Low impedance electrical connecting means for spaced-apart conductors

Multi-contact electrical connector for connecting a first plurality of conductors to a second plurality of conductors comprises an insulating housing having a plurality of side-by-side contact terminals therein, each terminal being a one-piece stamping having first and second contact portions for engagement with a first and second conductor respectively. The first and second contact portions also have first and second bypass contact surfaces thereon which are against each other. The spring means for maintaining contact force comprises a spring loop which extends circuitously from the first contact portion to the second contact portion. In use, the spring loop maintains the contact forces at all of the contact interfaces and the current flows from the first conductor through the first contact portion, through the bypass contact surfaces, through the second contact portion, and to the second conductor. The spring loop does not serve as a current path and self-inductance in the contact is thereby minimized.

FIELD OF THE INVENTION 
This invention relates to electrical connecting means for connecting a 
first plurality of conductors. The invention is disclosed and described 
below with particular reference to connectors for connecting conductor 
pads on an IC chip carrier to conductor pads on a circuit board, however, 
the principles of the invention can be used under many other 
circumstances, for example, in connectors for connecting conductors in a 
first cable to conductors in a second cable. 
BACKGROUND OF THE INVENTION 
The continuing trend toward reduction in the sizes of micro-electronic 
devices and towards the provision of increasing numbers of electrical 
functions on a single integrated circuit chip has required the producers 
of electrical connectors for connecting conductive pads on chip carriers 
to conductive pads on circuit boards to correspondingly reduce the size of 
their connectors. It is, however, always necessary in the design of an 
electrical connector to provide some minimum contact force at the 
electrical interfaces between the terminals in the connector and the 
conductors on the chip carrier and on the circuit board. These contact 
forces are maintained by providing the terminals in the connector with an 
integral spring means which forces the contact areas of the terminal 
against the contact pads on the chip carrier and on the circuit board. 
The extremely small size of present day micro-electronic devices and the 
close spacing of the terminal pads on the chip carrier and on the circuit 
board necessitates the use of relatively thin metal stock for the terminal 
in the connector and in order to obtain the required contact forces, 
designers have increasingly been resorting to the use of terminals having 
relatively long springs, that is, springs which are part of the terminal 
and which may extend sinuously from the chip carrier to the circuit board 
in order to obtain adequate contact forces at a reasonably constant or low 
spring rate over a relatively wide deflection range. In conventional 
connectors, the current flowing from the chip carrier to the circuit pad 
must flow through the spring and because of the length of the spring, 
self-inductance effects become significant in the connector. The 
self-inductance in the terminals of the connector give rise to problems, 
in that it tends to increase the power requirements of the circuit and 
thereby complicate the heat dissipation and signal propagate problems. 
These self-inductance effects are always present in electrical circuits and 
are often important in conventional solid state micro-electronic circuits 
containing IC devices with extremely short switching and rise times. The 
self-inductance effects are particularly significant in circuits operating 
under cryogenic conditions, such as Josephsen junction devices operating 
at near zero degrees K. Devices of this type have a switching time on the 
order of a picosecond. With signals of such short duration, the energy 
loss which results from even minor self-inductance effects may make the 
device unusable. 
The present invention is directed to the achievement of a connector for 
connecting first conductors to second conductors which gives the designer 
freedom to achieve the desired spring characteristics in the terminals of 
a connector without accompanying self-inductance in the terminals. In 
accordance with the principles of the invention, each terminal in the 
connector comprises first and second contact portions which are engageable 
with a first and second conductor respectively, and which are adjacent to 
each other. First and second bypass contact surfaces are provided on the 
contact surfaces and when current flows from the first conductor to the 
second conductor, it flows from the first conductor to the first contact 
portion, past the bypass contact surfaces to the second contact portion 
and then to the second conductor. Contact forces are maintained by an 
integral spring loop which extends circuitously from the first contact 
portion to the second contact portion and which, in use, is deflected so 
that it maintains the necessary contact forces between the conductors and 
the contact portions of the terminal and at the bypass contact interface. 
Little, if any, current flows through the spring loop and the inductance 
effects are thereby minimized or eliminated. The principles of the 
invention will find application in all circuits in which self-inductance 
effects may be significant. As mentioned above, the use of the invention 
is particularly beneficial in circuits having extremely short switching 
times, such as Josephsen type junction device circuits operating at near 
zero degrees K.

PRACTICE OF THE INVENTION 
Referring first to FIGS. 1-3, a connector in accordance with the invention 
may serve to connect first conductor contact surfaces 2 on one surface 6 
of a chip carrier 7 to second conductor contact surfaces 4 on the upper 
surface 12 of a circuit board 14. The chip carrier 7 has encapsulated 
therein an integrated circuit chip and conductors (not specifically shown) 
extend from the zone 8, in which the chip is encapsulated, through the 
substrate 9 to the edges of the substrate and to the previously identified 
first contact surfaces 2, which are arranged along each edge of the 
substrate. The second conductor contact surfaces 4 are arranged in four 
rows which form a square and extend outwardly to conductors 5 on the 
surface 12. The conductors 5 may extend, in turn, to holes in the circuit 
board which electrically extend to conductors on the underside 16 of the 
board. 
Chip carriers of the type shown in FIG. 2 are made in several sizes and 
have varying numbers of pads 2 along their edges; some chip carriers 
having 68 or 136 terminal pads. The spacing between adjacent terminal pads 
2 on chips having the maximum number of terminal pads is as low as 0.02" 
and connectors, in accordance with the invention, are capable of providing 
connections between chip carriers of this type and the conductors on the 
circuit on a circuit board. 
The connector assembly comprises an insulating housing 18, which may be of 
suitable plastic material and which is in the form of an open square frame 
and has a plurality of individual terminals, as shown at 20 therein. A 
single terminal 20 will be described with reference to FIG. 3 and further 
details of the connector will be described subsequently. 
The terminal 20 (FIG. 3) is stamped from conductive material, such as 
beryllium copper or phosphor bronze and comprises first and second contact 
portions 22, 24 which are immediately adjacent to each other at the left 
hand end of the terminal as viewed in FIG. 3. By virtue of the fact that 
the terminal is stamped from sheet metal, all parts of the terminal lie in 
a single plane, the plane of the material from which the terminal was 
stamped. The terminal is used in an edgewise orientation, as will be 
explained more fully below. The first contact portion 22 has a knob-like 
upper end 26, the rounded upper edge 28 of which functions as a first 
terminal contact surface. The lower portion 30 of first contact portion 22 
is integral with a spring loop 32 which, in the embodiment of FIG. 3, 
comprises two sinuous sections 34, 36 which are inclined leftwardly 
towards contact portion 22 and which extend beside an edge 41 of contact 
portion 24. 
The second contact portion 24 has a straight base 38, the lower edge 40 of 
which serves as a second terminal contact surface and this straight 
portion is connected to the sinuous section 36 by a transition section 42. 
An arm 44 extends upwardly from the left hand end of base 38 and has a 
barb-like free upper end 46. The first contact portion 22 has a projection 
48 which extends below the barb section 46 and serves as a positioning 
means and stop for preventing upward movement of the first contact portion 
beyond the position shown. 
The leftwardly facing side edge 50 of first contact portion 22 functions as 
a first bypass contact surface and the rightwardly facing inclined edge 52 
of the barb-like upper end 46 of arm 44 functions as a second bypass 
contact surface. These bypass contact surfaces are normally against each 
other as shown, and will move relative to each other when the terminal is 
put to use as described below. 
When the terminal 20 is placed in service, contact forces are applied, as 
shown at F.sub.1 and F.sub.2 to the first and second contact surfaces 
respectively, and the first contact portion moves relatively downwardly 
with respect to the second contact portion 24. The spring loop 32 is 
deflected upon application of the forces F.sub.1, F.sub.2 and thereby 
maintains the contact surface 28 against a complementary contact surface 
and the contact surface 40 against complementary contact surface. 
Furthermore, and during downwardly movement of contact portion 22, the 
inclined surfaces 50, 52 serve as a camming means and cause a slight 
lateral motion of the contact surface 28 so that it wipes over the 
complementary contact surface thereby to break through superficial films 
and establish a low resistance stable contact. 
During use of the terminal, the deflected spring loop means 32 will 
maintain contact forces at all of the contact interfaces, however, the 
current flowing from contact surface 28 to contact surface 40 will flow 
through the interface of the bypass contact surfaces 50, 52, rather than 
through the spring loop. It is thus apparent that inductance effects in 
the terminal will be held to an absolute minimum, since the current path 
from surface 28 to contact surface 40 is as short as it can possibly be. 
In effect, the mechanical functioning of the terminal, the operation of 
the spring means to maintain contact forces, is separated from the 
electrical function and the spring means can therefore be designed to 
obtain optimum force characteristics without regard to accompanying 
self-inductance problems. 
In the event that there is a small flow of current through the spring 
means, because of the construction resistance of the electrical interface 
50, 52, the very minor self-inductance effects produced can also be 
minimized by the use of a terminal, as shown in FIG. 4 and as will be 
described below. 
The connector housing 18 comprises a molded open square frame, each section 
54 of which has a rectangular cross section having a base 56 which is 
against the surface 12 of the circuit board 14, outwardly and inwardly 
facing side surfaces 60, 58, and a top surface 62, the top and inwardly 
facing side surfaces being recessed, as shown at 64, to provide a ledge 
upon which the marginal edge portions of the substrate 9 are supported. A 
plurality of terminal-receiving cavities 66 in the form of narrow slots 
extend inwardly from the bottom surface 56 and the side surfaces 58, 60. 
These slots having a width only slightly greater than the thickness of an 
individual terminal 20 so that the terminals will be supported against 
buckling in the slots, but the spring loops will be free to deform. The 
end portions 26 of the first contact portions of the terminals extend into 
the recess in the top and side surfaces 58, 62 so that the first contact 
surfaces 28 are exposed and the second contact surfaces 40 are normally 
disposed below the bottom surface 56. These surfaces move relatively 
towards each other when the connector is placed in service, as described 
below. 
The connector 18 is mounted on the circuit board 14 by means of fasteners 
76 which extend through holes in the circuit board from the underside 
thereof and are threaded into metallic threaded inserts 72 in the corners 
of the connector housing. An insulating plate 78 is placed beneath the 
connector on the underside 16 of the board and a metallic plate is 
disposed against the surface of the insulating plate 78. The metallic 
plate 80 stiffens and supports the circuit board in the vicinity in which 
the connector is clamped to the board and the insulating plate 76 
insulates conductors on the underside of the board from the plate 80. 
The cover and heat sink 10 comprises a square metallic plate which is also 
clamped to the upper surface 62 of the housing by means of fasteners 74 
threaded into the inserts 76. The surface of the substrate 9, which is 
adjacent to the heat sink 10, is preferably metallized with a very thin 
metallic coating and a thin metallic plate 69 is located against this 
surface and between the substrate and the lower surface of the plate 
portion 68 of the heat sink 10. The plate 69 is advantageously of a 
relatively soft conductive metal such as indium, so that when the heat 
sink plate is clamped against the upper surface 62 of the connector, the 
soft metallic plate will be deformed and will be pressed into intimate 
contact with the substrate and with the surface of the heat sink plate. 
The surfaces of plate 69 will then conform to the adjacent surfaces 
thereby to facilitate transfer of heat to the heat sink. The upper surface 
of the heat sink plate 68 is provided with fins 70 which facilitate the 
removal of heat by radiation. 
The connector and the chip carrier 7 are assembled to the circuit board 14 
by means of the fasteners 76. Thereafter, the chip carrier 7 is positioned 
in the central opening of the connector housing 18 so that the conductor 
surfaces 2 on the substrate are against the first contact surfaces 28 of 
the individual terminals. The heat sink 10 is then assembled to the upper 
surface of the connector housing and the fasteners 74 are tightened to 
draw the heat sink against the surface 62. Tightening of the fasteners 74 
has an effect of pressing the substrate against the contact surfaces 28, 
thereby developing the contact forces between the conductor contact 
surfaces and the terminal contact surfaces 2, 28, and 4, 40. The spring 32 
is deflected and maintains these contact forces as well as the contact 
forces at the bypass interface 50, 52 of each terminal. When the connector 
is assembled to the circuit board, the contact surfaces 40 are 
substantially coplanar with the lower side 56 of the connector housing. 
Connectors in accordance with the invention can be made in any desired size 
but the advantages of the invention are particularly important in the case 
of chip carriers having high count conductor pads 2 on their substrates, 
since the pads are closely spaced and the terminals in the connectors must 
be spaced with an equal degree of closeness. Terminals in accordance with 
the invention can, for example, be manufactured from stock metal having a 
thickness of about 0.008 to 0.010" and can be used in a connector designed 
for use with terminal pads having a center-to-center spacing of 0.02". 
FIG. 4 shows an alternative terminal in accordance with the invention and 
FIG. 5 illustrates the use of this terminal in a modified connector 
housing. The terminal 20' of FIG. 4 has many of the features, in slightly 
modified form, of the previously described terminal and the same reference 
numerals, differentiated by prime marks, are used to indicate 
corresponding structural features of the terminals 20 and 20'. The 
terminal 20' has a spiral spring loop means 32' comprising first and 
second convolutions 82, 84 which extend from the geometric center 86 of 
the spiral. This spring arrangement will provide for a relatively large 
displacement of the first contact portion 22' towards the second contact 
portion 24' and will maintain an almost constant spring rate over this 
large displacement range. There is always some slight constriction 
resistance at the bypass contact surfaces 50', 52', in FIG. 4, and a very 
small current may flow through the spring loop. If the inductance effects 
from even this very small current are objectionable, they can be minimized 
by the use of spiral type spring means of the type shown in FIG. 4 because 
of the fact that the oppositely extending convolutions 82, 84 will have 
the effect of cancelling any small self-inductance which arises in the 
spring system. 
The terminal of FIG. 4 has a semi-circular projection 50' at the transition 
section between the first contact portion 22' and the spring loop 32' and 
this projection is received in a complementary semi-circular notch 52' in 
the second contact portion 24'. The edges of the projection and the notch 
50', 52' serves as the bypass contact surfaces and in addition, this 
arrangement provides a pivotal action of the contact portion 22' when the 
load is applied to the contact surfaces 28', 40'. This pivoting effect 
further contributes to the attainment of a substantially constant spring 
rate in the terminal so that the terminal is extremely tolerant of wide 
variations in the distance separating the surface of the circuit board and 
the terminal pads on the substrate. 
The connector shown in FIG. 5 containing terminals of the type shown at 32' 
is similar in many respects to the connector shown in FIG. 1 and need not 
be described in detail. FIG. 5 also shows an alternative form of conductor 
pads 94, 96 on the circuit board and illustrates that more than one 
conductor pad 94, 96 can be contacted by an individual terminal. Also, an 
extra arm, shown at 92, can be provided on the terminal having a 
projection on its end which is received in a hole on the circuit board so 
that direct connection can be made to a conductor on the underside of the 
circuit board. Alternatively, the projection can extend directly from the 
section 38' as shown at 93. 
FIG. 6 shows an extremely simple form of terminal in accordance with the 
invention in which the spring loop 32" is substantially circular but with 
the width of the spring decreasing with increasing distance from the 
second contact portion 24" to the first contact portion 22". Both 
embodiments, as shown in FIGS. 4 and 6, have camming means or camming 
surfaces at the bypass contact surfaces to cause lateral movement, a 
so-called "contact wipe", of the first terminal contact surface over the 
pad surface. 
While all of the embodiments of the invention disclosed in the drawing are 
intended for use with integrated circuit packages for connecting substrate 
conductors to circuit board conductors, the principles of the invention 
can be used under a variety of other conditions. For example, inductance 
effects can become significant and troublesome in connectors which connect 
conductors in a first conductor cable to conductors in a second flat 
conductor cable. Connectors of this class must also have terminals which 
have spring means for maintaining contact forces at the terminal-cable 
conductor interfaces and the terminals used frequently have relatively 
long springs in order to achieve the required contact forces. The 
inductance effects arise in these springs and they can be minimized by the 
use of terminals having bypass contacts for the current, as discussed 
above. 
As mentioned previously, the principles of the invention are particularly 
important in circuits having extremely short switching times, such as 
circuits having Josephsen junction devices in which the switching times 
are of the order of a picosecond. Devices of this type can be used at 
temperatures close to 0.degree. K., with metals which are superconductive 
at these temperatures. When the principles of the invention are practiced 
under these conditions, it is desirable to plate the terminals with a 
metal which exhibits superconductivity at extremely low temperatures, such 
as niobium-tin alloys, tin, and indium, among others.