U.S. patent number 3,686,457 [Application Number 05/112,534] was granted by the patent office on 1972-08-22 for improved electrical contact having a heat sink layer.
This patent grant is currently assigned to Texas Instruments Incorporated. Invention is credited to Rene A. Dubac, Sheldon S. White, Joseph A. Willoughby.
United States Patent |
3,686,457 |
Dubac , et al. |
August 22, 1972 |
IMPROVED ELECTRICAL CONTACT HAVING A HEAT SINK LAYER
Abstract
An improved electrical contact including a heat sink layer
secured to a substrate and an electrical contact layer secured to a
surface of the heat sink layer. The heat sink layer and the contact
layer are each of a generally nonuniform cross-section, including
respective central portions of differing thicknesses with respect
to the peripheries thereof disposed in mating relationship, with
the contact layer terminating spaced inwardly from the periphery of
the heat sink layer.
Inventors: |
Dubac; Rene A. (Attleboro,
MA), White; Sheldon S. (Brookline, MA), Willoughby;
Joseph A. (Attleboro, MA) |
Assignee: |
Texas Instruments Incorporated
(Dallas, TX)
|
Family
ID: |
22344411 |
Appl.
No.: |
05/112,534 |
Filed: |
February 4, 1971 |
Current U.S.
Class: |
200/269; 29/877;
257/720; 29/830; 200/289; 257/781 |
Current CPC
Class: |
H01H
1/62 (20130101); Y10T 29/49126 (20150115); Y10T
29/4921 (20150115) |
Current International
Class: |
H01H
1/00 (20060101); H01H 1/62 (20060101); H01h
001/02 () |
Field of
Search: |
;29/63C
;200/166C,166BH,166J |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Jones; H. O.
Claims
WHAT IS CLAIMED IS:
1. A multilayer electrical contact member comprising a substrate
layer of electrically conductive metal material, a heat sink layer
of selected peripheral size formed of an electrically conductive
metal material which is characterized by relatively high thermal
conductivity, said heat sink layer having one layer surface thereof
secured in electrically conductive relation to said substrate
layer, and a contact surface layer of relatively smaller peripheral
size formed of an electrically conductive metal material which is
characterized by relatively low contact surface resistance, said
contact surface layer being secured in electrically and thermally
conductive relation to an opposite layer surface of said heat sink
layer with the periphery of said contact surface layer being spaced
inwardly from the periphery of said heat sink layer.
2. A multilayer electrical contact member comprising a substrate
layer of electrically conductive metal material, a heat sink layer
of selected peripheral size formed of copper, said heat sink layer
having one layer surface thereof secured in electrically conductive
relation to said substrate layer, and a contact surface layer of
relatively smaller peripheral size formed of a material selected
from the group consisting of silver, silver cadmium oxide, gold,
palladium, platinum and alloys thereof, said contact surface layer
being secured in electrically and thermally conductive relation to
an opposite layer surface of said heat sink layer with the
periphery of said contact surface layer being spaced inwardly from
the periphery of said heat sink layer.
3. A multilayer electrical contact member as set forth in claim 2
wherein said contact surface layer has a relatively greater
thickness at the central portion thereof than at said periphery of
said contact surface layer, and wherein said heat sink layer has a
recess on said opposite layer surface thereof partly accommodating
said relatively thicker central portion of said contact surface
layer therein.
4. A multilayer electrical contact member as set forth in claim 2
wherein said substrate layer is formed of low carbon steel.
5. A multilayer electrical contact member as set forth in claim 2
wherein said contact surface layer and said heat sink layer have
peripheral sizes such that said contact surface layer covers from
about 50 to 90 percent of said heat sink layer.
Description
The present invention relates generally to electrical contacts and
more particularly is directed to improved multi-layer electrical
contacts including a heat sink layer and an electrical contact
layer.
Various types of electrical contact arrangements have been
developed including numerous improvements, such as decreased
contact resistance, increased electrical lifetime, etc. However, as
technology has advanced resulting in decreased costs of various
elements utilized in electrical systems as well as increased
durability many electrical contact arrangements are still
considered to have a relatively limited lifetime, particularly when
exposed to continued repetitive operation in the presence of
electrical arcing, and in certain instances remain quite expensive
relative to the cost of other elements in such systems due to the
usage of precious metals in the contact. More particularly, the
current magnitude or amperage rating of the contact generally
determines the surface area of the contact material, while the
thickness of the contact arrangement generally governs the ultimate
lifetime of the contact, since continued arcing eventually results
in erosion of the contact material to a point at which the base
metal or substrate is exposed resulting in eventual contact
failure. Generally it is desirable to fabricate the exposed contact
area of a relatively good electrical conductor which is resistant
to corrosion and has a low contact resistance. Particularly
suitable materials in this regard are silver, gold, and other
precious metals which, of course, increase the cost of the contact.
In order to reduce the cost of the contact, while providing
suitable heat dissipation characteristics, in certain instances
multi-layer contact arrangements have been suggested in which a
heat sink such as a copper layer, is disposed intermediate the
precious metal contact layer and the substrate or base metal.
However, such contacts are still relatively expensive and are
expendable in that burn-through of the contact layer eventually
occurs, dictating the usage of increased quantities of expensive
precious metal relative to the heat sink layer. Furthermore,
ordinarily in fabricating such contacts the expense of fabrication
is increased in view of the associated wastage of material during
processing necessitating the implementation of scrap recovery
procedures in order to recover all or part of the precious metal
and/or copper scrap which is produced.
Accordingly, it is an object of the present invention to provide an
improved method for fabricating an electrical contact device in
which the usage of expensive materials is minimized and the cost of
fabrication is reduced.
It is another object of the present invention to provide an
improved method for fabricating an electrical contact device in
which substantially all of the material being processed is utilized
to eliminate the necessity for scrap recovery operations.
It is another object of the present invention to provide an
improved electrical contact device in which the usage of relatively
expensive material is minimized, while electrical lifetime is
maintained at a relatively high level.
It is another object of the present invention to provide an
improved electrical contact device which is extremely economical to
fabricate and durable in use.
Various additional objects and advantages of the present invention
will become readily apparent from the following detailed
description and accompanying drawings wherein:
FIG. 1 is a perspective generally diagrammatic view of a preferred
method for fabricating an electrical contact device in accordance
with the principles of the present invention;
FIG. 2 is a vertical sectional view of one embodiment of an
electrical contact device in accordance with the present
invention;
FIG. 3 is a plan view of the device illustrated in FIG. 2;
FIG. 4 is a vertical sectional view of another embodiment of an
electrical contact device in accordance with the present
invention;
FIG. 5 is a plan view of the device illustrated in FIG. 4;
FIG. 6 is a vertical sectional view of still another embodiment of
an electrical contact device in accordance with the present
invention; and
FIG. 7 is a plan view of the device illustrated in FIG. 6.
Referring generally to the drawings and initially to FIG. 1 wherein
a method of fabricating an electrical contact device in accordance
with the principles of the present invention is illustrated, a
continuous sheet of substrate or support material 10 is carried on
a roll 12 and advanced in the direction indicated. As shown, the
sheet of substrate material 10 may have a plurality of spaced pilot
or index apertures 14 to aid in suitably positioning the material
for subsequent processing operations. A suitably supported roll 16
carrying a coil of a first preselected metallic material 18 is
provided adjacent the sheet 10 and, as shown, is adapted to feed
the material 18 toward the surface of the sheet 10 where a first
securing means 20, such as a suitable welding apparatus, is
provided adjacent the sheet 10 to secure the leading edge of the
material 18 to the sheet. In addition, a suitably supported cutter
means 22 is arranged in alignment with the material 18 for
effecting a separation or cutting operation immediately subsequent
to the securement operation to effect the formation of segments of
the material 18, defining first bodies 24 of heat sink material,
which are, thus, successively deposited at spaced intervals on the
surface of the substrate sheet 10 as it is continuously advanced.
Subsequent to securement and separation the body 24 of heat sink
material is carried by the advancing substrate 10 to a position in
alignment with a first coining means 26 having a suitably shaped
die face 27 adapted to deform substantially the entire body 24 of
heat sink material into a preselected configuration to define a
heat sink layer 28 having a generally nonuniform cross section
including a central portion 29 of decreased thickness with respect
to the periphery thereof. Another suitably supported roll 30 which
carries a coil of a second preselected metallic material 32 is
disposed adjacent the output edge of the first coining means 26
and, as shown, is adapted to feed the material 32 onto the exposed
surfaces of the respective advancing heat sink layers 28. As the
material 32 is fed onto the heat sink layers, a second securing
means 34 such as a suitable welding apparatus, is provided for
securing the leading edge of the material 32 to the surface of the
heat sink layer 28. In addition, a suitably supported cutter means
36 is positioned in alignment with the material 32 for effecting a
cutting or separation operation immediately subsequent to the
securement operation to provide individual segments of a
predetermined length of the material 32, defining second bodies 38
of contact material which are, thus, successively secured to the
exposed surfaces of the respective heat sink layers 28 as the sheet
10 is continuously advanced. The advancing sheet 10 then carries
the heat sink layer 28 and the second body 38 to a position in
alignment with a second coining device 40 having a suitably shaped
die face 41 adapted to deform substantially the entire second body
38 into a preselected configuration defining an exposed contact
layer 42 having a generally nonuniform cross-section including a
central portion of an increased thickness with respect to the
periphery thereof and in mating relationship with the central
portion 29 of the heat sink layer 28, while terminating spaced
inwardly from the periphery of the heat sink layer, as shown. A
suitable separating device 44 is provided adjacent the output end
of the coining device 40 and is adapted to effect a cut through the
sheet 10 along the cut line 46 indicated so as to separate the
sheet 10 carrying the spaced respective heat sink and contact
layers into individual portions to define completed units 48.
The substrate material 10 carried on the roll 12 preferably
comprises a relatively thin sheet of a suitable metallic material.
In this regard the sheet 10 is selected with regard to properties
desirable in accordance with the ultimate environment and
application of the contact 48. For example, if increased structural
strength is desired thin coiled sheets of various types of low
carbon steels may be suitable such as that commonly identified as
SAE (Society of Automotive Engineers) No. 1010 low carbon steel
which comprises by weight approximately between 0.08 to 0.13
percent carbon, 0.30 to 0.60 percent manganese, 0.040 percent
(max.) phosphorous, 0.050 percent (max.) sulphur and the balance
iron. Similarly, in certain other instances suitable thin coiled
sheets of brass or bronze may be utilized, while in other instances
thin coiled sheets of phosphor bronze, various monel metals, etc.
may be utilized. In the illustrated embodiment the sheet is
utilized primarily as a carrier for the heat sink and contact
layers and is relatively thin, varying in thickness between
approximately 0.008 inch to 0.070 inch, although other thicknesses
may be appropriate in certain instances.
The roll 16 of material 18 preferably comprises a suitably
supported roll of a coiled rod-like member or wire of material
having a high thermal conductivity, such as substantially pure
copper wire. Copper wire is particularly advantageous in this
regard in view of its ready availability, low cost, and ease of
processing, in this form. The copper wire 18 preferably has a
circular cross-section for reasons of economy although other
cross-sectional configurations may be utilized if desired. The
copper wire 18 has a preselected diameter such that the bodies 24
formed therefrom are of a sufficient size to permit formation of
the heat sink layer 28 in the desired configuration. In the
illustrated embodiment the copper wire 18 may have a diameter of
between approximately 0.062 to 0.250 inch, although, if desired,
other sized wire may be utilized. The welding means 20 may comprise
any one of a variety of conventional welding apparatus, although in
view of the difficulty in welding copper due to its high thermal
conductivity it is generally desirable to utilize a suitable point
welding apparatus which is not shown in detail, since such
apparatus is conventionally available. The first coining or
deforming means 26 which is disposed adjacent the output edge of
the welding means 20 is suitably supported and may be operated
electrically, hydraulically or in other conventional ways, and is
arranged to deform substantially the entire body 18 to form the
heat sink layer 28 without any material loss, obviating the
necessity for subsequent scrap recovery operations. In this
connection the die face 27 may be shaped to deform the heat sink
layer 22 to include the generally centrally located depression 29
for accommodating the thicker central portion of the contact layer
42 in mating relationship therewith. Although in the illustrated
embodiment the heat sink layer 28 is shown in a generally circular
configuration, other configurations may be readily formed such as
rectangular shaped bodies, elliptically-shaped bodies, etc. an
important feature being the inclusion of a generally centrally
located depression of reduced thickness with regard to the
periphery thereof so as to form a layer having a nonuniform
cross-section to accommodate an increased thickness of contact
layer material at the central region thereof. In the illustrated
embodiment the heat sink layer 28 may be deformed to a thickness of
between approximately 0.010 to 0.125 inch, while the depression 29
may be formed to extend smoothly from the periphery progressively
decreasing in thickness or may be formed as an abrupt slot at the
center of the layer. Similarly the depression 29 may extend
inwardly from the exposed surface of the layer 28 a predetermined
distance depending upon the ultimate application intended for the
contact system, although preferably the depression region retains
approximately half the thickness of the layer 28 in order to avoid
adversely effecting the heat sink properties of the heat sink layer
28.
As the heat sink layer 28 is advanced in the direction indicated
toward the succeeding station at which the roll 30 is positioned
the contact body 38 is secured to the surface of the heat sink
layer 28 generally in alignment with the centrally located
depression 29. The contact body 38 preferably comprises a
preselected metallic material having a relatively high electrical
conductivity and low contact resistance, as well as good corrosion
resistance properties. Preferably the contact body comprises a
material, such as silver, silver cadmium oxide, gold, palladium,
platinum or alloys thereof. The contact body material 32 is
preferably initially provided in the form of a coiled generally
rod-like member, such as a circular wire coiled on the roll 30, as
previously explained in connection with the material 18, but may be
provided in other configurations, if desired. In the illustrated
embodiment the material 32 may have a diameter of between
approximately 0.020 to 0.187 inch depending upon the relative size
of the underlying copper heat sink layer 28 and the ultimate
properties desired for the completed contact unit 48, but is
reduced in thickness by approximately 50 percent or less by the
second coining means 40 except for the thicker central region
defined in the subsequently formed contact layer 42. The second
securing means 38 may again comprise a suitable point welding
apparatus adapted to rigidly attach the contact body 38 to the heat
sink layer 28. After separation of the segment defining the contact
body 38 from the coil 30 subsequent to the welding operation the
heat sink layer 28 with the contact body 38 secured to its surface
is advanced to a position in registration with the die face 41 of
the second coining means 40, as shown, which deforms substantially
the entire contact body 38 into the configuration defining the
contact layer 42 without producing any excess material, thereby
obviating the necessity for any scrap recovery operation. The space
defined by the depression 29 in the heat sink layer 28 is occupied
by the thicker central portion of the contact layer. Furthermore,
the contact layer 42 is deformed to extend over a predetermined
area of the exposed surface of the heat sink layer 28, but
terminates at a location spaced inwardly from the peripheral
boundary of the heat sink layer 28. The deformed contact layer 42,
thus, defines a configuration in which the central region is of an
increased thickness with regard to the peripheral portions thereof,
while its peripheral boundary is spaced inwardly from the periphery
of the heat sink layer 28. In a preferred embodiment the contact
layer 42 may occupy between approximately 50 to 90 percent of the
exposed surface area of the heat sink layer, thereby reducing the
usage of the relatively expensive contact layer material while
providing increased quantities of contact material at the critical
central region of the contact unit 48 where such material is
needed. As may be seen the sheet 10 including the heat sink layer
28 and the contact layer 42 is then advanced to a position in
registration with the separating means 44 which effects a cut along
the separation line 46 to provide the composite completed contact
unit 48. Although in the preceding description and accompany
drawing the segments of heat sink material and contact layer
material are secured to the substrate sheet at their respective
exposed end edges and hence are in a vertical orientation prior to
deformation, it should be noted that in certain instances the
segments may be disposed on the advancing substrate sheet in a
horizontal orientation with a portion of the outer surface of the
segment being secured in position prior to deformation.
Various embodiments of contact units such as the unit 48 are
illustrated and described in detail hereinafter indicative of
typical examples of contact units in accordance with the present
invention which may be fabricated utilizing a method such as that
described in detail in connection with FIG. 1 by varying the shape
of the die faces 27, 41 of the deforming means 26, 40
respectively.
Referring now in detail initially to FIGS. 2 and 3 which
respectively illustrate a vertical sectional view and a plan view
of one embodiment of a contact unit, indicated generally by the
reference numeral 52, in accordance with the present invention it
may be seen that the contact unit 52 includes a substrate 54
preferably fabricated of a preselected metallic material, such as
the material comprising the sheet 10 described in connection with
FIG. 1. A heat sink layer 56 of a first preselected metallic
material having a relatively high electrical and thermal
conductivity is disposed on one surface of the substrate 54, while
a contact layer 58 of a second preselected metallic material having
a relatively high electrical conductivity is disposed on an exposed
surface of the heat sink layer 56. The heat sink layer 56 and the
contact layer 58 may be affixed in position and deformed into the
illustrated configuration generally in accordance with the method
as described hereinabove in connection with FIG. 1. More
particularly, the substrate 54 may comprise a suitable low carbon
steel, such as described in connection with FIG. 1, or other
metallic material selected with a view to the contemplated usage of
the contact unit 52. The substrate 54 may be generally coextensive
with the overlying heat sink layer 56 or may be slightly larger, as
shown in the illustrated embodiment, in order to facilitate
disposition of the contact unit 52 in position in a desired
application. The heat sink layer 56 is preferably fabricated of a
material, such as copper, which is noted for its good electrical
and thermal conductivity, and is arranged in a generally circular
configuration, as particularly illustrated in FIG. 3, while having
a nonuniform cross-sectional configuration or thickness, including
a central region 56a of a reduced thickness with respect to the
periphery thereof. As shown, the contact layer 58 is secured to the
exposed surface of the heat sink layer 56 and preferably comprises
a material having a relatively high electrical conductivity and low
contact resistance, as well as good corrosion resistance
properties, such as silver, gold, palladium, platinum or alloys
thereof. In addition, in certain instances a material such as
silver cadmium oxide may be utilized in fabricating the contact
layer 58. The contact layer 58 similarly has a generally circular
configuration as shown in FIG. 3 and is also arranged to have a
generally nonuniform cross-section or thickness, including a
central region 58 a of an increased thickness with respect to the
peripheral portions thereof. The portion 58a of increased thickness
and the portion 56a of decreased thickness of the contact layer and
heat sink layer respectively are disposed in mating relationship
with respect to each other so as to define a structure in which an
increased amount of contact layer material is provided only at the
central portion of the contact system 52. In addition, as shown,
the contact layer 58 is arranged such that it is noncoextensive
with the heat sink layer 56 and terminates at a position spaced
inwardly from the peripheral boundary of the heat sink layer. Thus,
the total usage of the relatively more expensive contact layer
material is minimized, while providing an increased amount at the
central portion of the contact system. Such an arrangement has been
found to provide significant benefits in prolonging the electrical
lifetime of the unit, since it has been found that the central
region is generally subjected to the greatest electrical stress,
while the relatively larger area, less expensive heat sink layer 56
improves the heat dissipation properties of the unit 52 so as to
permit fabrication of a unit which is less expensive but has
improved electrical lifetime and current carrying characteristics.
In this connection a substantial cost and performance advantages
result from utilizing a system such as that illustrated in which
more expensive contact material is provided only at the central
region of the contact unit since such an arrangement minimizes the
total usage of expensive contact layer material by effecting
replacement of such material at less critical areas with less
expensive heat sink material. In a preferred embodiment of a unit,
such as that illustrated in FIGS. 2 and 3, in which the heat sink
layer and contact layer have generally circular-shaped peripheral
boundaries the contact layer 58 occupies between approximately 50
to 90 percent of the exposed surface area of the heat sink layer.
Furthermore, it may be noted that substantial economic savings
accrue in view of the replacement of more expensive contact
material with less expensive heat sink material since a circular
geometric configuration is involved in which the area varies with
the square of the diameter.
Although the embodiment illustrated in FIGS. 2 and 3 is shown
having a central region in which the thickness of the heat sink
layer is relatively abruptly reduced in a stepped configuration to
accommodate a corresponding abrupt increase in the thickness of the
contact layer, it may be desirable in certain instances to provide
such a system in which a smooth progressive decrease in thickness
in the heat sink layer is accomplished extending toward the center
thereof, while the contact layer is arranged to similarly
progressively increase in thickness extending toward the center
thereof. Such an embodiment is illustrated in detail in FIGS. 4 and
5. More particularly, in this embodiment a substrate 60 similar to
the substrate 54 is initially provided. A heat sink layer 62 is
secured to a surface of the substrate 60, the heat sink layer
including a generally centrally located region 62a of a reduced
thickness with respect to the periphery thereof and a contact layer
64 is secured to the exposed surface of the heat sink layer 62, the
contact layer having a generally centrally arranged portion 64a of
an increased thickness with respect to the periphery thereof
disposed in mating relationship with the reduced thickness portion
62a. The contact layer 64a is noncoextensive with the heat sink
layer 62, terminating spaced inwardly from the peripheral boundary
of the heat sink layer 62. The heat sink layer 62 again comprises a
material having a relatively good thermal and electrical
conductivity, such as copper, while the contact layer 64 again
comprises a material having a relatively high electrical
conductivity, low contact resistance, and good corrosion resistance
properties such as silver, gold, palladium, platinum or alloys
thereof or in certain instances silver cadmium oxide. In this
embodiment as shown particularly in FIG. 5 the heat sink layer and
contact layer are each formed in a generally elliptical
configuration which has been found to be advantageous in certain
instances. In addition, it may be seen that the heat sink layer 62
progressively decreases in thickness from the outer periphery
thereof toward the center while the contact layer 64 progressively
increases in thickness from the periphery thereof toward the center
thereof so as to define a contact system in which an increased
amount of contact material is provided only at the center thereof
so as to increase the electrical lifetime, while minimizing the
usage of relatively expensive contact material. In one example of a
contact arrangement such as that illustrated in FIG. 4 it has been
found that substantial advantages reside in arranging the relative
thicknesses of the heat sink layer 62 and contact layer 64 such
that there is a difference in relative thicknesses at the
respective centers of each of these layers of between approximately
1 to 5 percent, while the outer peripheral edges of each of these
respective layers are approximately equal in thickness with respect
to each other. In addition, it has been found particularly
advantageous in certain instances to arrange the relative surface
dimensions of the heat sink layer and the contact layer such that
the contact layer occupies between approximately 50 to 90 percent
of the exposed surface area of the heat sink layer in order to
provide a structure in which a substantial cost savings results due
to reduced usage of the relatively expensive contact layer material
while achieving improved electrical lifetime characteristics and
current carrying abilities as compared with conventional contact
units, utilizing substantially greater quantities of more expensive
contact material.
Referring now to FIGS. 6 and 7 another alternate embodiment of the
present invention is illustrated comprising a contact unit
indicated generally by the reference numeral 66 in which an
increased volume of contact material is provided only at the
central region thereof. More particularly, the illustrated
embodiment includes a substrate 68 similar to the substrate 60 in
the preceding embodiment, as well as a heat sink layer 70 secured
to a surface of the substrate 60 and preferably fabricated of a
material, such as copper having a high electrical and thermal
conductivity, and an electrical contact layer 72 secured to a
portion of the exposed surface of the heat sink layer 70, the
contact layer 72 being fabricated of a material having a relatively
high electrical conductivity and good corrosion resistance
properties, such as silver, gold, palladium, platinum or alloys
thereof or of a material such as silver cadmium oxide. In this
embodiment, the heat sink layer 70 includes a central region having
a plurality of stepped areas 70a and 70b which successively
decrease in thickness toward the center of the heat sink layer. The
areas 70a and 70b are defined by generally circular-shaped
peripheral boundaries, as particularly indicated in FIG. 7 so as to
define the heat sink layer 70 such that the thickness thereof
decreases progressively towards the center to permit the heat sink
layer to accommodate the overlying electrical contact layer 72
which is provided with complementary mating stepped regions 72a,
72b which successively increase in thickness approaching the center
thereof. More particularly, it may be seen that the contact layer
72 similarly includes generally circularly bounded stepped areas
72a, 72b which increase progressively in thickness toward the
center thereof and are arranged in mating relationship with the
regions 701, 70b of progressively decreasing thickness of the heat
sink layer 70 so as to provide a central area having a still
further increased amount of contact layer material at the center
thereof while minimizing the actual usage of contact layer material
at areas other than the center thereof, thereby providing a
completed contact unit in which a maximum volume of contact layer
material is replaced by less expensive heat sink material at areas
other than the critical central region of the unit so as to provide
a device having improved electrical capabilities in view of the
increased provision of contact layer material at areas of greatest
need while minimizing the overall usage of contact layer
material.
It should be readily apparent that various other alternative shapes
of contact arrangements may be readily provided utilizing the
above-described principles in which a central region of a decreased
thickness in the heat sink layer is provided with a corresponding
complementary central region of an increased thickness of contact
layer material being provided in mating relationship therewith so
as to define a contact unit in which the usage of relatively
expensive contact layer material is minimized, while providing a
device having requisite electrical lifetime and current carrying
capabilities.
Thus, a novel method has been described for fabricating an improved
electrical contact unit in which the usage of relatively expensive
contact layer material is minimized, while also eliminating the
problem of scrap generation and necessity for recovery thereof. In
addition, a number of contact units which may be fabricated in
accordance with the principles of such a method have been described
in detail.
Various changes and modifications in the above-described
embodiments will be readily apparent to those skilled in the art
and any of such changes or modifications are deemed to be within
the spirit and scope of the appended claims.
* * * * *