The parts of an electrical contact device are treated by sputter etching to remove the parent metal oxide. Prior to exposure of the electrodes to any oxygen, a sacrificial metal is sputter deposited on the parts. Preferably this sacrificial metal is one that oxidizes slowly and is readily dissolved by the liquid metal. The sacrificial metal may then be removed from unwanted areas. The remainder of the ring and the probe to be wet by the liquid metal are submerged in the liquid metal or the liquid metal is flushed over these areas, preferably while they are being slightly abraded, unitl all the sacrificial material on these portions is wet by the liquid metal. In doing so the liquid metal dissolves the sacrificial metal and permanently wets the parent metal. Preferred materials used in the process and for the electrodes of electrical contact devices are high purity (99.0%) nickel or AISI type 304 stainless steel for the electrical contact devices, gallium as the liquid metal, and gold as the sacrificial material

Berkopec, F. D.

Culp, D. H.

Lovell, R. R.

English

NASA Technical Reports Server

United States Patent WI 
Eovell et al. 
[I11 4,023,266 
1451 May 17, 1977 
PROCESS FOR PREPARING LIQUID METAL 
ELECTRICAL CONTACT DEVICE 
Inventors: Robert R. Lovell, N. Ridgeville; 
Frank D. Berkopec, Fairview Park; 
David H. Culp, Rocky River, all of 
Ohio 
Assignee: The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space , 
Administration, Washington, D.C. 
Filed: July 26, 1976 
Appl. No.: '708,658 
U.S. CI. ................................... 291628; 291597; 
291622; 291630 E 204132 R 
Int. C1.* ........................................ HOlR 43/00 
Field of Search ............. 291628, 630 E, 630 R, 
291622, 597, 527.1 , 527.2, 530; 3 10123 1, 
232, 242, 248, 249,251, 252; 2001262, 270, 
230, 23 1, 232, 233, 234, 235; 204132 R, 33, 
34, 323, 35; 15612, 5, 6, 18, 20 
References Cited 
UNITED STATES PATENTS 
3,966,570 611976 Yamagishi et al. .......... 204135 R X 
Primary Examiner-James R. Duzan 
Attorney, Agent, or Firm-N. T. Musial; G. E. Shook; 
John R. Manning 
ABSTRACT 
In a process or method according to the invention the 
parts of an electrical contact device, such as a slip ring 
comprising the ring to receive the liquid metal and the 
probe or brush for contacting the liquid metal are 
treated by sputter etching to remove the parent metal 
oxide. Prior to exposure of the electrodes to any oxy- 
gen, a sacrificial metal is sputter deposited on the parts. 
Preferably this sacrificial metal is one that oxidizes 
slowly and is readily dissolved by the liquid metal. The 
sacrificial metal may then be removed from unwanted 
areas. The remainder of the ring and the probe to be 
wet by the liquid metal are submerged in the liquid 
metal or the liquid metal is flushed over these areas, 
preferably while they are being slightly abraded, until 
all the sacrificial material on these portions is wet by 
the liquid metal. In doing so the liquid metal dissolves 
the sacrificial metal and permanently wets the parent 
metal. Preferred materials used in the process and for 
the electrodes of electrical contact devices are hiah 
3,144,533 8/1964 Donath .......................... 200/234 X purity (99.0%) nickel or AIS1 type 304 stainless stgel 
3,369,094 2/1968 Langberg et al. ............. 2001233 X for the electrical contact devices, gallium as the liquid 
3,497,426 2/1970 Okamura ......................... 204/32 R 
3,616,285 10/1971 Norris .......................... 204/32 R X 
3,909,569 9/1975 Jones .............................. 200/61.53 7 Claims, 1 Drawing Figure 
3,444,408 5/1969 Krulls ............................ 310/232 X . metal, a d  gold as the sacrificid material. 
https://ntrs.nasa.gov/search.jsp?R=19770019441 2020-03-20T07:23:58+00:00Z
U.S. Patent May 17, 1977 4,023,266 
4,023,266 rl 1 
PROCESS FOR PREPARING LIQUID METAL 
ELECTRICAL CONTACT DEVICE 
ORIGIN OF THE INVENTION 
The invention described herein was made by employ- 
ees of the United States government and may be manu- 
factured and used by or for the government for govern- 
mental purposes without the payment of any royalties 
thereon or therefor. - 
BACKGROUND OF THE INVENTION 
It is known to provide electrical contact devices such 
as slip ring arrangements for use particularly in space 
on satellites. For example, such a slip ring arrangement 
may involve a ring which contains a groove which acts 
as a reservoir for a metal which is liquid during opera- 
tion and retained. in the groove by surface tension. A 
probe which acts as a brush for the slip ring arrange- 
ment is immersed in the liquid metal and thereby 
makes electrical contact between the probe and the 
ring. One of the problems in preparing liquid metal 
electrical contact devices is to apply the charge of 
liquid metal in such a way that it wets the electrodes 
thereby making good electrical contact with it. 
Prior methods of wetting are based generally upon 
means whether mechanical or chemical to remove, the 
non-wetting oxide of the metals of which the slip ring 
and probe or brush are made, from the portions to be 
wet by the liquid metal. Failure to do so may sometimes 
cause the liquid metal falsely to wet an oxide or hy- 
drated oxide layer of the liquid metal on such portions 
over the parent metal of the electrode. Such false wet- 
ting tends to dewet in a vacuum environment and result 
in undesirable operation such as poor or erratic 
contacts. For example, a mechanical means of oxide 
removal and liquid metal wetting consists of machining 
the final configuration while the surfaces are sub- 
merged in gallium or in an inert atmosphere. This may 
be done with a cutting tool, or using a hand-held mate- 
rial with some abrasive properties. It is difficult if not 
impossible to avoid undesirable impregnation of the 
electrode with impurities when using such a process. 
Chemical means of oxide removal may consist of acid 
removal of the parent metal oxide or heating those 
parts of the liquid metal contacting surfaces in vacuum 
or in an inert atmosphere to a temperature which will 
drive off the oxide. Then the surfaces must be kept 
from exposure to any oxygen-containing atmosphere 
prior to being wet by the liquid metal. 
Both the mechanical and chemical methods de- 
scribed above preclude wetting the electrodes or slip 
ring parts after assembly because the lead-in wires and 
insulation materials are generally destroyed in the pro- 
cess. 
When using the mechanical methods it is difficult to 
keep the gallium or liquid metal in contact with the 
cutting tool and the slip ring or brush and also results in 
troublesome chips and requires relatively large 
amounts of liquid metal. These mechanical methods do 
not lend themselves readily for use with any except 
simple shapes. The mechanical methods are therefore 
relatively difficult in procedures and require consider- 
able preparatory effort and also are costly in terms of a 
required amount of liquid metal. 
The chemical means of oxide removal also involve 
assuring that the parent metal be in contact with the 
liquid metal prior to exposure to oxygen-containing 
L 
atmosphere. This requirements demands a facility or 
apparatus such as a dry box or vacuum chamber and 
further apparatus to apply the liquid metal. In addition, 
precautions must be taken to be sure that the parent 
5 metal is wet in the desired portions only, otherwise 
additional effort is needed to remove excess liquid 
metal from contact with undesired areas. 
SUMMARY OF TIliE INVENTION 
According to the invention a process of preparing the 
electrically contacting portions of relatively moveable 
members, such as a slip ring comprises sputter etching 
the parts between which electrical contact is to be 
made, sputter depositing these parts with a sacrificial 
15 material, and then wetting the parts with a liquid metal 
that dissolves the sacrificial material. Thus the liquid 
metal dissolves the sacrificial material and at the same 
time wets the parts between which the electrical 
contact through the intermediary of the liquid metal is 
BRIEF DESCRIPTION OF THE DRAWING 
The foregoing and other advantages and novel fea- 
tures of the invention and the objects thereof will be 
25 more fully understood from the following brief descrip- 
tion when read in connection with the accompanying 
drawing consisting of a sole FIGURE illustrating a slip 
ring which may be treated in accordance with the in- 
vention. 
DESCRIPTION OF THE PREFERRED 
EMBODIMENT 
An example of the process of the invention may be 
described in connection with the slip ring arrangement 
35 illustrated in cross-sectional view in the sole FIGURE. 
A ring 40 has a groove or reservoir 42 which is U- 
shaped in cross-section and €aces outwardly from the 
central axis 44 of the ring 40. The groove or reservoir 
42 is symmetrical with respect to a plane 46 at right 
40 angles to the axis 44 of the ring. A probe or brush 48 
rides within the groove 42 to make contact with the 
metal 50 which during operation is liquid and retained 
within the groove or reservoir 42 by surface tension. 
The liquid metal 50 wets both the walls of the groove 
45 42 and the probe 48 thereby making contact with the 
rotatable ring 40 and the probe 48. 
The probe 48 is chamfered along the sides as indi- 
cated, for example, at 52 symmetrically with respect to 
the plane 46 and further symmetrically with the central 
50 axis of the probe itself which has the same shape and 
presents the same face in either direction of motion 
with respect to the liquid metal as the ring or electrode 
40 rotates about its axis 44. Preferably the probe 48 has 
a thickness of about one-fifth the width of channel 42 
55 and is chamfered as shown t'o reduce the mechanical 
resistance to relative motion in the liquid so that it 
presents a kniie edge or a sharp edge in the direction of 
relative motion whether the motion is in one direction 
or the other with respect to the liquid metal as the rotor 
60 turns in one direction or the other about axis 44. Only 
one edge 43 is visible in the FIGURE. The slip ring 
device is described and claimed in U.S. Pat. application 
Ser. No. 708,659 of Frank D. Berkopec et al filed on 
the same day as this application. 
In preparing the parts the slip ring 40 or if there is an 
assembly the slip rings and brushes such as brush 48 are 
first machined to final dimensions, and mounted in 
fixtures which shield the areas on which the sputtered 
io 
20 tobemade. 
30 
65 
3 
4,023,266 
4 
sacrificial material is not required. The rings and configurations are not restricted to the simple ones 
brushes are then sputter etched, using ordinary, known heretofore employed. Furthermore it is convenient to 
techniques to remove the outer layer of the parent perform the process without the necessity of a vacuum 
metal which may have become oxidized. Next the de- chamber as it may be performed in an oxygen bearing 
sired parts comprising the walls of the groove 42 and 5 atmosphere such as air. The sputter deposition of a 
the part of probe 48 to be immersed in the liquid metal protective and sacrificial layer of a soluble. slowly oxi- 
are sputter deposited with the protective and sacrificial dizing metal on the areas to be wet, which sacrificial 
material, again using common, known techniques, to a layer is thereafter dissolved by the application of a 
thickness necessary to insure that the parent metal liquid metal, provides a superior method for wetting 
oxide does not form on the parent metal. The surfaces IO with liquid metal relatively moveable parts between 
of the parts are protected from oxidation between etch- which electrical contact is to be made by the intermedi- 
ing and sputter depositing while the parts are in the ary of the liquid metal. The process is especially useful 
sputter etchhputter deposit facility. Vacuum is main- for slip rings to be used in space, but may also be used 
tained between the “etch” and “sputter deposit’’ pro- for relays or switches having moveable parts between 
cesses. 
The sacrificial material may then be removed from What is claimed is 
areas which are not to be wet by the liquid metal, if any 1. A process for preparing parts between which elec- 
have been deposited thereon inadvertently. This re- trical contact is to be made comprising the steps of 
moval is accomplished with conventional equipment applying a sacrificial metal to said parts over the areas 
using clean, dry, cautious techniques. 20 of contact and wetting said areas with a liquid metal 
The slip ring and brush areas that are to be wet are which is a solvent for said sacrificial metal, whereby the 
then slightly abraded with a metal spatula of the same sacrificial metal is dissolved and the liquid metal wets 
or similar composition as the parts to be wet while the the areas underneath the dissolved sacrificial metal. 
areas are submerged in the liquid metal or while the 2. A process as claimed in claim 1 wherein said sacri- 
liquid metal is flushed over the areas being abraded. 25 ficial metal is gold and said liquid metal is gallium. 
Preferably several thicknesses of lint-free, slightly abra- 3. A process for preparing parts between which elec- 
sive fibrous material are wrapped about the spatula. A trical contact is to be made comprising the steps of 
cellulose tissue used in “clean rooms” has been satis- applying a sacrificial metal to said parts over the areas 
factory. The material is held taut around the rubbing of contact, abrading said areas, and wetting said areas 
edge of the spatula, and the rubbing edge is then ap- 30 with a liquid metal which is a solvent for said sacrificial 
plied to the area to be wet with a force of about % metal whereby the sacrificial metal is dissolved and the 
pound (about 1 Newton). Abrading is a positive means liquid metal wets the areas underneath the dissolved 
of insuring liquid metal-sacrificial material contact. sacrificial metal. 
This is continued briefly until all of the sacrificial mate- 4. The process as claimed in claim 3, wherein said 
rial in the area desired is dissolved and the area is wet 35 sacrificial metal is applied by sputter deposition. 
by a liquid metal. In the process the liquid metal dis- 5. The process as claimed in claim 3, wherein said 
solves the sacrificial material and permanently wets the abrading is performed at the same time as said wetting 
parent metal. In effect the deposit of the sacrificial ofsaidareas. 
material protects the parent metal from oxidation and 6. A process for preparing a slip ring comprising a 
when it is dissolved in the liquid metal the parent metal 40 channel and a probe between which electrical contact 
underneath the dissolved portion is easily and thor- is to be made by the intermediary of a liquid metal 
oughly wetted by the liquid metal. comprising the steps of removing any oxide from the 
Typical materials which may be used for the slip rings areas of said channel and said probe between which 
and brushes are high purity (99.0%) nickel or AIS1 type said contact is to be made, covering said oxide-free 
304 stainless steel for the slip ring..: and brushes respec- 45 areas with a sacrificial metal, applying liquid metal to 
tively, gold as the sacrificial material and gallium as the said channel wherein the liquid metal when liquid is 
liquid metal. retained by surface tension and to said probe over the 
The foregoing process may be used for any device said sacrificial metal-covered areas, thereby to dissolve 
requiring a wetted liquid metal contact, such as wetted the sacrificial metal in said liquid metal and wet with 
relays, which exhibit low electrical contact resistance, 50 said liquid metal the said areas. 
or the like. The invention provides a simple and posi- 7. A process as claimed in claim 6, said ring and said 
tive method for applying the liquid metal to the elec- probe consisting essentially of a metal not readily oxi- 
trodes which will be relatively moving and wetting the dized, said sacrificial metal consisting essentially of 
desired portions or parts thereof. Machining processes gold, and said. liquid metal consisting essentially of 
which may result in undesired chips are eliminated. 55 gallium. 
Areas to be wet may be more or less complicated and 
IS which electrical contact is to be made. 
* * * * *  
60 
65 


Process for preparing liquid metal electrical contact device

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server