US3325384A

US3325384A - Shaped cathode for electrolytic etching

Info

Publication number: US3325384A
Application number: US323476A
Authority: US
Inventors: John J Frantzen
Original assignee: Buckbee Mears Co
Current assignee: Buckbee Mears Co
Priority date: 1963-11-13
Filing date: 1963-11-13
Publication date: 1967-06-13
Anticipated expiration: 1984-06-13

Description

June 1%? J. J. FRANTZEN 3,32 3

SHAPED GATHODE FOR ELECTROLYTIC ETCHING Filed Nov. 13, 1963 INVENTOR JOHN J. FHA/V7125 A! ATTQRNEY United States Patent 3,325,384 SHAPED CATHODE FOR ELECTROLYTIC ETCI-IING John J. Frantzen, St. Paul, Minn., assignor to Buckbee- Mears Company, St. Paul, Minn., a corporation of Minnesota Filed Nov. 13, 1963, Ser. No. 323,476 3 Claims. (Cl. 204-143) This invention relates to electrolytic etching of circuit patterns in metallic workpieces and in particular is directed towards means for ensuring properly etched circuits of a variety of configurations.

In electrolytic etching a suitable source of DC. energy is connected across the anode, the workpiece, and the cathode with the latter two immersed in a suitable liquid electrolyte. The pattern to be etched is defined by a mask of etch resist material on the workpiece. The workface of the cathode is positioned with respect to the workpiece such that upon activating the energy source electrical current flow between the cathode and the workpiece removes or etches away those areas of the metallic workpiece not coated with resist material. The etching rate is deepndent upon many factors, one of which is the displacement between the cathode workface and the corresponding area of the workpiece. Obviously the greater the displacement the slower will be the rate of etch.

In the past there has been a limitation on the circuit designs which can be fabricated by electrolytic etching. Recognizing that there must be electrical circuit continuity from the energy source to the portion of the workpiece being etched through the electrolyte and the cathode back to, the energy source, circuit designs which could result in discontinuities in this electrical circuitry during etching heretofore could not be electrolytically etched. For example, consider the case of etching out a plurality of radially displaced annular areas from a flat metallic workpiece. Assuming that the energy source is connected to a peripheral area of the metallic workpiece, it was very possible that an outer annular area would be etched sufficiently to break electrical circuit continuity to an inner area before the latter was completely etched. Etching of the latter would then terminate, resulting in an incomplete article. Rather than take a change of this occurring, circuit patterns of this type were generally obtained by some other less desirable process.

The principal object of this invention is to provide means to insure that electrolytic etching progresses in a predetermined manner and rate so as to enlarge the range of circuit pattern designs which can be electrolytically etched by overcoming the disadvantages described above. This principal object is achieved by providing a cathode workface which is contoured to control the etching process. For example, the cathode workface surface may be tapered to provide different displacements between the cathode and the workpiece thereby resulting in a difference in the rate of etch of diiferent sections of the workpiece.

These and other objects and features of this invention will become apparent during the course of the following detailed description with reference to the accompanying drawings in which:

FIG. 1 illustrates an embodiment of this invention incorporated in an electrolytic etching apparatus for etching out of the workpiece a circuit pattern of concentric rings;

FIG. 2 is a sectional view of a part of the apparatus of FIG. 1.

In the figures the metallic workpiece comprises a thin layer of gold 11 bonded with a suitable insulative adhesive 12 to a supporting base of a sheet of aluminum ice 13. The concentric rings on the top surface of the workpiece illustrate the pattern to be etched in the work-. piece and are defined by masking the workpiece with etchresist material 14. The unshaded areas in FIG. 1 indicate those exposed areas from which the told is to be etched away while the shaded areas are protected during etching by the resist. Briefly, the workpiece can be prepared in the following manner. The gold is initially vapor blasted to mat its finish and then cleaned with a suitable solvent. A proper thickness of aluminum sheeting is cut into rectangular pieces which are cleaned and smoothened and then covered with a suitable adhesive material. The gold is then placed on the adhesive and its multiple layer assembly is subjected to a suitable pressure for a predetermined period of time to bond the layers together. To photoprint the desired circuit pattern on the workpiece, the gold is first thoroughly cleansed by light scrubbing, rinsing and then drying. Then the gold is coated with a suitable light sensitive material or enamel upon which is photoprinted the desired pattern in the well-known mane ner. Where the gold is protected, the light sensitive material is baked on, and in those areas where the gold is to be removed during etching, the enamel is removed during the photoprinting process so the selective areas are exposed for etching. It should be understood that the foregoing is only briefly illustrative of a process for preparing the workpiece and this and other methods are well known to those of ordinary skill in the art and can be used without detracting from the essence of the invention.

At a point on the peripheral area of the workpiece 10, an output terminal of the DC. energy source 15 is connected to the workpiece by a suitable electrical conductor 16. The cathode 17 is also connected to another output terminal of the energy source by a further conductor .18. The electrical circuit path is closed by a suitable electrolyte, not shown, in which the workpiece and the cathode are immersed. This solution may be a mixture of nickel chloride and reagent HCl. When the energy source 15 is activated, the electrical current passing between the workpiece and the cathode causes removal of the gold from the top surface of the workpiece in those areas not protected by the covering coating of resist material 14.

The workface of the electrode 17 is conical shaped and the remainder is cylindrical so that overall it somewhat resembles a sharpened stubby pencil. The apex of the cone is centered with respect to the annular areas to be etched out of the workpiece and is spaced a short distance above the workpiece. A flat projection of the tapered surface of the cathode would substantially encompass the extremities of the areas to be etched out of the workpiece. It was previously pointed out that the etching rate is dependent, inter alia, upon the displacement between the workpiece and the workface of the cathode. It can be visualized then that with the arrangement illustrated in FIGS. 1 and 2 the etching current will be concentrated to a greater degree at the center area of the workpiece than it is toward the outer peripheral areas thereof. The etching rate will correspondingly be faster at the center than at the periphery. In this manner then the annular areas will be etched out in successive order starting at the center of the workpiece radially outward so that the electrical circuit continuity between he energy source 15 and all areas of the workpiece will be maintained until the respective annular areas have been completely etched out.

In the practice of this invention, the workpiece 10' is prepared in the manner previously described or by some other equally suitable method. The workpiece and the cathode 17 are then detachably mounted in a holding fixture 20 which maintains orientation and position of the two units with respect to one another such as illustrated in FIGS. 1 and 2 with the apex of the cathode centered above the workpiece. With

conductors

16 and 18 connecting energy source to the workpiece and cathode respectively, the so-assembled units are immersed in the electrolyte and the energy source is activated. Although the amount of etching current and the period of time of application is a matter of choice and readily determinable either empirically or otherwise by those of ordinary skill in the art, in a typical case the apex of the cathode cone may be of an inch above the center of the workpiece and while the combination is immersed in the electrolyte of nickel chloride and reagent HCl alternately, 15 amps. are applied for ten seconds and 4 amps. for four minutes until the etching of the annular areas is complete, which may take in the order of twenty minutes.

After the etching is complete and the workpiece is detached from the holding fixture, it is cleaned by scrubbing with Triad, is then pumiced and dried in air. If desirable, the etched-out .annular areas can be filled with an insulating epoxy flush with the surface of the gold.

Although only one particular embodiment of this invention has been described, viz., a cone-shaped cathode in combination with a flat workpiece to etch out annular areas, obviously the teachings of the invention can be incorporated with the resulting advantages and features into apparatus for producing a variety of etched-out patterns. For any particular pattern to be etched out, the corresponding configuration of the workface of the cathode can be determined by design or empirically to provide a rate and manner of etching which will maintain the electrical circuitry continuity until the etching of all the disconnected areas is complete.

I claim:

1. A process for electrolytically etching a thin flat metallic workpiece masked to form a plurality of separate concentric annular areas out of the workpiece comprising: electrically connecting a source of energy to an outer edge of said workpiece; supporting a cathode having a coneshaped workface spaced away from said workpiece with the apex of the cone centrally located with respect to said workpiece such that energy concentration between the workpiece and the cathode is greater at the center than it is at the periphery of the workpiece during etching and progressively electrolytically etching said workpiece outwardly from the center to form said annular areas.

2. A process for electrolytically etching a plurality of radially displaced separate, concentric, annular areas from a thin fiat metallic workpiece having masked annular areas thereon comprising: a positioning pointed cylindrical cat11- ode orthogonal to said workpiece with the point spaced away from but centrally located with respect to the workpiece, the tapered area of the cathode between the point and the cylindrical section being substantially equal to the area of the workpiece in fiat projection; and etching the unmasked areas between said respective masked annular areas completely through progressively from the center radially outward.

3. A process for electrolytically etching out of a masked thin flat metallic workpiece a group of disconnected areas comprising the steps of: electrically connecting a source of energy to an outer edge of the masked workpiece; placing a cathode having a uniform. upwardly tapered workface over the masked workpiece so that the lowest part of the cathode workface is located furthest from the edge of the workpiece to which the energy source is connected and the tapered area is superim-.

posed over the workpiece; and keeping the workpiece and cathode in the same relative positions while etching the workpiece progressively outwardly from the area located directly under the lowest part of the cathode.

References Cited UNITED STATES PATENTS 2,492,214 12/1949 Fonda 204224 2,844,531 7/ 8 Prince 204-224 3,05 8,895 10/ 1962 Williams 204-334 3,239,441 3/1966 Marosi 204l43 FOREIGN PATENTS 809,936 3/ 1959 Great Britain.

JOHN H. MACK, Primary Examiner.

D. R. JORDAN, Assistant Examiner.

Claims

1. A PROCESS FOR ELECTROLYTICALLY ETCHING A THIN FLAT METALLIC WORKPIECE MASKED TO FORM A PLURALITY OF SEPARATE CONCENTRIC ANNULAR AREAS OUT OF THE WORKPIECE COMPRISING: ELECTRICALLY CONNECTING A SOURCE OF ENERGY TO AN OUTER EDGE OF SAID WORKPIECE; SUPPORTING A CATHODE HAVING THE CONESHAPED WORKFACE SPACED AWAY FROM SAID WORKPIECE WITH THE APEX OF THE CONE CENTRALLY LOCATED WITH RESPECT TO SAID WORKPIECE SUCH THAT ENERGY CONCENTRATION BETWEEN THE WORKPIECE AND THE CATHODE IS GREATER AT THE CENTER THAN IT IS AT THE PERIPHERY OF THE WORKPIECE DURING ETCHING AND PROGRESSIVELY ELECTROLYTICALLY ETCHING SAID WORKPIECE OUTWARDLY FROM THE CENTER TO FORM SAID ANNULAR AREAS.