US3771107A

US3771107A - Conductive metal powder connector

Info

Publication number: US3771107A
Application number: US00206830A
Authority: US
Inventors: K Forster; W Wheeler
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 1971-12-10
Filing date: 1971-12-10
Publication date: 1973-11-06
Anticipated expiration: 1990-11-06
Also published as: FI57855B; DE2259673A1; ES408613A1; JPS4865485A; CH544419A; DE2259673C3; SE389771B; CA973622A; FI57855C; BR7208675D0; NL7216226A; GB1374889A; IT967747B; FR2164156A5; AU460244B2; DE2259673B2; AU4840972A

Abstract

An electrically conductive metal powder interconnector incorporating a powder bed of submicron diameter nickel/gold particulate powders compacted and contained within a socket and encapsulated by a resilient sealing element. The structure provides a detachably pluggable electrical connector providing a low impedance electrical connection between electrical leads of component elements and other devices to which the elements are attached. Optionally, the structure can function as an interface with connector holes providing the electrical connection between the electrical leads which are located on opposite sides of the interface. Alternatively, the structure can function as a female connector for establishing an electrical contact between the connector and a male pin of a circuit module inserted into the connector.

Description

United States Patent [1 1 Forster et al.

Nov. 6, 1973 CONDUCTIVE METAL POWDER CONNECTOR Inventors: Kenneth R. Forster, Endicott;

Wendell ,1. Wheeler, Endwell, both of N.Y.

International Business Machines Corporation, Armonk, N.Y.

Filed: Dec. 10, 1971 Appl. No.2 206,830

[73] Assignee:

US. Cl. 339/96, 339/278 C Int. Cl l-I0lr 9/08 Field of Search 339/96, 118, 278

References Cited UNITED STATES PATENTS 3/1964 Marquis et a1 339/96 l1/1956 Mullan 11/1964 Olson et al 339/96 7/1968 Jordan 339/118 R OTHER PUBLICATIONS IBM Technical Bulletin, l'lorchos, Test Socket,

U 339/118 R tematively, the structure can function as a female con- 1l./1963, Vol. 6, No. 6, p. 39.

Primary Examiner-Joseph H. McGlynn Attorney-Charles S. Neave et a1.

[5 7] ABSTRACT nector for establishing an electrical contact between the connector and a male pin of a circuit module inserted into the connector.

3 Claims, 4 Drawing Figures 1 CONDUCTIVE METAL POWDER CONNECTOR BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to electrical connection devices, and more particularly, to a female connector of the type employing compacted submicron diameter nickel/gold particulate powders as a means for estab-' lishing an electrical contact between the female connector and a male connector tip inserted into the device.

2. Description of the Prior Art In the prior art, numerous resinous compositions have been made conductive by a physical inter-mixture of particles capable of carrying electrical current. These particles have been finely divided materials such as, copper, gold, carbon, and the like. These conductive plastics are empirically produced and the properties of the conductive mixtures obtained frequently vary from one batch to another. Such connector devices are generally unreliable.

Various other connector devices comprise a female type connector socket-filled with a liquid substance containing metal particles in suspension or other type of conductive fluent material. Such socket type connectors are adapted to receive a male connector tip into conductive engagement with the fluentmaterial'. In these connector devices, the electrical characteristics vary from one device to the other. i

The present day trend is to the miniaturization and micro-miniaturization of the electrical circuit equipment which involves high density packaging. This trend introduces problems such as providing consistently reliable electrical interconnecting devices that are pluggably detachable without thc need of heat to effect the connecting and disconnecting operations.

SUMMARY OF THE INVENTION In accordance with the invention, there is provided electrical connection devices comprising socket carrier receptacles utilizing submicron diameter nickel/gold particulate powders compacted to form a powder bed having controlled and predetermined volume fraction characteristics.Generally, the connected devices comprise one or more electrically conductive sockets loded with conductive metal powder and retained therein by an elastomeric encapsulating element or membrane. The membrane is bonded to the socket carrier. The female socket configurations are adapted to receive the protruding pin elements of a printed circuit card or printed circuit board, or the like. The compacting or volumetric displacement of the powder particulate is according to empirically determined standards and thereby produces reliably good electrical interconnections. The hardware can be fabricated to provide an interposer type interconnecting device enabling printed circuit board to printed circuit board, or printed circuit card to printed circuit board interconnections. Also, the sockets can be fabricated into printed circuit boards to accept the circuit module pins for mounting and electrical interconnection functions.

It is a principal object of the invention to provide a novel and improved electrical connector device which may be employed in a number of different ways, and which is simple in construction and provides an efficient electrical connection having a low connector. impedance characteristic and is capable of meeting present day high speed (nanosecond) signal transmission requirements.

Another object of the invention is to provide an improved female electrical connector device that may be made in very small sizes which provides an efficient low impedance electrical connection with a pluggably detachable cooperating male connector element.

Another object of the invention is to provide an electrical interconnection device that is protected from the external environmental elements.

A still further object of the invention is to provide an improved female electrical connector device which is extremely versatile in its applications and which has controllable insertion and withdrawal forces and makes it especially adaptable for use in muIti-pin connector arrangements.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of the preferred embodiments of the invention, as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary sectional view of a socket in a printed circuit board electrical connector constructed in accordance with the present invention;

FIG. 2 is a fragmentary sectional view of an interposer type electrical connector constructed in accordance with the present invention;

FIG. 3 is the design interconnection geometry for an electrical connector construction in accordance with the present invention; and

FIG. 4 is a diagrammatic showing of the current paths through a typical interposer type electrical connector device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, there is shown an improved electrical connector apparatus in accordance with the present invention and fabricated as a socket in a printed circuit board female type connector adapted to receive the electrical connecting pins of a circuit module. The structure comprises a printed circuit board 10 having one or more tubular shaped sockets 11. The board 10 is usually of a dielectric material such as epoxy glass, or the like. The sockets 11 are of conductive material such as copper, or gold plated copper, or the like, and may be formed in the board by conventional electrochemical processes. The sockets 11 are usually electrically interconnected with other circuitry on the board (not shown) and fabricated by conventional and wellknown printed circuit techniques. The sockets 11 are filled with a conductive submicron diameter size gold plated nickel material powder particulate and compacted to form the powder bed 12. The powder beds 12 are contained in the sockets 11 by means of an elastomeric encapsulating membrane 13. The membrane 13 When the module is detached from the printed circuit board 10, the membrane 13 functions to provided a wiping action to remove the powder particulates from the surface of the pins 14. Preferably, the elastomeric membrane 13 should have a relatively low coefficient of sliding friction and provide an easy deformation of the resilient surfaces. The electrical connection'is designed to be fully separable.

Referring to FIG. 2, there is a fragmentary showing of an interposer or socket carrier 20 having sockets 21. The sockets 21 are filled with conductive metal particulate and compacted to form the powder beds 22. The powder beds 22 are retained in the sockets 21 by elastomeric encapsulating membranes 23. The membranes 23 are bonded to each side of the socket carrier 20. The mating elements are printed circuit cards 24 fabricated of dielectric material and support the pins 25 which are soldered to the printed

circuit patterns

26, 27, and 28 that are on the external surfaces of the printed circuit cards 24.

The interposer or socket carrier member 20 can be fabricated to accommodate various area array connector pin configurations. The encapsulating membranes 23 are adapted to yieldably receive the male type connector pins 25 of the printed circuit cards 24, the pins being insertable through the membranes 23 into the powder beds 22 to establish an electrical connection between the pins 25 and the sockets 21.

The conductivity of the powder beds is contingent upon the volume fraction. The volume fraction may be defined as the ratio of the volume of the conductive powder to the volume of the spatial region to be occupied by the powder, defined as:

where V, the total volume of the powder bed m the weight of the powder 8 the true density of the powder For the powder submicron nickel/gold particulate of the preferred embodiment, the true density is determined as follows:

8 [m(Au)+m(Ni)] m(Ni)/8(Ni)] Alternatively, powder bed compaction characteristics are often defined by rheologists in the following manner:

a. Fraction solids content,

where:

pb bulk density ps solids density b. Voidage,

0. Porosity 1 (Vo m/S) V and The volume fraction in the range of from 15 to 30 percent appears to be an optimum ratio for compacting the powder so as to accept the connector pins in detachably pluggable connection. At lower values of volume fraction compacting the powder scatter increases rapidly and the powder bed is electrically unstable. At higher levels of volume fraction compacting it is extremely difficult to forceably insert the male connector pins. Also, the powder bed is not ideally suited for detachment operations and repeated male pin penetration.

FIG. 3 is the design interconnection geometry for an electrical connector construction in accordance with the present invention, where:

D1 is the connector pin diameter D2 is the socket diameter- Hm is the encapsulating membrane thickness C is the powder bed clearance L is the effective pin length Hs is the socket length Hb is the printed circuit board thickness.

The total connector resistance may be expressed as a summation of the principal conduction paths; that is, R total R pin socket R powder bed where:

R power bed= p powder bed lne l l/D1)/b 21rL ohms where:

p is the resistivity of the respective materials It is the socket thickness lne is the natural logarithm 7 FIG. 4 is an illustration of the current flow paths through the interposer type connection. Although the actual conduction path is complex, the principal current flow is radial from the pins to the conductive powder to the plated socket holes. A dual current path exists with the interposer design principles and the, current flow reverses in the next increment from the plated socket to the pin via the powder bed.

The following is a general conductance classification of materials:

Metal alloys 9 10" ohm CM Metal powders p 10 to l0" ohm CM Metal filled polymers p 10* to l0 ohm CM Conductive organics p 10 ohm CM Dielectrics The following is a brief theory summary of the resistance through a sphere (submicron metal ball) according to R. Holm, Electric Contacts, 4th Edition, Springer-Verlago Resistance through a sphere is as follows:

R (p sphere/1r) ((l/a) l/D) where:

R resistance p resistivity of the sphere a radius of the equipotential hemispherical surface of the sphere D radius of the sphere Then, the theory of conduction through powder beds is based on Kirchoffs First Law with a statement of the continuity principle stated as:

R: [1/(1/R1)+(1/R2) (1/ ")l for parallel resistor networks.

Now, an expression that furnishes a theoretical description of the conduction mechanism is as follows:

R powder bed WI [ps/21'r (l/a l/D)] where 7 mean number of conduction particle per chain Fl mean number of conducting chains While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

We claim:

' b. each socket containing a powder bed of conductive metal powder particulates wherein the powder bed is volume fraction compacted within the socket in a range of from -30 percent; and

c. a sealing membrane of resilient deformable material attached to the socket carrier and overlying the socket opening and being adapted to yieldably receive a male connector pin and admit the connector pin for forcible insertion into the powder bed and conductively engage therewith.

2. A female electrical connector device as defined in claim 1 wherein the powder bed is formed of submicron diameter size metal powder particulates.

3. A female electrical connector device as defined in 10 claim 1 wherein the powder bed is formed of submicron diameter nickel/gold particulate powders.

' 2 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3r77l'107 Dated November 6, 1973 Inventor) Kenneth R. Forster and Wendell J. Wheeler It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

I "I F In the speclflcation, column 4, llnes 15 to 19, the

formula should read as follows:

R total R pin R socket R powder bed Signed and sealed this 23rd day of April 1971;.

QSEAL) 'Attest:

EDWARD I-LFLETOHERJRO C. MARSHALL DANN tgttes ting, Officer Commissioner of Patents J

Claims

2. A female electrical connector device as defined in claim 1 wherein the powder bed is formed of submicron diameter size metal powder particulates.
3. A female electrical connector device as defined in claim 1 wherein the powder bed is formed of submicron diameter nickel/gold particulate powders.