Abstract:
Several embodiments of a hermetic terminal assembly are disclosed and an associated method. The terminal assembly includes a metallic body that has body a bottom portion. The bottom portion includes an interior surface, an exterior surface and at least one opening. The terminal assembly also includes a current-conducting pin extending longitudinally through the opening, and a prefabricated dielectric retainer receiving the pin and covering at least a portion of the interior surface and surrounding at least a portion of the opening. The terminal assembly includes a dielectric epoxy bonding to the body, the retainer and the pin, and providing a seal between the pin and the opening in the bottom portion through which the pin is extending. In another embodiment, the prefabricated retainer may be omitted entirely.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 10/071,542 filed on Feb. 8, 2002, the disclosure of which is hereby incorporated in its entirety. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to electric terminals, and more particularly to terminals of the type which include one or more conductor pins which project through and are secured to a metallic body portion by a hermetic seal for disposing the ends of the conductor pins on opposite sides of the body portion.  
         BACKGROUND OF THE INVENTION  
         [0003]    Hermetically sealed electric terminals provide an airtight electrical terminal for use in conjunction with hermetically sealed devices where leakage into or from such devices, by way of the terminals, is effectively precluded. For hermetically sealed electric terminals to function safely and effectively for its intended purpose, the terminals require that their conductor pins be electrically insulated from and hermetically sealed to the body portion through which they pass and that an optimum air path be established and thereafter maintained between adjacent portions of the pins and opposite sides of the body.  
           [0004]    In a conventional hermetic terminal assembly, exemplified by U.S. Pat. No. 3,160,460 to Wyzenbeek, a straight, current carrying pin is fixed in place within a lip defining a hole in the terminal body by a fusible glass-to-metal seal. A resilient insulator is bonded to the face of the body beyond the extent of the glass-to-metal seal. The insulator includes outwardly projecting portions bonded to the conductor pins which define a predetermined air path between adjacent portions of the pins and the body member. Such a hermetic terminal construction has been the standard in the industry for four decades.  
           [0005]    The primary object of the present invention is to provide a hermetic terminal assembly having conductor pins that are rigidly and hermetically secured to the body portion entirely by a resilient plastic which possesses the requisite materials properties, such as dielectric, moisture resistance, resistance to chemical breakdown, to provide for a hermetic seal. In addition to providing a hermetic seal between the conductor pins and the body, the same resilient plastic is bonded to the conductor pins to provide the desired air path between the pins and the face of the body portion.  
           [0006]    Another object of the present invention is to provide such a terminal that is simple and economical to manufacture, such as by plastic injection molding.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention provides a hermetic terminal assembly having a cup-shaped body portion with a generally flat bottom wall and at least one opening in the bottom wall defined by an annular lip. A current conducting terminal pin extends through each opening and beyond the lip on both ends of the body portion, the inner end of the terminal pin being on the dish side of the cup-shaped body portion, and the outer end of the terminal pin extending through and to the outer side of the body portion. A resilient plastic resin material is molded into place within the body portion and interlocks with the body portion and the terminal pins to fixedly secure the terminal pins in position relative to the body portion. The plastic resin material forms a hermetic seal between the terminal pin and the body portion. In addition, the plastic extends beyond the face of the body portion and covers the pin to provide the desired air path between the respective pins and each other and/or the face of the body portion.  
           [0008]    In alternate embodiments of the present invention, the terminal pins include shank portions with varying surface configurations that are intended to enhance the bonding of the plastic resin to the terminal pin and improve the hermeticity of the seal. The terminal pins may also include fuse portions that are intended to open in response to predetermined current loads seen at the terminal pins.  
           [0009]    In still another embodiment of the present invention, the terminal assembly includes a metallic body that has a bottom portion. The bottom portion includes an interior surface, an exterior surface and at least one opening having a wall. The terminal assembly also includes a current-conducting pin extending longitudinally through the opening, and a prefabricated dielectric retainer receiving the pin and covering at least a portion of the interior surface and surrounding at least a portion of the wall. The terminal assembly includes a dielectric epoxy bonding to the body, the retainer and the pin, and providing a seal between the pin and the opening in the bottom portion through which the pin is extending. Yet another variation of the invention is similar to the preceding embodiment but omits entirely the prefabricated retainer.  
           [0010]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0012]    [0012]FIG. 1 is a perspective view of a hermetic terminal assembly;  
         [0013]    [0013]FIG. 2 is a cross-sectional side view of a first embodiment of the hermetic terminal assembly of the present invention;  
         [0014]    [0014]FIG. 3 is a cross-sectional perspective view of the hermetic terminal assembly of FIG. 2;  
         [0015]    [0015]FIG. 4 is a cross-sectional side view of a second embodiment of the hermetic terminal assembly of the present invention;  
         [0016]    [0016]FIG. 5 is a cross-sectional perspective view of the hermetic terminal assembly of FIG. 4;  
         [0017]    [0017]FIG. 6 is a cross-sectional side view of a third embodiment of the hermetic terminal assembly of the present invention; and  
         [0018]    [0018]FIG. 7 is a cross-sectional perspective view of the hermetic terminal assembly of FIG. 6;  
         [0019]    [0019]FIG. 8 is an exploded view of a fourth embodiment of the hermetic terminal assembly of the present invention, shown before manufacture; and  
         [0020]    [0020]FIG. 9 is a cross-sectional side view of the fourth embodiment of the hermetic terminal assembly. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]    The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
         [0022]    Referring now to the drawings FIGS. 1, 2 and  3 , a hermetic terminal assembly  10  having a generally cup-shaped body portion  12  with a generally flat bottom  14  and side wall  16  with an outwardly flaring rim  18 . The bottom  14  of the body portion  12  has a dish-side interior surface  22 , an outside surface  24 , and a plurality of openings  26 . The openings  26  are each defined by an annular lip  28  with an inside wall surface  30 , a free edge  32  on the dish side, and a radius  34  on the outside.  
         [0023]    A current carrying terminal pin  36  with an outer end  38  and an inner end  40  may be fitted with a conventional terminal tab (not shown). The current carrying pin  36  is sealed within the opening  26  by a dielectric plastic resin material  44  that is molded directly into the body portion  12 , which bonds to the body portion  12  and terminal pin  36 . As molded, the plastic resin  44  creates a seal  46  that is an airtight hermetic seal between the terminal pin  36  and the body portion  12  such that leakage through the assembly  10 , by way of the terminal pins  36 , is prevented.  
         [0024]    In a preferred embodiment, the plastic resin  44  is molded in and around the body portion  12  on each side of the bottom  14 . The plastic resin  44  thereby covers both the dish-side surface  22  and the outside surface  24  of the bottom wall  20  and is mechanically interlocked with the body portion  12 . The plastic resin provides an dielectric oversurface that covers the inside and outside of the terminal  10  body portion  12 . Additionally, the plastic resin  44  may also include a sleeve portion  47  that bonds to and covers a portion of the terminal pin  36  projecting out of the body portion  12  to the outer end  38  of the to define the air path between the respective terminal pins  36  and/or the body portion  12 , as desired.  
         [0025]    On the dish-side, interior surface  22  of the body portion  12 , the molded plastic resin  44  forms a plurality of neck portions  48  each of which is adjacent to, and surrounds, the annular lip  28  defining an opening  26  in the bottom wall  20  of the body portion  12 . Each neck portion  48  extends along its respective terminal pin  36  toward the inner end  40  for about a quarter to a third of the distance that the terminal pin  36  protrudes from the dish-side surface  22  of the terminal  10  body portion  12 . In addition to providing a dielectric oversurface, the neck portions  48  increase the length of the hermetic seal  46  and better fixes the terminal pins  36  in place.  
         [0026]    Each terminal pin  36  has a shank portion  50  which passes through the terminal  10  body portion  12 . The plastic resin  44  fills the space between the inside wall  30  and the shank portion  50  of the terminal pin  36  to create the hermetic seal  46  and to bond the terminal pin  36  to the terminal  10  body portion  12 . Included in the shank portion  50  of the terminal pin  36  is a fuse section  52  which is encompassed by the seal  46  so as to be internal to the terminal  10  body portion  12 . The fuse section  52  has a necked down diameter from the remainder of the terminal pin  36 . The fuse section  52  is intended to open at currents in excess of a predetermined current-carrying capacity. Alternatively, the terminal pin  36  may be configured with a fuse that is external to the terminal  10  body portion  12 , such as a terminal pin that is disclosed in U.S. Pat. No. 5,017,740 to Honkomp et al., which is hereby incorporated into this disclosure by reference.  
         [0027]    The plastic resin  44 , molded to create the hermetic seal  46 , must possess the appropriate electrical and mechanical properties that are required for the application and operating environment in which the hermetic terminal assembly will be utilized. Typical minimum engineering material requirements may include:  
                                                   Physical Property   Requirement                           Hydrostatic Pressure   2250 psi           Hermeticity   1 × 10 −7  cc/sec He           Dielectric Voltage   Minimum 2500 V with &lt; 0.5 mA leakage           Insulation Resistance   &gt;10,000 MΩ at 500 Vdc           Operating Temperature   150° F. to 300° F.           Operating Environment   Mineral oil or refrigerant                      
 
         [0028]    A plastic resin that is suitable for use with the present invention is a moldable plastic resin which can provide the dielectric oversurface and hermetic seal  46  as disclosed. One such moldable plastic resin is polyphenyl sulfide (PPS), which is know under the tradename Ryton®. In addition, other moldable plastic resins that possess the necessary electrical and mechanical properties may also be used, including liquid crystalline polymer compositions (LCPs). An example of one such material is available commercially from DuPont under the tradename Zenite®.  
         [0029]    Further, there may be applications for the terminal assembly  10  of the present invention having less demanding operational or performance requirements, where a fully hermetic seal may not be not necessary, and a less-than-airtight, semi-hermetic seal or even non-hermetic seal is all that is required. It is fully contemplated that a terminal assembly  10  of the present invention may be applicable for use in such applications. Additional moldable plastic resins that may be suitable for use with this invention in such applications are polypropylenes, thermoplastic polyolefins, and polyvinylchlorides like Bakelite®.  
         [0030]    The terminal pin  36  is manufactured from an electrically conductive material, such as solid copper or steel. Alternatively, a bimetallic, copper core wire, having high electrical conductivity and possessing good hermetic bond characteristics with the plastic resin  44  may also be utilized.  
         [0031]    Referring now to FIGS. 3 and 4, a second embodiment of the hermetic terminal assembly  10 ′ of the present invention is illustrated. Elements and features common to both the first and second embodiments shown in the Figures are identified with like reference numerals.  
         [0032]    Included in the shank portion  50 ′ of the terminal pin  36 ′ is a section  54  having a scuffed surface  56  of increased surface roughness. Such a surface may be achieved by mechanical means, such as sanding or grit blasting the terminal pin  36 ′ or by other similar processes, or by chemical means. The scuffed surface  56  is included in terminal pin  36 ′ to create an increased surface area over which the plastic resin  44 ′ may contact and mechanically engage the terminal pin  36 ′ to increase the strength of the bond with the plastic resin  44 ′ and improve the hermeticity of the seal  46 ′. Although not shown in FIGS. 3 and 4, the terminal pin  36 ′ may also incorporate a fuse section, similar to that disclosed above. Such a fuse section could also include a scuffed surface  56 .  
         [0033]    Additionally, as described above, the plastic resin  44 ′ may also cover a portion of the projecting outer end  38 ′ of the terminal pin  36 ′ to define the air path between the respective terminal pins  36 ′ and/or the body portion  12 ′, as desired.  
         [0034]    Yet another embodiment of the hermetic terminal assembly  10 ″ of the present invention is shown in FIGS. 6 and 7. In this third embodiment, the terminal  10 ″ has a generally cup-shaped body portion  12 ″ with a side wall  16 ″ having an outwardly flaring rim  18 ″. The body portion does not have a generally continuous, closed bottom, but instead has only an inwardly extending peripheral lip  58  which extends from the side wall  16 ″ at the end opposite the rim  18 ″. The plastic resin  44 ″ is molded in and around the peripheral lip  58  and is thereby mechanically interlocked with the body portion  12 ″. As with those embodiments described above, the plastic resin  44 ″ may also be molded over a portion of the projecting outer end  38 ″ of the terminal pin  36 ″ to define the air path between the respective terminal pins  36 ′ and/or the body portion  12 ″, as desired.  
         [0035]    The terminal pin  36 ″ of the third embodiment of the present invention may also differ from the terminal pins  36  and  36 ′ disclosed above. As shown in FIG. 6, the shank portion  50 ″ of the terminal pin  36 ″ is a section  54 ′ forming a threaded surface  56 ′. Similar to that described above, the threaded surface  56 ′ is included in terminal pin  36 ″ to increase the surface area of the terminal pin  36 ″ over which the plastic resin  44 ″ may contact and mechanically engage the terminal pin  36 ″. The increased area of engagement correspondingly increases the strength of the bond between the terminal pin  36 ″ and the plastic resin  44 ″ and improves the hermeticity of the seal  46 ″. Again, the terminal pin  36 ″ may also incorporate a fuse section, similar to that disclosed with respect to FIGS. 1 and 2 above. Such a fuse section could also include a threaded surface  56 ′.  
         [0036]    A fourth embodiment of the terminal assembly  10 ′″ is depicted in FIGS. 8 and 9. Elements and features common to both the first and fourth embodiments shown in the Figures are identified with like reference numerals, and their detailed description will not be repeated. The fourth embodiment  10 ′″ includes a body portion  12 ′″ having a bottom portion  14 ′″, an opening  26 ′″ bounded by a wall  30 ′″, and a pin  36 ′″. The terminal assembly  10 ′″ includes a prefabricated retainer  70 . The retainer  70  may be pre-molded from dielectric plastic resin, such as Ryton® or Zenite, for example, and it may also made from other dielectric materials, including ceramics, such as, silicon nitride (Si 3 N 4 ), aluminum nitride (AIN), or zirconium oxide (ZrO 2 ).  
         [0037]    The retainer  70  includes at least one pin hole  72  and a countersunk portion  74  around the pin hole  72 . When the terminal assembly  10 ′″ includes more than one pin  36 ′″, the retainer  70  includes a corresponding number of pin holes  72 . The retainer  70  may also include a cavity  76  that communicates with the countersunk portion  74  of the pin hole  72 .  
         [0038]    Referring to the exploded view of the terminal assembly  10 ′″ during the manufacturing process and illustrated in FIG. 8, the terminal assembly  10 ′″ also includes a first epoxy ring  78  that is received in the countersunk portion  74  of the pin hole  72 . The epoxy ring  78  comprises a thermoset epoxy powder, which, when heated, cross links to cure and harden forming a strong bond with any surface with which it is in contact. The epoxy may be an electrically insulating epoxy, such as one the Corvel® epoxies, available from Rohm and Haas Powder Coatings, Flying Hills, Pa., or any other epoxy possessing similar characteristics. When cured, the epoxy provides a hard coverage material with electrical insulation properties, resistance to chemicals and low moisture permeability.  
         [0039]    The body portion  12 ′″ is placed over the retainer  70  and the first epoxy ring  78  such that the walls  30 ′″ of the openings  26 ′″ of the body portion  12 ′″ are received in and surrounded by the corresponding countersunk portions  74  of the pin holes  72 . The countersunk portions  74  are, accordingly, sleeve-like and appropriately sized and shaped to receive the walls  30 ′″. A second epoxy ring  80  is placed over the openings  26 ′″ on the exterior surface  24 ′″ of the bottom  14 ′″ of the body portion  12 ′″. The second epoxy ring  80  may be received in a corresponding countersunk portion  82  of the body portion  12 ′″.  
         [0040]    The terminal assembly  10 ′″ is processed in an oven or other heating chamber to cure the epoxy. For a Corvel®) 17000 Series epoxy, for example, curing may take place at a heating temperature of 180° C. for 40 minutes. It will be appreciated that the curing temperature and duration may vary depending on the characteristics of the particular epoxy that is used. During heating, the epoxy rings  78  and  80  flow into and fill the space created between the walls  30 ′″ of the body portion  12 ′″, the pin  36 ′″, the pin hole  72  and the countersunk portion  74  of the pin hole  72 . Moreover, overflow epoxy is received in the cavity  76 . Thus, upon curing, the hardened epoxy of the rings  78  and  80  provides a hermetic seal  46 ′″ surrounding each pin  36 ′″. For applications in which full hermeticity is not required, other epoxies providing lesser hermeticity may also be used.  
         [0041]    It will be appreciated that the thickness and size of the epoxy rings  78 ,  80  may be adjusted to provide a sufficient volume of epoxy such that the cured epoxy completely fills the void and forms an airtight seal  46 ′″ between the terminal pin  36 ′″ and the body portion  12 ′″ and such that leakage through the assembly  10 ′″, by way of the terminal pins  36 ′″, is prevented. As shown in FIG. 9, the seal  46 ′″ that is formed from the cured epoxy completely surrounds the portion of the terminal pin  36 ′″ that is bounded by the body portion  12 ′″ and the retainer  70 . In the embodiments in which an overflow cavity  76  is included, the cavity  76  is also sealed with the cured epoxy creating another surface  84  that bonds the retainer  70  with the interior surface  22 ′″ of the bottom  14 ′″ of the body portion  12 ′″ and forms a mechanical and insulating interlock.  
         [0042]    Is should be noted the amount of the epoxy that is available from the epoxy rings  78  and  80  is determined to completely fill the space between the pins  36 ′″ and the body portion  12 ′″ and also provide a mechanical interlock after the epoxy is cured. This amount is determined by taking into account that the thermal expansion characteristics of the epoxy and the metal of the body portion  12 ′″ are very different. The Corvell® 17000 Series epoxy, for example, has a coefficient of thermal expansion of 340×10 −7  in./in./° C., which may be 2.5 or more higher than the coefficient of thermal expansion of the metallic components (the body portion  12 ′″ and pins  36 ′″), which is typically about 135×10 −7  in./in./° C. Therefore, after curing, the epoxy that forms the seal  46 ′″ will shrink to a much greater extent that the surrounding metallic components. A sufficient amount of epoxy is provided to take into account the shrinkage effect, so that the seal  46 ′″ completely fills the space between the body portion  12 ′″ and the pins  36 ′″ and forms a mechanical interlock, as shown in FIG. 9.  
         [0043]    The properties of the seal  46 ′″ have been tested experimentally. A summary of representative tests conditions and corresponding results follows:  
                                                   Physical Property   Typical Measurement                           Pressure Test   5600 +/− 500 psi           Hermeticity   1 × 10 −7  atm cc/sec           Maximum Voltage   4700 V           Insulation Resistance   &gt;10,000 MD           Heat Shock   371° C.           Thermal cycling   120° C. to −25° C. for one week           Cryogenic test   −65° C. five cycles                      
 
         [0044]    Referring to FIG. 8, the terminal assembly  10 ′″ may be manufactured using an assembly board  90  that includes a plurality of pin fixtures  92  for supporting the terminal pins  36 ′″ during assembly. First, the terminal pins  36 ′″ are inserted into the fixtures  92  of the assembly board  90 . Then, the retainer  70  is placed over the terminal pins  36 ′″. The first epoxy rings  78  are placed in the countersunk portions  74  of the retainer  70  over the terminal pins  36 ′″. Then, the body portion  12 ′″ is placed over retainer  70  such that the walls  30 ′″ of the openings  26 ′″ of the body portion  12 ′″ are received into the countersunk portions  74  of the retainer  70 . Finally, the second epoxy ring  80  is placed over the body portion  12 ′″ and into a countersunk portion  82  of the body portion  12 ′″. The assembly board  90  with the terminal assemblies  10 ′″ thereon may then be transported to an oven for curing.  
         [0045]    As discussed above, the retainer  70  can be prefabricated from a variety of dielectric materials, including ceramic, plastic resins, or Ryton®), which also have the advantage not to stick on the pin fixtures  92 , which may be made of ceramic or metallic material. Thus, the terminal assembly  10 ′″ may be easily removed from the pin fixtures  92  after curing. It will be, therefore, appreciated that prefabrication of the retainer  70  contributes to ease of assembly and manufacturability. Furthermore, the retainer  70  adds strength to the terminal assembly  10 ′″ and provides a dielectric oversurface on the pins and body. Similarly, the use of the epoxy rings  78 ,  80  further simplifies the assembly and manufacturing process, while providing a seal  46 ′″ that has impressive hermeticity properties.  
         [0046]    Referring again to FIG. 9, at least a portion of the outer surface of the terminal assembly  10 ′″ may be coated with a thin layer  94  of plastic resin or other electrically insulating resin to provide additional electrical and chemical resistance. Additionally, an adhesive  96  may be applied to the inner surface  22 ′″ of the bottom  14 ′″ and/or other surfaces of the body portion  12 ′″ to enhance the bond between the retainer  70  and the body portion  12 ′″. The adhesive  96  may brushed or sprayed, and it may also be applied to the retainer  70  and the pins  36 ′″ at all their common contact surfaces. The Scotch-Grip™ rubber and Gasket Adhesive manufactured by 3M of St. Paul, Minn., may be used to prepare the adhesive  96 , for example. The adhesive  96  may also be used with the in situ plastic resin  44 ,  44 ′,  44 ″ of the first, second and third terminal assembly embodiments  10 , 10 ′,  10 ″.  
         [0047]    In a variation of the fourth embodiment  10 ′″, the retainer  70  may be omitted, while either retaining or omitting the plastic resin layer  94  to cover the body portion  12 ′″, after the epoxy rings  78 ,  80  are cured sealing the opening  26 ′″ between the body portion  12 ′″ and the pin  26 ′″, depending on the particular application.  
         [0048]    Of course, any of the features of the body portions  12 ,  12 ′,  12 ″,  12 ′″ or terminal pins  36 ,  36 ′,  36 ″,  36 ′″ may be combined in various ways to create a hermetic terminal assembly within the contemplation of the present invention.  
         [0049]    While the invention has been disclosed and described in it various embodiments, it is understood that the invention is capable of modification without departing from the spirit and scope of the invention as set forth in the appended claims.