Electrical contact having a particulate surface

The present invention comprises an electrical contact having solid homogenous conductive particles on the contact surface. The particles are of greater hardness than that of the contact material to deform the contact material and cause breakage or fracture of the oxide or other contaminating layer, or to penetrate the contaminating layer. The particles are applied to the contact surface by a technique which results in the particles being intimately bonded to the contact surface, usually as a layer of particles. A preferable technique for such particle application is hypervelocity oxygen fuel spraying (HVOF) or plasma spraying, by which the particles are embedded on the contact surfaces to provide a substantially permanent interparticle bond between the applied particles and the contact material.

FIELD OF THE INVENTION 
This invention relates to electrical contacts for providing electrical 
interconnection between conductive surfaces. 
BACKGROUND OF THE INVENTION 
Electrical contact surfaces are often subject to contamination caused by 
oxide buildup on the contact surface or by dirt, debris or other 
contaminants accumulating on the contact surface. As a result, the oxide 
or other contaminant prevents good electrical contact between the mating 
surfaces with consequent increase in contact resistance and the associated 
generation of increased heat. The resultant poor electrical connection is 
especially a problem in small area electrical contacts such as are 
employed in integrated circuit packages and other electronic packages 
where a large number of electrical leads or contact areas are provided in 
a relatively small area. 
SUMMARY OF THE INVENTION 
The present invention comprises an electrical contact having solid 
homogenous conductive particles on the contact surface. The particles are 
of greater hardness than that of the contact material to deform the 
contact material and cause breakage or fracture of the oxide or other 
contaminating layer, or to penetrate the contaminating layer. The 
particles are applied to the contact surface by a technique which results 
in the particles being intimately bonded to the contact surface, usually 
as a layer of particles. A preferable technique for such particle 
application is hypervelocity oxygen fuel spraying (HVOF) or plasma 
spraying, by which the particles are embedded on the contact surfaces to 
provide a substantially permanent interparticle bond between the applied 
particles and the contact material. 
The contact surface on which the particle layer is provided can be the 
outer surface of a single layer or multi-layer electrical contact 
structure. The contact surface can alternatively be the outer surface of a 
plated or other contact layer which is itself provided on a supporting 
structure. The contact surface can be, for example, on a contact pad or 
contact area of an integrated circuit or other electronic device or 
package, circuit board or other type of electrical device such as a 
switch, keypad and the like. The contact surface may also be on a 
resilient substrate or element such as shown in co-pending application, 
Ser. No. 08/294,370, filed Aug. 23, 1994 (AUG-C-549XX). The particles can 
also be provided on the conductive surface of an electrical shield, ground 
plane or gasket. 
The solid homogenous conductive particles can be composed of noble metals 
such as gold, silver, platinum and palladium, other metals such as copper, 
nickel and iron, or conductive compounds such as tungsten carbide or 
chromium carbide. A metal filler, such as cobalt, copper or silver can be 
added to the carbide to increase the conductivity. The particle sizes can 
range from about 200 microinches to about 1 microinch or less. The 
particle size should be greater than the thickness of the oxide or other 
contaminating coating in order to engage the underlying contact surface. 
The oxide thickness can vary considerably, and can typically be in the 
range of about 100 Angstroms to about 1 mil. The hardness of the particles 
typically is in the range of about 100-7000 on the Knoop scale. Particles 
of different sizes can be employed together and applied randomly to the 
contact surface. The particles may be in a continuous layer or in a 
non-continuous layer on a contact surface. 
The mating contact surface which engages the particulate surface can itself 
be a similar particulate surface or a nonparticle covered contact surface. 
The conductive particles can be applied to a conductive as well as a 
non-conductive substrate. For use with a non-conductive substrate, the 
particles can serve as the only conductive layer, or the conductive 
particles can be provided on an intermediate conductive plating or other 
layer which itself is on the nonconductive substrate.

DETAILED DESCRIPTION 
Referring to FIG. 1, there is shown an annular ring 30 which is connected 
to one or more circuit traces 32 of a printed circuit board 34. The ring 
is aligned around a hole through the circuit board and into which a lead 
35 of an electrical or electronic device is inserted. The ring is composed 
of a resilient core of material such as silicon rubber having a flexible 
conductive coating or layer on the surfaces of the ring. The opening 
through the annular ring is slightly smaller than the diameter of the 
electrical lead or pin to be inserted therethrough such that compressive 
force is provided between the inserted lead and surrounding ring to 
maintain the lead in position. 
The flexible conductive layer is provided preferably by a chemical grafting 
technique by which metallization is provided on the surfaces of the ring. 
The conductive coating can also be applied by techniques such as dipping, 
ink jet printing, roller coating, screen printing, or spray coating, which 
techniques are themselves known in the art. A particulate layer is 
provided over the conductive layer of the ring or at least over the 
contact portions of the conductive layer, in this case the circumferential 
wall 36 of the ring. The particulate layer is composed of conductive and 
homogeneous hard particles which are of greater hardness than the hardness 
of the mating contact surface or surfaces. In one embodiment, the 
particles are carborundum having a metal such as copper or silver disposed 
therein. A hardness typically in the range of about 100-7000 on the Knoop 
scale is suitable. Preferably, the particles are plasma injected onto the 
conductive coating. 
The conductive coating is sufficiently flexible and resilient to not impede 
the resilience of the core material. The ring can compress when in contact 
with a mating electrical lead and expand when out of mating contact 
without peeling or cracking of the conductive coating on the surface of 
the ring. 
The resilient interconnect ring can be fabricated by molding the core 
material in the desired shape. A metallization is applied to the ring 
surfaces preferably by chemical grafting, and the particulate layer is 
then applied to the surface of the metallization layer. Copper or other 
metal may optionally be electroless plated onto the metallization layer 
prior to application of the particulate layer. 
A further embodiment is illustrated in FIG. 2 which shows a right angle 
board to board connector which includes a connector body 80 formed of a 
suitable dielectric material such as FR-4, Teflon (PTFE) or phenolic, 
having on a first face 82 a plurality of conductive contact areas 84 
arranged in an intended pattern, and electrically connected via conductive 
traces 86 to corresponding contact areas 88 provided on an orthogonal face 
90 of the body. In use, the contact areas 84 are mated to corresponding 
contact areas of printed circuit board 100, and contact areas 88 are mated 
to corresponding contact areas of printed circuit board 102. The 
interconnection assembly of the two circuit boards and connector body is 
maintained by a suitable mechanism (not shown) and which per se is known 
in the connector field. 
The contact areas 84 and 88 have a particulate layer provided on the 
contact surfaces thereof. The surfaces of the body on which the contact 
areas 84 and 88 are formed may have raised pedestal areas, and which may 
have a resilient layer on which the conductive contact layer is provided. 
Referring to FIG. 2a, there is shown a portion of one of the surfaces of 
the connector body 80 having raised pedestals 81. A resilient layer 83 is 
provided on the outer surfaces of the pedestals, and over which a 
conductive layer 85 is provided having the particles embedded thereon in 
accordance with the invention. Alternatively, the connector body 80 may 
itself be of a resilient or elastomeric material which is compressed 
during engagement of the contact areas with the associated circuit boards 
to provided contact pressure. 
Referring to FIG. 3, an edge card connector is shown which comprises a body 
110 of elastomeric material having a plurality of raised ridges 112 onto 
each of which a conductor 114 is provided. The conductors extend down 
respective sides of the body, as illustrated and through openings in the 
bottom portion of the body and thence along the bottom surface of the 
body. The particulate layer is provided on at least the contact portions 
115 of the conductors 114. A circuit board or circuit card having contact 
areas corresponding to the contact areas of the connector is inserted, 
into the connector body for engagement with the respective contact 
portions 115 of the connector. The illustrated edge card connector has 
contacts on opposite sides to engage opposite rows of contact areas of a 
double sided circuit board or card. It will be recognized that single 
sided connectors can also be provided to engage and make contact with 
single sided circuit cards. Various other connector configurations are 
also contemplated to accommodate various electrical and electronic 
interconnect applications and configurations. 
Another embodiment is illustrated in FIGS. 4a through 4d wherein the 
conductive particulate coatings are provided within openings of a female 
socket or interconnect. The interconnect body 120 has a plurality of holes 
122 therethrough each of which has a conductive surface with particulate 
coating 124 for electrical contact of corresponding electrical pins 126 of 
a mating connector 128. Each of the conductive surfaces of the 
interconnect openings terminate on the back surface in an annular contact 
area 130 for mating with appropriate circuit board or other 
interconnections. Each of the connector openings can have an outwardly 
flared entry section 132 which also has a conductive coating. The 
particulate coating can also be provided on the contact surfaces of areas 
130. 
Referring to FIG. 5, there is shown an electrical test probe having a probe 
body 140 with an elastomeric spherical probe tip 142 secured at one end. 
The tip is an elastomeric ball having a conductive surface with 
particulate coating. The probe body has a conductive surface or may be of 
conductive material such as metal. The probe body is retained within a 
suitable fixture to position the tip over the contact area and to compress 
the tip against the contact area for electrical engagement therewith. 
The elastomeric spheres with conductive particulate surfaces can also be 
embodied in an interconnection device as shown in FIGS. 6a and 6b. The 
spheres 150 are retained within a suitable housing (not shown) which is 
interposed between a printed circuit board 152 having conductive pads 154, 
and an electronic device 156 also having conductive pads 158. The device 
is forced toward the printed circuit board against the biasing of the 
elastomeric spheres and the pad areas of the device and circuit board are 
interconnected by the interposed conductive spheres. The device is 
maintained in contact engagement with the circuit board by a suitable 
socket mechanism (not shown). 
The invention can also be usefully employed in the fabrication of 
electrical switches, such as shown in FIGS. 7a through 7c, In each of 
these switches, one or more conductive particulate contact areas 159 is 
applied to the switch actuator 161. A pushbutton switch is shown in FIG. 
7a in which a conductive particulate contact area 159 is provided on the 
actuator. Upon manual depression of the actuator, the contact area engages 
the confronting contact areas 163 of the switch terminals. It will be 
appreciated that various switch configurations can be provided to provide 
intended switch operation. A slide switch is shown in FIG. 7b in which the 
slidable actuator 165 includes particulate contact areas 167 on respective 
ends. A toggle switch is depicted in FIG. 7c in which the toggle mechanism 
170 includes particulate contact areas 172. The contact areas 174 of the 
switch terminals can also have the particulate layer mateable with the 
particulate layer of the actuator. 
The invention is not to be limited by what has been particularly shown and 
described, as variations and alternative implementations will occur to 
those of skill in the art without departing from the true scope of the 
invention.