Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Beam leads
Reexamination Certificate
1999-01-21
2002-03-12
Williams, Alexander O. (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Beam leads
C257S725000, C257S730000, C257S728000, C257S693000, C257S702000, C257S773000, C257S724000, C257S734000
Reexamination Certificate
active
06355981
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the field of electronic device packaging and fabrication. More particularly, the present invention relates to improved contacts for semiconductors, integrated circuits and other electronic circuits and discrete electronic components.
BACKGROUND OF THE INVENTION
The package of any electronic device must include contacts for electrically connecting signals, power and ground between the internals of the device and external circuitry. Simple examples of prior-art contacts are the wire leads that protrude from each end of a discrete diode or resistor, or the metal caps on each end of a fuse.
A sophisticated electronic device, such as a microprocessor, may require several hundred contacts. For such devices, surface mount techniques are typically used. The leads of a surface mount device simply contact wires or conductors on the surface of the circuit board, for example, the motherboard of a personal computer system, to which the device is attached. Surface mount leads do not penetrate through the circuit board like a diode or resistor lead typically does, nor do they require a socket as a fuse does. Soldering is typically used to both electronic and mechanically connect surface mount leads to the circuit board.
FIG. 1
illustrates a prior-art integrated circuit that is surface mounted over a circuit board. This integrated circuit includes a silicon (Si) circuit
101
. Insulating film
102
coats the underside of silicon circuit
101
to protect and passivate it. Epoxy layer
103
and a silicon cap
104
cover silicon circuit
101
. Epoxy layer
103
and silicon cap
104
also cover metal bridge
105
.
Metal bridge
105
electrically connects silicon circuit
101
to silicon post
106
. Epoxy section
111
mechanically secures silicon circuit
101
, metal bridge
105
and silicon post
106
. Nickel (Ni) plate
107
covers silicon post
106
and forms a butt-joint with metal bridge
105
. Nickel plate
107
is electrically coupled to silicon post
106
and metal bridge
105
. Nickel plate
107
provides the integrated circuit with a connection point to external circuitry.
This prior-art contact comprises:
1) metal bridge
105
,
2) silicon post
106
,
3) nickel plate
107
, and
4) epoxy section
111
.
As illustrated in
FIG. 1
, the contact of the integrated circuit has been soldered to circuit board conductor
109
with solder fillet
108
. Circuit board conductor
109
has been formed over circuit board substrate
110
.
The contact for the integrated circuit illustrated in
FIG. 1
provides for various advantages. For example, nickel plate
107
covers the sidewalls of silicon post
106
, which helps to strengthen the bonding between the integrated circuit and the circuit board. This is due to the fact that solder can be placed on nickel plate
107
on the sidewalls of silicon post
106
as illustrated in FIG.
1
. It also facilitates inspection during surface mount of the integrated circuit to the circuit board. Whether a good mount is made can be easily confirmed by looking at the solder on the sidewalls of silicon post
106
.
Furthermore, nickel plate
107
extends over the sidewalls of silicon post
106
and contacts the side of metal bridge
105
, forming a butt-joint interface between nickel plate
107
and metal bridge
105
. This provides for an electrical contact between circuit board conductor
109
and silicon circuit
101
.
The butt-joint interface of the integrated circuit contact of
FIG. 1
, however, cannot be formed with much certainty or control over its resulting reliability or bonding adhesion between nickel plate
107
and metal bridge
105
. There are a number of reasons for this. The physical surface of the side of metal bridge
105
might not be flat enough to ensure a reliable bond at this butt-joint interface. Furthermore, the side of metal bridge
105
is difficult to clean because of its location on the side of the wafer. The bond at this butt-joint interface therefore might be weakened if the side of metal bridge
105
is not flat or has not been thoroughly cleaned.
The formation of this butt-joint interface also limits the materials that can be used for nickel plate
107
and metal bridge
105
. This is so because metal bridge
105
and nickel plate
107
can comprise more than one metal layer. The bonding layer of nickel plate
107
then has to be formed so as to bond with each metal layer at the side of metal bridge
105
in order to form an effective contact. Accordingly, the selection of materials that can be used for metal bridge
105
and for the bonding layer of nickel plate
107
is limited.
FIG. 2
shows a prior-art contact that avoids a butt-joint by using a wrap-around flange contact. Silicon circuit
101
, insulating film
102
, epoxy layer
103
, silicon cap
104
, metal bridge
105
, silicon post
106
, solder filet
108
, circuit board conductor
109
, circuit board substrate
110
, and epoxy section
111
are similar to that of the above described butt-joint contact. However, nickel plate
107
and metal bridge
105
have a horizontal flange interface
113
. While the wrap around flange avoids the problems associated with a butt-joint, it is still a relatively complex design, requiring a relatively complex series of processing steps and a relatively large amount of wafer area dedicated to contact fabrication.
SUMMARY AND OBJECTS OF THE INVENTION
An object of the present invention is to simplify the process of fabricating contacts for electronic devices.
Another object is to increase the simplicity and the reliability of contacts for electronic devices.
A further object is to increase the wafer packing density of an electronic circuit by reducing the substrate area that is used for fabricating the device's contacts.
Another object is to provide contacts that have physical and electronic properties applicable to varied types of electronic devices.
Accordingly, a contact for an electronic device is described that comprises a substrate post and a lower wire that runs down the inside surface of the post to connect with an upper wire where not covered by the bottom surface of the substrate.
Such a contact is fabricated by forming a trench in the top surface of a substrate. The trench may be located near the edge of an electronic circuit or discrete component formed using or attached to the substrate. Optionally, an insulation layer is formed that has a through hole at a connection point within the circuit or component, and that ends part way through the trench. An upper wire is formed that runs from the connection point into the trench. The top of the substrate is encapsulated, thus forming an encapsulant protrusion in the trench.
The substrate is selectively thinned from the bottom, thus forming the bottom surface of a substrate post that is located near the trench, exposing part of the bottom surface of the upper wire and forming the inside surface of the substrate post. Optionally, the thinning of the substrate's bottom surface leaves a portion of the bottom surface of the substrate substantially co-planar with the bottom of the contacts.
A lower wire is formed that runs on the bottom of the substrate from the exposed portion of the upper wire, down the inside surface of the substrate post, and optionally across its bottom surface. Optionally, the surfaces of the substrate post between adjacent posts are defined by sawing or etching. Finally, the wafer is diced, thus forming the outside surface of the substrate post.
Alternatively, no post is used. Rather, the contact comprises a wire running over encapsulant that protrudes from the bottom surface of the substrate. The encapsulant protrusion is formed in a substrate trench that is subsequently removed by bottom thinning. Optionally, the bottom surface of the wire on the substrate protrusion can be covered by a contact layer. Optionally, the wire can be insulated from the substrate by an insulation layer. Optionally, the thinning of the substrate's bottom surface leaves a portion of the bottom surface of the subs
Richards John G.
Richmond, III Donald P.
Sander Wendell B.
Blakely , Sokoloff, Taylor & Zafman LLP
ChipScale, Inc.
Williams Alexander O.
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