Partially-overcoated elongate contact structures

Details Partially-overcoated elongate contact structures Partially-overcoated elongate contact structures

1997-09-10

2001-10-23

Cuneo, Kamand (Department: 2841)

Electricity: conductors and insulators

Conduits, cables or conductors

Preformed panel circuit arrangement

C174S267000, C361S774000

Reexamination Certificate

active

06307161

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to interconnection elements (contact structures) for electronic components and, more particularly to interconnection elements for making electrical connections to microminiature electronic components.
BACKGROUND OF THE INVENTION
As is described in one or more of the above-referenced patent applications, elongate interconnection elements (contact structures) extending from a one electronic component (e.g., a semiconductor device) can be used to make electrical connections to terminals of another electronic component (e.g., a printed circuit board).
These connections can be of a “permanent” nature (e.g., soldered connections) or of a “temporary” nature (e.g., pressure connections). In many of the above-referenced patent applications, elongate interconnection elements which are resilient, and which are particularly well-suited to making pressure connections between electronic components, are described.
FULLY-OVERCOATED. ELONGATE, RESILIENT CONTACT STRUCTURES
An example of elongate resilient (spring) contact structures which are particularly well-suited to making pressure connections is found in the aforementioned, commonly-owned U.S. Pat. No. 5,476,211. Therein is described methods for making resilient interconnection elements for microelectronics applications involving mounting an end of a flexible elongate core element (e.g., wire “stem” or “skeleton”) to a terminal on an electronic component, and overcoating the flexible core element and adjacent surface of the terminal with a “shell” of one or more metallic materials having a predetermined combination of thickness, yield strength and elastic modulus to ensure predetermined force-to-deflection characteristics of the resulting spring contacts. Exemplary materials for the core element include gold. Exemplary materials for the coating include nickel and its alloys. The resulting spring contact element is suitably used to effect pressure, or demountable, connections between two or more electronic components, including semiconductor devices.
An example of a resilient contact structure fabricated in the manner set forth immediately hereinabove is shown in
FIG. 1
, which is comparable to
FIG. 5
of the aforementioned 08/452,255 and PCT/95/14909.
FIG. 1
illustrates an exemplary resilient contact structure
100
, formed as follows. An elongate core element
102
has had its proximal end
102
a
bonded to a terminal
112
on an electronic component
108
, and is shaped to have a spring-shape, and is severed to have a ball at its distal, free end (tip)
102
b
. Severing may be accomplished by electronic flameoff (sparking), which may be enhanced in the manner described in commonly-owned U.S. Pat. No. 5,601,740 (issued Feb. 11, 1997).
The core element
102
is formed of a relatively soft (low yield strength) material that will not exhibit a significant amount of resiliency. In order that the resulting spring contact element can be resilient, functioning as a spring and reacting a force (labelled “F”) directed axially (i.e, generally in the z-axis direction) downward upon the wire stem, the core element
102
is overcoated, as follows.
One or more layers of metallic material having a relatively high yield strength are applied, such as by plating, onto the core element
102
. In the case of multiple layers, the outermost (top) layer is a conductive material. The principal results achieved by overcoating the core element
102
are: (a) imparting a desired degree of resiliency to a resulting contact structure; and (b) securely anchoring the resulting contact structure to the terminal of the electronic component.
FIG. 1
shows that the core element
102
is overcoated with a multi-layer (two layer) coating enveloping (covering the entirety of) the core element
102
. A first, inner coating layer
120
covers the core element
102
, and a second, outer (top) coating layer
122
covers the first layer
120
. The first layer
120
covers the terminal
112
to which the proximal end
102
a
of the core element
102
is bonded, and securely anchors the core element thereto. The second layer
122
covers the first layer
120
in the area of the terminal
112
, and augments anchoring the core element
102
to the terminal
112
.
Vis-a-vis the two layers
120
and
122
overcoating the wire stem
102
, one (or both) imparts resiliency to the (otherwise non-resilient) wire stem, and the outer layer (or both layers) is electrically conductive. For example:
the core element
102
is a soft gold material, and has a diameter of 0.0007-0.0020 inches (0.7 mils-2.0 mils);
the inner coating
120
is a copper “strike”, having a thickness of 5-10 &mgr;″ (microinches); and
the outer coating
122
is nickel, and has a thickness of 0.0020 inches.
Generally, a coating such as copper would be chosen for two reasons: (i) to enhance the plating ability of the underlying core element (as is known, certain materials are notoriously difficult to plate, for example with nickel), and/or (ii) to ensure good electrical current carrying characteristics for the resulting overcoated core element (copper is known to be a good conductor of electricity).
Generally, a coating such as nickel, or its alloys, would be chosen for its mechanical characteristics, among which are its high yield strength, to be able to elastically react applied forces, and its ability to firmly anchor the resulting resilient contact structure to the contact area (e.g., terminal).
In some instances, it would be desirable that a top (e.g., third) overcoat layer would provide solderability or the like, and would be galvanically compatible with the material of the contact area. In such instances, for example, a thin top coat hard gold, having a thickness of approximately 100 &mgr;″ (100 micro-inches, 0.0001 inches) would be in order.
In high frequency applications, there would be a tendency for current to be distributed along the outer layer(s) of the coated wire stem. In such a case, gold is a good choice for the outer layer of a multi-layer overcoat.
FIG. 1A
, which corresponds to
FIG. 5B
of the aforementioned 08/452,255 and PCT/95/14909, shows a resilient contact structure
130
wherein a core element
132
(compare
102
) has only one layer
144
overcoating and jacketing (partially covering) the core element
132
, and encompassing the terminal
112
of the component
108
. In this case (jacketing), the overcoat layer
144
extends from the proximal (bonded) end
132
a
of the core element
132
only partially towards the distal (free) end
132
b
of the core element
132
. This can be accomplished by masking an end portion of the core element
132
which is adjacent the distal end
132
b
of the core element
132
prior to overcoating the core element
132
, then overcoating the core element
132
, then removing the masking material from the distal end portion of the core element
132
. Evidently, if the coating is non-conductive, it is important that the core element
132
itself be electrically conductive.
PACKAGES HAVING ELONGATE RESILIENT CONTACT STRUCTURES
The electronic component to which the interconnection elements (e.g.,
100
) can be mounted may be an interconnection substrate.
FIG. 2
, corresponding to
FIG. 23A
of the aforementioned 08/452,255 and 95/14909, illustrates an embodiment
200
of a semiconductor package which is based on a multi-layer substrate
210
, such as a multi-layer printed circuit board (PCB) substrate.
The multi-layer substrate
210
is illustrated as having two (can be more than two) insulating layers
212
and
214
, the layer
212
being disposed atop (as viewed) the layer
214
. The bottom surfaces of the layers
212
and
214
are provided with patterned conductive traces
216
and
218
, respectively, in a known manner.
The top (as viewed) insulating layer
212
is formed as a square ring, having a central opening
220
, and the bottom (as viewed) insulating layer
214
is also formed as a square ring, having a central opening
222
aligned with the central opening
220
. As illustrated, the top layer
2

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