Method and apparatus for electrochemical etching

Abstract

A method and apparatus for electrochemical etching are disclosed. The method comprises immersing parts of objects (2) to be etched in an electrolyte (4), applying a voltage between the objects (2) and at least one electrode (6) to cause an electrochemical reaction between the objects (2) and the electrolyte (4), and positioning the objects (2) and electrodes (6) relative to each other such that a reaction product accumulates on the objects (2) during the reaction to reduce the rate of the reaction.

Claims

1. An electrochemical etching method comprising: immersing at least one first part of at least one object to be etched and at least part of at least one electrode in an electrolyte; and applying a voltage between said at least one object and said at least one electrode to cause an electrochemical reaction between said at least one first part and said electrolyte to cause at least one reaction product; wherein said at least one first part and said at least one electrode are positioned relative to each other such that at least part of said at least one reaction product flows downwards by means of gravity and accumulates on said at least one first part to reduce a reaction rate of said electrochemical reaction; further comprising providing a magnetic field in the vicinity of said at least one first part to cause flow of said electrolyte to adjust said reaction rate, wherein a strength of said magnetic field decreases in a downward direction.

2. A method according to claim 1, further comprising adjusting said magnetic field to control a rate of electrochemical etching of said at least one first part.

3. A method according to claim 1, further comprising surrounding at least one second part of said at least one object by at least one electrically insulating material.

4. A method according to claim 3, wherein said at least one electrically insulating material is a fluid immiscible with the electrolyte and is more dense than the electrolyte.

5. A method according to claim 4, wherein said at least one electrically insulating material comprises perfluorinated carbon fluid.

6. A method according to claim 1, further comprising controlling said voltage.

7. A method according to claim 5, wherein said voltage is controlled in dependence on an electrical current drawn by said electrochemical reaction.

8. A method according to claim 5, wherein said voltage is controlled in dependence on a profile of at least part of said at least one first part.

9. A method according to claim 1, wherein said at least one first part is elongate.

10. A method according to claim 1, wherein said at least one first part is a sheet of material.

11. An electrochemical etching apparatus comprising: at least one electrode; at least one container for accommodating at least one first part of at least one object to be etched such that said at least one first part and at least part of said at least one electrode are immersed in an electrolyte; and at least one voltage application device for applying a voltage between said at least one object and said at least one electrode to cause an electrochemical reaction between said at least one first part and said electrolyte to cause at least one reaction product; wherein said at least one first part and said at least one electrode are positioned relative to each other such that at least part of said at least one reaction product flows downward by means of gravity and accumulates on said at least one first part to reduce a reaction rate of said electrochemical reaction; further comprising at least one magnetic field generating device for providing a magnetic field in the vicinity of said at least one first part to cause flow of said electrolyte to adjust said reaction rate, wherein a strength of said magnetic field decreases in a downward direction.

12. An apparatus according to claim 11, wherein said at least one magnetic field generating device is adapted to provide an adjustable magnetic field.

13. An apparatus according to claim 11, wherein said at least one container is adapted to accommodate at least one second part of said at least one object such that said at least one second part is surrounded by at least one electrically insulating material.

14. An apparatus according to claim 11, further comprising at least one voltage control device for controlling said voltage.

15. An apparatus according to claim 14, wherein said at least one voltage control device is adapted to control said voltage in dependence on an electrical current drawn by at least part of said apparatus.

16. An apparatus according to claim 14, wherein said at least one voltage control device is adapted to control said voltage in dependence on a profile of at least part of said at least one first part.

17. An apparatus according to claim 13, wherein said at least one electrically insulating material is a fluid immiscible with the electrolyte and is more dense than the electrolyte.

18. An apparatus according to claim 13, wherein said at least one electrically insulating material comprises perfluorinated carbon fluid.

19. A method according to claim 3, wherein said at least one object is arranged such that said at least one second part is lower than said at least one first part.

20. An apparatus according to claim 13, wherein said container is adapted to accommodate said at least one first part and said at least one second part of said object such that said at least one second part is lower than said at least one first part.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) A preferred embodiment of the present invention will now be described, by way of example only and not in any limitative sense, with reference to the accompanying drawings, in which:

(2) FIG. 1 is a front view of an electrochemical etching apparatus embodying the present invention;

(3) FIG. 2 is a side view of the apparatus of FIG. 1;

(4) FIG. 3 is a perspective view of the apparatus of FIG. 1;

(5) FIG. 4 is a graph showing a profile of a current drawn from the power supplying means during a process embodying the present invention;

(6) FIG. 5 is an image, generated by a scanning electron microscope, of a probe etched according to an embodiment of the present invention; and

(7) FIG. 6 is an image, generated by a scanning electron microscope, of an edge of a razor blade etched according to an embodiment of the present invention.

DETAILED DESCRIPTION

(8) Referring to FIGS. 1 to 3, five cylindrically-shaped pieces of tungsten wire (2) of diameter 10 mm are secured to a stainless steel block (12) using stainless steel screws (14). One end of an insulated wire (16) is also secured to the block (12) by means of a screw (14), while another end of the wire (16) is connected to a power supply (not shown). The block (12), screws (14) and lower parts of each of the pieces of tungsten wire (2) are immersed in an electrically insulating layer of C-15 perfluorinated carbon fluid (10), while the upper parts of the pieces of tungsten wire (2) protrude upwards from the fluid (10) into a layer of potassium hydroxide electrolyte (4) above. Positioned above the pieces of tungsten wire (2) are two U-shaped stainless steel electrodes (6) connected to the power supply and a substantially rectangular permanent magnet (8), the magnet (8) secured between the electrodes (6) by means of two plastic struts (18) adhered to both the magnet (8) and each electrode (6). The magnet (8) is oriented such that one of its poles points towards the pieces (2). In FIGS. 1-3, the face of the magnet (8) nearest the pieces (2) is a pole of the magnet. The magnet (8), struts (18) and a part of each electrode (6) are immersed in the electrolyte (4). The electrodes (8) are placed at a distance of 20 mm above the ends of the pieces of tungsten wire (2). The fluid (10) and electrolyte (4) are contained within a glass container (20).

(9) The pieces of tungsten wire (2) and electrodes (4) are energised by a voltage supplied by the power supply. The voltage supplied by the power supply to the pieces of tungsten wire (2) and the electrodes (4) is controlled by a microcontroller and a computer program. The microcontroller measures a current drawn from the power supply during the etching process and the computer program adjusts a duty cycle and polarity of the voltage supplied depending on the current drawn. An example of a profile of the current drawn from the power supply during an etching process embodying the present invention is shown in FIG. 4.

(10) While the pieces of tungsten wire (2) and the electrodes (4) are energised, a voltage is applied between the pieces (2) and the electrodes (4) causing an electrochemical reaction to take place at the interface between the surface of each piece of tungsten wire (2) that is exposed to the electrolyte (4) and the electrolyte. The product of the reaction is denser than the electrolyte. The product forms a layer around each piece of tungsten wire (2) from which it originated and flows downwards, in a viscous manner, due to the force of gravity. Each layer of the product surrounding each piece of tungsten wire (2) partially insulates the surface of the respective piece of tungsten wire (2) from the electrolyte (4), consequently reducing a rate at which the surface of that piece of tungsten wire (2) decomposes. As the reaction continues, the product near to each piece of tungsten wire (2) accumulates, creating a layer of product near to each piece of tungsten wire (2) which is thinner at the ends of the pieces of tungsten wire (2) closest to the electrodes (6) than at the opposite ends of the pieces of tungsten wire (2), consequently causing the rate at which each point on the surface of each piece of tungsten wire (2) decomposes to be dependent on a distance of those points from the electrodes (6). As a result, each piece (2) decomposes into a substantially conically-shaped piece of tungsten with a sharp point at the end of each piece of tungsten nearest the electrodes (6).

(11) During the electrochemical reaction, the magnet (8) radiates a magnetic field (not shown) which interacts with ions in the electrolyte. Given the position and orientation of the magnet (8) as shown in FIGS. 1-3 and described above, the magnetic field accelerates the ions moving toward each piece of tungsten wire (2), by means of a Lorentz force, along a substantially circular path around each piece (2), creating a flow. Since the magnetic field strength decreases with distance from the magnet (8), a rate of the flow around each piece of tungsten wire (2) also decreases with that distance, the flow rate being proportional to the Lorentz force and therefore to the magnetic field strength. As a result, the greater flow rate at the ends of each piece of tungsten wire (2) nearest the magnet (8) causes faster circulation of the electrolyte around each piece of tungsten wire (2). The rate of decomposition of the surface of each piece of tungsten wire (2) is proportional to a rate of this circulation, therefore the generation of a circulation profile around each piece (2), via the presence of the magnetic field in the electrolyte, causes the decomposition of the surface of each piece of tungsten wire (2) to be well-defined and controllable in terms of the magnetic field.

(12) If two or more pieces of tungsten wire (2) are to be etched simultaneously, the etching process may be allowed to continue for a period of time after one or more sharp points have been formed, for the purpose of equalising the lengths and sharpnesses of the pieces of tungsten wire (2). The combination of the divergent magnetic field and the accumulation of the product during the reaction ensures that each piece of tungsten wire (2) experiences a rate of etching dependent on its proximity to the magnet (8), and therefore that a piece of tungsten wire (2) to be etched that is longer than another when the reaction begins, and therefore is closer to the magnet (8), is etched at a greater rate than a shorter piece of tungsten wire (2).

(13) The embodiment described above may be adapted for the etching of conductive sheets such as stainless steel razor blades rather than the aforementioned pieces of tungsten wire (2) by replacing the piece or pieces of tungsten wire (2) with the sheet or sheets, substituting the potassium hydroxide for 2M hydrochloric acid as the electrolyte (4) and appropriately adjusting the computer program.

(14) The object or objects to be etched may be made from a material other than tungsten or stainless steel. Any conductive material that can be electrochemically etched and that has a chemical by-product that flows downwards and partially insulates the object from further etching in the manner described above is suitable. Examples of such materials are nickel, copper, and silicon.

(15) It will be appreciated by persons skilled in the art that the above embodiment has been described by way of example only and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims.