Patent Application
20120290021
The present disclosure relates to a battery feedthrough, and in particular for a coating material for a battery feedthrough for an implantable medical device.
Implantable medical devices typically rely on battery power to perform their therapeutic or diagnostic tasks. A battery supplies power to electrical components within the implantable medical device. A battery used with implantable medical devices may typically comprise chemical materials that provide for one or more electrochemical cells that produce electricity. These chemicals are often corrosive to the other materials within the implantable medical device. Therefore, the battery is typically configured with a battery feedthrough to permit a conductor to carry electrical current from the one or more electrochemical cells while keeping the corrosive materials contained within the battery.
In general, the present disclosure is directed to a coating that is formed on an interior portion of a battery feedthrough. The coating may help prevent the formation of potential electrical shorts at the feedthrough, such as shorts that may occur due to “lithium ball” formation, and also may prevent or reduce low leakage current between the conductor pin being passed through the feedthrough and a ferrule of the feedthrough. The coating material of the present disclosure is formed by forming a preform out of the coating material, placing the preform around the conductor pin, and melting the preform so that the coating material substantially covers a portion of the conductor pin, a portion of the ferrule, and a portion of an insulation sleeve that is disposed between the pin and the ferrule. In one example, the preform is made by extruding the coating material to form a small tubular preform.
In one example, the present disclosure is directed to a battery feedthrough comprising a ferrule having a first side, a second side, and a passage extending from the first side to the second side, a pin for conducting electricity between the first side of the ferrule and the second side of the ferrule, the pin extending through the passage, an insulation sleeve disposed between the pin and the ferrule within the passage, wherein the insulation sleeve electrically isolates the pin from the ferrule, there being a first junction between the pin and the insulation sleeve and a second junction between the insulation sleeve and the ferrule, and a coating comprising a polymer disposed over the pin on the first side of the ferrule, wherein the coating is formed by forming a preform comprising the polymer, placing the preform around at least a first portion of the pin on the first side of the ferrule, and melting the preform so that the polymer substantially covers a second portion of the pin, the first junction, a portion of the insulation sleeve, the second junction, and a portion of the ferrule on the first side of the ferrule.
In another example, the present disclosure is directed to an implantable medical device comprising a device housing, electronics located within the device housing, the electronics being configured to provide for a medical therapy, a battery located within the device housing, the battery comprising a battery housing enclosing an electrochemical battery cell, and a feedthrough comprising a ferrule mounted in an opening in the battery housing, the ferrule having an interior side disposed within the battery housing, an exterior side disposed outside the battery housing, and a passage extending between the interior side and the exterior side, a pin for conducting electrical current between the electrochemical battery cell and the electronics, the pin extending through the passage, an insulation sleeve disposed between the pin and the ferrule within the passage, wherein the insulation sleeve electrically isolates the pin from the ferrule, there being a first junction between the pin and the insulation sleeve and a second junction between the insulation sleeve and the ferrule, and a coating comprising a polymer disposed over the pin on the interior side of the ferrule, wherein the coating is formed by forming a preform from the polymer, placing the preform around at least a first portion of the pin on the first side of the ferrule, and melting the preform so that the polymer flows to cover a second portion of the pin, the first junction, a portion of the insulation sleeve, the second junction, and a portion of the ferrule on the interior side of the ferrule.
In another example, the present invention is directed to a method comprising forming a preform comprising a polymer, placing the preform around at least a first portion of a pin extending through a passage of a ferrule, wherein an insulation sleeve is disposed in the passage between the pin and the ferrule, there being a first junction between the pin and the insulation sleeve and a second junction between the insulation sleeve and the ferrule, and melting the preform so that the polymer flows to substantially cover a second portion of the pin, the first junction, a portion of the insulation sleeve, the second junction, and a portion of the ferrule.
This summary is intended to provide an overview of the subject matter described in this disclosure. It is not intended to provide an exclusive or exhaustive explanation of the techniques as described in detail within the accompanying drawings and description below. The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.
In general, the present disclosure is directed to techniques for coating portions of a battery feedthrough usable with a medical device, such as an implantable medical device (IMD), such that the potential for internal short circuits between a conductor passing through the feedthrough and the feedthrough ferrule is reduced and so that low leakage current between the pin and feedthrough is reduced. The coating is formed by forming a preform from a polymer used to make the coating, placing the preform around the conductor pin, and melting the preform so that the polymer flows to substantially cover a portion of the pin, a portion of the ferrule, and a portion of an insulation sleeve disposed between the pin and the ferrule. In some examples, the preform is made by extruding the polymer to form a generally tubular-shaped preform that the pin is inserted through. The method of forming a preform, placing the preform around the pin, and melting the preform provides for precise control over the placement of the final coating and provides for more efficient manufacture of the battery feedthrough.
IMD 16 may include a fixation assembly, such as a set of active fixation tines, to secure IMD 16 to a patient tissue (described below with respect to
Depending on the location of implant, IMD 16 may include other stimulation functionalities. For example, IMD 16 may provide atrioventricular nodal stimulation, fat pad stimulation, vagal stimulation, or other types of neurostimulation. In other examples, IMD 16 may be a monitor that senses one or more parameters of heart 14 and may not provide any stimulation functionality. In some examples, system 16 may include a plurality of leadless IMDs 16, e.g., to provide stimulation and/or sensing at a variety of locations.
A user interacts with programmer 18 to communicate with IMD 16. For example, the user may interact with programmer 18 to retrieve physiological or diagnostic information from IMD 16. A user may also interact with programmer 18 to program IMD 16, e.g., select values for operational parameters of the IMD 16. For example, the user may use programmer 18 to retrieve information from IMD 16 regarding the rhythm of heart 14, trends therein over time, or arrhythmic episodes.
As an example, the user may use programmer 18 to retrieve information from IMD 16 regarding other sensed physiological parameters of patient 12 or information derived from sensed physiological parameters, such as intracardiac or intravascular pressure, intracardiac or intravascular fluid flow, activity, posture, tissue oxygen levels, respiration, tissue perfusion, heart sounds, cardiac electrogram (EGM), intracardiac impedance, or thoracic impedance. In some examples, the user may use programmer 18 to retrieve information from IMD 16 regarding the performance or integrity of IMD 16 or other components of system 16, or a power source of IMD 16. As another example, the user may interact with programmer 18 to program, e.g., select parameters for, therapies provided by IMD 16, such as pacing and, optionally, neurostimulation.
IMD 16 and programmer 18 may communicate via wireless communication link 28 using any techniques known in the art. Examples of communication techniques may include, for example, low frequency or radiofrequency (RF) telemetry, but other techniques are also contemplated. In some examples, programmer 18 may include a programming head that may be placed proximate to the patient's body near the IMD 16 implant site in order to improve the quality or security of communication between IMD 16 and programmer 18.
As shown in
Pressure sensor 32 may be implanted within pulmonary artery 34, for example, using a delivery catheter. For example, a physician may deliver pressure sensor(s) 32 transvenously via a delivery catheter through either the internal jugular or femoral veins. The delivery catheter then extends through superior vena cava 48, right atrioventricular valve 42, right ventricle 20, and pulmonary valve 44 into pulmonary artery 34. In other examples, pressure sensor 32 may be implanted after a physician has opened the patient's chest by cutting through the sternum.
Pressure sensor 32 generates pressure information representing a pressure signal as a function of the fluid pressure in pulmonary artery 34, for example. Pressure sensor 32 may transmit the signal to another device, such as IMD 16, programmer 18, and/or another device, such as external monitoring equipment, which may receive, monitor, and analyze the pressure signal in order to determine a cardiac cycle length and/or other pressure metrics. In other examples, pressure sensor 32 may itself analyze the pressure information in order to determine a cardiac cycle length and/or other pressure metrics according to the techniques described herein. Further description of the collection and analysis of pressure data by pressure sensor 32 is described in U.S. Provisional Patent Application No. 61/368,437, titled “MEASUREMENT OF CARDIAC CYCLE LENGTH AND PRESSURE METRICS FROM PULMONARY ARTERIAL PRESSURE,” and filed Jul. 28, 2010, the entire contents of which are incorporated by reference as if reproduced herein.
IMD 16 may also comprise a device housing 60 that encloses control electronics 56 and battery 58. Device housing 60 is formed from a biocompatible material, such as a stainless steel or titanium alloy. In some examples, the housings of control electronics 56 and battery 58 may include a parylene coating. IMD 16 may also include a delivery tool interface 62 that is configured to connect to a delivery device, such as a catheter, to deliver and position IMD 16 during implantation. In one example, shown in
In one example, active fixation tines 54 are deployable from a spring-loaded position in which distal ends 64 of active fixation tines 54 point away from electronic subassembly 52 to a hooked position in which active fixation tines 54 bend back towards electronic subassembly 52. For example, active fixation tines 54 are shown in a hooked position in
In some examples, all or a portion of fixation subassembly 50, such as active fixation tines 54, may include one or more coatings. For example, fixation subassembly 50 may include a radio-opaque coating to provide visibility during fluoroscopy. In one such example, one or more of active fixation tines 54 may include one or more radio-opaque markers. As another example, active fixation tines 54 may be coated with a tissue growth promoter or a tissue growth inhibitor. A tissue growth promoter may be useful to increase the holding force of active fixation tines 54, whereas a tissue growth inhibitor may be useful to facilitate removal of IMD 16 during an explantation procedure, which may occur many years after the implantation of IMD 16.
As one example, IMD 16 and fixation subassembly 50 may comprise features of the fixation assemblies disclosed in U.S. Provisional Patent Application No. 61/428,067, titled, “IMPLANTABLE MEDICAL DEVICE FIXATION” and filed Dec. 29, 2010, the entire contents of which are incorporated by reference herein. Examples of other fixation structures are described in U.S. Provisional Patent Application No. 61/428,127, titled “IMPLANTABLE MEDICAL DEVICE FIXATION TESTING,” filed on Dec. 29, 2010, assigned to the assignee of the present disclosure, the entire contents of which are incorporated herein by reference as if reproduced herein.
In the example shown in
A feedthrough 82 mounted in an opening 84 of battery housing 78 provides a means for passing electrical energy from electrochemical battery cell(s) 80 to electronics 74 in order to energize electronics 74 with the energy generated by electrochemical battery cells(s) 80. In one example, feedthrough 82 comprises a ferrule 86 having a first side 88 and a second side 90. As shown in
As shown in
Ferrule 86 may also comprise a weld zone 87 that provides a surface for welding ferrule 86 to housing 78 of battery 76 or device housing 72 of IMD 70. Weld zone 87 may comprise a profile that corresponds to a profile of the housing to which ferrule 86 is being welded. For example, as best seen in
In one example, ferrule 86 also comprises a fill port 112 that extends from interior side 88 to exterior side 90. Fill port 112 provides a pathway for filling electrochemical battery cell(s) 80 with electrolyte during manufacture of battery 76. In one example, fill port 112 is left open when making feedthrough 82 (e.g., when inserting pin 94 through passage 92, disposing insulation sleeve 96 between pin 94 and ferrule 86, forming coating 102 around pin 94), and when mounting the assembled feedthrough 82 in opening 84 in battery housing 82. The electrolyte material is then injected through fill port 112, e.g. with a needle or other injection apparatus, so that a desired amount of electrolyte material is within electrochemical battery cell(s) 80. After filling electrochemical battery cell(s) 80 with the electrolyte material, fill port 112 may be sealed, e.g., with a sealing weld, in order to prevent the electrolyte from leaking out through fill port 112.
Ferrule 86 may be made from any material that is practical for use with IMD 70. In one example, the material of ferrule 86 is generally easily formable into the desired shape of ferrule 86, e.g., through casting or machining ferrule 86, and is chemically inert to the electrolytes within battery 76. In one example, ferrule 86 comprises at least one of an aluminum-containing titanium alloy, such as Grade 23 titanium (e.g., between about 5.5 at. % and about 6.5 at. % aluminum (Al), between about 3.5 at. % and about 4.5 at. % vanadium (V), about 0.08 at. % carbon (C), about 0.13 at. % oxygen (O), and the balance titanium (Ti)), Grade 5 titanium, also known as Ti6Al4V titanium alloy (e.g., about 6 at. % Al, about 4 at. % V, less than about 0.08 at. % C, less than about 0.2 at. % O, less than about 0.05 at. % nitrogen (N), less than about 0.4 at. % iron (Fe), less than about 0.015 at. % hydrogen (H), and the balance Ti), or Grade 9 titanium, also known as Ti3Al2.5V (e.g., about 3 at. % Al, about 2.5 at. % V, less than about 0.05 at. % C, less than about 0.12 at. % O, less than about 0.02 at. % N, less than about 0.015 at. % H, and the balance Ti), a commercially pure titanium (e.g., Grade 1 titanium, Grade 2 titanium, Grade 3 titanium, and Grade 4 titanium), aluminum, or a stainless steel.
Pin 94 provides a conduction pathway for electrical energy generated by electrochemical battery cell 80 to electronics 74 of IMD 70. In one example, pin 94 is electrically coupled to an electrode within battery cell 80, such as by being welded to the anode or the cathode of battery cell 80. In one example, pin 94 is electrically connected to the cathode, and the anode is attached and electrically connected to an interior wall of battery housing 78. In another example, the electrical connections may be reversed, e.g. with a pin being electrically coupled to the anode and the cathode electrically coupled to an interior wall of the battery housing. The other end of pin 94 is electrically coupled to electronics 74, such as by being bonded or welded to a connection pad of electronics 74.
In one example, pin 94 comprises an electrically conductive material that is capable of carrying the desired current from battery 76 to electronics while still being substantially chemically inert to the electrolytes within battery cell 80. In one example, pin 94 comprises at least one of an aluminum-containing titanium alloy, such as Grade 23 titanium, Grade 5 titanium, or Grade 9 titanium, a niobium-containing titanium alloy, such as Grade 36 titanium (e.g., about 45 at. % niobium (Nb), and the balance titanium), a commercially pure titanium (e.g., Grade 1 titanium, Grade 2 titanium, Grade 3 titanium, and Grade 4 titanium), niobium, or stainless steel.
Pin 94 may have any cross-sectional shape that is practical for transmitting electrical energy from battery cell 80 to electronics 74. In one example, pin 94 has a cross-sectional shape that corresponds to the cross-sectional shape of pocket 104 on interior side 88 of ferrule 86. For example, as best seen in
Insulation sleeve 96 electrically isolates pin 94 from ferrule 86 and also provides a seal to prevent the electrolyte material of battery cell 80 from leaking out of battery 76 through feedthrough 82. In one example, insulation sleeve 96 hermetically seals between pin 94 and ferrule 86, such as by providing a first hermetic seal between pin 94 and insulation sleeve (e.g., at first junction 98) and a second hermetic seal between ferrule 86 and insulation sleeve 96 (e.g., at second junction 100). In one example, insulation sleeve 96 comprises at least one of a boro-aluminate glass, such as LaBor-4 glass (e.g., glass having a molar concentration of about 30 B2O3, 20 CaO, about 20 Mg, about 15 Al2O3, about 10 SiO2, and about 5 La2O3). Other glasses may be used to form insulation sleeve 96, such as CaBAl-12 glass (e.g., glass having a molar concentration of about 40 B2O3, about 20 Al2O3, about 20 MgO, and about 20 CaO), Ta-23 glass (e.g., glass having a weight % of about 45 wt. % SiO2, about 20 wt. % Al2O3, about 12 wt. % CaO, about 8 wt. % B2O3, about 7 wt. % MgO, about 6 wt. % SrO, and about 2 wt. % La2O3), and Corning 9013 glass. Further description of potential materials of insulation sleeve are provided in the commonly-assigned U.S. Pat. No. 5,306,581 to Taylor et al, issued on Apr. 26, 1994, and U.S. Publication No. 2009/0321107 to Taylor et al., published on Dec. 31, 2009, the disclosures of which are incorporated by reference as if reproduced herein.
In some examples, feedthrough 82 as shown in
It has been found that a coating material may be applied around pin 94 that reduces or prevents low leakage current between pin 94 and ferrule 86 and may also prevent the formation of lithium balls or other potential short circuiting structures between pin 94 and ferrule 86. The coating material is electrically insulating, and in some examples, prevents the formation of lithium balls or other short-circuiting structures on the surface of the coating.
One material that has been found to be useful for coating pin 94 is ethylene tetrafluoroethylene (ETFE). In some feedthroughs, a suspension of ETFE powder in a liquid (such as ethanol) is applied onto a pin, ferrule, or insulation sleeve desired to be coated with ETFE. The liquid may then evaporated off leaving behind the ETFE powder generally in the desired location for the coating. After evaporating the liquid from the ETFE powder, the ETFE powder may be melted so that the ETFE material flows around the pin and/or the ferrule and/or the insulation sleeve to form a coating. In some cases, multiple cycles of applying a coat of the ETFE suspension, evaporating the liquid, and melting the deposited powder may be performed so that there is adequate coverage and adequate thickness of the final coating.
The process of coating the pin and/or the ferrule and/or the insulation sleeve with the ETFE solution may be labor intensive and time consuming. Moreover, for very small feedthroughs, it may be difficult or impossible to apply the ETFE suspension only to the portion of the feedthrough upon which an ETFE coating is desired. For example, as described above, in some examples of feedthrough 82 shown in
In some examples, the present disclosure may provide a solution to the detrimental results that occurr when forming a coating by applying an ETFE-powder suspension. Rather than using a suspension of the coating material, such as ETFE, the present disclosure may use a preform 120 (
Preform 120 may provide for easy placement at a desired location of coating 102 because preform 120 may be an easily manipulatable, solid structure that can easily be placed around pin 94 prior to melting. Preform 120 may also allow the coating material to be placed only in the desired location so that some of the coating material will not be dispersed to undesired locations of the feedthrough or IMD. Further, as described with respect to the Examples below, preform 120 may provide for a reduction in manufacturing time and costs.
In one example, preform 120 comprises a lumen 121 through which pin 94 is inserted. In the example shown in
In one example, preform 120 may have an inner diameter IDPreform that is large enough for a loose fit with pin 94, e.g., with an inner diameter IDPreform that is at least about 0.01 millimeters (about 0.00039 inches) larger than the outer diameter of pin 94, for example at least about 0.025 millimeters (0.00098 inches) larger, such as at least about 0.05 millimeters (0.00197 inches) larger than the outer diameter of pin 94. In one example, preform 120 may have an outer diameter ODPreform that provides for an interference fit with pocket 104, e.g., with an outer diameter ODPreform that is less than about 0.01 millimeters (about 0.00039 inches) smaller than the inner diameter IDPocket of pocket 104, for example less than about 0.005 millimeters (about 0.000197 inches), such as an outer diameter ODPreform of preform 120 that is approximately equal to the inner diameter IDPocket of pocket 104.
In one example, preform 120 is configured to have sufficient polymer material so that, when melted, it forms a coating 102 that substantially fills pocket 104, as shown in
Preform 120 may be made from any material that is capable of substantially wetting and covering a portion of pin 94, a portion of ferrule 86, and a portion of insulation sleeve 96 to form coating 102. In one example, preform 120 comprises a thermoplastic polymer with a melting temperature that is lower than an annealing temperature of insulation sleeve 96 so that when preform 120 is melted to form coating, insulation sleeve 96 is not altered. In one example, insulation sleeve 96 has an annealing temperature of around 600° C. and preform 120 comprises a material with a melting temperature that is substantially less than the 600° C. annealing temperature of insulation sleeve 96, e.g., between about 300° C. and about 400° C. Preform 120 may also comprise a material that is chemically inert to the compounds within battery 76, such as the electrolytes within battery cell 80. In one example, preform 120 consists essentially of one or more materials that are chemically inert to the compounds within battery 76, such as the electrolytes within battery cell 80. In some examples, preform 120 comprises a material that has a melt flow index that is sufficient so that when melted, the resulting coating 102 substantially wets the entirety of portion 106 of pin 94, substantially wets the entirety of portion 108 of insulation sleeve 96, and substantially wets the entirety of portion 110 of ferrule 86, as well as substantially wetting the entirety of first junction 98 and second junction 110. Examples of thermoplastic polymers that may be used to make preform 120 include, but are not limited to, ethylene tetrafluoroethylene (ETFE), fluronated ethylene propylene (FEP), perfluoroalkoxy polymer (PFA), high-density polyethylene (HDPE), a polyethersulfone, polyetheretherketone (PEEK), or other engineered plastics such as acrylonitrile butadiene styrene (ABS), polycarbonates (PC), Polyamides (PA), polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polyphenylene oxide (PPO), polyetherketone (PEK), polyimides, polyphenylene sulfide (PPS), and polyoxymethylene plastic (POM).
As its name suggests, preform 120 may be formed prior to being positioned around pin 94. Preform 120 may be formed by several methods. In one example, preform 120 is formed by extruding a thermoplastic polymer, such as ETFE or one of the other thermoplastic polymers described above, into the desired cross-sectional shape of preform 120. Extrusion is a process of producing thermoplastic components by melting a raw polymer material, and forcing the melted polymer material through a die having a cross section that is larger and proportional to the desired cross-sectional shape of the final component.
Other methods of forming preform 120, such as by molding the polymer into a desired preform shape, or punching out the desired preform shape, may be used. However, extruding preform 120 may have advantages over other methods of forming the preform shape. For example, as described above, in some examples, the inner diameter IDPreform and outer diameter ODPreform may be selected to provide a close, or slip, fit over pin 94 and within pocket 104. Extrusion techniques allow for greater dimensional control of the diameters IDPreform and ODPreform. For example, extrusion of ETFE has been shown to allow control down to within as little as about 0.005 millimeters (about 0.0002 inches) of a desired dimension. While molding, punching, or machining a part down to that level of precision is possible, it may be prohibitively expensive. Moreover, it is more difficult to mold, punch, or machine a part that is very small. For example, as noted above, in some examples preform 120 may have a desired inner diameter IDPreform of between about 0.05 millimeters and about 0.55 millimeters and a desired outer diameter ODPreform of between about 0.24 millimeters and about 1 millimeter. Molding, machining, or punching out a preform with these small dimensions may be difficult or expensive. Extruding the preform may also provide for economy of scale, because a long tube of the preform material may be extruded with the desired cross section and dimensions, such as generally cylindrical with the desired inner diameter IDPreform and outer diameter ODPreform, and then the long tube may be cut down into a plurality of preforms 120.
It is also believed that the process of extruding may provide a benefit at the molecular level. Thermoplastic parts that are molded, e.g., by injection molding, punched out, or machined tend to have a generally random distribution of the orientation of forming stresses. Extruded thermoplastic parts tend to have the forming stresses oriented generally parallel to the direction of extrusion, particularly if the neck down ratio of the polymer material (e.g., a measurement of the stretching of the polymer material, the ratio of the cross-sectional area of the extrusion die compared to the cross-sectional area of the preform, sometimes referred to as the draw ratio or draw down ratio) is relatively high. For example, ETFE has a neck down ratio of between about 80:1 and 100:1, such that the forming stresses are generally substantially oriented with the direction of extrusion, which corresponds, for example, to the axial direction of the example preform 120 shown in
It is believed that the orientation of the forming stresses along the axial direction of preform 120, in some examples, may allow the polymer material to better wet within pocket 104, particularly when the cross-sectional area of pocket 104, pin 94, and preform 120 are very small, e.g., as described above. While not being limited theory, it is theorized that as an extruded preform 120 is melted down and goes through annealing, glass transition, and then melting, that the generally oriented forming stresses may better allow the polymer material to become shorter and wider within pocket 104, which is believed to better wet and conform to portion 106 of pin 94, portion 108 of insulation sleeve 96, and portion 110 of ferrule. Thus, in some examples, it is believed, an extruded preform 120 may be better able to provide form complete wetting and coating, which may allow a coating 102 made from an extruded preform 120 to provide a conformal coating that avoids low leakage current between pin 94 and ferrule 86 or the formation of lithium balls.
In one example method 150, forming preform 120 (152) comprises extruding the polymer to form the preform 120. As noted above, extruding the polymer to form preform 120 allows for good dimensional control over preform 120, such as over the inner diameter IDPreform and outer diameter ODPreform of preform 120. Extrusion also allows for the formation of a small preform 120 to be used in a small feedthrough 82, such as in a feedthrough 82 to be used in a small leadless pacemaker (e.g., IMD 16 of
In one example, feedthrough 82 comprises a pocket 104 disposed around pin 94 on a first side 88 of ferrule 86. In one example of method 150, forming preform 120 (152) comprises forming preform 120 to have a cross-sectional shape that corresponds to a cross-sectional shape of pocket 104. In one example, described above, pocket 104 has a generally cylindrical shape (e.g., a generally circular or elliptical cross section), such that forming preform (104) comprises forming a generally cylindrical preform 120 having an outer diameter ODPreform that is smaller than an inner diameter IDPocket of pocket 104. In one example method 150, placing preform 120 around pin 94 (154) comprises placing at least a portion of preform 120 within pocket 104. In one example method 150, melting preform (156) comprises substantially filling pocket 104 with the polymer of preform 120 in order to substantially wet pin 94 within pocket 104, first junction 98, insulation sleeve 96 within pocket, second junction 100, and a portion of ferrule 86 within pocket 104.
In one example of method 150, melting preform 120 (156) comprises the polymer of preform 120 forming a conformal coating 102 over portion 106 of pin 94, first junction 98, portion 108 of insulation sleeve 96, second junction 100, and portion 110 of ferrule 86, e.g., wherein coating 102 substantially conforms to the geometry of portion 106 of pin 94, first junction 98, portion 108 of insulation sleeve 96, second junction 100, and portion 110 of ferrule 86. Melting preform 120 (156) may be carried out by baking preform 120, pin 94, insulation sleeve 96, and ferrule 86 in an oven in the presence of a vacuum (also referred to as vacuum baking) In one example, melting preform 120 (156) comprises baking preform 120, pin 94, insulation sleeve 96, and ferrule 86 at a temperature of between about 300° C. and about 350° C., such as between about 315° C. and about 325° C., for example about 320° C., for between about 1 hour and about 5 hours, for example between about 1 hour and about for about 3.5 hours, such as for about 70 minutes, under a vacuum.
Forty eight feedthrough assemblies 82 were made, each comprising a ferrule 86 with a passage 92 therethrough, a pin 94 extending through the passage 92, and an insulation sleeve 96 disposed between the pin 94 and the ferrule 86 within the passage 92. The forty eight feedthrough assemblies 82 were placed in two fixtures, with each fixture holding twenty four feedthrough assemblies 82. Preforms made from ethylene tetrafluoroethylene (ETFE) were made by extruding ETFE (NEOFLON EP 610 grade ETFE, Daikin Industries, Ltd., Osaka, Japan) to form tubing having an inner diameter of about 0.25 millimeters and an outer diameter of about 0.55 mm. Forty eight individual preforms 120 were formed by cutting sections of the extruded tubing, with each preform 120 section having a length of about 1 mm.
Each of the forty eight preforms 120 was manually placed on a respective feedthrough assembly 82, with the pin 94 of each respective feedthrough assembly 82 being inserted through a lumen of a respective preform 120. The time to manually place the forty eight preforms 120 was measured as about 67 minutes. The two fixtures (holding the forty eight feedthrough assemblies 82 with forty eight preforms 120 placed thereon) were placed into a vacuum bake oven, where the feedthrough assemblies 82 and preforms 120 were baked for about 3.5 hours in a vacuum at a temperature of about 320° C. to melt preform 120 to form an ETFE coating 102.
The overall labor time for each feedthrough 82 with a coating 102 was about 1.4 minutes per part (about 67 minutes total for 48 parts). The overall baking time per part was about 4.4 minutes of oven time per part (about 210 minutes (3.5 hours) for 48 parts).
An additional forty eight (48) feedthrough assemblies were made, also comprising a ferrule 86 with a passage 92 therethrough, a pin 94 extending through the passage 92, and an insulation sleeve 96 disposed between the pin 94 and the ferrule 86 within the passage 92. The forty eight feedthrough assemblies were placed in two fixtures, with each fixture holding twenty four feedthrough assemblies. ETFE was manually coated onto the feedthrough assemblies by applying ETFE powder (TEFZEL ETFE resin powder, E.I. du Pont de Nemours and Co., Wilmington, Del.) in suspension within ethanol liquid.
In order to achieve adequate thickness and coverage of the resulting ETFE coating, a total of three coats of the ETFE powder suspension were applied to each feedthrough assembly. After each coat was applied, the feedthrough assemblies were put through a vacuum bake cycle of about 3.5 hours at a temperature of about 320° C. The application of the ETFE powder suspension required a total of about two (2) hours of labor per coat for all forty eight feedthrough assemblies, for a total of about six (6) hours of labor time for coating and a total of about 10.5 hours (3 cycles of about 3.5 hours each) of bake time.
The overall labor time to apply an ETFE coating by the method of Comparative Example 2 was about 7.5 minutes of labor per part (about 360 minutes (6 hours) total for 48 parts). The overall baking time per part was about 13.1 minutes of bake time per part (about 630 minutes (10.5 hours) total for 48 parts).
As can be seen by the comparison of the method of forming ETFE coating 102 by the method of Example 1 and the method of forming an ETFE coating by the method of Comparative Example 2, there is an average reduction in labor time of about 6.1 minutes per part and an average reduction in bake time of about 8.7 minutes per part. This translates to about an 81.3% reduction in labor and a 66.7% reduction in oven time. As an example, if the standard hourly manufacturing labor rate is about $65 per hour, then the use of the method of Example 1 will result in a labor savings of about $6.61 per feedthrough over the method of Comparative Example 2. The method of Example 1 will also result in a 66.7% reduction in the costs of operating the oven that is used for the vacuum bake.
Various examples have been described. These and other examples are within the scope of the following claims.
