Fabrication Methods

Fabricating the Electrode Array Dime Mold

A sheet of Teflon, with a thickness of 1.6 mm, was placed inside the Universal Laser System Inc’s M-300 Laser Platform at the upper left-hand corner.  The placement of the Teflon was determined by the cutting track of the laser.  The accompanied software, “Engrave Lab”, was utilized to create a simple tracing plan for the laser to simulate.  The diameter of the computer drawn circle was set at 12.6 mm. 

            Before the software initiated the laser, a few other settings had to be adjusted with the machinery.  The “Power Setting” of the 30-watt laser was set to 75% power, while the “Cutting Speed” was optioned at 0.9%.  “Pulses per Inch” (PPI) was positioned at 500.  Once specifications were input, the software began cutting the dime mold.

The newly cut dime mold was then placed on the Jet Turret Milling Machine, model JTM-2.  The milling machine was used to create the necessary divots to hold the electrode balls.  The measurement of the drill bit used was 0.20 mm.  Since this bit was too small for the milling machine housing, a smaller chuck was purchased in order for the drill bit to reach an adequate size for usage within the milling machine.  The little drill chuck measured as 33.3 mm in size.  The speed at which the drill bit was spun was 2,720 RPMs.  Spacing between the outer diameters of 5 divots was around, but not over, 0.400mm.  The divots were also aligned as linear as possible.

         Upon completion of the divots, the dime mold was placed in the K&S 982 Dicing Saw.  The particular blade used within the saw had particular dimensions to achieve a linear groove of 300 µm.  Diameter of the blade was 0.0556 mm while the width was 0.2286 mm.  The Diamond Grit measured as 0.046 mm and the Binder number read R7-3.  The hub that holds the blade within the machine is equally as important.  Diameter of the hub measured as 49.5 mm. Upon blade – hub assembly, the combine parts were fixed within the dicing saw.  Using the dicing saw viewfinder, the blade was aligned with the 5 divots.  A cutting program must be input before the dicing saw can operate.  The cut depth was set to 0.26 mm while the cutting speed was 4.15 mm/sec.  This particular program created a single straight cut through the center of all five divots.  Once complete, the dime mold was rotated 90 degrees in order to cut the cross channels.  There was one cross channel per divot, plus a few extra.  The blade used for the cross channels were almost identical.  The only difference was a change of width, which became 0.1016 mm.  The cut depth and speed are also identical to the previous program.  After the five divot cross channels were complete, addition cross channels were added.  These channels were 0.400 mm in width to aid in the restraint of the wires beyond the electrode tips.

Fabricating the Electrode Array Docking Platform

         The ideal docking platform was made from 6061-T6 aluminum.  The dimensions for the platform were 115 mm by 115 mm by 19 mm.  The groove created to hold the mold was cut with the Jet Turret Milling Machine, model JTM-2.  A square-end endmill, measuring at 12.7 mm, was inserted into the machine.  The speed at which the endmill was run was 2,000 RPM.  The cut was first made at 62.5 mm from the end of the aluminum block, while the cut-depth at which the machine is set was 0.4 mm.  Once all the distances were set, a 26 mm channel was linearly cut into the aluminum.  The dime mold can be properly fixed to the docking platform via a small piece of double-sided tape.

Docking Platform for the mold

          Fabricating the Implantable Electrode Array.

            Before starting, the Teflon mold was thoroughly cleaned with water and a compressed air gun. Any debris or uncured silicone in the channel from previous use was removed.  The mold was placed in the docking platform, which was then setup under the microscope. The microscope was adjusted so the divots for the electrode ball tip were clearly visible. This took some time due to the small dimensions of the mold.  The docking platform was anchored to microscope.  This was accomplished by double-sided tape.  10 dummy wires (diameter <0.150 mm) were cut approximately 7 inches in length.  These dummy wires were used to aid in the restraint of the electrode wire beyond the electrode tips.  The wires were taped on the left side of the docking platform.  Five wires (90% platinum and 10% iridium) with ball tips of 0.2 mm diameter and an overall length of approximately 76 mm were created.  One by one, these wires were placed in the mold using tweezers.

            The wires were placed in the mold, starting from the last divot and proceeding up the mold sequentially.  The ball tips were placed in the divots and oriented with the wires leading from the mold distally. Pressure was applied with a pair of tweezers to make sure the ball tips remain in place. The dummy wire was placed in the side channels to anchor the electrode in place, although this step is not necessary if the electrode has the exact diameter of 0.200 mm. The loose ends of the dummy wires were taped to the right side of the docking platform.  Before silicone was added, a piece of double sided tape approximately 1 inch long was required.  Silicone was slowly added on top of the channel. Considering the channel’s small size, only enough silicone was added so that the electrode channel was completely filled.  Double sided tape was then attached on the top end of the mold beyond the first ball tip. Pressure was applied, by thumb, in the distal direction.  This made sure the excess silicone was pushed out through the main and side channels.  The other side of the tape was then removed, generating visibility of the wires.  If any wires pushed out of the main channel, tweezers were used to push them back into the channel.  Dummy wires could then be safely removed from the side channels.  The silicone was allowed to cure for approximately 20 to 30 minutes, allowing for proper solidification.

            After silicone cured, the tape was slowly removed.  As the surface chemistry of Teflon prevented silicone from curing in the mold, the tape adhesive removed the cured silicone along with the 5 wires.  Now the tape was placed on the docking platform under the microscope.  A sharp blade was used to carefully cut the extra silicone spurs around the electrode.  After cutting all the extra silicone, the five channel electrode array could now be prepped for implantation.