Patent Publication Number: US-7581958-B2

Title: High voltage heater termination

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of U.S. Provisional Application No. 60/765,290, filed on Feb. 3, 2006. The disclosure of the above application is incorporated herein by reference. 

   FIELD 
   The present disclosure relates generally to electric heaters, and more particularly to heater termination structures for connecting the electric heaters to power supplies. 
   BACKGROUND 
   The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
   Some forms of electric heaters generally include a substrate, a resistive heating element embedded within or disposed proximate the substrate, and a protective layer disposed over the resistive heating element. The resistive heating element is commonly terminated in a pair of terminal pads, which are not covered by the protective layer, for connecting a pair of lead wires extending from a power source. The connection between the terminal pads and the lead wires is generally insulated from the outside environment to prevent against accidental discharge of the voltage applied by the power source. Conventional termination structures, however, often include numerous parts that define interfaces with enclosed air gaps. Air gaps pose serious arcing problems, particularly when the electric heater is used in a semiconductor manufacturing process, where a relatively high voltage is applied in a vacuum environment. 
   Generally, arcing is a result of an electrical breakdown that occurs when a voltage applied across an air gap exceeds a threshold breakdown field for the air. Under this high electric field, free electrons in the air gap produce ionizing collisions with air molecules, and thus the air gap becomes an electric current path in addition to a designated electric current path within a conductive element. Unfortunately, arcing often damages the insulation of the termination structure and may lead to malfunction of the termination structure and the overall heater. 
   Arcing from electrical terminations across an air gap to a conductive surface typically occurs when the electric heater is operated above 340 peak voltage and is dependent upon both the molecular density of the air and the span of the air gap over which the voltage gradient exists. Because the breakdown voltage for a typical air gap in a vacuum chamber initially decreases as the air pressure is reduced below 1 atmosphere, arcing is thus more likely to occur to or from a terminal of an energized heater during evacuation or filling. The conventional termination structure for an electric heater has proven to be especially susceptible to arcing in this vacuum environment, for example, when the electric heater is used in a semiconductor manufacturing process. 
   SUMMARY 
   In one preferred form, a connector for connecting a lead wire to a terminal pad is provided that comprises a dielectric enclosure surrounding the terminal pad and defining a cavity open to the terminal pad. The dielectric enclosure comprises an upper element and a lower element in contact with the upper element along a contour-matched interface. A conductive plug is disposed within the cavity for electrically connecting the terminal pad to the lead wire. 
   In another preferred form, a dielectric enclosure is provided that defines a cavity open to a first exterior surface and a channel communicating the cavity to at least one second exterior surface. The cavity and the channel provide a conduit for an electrical connection, wherein the dielectric enclosure is adapted to receive a terminal pad within the cavity proximate the first exterior surface and to receive a lead wire within the channel proximate the second exterior surface. 
   In yet another preferred form, a connector assembly is provided that comprises a first element and a second element in contact with the first element along a contour-matched interface. The first element and the second element each comprising a recess and a groove, the recesses cooperatively forming a cavity and the grooves cooperatively forming a channel communicating the cavity to exterior surfaces of the first element and the second element. The connector assembly further comprises a conductive plug disposed within the cavity and adapted for engaging a lead wire and a terminal pad. 
   In still another preferred form, a heater is provided that comprises a resistive heating element, a terminal pad connected to the resistive heating element, and a connector for connecting the terminal pad to a lead wire. The connector comprises a first element and a second element in contact with the first element along a contour-matched interface. The first element and the second element each comprise a recess and a groove, the recesses cooperatively forming a cavity and the grooves cooperatively forming a channel communicating the cavity to exterior surfaces of the first element and the second element. Additionally, a conductive plug is disposed within the cavity and adapted for engaging the lead wire and the terminal pad. 
   Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 

   
     DRAWINGS 
     The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
       FIG. 1  is a top view of a substrate having a resistive heating element and terminal pads connected to the resistive heating element in accordance with the teachings of the present disclosure; 
       FIG. 2  is a cross sectional view, taken along line  2 - 2  of  FIG. 1 , illustrating terminal pads in greater detail in accordance with the teachings of the present disclosure; 
       FIG. 3  is a perspective view of a connector assembly constructed in accordance with the teachings of the present disclosure; 
       FIG. 4  is a perspective view illustrating an exploded connector assembly and a second, assembled, connector assembly constructed in accordance with the teachings of the present disclosure; 
       FIG. 5   a  is a perspective view of the top of an upper element of a dielectric enclosure constructed in accordance with the teachings of the present disclosure; 
       FIG. 5   b  is a perspective view of the bottom of the upper element of a dielectric enclosure constructed in accordance with the teachings of the present disclosure; 
       FIG. 6   a  is a perspective view of the top of a lower element of a dielectric enclosure constructed in accordance with the teachings of the present disclosure; 
       FIG. 6   b  is a perspective view of the bottom of the lower element of a dielectric enclosure constructed in accordance with the teachings of the present disclosure; 
       FIG. 7  is a top view of the connector assembly in accordance with the teachings of the present disclosure; 
       FIG. 8  is a cross-sectional view, taken along line  8 - 8  of  FIG. 7 , of the connector assembly in accordance with the teachings of the present disclosure; 
       FIG. 9  is a cross-sectional view, taken along line  9 - 9  of  FIG. 7 , of the connector assembly in accordance with the teachings of the present disclosure; 
       FIG. 10  is a perspective view of a conductive plug constructed in accordance with the teachings of the present disclosure; 
       FIG. 11   a  is a top view of an alternate embodiment of the conductive plug having an alignment feature and constructed in accordance with the teachings of the present disclosure; 
       FIG. 11   b  is a top view of another alternate embodiment of the conductive plug having an alignment feature and constructed in accordance with the teachings of the present disclosure; 
       FIG. 12  is a perspective view of a spring constructed in accordance with the teachings of the present disclosure; and 
       FIG. 13  is a perspective view of an alternate form of a clamping device constructed in accordance with the teachings of the present disclosure. 
   

   Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
   DETAILED DESCRIPTION 
   The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
   Referring to  FIGS. 1 and 2 , a heater constructed in accordance with the teachings of the present disclosure is illustrated and generally indicated by reference numeral  10 . The heater  10  includes a substrate  12 , a resistive heating element  14  disposed on the substrate  12 , and a pair of terminal pads  16  for connecting the resistive heating element  14  to a pair of lead wires  18 . A protective layer  19  is preferably disposed over the resistive heating element  14  for insulation and protection from the outside environment. The resistive heating element  14  can be, by way of example, a resistive wire or a resistive film, among others. One example of such a film resistive heating element  14  is disclosed in U.S. Pat. No. 6,037,574, titled “Quartz Substrate Heater,” which is commonly assigned with the present application and the contents of which are incorporated by reference herein in their entirety. 
   Referring now to  FIGS. 3 and 4 , a connector assembly in accordance with one form of the present disclosure is illustrated and generally indicated by reference numeral  20 . Generally, the connector assembly  20  (also referred to herein as a “connector”) is adapted for placement onto the substrate  12  or a heater  10 , and more specifically onto the protective layer  19  and over the terminal pads  16 , for securing and protecting the connection between the terminal pads  16  and the lead wires  18  as previously illustrated and described. 
   The connector assembly  20  generally includes a dielectric enclosure  22  and a conductive plug  24  disposed therein. As shown, the dielectric enclosure  22  includes an upper element  28  and a lower element  30 , wherein the lower element  30  is in contact with the upper element  28  along a contour-matched interface  32 . The contour-matched interface  32  is preferably defined by contact surfaces  34  and  35 , of the upper element  28  and lower element  30  respectively, which are substantially flat in the illustrated embodiment and in intimate contact with each other. As used herein, the term “contour-matched”should be construed to mean that the mating surfaces of the upper element  28  and the lower element  30  are matched, or their mating surface geometry is substantially identical, such that intimate contact between the upper element  28  and the lower element  30  is achieved. Additionally, the term “contour-matched” shall be construed to include mating surface geometry that is not only flat as illustrated herein, but mating surface geometry that is otherwise curved, flat, and/or a combination of curved and flat. Moreover, the mating surfaces may be oriented other than as shown with the upper element  28  and the lower element  30 , for example, with a vertical or angled orientation rather than the relatively horizontal orientation as shown and described. As such, the dielectric enclosure  22  could alternately comprise any number of elements in a variety of orientations rather than the two (2) elements (upper element  28  and lower element  30 ) as shown and described. Such alternate elements are hereinafter referred to as a “first element,” a “second element,” a “third element,” and so on. It should be understood that such variations are within the scope of the present disclosure. 
   As shown in  FIG. 4 , the lower element  30  and the heater  10  also define a contour-matched interface  31 . As such, the lower element  30  defines a lower contact surface  40 , and the heater  10  defines a contact surface area  37  (shown dashed) on the surface of the protective layer  19 . Therefore, the lower contact surface  40  of the lower element and the contact surface area  37  of the heater  10  are in intimate contact as with the upper element  28  and the lower element  30 . Such intimate contact, or contour-matched interface, reduces the possibility of air gaps being present in the overall connector assembly  20  and thus reduces the likelihood of undesirable arcing. To further achieve the contour-matched interfaces as described herein, in one form of the disclosure, the profile tolerances for the surfaces defining the contour-matched interfaces is approximately ±0.001 inches (±0.00254 cm). Such tolerances are exemplary only and should not be construed as limiting the scope of the present invention. 
   Referring to  FIGS. 5   a  and  5   b , the upper element  28  further comprises a recess  36 , preferably in the form of a blind hole as shown, for receiving the conductive plug  24 . Additionally, the upper element defines a groove  42  that is adapted to receive a lead wire  18 . Similarly, as illustrated in greater detail in  FIGS. 6   a  and  6   b , the lower element  30  comprises a recess  38 , preferably in the form of a through hole, which is open to the lower contact surface  40  of the lower element  30 . The lower contact surface  40  is adapted for contact with the protective layer  19  as previously described, and the recess  38  provides access for the conductive plug  24  to contact the terminal pad  16 , which is described in greater detail below. As further shown, the lower element  30  also comprises a groove  43  that is adapted to receive a lead wire  18 , the details of which are described in greater detail below. 
   Referring now to  FIGS. 7 through 9 , the recess  36  of the upper element  28  and the recess  38  of the lower element  30  are so configured that they cooperatively define a cavity  39  adapted to receive the conductive plug  24  therein. Additionally, grooves  42  and  43  of the upper element  28  and the lower element  30 , respectively, cooperatively form a channel  44  for insertion of the lead wire  18 . As shown, the grooves  42  and  43  extend from the cavity  39  to exterior surfaces  45  and  46  of the dielectric enclosure  22  in order to receive the external lead wire  18 . 
   As shown in greater detail in  FIG. 8 , the lead wire  18  comprises an outer metal or protective sheath  51  and an inner insulating sheath  53  that surrounds the individual wire strands  55 . Preferably, the outer protective sheath  51  is removed such that the inner insulating sheath  53  is disposed within and is in contact with the channel  44 . Accordingly, the interface between the lead wire  18  and the channel  44  is such that the inner insulating sheath  53  of the lead wire  18  is compressed and thus completely fills the channel  44  along at least a portion thereof to interrupt the air gap from the cavity  39  to the exterior of the dielectric enclosure  20 . The metal or protective sheath  51  and the inner insulating sheath  53  surround and protect the wire strands  55  along the length of the lead wire  18 , except for the portion to be inserted into the receptacle  47  of the conductive plug  24 , which establishes an electrical connection between the conductive plug  24  and the lead wire  18 . As such, the insulating sheath  53  provides an additional barrier against air gaps and thus aids in reducing the possibility of undesirable arcing. Additionally, the inner insulating sheath  53  is preferably a ceramic fiber material such as Nextel®. The metal or protective sheath  51  is preferably a metallic braid such as nickel, which maintains the inner insulating sheath  53 , provides mechanical armor, withstands high temperatures, and also provides an electrical ground reference. Generally, the effectiveness of the connector assembly  20  requires wire with an electrical rating equal to or greater than the voltages and currents intended for the connector assembly  20 . 
   As further shown, the receptacle  47  of the conductive plug  24  is disposed adjacent to the channel  44  of the dielectric enclosure  22  and is in communication therewith. When the conductive plug  24  is placed within the cavity  39 , the conductive plug  24  is disposed immediately above and in contact with the terminal pad  16  (not shown), with the receptacle  47  aligned with the channel  44 . Therefore, when the lead wire  18  is disposed within the channel  44  of the dielectric enclosure  22  and into the receptacle  47  of the conductive plug  24 , an electrical connection is established between the lead wire  18  and the terminal pad  16 . Accordingly, the conductive plug  24  is preferably made of nickel or any other electrically conductive material that can withstand the relatively high currents and resulting temperatures. 
   The dielectric enclosure  22  is preferably made of a ceramic material such as, by way of example, alumina or steatite. However, it should be understood that dielectric materials other than those specifically identified herein shall be construed as falling within the scope of the present disclosure so long as they provide the proper level of insulation and protection for the connector assembly  20 . Alternatively, the dielectric enclosure  22  may be made of any dielectric material other than alumina or steatite with a coating of alumina or steatite. (Do we need a figure showing the coating?) 
   As shown in greater detail in  FIG. 10 , the conductive plug  24  preferably defines a cylindrical shape and comprises a receptacle  47  formed through an external wall  41  for receiving the lead wire  18 . Although the receptacle  47  is illustrated in the form of a through hole, it should be understood that a blind hole or other geometrical shape that is adapted to properly receive the lead wire  18  shall be construed to be within the scope of the present disclosure. In one form, the conductive plug  24  preferably comprises a dimple  49  formed on its upper surface  61 , which is formed after the lead wire  18  is inserted into the receptacle  47  in order to firmly secure the lead wire  18  within the receptacle  47 . 
   As shown in  FIGS. 11   a  and  11   b , each of the conductive plug  24  and the lower element  30  may define a shape, or an alignment feature, that provides alignment of the receptacle  47  of the conductive plug  24  with the channel  44  of the dielectric enclosure  22 . (The upper element  28  is not shown for purposes of clarity). The conductive plug  24 ′ in one form comprises a key  100  that engages a slot  102  formed in the lower element  30 ′ as illustrated in  FIG. 11   a . As shown in  FIG. 11   b , the conductive plug  24 ″ alternately defines a square geometry that fits within a square recess  38 ″ of the lower element  30 ″. It should be understood that the embodiments illustrated herein for improved alignment are exemplary only and should not be construed as limiting the scope of the present invention. Other geometries that provide improved alignment of the conductive plug  24  may also be employed while remaining within the scope of the present invention. Additionally, the alignment features as illustrated and described herein may or may not extend all the way to the bottom surface  40  (not shown) of the lower element  30 , such that the footprint of the conductive plug  24  against the terminal pad  16  (not shown) can take on a different shape other than the key or the square. 
   To ensure close contact between the terminal pad  16  and the conductive plug  24 , a spring element  48  is preferably disposed within the recess  36  of the upper element  28  with the conductive plug  24  disposed between the terminal pad  16  and the spring  48 . The spring element  48  exerts a biasing force against the conductive plug  24  and presses the conductive plug  24  against the terminal pad  16 . Preferably, the spring element  48  is made of a spring tempered nickel or iron alloy such as Inconel® X-750 or A286 that is consistent with operational temperatures of the connector. 
   As shown in  FIG. 12 , the spring  48  is preferably a “wave” spring due to its advantageous spring force over a relatively short distance. However, other types of springs may be employed while remaining within the scope of the present disclosure so long as the spring is relatively small to fit within the recess  36  and has a relatively low aspect ratio (height to diameter). 
   Referring back to  FIGS. 3 and 4 , a clamping device  50  is provided over the dielectric enclosure  22  to clamp the upper element  28  against the lower element  30 , to clamp the inner insulating sheath  53  within the channel  44 , and also to firmly secure the connector assembly  20  to the substrate  12 . The clamping device  50  comprises opposing flanges  52  and an extension  54  defining a distal tab  56 . The opposing flanges  52  are adapted to receive fasteners  58 , which secure the clamping device  50  to the substrate  12 . Although mechanical bolts  60  and nuts  62  are illustrated in one form of the present disclosure, it should be understood that other types of fasteners, furthermore not limited to mechanical, shall be construed as falling within the scope of the present disclosure. Additionally, any number of flanges  52  may also be employed while remaining within the scope of the present disclosure. 
   The distal tab  56  of the extension  54  is adapted for engagement with a first clamp  64  that is secured around the lead wire  18  as shown. Accordingly, the extension  54  provides additional stability proximate the connection between the lead wire  18  and the dielectric enclosure  22  to act as a strain relief. 
   As further shown, a second clamp  70  is disposed around the lead wire  18  proximate the dielectric enclosure  22 . The clamp  70  compresses the sheathing around the lead wire  18  to terminate the metal or protective sheath  51  and to allow the inner insulating sheath  53  and the individual wire strands  55  to pass from the outside environment through the dielectric enclosure  22 . Accordingly, the relatively high voltage present in the wire strands  55  and passing through the dielectric enclosure  22  remains insulated without direct air gap to ground potentials existing on the metal or protective sheath  51  and outside the connector assembly  20 . 
   The clamping device  50  also comprises side walls  63  between the flanges  52  and an upper surface  65  as shown. At the intersection of the side walls  63  and the upper surface  65 , the clamping device  50  further comprises ears  67 , which are configured to allow for vertical displacement of the flanges  52  when the clamping device  50  is secured to the substrate  12 . More specifically, the nominal position of the flanges  52  is slightly higher than the nominal position of the lower contact surface  40  of the lower element  30  when the dielectric enclosure  22  is positioned under the clamping device  50 . In other words, the overall height of the dielectric enclosure  22  is slightly higher than the overall height of the clamping device  50 . The slightly higher position of the flanges  52  is shown as dimension “t” for purposes of illustration. As a result, when the fasteners  58  are tightened through the substrate  12 , the upper surface  65  of the clamping device  50  engages the dielectric enclosure  22 , and the ears  67  flex and thus allow the side walls  63  and the flanges  52  to be vertically displaced. Accordingly, an advantageous clamping load is provided to the dielectric enclosure  22  and the substrate  12 , thus maintaining intimate contact between all contour-matched surfaces, between the lead wire  18  and the receptacle  47 , and providing sufficient clamping force to overcome the spring forces holding the conductive plug  24  to the termination pad  16 . 
   In an alternate form as shown in  FIG. 13 , the clamping device  50 ′ defines a U-shape member  72 , which also defines opposing flanges  74 . Similarly, the opposing flanges  74  are adapted to receive fasteners  76 , which secure the clamping device  50 ′ to the substrate  12 . A clamp  78 , which also compresses the sheathing around the lead wire  18  to terminate the wire strands  55  at the dielectric enclosure  22 , defines loops  80  as shown. The loops  80  are adapted to receive wires (not shown), which extend through the loops  80  and also through the fasteners  76 . Accordingly, the wires secure the lead wire  18  to the overall connector assembly  20 , and the clamping device  50 ′ secures the connector assembly  20  to the substrate  12 . 
   The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.