Abstract:
An etching system for etching openings in a metal web including multiple etching station for etching a metal web from opposite sides with each of the etching stations including a set of first bank of oscillateable nozzles located in a first chamber in the etching station, with the first bank of oscillateable nozzles having predetermined spacings from one another, and operable for directing etchant at a first side of a metal web and a second bank of oscillateable nozzles located in a second chamber in the etching station, with the second bank of oscillateable nozzles having a predetermined spacing substantially identical to the first bank of oscillateable nozzles with the second set of oscillateable nozzles laterally offset from the first set of nozzles, so as not to spray on directly opposite regions located on the metal web with the banks of the nozzles in adjacent etching stations offset from each other with the oscillation axis of the nozzles is at an angle off normal so that etchant is sprayed in elliptical patterns on the metal web to more uniformly distribute etchant across the metal web.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to etching metal webs and more particularly to more uniformly distributing etchant across the metal web to more accurately etch metal webs such as aperture masks. 
     BACKGROUND OF THE INVENTION 
     In the etching of metal webs, and, in particular, in the etching of metal webs from opposite sides it is difficult to uniformly control the distribution of etchant throughout the metal web. If holes are being etched in the metal web, the size and shape of the holes may vary substantially as a result of non-uniform etchant distribution. 
     One method used to more uniformly distribute the etchant is to place a first set of oscillateable etchant spray nozzles above the metal web and a second set of oscillateable etchant spray nozzles below the metal web, with both sets of oscillateable nozzles spraying etchant directly onto the metal web. The result is an etching process which has better dimensional controls, since the oscillating nozzles can more uniformly distribute the etchant on the metal web. 
     However, even with oscillating the nozzles, the spray patterns are not uniform, often resulting in uneven etching. The problem with uneven etching is that once breakthrough occurs in a metal web, that is, a hole has been formed in the web, etching proceeds at a much more rapid rate, since fresh etchant is continuously applied to the sides of the hole. The result is that a first pre-breakthrough etching rate exists, and a second post-breakthrough etching rate exists after the opening or hole is formed. Consequently, if all the holes in the metal are not begun to be enlarged at the same time the holes can become irregular and misshapen as a result of the different etching rates before and after breakthrough. 
     One of the goals of the present invention is to more uniformly distribute etchant to have the breakthrough occur at substantially the same time throughout the metal web. If the rate of etching proceeds at a constant rate throughout the metal web, one can accurately control the final dimensions of any openings formed in the metal web. 
     The present invention provides a process and apparatus for more uniformly distributing the etchant across the metal web in order to obtain breakthrough at substantially the same time throughout the metal web. 
     BRIEF SUMMARY OF THE INVENTION 
     An etching system for etching openings in a metal web including an etching station for etching a metal web from opposite sides with the etching system including a first bank of oscillateable nozzles located in a first chamber in the etching station, with the first bank of oscillateable nozzles having predetermined spacings from one another, and operable for directing etchant at a fast side of a metal web. The system includes a second bank of oscillateable nozzles located in a second chamber in the etching station, with the second bank of oscillateable nozzles having a predetermined spacing substantially identical to the first bank of oscillateable nozzles with the second set of oscillateable nozzles laterally offset from the first set of nozzles, so as not to spray on directly opposite regions located on the metal web. In addition the oscillation axis of the nozzles is off normal so that etchant is sprayed in elliptical patterns on the metal web. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial schematic view of upper and lower etching chambers located proximate a moving web; 
     FIG. 2 is a view taken along lines 2--2 of FIG. 1; 
     FIG. 3 is a view taken along lines 3--3 of FIG. 1; 
     FIG. 4 shows a partial sectional view of an etching station upper spray nozzles and lower nozzles with the lower spray nozzles located in phantom; 
     FIG. 5 shows a partial sectional view of the oscillating system of the present invention and a partial spray pattern as a result of the oscillation; and 
     FIG. 6 shows a graph representing the depth of etch as a function of mask position for various types of etchant distribution systems. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a partial schematic side view of etching stations 20, 21 and 22, with a metal web 9 extending horizontally therethrough. As web 9 passes through the etching stations, each of the nozzles sprays etchant onto the metal web. Etching station 20 includes an upper etching chamber 20a and a lower etching chamber 20b. Etching chamber 20a includes upper header 20h with a plurality of nozzles 20n  which are oscillateable about header axis h x  Similarly, etching chamber 20b located on the underside of web 9 includes header 20h&#39; which have nozzles 20n&#39; which are oscillateable about header axis h&#39; x  through header 20h&#39;. To illustrate the vertical spacing and alignment of the nozzles, FIG. 1 shows planes y 1 , y 2 , y 3 , y 4  and y 5  drawn through lower nozzles 20n&#39; and upper nozzles 20n which are located in etching chamber 20. Similarly, etching chambers 21 and 22 have the same vertical spacing and vertical alignment of etching nozzles located therein. 
     FIGS. 2 and 3 illustrate in partial schematic the location and arrangement of the oscillating nozzles in each etching chamber. The bank of upper nozzle and the bank of lower nozzles are laterally offset from one another with the bank of nozzles in adjacent chambers also offset from adjacent banks of nozzles. Reference numeral 20n identifies the first set of upper oscillateable nozzles in chamber 20. The oscillateable nozzles 20n located on five headers 20h which are located in a spaced and parallel relationship to one another. Located on each of headers 20h are oscillateable nozzles 20n which direct etchant onto the top of web 9. A driving mechanism 30 oscillates headers 20h and nozzles 20n to spray etchant laterally across the top surface 9a of web 9. 
     Etching chamber 21a includes a second set of identical oscillateable upper nozzles 21n. In addition etching chamber 21 includes an extra row of nozzles. Similarly, etching chamber 22a includes a third set of identical oscillateable upper nozzles 22n. Oscillatable nozzles 20n and 22n are identical in their position and oscillation with respect to web 9, while oscillateable nozzles 21n are offset from the nozzles 20n and 22n. To illustrate the offset relationship of the upper nozzles, a series of parallel spaced reference planes x 1  through x 11  extend vertically through stations 20, 21 and 22. To illustrate the offset relationship of the upper nozzles with respect to the lower nozzles, reference should be made to FIG. 4 which shows the upper nozzles 20n in solid and the lower nozzles 20n&#39; in phantom. 
     FIG. 4 illustrates the lateral offset of the upper and lower banks of the oscillating nozzles which occurs in a single etching station. The bank of upper nozzles 20n located above web 9 is shown in solid lines, and a bank of lower oscillating nozzles 20n&#39; is shown in dashed lines. Attention is called to the fact that each of the nozzles is located on equally spaced planes y 1  through y 5 , which are perpendicular to web 9 and extend vertically downward from the top oscillating nozzles 20n through the lower oscillating nozzles 20n&#39;. FIG. 4 illustrates the lateral offset of upper nozzles 20n from the lower nozzles 20n&#39;. The upper nozzles 20n are located in even planes x 2 , x 4 , etc., while the lower nozzles 20n&#39; are partial in odd planes, x 1 , x 3 , x 5 , etc. From the drawing, it can be seen that lower nozzles 20n&#39; are spaced midway between the upper nozzles 20n and staggered thereout, so as not to direct etchant on the opposed portions on the top and bottom of web 9. Thus, FIG. 4 illustrates that the grid pattern formed by the nozzles in the upper chamber and lower chamber of the same etching station are substantially identical except they are offset from one another so they do not spray etchant onto opposed regions on the opposite sides of web 9. 
     To illustrate the offsetting of nozzles in each etching station with respect to adjacent etching stations, reference should be made to FIGS. 2 and 3. FIGS. 2 and 3 are laid out so that the upper and lower views of etching chambers 20, 21 and 22 are in alignment with one another. To illustrate the offset of nozzles 20n, 21n and 22n in upper etching chamber 20, 21 and 22, reference planes have been drawn perpendicular to web 9 and are identified by x 1  through x 11 . The position of planes x 1  through x 11  are also shown in FIG. 3 to show the position of the lower bank of nozzles 20n&#39;, 21n&#39; and 22n&#39; with respect to the same reference planes. 
     FIG. 2 shows that the upper nozzles 20n and 22n are located in even reference planes x 2 , x 4 , x 6 , x 8  and x 10 , while the central station oscillating nozzles 21 oscillate about the odd planes which extend along planes x 1 , x 3 , x 5 , x 7 , x 9  and x 11 . Thus, it is apparent that the nozzles in the top chambers of adjacent etching stations are offset from one another. Similarly, the nozzles in each of the bottom etching stations are also offset from one another. That is, the lower bank of nozzles 21n&#39; oscillate about even planes x 2 , x 4 , x 6 , x 8  and x 10 , while nozzles 20n&#39; in station 20b and nozzles 22n&#39; in station 22b oscillate about the odd planes x 1 , x 3 , x 5 , x 7 , x 9  and x 11 . Thus, is can be seen that not only the top and bottom banks of nozzles are offset from one another, but both the top and bottom banks of nozzles in adjacent etching stations are offset from one another, thus providing a double offset so that no one region of the web receives a same or similar spray etching from an adjacent etching station. 
     FIG. 5 shows a partial schematic taken along lines 5--5 of FIG. 1. FIG. 5 illustrates a mechanism for oscillating the upper and lower banks of nozzles as well as a partial nozzle spray pattern 61 on the upper side 9a of web 9 and a partial nozzle spray pattern 60 on the lower side 9b of web 9. 
     A further feature of the invention is the use of axis of oscillations of the nozzles which are offset a predetermined angle from a vertical axis to provide an elliptical type spray pattern on both the top and bottom of the mask. 
     To illustrate the relationship of the oscillating nozzles of the upper and lower chamber in a single etching station reference should be made to FIG. 5. Since each of the oscillating nozzles is identical in the upper and lower chamber, only one nozzles will be described with respect to its oscillation about an axis h x  extending through its header. 
     Reference numeral 21n identifies an oscillating nozzles having a pivot pin 41 and an arm 42. Oscillating nozzle 21n is located on header 21h and oscillates about header axis h x . When the oscillating nozzles 21 n are operating, a motor 30 drives a crank 51 which connects to arms 52 and 57. Arm 52 connects to upper pivotal plate 54 and lower pivotal plate 53. Pivotal plate 54 pivots about pivot pin 54a, and, similarly, lower pivot plate 53 pivots about pivot pin 53a. The back and forth movement of arm 52 moves arm 57 which is pivotally connected to plate 54 by pivot pin 54b and to plate 53 by pivot pin 53b. Since pivot pins 53a and 54a are fixed, pivot plate 54 forces member 55 to oscillate back and forth in a direction indicated by the arrows. Similarly, pivot plate 53 forces member 56 to oscillate back and forth in the direction indicated by arrows. As a result of the driving action of motor 30, the upper nozzles 21n which are connected to member 55 oscillate about a non-vertical axis x. Similarly, the lower nozzles oscillate about a lower non-vertical axis z&#39; x . which is parallel to axis z x . As the upper and lower nozzles oscillate, they spray etchant onto web 9. The upper overlapping spray pattern of three adjacent rows of nozzles is indicated by reference numeral 61, and comprises a plurality of elliptical shaped regions. Similarly, the lower overlapping spray pattern of three adjacent rows of nozzles is indicated by reference numeral 60 on the underside of web 9 and also comprises a plurality of elliptical shaped regions which, as shown in the drawing, are biased to the right, while the spray pattern on top is biased to the left. While the spray pattern in adjacent station is substantially identical, the spray pattern in adjacent station is offset since the nozzles in adjacent station are offset from one another. 
     The elliptical shaped regions 60 and 61 result from the axis z x  of each of the nozzles being offset at an angle of approximately 33 degrees from a line extending perpendicular to web surface 9. Reference letter theta on the drawing indicates the offset angle. In the preferred embodiment it is preferred that the nozzles are spaced about five to twelve inches from the metal web and that the nozzles oscillate within frequency range of 30 to 60 cycles per minute an have a maximum oscillation angle about axis z x&#39;  or axis z x  which ranges from about 10 degrees to 30 degrees on each side of the axis z x&#39;  or axis z x . 
     To illustrate the depth of etch on a metal web under different oscillating spray conditions, reference should be made to FIG. 6. The vertical axis identifies the depth of etch, while the horizontal axis identifies the lateral position across a shadow mask. The reference A o  indicates the center of the mask, A e1  indicates the left edge of the mask, indicates the right edge of the mask. 
     Graph 71 identifies the variation of depth of etch when stationary nozzles are used. Note the depth of etch varies considerably from one side of the mask to the other side. Under these conditions, breakthrough would occur throughout the mask at different times. 
     Graph 72 identifies the variation of depth of etch from one side of the mask to the other side of the mask in prior art systems. Note that the depth of etch, although varying considerably from one side to the other, is better than if stationary nozzles were used. 
     Graph 73 identifies the variation of depth of nozzle depth of edge from one side of the mask to the other side with the etchant distribution system of present invention. Note the depth of etch remains substantially constant from one side of the mask to the other side. The result is that, when etching a metal web from opposite sides, the goal of obtaining a breakthrough at virtually identical times will be substantially achieved. With breakthrough occurring in the mask at virtually the same time, one is assured that, although different etching rates exist prior to and after breakthrough, the etching at varying regions across the mask will be substantially the same so that the final dimensions of the aperture can be more accurately controlled.