US3423261A - Method of etching fine filamentary apertures in thin metal sheets - Google Patents

Description

Jan. 21, 1969 J, J, F Z Y 3,423,261

METHOD OF E ING FI AMENTARY APERTURE THIN META HEETS Filed March 1965 7 /A '.Z i-

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Fig 7 JOHN J. FRANTZE/V BYW 7 ATTNEYS United States Patent 3,423,261 METHOD OF ETCHING FINE FILAMENTARY APERTURES IN THIN METAL SHEETS John J. Frantzen, St. Paul, Minn., assignor to Buckbee- Mears Company, St. Paul, Minn a corporation of Minnesota Filed Mar. 8, 1965, Ser. No. 437,969 US. Cl. 15611 Int. Cl. C23f 1/02 2 Claims ABSTRACT OF THE DISCLOSURE This invention relates generally to the production of precision articles by etching. More particularly the invention is directed to a process for producing improved articles of metallic, sheet-like construction containing a plurality of precision-formed filamentary apertures and in which the articles are of sufficient thickness relative to their other dimensions to be substantially rigid or inflexible so that they are mechanically stable.

Experience has taught that in the art of making precision articles by etching a metallic plate, as the thickness of the plate increases the quality of definition of the etch decreases. This is principally due to the undercutting effect of the etchant which is a natural result of the etching time period being greater near the surface of the plate to which the etchant is applied as compared to the other more further removed surface. Where physical stability or rigidity of the finished article has been an important factor requiring that the article be produced from a relatively thick sheet of metallic material, a bimetal process is often used. A type of bimetal process for etching a metal plate is described in the Golay Patent 2,829,460. As described more thoroughly therein, this process involves coating a relatively thick plate of the basic metal with a thin layer of a different metal which in turn is coated with a non-metallicprotective material. In those areas where apertures are to be etched, the protective coating is removed and an etchant is applied to the thin metallic layer to remove this material from the unprotected areas. This etchant does not attack the thicker base metal. Sharply defined, precise dimensions can be maintained in etching through this thin metal layer. As the next step, an etchant which will not attack the thin metal layer is applied to remove the base material underlying the exposed areas. Even though the dimensions of the aperture formed through the thicker layer may be indefinite, the effective dimensions of the aperture are defined by the etched-out portion of the thin metal layer and therefore the degree of precision which is required is maintained. There are variations in this bimetal process. For example, the thin metal layer pattern can be electroformed onto the thicker base material rather than etched out. In any event, in order to overcome the effect of undercutting which limits the degree of precision and definition, the two metallic layers are of different materials so-that they are not both attacked by the same etchant. The principal disadvantage of the bimetal process is that the article is then produced from two different metals which have different characteristics which does create problems in some areas of use. Specifically, articles 3,423,261 Patented Jan. 21, 1969 "ice constructed by the bimetal process which have been used in environmental conditions in which relatively large variations in temperature take place, have been damaged or otherwise rendered useless because of the different coefficients of expansion of the metals involved. It is the object of this invention to overcome the disadvantages of the bimetal process which have been encountered heretofore.

Articles constructed according to the teachings of the instant invention can be considered, in a general sense, to be made according to a bimetal process but yet the finished article has virtually all the physical characteristics of an article which is constructed from a single metallic material. Briefly, in this improved process, the relatively thick strengthening base sheet of a first metallic material is coated with a very thin layer of a different metallic material. The pattern which defines the apertures to be formed, is laid out over this coating with a thin layer of metallic material which is the same as that in the base sheet. This may be done by electroforming or etching or the like. The base sheet can then be selectively etched from its underside in those areas corresponding to where the apertures are desired. The very thin coating layer will prevent the etchant from attacking the pattern-defining, top, thin layer of the same metal. When the base sheet has been suitably etched, the very thin coating material can be quickly stripped away because of its thinness so that apertures passing completely through the article are formed. As in the bimetal process, the thin layer defines the precision dimensions for the aperture. Because the great bulk of the metallic material in the finished product is to such an overwhelming degree a single metallic material, the article has, for all practical purposes, all of the physical characteristics of an article constructed solely from this single material.

Features and advantages of this invention will become apparent during the course of the following detailed description with reference to the accompanying drawings in which:

FIG. 1 is a fragmentary top view of a rectangularshaped metallic plate article containing filamentary apertures made according to the teachings of thi invention.

FIGS. 27 are sectional views taken along line 7-7 illustrating the same article as it appears during various stages of the process of this invention.

An example of the type of articles that can be constructed according to the teachings of this invention is illustrated in fragmentary form in FIG. 1. This article, which is identified generally by thenumeral 10, may be a flat, relatively rigid 3" x 3 square sheet with suitable locating or mounting holes, not shown, at its edges. Thisarticle 10 contains a plurality of filamentary apertures 11 which may all be of equal size or may vary in size and pattern as desired, depending on the ultimate use for the article. Articles of this nature may be used as stencils, as viewing masks, or a variety of other uses. In any event, it is contemplated that the intended use is such that the article must be structurally stable, i.e., relatively rigid or inflexible, and the apertures must be formed to a relatively high degree of precision.

FIG. 7 is a view of the finished article taken along section 77 of FIG. 1. FIGS. 2-6 illustrate the condition of the article during various steps of the inventive process. Although in the following detailed description of the invention certain materials will be specified for use in the construction of the article, it should be understood that a variety of materials can be utilized providing they are compatible with the various processing steps included in the invention and as recited in the appended claims.

Thebase supporting layer 12 may be a 3" x 3 sheet of nickel having a thickness in the order of .005 inch.

This order of thickness as compared to the other dimensions of the base sheet affords the latter a substantially rigid or inflexible construction as required for the intended use. The top surface of thebase sheet 12, after being suitably cleaned, is coated with a very thin layer ofgold 13 which may be flashed onto the nickel surface to a thickness in the order of .0001 inch, as illustrated in FIG. 2. Gold plating to a thickness in this order of magnitude relative to the thickness of thebase sheet 12 will in general adequately serve its intended function, which will be apparent shortly, but will have negligible effect on the structural characteristics of the finished article. The upper exposed surface of thegold layer 13 is then coated with a suitable light sensitive enamel and the desired pattern of filamentary apertures is photoprinted thereon in the usual and well-known manner. The photoprinting step results in theprotective enamel 14 covering only those areas of the gold plating which corresponds to the areas defining the filamentary apertures which are to be formed, as seen in FIG. 3. The goldplated nickel article containing the partial enamel coating is then placed in suitable electroplating bath and a thin layer ofnickel 15 is deposited on the gold plating in those areas not covered by theprotective enamel 14, in the well-known manner. The nickel is preferably electroplated in this manner, and as illustrated in FIG. 4, to a thickness in the order of .0004 to .0005 inch. Next, the bottom surface of the base sheet ofnickel 12 is covered with a protective coating of light sensitive enamel and the negative image of the pattern which was photoprinted on the gold plating is photoprinted on this bottom surface in the well known manner. As a result of this photoprinting step,protective enamel 16 remains on those areas of the bottom surface which underlie those top surface areas which are covered by thethin nickel layer 15 over the gold plating as seen in FIG. 5. There is an absence of protective enamel on the bottom surface in those areas underlying the top surface areas which are coated with theprotective enamel 14 over the gold plating. As stated earlier, those top surface areas covered by theenamel 14 so that they are void of thin-layer nickel 15, define the filamentary apertures which are to be formed. A suitable etchant is then applied in the well known manner to the bottom surface of thebase nickel 12 so that it attacks the nickel in those areas unprotected by theenamel 16. FIG. 6 illustrates the general pattern of the openings etched through the relatively thickbase sheet nickel 12. This tapered effect is due to the fact that the etchant has a longer reaction time with the material closest to the surface at which it in applied than it has with the material at the further surface. The etching of thebase sheet 12 is continued until the base sheet nickel which underlies the enamel coatedareas 14 has been removed. It goes almost without saying that the etching should not be allowed to continue to an extent where it would cause a structural deficiency by over-etching the base sheet. The etchant which is applied to thebase sheet 12 does not attack the pattern-defining thin layer ofnickel 15 since it is shielded from the latter by the verythin gold plating 13.

After etching the areas ofenamel 14 and 16 are removed, either chemically or by stripping, so that the article appears as illustrated in FIG. 6. Finally, thegold plating 13 is removed from those areas underlying the aperture-defining areas of the upper thin layer of nickel. Because the gold plating is so very thin, it is readily stripped away or it can be etched away chemically. The end result is as illustrated in FIG. 7. The filamentary apertures, 11, shown in sectional view are effectively defined by the thin layer ofnickel 15 with the desired precision even though etching done through the relatively thick supportingbase sheet 12 would not have provided the degree of precision required. The minute amount of gold in the finished article, as compared to the great bulk of nickel, with the gold limited to an extremely thin plating or flash coating, has negligible effect on the physical and structural characteristics of the finished article. These characteristics are then determined for all practical purposes by the dominant nickel material.

Although in the foregoing description, the aperturedefining pattern is formed by the upper thin layer of nickel being electroformed or deposited over the gold plating, this can be done in other ways. For example, instead of coating the gold plating 13 with enamel, a uniform thin layer of nickel can be placed over the gold plating by, for example, electroforming to a thickness in the order of .0004.0005 inch. This thin layer of nickel can then be coated with enamel and a suitable pattern photoprinted thereon. In this event, the pattern would be the same as that photoprinted on the bottom surface of thebase sheet nickel 12, such as illustrated in FIG. 5. The thin layer of nickel would then be etched and only those areas not protected by the enamel, which would correspond toareas 14 shown in FIG. 5, would be etched away leaving the other areas of nickel, 15, intact in the same manner as illustrated in FIG. 5. Electroforming the thin layer of aperture-defining pattern of nickel has been found preferable, however, since it provides better definition of the filamentary apertures.

Articles constructed according to this invention have been used in environmental conditions in which the temperature has varied over a wide range with no resulting impairment in the physical structure nor reduction in the effective use thereof. This can be compared to the difiiculties encountered where a different metal has been used in the bimetal process for forming the aperture-defining pattern resulting in loss of reliability and permanent damage.

I claim:

1. A method for producing a substantially inflexible metallic sheet article containing a pattern of a plurality of precision filamentary apertures, comprising the steps of:

(a) coating a surface of a relatively thick substantially inflexible base sheet of nickel with a flash coating of gold in the order of the thickness of the base sheet of nickel;

(b) forming on the gold flash coating a thin layer of nickel arranged in a pattern defining a plurality of filamentary apertures, said thin layer being substantially thinner than the base sheet yet not less than four times the thickness of the gold flash coating;

(0) chemically etching away areas of the base sheet of nickel which underlie the aperture areas in the thin layer of nickel with a chemical etchant which does not react with the gold flash coating; and

((1) then removing the areas of the gold flash coating corresponding to the aperture areas of the nickel.

2. The invention as described in claim 1 wherein the patterned thin layer of nickel is formed on the gold flash coating by:

(a) first covering the gold flash coating with a lightsensitive enamel;

(b) then exposing the enamel to actinic light so that only the areas of the enamel corresponding to the desired aperture areas are hardened by the light from the source;

(c) removing the unhardened areas of enamel; and

(d) electrodepositing nickel to the desired thickness on the gold flash coating in those areas from which the enamel had been removed.

References Cited UNITED STATES PATENTS 2,469,689 5/1949 Gresham 204-24 2,649,361 8/1953 Springer et al 156-48 JACOB H. STEINBERG, Primary Examiner.

US. Cl. X.R.

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