Patent Publication Number: US-2011059331-A1

Title: Diverting a capillary flow of braze material during a brazing method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application claims priority from Australian Patent Application No. 2009-213037, entitled “Braze Join,” filed on 9 Sep., 2009, which is hereby incorporated by reference herein. 
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates generally to the braze joining of components, and more particularly, diverting a capillary flow of braze material during a brazing method. 
     2. Related Art 
     Often it is a requirement to join together components in an implantable medical device (IMD) to form a hermetic seal. The hermetic seal functions to prevent the ingress of bodily fluids into the IMD and/or the leakage of non biocompatible material from the interior of the IMD to the human body upon implantation of the device. One example process used to hermetically join components is the process of brazing or braze welding and a particular application of this process is the braze joining of a feedthrough component (e.g., a component that permits an electrical signal to be conducted from one side of the feedthrough component to the other side of the feed through component, as will be described in greater detail below) to another component such as the hermetically sealed body or enclosure of an IMD. Alternatively, the feedthrough component may be joined to a mounting component, such as a flange, which is in turn is joined to the body or enclosure of the IMD by a process such as laser welding or the like. 
     A feedthrough component typically comprises an insulating material such as ceramic or glass through which extends one or more electrically conductive elements. These conductive elements convey electrical power and/or electrical signal information essential for the operation of the IMD. With the increasing miniaturisation of IMDs, the otherwise effective process of braze joining becomes problematic. The primary problem is as a result of the relatively small size and/or small mass of one or more of the components being joined together, and as a consequence, the relatively low thermal mass of those components. As the braze joining process involves the heating of both of the components above the melting point of the relevant brazing material, this can result in substantial heat stresses applied to the components, thereby causing distortion and even fracturing or cracking of materials resulting in low yields for the braze joining process. This may also occur where a hermetic join is required. 
     SUMMARY 
     According to a first aspect the present invention, there is a method for joining a first component to a second component with a brazing material, the first component including an aperture for receiving the second component. The method comprises positioning the second component within the first component via the aperture to form a gap between an inner surface of the first component and an outer surface of the second component, introducing by capillary action brazing material into the gap between the first component and the second component, and forming a join between the first and second component upon cooling of the brazing material introduced by capillary action. According to this first aspect of the present invention, the capillary flow of brazing material in the gap is diverted via a capillary flow diverter located in the gap between the first and second component. 
     According to another aspect of the present invention, there is an assembly including a first component and a second component joined together with brazing material. The assembly comprises a first component including an aperture for receiving the second component, the second component, wherein the second component located within the first component, an area between an inner surface of the first component and an outer surface of the second component, the area containing solidified braze material, the braze material joining the first component to the second component, and a capillary flow diverter sized and dimensioned to divert capillary flow of liquefied brazing material in the area during the joining of the first component and the second component. A capillary meniscus extends from the surface of the first component to the surface of the second component. 
     According to another aspect of the present invention, there is a method for joining a first component to a second component with a brazing material, the first component including an aperture for receiving the second component. The method comprises positioning the second component within the first component via the aperture to form a gap between an inner surface of the first component and an outer surface of the second component, stacking a plurality of braze material members at least one of about the second component or within the first component, liquefying at least a portion of the braze material members, and introducing by capillary action the brazing material into the gap between the first component and the second component. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Illustrative embodiments of the present invention will be discussed with reference to the accompanying drawings wherein: 
         FIG. 1  is a perspective sectional view of the interior components of an implantable DACS actuator; 
         FIG. 2  is an exploded view of an assembly including a first component and a second component of the implantable DACS actuator illustrated in  FIG. 1  to be joined together in accordance with an illustrative embodiment of the present invention; 
         FIG. 3  is a cut away sectional perspective view of the mounting flange of the assembly illustrated in  FIG. 2 ; 
         FIG. 4  is a second perspective view of the mounting flange illustrated in  FIG. 3 ; 
         FIG. 5  is a perspective view of a collar member of the assembly illustrated in  FIG. 2 ; 
         FIG. 6  is a perspective view of washers of brazing material forming part of the assembly illustrated in  FIG. 2 ; 
         FIG. 7  is a side sectional view of the assembly illustrated in  FIG. 2  as assembled prior to heating in an oven; 
         FIG. 8  is a top sectional view taken through section  8 - 8  of the assembly illustrated in  FIG. 7 ; 
         FIG. 9  is a sectional view of the assembly illustrated in  FIG. 7  depicting the capillary flow of brazing material in accordance with an illustrative embodiment of the present invention; 
         FIG. 10  is a sectional view of the mounting flange and collar member of the assembly illustrated in  FIG. 7  once again depicting the capillary flow of brazing material; 
         FIG. 11  is a sectional perspective view of the collar member and washers of brazing material forming part of the assembly illustrated in  FIG. 7 ; 
         FIG. 12  is a side perspective view depicting the location of the assembled assembly of  FIG. 7  with respect to the body of the implantable DACS actuator illustrated in  FIG. 1 ; 
         FIGS. 13   a  and  13   b  are top plan and perspective views of a mounting flange in accordance with an illustrative embodiment of the present invention; 
         FIGS. 14   a  and  14   b  are top plan and perspective views of a mounting flange in accordance with a further illustrative embodiment of the present invention; 
         FIGS. 15   a  and  15   b  are top plan and perspective views of a mounting flange in accordance with another illustrative embodiment of the present invention; and 
         FIGS. 16   a  and  16   b  are top plan and perspective views of a mounting flange in accordance with yet another illustrative embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     An embodiment of the present invention includes a method for forming a braze join between components that is capable of reducing the heat effects of the brazing process on the components being joined together. An embodiment of the present invention includes a method for joining a flange to a feedthrough component with a brazing material. In this embodiment, the flange includes an aperture for receiving the feedthrough component. The method comprises positioning the feedthrough component within the flange via the aperture to form a gap between an inner surface of the flange and an outer surface of the feedthrough component, followed by introducing by capillary action brazing material into the gap between the flange and the feedthrough component. A join is then formed between the flange and the feedthrough component upon cooling of the brazing material introduced by capillary action. According to this embodiment, the capillary flow of brazing material in the gap is diverted via a capillary flow diverter located in the gap between the first and second component. Still further, according to this embodiment, solidified brazing material is initially deployed as a number of circular washers about the feedthrough component and/or in the aperture of the flange. Each of the washers includes a slit which allows the washers to be flexed when placed into position. These washers melt for form the liquefied brazing material just discussed. 
     Referring to  FIG. 1 , there is shown an example IMD in the form of a hearing aid device incorporating a feedthrough component in which the present invention may be utilized. In this example, IMD is an actuator  100  which operates by direct acoustic cochlear stimulation (DACS) to directly stimulate the inner ear fluid (perilymph) by simulating the operation of a normally functioning middle ear. As would be apparent to those of skill in the art, the present invention will also be applicable to other IMDs such as cochlear implants (described in greater detail below), neural stimulators, internal drug pumps, incontinence devices, bone growth stimulators and the like where a hermetic join is required to be formed between components. 
     Embodiments of the present invention are further applicable to other types of active implantable medical devices (AIMDs), such as, auditory brain stimulators, also sometimes referred to as an auditory brainstem implant (ABI), other implanted hearing aids or hearing prostheses, retinal prostheses, cardiac related devices such as pacers (also referred to as pacemakers) or defibrillators, implanted drug pumps, other electro-mechanical stimulation devices, or other implanted electrical devices. 
     Actuator  100  includes a housing  180  formed from titanium tubing that is substantially cylindrical and of circular cross section. Actuator  100  further includes a titanium diaphragm  150 , a titanium protection ring  155  and a multi-pin feedthrough component  115  which is joined to a mounting flange  110  which in turn is laser welded to housing  180 . In this example, feedthrough component  115  is a ceramic feedthrough component formed from alumina by a powder injection moulding (PIM) process. 
     As would be appreciated by those of skill in the art, some embodiments of the present invention may utilize a ceramic feedthrough component as opposed to a feedthrough component of the glass type variety due to the increased density of the ceramic material and its strength of bond to biocompatible materials such as titanium, platinum and the like. In some embodiments, some or all of these features may improve the likelihood of achieving a hermetic seal that meets the strict quality requirements required of an IMD, thereby resulting in improved yields. In addition, the PIM process allows more complex geometries to be achieved as compared to other over moulding processes such as those involving glass which can be restricted by the inherent viscosity characteristics of the glass material. 
     Coupling rod  160 , which is part of the moving mechanical output structure of electromechanical driving arrangement of actuator  100  is hermetically welded to diaphragm  150 . This assembly provides a hermetically closed housing  180  that is suitable for implantation in the human body. Lead  170  which conveys the electrical input signal to actuator  100  is connected by leads  171  to contact pins  116  which extend through feedthrough component  115 . Armature  140 , shaft  135  and coupling rod  160  form the moving part of actuator  100  which is driven by coil  130  between permanent magnets  145  responsive to the electrical input signal from contact pins  116 . 
     Shaft  135  is made of titanium to enable hermetic closing of actuator  100  by welding it to diaphragm  150  which also elastically supports the end of shaft  135  and performs the function of a restoring spring. As such, diaphragm  150  prevents magnetic snap over. On the other side, shaft  135  is supported in the longitudinal direction by a spring bearing  125  having a spring constant sufficient to provoke, together with diaphragm  150 , the demanded dynamic characteristic of this spring-mass structure to drive artificial incus  165 . 
     Further details of DACS actuators of the type referred to above are described in PCT Application No. PCT/AU2005/001801 (WO 2006/058368) entitled IMPLANTABLE ACTUATOR FOR HEARING AID APPLICATIONS, published 8 Jun. 2006, the details of the DACS actuators disclosed therein are usable in some embodiments of the present invention involving application to DACS. 
     The overall dimensions of actuator  100  are Ø3.75×9.3 mm (not including coupling rod  160  and artificial incus  165 ) resulting in dimensional requirements for the ceramic feedthrough component  115  of Ø2.17 mm×1.49 mm thickness which is significantly reduced when compared to the feedthrough of other IMDs. As an example, a typical cochlear implant would be expected to have dimensions in the order of Ø8.00×1 mm-2 mm thickness. Known methods of braze joining (see for example PCT Application No. PCT/AU2006/002012 (WO 2007/070989) entitled IMPROVED BRAZE JOIN, published 28 Jun. 2007, some or all of the methods, systems and apparatuses pertaining to braze joining disclosed therein usable in some embodiments of the present invention) for braze joining feedthrough component  115  to the surrounding flange  110  may result in the generation of large thermal stresses potentially resulting in the fracture or cracking of feedthrough component  115  during the brazing process. 
     The generation of these thermal stresses is primarily due to the small thermal mass of feedthrough component  115  which makes the brazing process especially sensitive to process variations. As an example, the total mass of the DACS actuator  100  described with reference to  FIG. 1  is 0.45 grams of which the ceramic feedthrough component  115  makes up approximately 0.025 grams. In addition, smaller components have an increasingly large surface area to volume ratio, thereby adding to their propensity to overheat during the braze joining process potentially resulting in potential stress cracking of the component. 
     Referring now to  FIG. 2 , there is shown an exploded perspective view of an assembly  200  including a first component (in this example mounting flange  110 ) to be joined to a second component (in this example feedthrough component  115 ) according to a first illustrative embodiment of the present invention. Assembly  200  includes a mounting flange  110 , formed in this illustrative embodiment of titanium, having an aperture  230  for receiving a feedthrough component  115  incorporating contact pins  116  which in practice would be integrated into feedthrough component  115  by a moulding process prior to joining Assembly  200  further includes a collar member  210  and four stackable circlets or washers  220  of brazing material which in this illustrative embodiment is a Titanium alloy consisting of 60% Ti, 25% Cu and 15% Ni. In some embodiments, the weight and/or mass of either of the feedthrough component  115  and/or the mounting flange  110  is less than 0.05 grams. 
     Referring now to  FIGS. 3 and 4 , there are shown detailed perspective views of mounting flange  110  which at its bottom end includes an inwardly extending ledge portion  231  which matches complementary circumferential recess region  117  located on the bottom end of feedthrough component  115  (as best seen in  FIG. 2 ). In this illustrative embodiment, ledge portion  231  functions to both locate and support feedthrough component  115  within mounting flange  110  on assembly. Ledge portion  231  in this illustrative embodiment also includes three regularly spaced arcuate shaped cut-outs  232 . 
     The inner sidewall or surface  235  of mounting flange  110  further includes three inwardly extending arcuate projection members  233  forming a generally trilobular arrangement which on assembly abuts the outer surface  118  of feedthrough component  115 , thereby centrally locating feedthrough component  115  within mounting flange  110 . Mounting flange  110  also includes an upper shoulder portion  234  which functions as a seating region to seat collar  210  and washers  220  on assembly. 
     Referring now to  FIG. 5 , there is shown a detail perspective view of collar member  210  which on assembly seats on upper shoulder portion  234  of mounting flange  110 . Collar member  210  includes six regularly spaced semicircular cut-out regions  211 . As shown in  FIG. 6 , the brazing material is deployed as a number of circular washers  220  each incorporating a slit  221  which allows the washers  220  to be flexed when placed around collar member  210  on assembly. In this illustrative embodiment, each washer is 0.1 mm thick. 
     Referring now to  FIG. 7 , there is shown a formed assembly  200  prior to heating in an oven. Feedthrough component  115  is first positioned in mounting flange  110  via aperture  230  so that recess region  117  of feedthrough  115  is supported by ledge portion  231  of mounting flange  110 , thereby locating the feedthrough component  115  within mounting flange  110  in a vertical sense. As can be seen in the sectional view of formed assembly  200  depicted in  FIG. 8 , inwardly extending arcuate projection members  233  formed in the sidewall or inner surface  235  of mounting collar  110  form a slight interference fit or press fit arrangement at three spaced locations  233   a  with the outer surface  118  of feedthrough component  115 . This functions to locate the feedthrough component  115  within the mounting flange  110  in a horizontal sense. 
     In this example, where mounting collar  110  is of a generally cylindrical configuration, this horizontal positioning corresponds to location in a radial sense within mounting flange  110 . Accordingly, in this embodiment projection members  233  in combination with ledge portion  231  position feedthrough component  115  to provide a precise gap  238  between the outer surface  118  of the feedthrough component  115  and the inner surface  235  of the mounting flange  110 . 
     In this illustrative embodiment, gap  238  is of the order of 15 microns, and at least less than 20 microns, which as would be appreciated by those of skill in the art is significantly smaller than corresponding spacing in prior art feedthroughs such as the feedthrough described in International Patent Application Publication No. WO 2007/070989, which is of the order of 50-70 microns. Accordingly, the attainable positioning tolerance in the brazing process in this illustrative embodiment is in the order of a few microns in the radial dimension. 
     Collar  210  is then placed over the top portion of feedthrough component  115  and seats on shoulder portion  234  of mounting flange  110 . The stackable washers  220  are then placed over the collar  210  with the slits  221  of each washer  220  rotationally positioned 90 degrees with respect to each other. As previously described, the slit  221  allows the washer  220  to be flexed or stretched when being placed over collar  210  resulting in the washer  220  sitting tightly against collar  210  and assisting assembly prior to heating. 
     The assembled component is then placed in an infrared brazing oven and subjected to a predetermined time and temperature profile. In one illustrative embodiment, the temperature of the oven is raised in a controlled ramping stage up to a maximum temperature of 1010 degrees C. over a 20 minute time period and then held at this “hold” temperature for 5 minutes. The temperature is then lowered in a further controlled ramping stage to room temperature. The maximum hold temperature is selected to correspond to the temperature of the brazing material required to create a capillary melt flow and to take into account any thermal transfer or shielding effects that may arise from mounting apparatus within the oven. 
     A jig may be utilized to maintain the assembly of the flange and the feedthrough component vertical during the heating operation, and may also be used to more evenly dissipate heat around the assembly. 
     In an exemplary embodiment, heating liquefies the braze material (i.e., turns the braze material molten), and facing surfaces of the flange and the feedthrough component are fused together upon cooling of the braze material. The solidified braze material also fills in some or all voids between the flange and the feedthrough component. The braze material forms a hermetic seal between the surfaces. In an exemplary embodiment, the braze material completely surrounds a diameter of the feedthrough component. 
     In an exemplary embodiment of the present invention, localized heat sink strips may be embedded into the feedthrough component or otherwise attached to the feedthrough to enhance heat dissipation. 
     In an exemplary embodiment of the present invention, the liquefied braze material is capillarily confined between the feedthrough component  115  and the flange  110  and/or between those respective components and the titanium collar  210 . In an exemplary embodiment of the present invention, a capillary meniscus extending from a surface of the feedthrough component  115  to the flange  110  and/or from those respective components to the titanium collar  210  may be formed, and may be present upon solidification of the braze material upon cooling. That is, a capillary meniscus is formed extending between the two components that are brazed together. 
     In addition, the controlled ramp up and down from the hold temperature may include further intermediate hold points to allow the components to reach thermal equilibrium. 
     Referring now to  FIGS. 9 and 10 , there is shown various sectional views of the components of assembly  200  illustrating the direction of capillary flow of brazing material. Upon heating to the melt temperature of the stackable washers  220 , the stackable washers  220  melt and are drawn by capillary action through the semicircle cut-out regions  211  of collar member  210  into gap  238 . 
     During this process, ledge portion  231  of mounting flange  110  functions as a capillary flow diverter to divert or change the direction of the capillary flow in gap  238  of molten brazing material during the braze joining process by in this case providing a horizontal restraint plane. This promotes uniform capillary flow of brazing material between the feedthrough component  115  and the mounting flange  110  and has the added benefit of reducing the propensity of flooding of the feedthrough component  115  with brazing material. 
     In this illustrative embodiment, the ledge portion  231  further includes radially arranged semicircular cut-outs  232  which also function as air channels to promote diametrically even flow or more even flow of brazing material. Each cut-out  232  is the equivalent of 0.3 mm full circular radius and of equivalent thickness to the ledge portion  231 . In this illustrative embodiment, cut-outs  232  are shifted 120° relative to the three arcuate projection members  233 , this arrangement functioning to promote capillary pull of the molten braze material through ledge portion  231  (as is depicted by way of example in  FIG. 10 ). 
     In this illustrative embodiment, gap  238  includes a further capillary flow diverter in the form of the inwardly extending arcuate projection members  233  that are formed in the sidewall or inner surface  235  of mounting flange  110  which function to divert or change the direction of capillary flow of brazing material and further evenly distribute this material onto ledge portion  231 . As may be seen, the projection members  233  are located in the gap between the mounting flange  110  and the feedthrough component  115 . It is noted that these projections may extend either from the mounting flange  110  or the feedthrough component  115 , or both, in some embodiments. In an exemplary embodiment, the projection members  233  form a press fit or a slip fit arrangement between the mounting flange  110  and the feedthrough component  115 . 
     In addition, this arrangement forms respective air channels between each of the arcuate projection members  233  which also function to promote even or more even capillary flow. In an exemplary embodiment, the capillary flow diverter also functions to locate the feedthrough component  115  vertically and/or horizontally within the mounting flange  110  during the joining operation. In an exemplary embodiment, the capillary flow diverter includes a ledge portion formed in the mounting flange  110  to support the feedthrough component  115  during the joining process. As will be understood, with reference to the gap  238 , it is noted that in some embodiments of the present invention, at least one air channel can be formed combination with the capillary flow diverter to promote capillary flow of brazing material in the gap. 
     While in this illustrative embodiment the modifications in structure of the components to incorporate a capillary flow diverter arrangement or means in the gap  238  between them have been principally made in the mounting flange  100  (or first component), as will by now be inferred, in alternative embodiments, the capillary flow diverter arrangement can be implemented in part or in full in the received second component which in this case is the feedthrough component  115  which is received within the first component. As an example, the trilobular structure of the inwardly extending arcuate projection members  233  that are formed in the sidewall or inner surface  235  of mounting flange  110  could be implemented on the outer surface  118  of feedthrough component  115  or alternatively a number of interleaved structures could be formed alternatively on the inner and outer walls of the first and second components respectively to change the direction of capillary flow of brazing material and evenly distribute the volume of brazing material. 
     It is noted that while in prior brazing techniques, the flow of brazing material in the contact regions between the inner surface  235  of mounting flange and the outer surface  118  of feedthrough component  115  would have been believed to be restricted, embodiments of the present invention are implemented such that in these contact regions, there is a slight variation in the “contact” regions between these components such that perfect point contact between the respective surfaces is avoided. In an exemplary embodiment, this permits or otherwise enhances the flow of molten brazing material into these regions to form a braze join. 
     Referring now to  FIGS. 13   a  to  16   b , there are shown top plan and perspective views of mounting flanges  1310 ,  1410 ,  1510 ,  1610  respectively in accordance with further embodiments of the present invention. In the embodiments of  FIGS. 13   a  and  13   b  the inwardly extending projection members are formed as straight chord like members  1333 , while in the embodiments of  FIGS. 14   a  and  14   b , the inwardly extending projection members are formed as semi-circular rib members  1433 . Similarly, in the embodiments of  FIGS. 15   a  and  15   b , the inwardly extending projection members are formed as flattened rib members  1533  whereas in the embodiments of  FIGS. 16   a  and  16   b , the inwardly extending projection members are in the form of angular serrations  1633 . As would be appreciated by those skilled in the art, the number, size and shape of the inwardly extending projection members and more generally the capillary flow diverter may be modified according to requirements. In an exemplary embodiment any or all of these various components, and variations thereof, may be used in some or all of the brazing processes described herein. 
     While in the illustrative embodiments depicted in the Figures are such that the inwardly extending projection members extend generally along the length of the inner surface  235  of mounting flange  110 , in other embodiments, these projection members may be a series of spaced elements either regularly or irregularly spaced about the inner surface  235  of mounting flange  110  and/or about the outer surface  118  of feedthrough component  115  to divert the direction of capillary flow of brazing material in gap  238 . In a further embodiment, the outer surface of feedthrough component  115  may be roughened or otherwise formed to have a rough surface to provide an additional capillary flow diverter effect to divert the direction of capillary flow of brazing material. 
     While the illustrative embodiments presented above have been described with respect to circular components, in other embodiments of the present invention, components of other geometries including but not limited to square, rectangular, oval or complementary non regular geometries may be used. 
     Referring now to  FIG. 11 , there is shown a sectional view depicting an arrangement of stackable washers  220  and collar member  210  in accordance with an illustrative embodiment of the present invention. In an exemplary embodiment employing a number of individual washers or more generally stackable members of brazing material that are configured to surround the received component, in contrast to a corresponding single washer of brazing material, the use of a number of individual stackable members or washers  220  of brazing material allows the amount of brazing material used to form the braze join to be controlled very precisely, at least more precisely with respect to the corresponding single washer of brazing material. In an exemplary embodiment, variations to the brazing process may be implemented including the removal or the addition of a single washer  220  or more than a single washer  220  to assembly  200 , thereby precisely varying the volume of brazing material (in this case TiCuNi) available during the brazing process. 
     As shown in  FIG. 11 , the stacking of individual washers  220  may be such, in exemplary embodiments, to provide an air gap  223  between each washer  220  which also functions to promote even or more even melting and even or more even capillary flow of brazing material. As described previously, each stackable washer  220  may include an opening or slit  221  that facilitates the placing of individual washers  220  around collar member  210 . In accordance with one illustrative embodiment of the present invention, four washers  220  are employed with the slit  221  of each washer  220  placed at an equiangular spacing offset with respect to each other (i.e. in this case 90 degrees as best seen in  FIG. 6 ). This arrangement forms an air gap  223  at each layer which facilitates the even or more even melting and even or more even capillary flow of brazing material. As would be appreciated by those skilled in the art, this arrangement can be modified depending on the number of washers. In addition, the slit may cause each individual washer  220  to twist slightly which further accentuates air gaps  223  between each layer. 
     The formation of air gaps  223  in the brazing material may facilitate the capillary flow of the braze material as the air gaps provide a substantially increased surface area for heat to dissipate. This enhances the rapidity and extent of melting of the brazing material ensuring that the brazing material melts uniformly and becomes an homogeneous fluid pool of brazing material. 
     In another illustrative embodiment, the brazing material is in the form of a sponge incorporating internal air gaps or pockets, thereby further facilitating even or more even capillary flow of the brazing material. The sponge form of brazing material may be formed in one of many different ways including but not limited to, acid etching/bubbling of a sheet metal form of the stock brazing material, electro discharge machining (EDM) of the stock brazing material or high pressure micro blasting with grit of the stock brazing material. 
     Referring now to  FIG. 12 , there is shown the assembly  200  after a braze join has been formed between mounting flange  110  and feedthrough component  115  as further attached to the housing  180  of an implantable DACS actuator such as that referred to in  FIG. 1 . In accordance with an exemplary embodiment of the present invention, brazing material  225  has been drawn through collar member  210  and into the gap  238  between mounting flange  110  and feedthrough component  115 , this capillary flow being diverted in this illustrative embodiment by ledge portion  231  and inwardly extending projection members  233  formed in the inner wall  235  of mounting flange  110  and further promoted by air channels in the form of circular cut-outs  232  in ledge portion  231  and between inwardly extending projection members  233 . In this illustrative embodiment, ledge portion  231  and inwardly extending projection members  233  also function to locate feedthrough component  115  within mounting flange  110 . 
     Some embodiments of the present invention are effective to provide a braze join which is suited to joining small scale components which otherwise would be subject to high thermal stresses. These high thermal stresses potentially causing defects in the components. 
     While the present invention has been described in one non limiting example with reference to the joining of a feedthrough component to a mounting flange in a DACS actuator, some or all embodiments of the present invention are applicable to other braze joins to reduce the effects of thermal stress introduced into one or more of the components being joined. As an example, an embodiment of the present invention could be applied to metal to metal joins, metal to glass joins, glass to glass joins or ceramic to ceramic joins and any braze material including gold alloys, various alloys of titanium including TiCuNi, TiNi, TiCuAg and silver alloys. 
     As detailed above, embodiments of the present invention may be utilized to fabricate a hearing prosthesis, which as detailed above, may be a DACS. Embodiments of the present invention may further be used to fabricate a cochlear prosthesis (commonly referred to as cochlear prosthetic devices, cochlear implants, cochlear devices, and the like; simply “cochlear implants” herein.) Cochlear implants deliver electrical stimulation to the cochlea of a recipient. As used herein, cochlear implants also include hearing prostheses that deliver electrical stimulation in combination with other types of stimulation, such as acoustic or mechanical stimulation (sometimes referred to as mixed-mode devices). It would be appreciated that embodiments of the present invention may be implemented in any cochlear implant or other hearing prosthesis now known or later developed, including auditory brain stimulators, or implantable hearing prostheses that mechanically stimulate components of the recipient&#39;s middle or inner ear. 
       FIG. 17  is perspective view of a cochlear implant, referred to as cochlear implant  1700 , implanted in a recipient. The recipient has an outer ear  1701 , a middle ear  1705  and an inner ear  1707 . Components of outer ear  1701 , middle ear  105  and inner ear  1707  are described below, followed by a description of cochlear implant  1700 . 
     In a fully functional ear, outer ear  1701  comprises an auricle  1710  and an ear canal  1702 . An acoustic pressure or sound wave  1703  is collected by auricle  1710  and channeled into and through ear canal  1702 . Disposed across the distal end of ear cannel  1702  is a tympanic membrane  1704  which vibrates in response to sound wave  1703 . This vibration is coupled to oval window or fenestra ovalis  1712  through three bones of middle ear  1705 , collectively referred to as the ossicles  1706  and comprising the malleus  1708 , the incus  1709  and the stapes  1711 . Bones  1708 ,  1709  and  1711  of middle ear  1705  serve to filter and amplify sound wave  1703 , causing oval window  1712  to articulate, or vibrate in response to vibration of tympanic membrane  1704 . This vibration sets up waves of fluid motion of the perilymph within cochlea  1740 . Such fluid motion, in turn, activates tiny hair cells (not shown) inside of cochlea  1740 . Activation of the hair cells causes appropriate nerve impulses to be generated and transferred through the spiral ganglion cells (not shown) and auditory nerve  1714  to the brain (also not shown) where they are perceived as sound. 
     As shown, cochlear implant  1700  comprises one or more components which are temporarily or permanently implanted in the recipient. Cochlear implant  1700  is shown in  FIG. 17  with an external device  1742  which, as described below, is configured to provide power to the cochlear implant. 
     In the illustrative arrangement of  FIG. 17 , external device  1742  may comprise a power source (not shown) disposed in a Behind-The-Ear (BTE) unit  1726 . External device  1742  also includes components of a transcutaneous energy transfer link, referred to as an external energy transfer assembly. The transcutaneous energy transfer link is used to transfer power and/or data to cochlear implant  1700 . As would be appreciated, various types of energy transfer, such as infrared (IR), electromagnetic, capacitive and inductive transfer, may be used to transfer the power and/or data from external device  1742  to cochlear implant  1700 . In the illustrative embodiments of  FIG. 17 , the external energy transfer assembly comprises an external coil  1730  that forms part of an inductive radio frequency (RF) communication link. External coil  1730  is typically a wire antenna coil comprised of multiple turns of electrically insulated single-strand or multi-strand platinum or gold wire. External device  1742  also includes a magnet (not shown) positioned within the turns of wire of external coil  1730 . It should be appreciated that the external device shown in  FIG. 17  is merely illustrative, and other external devices may be used with embodiments of the present invention. 
     Cochlear implant  1700  comprises an internal energy transfer assembly  1732  which may be positioned in a recess of the temporal bone adjacent auricle  1710  of the recipient. As detailed below, internal energy transfer assembly  1732  is a component of the transcutaneous energy transfer link and receives power and/or data from external device  1742 . In the illustrative embodiment, the energy transfer link comprises an inductive RF link, and internal energy transfer assembly  1732  comprises a primary internal coil  1736 . Internal coil  1736  is typically a wire antenna coil comprised of multiple turns of electrically insulated single-strand or multi-strand platinum or gold wire. Positioned substantially within the wire coils is an implantable microphone system (not shown). As described in detail below, the implantable microphone assembly includes a microphone (not shown), and a magnet (also not shown) fixed relative to the internal coil. 
     Cochlear implant  1700  further comprises a main implantable component  1720  and an elongate electrode assembly  1718  extending from the main implantable component  1720 . In embodiments of the present invention, internal energy transfer assembly  1732  and main implantable component  1720  are hermetically sealed within a biocompatible housing. In embodiments of the present invention, main implantable component  1720  includes a sound processing unit (not shown) to convert the sound signals received by the implantable microphone in internal energy transfer assembly  1732  to data signals, although in other embodiments, the sound processing unit may be located in the external components of the cochlear implant. Main implantable component  1720  further includes a stimulator unit (also not shown) which generates electrical stimulation signals based on the data signals. The electrical stimulation signals are delivered to the recipient via elongate electrode assembly  1718 . 
     Elongate electrode assembly  1718  has a proximal end connected to main implantable component  1720 , and a distal end implanted in cochlea  1740 . In an exemplary embodiment, the electrode assembly  1718  is connected to the main implantable component  1720  via a feedthrough component, which may be manufactured according to the embodiments described herein. The feedthrough component permits the maintenance of the hermetic seal of the biocompatible housing just discussed, while permitting electrical signals to pass through the hermetic seal from/to the main implantable component  1720  to/from the electrode assembly  1718 . In an exemplary embodiment, the flange brazed to the feedthrough component may be laser welded to the housing to attach the feedthrough to the housing. In embodiments of the present invention, internal energy transfer assembly  1732  and main implantable component  1720  are hermetically sealed within a biocompatible housing. 
     Electrode assembly  1718  extends from main implantable component  1720  to cochlea  1740  through mastoid bone  1719 . In some embodiments electrode assembly  1718  may be implanted at least in basal region  1716 , and sometimes further. For example, electrode assembly  1718  may extend towards apical end of cochlea  1740 , referred to as cochlea apex  1734 . In certain circumstances, electrode assembly  1718  may be inserted into cochlea  1740  via a cochleostomy  1722 . In other circumstances, a cochleostomy may be formed through round window  1721 , oval window  1712 , the promontory  1723  or through an apical turn  1747  of cochlea  1740 . 
     Electrode assembly  1718  comprises a longitudinally aligned and distally extending array  1746  of electrodes  1748 , sometimes referred to as electrode array  1746  herein, disposed along a length thereof. Although electrode array  1746  may be disposed on electrode assembly  1718 , in most practical applications, electrode array  1746  is integrated into electrode assembly  1718 . As such, electrode array  1746  is referred to herein as being disposed in electrode assembly  1718 . As noted, a stimulator unit generates stimulation signals which are applied by electrodes  1748  to cochlea  1740 , thereby stimulating auditory nerve  1714 . 
     Cochlear implant  1700  may comprises a totally implantable prosthesis that is capable of operating, at least for a period of time, without the need for external device  1742 . Therefore, cochlear implant  1700  further comprises a rechargeable power source (not shown) that stores power received from external device  1742 . The power source may comprise, for example, a rechargeable battery. During operation of cochlear implant  1700 , the power stored by the power source is distributed to the various other implanted components as needed. The power source may be located in main implantable component  1720 , or disposed in a separate implanted location. 
     The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement of any form of suggestion that such prior art forms part of the common general knowledge. 
     The invention described and claimed herein is not to be limited in scope by the specific preferred embodiments herein disclosed, since these embodiments are intended as illustrations, and not limitations, of several aspects of the invention. Any equivalent embodiments are intended to be within the scope of this invention. Indeed, various modifications of the invention in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description. Such modifications are also intended to fall within the scope of the appended claims.