Micro-fabricated group electroplating technique

Abstract

Methods, and devices produced by the methods, for electroplating a multitude of micro-scale electrodes that are electrically isolated from each other on a cable or other device is described. A localized area of connections on another end of the cable is shorted together by depositing a metal sheet or other conductive material over the localized area. The metal sheet is connected to a terminal of a power supply, and the electrode end of the cable is immersed in an electrolyte solution for electrodeposition by electroplating. After the electrodes are electroplated, the metal sheet is removed from the cable in order to re-isolate the electrodes.

Claims

1. A method of electroplating electrodes on a cable, the method comprising: providing a cable having a first end with a plurality of recessed conductive pads arranged in recesses of a surface mount array, each recessed conductive pad arranged in one of the recesses of the surface mount array and individually connected by an electrical conductor through the cable to a respective recessed electrode at a second end of the cable, the recesses of the surface mount array being below a top surface of the surface mount array; depositing, using at least one of thermal evaporation, sputtering deposition, or chemical vapor deposition, a continuous sheet of conductive material over the top surface of the surface mount array and into the recesses of the surface mount array such that the recessed conductive pads are electrically shorted with one another, the continuous sheet of conductive material having a tab portion that is over the top surface of the surface mount array; immersing the recessed electrodes at the second end of the cable in an electrolyte solution; connecting a power supply to the tab portion of the conductive material at the first end, thereby contemporaneously connecting the power supply to the recessed electrodes at the second end; electroplating the recessed electrodes at the second end with a metal such that the metal covers the electrodes and fills recesses corresponding to the recessed electrodes to a top surface of a surrounding insulator using the power supply and the electrolyte solution; and removing the continuous sheet of conductive material by chemically etching the tab portion from the surface mount array to electrically isolate the recessed conductive pads from one another.

2. The method of claim 1 wherein the recessed conductive pads in the surface mount array are each less than 100 m in width and less than 100 m from one another.

3. The method of claim 1 wherein the metal includes platinum black.

4. The method of claim 1 further comprising: depositing the continuous sheet of conductive material over the first end of the cable such that the continuous sheet of conductive material is larger than the surface mount array; applying photoresist to the first end of the cable; exposing a photomask to the first end of the cable; and removing excess conductive material to leave the continuous sheet of conductive material over the surface mount array.

5. The method of claim 1 wherein the continuous sheet comprises a material selected from the group consisting of aluminum, gold, platinum, silver, and titanium.

6. The method of claim 1 wherein the metal is selected from the group consisting of pure platinum, gold, and iridium.

7. The method of claim 1 wherein the surface mount array is square or rectangular.

8. The method of claim 1 wherein the surface mount array is circular.

9. The method of claim 1 further comprising: mounting an integrated circuit (IC) chip or IC socket to the surface mount array of the cable.

10. The method of claim 9 wherein the IC chip comprises a plurality of metal pads in a two-dimensional array on a bottom of the IC chip, each metal pad of the IC chip connected to the surface mount array of the cable by conductive epoxy.

11. A method of electroplating electrodes on a cable, the method comprising: providing a cable having a first end with a plurality of recessed conductive pads suitable for connecting with one or more electrical components, each recessed conductive pad arranged in one of recesses of a localized tap area and individually connected by an electrical conductor to a respective lead in the localized tap area and through the cable to a respective recessed electrode at a second end of the cable, wherein at least one of the plurality of recessed conductive pads is arranged in a recess of the localized tap area; depositing, using at least one of thermal evaporation, sputtering deposition, or chemical vapor deposition, a continuous sheet of conductive material over the top surface of the localized tap area and into the recessed conductive pads and the recess such that the leads are electrically shorted with one another, the continuous sheet of conductive material having a tab portion that is over the top surface of the localized tap area; immersing the recessed electrodes at the second end of the cable in an electrolyte solution; connecting a power supply to the tab portion of the conductive material, thereby contemporaneously connecting the power supply to the recessed electrodes at the second end; electroplating the recessed electrodes at the second end with a metal such that the metal covers the electrodes and fills recesses corresponding to the recessed electrodes to a top surface of a surrounding insulator using the power supply and the electrolyte solution; and removing the continuous sheet of conductive material by chemically etching the tab portion from the localized tap area to electrically isolate the leads from one another.

12. The method of claim 11 further comprising: depositing the continuous sheet of conductive material over the localized tap area such that the continuous sheet of conductive material is larger than the localized tap area; applying photoresist to the first end of the cable; exposing a photomask to the first end of the cable; and removing excess conductive material to leave the continuous sheet of conductive material over the localized tap area.

13. The method of claim 11 further comprising: mounting an integrated circuit (IC) chip or IC socket to the localized tap area of the cable.

14. The method of claim 13 wherein the IC chip comprises a plurality of metal pads in a two-dimensional array on a bottom of the IC chip, each metal pad of the IC chip connected to the localized tap area of the cable by conductive epoxy.

15. The method of claim 1 wherein the continuous sheet is a rounded corner rectangle.

16. The method of claim 11 wherein the continuous sheet is a rounded corner rectangle.

17. The method of claim 1 wherein the connecting is performed using a single connection clip.

18. The method of claim 11 wherein the connecting is performed using a single connection clip.

19. The method of claim 1 wherein the tab portion ends at an outer edge of the top surface.

20. The method of claim 11 wherein the tab portion ends at an outer edge of the top surface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a perspective illustration of a ribbon cable in accordance with an embodiment.

(2) FIG. 2 is an illustration of a ribbon cable with electrodes surgically mated to an eyeball in accordance with an embodiment.

(3) FIG. 3 illustrates a wearable transmitter assembly in accordance with an embodiment.

(4) FIG. 4A illustrates deposition of metal traces and electrodes on a ribbon cable in accordance with an embodiment.

(5) FIG. 4B illustrates embedding the traces and leaving the electrodes open in accordance with an embodiment.

(6) FIG. 4C illustrates depositing a continuous sheet of conductive material in accordance with an embodiment.

(7) FIG. 4D illustrates the result of electroplating in accordance with an embodiment.

(8) FIG. 4E illustrates removing the conductive sheet in accordance with an embodiment.

(9) FIG. 5A illustrates depositing parylene in accordance with an embodiment.

(10) FIG. 5B illustrates depositing metal over the parylene of FIG. 5A.

(11) FIG. 5C illustrates depositing parylene over the metal of FIG. 5B.

(12) FIG. 5D illustrates applying photoresist as a mask over the workpiece of FIG. 5C to open electrodes in accordance with an embodiment.

(13) FIG. 5E illustrates opening the electrodes of FIG. 5D.

(14) FIG. 5F illustrates the result of removing photoresist of FIG. 5E.

(15) FIG. 5G illustrates depositing aluminum over the workpiece of FIG. 5F.

(16) FIG. 5H illustrates applying photoresist as a mask to pattern the aluminum of FIG. 5G.

(17) FIG. 5I illustrates the results of patterning the aluminum of FIG. 5H.

(18) FIG. 5J illustrates removing all but a tab of aluminum from the workpiece of FIG. 5I.

(19) FIG. 5K illustrates the result of removing photoresist from the workpiece of FIG. 5K.

(20) FIG. 5L illustrates applying voltage to the tab of aluminum to electroplate the workpiece of FIG. 5L.

(21) FIG. 5M illustrates the result of removing the tab from the workpiece of FIG. 5L.

(22) FIG. 6 diagrams an electroplating system in accordance with an embodiment.

(23) FIG. 7 illustrates a laboratory electroplating system in accordance with an embodiment.

(24) FIG. 8 illustrates a close-up view of a dual metal layer electrode array in accordance with an embodiment.

(25) FIG. 9A is an image of electrodes before plating.

(26) FIG. 9B is an image of electrodes after plating in accordance with an embodiment.

(27) FIG. 10 is a flowchart of a process in accordance with an embodiment.

(28) FIG. 11 is a flowchart of a process in accordance with an embodiment.

(29) Reference to the remaining portions of the specification, including the drawings and claims, will realize other features and advantages of the present invention. Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with respect to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements.

DETAILED DESCRIPTION

(30) Aspects are generally described regarding group electroplating technique with platinum black (Pt-black) or other plating substances to modify the surface of a multi-electrode array, which can be used on next-generation 1024-pixel retinal implants. This method is not only time efficient but also process friendly.

(31) A large number of isolated electrodes on one end of a cable can be electroplated by adhering, sputtering, thermally evaporating onto, or otherwise depositing a sheet of metal over another end of a cable where an IC or other components will sit to connect with the electrodes. The metal sheet is used as a common contact point for an electroplating power supply. Meanwhile, the other end of the cable with the electrodes is submerged in an electrolyte as a cathode (or anode). The metal or other conductive substance to be plated is submerged in the electrolyte as an anode (or cathode). After the electrodes are electroplated, the metal sheet is peeled, dissolved, or otherwise removed from the contacts where the IC will sit, and the IC (or other components) are then connected.

(32) Technical advantages of aspects of the invention are that a large number of electrically isolated electrodes can be quickly and efficiently plated all at once without having to manually make an electrical connection to each electrode. The resulting electroplating can increase surface roughness of each electrode, increasing surface area in contact with tissue in biological subjects, decrease impedance, and increase capacitance. The electroplating can make the electrodes last longer as well in the corrosive body fluids of a mammal, such as a human being.

(33) FIG. 1 is a perspective illustration of a nearly-finished ribbon cable in accordance with an embodiment. System 100 includes ribbon cable 102, which has a portion 104 on which IC chip 126 is connected. Capacitors 124, power coil 120, and data coil 122 are connected to IC chip 126 by electrical traces 132 embedded in ribbon cable 102.

(34) Electrical conductor traces 132 travel from ribbon cable portion 104 through central portion 106 and on to ribbon cable portion 116. Ribbon cable 102 has portion 116 into which electrode array 128 is integrally formed.

(35) Integrally formed parts include those that are deposited, etched, cured, or formed at the same time as one another such that the result is that they are connected by a common material with one another, or as otherwise known in the art.

(36) A longitudinal direction on a ribbon cable is a direction of longest measurements of the cable, or as otherwise known in the art. For example, a longitudinal direction in the figure is one running between the coil end and electrode end of the ribbon cable.

(37) A lateral direction on a ribbon cable is a direction perpendicular to the longitudinal direction and within the plane of the ribbon cable, or as otherwise known in the art. For example, a lateral direction in the figure is one running from a far side of the cable (in the page) to a near side.

(38) A height of a ribbon cable includes a direction of smallest dimensions, or as otherwise known in the art. For example, a height of the ribbon cable in the figure is one running vertically in the plane of the page.

(39) A ribbon cable includes any cable having a flattened portion with conductors running side by side in the flattened portion, or as otherwise known in the art. A ribbon cable may be micro-fabricated or constructed using classical methods.

(40) Before ribbon cable 102 has IC 126 attached, its electrodes will be electroplated in accordance with an embodiment. Afterwards, the cable can be used in surgical implants.

(41) FIG. 2 is an illustration of a ribbon cable with electrodes surgically mated to an eyeball in accordance with an embodiment. Parylene ribbon cable 202 penetrates through the eye wall, allowing electrode array 228 to stimulate the eyeball's retina, specifically stimulating retinal ganglion cells within the eyeball. Application-specific integrated circuit (ASIC) 226 and receiver coil 220 are sutured between the conjunctiva and eyelid.

(42) FIG. 3 illustrates a wearable transmitter assembly in accordance with an embodiment.

(43) External unit 300 includes transmitter coil 306 housed in transmitter assembly 308. Transmitter assembly 308 is positioned to the side of a user's eye by glasses 312. Other positioning means besides glasses are envisioned.

(44) Glasses 312 hold miniature camera 310 and video processor 304, which are connected by cable 302 to adaptor 318. Cable 314 connects another port of adaptor 318 to battery pack 316, which can be worn on a belt.

(45) FIGS. 4A-4E illustrate a process flow for a group electroplating technique in accordance with an embodiment.

(46) In FIG. 4A, a metal layer of titanium and/or gold are deposited on top of parylene to make workpiece 400. On the left side of workpiece 400 is a localized tap area 442 of conductive pads 440 that are suitable for connecting with one or more electrical components, such as IC chips, capacitors, resistors, inductors, transistors, and other components. They are connected by conductive metal to electrical leads 432, which run from first end 446 to opposing end 448 of the cable workpiece. Each electrical lead 432 is connected to a single electrode 444.

(47) Biocompatible materials include those that have been determined by a government agency to avoid corrosion by bodily fluids for extended periods as well as be nontoxic. Titanium, gold, parylene, and polyimide are among the many biocompatible materials available for use in humans. For example, parylene has demonstrated bio-compatibility as a United States Pharmacopeial Convention (USP) Class VI biocompatible polymer.

(48) Conductive pads 440 may be metal terminals, solder pads, connecting pads, or other conductive structures suitable for attaching electrical components. For IC chip components, the conductive pads may be configured to mate with a ball grid array (BGA), pin grid array (PGA), quad flat package (QFP) IC chips. Preferably, a conductive epoxy squeegee technique, combined with photo-patternable adhesives, achieves a high connection yield for high lean count IC chips with appropriate terminals.

(49) A suitable conductive epoxy squeegee technique is described in Jay H. C. Chang, Ray Huang, and Y. C. Tai, High density 256-channel chip integration with flexible parylene pocket, Proceeding of 16th International Conference on Solid-State Sensors, Actuators, and Microsystems (Transducers 2011), Beijing, China, 2011, pp. 378-381, which is hereby incorporated by reference.

(50) In FIG. 4B, parylene is deposited on top of the metal layer sufficient to embed the electrical leads for most of the cable but keep portions of conductive pads 440 and electrodes 444 clear.

(51) In FIG. 4C, aluminum coating 450 is applied by thermal evaporation to conductive pads 440 in localized tap area 442 such that leads 432 (FIG. 4A) and electrodes 444 are electrically shorted together through conductive aluminum coating 450.

(52) In FIG. 4D, platinum black is electroplated over exposed electrodes 444 at end 448 using a power supply connected with conductive metal sheet 450.

(53) In FIG. 4E, conductive aluminum tab 450 has been removed from end 446 to expose conductive pads 440.

(54) FIGS. 5A-5M illustrate micro-fabrication steps to create a ribbon cable with electroplated electrodes.

(55) FIG. 5A shows a bottom layer of parylene polymer being deposited on a flat surface of silicone to create the beginning of workpiece 550.

(56) FIG. 5B shows a metal layer 552 of traces, conductive pads, electrodes, and other features deposited onto the parylene. This may occur in several steps of depositing metal, photomasking and exposing, and etching.

(57) FIG. 5C shows parylene layer 554 deposited over metal layer 552 to encapsulate and embed metal layer 552.

(58) FIG. 5D shows photoresist layer 556 patterned on top of workpiece 550. The pattern for photoresist layer 556 includes open areas to the metal layer for conductive pads and electrodes.

(59) FIG. 5E shows the results of dissolving or etching away parylene in the unprotected areas of parylene not covered by developed photoresist. The parylene in the uncovered areas is removed all of the way down to metal layer 552 to create openings 558 to the metal conductive pads and electrodes of workpiece 550.

(60) FIG. 5F shows the results of removing the photoresist layer from the previous operation.

(61) FIG. 5G shows the deposition of aluminum layer 560 by thermal evaporation over workpiece 550. This layer will become the conductive tab that shorts all of the conductive tabs together. Other metals, such as titanium, can also be used. Preferably, the electrically conductive material for the tab should be able to be cleanly removed later by etching, peeling, or other methods without destroying the conductive pads or insulative parylene below.

(62) FIG. 5H shows photoresist layer 562 being applied over aluminum layer 560.

(63) FIG. 5I shows photoresist layer 562 being masked, exposed, and washed to reveal portions of aluminum layer 560 that will be removed.

(64) FIG. 5J shows the remaining tab portion of aluminum layer 560 under photoresist layer 562, minus the portion of aluminum layer 560 that covered other portions of the cable. The remaining portion 560 shorts all of the conductive pads (and electrodes) together as a conductive tab.

(65) In some embodiments, a conductive tape is adhered to the end of the cable with the conductive pads that shorts together the conductive pads. Using conductive tape can avoid the metal deposition, masking, etc. operations shown in FIGS. 5G-5I. However, conductive tape may not bond properly to each and every conductive pad, which can be 100 m in width and 100 m from one another and slightly recessed from the cable surface.

(66) FIG. 5K shows workpiece 550 and aluminum layer 560 after the photoresist layer is removed.

(67) FIG. 5L shows workpiece 550 being electroplated using a single connection clip 564 to aluminum tab 560 for an electroplating voltage source. With the opposing end of the cablewith the electrodesimmersed in an electrolyte solution, the electrodes are all plated with plating material 566.

(68) FIG. 5M shows workpiece 550 with the voltage source and aluminum tab removed, leaving ribbon cable 550 with electrodes each plated with plating material 566. The aluminum tab can be dissolved away by etching solution.

(69) If a conductive tape is used for the tab, it can be peeled way. Aluminum, gold, platinum, silver, titanium, and other metals and non-metals may be suitable conductive materials for temporarily shorting the conductive pads together.

(70) The array of conductive pads can be in a regularly spaced array or be randomly or non-regularly spaced. The array can be square, rectangular, circular, or other shapes. The array can be planar, or it can vary in height.

(71) FIG. 6 diagrams an electroplating system in accordance with an embodiment. In system 600, voltage source pulse generator 674 is connected in series with 1 M resistor 672 to give a relatively stable current during plating. Oscilloscope 670 monitors the voltage across the resistor, from which the plating current can be derived.

(72) Vessel 676 holds electrolyte solution 678 into which platinum counter electrode 680 and the electrode end 682 of a ribbon cable are immersed on opposite ends. The positive terminal of power supply 674 is connected to counter electrode 680. The negative terminal of power supply 674 is connected in one location at conductive sheet 682, which is electrically connected to each and every electrode 644 through the ribbon cable. A 5 volt potential is applied in the exemplary embodiment.

(73) FIG. 7 illustrates an electroplating system in accordance with an embodiment. In the laboratory setup, an alligator clip is for the negative voltage is connected with conductive tab 682 of a ribbon cable, which connects the negative voltage to electrodes 644. Electrodes 644 are immersed in electrolyte solution 678. Also immersed in electrolyte solution 678 is platinum counter electrode 680, which is attached by an alligator clip to the positive voltage of the power supply.

(74) Samples with 16-electrode arrays are shown, each array with electrode sizes of 66 m66 m. A custom holder is designed for samples to be electroplated on a silicon wafer, which is mechanically reliable.

(75) FIG. 8 illustrates a close-up view of a dual metal layer electrode array in accordance with an embodiment. A dual metal layer electrode array can pack more lines for electrodes in a smaller amount of area than a single metal layer. In electrode array 828, conductive pad 840 is connected through a via to bottom layer traces 844, which run underneath top layer traces 846. Conductive pad 842 is connected to top layer trace 846. Each of the electrodes can be plated in accordance with the methods described.

(76) FIG. 9A is an image of electrodes before plating. The dark regions around each square electrode are an artifact of the micrograph; the dark regions around each square are simply parylene that is slanted down in a bezel to meet the square metal electrode.

(77) FIG. 9B is an image of electrodes after plating in accordance with an embodiment. In this micrograph, the electrodes have been plated with platinum black, which appears completely black in the image.

(78) FIG. 10 is a flowchart of process 1000 in accordance with an embodiment. In operation 1001, a cable is provided having a first end with a plurality of conductive pads arranged in a surface mount array, each conductive pad individually connected by an electrical conductor through the cable to a respective electrode at a second end of the cable. In operation 1002, a continuous sheet of conductive material is deposited over the surface mount array such that the conductive pads are electrically shorted with one another. In operation 1003, the electrodes at the second end of the cable are immersed in an electrolyte solution. In operation 1004, a power supply is connected to the sheet of conductive material at the first end, thereby contemporaneously connecting the power supply to the electrodes at the second end of the ribbon cable. In operation 1005, the electrodes are electroplated using the power supply and the electrolyte solution. In operation 1006, the continuous sheet of conductive material is removed from the surface mount array to electrically isolate the conductive pads from one another.

(79) FIG. 11 is a flowchart of process 1100 in accordance with an embodiment. In operation 1101, a cable having a first end with a plurality of conductive pads suitable for connecting with one or more electrical components, each conductive pad individually connected by an electrical conductor to a respective lead in a localized tap area and through the cable to a respective electrode at a second end of the cable. In operation 1102, a continuous sheet of conductive material is deposited over the localized tap area such that the leads are electrically shorted with one another. In operation 1103, the electrodes are immersed at the second end of the cable in an electrolyte solution. In operation 1104, a power supply is connected to the sheet of conductive material, thereby contemporaneously connecting the power supply to the electrodes at the second end. In operation 1105, the electrodes are electroplated using the power supply and the electrolyte solution. In operation 1106, the continuous sheet of conductive material is removed from the localized tap area to electrically isolate the leads from one another.

(80) The invention has been described with reference to various specific and illustrative embodiments. However, it should be understood that many variations and modifications may be made while remaining within the spirit and scope of the following claims.