Package for an implantable neural stimulation device

Abstract

An implantable device having a biocompatible hermetic package made from a biocompatible electrically non-conductive substrate and a cover bonded to the substrate. In integrated circuit and passive circuits all bonded directly to the substrate.

Claims

1. An implantable device, comprising: a biocompatible electrically non-conductive substrate; a plurality of electrically conductive vias through the electrically non-conductive substrate, forming a via substrate; an integrated circuit attached directly to the via substrate; discrete passive circuits attached directly to the via substrate to the side of the integrated circuit; a biocompatible cover brazed to the via substrate with a biocompatible braze, the cover and the via substrate forming a hermetic package; conductive traces deposited on the via substrate; and a braze stop on the via substrate and along a periphery of the via substrate surrounding the conductive traces and separating a braze joint from the conductive traces.

2. The implantable device according to claim 1, further comprising a flexible circuit connected to the via substrate and including electrodes suitable to stimulate neural tissue.

3. The implantable device according to claim 1, further comprising a polymer body supporting the hermetic package and suitable to be attached to a sclera.

4. The implantable device according to claim 3, further comprising suture tabs on the polymer body suitable for attaching the polymer body to a sclera.

5. The implantable device according to claim 1, wherein the cover has convex in profile.

6. The implantable device according to claim 1, wherein the cover has concave in profile.

7. The implantable device according to claim 1, wherein the integrated circuit is a flip-chip circuit.

8. The implantable device according to claim 1, wherein the cover is brazed to the via substrate.

9. The implantable device according to claim 8, further comprising a braze stop on the via substrate and along a periphery of the via substrate surrounding the conductive traces and separating a braze joint from the conductive traces.

10. The implantable device according to claim 1, wherein the conductive traces are metal traces.

11. The implantable device according to claim 10, wherein the metal traces are chosen to withstand braze temperatures.

12. The implantable device according to claim 11, wherein the metal traces comprise one or more of the metals titanium, tantalum, gold, palladium, platinum or layers or alloys thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a perspective view of the implanted portion of the preferred retinal prosthesis.

(2) FIG. 2 is a side view of the implanted portion of the preferred retinal prosthesis showing the strap fan tail in more detail.

(3) FIG. 3 is a perspective view of a partially built package showing the substrate, chip and the package wall.

(4) FIG. 4 is a perspective view of the hybrid stack placed on top of the chip.

(5) FIG. 5 is a perspective view of the partially built package showing the hybrid stack placed inside.

(6) FIG. 6 is a perspective view of the lid to be welded to the top of the package.

(7) FIG. 7 is a view of the completed package attached to an electrode array.

(8) FIG. 8 is a cross-section of the package.

(9) FIG. 9 is a perspective view of the implanted portion of the preferred retinal prosthesis.

(10) FIG. 10 is a cross-section of the three stack package.

(11) FIG. 11 is a cross-section of the three stack package.

(12) FIG. 12 is a cross-section of the two stack package.

(13) FIG. 13 is a cross-section of the two stack package.

(14) FIG. 14 is a cross-section of the two stack package.

(15) FIG. 15 is a cross-section of the one stack package.

(16) FIG. 16 is a cross-section of the folded stack package.

(17) FIG. 17 is a cross-section of the package.

(18) FIG. 18 is a cross-section of the package.

(19) FIG. 19 is a cross-section of the lid shaping package.

(20) FIG. 20 is a cross-section of the lid shaping package.

(21) FIGS. 21 and 22 are cross-sections the package showing interconnects in detail.

DETAILED DESCRIPTION OF THE INVENTION

(22) The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles of the invention. The scope of the invention should be determined with reference to the claims.

(23) The present invention is an improved hermetic package for implanting electronics within a body. Electronics are commonly implanted in the body for neural stimulation and other purposes. The improved package allows for miniaturization of the package which is particularly useful in a retinal or other visual prosthesis for electrical stimulation of the retina.

(24) FIG. 1 shows a perspective view of the implanted portion of the preferred retinal prosthesis. A flexible circuit includes a flexible circuit electrode array 10 which is mounted by a retinal tack (not shown) or similar means to the epiretinal surface. The flexible circuit electrode array 10 is electrically coupled by a flexible circuit cable 12, which pierces the sclera in the pars plana region, and is electrically coupled to an electronics package 14, external to the sclera. Further an electrode array fan tail 15 is formed of molded silicone and attaches the electrode array cable 12 to a molded body 18 to reduce possible damage from any stresses applied during implantation.

(25) The electronics package 14 is electrically coupled to a secondary inductive coil 16. Preferably the secondary inductive coil 16 is made from wound wire. Alternatively, the secondary inductive coil 16 may be made from a flexible circuit polymer sandwich with wire traces deposited between layers of flexible circuit polymer. The electronics package 14 and secondary inductive coil 16 are held together by the molded body 18. The molded body 18 holds the electronics package 14 and secondary inductive coil 16 end to end. This is beneficial as it reduces the height the entire device rises above the sclera. The design of the electronic package (described below) along with a molded body 18 which holds the secondary inductive coil 16 and electronics package 14 in the end to end orientation minimizes the thickness or height above the sclera of the entire device. This is important to minimize any obstruction of natural eye movement.

(26) The molded body 18 may also include suture tabs 20. The molded body 18 narrows to form a strap 22 which surrounds the sclera and holds the molded body 18, secondary inductive coil 16, and electronics package 14 in place. The molded body 18, suture tabs 20 and strap 22 are preferably an integrated unit made of silicone elastomer. Silicone elastomer can be formed in a pre-curved shape to match the curvature of a typical sclera. However, silicone remains flexible enough to accommodate implantation and to adapt to variations in the curvature of an individual sclera. The secondary inductive coil 16 and molded body 18 are preferably oval shaped. A strap 22 can better support an oval shaped secondary inductive coil 16.

(27) Further it is advantageous to provide a sleeve or coating 50 that promotes healing of the scleratomy. Polymers such as polyimide, which may be used to form the flexible circuit cable 12 and flexible circuit electrode array 10, are generally very smooth and do not promote a good bond between the flexible circuit cable 12 and scleral tissue. A sleeve or coating of polyester, collagen, silicon, GORETEX, or similar material would bond with scleral tissue and promote healing. In particular, a porous material will allow scleral tissue to grow into the pores promoting a good bond.

(28) It should be noted that the entire implant is attached to and supported by the sclera. An eye moves constantly. The eye moves to scan a scene and also has a jitter motion to improve acuity. Even though such motion is useless in the blind, it often continues long after a person has lost their sight. By placing the device under the rectus muscles with the electronics package in an area of fatty tissue between the rectus muscles, eye motion does not cause any flexing which might fatigue, and eventually damage, the device.

(29) FIG. 2 shows side view of the implanted portion of the retinal prosthesis, in particular, emphasizing the strap fan tail 24. When implanting the retinal prosthesis, it is necessary to pass the strap 22 under the eye muscles to surround the sclera. The secondary inductive coil 16 and molded body 18 must also follow the strap 22 under the lateral rectus muscle on the side of the sclera. The implanted portion of the retinal prosthesis is very delicate. It is easy to tear the molded body 18 or break wires in the secondary inductive coil 16 or electrode array cable 12. In order to allow the molded body 18 to slide smoothly under the lateral rectus muscle, the molded body 18 is shaped in the form of a strap fan tail 24 on the end opposite the electronics package 14.

(30) FIG. 3 shows the hermetic electronics package 14 is composed of a ceramic substrate 60 brazed to a metal case wall 62 which is enclosed by a laser welded metal lid 84. The metal of the wall 62 and metal lid 84 may be any biocompatible metal such as Titanium, niobium, platinum, iridium, palladium or combinations of such metals. The ceramic substrate is preferably alumina but may include other ceramics such as zirconia. The ceramic substrate 60 includes vias (not shown) made from biocompatible metal and a ceramic binder using thick-film techniques. The biocompatible metal and ceramic binder is preferably platinum flakes in a ceramic paste or frit which is the ceramic used to make the substrate. After the vias have been filled, the substrate 60 is fired and lapped to thickness. The firing process causes the ceramic to vitrify biding the ceramic of the substrate with the ceramic of the paste forming a hermetic bond. Thin-film metallization 66 is applied to both the inside and outside surfaces of the ceramic substrate 60 and an ASIC (Application Specific Integrated Circuit) integrated circuit chip 64 is bonded to the thin film metallization on the inside of the ceramic substrate 60.

(31) The inside thin film metallization 66 includes a gold layer to allow electrical connection using wire bonding. The inside film metallization includes preferably two to three layers with a preferred gold top layer. The next layer to the ceramic is a titanium or tantalum or mixture or alloy thereof. The next layer is preferably palladium or platinum layer or an alloy thereof. All these metals are biocompatible. The preferred metallization includes a titanium, palladium and gold layer. Gold is a preferred top layer because it is corrosion resistant and can be cold bonded with gold wire.

(32) The outside thin film metallization includes a titanium adhesion layer and a platinum layer for connection to platinum electrode array traces. Platinum can be substituted by palladium or palladium/platinum alloy. If gold-gold wire bonding is desired a gold top layer is applied.

(33) The package wall 62 is brazed to the ceramic substrate 60 in a vacuum furnace using a biocompatible braze material in the braze joint. Preferably, the braze material is a nickel titanium alloy. The braze temperature is approximately 1000 Celsius. Therefore the vias and thin film metallization 66 must be selected to withstand this temperature. Also, the electronics must be installed after brazing. The chip 64 is installed inside the package using thermocompression flip-chip technology. The chip is underfilled with epoxy to avoid connection failures due to thermal mismatch or vibration.

(34) FIGS. 4 and 5 show off-chip electrical components 70, which may include capacitors, diodes, resistors or inductors (passives), are installed on a stack substrate 72 attached to the back of the chip 64, and connections between the stack substrate 72 and ceramic substrate 60 are made using gold wire bonds 82. The stack substrate 72 is attached to the chip 64 with non-conductive epoxy, and the passives 70 are attached to the stack substrate 72 with conductive epoxy.

(35) FIG. 6 shows the electronics package 14 is enclosed by a metal lid 84 that, after a vacuum bake-out to remove volatiles and moisture, is attached using laser welding. A getter (moisture absorbent material) may be added after vacuum bake-out and before laser welding of the metal lid 84. The metal lid 84 further has a metal lip 86 to protect components from the welding process and further insure a good hermetic seal. The entire package is hermetically encased. Hermeticity of the vias, braze, and the entire package is verified throughout the manufacturing process. The cylindrical package was designed to have a low profile to minimize its impact on the eye when implanted.

(36) The implant secondary inductive coil 16, which provides a means of establishing the inductive link between the external video processor (not shown) and the implanted device, preferably consists of gold wire. The wire is insulated with a layer of silicone. The secondary inductive coil 16 is oval shaped. The conductive wires are wound in defined pitches and curvature shape to satisfy both the electrical functional requirements and the surgical constraints. The secondary inductive coil 16, together with the tuning capacitors in the chip 64, forms a parallel resonant tank that is tuned at the carrier frequency to receive both power and data.

(37) FIG. 7 shows the flexible circuit, includes platinum conductors 94 insulated from each other and the external environment by a biocompatible dielectric polymer 96, preferably polyimide. One end of the array contains exposed electrode sites that are placed in close proximity to the retinal surface 10. The other end contains bond pads 92 that permit electrical connection to the electronics package 14. The electronic package 14 is attached to the flexible circuit using a flip-chip bumping process, and epoxy underfilled. In the flip-chip bumping process, bumps containing conductive adhesive placed on bond pads 92 and bumps containing conductive adhesive placed on the electronic package 14 are aligned and melted to build a conductive connection between the bond pads 92 and the electronic package 14. Leads 76 for the secondary inductive coil 16 are attached to gold pads 78 on the ceramic substrate 60 using thermal compression bonding, and are then covered in epoxy. The electrode array cable 12 is laser welded to the assembly junction and underfilled with epoxy. The junction of the secondary inductive coil 16, array 1, and electronic package 14 are encapsulated with a silicone overmold 90 that connects them together mechanically. When assembled, the hermetic electronics package 14 sits about 3 mm away from the end of the secondary inductive coil.

(38) Since the implant device is implanted just under the conjunctiva it is possible to irritate or even erode through the conjunctiva. Eroding through the conjunctiva leaves the body open to infection. We can do several things to lessen the likelihood of conjunctiva irritation or erosion. First, it is important to keep the over all thickness of the implant to a minimum. Even though it is advantageous to mount both the electronics package 14 and the secondary inductive coil 16 on the lateral side of the sclera, the electronics package 14 is mounted higher than, but not covering, the secondary inductive coil 16. In other words the thickness of the secondary inductive coil 16 and electronics package should not be cumulative.

(39) It is also advantageous to place protective material between the implant device and the conjunctiva. This is particularly important at the scleratomy, where the thin film electrode cable 12 penetrates the sclera. The thin film electrode array cable 12 must penetrate the sclera through the pars plana, not the retina. The scleratomy is, therefore, the point where the device comes closest to the conjunctiva. The protective material can be provided as a flap attached to the implant device or a separate piece placed by the surgeon at the time of implantation. Further material over the scleratomy will promote healing and sealing of the scleratomy. Suitable materials include DACRON, TEFLON, GORETEX (ePTFE), TUTOPLAST (sterilized sclera), MERSILENE (polyester) or silicone.

(40) FIG. 8 shows the package 14 containing a ceramic substrate 60, with metallized vias 65 and thin-film metallization 66. The package 14 contains a metal case wall 62 which is connected to the ceramic substrate 60 by braze joint 61. On the ceramic substrate 60 an underfill 69 is applied. On the underfill 69 an integrated circuit chip 64 is positioned. On the integrated circuit chip 64 a ceramic hybrid substrate 68 is positioned. On the ceramic hybrid substrate 68 passives 70 are placed. Wirebonds 67 are leading from the ceramic substrate 60 to the ceramic hybrid substrate 68. A metal lid 84 is connected to the metal case wall 62 by laser welded joint 63 whereby the package 14 is sealed.

(41) FIG. 9 shows a perspective view of the implanted portion of the preferred retinal prosthesis which is an alternative to the retinal prosthesis shown in FIG. 1.

(42) The electronics package 14 is electrically coupled to a secondary inductive coil 16. Preferably the secondary inductive coil 16 is made from wound wire. Alternatively, the secondary inductive coil 16 may be made from a flexible circuit polymer sandwich with wire traces deposited between layers of flexible circuit polymer. The electronics package 14 and secondary inductive coil 16 are held together by the molded body 18. The molded body 18 holds the electronics package 14 and secondary inductive coil 16 end to end. The secondary inductive coil 16 is placed around the electronics package 14 in the molded body 18. The molded body 18 holds the secondary inductive coil 16 and electronics package 14 in the end to end orientation and minimizes the thickness or height above the sclera of the entire device.

(43) Lid 84 and case wall 62 may also contain titanium or titanium alloy or other metals and metal alloys including platinum, palladium, gold, silver, ruthenium, or ruthenium oxide. Lid 84 and case wall 62 may also contain a polymer, copolymer or block copolymer or polymer mixtures or polymer multilayer containing parylene, polyimide, silicone, epoxy, or PEEK polymer. Via substrate may be preferably contain alumina or zirconia with platinum vias.

(44) FIG. 15 shows a one stack assembly. One stack means that all of the parts are on a flip chip circuit 64, with our without a separate demux. A via substrate 60 is placed on the bottom below a flip chip circuit 64 which includes RF Transceiver, power recovery, drivers, and an optional demux. Discrete passives 70 are placed directly on the via substrate 60 to side of the flip-chip circuit 64.

(45) FIG. 12, FIG. 13 and FIG. 14 show two stack assemblies. FIG. 16 shows a folded stack assembly. FIG. 12 shows a ceramic substrate next to RF transceiver/power recovery chip and both placed on a flipchip driver/demux. FIG. 13 shows ceramic substrate on a flipchip driver/demux. RF transceiver/power recovery chip is provided on the ceramic substrate. FIG. 14 shows ceramic substrate on to of a flipchip driver/demux. RF transceiver/power recovery chip is provided not directly on the ceramic substrate. The difference between FIG. 13 and FIG. 14 is that in FIG. 13 the ceramic substrate is in direct contact with RF transceiver/power recovery chip but not in FIG. 14. The substrate can be ceramic but also any kind of polymer or glass. FIG. 16 shows a folded stack substrate and a flipchip demux on the bottom and an IC placed on the flip chip demux. The substrate is folded twice.

(46) FIG. 10 and FIG. 11 show a three stack assembly. A three stack demux flip-chip bonded to substrate with chip and hybrid wire-bonded above is preferred. FIG. 10 shows a ceramic substrate on a IC including a RF transceiver/power recovery drivers and the IC is placed on a flipchip driver/demux. FIG. 11 shows a similar assembly as FIG. 10 however the ceramic substrate is placed on pedestal which is placed between the substrate and the IC.

(47) FIG. 17 and FIG. 18 show additional flip chip configurations. Both figures have a similar assembly. However, in FIG. 17 the IC is bonded to flipchip demux by a bump bond. In FIG. 18 a double sided multilayer ceramic substrate is bonded to the IC by a bump bond.

(48) They can be two stack or folded stack and could be one or two-sided. It may be passive on the substrate next to IC. A pedestal is useful but optional to make room for wire bonds. A through via means that via goes through the IC. A bump bond to IC and then bump bond to IC to passive substrate or demux is possible. Bond pads on IC to line up with vias to eliminate the inside metallization can be provided. Driver IC flipchip can be bonded to substrate with passives. Demux flip-chip can be bonded to via substrate and the two substrates can be wire-bonded or flex circuit bonded together. Driver portion can be moved to demux chip and everything else to a separate chip to reduce interconnect lines. Two stack chip can be provided with smaller chip (RF and demux) and hybrid above. It may include wire-bonds directly from the Hybrid to the chip. Chip may include a demux driver on the same wafer.

(49) FIG. 19 and FIG. 20 show different variations of the lid shape. Possible is a concave lid to conform to eye.

(50) FIG. 21 and FIG. 22 are cross-sections the package showing redistribution routing and interconnect traces 66 in detail. Both figures show redistribution routings and interconnect traces 66 on the top and the bottom of via substrate 60. Redistribution routing on top of the via substrate and the braze stop on top of the via substrate contain preferably metals like Ti, Zr, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, mixtures, layers or alloys thereof. The top layer of the top redistribution routing is gold or gold alloy. Redistribution routing on bottom of the via substrate and the braze stop on top of the via substrate contain preferably metals like Ti, Zr, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, mixtures, layers or alloys thereof. The top layer of the top redistribution routing is platinum or platinum alloy. Interconnect and redistribution routing is the connection the bond between flexible circuit and via substrate on the bottom of the substrate and a connection between the flip chip circuit 64 and the substrate on top of the substrate. Additional braze stop traces 102 surround the redistribution and interconnect traces 66 to prevent the braze metal 104 from running into the redistribution and interconnect traces 66. The walls in FIG. 22 show the same braze metal 104 as mentioned before as a flange.

(51) Accordingly, what has been shown is an improved method making a hermetic package for implantation in a body. While the invention has been described by means of specific embodiments and applications thereof, it is understood that numerous modifications and variations could be made thereto by those skilled in the art without departing from the spirit and scope of the invention. It is therefore to be understood that within the scope of the claims, the invention may be practiced otherwise than as specifically described herein.