The entire mask and frame assembly is then removed from the support. The dies are spaced sufficiently when retracted to insure that the mask and frame can be inserted between them and placed on supports 36.
It can be seen therefore that the positioning of the exposed areas of the photosensitive resist coatings is precise with respect to each other on the opposite sides of the mask, and the exposed areas are also properly positioned with respect to the centers of the desired spherical shape of the center wall portions 11 of the mask.
Then, the mask is treated as is normally done for etching. The coatings are developed and removed in the exposed areas and the holes are chemically milled through the mask in the center portions 11 in the areas where the photosensitive resist coatings have been exposed. The etching process is done as desired to obtain the desired configuration of the holes. A hole or aperture through the mask is shown after forming in FIG. 12, and it can be seen that the lower portion 68 of the hole is of larger diameter than the upper portion 69 of the hole. The mask and frame assemblies then are completely formed, in a repeatable fashion because all of the processes have precisely located the reference points comprising the points 22 of the springs with respect to the other mechanism being used so that the openings through the center portion 11 of the masks are precisely located with respect to the ends 22 of the springs.
In a separate process, the forming of the panels or screens as shown in the flow chart of FIG. 1 is taking place. The panels indicated at 75 in FIG. 13 are formed in the desired manner with peripheral walls or flanges 76, and include stud members 77 fixed to the flanges 76. The studs 77 are fixed to the flanges and extend inwardly from the flanges. The panels 75 are made of suitable material, and the studs are attached in a known manner, and form the supports for a mask and frame assembly when the unit is to be finally assembled.
The inner surface of this panel must have phosphor dots thereon positioned where beams from the electron guns of the television picture tube will illuminate these dots when the beam is passed through the shadow mask openings. These phosphor dots are usually formed with three separate colors, namely green, blue and red, in a triad dot. Three guns are normally used in a television tube. A beam from one gun will be used for the red dots, a beam from another gun will be used for the blue dots, and a beam from a third gun will be used for the green dots. It is therefore important that the openings through the mask in which these beams pass illuminate only the correct dot. Thus the location of the dots is critical.
In order to insure that the screening process, or the process whereby the dots are formed on the panel or screen 75 is precise, a master mask illustrated generally at 80 is used. It can be seen that this is a master mask made up in the same manner as the previous one, and supported on supports 82 fixed to a table or lighthouse. The supports 82 correspond in position to springs 17 on a mask and frame assembly. As will be seen when the final assembly is explained, the studs 77 have conical holes therein for receiving the pointed ends of rods 82A on the supports 82.
The master mask shown at 83 is formed to correspond to the shape of a production mask, so that the exposing light 84 will project precisely onto the areas of the panel on which the phosphor dots are to be formed. While the master masks are identical to production run masks i.e. the hole centers are the same, the apertures or holes in the master masks can be made smaller than the etched apertures in the production masks. The exposure and screening process is repeated three times for each panel, each time with a separate and different master mask and light source to properly position each of the three desired dots. The three screenings are done in a conventional manner with the exception that a curved master mask 83 is utilized, and there is no pairing of the masks and panels. The supports 82 and 82A are precisely located so that the panel studs 77 are positioned in the same relationship to the mask 83 as they will be with a production mask.
Then, in the final assembly, as shown in FIG. 14, a mask and frame assembly 31 with the apertures formed therein (the apertures are not shown) is positioned inside a panel by merely slipping the spring ends 22 into the apertures or holes 78 (see FIG. 17) of the studs so that the spring ends 22 center in the holes 78 to form a three point suspension for the mask and frame inside panel.
When this is done, the apertures in the mask and frame assembly 31 that is inserted and supported by studs 77 will be precisely located in relation to the triad dots on the screen 75. Interchangeability is thus made possible.
In the previous attempts in interchangeability, shifting of the apertures in the masks, and misalignment of the apertures 69 (see FIG. 12) formed from the concave surface of the mask with respect to theapertures 68 formed in the convex surface of the mask has caused a high rate of rejection. This is primarily due to the use of flat master patterns, and not precisely holding the mask during the exposing of the photosensitive resist coatings prior to etching. In the present process, holding the masks against die surfaces when exposing the resist coating insures that the apertures of one mask will be identical (same center distance) as the apertures of another mask. Also, the apertures formed from one side will be centered with the apertures formed from the other side when the dies are used.
Likewise, another defect has arisen because of the use of a flat master for exposing the phosphor dots on the panels during the screening operations. When a flat master is used, the positioning of the apertures cannot be as exact for a number of reasons, including the fact that apertures in a curved mask have their axis intersecting at a common center point, which is the generating point of the spherical surfaces of the mask.
Additionally, the points 22 of the springs are used for reference purposes in locating the mask and frame as they are assembled together, so that repeatability is possible.
Even in screening the panels, the studs 77 are referenced to supports 82A which are precisely located with respect to the master pattern.
The exposure of the mask blanks prior to etching can take place with the blank positioned close to, but not touching the die walls 54 or 65. The curved shape of the die walls aids in precisely locating the exposed areas because of the curved shape even if the blank does not touch the die wall.
1. A method of manufacturing shadow-mask types of color cathode ray tubes having a face panel, and a shadow mask mounted adjacent said panel comprising the steps of:
forming a mask and support means assembly with said mask having an imperforate, curved surface; providing at least one surface of said mask in which apertures are to be formed with a coating of a sensitized resist; supporting said one surface of said mask adjacent a master exposing die formed to correspond to the desired curved shape of said mask, and exposing portions of the resist coating on said one surface of said mask while said one surface is supported; developing and etching said mask to create an aperture pattern in the exposed areas; and mounting said mask in a cathode ray tube face panel having means to provide repeatable positioning for any mask with respect to preselected portions of said cathode ray face panel.
2. The process as specified in claim 1 comprising the further steps of screening said face panel using a screening master mask having a curved shape substantially corresponding to the curved shape of a shadow mask after forming.
3. The process according to claim 2 wherein said face panel is provided with mounting means defining three points of support, and wherein the step of forming a mask and support means assembly includes mounting cooperating support means for said mounting means on said first mentioned mask while supporting said cooperating support means and said first mentioned mask in a fixture supporting said first mentioned mask on its outer surface.
4. The process as described in claim 1 wherein said curved mask surface is a face surface, and wherein the forming of a mask and support means assembly comprises the steps of supporting said mask on said curved face surface in a fixture defining the desired curve, providing a frame member having three support means defining three point support for said frame and referenced with respect to a desired plane, supporting said frame member on said three support means and in proper position with respect to said mask supported in said fixture, and attaching said mask and frame member together when the three support means are properly referenced with respect to the curved face surface of said mask.
5. The process according to claim 2 including the steps of screening on said panel member a phosphor pattern determined by exposing said panel through a plurality of apertured masters, each master being curved to conform to the curvature of a mask to be used with said panels, one of said masters being used for screening each of a plurality of different color phosphor dots.
6. The process according to claim 4 wherein said mask is coated with a photo etch resist coating on opposite surfaces thereof after said frame member is attached, and the step of exposing includes the step of supporting said mask on both of said opposite surfaces in die members having apertures therethrough for exposing the opposite surfaces of said mask, said die members being movably supported with respect to each other for movement toward and away from said mask.
7. A process for manufacturing color television masks and panel assemblies comprising the steps of forming a mask blank from an imperforate wall portion into a desired shape having a curved configuration to form one convex and one concave surface, forming a frame member for supporting said mask blank, attaching mounting members to said frame member with respect to a predetermined reference plane, said mounting members comprising at least three points of support positioned accurately with respect to said plane, providing a fixture for connecting said mask blank and said frame together including checking means supporting said mask blank directly on one curved surface and having at least a plurality of reference contact members engaging said one curved surface in a plurality of separate contact points to insure accuracy of said one curved surface, and supporting said mask blank on said checking means in contact with said reference contact members, providing separate fixedly positioned support means on said fixture, in a predetermined reference relationship to said checking means to receive said mounting members, supporting said mounting members attached to said frame on said separate support means on said fixture, fixing said mask blank and frame together in an assembly while the frame is sup ported by said mounting members on said separate support means in a precise predetermined reference relationship to the curved surface of said mask blank supported on said checking means, providing a die member having a curved die surface corresponding to at least one of the curved surfaces of said mask blank, said die member having a plurality of apertures opening to said curved die surface, coating said mask blank with a suitable photosensitive etch resist coating, supporting said mask blank closely adjacent said curved die surface with the curved surfaces substantially in registry, and exposing the coating on said mask blank in predetermined areas to provide areas in which etching can occur to form apertures in said mask blank.
8. The process according to claim 7 including the further step of having a pair of movable die members mounted for movement toward and away from each other in a predetermined relationship and position relative to each other, said die members each having a die surface corresponding to the concave and convex surface of said mask blank, respectively, each of said die members having apertures formed therethrough and open to the die surface thereof in a predetermined relationship to the apertures of the other die member, said apertures being arranged in a desired pattern, supporting said mask blank adjacent to the die surfaces of both of said die members, and exposing the photosensitive resist coating on said mask blank when said mask blank is supported adjacent said die surfaces.