CA2075306A1 - Process for metal-coating of electrically conductive metallic items - Google Patents
Process for metal-coating of electrically conductive metallic itemsInfo
- Publication number
- CA2075306A1 CA2075306A1 CA 2075306 CA2075306A CA2075306A1 CA 2075306 A1 CA2075306 A1 CA 2075306A1 CA 2075306 CA2075306 CA 2075306 CA 2075306 A CA2075306 A CA 2075306A CA 2075306 A1 CA2075306 A1 CA 2075306A1
- Authority
- CA
- Canada
- Prior art keywords
- metal
- copper
- aluminum
- electrodeposition
- hard
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Landscapes
- Electroplating Methods And Accessories (AREA)
Abstract
ABSTRACT
A method of electrochemically depositing a crushable copper layer on a base surface of aluminum or nickel includes controlling the current density during the electrodeposition such that, over at least a portion of the time during which the copper is being deposited, the current density level is high enough to ensure that at least some of the copper atoms are deposited with gaps and interstices between them. The crushable deposition of other metals is also contemplated.
A method of electrochemically depositing a crushable copper layer on a base surface of aluminum or nickel includes controlling the current density during the electrodeposition such that, over at least a portion of the time during which the copper is being deposited, the current density level is high enough to ensure that at least some of the copper atoms are deposited with gaps and interstices between them. The crushable deposition of other metals is also contemplated.
Description
I~ROCESS FOR METAI~COATING OF EL~CTRICALLY
( ONDUCTIVE METALLIC ll~EMS
This invention relates generally to an electrochemical metallizing process for providing a controlled coating of copper and nickel on a metallic aluminum 5 base.
BACKGROU~D OF THIS INVENTION
Electrical connectors, of tlle kind generally used to connect electrical wires, stranded bare conductors or insulated cables, are typically of copper or of aluminum. Aluminum based connectors are generally preferred for use with 10 aluminum wires, bare stranded conductors or insulated cables, in order to avoid galvanic action and corrosion at the face connection location of the connectors for two dissimilar metals when exposed to aggressive environments. However, it is well known that aluminum quickly develops a hard oxide layer on its surfa~e, so that when two aluminum connectors are connected together, the two hard 15 aluminum oxide layers on the connectors act as dielectrics and interfere with good electrical con~act.
It i9 known that, where two dissimilar connectors must be joined together for practical reasons, such as where a bare aluminum conductor must be joined toa bare copper conductor, special precautions must be taken. The hard aluminum 20 oxide dielectric is still present on the aluminum connector and interferes with good electrical contact. Also, due to the presence of two dissimilar metal~, galvanicactivity adversely affects good electrical contact and shortens the life of the connectors.
It is known to apply contact aids such as a sealing layer of g~ease 2S impregnated with hard metallic particles in the connectors' contact faces to prevent the ingress of moisture and to bre~ through the hard aluminum o~cide unda pressure and increase the contact surface area. Also, it is known to mechanically use an adequate number of high strength bolt3, special washas and increased connector sizes. Also, it is hlown to apply a coating of hot-dip tin, to both 30 aluminum and copper connectors, so as to achieve a similar face to face contact with each other. The object is to reduce galvanic activity, break through the hard aluminum oxide dielec~ic, increase and try to maintain high contact surface area 207~3~6 and hence improve electrical contact and life of the connectors. These above attempts are not cost effective and essentially act as palliatives to the connectors in aggressive environments such as acid rain, ocean/sea coasts, highway/road salt and direct industrial contaminants. These methodologies have been extensively S exarnined by the Canadian Electrical Association (CEA) as noted in their reports prepared by Institut de Recherche d'Hydro-Ouébec (IREQ).
In spite of the above, a further problem tends to remain. Where the two connec~ors' conductive surfaces are to be forced together under high pressure (for exarnple using bolts) so that the electric current can pass from one to the other 10 through the contact faces, the inherent roughness of any metal face restricts the actual conhct of the two juxtaposed faces to specific, isolated points, and the electrical current is concentrated at those points. This causes resistance to nse due ~o the restricted nature of the contact points, and results in the generation ofadverse thermal characteristics (high heat) and a drop in bolt torque loading. This 15 process result is inter-dependent, hence, an imbalance is self-aggravating and eventually the connectors self-destruct, or e~perience a shortened life under operating conditions.
GENERAL DESCRIPIlON OF THIS INVEN~ON
In view of the difficulties menticned, it is an object of an aspect of this 20 invention to deposit and control the electrochemical metallizing deposition of the copper and nickel layers in such a way that at least a portion of the copper andnickel layer is lat~ced, "crus}uble~ or easily powdered. In essence, this is accomplished by controlling the voltage applied for electrochemical deposition, which in turn controls the current. It is well known that in order to obtain by 25 conventional electrolytical deposition, a hard, shiny copper outer surface, a low rate of deposition is required. A rule of thumb is that, for this kind of hard surface, it takes about one hour to deposit one mil of copper. In order to obtain such a hard surface, the electric voltage and current density has to be relatively low. It is believed that the relatively low voltage and current allows the individual 30 copper atoms to bond together in a tight formation without significant gaps or interstices. In electrochemical metallizing, as the electric voltage and currentincreases (i.e. the current density increases) the rate at which the copper atoms are bonded increases proportionately. At a certain threshold current density (the current per unit area of the item being coated), the co~er atoms are bonding so fast that it is not possible to achieve a tight, void-free configuration throughout.
As a result, the copper is deposited in a crushable form, with many gaps and S interstices, and as a rule of thumb it takes under two minutes to deposit one mil of copper. For example, if the high voltage and high current density deposition of copper were carried on continuously throughout the deposition process, the result would be a co~er layer which is relatively crushable and easily powdered, including at the outer surface. When two such surfaces are forced together under10 great pressure, they will tend to deform, crush upon themselves and press-fit into each other to provide a larger effective surface area of contact for the connectors' operating electrical current than would have been the case if the metal depositing electric current density were relatively low, and the copper atoms bonded in a tight, dense formation.
More particularly, this invention provides a method of electrochemically depositing a crushable layer of a first metal on a base surface of a second metal, when such base surface is immersed in a suitable electrolyte with a direct electric current flowing through the electrolyte between said base surface and an electrode that is also immersed in the electrolyte, the method comprising controlling the current such that, over at least a portion of the time during which the first metal is being electrod~pnsited, the current density is high enough to ensure that at least some of the atoms of the first metal are deposited with gaps and interstices between them.
GEN13~RAL DES~ION OF THE DRAWINGS
Figure 1 is a vertical sectional view through a container useful in the process of removing the hard oxide from an aluminum connector;
Figure 2 is a vertical sectional view through an electrolytic cell utilized in the process of this invention;
Figures 3, 4, 5 and 6 are sertional views through a portion of a connector, using an exaggerated scale, showing the various eonfigura~ons of the copper layer that is electrodeposited by the method of this invention, and
( ONDUCTIVE METALLIC ll~EMS
This invention relates generally to an electrochemical metallizing process for providing a controlled coating of copper and nickel on a metallic aluminum 5 base.
BACKGROU~D OF THIS INVENTION
Electrical connectors, of tlle kind generally used to connect electrical wires, stranded bare conductors or insulated cables, are typically of copper or of aluminum. Aluminum based connectors are generally preferred for use with 10 aluminum wires, bare stranded conductors or insulated cables, in order to avoid galvanic action and corrosion at the face connection location of the connectors for two dissimilar metals when exposed to aggressive environments. However, it is well known that aluminum quickly develops a hard oxide layer on its surfa~e, so that when two aluminum connectors are connected together, the two hard 15 aluminum oxide layers on the connectors act as dielectrics and interfere with good electrical con~act.
It i9 known that, where two dissimilar connectors must be joined together for practical reasons, such as where a bare aluminum conductor must be joined toa bare copper conductor, special precautions must be taken. The hard aluminum 20 oxide dielectric is still present on the aluminum connector and interferes with good electrical contact. Also, due to the presence of two dissimilar metal~, galvanicactivity adversely affects good electrical contact and shortens the life of the connectors.
It is known to apply contact aids such as a sealing layer of g~ease 2S impregnated with hard metallic particles in the connectors' contact faces to prevent the ingress of moisture and to bre~ through the hard aluminum o~cide unda pressure and increase the contact surface area. Also, it is known to mechanically use an adequate number of high strength bolt3, special washas and increased connector sizes. Also, it is hlown to apply a coating of hot-dip tin, to both 30 aluminum and copper connectors, so as to achieve a similar face to face contact with each other. The object is to reduce galvanic activity, break through the hard aluminum oxide dielec~ic, increase and try to maintain high contact surface area 207~3~6 and hence improve electrical contact and life of the connectors. These above attempts are not cost effective and essentially act as palliatives to the connectors in aggressive environments such as acid rain, ocean/sea coasts, highway/road salt and direct industrial contaminants. These methodologies have been extensively S exarnined by the Canadian Electrical Association (CEA) as noted in their reports prepared by Institut de Recherche d'Hydro-Ouébec (IREQ).
In spite of the above, a further problem tends to remain. Where the two connec~ors' conductive surfaces are to be forced together under high pressure (for exarnple using bolts) so that the electric current can pass from one to the other 10 through the contact faces, the inherent roughness of any metal face restricts the actual conhct of the two juxtaposed faces to specific, isolated points, and the electrical current is concentrated at those points. This causes resistance to nse due ~o the restricted nature of the contact points, and results in the generation ofadverse thermal characteristics (high heat) and a drop in bolt torque loading. This 15 process result is inter-dependent, hence, an imbalance is self-aggravating and eventually the connectors self-destruct, or e~perience a shortened life under operating conditions.
GENERAL DESCRIPIlON OF THIS INVEN~ON
In view of the difficulties menticned, it is an object of an aspect of this 20 invention to deposit and control the electrochemical metallizing deposition of the copper and nickel layers in such a way that at least a portion of the copper andnickel layer is lat~ced, "crus}uble~ or easily powdered. In essence, this is accomplished by controlling the voltage applied for electrochemical deposition, which in turn controls the current. It is well known that in order to obtain by 25 conventional electrolytical deposition, a hard, shiny copper outer surface, a low rate of deposition is required. A rule of thumb is that, for this kind of hard surface, it takes about one hour to deposit one mil of copper. In order to obtain such a hard surface, the electric voltage and current density has to be relatively low. It is believed that the relatively low voltage and current allows the individual 30 copper atoms to bond together in a tight formation without significant gaps or interstices. In electrochemical metallizing, as the electric voltage and currentincreases (i.e. the current density increases) the rate at which the copper atoms are bonded increases proportionately. At a certain threshold current density (the current per unit area of the item being coated), the co~er atoms are bonding so fast that it is not possible to achieve a tight, void-free configuration throughout.
As a result, the copper is deposited in a crushable form, with many gaps and S interstices, and as a rule of thumb it takes under two minutes to deposit one mil of copper. For example, if the high voltage and high current density deposition of copper were carried on continuously throughout the deposition process, the result would be a co~er layer which is relatively crushable and easily powdered, including at the outer surface. When two such surfaces are forced together under10 great pressure, they will tend to deform, crush upon themselves and press-fit into each other to provide a larger effective surface area of contact for the connectors' operating electrical current than would have been the case if the metal depositing electric current density were relatively low, and the copper atoms bonded in a tight, dense formation.
More particularly, this invention provides a method of electrochemically depositing a crushable layer of a first metal on a base surface of a second metal, when such base surface is immersed in a suitable electrolyte with a direct electric current flowing through the electrolyte between said base surface and an electrode that is also immersed in the electrolyte, the method comprising controlling the current such that, over at least a portion of the time during which the first metal is being electrod~pnsited, the current density is high enough to ensure that at least some of the atoms of the first metal are deposited with gaps and interstices between them.
GEN13~RAL DES~ION OF THE DRAWINGS
Figure 1 is a vertical sectional view through a container useful in the process of removing the hard oxide from an aluminum connector;
Figure 2 is a vertical sectional view through an electrolytic cell utilized in the process of this invention;
Figures 3, 4, 5 and 6 are sertional views through a portion of a connector, using an exaggerated scale, showing the various eonfigura~ons of the copper layer that is electrodeposited by the method of this invention, and
Claims (20)
1. A method of electrochemically depositing a crushable layer of a first metal on a base surface of a second metal, when such base surface is immersed in a suitable electrolyte with a direct electric current flowing through the electrolyte between said base surface and an electrode that is also immersed in the electrolyte, themethod comprising controlling the current such that, over at least a portion of the time during which the first metal is being elertrodeposited, the current density is high enough to ensure that at least some of the atoms of the first metal are deposited with gaps and interstices between them.
2. The method claimed in claim 1, in which said portion of the time is substantially the entire time of electrodeposition.
3. The method claimed in claim 1, in which said portion of the time is the latter portion of the time of deposition.
4. The method claimed in claim 1 in which said portion of the time begins and ends intermediate the start and finish of the time of electrodeposition, whereby the layer includes a hard, dense inner lamina of the first metal adjacent the base surface, a crushable intermediate lamina of outwardly adjacent the inner lamina,and a hard, dense outer lamina of the first metal outwardly adjacent the intermediate lamina.
5. The method claimed in claim 1, in which said second metal is nickel, and saidfirst metal is copper.
6. The method claimed in claim 1, in which said second metal is aluminum, said first metal is copper, and in which, prior to electrodeposition of the copper, any hard aluminum oxide is removed.
7. The method claimed in claim 5, in which, prior to electrodeposition of the copper, the nickel base surface is electrodeposited on aluminum from which any hard oxide layer has been removed.
8. The method claimed in claim 1, in which, during the deposition of the copper atoms with gaps and interstices between them, the current density is at least 8 amps per square inch of surface area.
9. The method claimed in claim 2, in which said second metal is nickel, and saidfirst metal is copper.
10. The method claimed in claim 2, in which said second metal is aluminum, said first metal is copper, and in which, prior to electrodeposition of the copper, any hard aluminum oxide is removed.
11. The method claimed in claim 9, in which, prior to electrodeposition of the copper, the nickel base surface is electrodeposited on aluminum from which any hard oxide layer has been removed.
12. The method claimed in claim 2, in which, during the deposition of the copperatoms with gaps and interstices between them, the current density is at least 8 atoms per square inch of surface area.
13. The method claimed in claim 3, in which said second metal is nickel, and said first metal is copper.
14. The method claimed in claim 3, in which said second metal is aluminum, said first metal is copper, and in which, prior to electrodeposition of the copper, any hard aluminum oxide is removed.
15. The method claimed in claim 13, in which, prior to electrodeposition of the copper, the nickel base surface is electrodeposited on aluminum from which any hard oxide layer has been removed.
16. The method claimed in claim 3, in which, the first metal is copper, and in which, during the deposition of the copper atoms with gaps and interstices between them, the current density is at least 8 amps per square inch of surface area.
17. The method claimed in claim 4, in which said second metal constituting the base surface is nickel.
18. The method claimed in claim 4, in which said second metal constituting the base surface is aluminum, the first metal is copper, and in which, prior to electrodeposition of the copper, any hard aluminum oxide is removed.
19. The method claimed in claim 17, in which the first metal is cover, and in which, prior to electrodeposition of the copper, the nickel base surface is electrodeposited on aluminum from which any hard oxide layer has been removed.
20. The method claimed in claim 4, in which the first metal is copper, and in which, during the deposition of the copper atoms with gaps and interstices between them, the current density is at least 8 amps per square inch of surface area.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/734,768 | 1991-07-23 | ||
| US74376891A | 1991-08-12 | 1991-08-12 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2075306A1 true CA2075306A1 (en) | 1993-02-13 |
Family
ID=24990091
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2075306 Abandoned CA2075306A1 (en) | 1991-08-12 | 1992-08-05 | Process for metal-coating of electrically conductive metallic items |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2075306A1 (en) |
-
1992
- 1992-08-05 CA CA 2075306 patent/CA2075306A1/en not_active Abandoned
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| Date | Code | Title | Description |
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| FZDE | Dead |