Vertical action contact spring

An electrical connector for establishing electrical connection between spaced printed circuit boards, for example, comprising a spiral-wound elongated spring member formed of a one-piece blank and being longitudinally resilient for establishing firm surface contact between circuit boards and radially resilient to provide firm contact in a surrounding receptacle when either end of the connector is compressed. A signal connector is fitted into a carrier block and surrounded by ground connectors to protect the signal from interference. The connector design is small in overall length to minimize connector-length related disturbances to the signal.

BACKGROUND OF THE INVENTION 
The present invention is directed to electrical contact springs, 
particularly to those used for establishing and maintaining electrical 
connections between circuit boards. 
When transmitting signals from board to board in an electrical circuit, it 
is essential that the integrity of the signals be protected or shielded 
from interferring with each other through noise, etc. Additionally, the 
length of the signal circuit must be relatively short to avoid 
disturbances of signal integrity related to length of connector. 
Prior art patents directed to electrical connectors include U.S. Pat. Nos. 
4,161,346, 4,505,529 and 4,752,231. 
U.S. Pat. No. 4,161,346 is directed to an electrical connector for 
interconnecting electrical circuits on two electronic circuit boards 
involving surface to surface contact between generally parallel surfaces. 
The patent discloses a connector element having a symmetrical, sinuous 
shape including a spring section for exerting a determined contact force 
and establishing the electrical connection. In addition, the connecting 
element is provided with a separate shorting beam into connector opposed 
ends and the connecting element to provide a shorter electrical path and 
to act as a spring for retaining the contact element within its housing. 
U.S. Pat. No. 4,505,529 relates to a connector for electrically 
interconnecting printed circuit boards in the form with three elongated 
beams extending between contact surfaces with the configuration of the 
contact element being such that it buckles under compression forces to 
provide spring forces. 
U.S. Pat. No. 4,752,231 is directed to an electrical connector including a 
rigid insulating housing bolted between parallel circuit boards and having 
electrical connectors located within and positioned by the rigid housing 
for establishing electrical contact between the circuit boards. The 
connectors themselves are in the form of semi-elliptic springs having 
outwardly projecting tips for establishing contact with opposing portions 
of the circuit board. 
U.S. Pat. No. 4,778,404 is of interest and is directed to a spring terminal 
having an intermediate spring portion form of spring sections joined at 
their adjacent ends to form a zig zag configuration. The terminal is held 
in a fixed position and is generally adapted for use in difficult 
environmental situations where mating connector members must be fully 
sealed. 
A commercially available electrical connector includes telescoping, 
longitudinally connected spring loaded elements in the form of "pogo 
stick" for providing spring biased connectors. 
Each of the foregoing devices involves complex connector constructions 
including multiple components in several cases and complicated assembly 
techniques. Additionally, the block members used for holding and 
positioning the connectors also have intricate designs to accommodate 
assembly and functioning of the connectors. The complexities of design, 
assembly, and operation of these connectors are drawbacks in electronic 
circuit board devices having a multitude of connections and where 
available space is limited and are counterproductive as they increase 
opportunities for loss of signal integrity. 
SUMMARY OF THE INVENTION 
The present invention is directed to an electrical contact spring used for 
interconnecting parallel circuit boards in which the spring is received 
and positioned in a metal block between the circuit boards. The spring 
connector consists of a single metallic element wound in the form of a 
spiral about its longitudinal axis and providing for electrical contract 
at its opposite ends positioned between parallel circuit boards and having 
longitudinal resiliency to establish firm spring electrical contact 
between the circuit boards. Additionally, the contact spring tends to 
expand radially when compressed to promote firm engagement between the 
spring itself and the cylindrical walls of matrix or holding block used 
for receiving and positioning a multitude of contact springs. 
The contact spring according to the present invention has the following 
advantages over the prior art. The spring is fabricated from a single 
blank by rolling the blank into a spiral and coining the tips to provide 
surface contact between opposed circuit board pads. For assembly, the 
connectors are inserted into cylindrical bores or holes in a holding block 
and are retained within the bores as the springs expand radially. The 
spring members are resilient and return to the original position after 
compression forces are released and they are not permanently deformed. 
A metal block containing electrical contact springs of the present 
invention is placed between parallel circuit boards and provides a means 
of transmitting shielded signals from board to board. For transmitting 
signals, a contact spring is placed in an insulating sleeve and located in 
a hole or bore in the metal block. The insulated signal spring is 
surrounded by shielding or grounding circuits in order to protect the 
signals through the metal block interface from interfering with one 
another with noise and so forth. The shielding or grounding circuits are 
insuulated contact springs fitted in holes through the metal block located 
around the signal carrying connectors and serve to protect signals from 
interference. 
A contact spring according to the invention provides a signal circuit of 
relatively short length through the connector block. The short length of 
the signal circuit reduces the opportunity for disturbing signal 
integrity. 
OBJECTS OF THE INVENTION 
It is an object of the invention to provide a one piece electrical contact 
spring which is formed by rolling a one piece blank spiral form to provide 
a longitudinally and laterally resilient contact spring. 
Another object of the present invention is to provide an electrical contact 
element in the form of a spiral spring which yields longitudinally to 
provide spring contact between opposed circuit boards and yields radially 
to provide firm contact positioning the spring within its carrier member. 
A further object of the invention is to provide an arrangement for 
transmitting shielded signals between circuit boards through a signal 
circuit connector of short length minimizing the opportunities for 
disturbing signal integrity. 
Another further objects of the invention will occur to those skilled in the 
art with an understanding of the detailed description of the invention or 
upon employment of the invention in practice.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The present invention is used with electronic components such as circuit 
boards in which a multitude of electrical connections must be established 
between components. As shown in FIG. 1, a sub-assembly of an electrical 
device 10 including an PC board 12 and a back plane 14 are generally 
parallel and are fitted with pads 16 for establishing electrical 
connection therebetween. A retaining block 18 is a conductive metal and 
has a multitude of holes 20 therein for receiving connectors 22 according 
to the invention. In one case, a signal connector 22a is placed within an 
insulating plastic or other dielectric sleeve 24 for insertion into the 
retaining block. In another case a ground connector 22b is placed within 
the retaining block bore as a ground connection between PCB pads, 
retaining block, and back plane. 
In order to protect transmitted signals from interference, each signal 
connector 22a is surrounded by ground connectors 22b such that signal 
connectors are spaced from each other in length and width of the retaining 
block by means of a ground connector. The surrounding ground connectors 
and the metal retaining block provide such signal integrity protection. 
A connector 22 according to the present invention, comprises a spiral wound 
longitudinally compressable spring connector for establishing electrical 
contact between spaced electronic board members. The spaced boards have a 
number of corresponding electrical surfaces or pads 16 which require 
contact by a multitude of connectors. The connector 22 is a one-piece 
spiral-would coil of conductive material having longitudinally spaced 
contact tips 26 for establishing contact with PCB and back plane pads 16. 
Additionally, opposite tips flex independently of each other. It will be 
observed that each end or tip 26 of the connector is rolled or coined in 
the form of a dome (FIG. 3) 28 to provide a contact surface for purposes 
of establishing an electrical connection. In another aspect of the 
invention, the connector expands radially of its longitudinal axis as it 
is compressed more firmly to secure the connector within its receiving 
bore of the metal block. This has an advantage in that it is not necessary 
to press the spring uniformly from both ends. Indeed, the spring connector 
may be compressed from one end and will expand radially into firm and 
immovable contact with its receptacle. This has the advantage of allowing 
flexibility in assembling circuit board members from either end of the 
spring connector in whatever sequence is desired. 
FIG. 2 illustrates a developed blank 30 from which the spring connector is 
fabricated. The blank is generally Y-shaped including a rectangular base 
portion 32 and a pair of outwardly divergent arms 34 projecting from one 
side of the base. Any suitable angle of divergence .alpha. may be selected 
and in the embodiment shown in FIG. 2 the angle is 30.degree.. The outer 
ends of each arm are trimmed to form tips 36 which become the outer 
extremities of the connector in rolled form. Preferably the blank is 
formed of a suitable conductive metal such as berylium cooper of high 
tensile strength and a thickness of approximately 3 to 4 mils. The 
berylium cooper blank may be plated with an outer gold layer over a nickel 
base. The spring is formed by rolling into a tight spiral having at least 
3 complete coils when placed in a 30 mil diameter gage. 
As shown in FIG. 3, the tip 36 at each end of the spring is coined over 
forming a dome-shaped contact area 28 to assure an electrical connection 
based on the surface of the spring and not a tip or edge. 
FIG. 4 illustrates the spring connector in free form including a central or 
waist section 38 and longitudinally projecting spring action arms 40. Each 
of the tips deflects independently of the other a distance of 
approximately 10 percent of the overall length between tips of the 
connector with no set. Additionally, the spring connector is capable of a 
reduction in waist diameter d to approximately 0.8d to accommodate 
insertion in a bore 20 or sleeve 24 of the retaining block while 
maintaining spring action of each of the contact arms. A specific form of 
contact spring has the following approximate dimensions in inches: overall 
length (ol) 0.208; waist length (wl) 0.090; waist diameter free state (d) 
0.036; waist diameter in service 0.030; and contact arm deflection (dfl) 
of 0.020 under a force of 50-100 grams without set. 
A significant advantage of the invention is the relatively short length of 
the signal circuit through the connector block made possible by the short 
overall length of the connector reducing the opportunity for disturbing 
signal integrity through factors related to length of signal connector 
circuit. 
It will be understood from the above description that the contact spring is 
formed using conventional materials and provides a connector of 
considerable advantage when compared to springs of the prior art.