Abstract:
This invention teaches methods of making a hermetic terminal assembly comprising the steps of: inserting temporary stops, shims and jigs on the bottom face of a terminal assembly thereby blocking assembly core open passageways; mounting the terminal assembly inside a vacuum chamber using a temporary assembly perimeter seal and flange or threaded assembly interfaces; mixing a seal admixture and hardener in a mixer conveyor to form a polymer seal material; conveying the polymer seal material into a polymer reservoir; feeding the polymer seal material from the reservoir through a polymer outlet valve and at least one polymer outlet tube into the terminal assembly core thereby filling interstitial spaces in the core adjacent to service conduits, temporary stop, and the terminal assembly casing; drying the polymer seal material at room temperature thereby hermetically sealing the core of the terminal assembly; removing the terminal assembly from the vacuum chamber, and; removing the temporary stops, shims.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of U.S. Provisional Application 60/472,545, filed May 22, 2003 and Provisional Application 60/472,543, filed May 22, 2003, both herein incorporated by reference in their entirety. This application is also related to U.S. application Ser. No. 10/716,060, filed Nov. 18, 2003 and U.S. patent application Ser. No. 10/837,993, filed the same day as this application, entitled “Hermetic Terminal Assembly for Hermetic Inverters/Converters”, both herein incorporated by reference in their entirety. 

   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
   This invention was made with Government support under Contract No. DE-AC05-00OR22725 awarded to UT-Battelle, LLC, by the U.S. Department of Energy. The Government has certain rights in this invention. 

   TECHNICAL FIELD 
   The field of the invention relates to methods for making seal materials in hermetic terminal assemblies and more particularly to vacuum pressure casting of the seal material which produces a more durable hermetic terminal assembly for hermetic inverters/converters using refrigerant for cooling. 
   DESCRIPTION OF THE BACKGROUND ART 
   The reliability of the methods of making hermetically sealed terminal assemblies used in compressors is well recognized. Terminal assemblies made by the Vitrus Company, Amphenol, and Ceramaseal are typical examples of compressor assemblies made with standard methods. Examples of compressor assemblies are also disclosed in U.S. Pat. No. 4,584,433, issued to B. Bowsky, et al. on Apr. 22, 1986; U.S. Pat. No. 5,471,015, issued to F. Dieter Paterek, et al. On Nov. 28, 1995. These two aforementioned patents were further concerned with conductive pin fusing and with pin design, respectively. U.S. Pat. No. 4,580,003, issued to B. Bowsky et al. on Apr. 1, 1986 teaches an aperture with flattened neck portion. U.S. Pat. No. 4,584,333, issued to B. Bowsky et. al. on Apr. 22, 1986, teaches the relative coefficients of expansion and softening point temperatures in U.S. Pat. No. 5,471,015, issued to F. D. Paterek et. al. on Nov. 28, 1995. U.S. Pat. No. 6,509,525 issued to Honkomp et al. on Jan. 21, 2003 further teaches an arc-resistant assembly. 
   The electrical current level and differential pressure experienced by compressor terminal assemblies is generally less than hermetic refrigerant container terminal assemblies that contain power electronic inverter/converter components. Hermetic terminal assemblies for inverters/converters require the longitudinal and radial coefficients of thermal expansions of the conductors to be compatible with those of the seal material (glass, ceramic, polymer, or other equivalent material). Furthermore, the chosen seal material between the terminal assembly and the material of the hermetic container must be compatible. Methods for making terminal assemblies used for the hermetic inverters/converters are distinct from the available hermetic terminal/connector assembly methods because: 
   (1) The electrical rating of the hermetic inverter/converter is generally much higher than that of a hermetic compressor. A 50 kW motor requires an inverter/converter that roughly corresponds to 1150-amp 3-phase line current for a 42-volt DC-link, and to 120-amp line current for a 400-volt DC-link. 
   (2) The DC-link bus, signal leads, and refrigerant tubing are extra items that differ from the AC electric power of a compressor. The DC-link-current magnitudes are also high. They are roughly 1400 amp and 150 amp, respectively, for the above two cases. 
   (3) The DC-link requires a low inductance circuit. 
   (4) There are minimums of six gate signal inputs that require low interference and short connections. 
   (5) Other additional diagnostic signals may also need to be included. 
   SUMMARY OF THE INVENTION 
   Power electronic dies in inverters/converters, such as those of the IGBT or MOSFET, have little thermal capacity and a critical junction temperature and can be located in high pressure regions of hermetic containers. The electrolytic capacitors in the same inverter/converter have better thermal capacity but should not be mounted in high pressure regions of hermetic containers to prevent contamination from sipping into the gap material between the positive and negative foils. Electrical and mechanical services for these power electronic devices placed inside hermetic containers require specialized seal materials and methods for making the terminal assemblies at the service conduit penetrations. 
   The polymer seal material can be hardened either at room temperature or at a higher baking temperature depending on the admixture of the polymer seal material. The baking step provides additional handling time before the polymer seal material sets. This invention teaches both hardening methods. 
     FIGS. 1   a  and  1   b  show embodiments for a method of vacuum pressure casting seal material used in hermetic terminal assemblies.  FIG. 2  shows a hermetic container, using the terminal assembly, which can be made of steel or other magnetic or non-magnetic materials as long as these materials meet the pressure and sealing requirements. There are two zones inside the hermetic container; one is the liquid refrigerant zone and the other is the vapor refrigerant zone. The liquid refrigerant zone is good for cooling the power electronic dies and any other critical components. The vapor refrigerant zone is good for cooling the less critical components having relatively higher thermal capacities. The zone outside the hermetic container is cooled but without a high pressure. It has an ambient pressure. This zone can be used to cool the components such as the electrolytic capacitors. A thermally isolated housing is separating this zone from the ambient. The hermetic container and the thermally isolated housing with metal mesh (or foil) can be used for EMI shielding. A need exists for a method of making the hermetic terminal assemblies that provide electrical and mechanical services to the inverter/converter. 
   The hermetic terminal assembly method in this invention provides for routing AC power terminals, DC-link bus, signal leads, refrigerant tubing, and any additional wires for simplifying the manufacturing process and reducing the cost. 
     FIG. 3  shows an alternate embodiment of the hermetic inverter/converter with the terminal assembly housing electrical connections only. The liquid refrigerant supply tube comes from the top of the hermetic container, and mates to a distributor built into the terminal assembly, fitting in as the terminal assembly is inserted. 
   This invention teaches methods of making a hermetic terminal assembly comprising the steps of: inserting temporary stops, shims and jigs on the bottom face of a terminal assembly thereby blocking assembly core open passageways; mounting the terminal assembly inside a vacuum chamber using a temporary assembly perimeter seal and flange or threaded assembly interfaces; mixing a seal admixture and hardener in a mixer conveyor to form a polymer seal material; conveying the polymer seal material into a polymer reservoir; feeding the polymer seal material from the reservoir through a polymer outlet valve and at least one polymer outlet tube into the terminal assembly core thereby filling interstitial spaces in the core adjacent to service conduits, temporary stop, and the terminal assembly casing; drying the polymer seal material at room temperature thereby hermetically sealing the core of the terminal assembly; removing the terminal assembly from the vacuum chamber, and; removing the temporary stops, shims and jigs. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1   a  shows a preferred embodiment for a method of vacuum pressure casting seal material used in hermetic terminal assemblies wherein the polymer seal material is dryed at room temperature. 
       FIG. 1   b  shows another embodiment for a method of vacuum pressure casting seal material used in hermetic terminal assemblies wherein the polymer seal material is cured at higher than room temperature. 
       FIG. 2  shows an example of a hermetic inverter/converter with terminal assembly of electrical connections and tubing. 
       FIG. 3  shows an example of a hermetic inverter/converter with electrical only terminal assembly. 
       FIG. 4  shows the seal diameter, d, and shearing stress on seal material. 
       FIG. 5   a  is a side view of an embodiment of the hermetic terminal assembly. 
       FIG. 5   b  is a front view of an embodiment of the hermetic terminal assembly. 
       FIG. 6  shows another embodiment of the hermetic terminal assembly using tapered or bent shapes for stress modification. 
       FIG. 7  is an example of flange O-ring mounting for the terminal assembly. 
       FIG. 8  is an example of threaded O-ring mounting for the terminal assembly. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1   a  shows an embodiment for a method of vacuum pressure casting seal material used in hermetic terminal assemblies wherein the polymer seal material is cured at room temperature. The pressure inside the vacuum chamber  96  is controlled by two control valves  99  to achieve either atmospheric or higher pressure  98  or vacuum  97 . The bottom face of the terminal assembly  86  uses a temporary stop  82  of wax or an equivalent substance, such as gypsum or silicon rubber that can be removed after the polymer seal material is cured, to contain the polymer seal material  85  during manufacturing. Shims or jigs  84  are used to maintain alignment of the service conduits during manufacturing. If the terminal assembly  86  contains refrigerant tubes, the lower ends of the tubes are stopped with temporary plugs  83  or other equivalent means. The vacuum chamber  96  is placed over the terminal assembly  86  with O-ring type temporary assembly perimeter seal  80  plus flange or threaded interfaces  89  to produce a vacuum seal between the terminal assembly  86  and the vacuum chamber  96 . The seal admixture  93  comprising a mixture of at least one polymer and at least one material selected from the group consisting of graphite fibers, ceramic powder, glass powder, and glass fibers is then mixed with the hardener  92  before being delivered to the polymer reservoir  91  through a mixer conveyor  94 . To prevent premature hardening, the seal admixture  93  is mixed with the hardener  92  immediately before feeding. A polymer outlet valve  95  that leads to the inside of the vacuum chamber  96  controls the flow of the polymer. Multiple polymer outlet tubes  87  can be used as an option. The setup can be mounted on a shaker  81  to produce vibration during casting. An optional control arm  88  that moves the polymer outlet tube can be incorporated to the vacuum chamber  96  for controlling the polymer distribution. The polymer tubing  87  and polymer outlet valve  95  can be disposable for easy cleaning. After the seal material  85  is placed in the terminal assembly  86 , the polymer outlet valve  95  is closed. Subsequently, the control valves  99  can alternate the pressure in the vacuum chamber  96  from vacuum  97  to pressure  98  for exerting settling forces on the seal material  85  thereby eliminating voids in the seal material  85  caused by, for example, vacuum or air pockets. After the seal material  85  is hardened, the temporary stop  82  and the shims or jigs  84  are removed. 
     FIG. 1   b  shows an embodiment for a method of vacuum pressure casting seal material of a higher-than-room temperature cured polymer mix used in hermetic terminal assemblies. The pressure inside the vacuum chamber  96  is controlled by two control valves  99  to achieve either a pressure (atmospheric or higher)  98  or vacuum  97 . The bottom face of the terminal assembly  86  uses a temporary stop  82  of gypsum or an equivalent substance that can withstand the baking temperature and be taken away after the polymer is cured to contain the polymer seal material  85  during manufacturing. Shims or jigs  84  are used to maintain alignment of the service conduits during manufacturing. If the terminal assembly  86  contains refrigerant tubes, the lower ends of the tubes are stopped with temporary plugs  83  or other equivalent means. The vacuum chamber  96  is placed over the terminal assembly  86  with O-ring type temporary assembly perimeter seal  80  plus flange or threaded interfaces  89  to produce a vacuum seal between the terminal assembly  86  and the vacuum chamber  96 . The seal admixture comprising at least one polymer and at least one thermal expansion controlling material selected from the group consisting of glass powder, ceramic powder, glass fibers, and graphite fibers, is mixed with a higher-temperature hardener to form a seal premixture  90  before being delivered to the polymer reservoir  91 . A polymer outlet valve  95  leading to the inside of the vacuum chamber  96  controls the flow of the premixture  90 . Multiple polymer outlet tubes  87  can be used as an option. The setup can be mounted on an optional shaker  81  to produce vibration during casting. An optional control arm  88  that moves the polymer outlet tube can be incorporated into the vacuum chamber  96  for controlling the polymer distribution. The polymer tubing  87  and polymer outlet valve  95  can be reused because, without going through a baking process, the polymer in the tubing  87  and polymer outlet valve  95  is not hardened. After the seal premixture  90  is placed in the terminal, the polymer outlet valve  98  is closed. Subsequently, the control valves  99  can alternate the pressure in the vacuum chamber  96  from vacuum  97  to pressure  98  for exerting settling forces on the seal material  85  thereby eliminating voids in the seal material  85  caused by, for example, vacuum or air pockets. The terminal  86  is then placed in an oven (not shown) for curing the seal material  85 . After being properly baked thereby hardening the seal material  85 , the temporary stop  82  and the shims or jigs  84  are removed. 
     FIG. 2  shows a preferred arrangement of the hermetically sealed terminal assembly  1 , manufactured using vacuum pressure casting of this invention, mounted in a multi-zone hermetic inverter/converter cooling chamber  40 . The hermetic container  2  can be made of steel, magnetic material, non-magnetic material, metal, and non-metal pressure vessel materials that meet the pressure, temperature and sealing requirements of the refrigerant and the EMI shielding requirements of the electronic components. A joint seam  6  is integral with the walls of the hermetic container  2 . The hermetic container  2  has a sealed terminal assembly  1  having service conduits  3  selected from the group consisting of AC phase conductors, DC link conductors, gate signal leads, diagnostic signal wires, and refrigerant tubing. The hermetic container  2  also has at least one vapor refrigerant outlet  5 . There are two zones inside the hermetic container  2 ; one is the liquid refrigerant zone  9  and the other is the vapor refrigerant zone  10 . The liquid refrigerant zone  9  is suitable for cooling the power electronic dies and other critical components using direct liquid refrigerant contact cooling. The vapor refrigerant zone  10  is suitable for cooling the less critical, high thermal capacity components using direct vapor refrigerant contact cooling. The ambient cooling zone  8 , outside the hermetic container  2 , provides cooled ambient pressure conditions for cooling components such as the electrolytic capacitors at atmospheric pressure. A thermally isolated housing  4  isolates the ambient cooling zone  8  from the ambient and creates a cooled interstitial space between the refrigerant filled hermetic container  2  and the thermally isolated housing  4 . The interstitial space is the ambient cooling zone  8  that is cooled by indirect heat transfer to the refrigerant through the refrigerant filled hermetic container  2 . The hermetic container  2  and the thermally isolated housing  4  with metal mesh (or foil) can be used for EMI shielding. 
     FIG. 3  shows another preferred arrangement of the hermetically sealed terminal assembly  1  with a liquid refrigerant supply tube  7  routed from the top of the hermetic container  2  and mating to a distributor (not shown) built into the terminal assembly  1 . The terminal assembly  1  is mounted in a multi-zone hermetic inverter/converter cooling chamber  40 . The hermetic container  2  can be made of steel, magnetic material, non-magnetic material, metal, and non-metal pressure vessel materials that meet the pressure, temperature and sealing requirements of the refrigerant and the EMI shielding requirements of the electronic components. A joint seam  6  is integral with the walls of the hermetic container  2 . The sealed terminal assembly  1  has service conduits  11  selected from the group consisting of AC phase conductors, DC link conductors, gate signal leads, and diagnostic signal wires. The hermetic container  2  also has at least one vapor refrigerant outlet  5 . There are two zones inside the hermetic container  2 ; one is the liquid refrigerant zone  9  and the other is the vapor refrigerant zone  10 . The liquid refrigerant zone  9  is suitable for cooling the power electronic dies and other critical components using direct liquid refrigerant contact cooling. The vapor refrigerant zone  10  is suitable for cooling the less critical, high thermal capacity components using direct vapor refrigerant contact cooling. The ambient cooling zone  8 , outside the hermetic container  2 , provides cooled ambient pressure conditions for cooling components such as the electrolytic capacitors at atmospheric pressure. A thermally isolated housing  4  isolates the ambient cooling zone  8  from the ambient and creates a cooled interstitial space between the refrigerant filled hermetic container  2  and the thermally isolated housing  4 . The interstitial space is the ambient cooling zone  8  that is cooled by indirect heat transfer to the refrigerant through the refrigerant filled hermetic container  2 . The hermetic container  2  and the thermally isolated housing  4  with metal mesh (or foil) can be used for EMI shielding. 
     FIG. 4  shows the shear stress  31  imposed by force  33  on the seal material  32  of a sealed hermetic terminal with an outer diameter, d, with the seal material  32  adhering to the terminal casing inner wall. Under a given pressure difference, ΔP, between the inside and the outside of the hermetic container, the force  33  pushing the seal material towards outside of the container is 
               π   ·     d   2       4     ⁢   Δ   ⁢           ⁢     P   .           
This force is countered by the seal material  32  having an interfacing periphery area of π·d·L. The shearing stress  31  on the seal material  32  is the force divided by the peripheral area, which yields:
 
             Shearing   ⁢           ⁢   stress     =             π   ·     d   2       4     ⁢   Δ   ⁢           ⁢   P       π   ·   d   ·   L       =         d   ·   Δ     ⁢           ⁢   P       4   ·   L               
Under a given pressure difference ΔP and seal length L, the shearing stress of the seal material goes up in proportion to the seal diameter d. Therefore, for a relatively large seal diameter we can transfer part of the shearing stress  31  to a compression stress for the seal material  32  using service conduits with tapered shapes.
 
     FIG. 5   a  is a side view of an embodiment of the hermetic terminal assembly  40  mounted in a hermetic container  41 . The terminal assembly casing  42  encompasses a collection of service conduits identified as; negative DC link conductor  43 , positive DC link conductor  44 , refrigerant tubing  45 , AC phase conductor  46 , diagnostic signal wires  47 , gate signal leads  48 , and seal material  49 .  FIG. 4   b  is a front view of the hermetic terminal assembly  40  showing the same components. 
     FIGS. 5   a  and  5   b  show an example of the hermetic terminal assembly made using this invention method. The terminal can be used in conjunction with the cascaded die mounting technology described in U.S. patent application Ser. No. 10/716,060, filed Nov. 18, 2003. The routed services are shown, but not limited to, AC phase conductors, DC link conductors, gate signal leads, diagnostic signal wires, and refrigerant tubing. These services are routed into the hermetic container through the hermetic terminal assembly that is mounted to the container using a flange or threaded interfacing piece. A seal material is injected into the gaps and space among the service conduits and the inner wall of the terminal assembly casing. 
   The seal material is made of material that can be injected or poured and has a thermal expansion coefficient similar to that of the service conduits that are contacting the seal materials. The mechanical strength and the dielectric property of the seal material are sufficiently high for the temperature range that the terminal may encounter. As an example, the seal material can be a polymer containing graphite fibers for matching the thermal expansion coefficient of the service conduits and for reinforcing the mechanical strength of the seal material. 
   The DC link conductors can be arranged to have as much parallel arrangement as possible for lowering the inductance of the DC bus. The refrigerant tubing can also go through the terminal for the purpose of reducing the number of individual terminals. 
   Another embodiment of the terminal assembly made with this invention method, shown in  FIG. 3 , moves the refrigerant tubing  45  penetrations from the hermetic terminal assembly  40  to the top of the hermetic container  41  thereby supplying refrigerant to a refrigerant distributor (not shown) embedded in the terminal assembly  40 . 
     FIG. 6  is a side view of an embodiment of the hermetic terminal assembly mounted in a hermetic container  51  that transfers a portion of the seal material  59  shearing stress to a compression stress using service conduits with tapered and bent shapes. The terminal assembly casing  52  encompasses a collection of service conduits identified as; negative DC link conductor  53 , positive DC link conductor  54 , refrigerant tubing  55 , AC phase conductor  56 , diagnostic signal wires  57 , gate signal leads  58 , and seal material  59 . 
     FIG. 7  is a mounting arrangement for the hermetic terminal assembly  61  where a terminal flange  64 , housing the terminal assembly  61 , is bolted to the hermetic container  62  with an O-ring seal  65  at the mating point. An optional boss  63  is used to provide bolt hole threading. 
     FIG. 8  is a mounting arrangement for the hermetic terminal assembly  71  where a threaded terminal coupling  74 , housing the terminal assembly  71 , is threaded to the hermetic container  72  with an O-ring seal  75  at the mating point. 
   Some of the distinctive features of the assembly include: 
   1. A single terminal assembly to bring services that include but are not limited to the AC phase conductors, DC link conductors, gate signal leads, diagnostic signal wires, and refrigerant tubing are brought into the hermetic container through a flange or threaded interfacing piece.
 
2. The terminal assembly can be built with only electrical connections as shown in  FIG. 2 .
 
3. The seal material can be injected or poured and has a thermal expansion coefficient similar to that of the materials of the service conduits that are contacting the seal materials. The mechanical strength and the dielectric property of the seal material should be sufficiently high for the temperature range that the terminal may encounter. As an example, the seal material can be a polymer and graphite fibers mixture for matching the thermal expansion coefficient of the contacting materials and for reinforcing the mechanical strength of the seal material.
 
5. For a relatively large seal diameter part of the shearing stress can optionally be converted to a compression stress for the seal material using tapered or bent service conduits.
 
6. The DC link conductors can be in an axially aligned arrangement for lowering the inductance of the DC bus.
 
7. The refrigerant tubing can penetrate through the terminal for the purpose of reducing the number of individual terminals.
 
8. The gate-signal service conduit can feed the gate-drive circuit inside the hermetic container or outside of the container in the ambient pressure cooling zone.
 
9. The diagnostic-signal service conduit for the liquid refrigerant level, the die temperatures, over-currents, and over-voltages can also penetrate through the terminal assembly.
 
10. Additional leads can also be brought out from the terminal assembly if needed.
 
11. Either the flange with O-ring seal (or gasket) or the threaded interface with O-ring seal (or gasket) can be selected for mounting the terminal assembly.
 
   The hermetic terminal assembly has potential for use in numerous industrial and military applications. Applications requiring high power and high differential pressure can be simplified using a total system approach to their interconnections. It is likely that a reduction in size and costs may be achieved. Systems that can benefit in this manner include: Automotive—future hybrid and fuel cell inverter and converter power requirements; Avionics and space—high power and differential pressures requirements offer unique challenges in hermetic terminal requirements, system approaches lowering volume and size can open up new possibilities for technical advancements. These advantages also pertain to and naval and marine underwater applications such as oil drilling and deep sea mining and exploration; Medical usages involving power requirements utilizing cryogenic, nuclear and laser techniques; Semiconductor processing requirements which currently require high vacuum systems for device fabrication. Uses can be expanded to also include more compact, lighter weight air conditioning and refrigeration compressor systems. 
   While there has been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications can be made therein without departing from the scope.