CA2069390A1

CA2069390A1 - Corrosion resistant high temperature contacts or electrical connectors and method of fabrication thereof

Info

Publication number: CA2069390A1
Application number: CA002069390A
Authority: CA
Inventors: James Alexander Evert Bell; Bruce Randolph Conrad; Douglas Albert Hope
Original assignee: Vale Canada Ltd
Current assignee: Vale Canada Ltd
Priority date: 1991-09-05
Filing date: 1992-05-25
Publication date: 1993-03-06
Also published as: EP0531099A2; JPH05230690A; EP0531099A3

Abstract

CORROSION RESISTANT HIGH TEMPERATURE CONTACTS OR
ELECTRICAL CONNECTORS AND METHOD OF FABRICATION THEREOF

ABSTRACT

The invention provides a composite material specifically adapted for use as high temperature corrosion resistant electrical connectors. A conductiblenickel-base substrate alloy having corrosion resistance, strength and creep resistance is used to hold shape at 200°C. An interlayer of substantially pure nickel is electrolytically plated over the nickel-base substrate. A noble metal surface isdiffusion bonded to the electrolytic nickel interlayer. The noble metal surface cannot be hardened by organic additives which accelerate corrosion at 200°C. Alternatively, if a copper-base substrate is used, a layer of wrought pure nickel is bonded to the substrate then a layer of electroplated nickel is used to overplate the wrought nickel and the copper-base substrate. A noble metal surface is then diffusion bonded to the electrolytic nickel layer.

Description

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, ^1- PC-4100 CORROS~ON RESISl[ANT HIGH TEMPERATURE C,'ONTACIS OR
ELECl[RiCAL (::ONNECIORS AND ME~OD OF FAB CAlrON THEREOF
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DISCUSSION OF l~lE PRIOR ART AND PR(~BLEM
3~1ectrical contacts or connectors for electronic applications is an old but 5 still evolving art. Generally these contacts are manufactùred by roll bonding of ~wrought alloys or by electrolytic plating~methods. The roll bond~ng of wrought alloys is well taught by Robert J. Russell "Properties of Incoloy Clad Wrought Gold AlIoyj" Solid State Technology. In the method of manufacture taught by Russell, a strip of gold or gold alloyed with Ni, Cu, Ag,~ Co, Pt or palladium alloyed with Ag is 10 ~ ~ ~roll bonded onto a wrought nickel alloyj slit to width, then roll bonded as an inlay into a copper-base alloy such as CA725 (Cu-lONi-4Sn), armealed to achieve the precipitation hardening of the composite and rolled to finish gauge. As will be shown in the body of this disclosure this manufacturing process has technical shortcomings in some high temperature, polluted environments. It is also costly to 15 produce contacts using the process of Russell.

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-2- PC-41~0 Most of the contacts used in the electronics industry today are electrolytically plated ~nainly because electroplating provides cost advantages. In electroplating processes, the base metal, usually CA725 or beryllium copper is typically electrolytically plated with nickel to a thickness of 1 to 10 micrometers S usually 3.5 micrometers, then overplated only in the actual contact area with "hard"
gold to a thickness of 0.5 to 1.5 micrometers. The contacts are strung together and mechanically forrned into the final or semi-final shape prior to the hard gold plating because the "hard" gold is brittle. The "hard" gold bath is different than a "soft" gold bath in that either Ni or Co from .5 to 1 percent and some organic hardeners are10 incorporated in the plated gold. While these contacts have several desirable feature, i.e. a hardened gold surface for wear and low contact resistance, and a barrier nickel underlayer to the copper alloy, we have discovered that they have several undesirable features which preclude their use in anything but the least hostile environments.

Other mixed roll bonding - plating methods of manufactul~ng have !~
lS been devised. For instance AT&T produces a contact known as DGR-156. DGR-156 is produced by plating Ni on CA725 copper base alloy, then overplating v~ith a thick layer of 60% Pd - 40% Ag alloy, and then overplating with a thin flash of hard gold to form a semi-finished composite sheet. The semi-finished composite sheet is then rolled to wherein thickness of the Pd-Ag layer is around O.S micrometers and 20 thickness of the Au flash end is about 0.1 to 0.2 micrometers. This rolled material is finally heat treated to diffuse the Au into the Pd-Ag so that the surface is around 75% Au to form lfinished DGR-156.
, The co-plating of Pd and Ag is described by Cohen et al. in U.S. Patent No. 4,269,671. As will be shown, this contact material also has limited usefulness in 25 severe service.

Another new contact material made by the electrolytic process is palladium-n~ckel as described by Abys et al. in "Metal Finishing" of July 1991 and ~n U.S. Patent Nos. 4,427,502, 4,468,296, 4,486,274 and 4,911,798. This Pd-5 to 20 wt% Ni alloy is usually plated to a thickness of 0.25 to 1.5 rnicrometers overtop of 3.75 rnicrometers of nickel which was plated over the copper base CA725 material. A
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cobalt hard gold cap is plated overtop of the Pd-Ni to a thickness Or 0.125 micrometers. This newer plated contac~ material has several advantages, the nickel in the palladium reduces the undesirable hydrogen embrittlement of pure Pd material and increases the hardness of the contact to a l~opp hardness with a 50 gm load of 5 430 KHN at 16 wt% Ni. These connectors have about the same performance as hardgold connectors of the same thickness and are generally cheaper. However, as will be shown in this disclosure, this material also has poor high temperature performance characteristics. ;
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Yet another method to making connectoIs is disclosed by Bell et al. in U.S. 4,956,026. This method electroplates nickel over an age hardenable base and0.3 microinches (0.76 micrometers) of soft gold on the surface. The composite isthen heat treated m such a manner as to precipitation harden the age hardenable ~ '!
substrate and at the same time diffuse Ni in to the surface Au layer. l'he diffusion of the Ni into the soft pure Au to a level of 2 to 10% Ni as disclosed by Bell et al. in U.S. Patent 4,505,060, hardens the Au so as to improve its wear characteristics. Note that the Knopp hardness KHN50 is 300 for 10 wt.% Ni in Au (Russell, et al.) ~.
cornpared to KN050 grams of 70 for pure gold.
.~ '~'., ' ' ' It has been discovered that all of cornmon connections tested were unsuitable for use in high temperature or corrosive gas atrnospheres. Specifically, it 20 has been discovered that the degradation of contacts in a rnixed gas corrosion test including industrial atmospheres shows that the deleterious oxidation (or sulphidization) may occur by copper migration through the electrolytically plated nickel underlayer or by m~gration of the Cu corrosion product from an e~osed edge.
It has also been discovered that all the electrolytically prepared contacts, i.e., hard ~
gold, gold flash Pd-Ni, and gold flash Pd-Ag contacts have poor high temperature `;
oxidation resistance.

It is an object of this invention to provide a composite material for use in electrical contacts resistant to corrosion.

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~4~ PC-a,100 It is a further object of this invention to provide a composite material for manufacturing of electrical contacts ~hat is resistant to oxidation at elevated temperatures.
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~A~ DRAWING

Figure 1 is a schematic chart comparing circuit resistance of various contacts after an exposure of 100C for 1000 hours;

Figure 2 is a schematic chart comparing circuit resistance of various contacts after an e~osure of 150C for up to 1000 hours; and Figure 3 is a schematic chart comparing circuit resistance of various contacts after an exposure of 200C for up to 1000 hours.
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SUMMARY OF INVENTION
The invention provides a composite material specifically adapted for use as high temperature corrosion resistant elect~ical cor nectors. A conductible - -nickel-base substrate alloy having corrosion resistance, strength and creep resistance -is used to hold shape at 200C. An interlayer of substantially pure nickel is electrolytically plated over the nickel-base substrate. A noble metal surface isdiffusion bonded to the electrolytic nickel interlayer. The noble metal surface cannot be hardened by organic additives which accelerate corrosion at 200C. Alternatively, if a copper-base substrate is used, a layer of wrought pure nickel is bonded to the substrate then a layer of electroplated nickel is used to oveIplate the wrought nickel and the copper-base substrate. A noble metal surface is then diffusion bonded to the IY ~;`
electrolytic nickel layer. ~ ~

DESCRIPTION Ol~ PREEERRED EMBODIMENT . .
Description of Tes1;ng , . i 2S Various forms of NIGOLDT~ alloy were compared to contact materials having general acceptance in the industry. A summaIy of materials tested is g~ven below in Table :L.
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~_ _ _ . =-- _ Malr~rial Base lnt~ayl2r Surface Overplat~ }Icat El~bhc ~Im) (,umI ~eatcd Ni ~ ¦

_ 1__ ¦ NlGOLDT~Ni Ni O 0.5 Au-10% Ni O Yes _ ¦ NlGOLD~Cu I CA725 __ 0.4 Au~10% Ni __ es ¦ 2 2.5 Ni 0.4 Au " 0 Yes . __ -- . ... _ .. __ 3 10.0 Ni 0.4 Au " 0 Ycs ¦ , .
. __ I ,, ¦ 4 1.4 Ni 0.6 Au " Yes .- . _ 2.5 Ni 0.6 Au " Yr~s ¦
i ~___ . . .
6 10.0 Ni 0.6 All " Ycs _ .. __ . .. __ _ ,_ __ t0 ¦ Hard Gold I CA725 1.4 Ni 0.4 Au-Hard 0 No ~ _ 2 .10.0 Ni 0.4 Au l~anl 0 , ~ No 3 . 1~4 Ni 0.6 " _. No 4 10.0 Ni 0.6 " o No G.F. Pd-Ni CA725 2 5 Ni0.625 Pd-20 Ni 0.125 Au-Hard No ¦ DGR-156 CA725 8.5 Ni æ8 Pd40 Ag 0.225 Yes - ---_ ~ ,,,_, ;~:
'' ': `' ' NIGOLDTM alloy - Ni. These coupons were prepared by plating soft pure gold to a thickness of 0.5 rnicrometers on solid pure nickel and heat treating the coupons in a reducing atmosphere according to the teaching of U.S. Patent No.
4,505,060 to diffuse 5-10% Ni to the surface of the gold. All elemental amounts are 20 ~ expressed ~n weight percent unless specifically ~nd~cated otherwise.

:, NIGOLD~M alloy - Cu coupons were prepared by plating 1.4, 2.5 and 10 micrometers of pUTe Ni on a copper base substrate CA725 (a copper alloy widely used as a connector spring material). I~e n~ckel was overplated with 0.4 and 0.6m~crometers of pure soft gold and heat treated the same as the NIGOLD~M alloy - Ni ,.

25 samples.
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-6- PC-~100 Hard Gold ! ' 1.4 and 10 rn~croinches of rickel was plated on top of alloy CA725 and then overplated with 0.4 and 0.6 micrometers of conventional cobalt hardened gold.
~is is the standard Hard Gold connector.

S Gold Flash Palladium Nickeli - G.F. Pd-Ni 0.125 micrometers of cobalt hardened gold was plated on 0.625 micrometers of 80/20 palladiurn/nickel on top of 2.5 m~crometers of nickel on top of alloy CA725 by AT&T.
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A clad inlay rnaterial of 0.~i25 micrometers of pure gold on 2.28 micrometers of 60% Pd/40% Ag on 8.1 m~crometers of nickel on top of CA725.
Contact was heat treated so the surface was 75% Au, 1 15% Au. DGR-156 was tested as a 4mm wide strip.

E~posure All coupons were cut along at least one edge and exposed to a Class 111 ~ ~ ;
Battelle flow~ng mixed gas test. ~is test e~posed the coupon to an atmosphere of ~ " ~;
20 Cl2, 200 NO2, 100 H2S e~pressed in parts per billion at 30C and 704/4 relative ;~ ~i hurnidity for periods of 2 to 10 days. ~e Class lll Battelle n~ixed gas test is widely '~
accepted in ~e industry as the simulating long term exposure in severe industrial ,;
20 environments.

- Test Results ;
The test results are g~ven below in Table 2. ~ ~

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TABLl~ 2 _ - . . _ . .
Specimen~ ure Da;cripd~Dn% Surface 1~18e C~cp l~ge Crc~p I
Days i3attelle _~ =_ Cov~7ed cut mm Plat}~d mm ¦
m Pores/cm2 Pore decoradon l .
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_____ ~__ _~ __ _ NlGOLD~Ni 2 O O O O O
._ 6 O _ -- 0 -_ . I
NIGOLD~ Cu I 2 1000 0.28 30 1.5 O
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5 l 6 1000 Joined 95 3 Some ~ _ 3 6 100 0.8 50 3 0 4 2 1000 0.1 20 1.7 0 __ . __ . _ 6 1000 Joined 95 3.0 Some . . ___ _ .. __ . _ llard Gold I 2 100 0.1 40 -l 4 0 __ - --- ... _ , _____ .__ ..
l 6 80 0.5 10 3.0 0 v . . ._ _ . .__ ... _ 2 ~ _6 6 _ 0.5 5~__ 3.0 O ~: .
3 6 80 0.5 10 3.5 0 I .; .
4------ 6 _ _.1__ : .. ~ ~ .. ............ .;
DGR-156 2.0 Entire l . surface ¦
. _ ___ - :. _ covered G.F. Pd-Ni 2 50 0.1 2 1.4 0 _. ,~,~ _ . .. _ 0.5 7 3~0 0 I :
___ - _ _ _ ~ , , The corrosion products show up on the surface as dark spots. Asi the length of the exposure increased from 2 to 10 days the degradation at any particular pore or spot increased. Dark corrosion products also were found to creep over the 20 surface from the edges.

NIGOLD~M alloy - Ni. In this spec~men, which notably contains no copper, had no corrosion spots and no corrosion products creep~ng around the edge (edge creep). This material passed a 10 day Battelle Test.

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NIGOLDTM alloy - Cu. All of the NIGOLD specirnens on copper substrates exhibited extensive corrosion and edge creep (3mm in 6 days). Generally, there was little difference in corrosion w~th increase in thickens of the Au layer.
Generally, the thicker the nickel underlayer, the less corroded the specimen. All of S these specimens failed this test.

Hard Gold Generally the hard gold was superior to NIGOLDTM alloy - Cu. The thickness of the Au layer had little effect on the results. Again, the thicker the nickel interlayer, the less corroded the specimen. All specimens showed extensive edge -creep (3mm in 6 days). All of the specirnens failed the Battelle test. ~ ;~

DGR-156 ~,~
Since this contact strip was only 4rmn wide, the entire surface ,vas ,~
covered by edge creep and failed the test.
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G.F. Pd-Ni Generally, these results were about the same as the hard gold. Again all coupons eventually failed the test.
., 'I~ese results were entirely une~pected. The only suitable material was on a copper free substrate. 111is may indicate that enough copper is migrating through a 10 rnicrometer thick layer of electroplate Ni to cause the forrnation of deleterious copper corrosion products on the surface. Also, copper from cut edge on a contact may migrate over the surface up to 3rnrn in 10 days at 30C.

These results have profound importance in design of new cormectors for high temperature, corrosive atmosphere service.
. ~1" - ' Con~act Resistance on l~ermal A~ing To measure the high temperature stability of the samples of NIGOLDTM
alloy - Ni, NIGOLDTM alloy - Cu, Hard Gold, DG156, and G.F. Pd-Ni were placed in an '.': ,;

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-9- PC-'1100 oven for 100, 500 and 1000 hours at 100C, 150C and 200C. The contact resistance was determined by probing with a 50g load or without wip~ng accordingto ASTM B-667.

The results are summarized in Figures 1, 2 and 3 which show the resistance in rnillivolts for the various matenals after exposure at 100, 150, and 200C respectively. Exposure tirnes are for 1000 hours except where a high resistance reading was noted and a shorter exposure time is noted. In power applications (greater than 10amps) contact resistance values higher than 5 rnillio~mms can result in signi~icant contact hea~ng and accelerated failure. Insignal (low power) circuits a contact resistance below 5 milliohms is generally acceptable.

These results show that where only oxygen and nitrogen is in the atmosphere that NIGOLD7M alloy on pure nickel is the most therrnally stable material.
NIGOLD~ alloy on electroplated Ni in copper is the next best and has a service temperature capability in excess of 20()C for over 1000 hours. Hard Gold becomes unacceptable in sen~ices between 100 to 150C presumably because of the degradation in the organic hardeners in the deposit. DGR is the second best material compared to NIGOLD~M alloy, but DGR fails somewhere from 150 to 200C. The G.F.
Pd-Ni also fails somewhere between 100 and 150C.

From these unexpected results and the observations the design for ~ .
connectors specif;ically adapted for high temperaturè and corrosive gaseous atmospheres has been ascertained. Generally, the requirements of a connector arepassing a 10 day Battelle Class lll test without spotting visible to the unaided eye while simultaneously maintaining a contact resistance of less than 5 milliohms with a 50g load after 1000 hours over 200C as specified in test ASTM B-667.
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The contact surface should be a noble metal. The noble metal surface advantageously ;s A~, Pd, Ni or an alloy of any combination thereof. Most advantageously, gold is used as the contact metal. If good wear resistance is required, the gold should be alloyed with up to 10% Ni to harden it. The thickness ~: .

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of the contact surface layer is most advantageously less than 0.4 micrometers. Hard gold containing organics is not desilable as a plated surface. The noble metal alloy advantageously is formed frorn strip and roll bonded. ~e precious metal can be electroplated, but the deposit must be free from organics. If pure gold is deposited, it S can be heat treated to diffuse Ni from the substrate into the Au as taught by Bell et ~ ~
al. The least cost method for thin surface layers is probably electroplating and ~ ~.
annealing as taught by Bell et al in U.S. Pat. No. 4,505,060 ('060). The entire specification of the '060 patent is hereby incorporated. The porosity of the surface layer does not appear to be cIitical. -The best high temperature colrosion resistant contact is soft gold plated on pure wrought Ni heat treated to interdiffusion the Ni and Au then bonded with a as little contact as possible to copper-base spring material, or akernately bonded to a copper-free spnng material like PERMANICKEL~ alloy 300 (nickel-titanium alloy) or DURANICKEL~ alloy 301 (nickel-aluminum-ti~arlium alloy). (PERMANICKEl. and DURANICKEL are registered trademarks of the Inco farnily of companies. This discovery also shows that the fabrication method of 4,956,026 is also applicable if a PERMANICKEL or DURANICKEL base alloy is used.
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Nominal composition specifications by weight percent for PF.RMANlCKEL alloy 300 and DURANICKEL alloy 301 are below in Table 3 .'.';

i r ~ , PERMANICKEL ~lloy300 ¦ DURANlCKleL alloy 301 ¦
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S Ni 98.5 96.5 C 0.2 _ 0.15 _ Mn 0.25 0.25 Fe 0 3 __ 0.3 Cu 0.13 0.13 _ . _ _. _ . .
Ti 0.4 0.63 . ., Mg 0.35 . _ .__ S 0.005 O.OOS
_ ._ .... n ..
Si 0.18 0.5 ~. .
Al - ~ ' ' ~ ':
lt has been discovered that wrought nickel interlayers for supporting .
noble metal sul~aces may be used over copper contain~TIg substrates in hostile environments. Electroplating over other substrates containing no copper is acceptable. Most advantageously, wrought nickel has a thickness of at least 10 20 ~ microns and electroplated nickel interlayers have a thickness of 1 to 10 microns. For , instance PERMANlCKELQ alloy or DURANICKEL0 alloy each have acceptable properties. Advantageously, the copper-free substrate provides corrosion resistance, strength and creep resistance to hold shape at 200C in an air atmosphere. The copper-free substrate most advantageously must also possess the required spring ~25 properties and stress relaxation requirements associated wi~ alloy CA725.

lf a copper conta~ning substrate ;s used, a substantially pure wrought nickel interlayer such as Nickel 290 is required. ~or purposes of this specification, substanlially pure is defined as at least 98% nickel. Most advantageously, 99.9%pure wrought n~ckel is used.

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~0~93~0 :, Inlays of wrought pure Ni 2~0 onto CA725 StIip are not acceptable because of edge creep. If any inlay or roll bonding of pure nickel sheet onto CA725 is used then the roll bonded bimetallic must be electrolytically overplated with 3 to 10 micrometeIs of Ni to prevent edge creep, the Au must then be overplated and S interdiffused with the Ni as taught by Bell et al.

CA725 can be used as a substrate if used with a thicker interlay of wrought pure Ni and wherein the CA725 generally is not attached to the nickel; and Ni only makes a point on line contact with the wrought pure Ni on the side opposite the contact point. For instance, a wire of CA725 wrapped around pure wrought 10 nickel strips where the wire is as remote as possible from the contact point is acceptable. Other acceptable configurations would be a pure wrought nickel stripon the inside and on strip CA725 dimpled so it only touches the wrought nickel at i one point on the outside. These designs facilitate elimination of edge creep of the corrosion products from the copper conta~ning substrate. )~

While in accordance with the provisions of the statute, there is ~:
illustrated and described herein specific embodiments of the invention. Those skilled in the art will understand that changes may be made in the form of the inventioncovered by the claims and the certain features of the invention may sometimes beused to advantage without a corresponding use of the other features.
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Claims

1. A composite material for use in electrical connectors comprising:
a) a nickel-base conductible substrate alloy, the substrate alloy having suitable corrosion resistance, strength and creep resistance to hold shape at 200°C;
b) an interlayer of substantially pure electrolytic nickel having a thickness bonded to substrate (a); and c) a noble metal diffusion bonded to the interlayer of substantially pure electrolytic nickel for increasing hardness of the noble metal and the noble metal surface being free of organic hardeners.

2. The composite material of claim 1 wherein the noble metal is selected from the group consisting of gold and gold-nickel alloys containing from 1 to 10% Ni and the noble metal has a thickness less than 0.4,µm.

3. The composite material of claim 1 wherein the noble metal containing surface includes a gold-nickel alloy produced by interdiffusion of pure soft gold plate and the interlayer of substantially pure electrolytic nickel substrate.

4. The composite material of claim 1 wherein the noble metal surface is made from an alloy formed from the group consisting of Au, Pd and Ni.

5. The composite material of claim 1 wherein the nickel-base substrate is selected from the group consisting of nickel-aluminum-titanium alloys and nickel-titanium alloys.

6. The composite material of claim 1 wherein the thickness of the interlayer is 1 to 10 micrometers.

7. A composite material for use in electrical connectors comprising:
a) a conductible copper base substrate alloy, the copper-base substrate alloy having spring properties and creep resistance properties;
b) an interlayer of substantially pure wrought nickel having a thickness of at least 10 microns mechanically bonded to the copper-base substrate to form a clad intermediate product of the copper-base substrate and the wrought nickel; and c) an electrodeposited layer of nickel 3 to 10 microns in thickness enveloping the clad intermediate product of the copper-base substrate and the wrought nickel;
d) a noble metal surface diffusion bonded to the electrodeposited nickel adjacent to the interlayer of substantially pure wrought nickel for increasing hardness of the noble metal and the noble metal being free of organic hardeners.

8. The composite material of claim 7 wherein the noble metal is selected from the group consisting of gold and gold-nickel alloys containing from 1 to 10% Ni and the noble metal has a thickness less than 0.4 µm.

9. The composite material of claim 7 wherein the noble metal containing surface includes a gold-nickel alloy produced by interdiffusion of pure soft gold plate and the pure nickel substrate.

10. The composite material of claim 7 wherein the noble metal surface is made from an alloy formed from the group consisting of Au, Pd and Ni.

11. The composite material of claim 7 wherein the interlayer is wrought nickel having a purity of at least 99.9%.

12. A method of producing a composite material useful to form electrical contacts comprising:

a) providing a nickel-base conductible substrate alloy having sufficient corrosion resistance, strength and creep resistance to hold shape at 200°C;
b) bonding an interlayer of substantially pure electrolytic nickel to the substrate; and c) diffusion bonding noble metal alloy to the interlayer of substantially pure electrolytic nickel to harden the noble metal and the noble metal being free of organic hardeners.

13. The method of claim 12 wherein step b) includes electrodepositing nickel over the conductible substrate and step c) includes electrodepositing soft gold to the interlayer and further including step d) of heat treating the composite material to diffuse nickel into the soft gold.

14. A method of producing a composite material useful to form electrical contacts comprising:

a) providing a conductible copper-base substrate alloy having spring properties and creep resistance properties;
b) mechanically bonding a 3 to 10 microns interlayer of wrought nickel to the copper-containing substrate to form a clad intermediate product of copper-base substrate and wrought nickel;
c) electroplating nickel to cover the clad intermediate product of copper-base substrate and wrought nickel;
d) diffusion bonding a noble metal surface to the electroplated nickel adjacent the wrought nickel to harden the noble metal and the noble metal being free of organic hardeners; and e) heat treating to harden the noble metal containing surface with nickel.

15. The method of claim 14 wherein the electroplating of nickel occurs prior to the mechanical bonding with nickel.