Note: Descriptions are shown in the official language in which they were submitted.
~.1'7~ 23
Electrical contact terminal and multi-contact connector
This invention relates to sheet metal electrical contact terminals
and to multi-contact electrical connectors which contain sheet metal terminals.
United States Patent 4,188,085, United States Patent 3,871,736, and
United States Patent 4,176,895, all describe sheet metal electrical contact
terminals which have all of the parts of the terminal lying in a single plane,
which is the plane of the metal stock from which the terminal was formed.
Terminals of this flat type are extremely thin and can be placed on closely
spaced centers in a multi-contact electrical connector. Flat terminals of
10 the type described in the above identified United States Patents are, therefore,
extremely useful when electrical connections must be made with closely spaced
terminal pads on a circuit board and under similar circumstances where close
spacing is required in an electrical connector.
A flat terminal which has all of its parts lying in the plane of
the sheet metal stock from which it was formed is comparatively stiff, or rigid,
as compared with a terminal manufactured by forming the sheet metal normally
or at right angles to the sheet metal stock. The latter type of contact
terminal, which is more widely used than flat terminals, can be provided with
flexible contact members having a high degree of flexibility. A flat terminal
20 which has all of its parts lying in the plane of the sheet metal stock will
have relatively stiff flexible contact members which are capable of only
limited movement when they are flexed. This problem rrlay be overcome to some
extent by designing the flat terminal with an extremely long contact arm, as
shown in United States Patent 4,176,895. The use of a long contact arm,
however, is undesirable under many circumstances. The terminal itself must be
relatively large because of the length of the contact arm and the connector in
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which the terminal is used must, therefore, have a relatively large housing.
Furthermore, the use of an extremely long contact arm which carries the
electrical current when the terminal is put to use causes self-inductance
effects which are intolerable under many circumstances. Some telephone
equipment, for example, has switching times of the order 10-3 seconds and
under current conditions such as these, the rate of change of the current with
time is extremely high notwithstanding the fact that the actual magnitude of
the current may be relatively low. The high rate of change of the current
gives rise to the self-inductance effects which may hamper the operation of
the equipment on which the connector is being used.
The present invention in accordance with one aspect thereof, is
directed to the achievement of a flat terminal having all of its parts lying
in the plane of the metal from which the terminal was produced and which has
minimal self-inductance effects when it is used under circumstances of rapid
switching. In accordance with a further aspect, the invention is directed
to the achievement of a flat terminal capable of developing relatively high
contact forces when desired, and which has a flexible contact arm capable of
flexure to the extent required in an electrical connector. In accordance with
a further aspect, the invention is directed to the achievement of a multi-
2r) contact electrical connector having flat extremely thin contact terminals
therein on closely spaced centers.
An electrical terminal in accordance with the invention is formed
from sheet metal stock by stamping or etching and has all of its parts in a
single flat plane which is defined by the thickness of the metal from which
the terminal was produced. The terminal has a contact arm having a fixed end
and a free end, a portion of the edge adjacent to the free end being a contact
portion of the terminal which engages a complementary terminal device. The
terminal is characterized in that it has a yoke section from which the contact
arm extends and which has a spring arm extending from the yoke section beside
the contact arm. The contact arm and the spring arm have opposed bearing edge
portions which are against each other when the contact arm is flexed towards
thc spring arm so that the spring arm supports the contact arm. The contact
force which is developed when the terminal is put to use is imposed by the
spring arm which is flexed by the contact arm. The current passing through
the terminal passes from ~he contact portion of the contact arm to the yoke
portion through ~he contact arm and not through the relatively long spring arm.
A terminal in accordance with the invention can be used in a multi-
contact electrical connector having a housing in which there are provided a
plurality of side-by-side cavities each of which has a contact terminal
therein. The contact portions of the spring arms project through openings in
the housing past one surface of the housing so that a circuit board clamped
against that surface is engaged by the contact portions of the terminals.
A channel-shaped frame assembly is provided in which the housing is positioned
and which also receives a circuit board. A clamp is provided on this frame
assembly for clamping the circuit board against ~he one surface of the housing
thereby to engage the conductors on the circuit board with the contact
portions of the terminals in the housing.
Figure 1 is a cross-sectional view of a multi-contact electrical
connector having contact terminals in accordance with the invention contained
therein, this view showing the positions of the parts when the connector is
not mated with a complementary circuit board.
Figure 2 is a view similar to Figure 1, showing the positions of the
parts when the connector is mated with a circuit board.
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Figure 3 is a perspective view of a terminal in the as-stamped
condition.
Figures 4 - 6 illustrate the essential steps involved in the
operations of severing individual terminals from a carrier strip and inserting
the terminals into a connector housing.
Figure 7 is a diagram which illustrates the deflection of the
contact arm of the terminal.
Figure 8 is a force/deflection diagram illustrating the functioning
of the contact arm of the terminal.
Figures 9 and 10 are perspective views of the connector, the
connector shown in assembled condition in Figure 9 and with the parts exploded
from each other in Figure 10.
Referring first to Figures 1 and 2, a terminal 2, in accordance with
the invention, serves to connect conductors 18 on the underside of one printed
circuit board 14 to conductors 20 on a surface 22 of a smaller printed circuit
board 24. The terminal is contained in a housing 46 of a connector 3
mounted on the upper surface 12 of circuit board 14 and the terminal has a
solder post 10 which extends through an opening 16 in the circuit board and
is soldered to the conductor 18, as shown. It will be understood that the
connector 3 contains a plurality of terminals on closely spaced centers.
The terminal 2 comprises a yoke section 4 having extending
therefrom a contact arm 6 and a spring arm 8 in side-by-side spaced-apart
relationship. These arms extend from the upper edge of the yoke and the
previously identified solder tab or post 10 extends from the lower edge of the
yoke. The contact arm has a fixed end 26 which is integral with the yoke and
extends obliquely away from the spring arm to a generally circular free end
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portion 28. At the end of this circular portion, ~here is provided an
extension 30 which is directed towards the spring arm and edge 32 of this
extension serves as a bearing portion for cooperation with a bearing portion
44 on the spring arm 8. The edge of the circular portion which is outwardly
directed, as shown at 34, serves as a contact portion of the terminal and
engages the conductor 20 on the circuit board 24. An ear 36 is provided on
the circular portion 28 and has an edge which bears against the inside
surface of the housing cavity 48 so that the contact arm cannot move leftwardly
in a cou~ter-clockwise direc~ion from the position shown in Figure 1.
The spring arm 8 has a lower portion which is of substantially
uniform width and which extends normally of the yoke 4 of the terminal. This
lower portion merges with a spring portion 38 which is reversely curved, as
shown at 40, and which merges with a depending portion 41. The free end 42
of the spring arm is adjacent to the extension 30 of the contact arm 6. The
rightwardly facing edge 43 of the free end of the spring arm serves as a
stop to prevent overstressing. The leftwardly facing edge 44 is normally against
the bearing surface edge 32 of the contact arm 6.
The connector 3, Figures 9 and 10, comprises an insulating housing
46 having a plurality of side-by-side cavities 48 therein extending upwardly
from the lower end of the connector as viewed in the drawing. These cavities
are dimensioned snugly to receive the terminals as shown, and the lefthand wall
50 of the housing 46 has an opening therein 52, through which parts of the
circular free end portion 28 of the contact arm project. The insulating
housing has a leftwardly extending flange 54 which serves as a support for
the circuit board 24, as shown in Figure 2, and this flange also supports, in
part, a frame assembly 56 which is assembled to the housing.
The frame assembly is of stamped and formed sheet metal, preferably
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steel, and is generally channel-shaped having sidewalls 58, 62 and a base 60.
The sidewall 58 is disposed against the rightwardly facing surface of the
housing as viewed in Figure 1, and has a lance 64 struck from its upper end
portion which is received in a recess in the housing. The frame assembly is
also retained on the housing by ears 57 on the frame which are received in
openings 59 in the housing.
The sidewall 62 is reversely bent, as shown at 66, at its upper end
to provide a depending arm as shown at 68, which is spaced from the sidewall
62. A cam shaft 70 is supported between the arm 68 and the sidewall 62 and
has spaced-apart eccentric cams 72 mounted thereon. Openings are provided
in the sidewall 62, the depending arm 68, and in a U-shaped spring member 74
to provide clearance for these cams. The housing 46 has an extension 69 on
its lefthand end as viewed in Figure 10, and a recess 67 in this housing
receives the end portion of the U-shaped spring member 74 and the end portion
of the shaft 70. The channel-shaped spring member 74 has an integral biasing
spring 71 thereon which bears against the lefthand end of the shaft 70 and
stabilizes it in the frame assembly 56. Shaft 70 is supported adjacent to
its righthand end between ears 73, 75 on the sidewall 62 and on the depending
portion 68 of the frame assembly 56. The shaft 70 is movable in a horizontal
direction towards the wall 50 so that circuit boards of varying thicknesses
can be received in the trough 76 defined by the sidewall 62 and the housing
wall 50.
In order to firmly clamp the circuit board against the contact
surfaces 34 of the contact arms 6 of the terminals, the U-shaped spring 74 is
mounted on the sidewall 62 and the depending arm 68 of the frame 56. This
spring 74 may not be required under all the circumstances but can be used when
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it is desired to have extremely high forces at the electrical interfaces
between the contact portions 34 of the terminals and the ~erminal pads on
the circuit board 24.
In use, edge portions of the circuit board are inserted into the
trough 76 as shown in Figure 2, and the shaft 70 is thereafter rotated through
an angle of substantially 190 to the position shown in Figure 2. During
such rotation of the shaft, the cams 72 will progressively push the circuit
board 24 against the contact terminals 2 and the spring 74 will be flexed
as shown, so that it will develop the required clamping force. The contact
arm 6 is flexed in a genera~ly clockwise direction as the cam is rotated so
that the contact arm pushes the spring arm 8 to the position in Figure 2.
The manner in which the contact arm is flexed and the spring arm 8 is
stressed when the parts are in the positions of Figure 2 is discussed more
fully below.
Terminals in accordance with the invention can be produced of any
suitable material by simply removing material from flat stock metal. The
removal of the material will ordinarily be carried out by a simple stamping
operation to produce terminals in strip form, as shown in Figure 3, however,
such terminals might under some circumstances, be manufactured by chemical
etching of the strip. In any event, the finished terminal will have all of its
parts lying in the plane of the original stock metal so that the cantilever
beams, the contact arm, and the spring arm, are relatively stiff, although
they are flexible.
Referring now to Figures 3 - 6, the terminals as stamped are integral
with a continuous carrier strip 78 and in the as-stamped condition, differ
from the terminals as installed in the housing in that each terminal has an
extension 84 of the yoke 4 and an additional solder post 86. Also, the end
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of ~he contact arm is integral with the end of the spring arm, as shown at
80, and the short lower portion on the end of the contact arm extends through
a complete circle, as shown at 82. The material indicated at 80 and 82 is
removed prior to insertion of the terminal into the housing cavity 48 as shown
at 80', 82' Figure 4. The yoke extension 84 and the second solder post 86 may
also be removed, as indicated in Figure 4. Alternatively, the yoke extension
and second solder leg may remain on the terminal and the tab 10 may be
removed. When the terminals are provided on closely spaced centers, alternate
terminals may thus have the leg 10 removed and the remaining terminals have
the leg 86 removed so that a grid hole pattern in the circuit board can be
provided for more convenient spacing and location of the conductors on the
circuit board.
Terminals 2 are installed in the housing 46 in the general manner
shown in Figures 4 - 6, and preferably by means of insertion machinery having
the elements described below for guiding and inserting the terminals. The
housing 46 is supported in a housing support 88 that has a recess 90 in which
the housing is supported with the open lower end of a cavity 48 disposed above
the leading terminal on the strip 78. At the insertion station, a contact arm
flexing and guiding tool 92 moves against the contact portion 34 of the contact
arm 6 and an inserter 94 moves into surrounding relationship with the solder
tab 10 of the terminal. The upper surface 95 of this inserter thus bears
against the lower edge of the yoke portion 4 of the tcrminal so that when the
inserter 94 moves upwardly, the terminal will be pushed into the cavity 48.
Prior to upward movement of the inserter, the flexing and guiding tool 92 moves
rightwardly from the position of Figure 4 to the position of Figure 5, in which
the righthand surface 91 of this tool is coplanar with the adjacent internal
surface 97 of the housing 46.
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When the flexing tool 92 moves from the position of Figure 4 to the
position of Figure 5, it moves the contact arm 6 rightwardly to the position
shown in Figure 5. During this movement of the contact arm 6, the edge 32
- of the contact arm moves against the bearing portion 44 at the end of the
depending section 41 of the spring arm 8. The section 41 of the spring arm
is also flexed as shown in Figure 5. As will be explained below, the spring
arm 6 is overstressed when it is initially flexed as shown in Figures 4
and 5 and after overstressing, the contact arm is supported by the spring arm
when the terminal is placed in service as shown in Figures 1 and 2.
When the terminal 2 is held in the insertion tooling as shown in
Figure 5~ the terminal is sheared from the carrier strip 78 by a shearing
means and thereafter the inserter 94 moves upwardly from the position of
l'igure 6. A guide means 96 is provided against the righthand edge of the
terminal and in alignment with the surface 99 of the cavity so that the
terminal will move smoothly into the cavity 48. When the tooling is then
removed from beneath the terminal and the housing is removed from the housing
support 88, the contact arm 6 will move leftwardly until the ear 36 is
against the internal surface of the cavity, as shown in Figure 1.
It will be apparent from the foregoing description that the
2() electrical function of the terminal is performed primarily by the contact arm 6
in that the current will flow from the contact portion 34 along this arm to
the yoke 4 and through the solder post 10 to the conductor 18. The contact
arm is substantially straight and extremely short, so that inductance effects
will be minimized. Current will not tend to flow across the bearing portions
32, 44 and through the spring arm because of the fact that this current path
would present a higher resistance. The contact arm is flexed when the circuit
117~)3'~3
board 24 positioned against the surface of the wall 50 of the housing 46 but
its flexure makes only a minor contribution to the contact force developed in
the electrical interface of the terminal and the circuit board in Figure 2.
Most of the contact force is developed in the spring arm 8 and is transmitted
to the contact arm 6 through the upper portion 28 of the contact arm directly
to the terminal pad on the circuit board 24. Thus, the intermediate shank
position of this contact arm 6 is not subjected to the contact force which is
present at the electrical interface. The spring arm can, of course, be
designed to provide optimum properties and characteristics for the particular
use to which the connector will be put. If extremely high contact forces are
desired, this spring arm & can be made relatively stiff so that it will
develop such high forces. Alternatively, if a contact force of limited
magnitude is desired, the contact force can be reduced by redesigning the
spring arm of the terminal.
While the principles of the invention will be apparent from the
foregoing discussion, the following discussion of the performance of a
specific terminal in accordance with the invention will provide a deeper
understanding of the invention and the manner in which terminals can be designed
specifically for particular applications. The following discussion is based
on studies of a terminal produced from phosphor bronze stock metal having a
thickness of 0.25mm and in a relatively hard temper. The terminal had an
overall height of 14.8mm and a width of about 4.99mm. The dimensions of
the parts in the terminal were selected to produce a contact force of about
600 gms.
Figure 7 is a diagram which shows the relative positions of the
upper end of the contact arm at different stages of the assembly operation in
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3 ~ 3
which the terminal is inserted into the cavity 48. ~n this view, the line 98
indicates the position of the contact arm 6 prior to flexing of this arm
inwardly towards the spring arm, in other words, the position of the arm,
as it appears in Figure 4 of the drawing. The line 100 denotes the position
of the contact arm when the parts are in the position of Figure 6 or Figure 2,
that is, when the contact arm is flexed rightwardly to its extreme position.
When this arm 6 is flexed by the flexing tool 94, the material in the arm
yields and plastically flows so that the arm has a tendency to return only to
the position indicated by the line 102 as the result of springback. However,
when the connector housing is removed from the housing support 88, the spring
arm 8 pushes the contact arm leftwardly beyond its normal position 102 to
the position 104. The spring arm is of course flexed rightwardly when the
parts are moved to the position of Figure 5 and it has a tendency to return
to its normal position, and it is this tendency of the spring arm to return to
its normal position that pushes the contact arm to the position indicated by
the line 104.
Figure 8 is a force travel diagram showing the position of the
upper end of the contact arm during the assembly process. The reference
numerals 98, 100, 102, 104 have been applied to Figure 8, with prime marks,
so that the curve shown in Figure 8 can be correlated with the arm positions
shown in Figure 7. As shown in Figure 8, the upper end of the arm 6 is
moved a total of 0.97mm when it is flexed from the position of Figure 4 to
the position of Figure S and during such flexure, the load remains substantial]y
constant after it has risen to a plateau value. When the connector is
removed from the connector support 88, the upper end of the contact arm 6
moves leftwardly past the condition of no load, as shown at 102', and is
flexed in a manner such that it is loaded in the opposite direction, as
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11 ~'( ~3~3
indicated at 104'.
The significance of the diagram of Figure 8 is that the contact arm
is flexed leftwardly from its normal position in the assembled connector so that
when the circuit board is inserted into the trough 76 and clamped against the
surface 50, the initial portion of the travel of the contact arm merely has
the effect of unloading the stresses in the arm 6 and returning it to its
unstressed position, as indicated by the line 102 in Figure 7. Thereafter,
the arm is flexed rightwardly to the position indicated by the line 100 in
Figure 7.
The fact that the contact arm and the spring arm are both in a
flexed condition and are resiliently biased towards each other results in the
capability in the contact arm for an increased amount of travel in normal
usage, as compared in the amount which would be obtainable if the contact arm
were not flexed leftwardly when it is in its Figure 1 position and, therefore
preloaded against the lower end of the spring arm. The spring arm can, of
course, withstand the flexure which it must undergo in the ordinary use of
the connector by virtue of its substantial mass and its dimensions.
The specific terminal in accordance with the invention which has been
described above has a circular free end 28 on the contact arm 6 which is
capable of rotation relative to the shank portion of the contact arm when
the load, the contact force, is applied against the contact portion 34 and
the reaction force is applied against the bearing portion 32 by the spring arm.
The capability for this rotation increases the overall ran8e of movement of
the contact area 34 rightwardly, as viewed in the drawing, when the circuit
board is mated with the connector. In other words, the shank portion of the
contact arm 6 which extends from the base portion 26 to the free end undergoes
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flexure when the contact arm is stressed and this flexure of the arm results
in some movement of the contact zone 34 rightwardly from the position of
Figure 1. In addition, the rotation of the circular upper end 28 of the
contact arm also results in some rightward movement of the contact portion 34
from the position of Figure 1 and the total amount of movement of the contact
portion 34 is therefore the sum of the movement contributed by the shank portion
of the contact arm and the portion contributed as the result of the rotation
of the circular upper portion of the contact arm.
This characteristic of the disclosed embodiment is highly
advantageous in that it permits the designer of a specific terminal to achieve
a greater amount of movement of the contact portion 34 than would be obtainable
if all of the movement were simply a result of flexure of the shank portion
of the contact arm. Additionally, the rotation of the circular upper portion
28 of the contact arm contributes to the achievement of a wiping motion on
the contact surfaces since the actual zone of contact moves relatively over
the zone of ccntact on the circuit board 24 as the circuit board is clamped in
the connector.
Terminals in accordance with the invention can be plated with a
conductive metal as desired and as indicated by the environment of the intended
use. Tin plating or plating with a tin-lead alloy may be satisfactory under
many circumstances, particularly in view of the fact that high contact forces
can be obtained from the terminal if desired. Gold plating may be used if
an extremely low resistance is required. If terminals in accordance with the
invention are used under cryogenic conditions, a plating of indium or pure tin
may be used.
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