Patent Publication Number: US-6217737-B1

Title: Method for forming a corrosion-resistant conductive connector shell

Description:
BACKGROUND 
     The present invention relates to electrical connectors, and more particularly to connectors for use in corrosive environments such as are found near oceans and the like. 
     Electrical connectors are widely used in aircraft and other vehicles that are required to be exposed to corrosive contamination by salt spray, for example. While being otherwise desirable for low cost and light weight, connectors having aluminum outer shells have been generally rejected in high-performance applications because of rapid corrosion under exposure to salt spray environments. Conventional surface treatments have proven unsatisfactory for a number of reasons. For example: 
     1. Ordinary anodic coatings are easily scratched through, corrosion proceeding rapidly from even very small lesions; 
     2. Hard anodic coatings by themselves are porous, being ineffective for excluding corrosives; 
     3. All anodic coatings are non-conductive, whereas electrical conductivity is usually required; 
     4. Conventional paint is also non-conductive and easily scratched, and conductive paint affords less corrosion resistance than conventional paint; 
     5. Plated coatings by themselves are typically effective for sealing out corrosives, but are subject to scratching; and nicking resulting in rapid corrosion; and 
     6. Connector shells formed of corrosion-resistant steel are excessively expensive to produce and undesirably heavy; and substitution of titanium is even more expensive, being also fifty percent heavier than aluminum. 
     Thus there is a need for a lightweight corrosion-resistant conductive connector shell that overcomes the disadvantages of the prior art. 
     SUMMARY 
     The present invention meets this need by providing an aluminum shell having a combination of anodic and plated coatings. In one aspect of the invention, a corrosion-resistant and electrically conductive connector shell includes a shell member formed of an aluminum alloy; an anodic surface coating formed on and extending into the shell member, the anodic surface coating having a hardness of not less than R C  60; and a conductive coating covering and sealing the anodic surface coating. The term “shell” is inclusive of components thereof such as coupling ring, backshell, etc. 
     The anodic surface coating can have a thickness being between approximately 0.0008 inch and approximately 0.0018 inch. The hardness of the anodic surface coating can be approximately R C  72. 
     The conductive coating preferably includes metallic plating for high conductivity. Preferred plating is a layer of ion vapor deposited high purity aluminum and having a thickness effective for sealing the anodic coating. The layer of high purity aluminum can have a thickness of at least approximately 0.0002 inch. 
     Alternatively, the metallic plating can include a layer of cadmium that preferably has a thickness of at least approximately 0.0002 inch for durability and wear resistance. In a further alternative, the metallic plating can include a layer of a first metal on the anodic surface coating, and a layer of a second metal on the layer of first metal. The layer of first metal can have a thickness of at least approximately 0.00002 inch being effective for bonding the layer of second metal. In yet another alternative, the plating can include cadmium. 
     The connector shell can be part of a connector assembly in combination with an insulative carrier supported by the connector shell, and at least one electrical contact extending within the carrier in electrical isolation from the shell. 
     In another aspect of the invention, a method for forming a corrosion-resistant and electrically conductive connector shell includes the steps of: 
     (a) providing an aluminum alloy shell member; 
     (b) forming an anodic coating on and extending into the shell member; and 
     (c) plating a sealed conductive coating on the anodic coating. 
     The forming step can include extending the anodic coating to a depth of at least approximately 0.0008 inch at a hardness of at least R C  60. Preferably the plating step can include ion vapor deposition of high purity aluminum to a thickness effective for sealing the anodic coating. The plating step can further include extending the high purity aluminum to a thickness of at least approximately 0.0002 inch. 
     Alternatively, the plating step can include plating a layer of a first metal on the anodic coating, and sealingly plating a layer of a second metal on the layer of first metal. The plating step can include extending the layer of first metal to a thickness of at least approximately 0.00002 inch and extending the layer of second metal to a thickness of at least approximately 0.0002 inch for providing a desired combination of resistance to wear and corrosion, the second metal being cadmium. 
    
    
     DRAWINGS 
     These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description, appended claims, and accompanying drawings, where: 
     FIG. 1 is a side view of an electrical connector including a connector shell according to the present invention; 
     FIG. 2 is a side sectional detail view of a surface portion of the connector shell of FIG. 1; and 
     FIG. 3 is a flow diagram of a process for forming the connector shell of FIG.  1 . 
    
    
     DESCRIPTION 
     The present invention is directed to an electrical connector shell that is particularly effective in harsh environments. With reference to FIGS. 1 and 2 of the drawings, a connector assembly  10  includes a connector shell  11  that is made from a base member  12  having an anodic coating  14  and a conductive coating  16  having a thickness C. The coating  16  can include a first plated layer  18  and a second plated layer  20 . In a preferred alternative that is further described below, the conductive coating  16  can have just one layer being a sacrificial anode of ion-vapor-deposited (IVD) high purity aluminum. 
     The base member  12  is formed of a suitable aluminum alloy for providing a desired combination of light weight and high strength. The anodic coating  14  transforms a portion of the base member  12  at the surface thereof to a non-conductive material, the coating  14  extending slightly below the surface and also slightly enlarging the base member  12 . In other words, the anodic coating  14  has a thickness A, a portion B of which extends below the original surface of the base member  12 . Preferably, the anodic coating  14  is formed by a process that is commercially known as “hard anodizing” or “Type III anodizing” which produces a surface hardness of not less than R C  60 and typically R C  72, wherein the term “R C ” means the Rockwell C Scale as is commonly known. In contrast to conventional anodizing in which the thickness A is approximately 0.0002 inch, the thickness A using the preferred hard anodizing is between approximately 0.0008 inch and approximately 0.0018 inch, being typically approximately 0.0015 inch. The anodic coating  14  advantageously improves the durability of the connector shell  11  by providing greatly increased resistance to scraping, nicking, and wear of the base member  12 . In commercial processes of hard anodizing, there typically is a supplemental treatment of immersion in heated water, dilute nitric acid, or a dichromate solution, the dichromate treatment having the effect of closing pores of the anodic coating. 
     A principal feature of the present invention is that the conductive coating  16  also seals microscopic voids or fissures that are normally present in the anodic coating  14 , and providing a more effective seal in case of the anodic coating  14  having a supplemental treatment as described above. In the preferred configuration, the conductive coating  16  is formed as a single conductive coating of high purity aluminum being applied by ion vapor deposition (IVD) to the thickness C. The thickness C is made sufficiently great to be effective for sealing the anodic coating. Preferably the thickness C is extended to at least approximately 0.0002 inch for further protecting the base member  12 . 
     The exemplary configuration of the conductive coating  16  has the thickness C including a thickness D of the first plated layer  18  and a thickness E of the second plated layer  20  as further shown in FIG.  2 . The second plated layer  20  is formed of a metal having suitable characteristics of conductivity, corrosion resistance and wear resistance, such as cadmium. Other suitable materials for the second plated layer include zinc. The first plated layer  18  is provided when needed as a transitional material between the anodic coating  14  and the second plated material, such as for mechanical bonding and/or resistance to electrolytic corrosion. In one tested implementation wherein the second plated layer  20  is formed of cadmium, the first plated layer  18  is formed of nickel, for preventing electrolytic corrosion and for securely anchoring the second plated layer  20 . The first plated layer  18  can be formed by electroless plating, this process being dictated by the nonconductive property of the anodic coating  14 , and advantageously resulting in penetration of the microscopic fissures therein to provide electrical continuity between the base member  12  and the conductive coating  16 . The thickness D of the first plated layer  18  is preferably not less than approximately 0.00002 inch for providing effective isolation of the second plated layer  20  from the base member  12 . Tests of the configuration wherein the first plated layer  18  is nickel and the second layer  20  is cadmium, some dissolving of the anodic coating  14  was observed, indicating that a desired effectiveness of the conductive coating  16  may depend on an initial formation of the anodic coating  14  to an augmented thickness. Other suitable materials for the first plated layer  18  include IVD deposited aluminum. 
     FIG. 3 shows a process  40  for producing the connector shell  11 , including a form base step  42  for forming the base member  12 , a hard anodize step  44  for forming the anodic coating  14 , a first plating step  46  for forming the first plated layer  18 , and a second plating step  48  for forming the second plated layer  20 . In the form base step  42 , the base member  12  can be machined, die cast, forged, or produced by any combination of these and other well known processes whereby the surface is not excessively rough. In the hard anodize step  44 , no particular restrictions are needed, although it is preferred to include a supplemental treatment such as dipping in a dichromate solution for sealing pores of the coating  14 . In the first plating step  46 , it is preferred that particular care be taken to insure complete coverage, such as by tumbling or the like in an electroless bath. The second plating step  48  can be by conventional electroplating. In the preferred configuration having the single layer of high purity aluminum, the second plating step  48  is omitted. 
     A further shown in FIG. 1, the connector shell  11  forms a principal component of the connector assembly  10  having one or more electrical contacts  22 , an insulative carrier  24 , and other components that are customary or otherwise known in the electrical connector arts. 
     Thus the connector shell  11  and connector assemblies made therefrom exhibit a desired combination of strength, light weight and low cost resulting from the use of aluminum, durability and wear resistance as imparted by the anodic coating  14 , and a combination of electrical conductivity and corrosion resistance resulting from the metallic plating that permeates microscopic fissures that can exist in the anodic coating  14 . 
     Although the present invention has been described in considerable detail with reference to certain preferred versions thereof, other versions are possible. For example, the conductive coating  16  can be formed by direct application of any suitable sacrificial coating to the surface of the anodic coating  14 . Therefore, the spirit and scope of the appended claims should not necessarily be limited to the description of the preferred versions contained herein.