Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2001-02-13
2003-07-01
Eley, Timothy V. (Department: 3723)
Metal working
Method of mechanical manufacture
Electrical device making
C029S606000, C029S868000, C029S872000, C029S857000
Reexamination Certificate
active
06584677
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to the fabrication of electrical interconnectors used to electrically connect printed circuit boards and other electrical components in a vertical or z-axis direction to form three-dimensional electronic modules. More particularly, the present invention relates to a new and improved machine and method for fabricating z-axis interconnectors of the type formed from helically coiled strands of wire, in which at least one longitudinal segment of the coiled strands is untwisted in an anti-helical direction to expand the strands of wire into a resilient bulge. Bulges of the interconnector are then inserted into vias of vertically stacked printed circuit boards to establish an electrical connection through the z-axis interconnector between the printed circuit boards of the three dimensional module.
BACKGROUND OF THE INVENTION
The evolution of computer and electronic systems has demanded ever-increasing levels of performance. In most regards, the increased performance has been achieved by electronic components of ever-decreasing physical size. The diminished size itself has been responsible for some level of increased performance because of the reduced lengths of the paths through which the signals must travel between separate components of the systems. Reduced length signal paths allow the electronic components to switch at higher frequencies and reduce the latency of the signal conduction through relatively longer paths. One technique of reducing the size of the electronic components is to condense or diminish the space between the electronic components. Diminished size also allows more components to be included in a system, which is another technique of achieving increased performance because of the increased number of components.
One particularly effective approach to condensing the size between electronic components is to attach multiple semiconductor integrated circuits or “chips” on printed circuit boards, and then stack multiple printed circuit boards to form a three-dimensional configuration or module. Electrical interconnectors are then extended vertically, in the z-axis dimension, between the printed circuit boards which are oriented in the horizontal x-axis and y-axis dimensions. The z-axis interconnectors, in conjunction with conductor traces of each printed circuit board, connect the chips of the module with short signal paths for efficient functionality. The relatively high concentration of chips, which are connected by the three-dimensional, relatively short length signal paths, are capable of achieving very high levels of functionality.
The vertical electrical connections between the stacked printed circuit boards are established by using z-axis interconnectors. Z-axis interconnectors contact and extend through plated through holes or “vias” formed in each of the printed circuit boards. The chips of each printed circuit board are connected to the vias by conductor traces formed on or within each printed circuit board. The vias are formed in each individual printed circuit board of the three-dimensional modules at the same locations, so that when the printed circuit boards are stacked in the three-dimensional module, the vias of all of the printed circuit boards are aligned vertically in the z-axis. The z-axis interconnectors are then inserted vertically through the aligned vias to establish an electrical contact and connection between the vertically oriented vias of each module.
Because of differences between the individual chips on each printed circuit board and the necessity to electrically interconnect to the chips of each module in a three-dimensional sense, it is not always required that the z-axis interconnectors electrically connect to the vias of each printed circuit board. Instead, those vias on those circuit boards for which no electrical connection is desired are not connected to the traces of that printed circuit board. In other words, the via is formed but not connected to any of the components on that printed circuit board. When the z-axis interconnector is inserted through such a via, a mechanical connection is established, but no electrical connection to the other components of the printed circuit board is made. Alternatively, each of the z-axis interconnectors may have the capability of selectively contacting or not contacting each via through which the interconnector extends. Not contacting a via results in no electrical connection at that via. Of course, no mechanical connection exists at that via either, in this example.
A number of different types of z-axis interconnectors have been proposed. One particularly advantageous type of z-axis interconnector is known as a “twist pin.” Twist pin z-axis interconnectors are described in U.S. Pat. Nos. 5,014,419, 5,064,192, and 5,112,232, all of which are assigned to the assignee hereof.
An example of a prior art twist pin
50
is shown in FIG.
1
. The twist pin
50
is formed from a length of wire
52
which has been formed conventionally by helically coiling a number of outer strands
54
around a center core strand
56
in a planetary manner, as shown in FIG.
2
. At selected positions along the length of the wire
52
, a bulge
58
is formed by untwisting the outer strands
54
in a reverse or anti-helical direction. As a result of untwisting the strands
54
in the anti-helical direction, the space consumed by the outer strands
54
increases, causing the outer strands
54
to bend or expand outward from the center strand
56
and create a larger diameter for the bulge
58
than the diameter of the regular stranded wire
52
. The laterally outward extent of the bulge
58
is illustrated in
FIG. 3
, compared to FIG.
2
.
The strands
54
and
56
of the wire
52
are preferably formed from beryllium copper. The beryllium copper provides necessary mechanical characteristics to maintain the shape of the wire in the stranded configuration, to allow the outer strands
54
to bend outward at each bulge
58
when untwisted, and to cause the bulges
58
to apply resilient radial contact force on the vias of the printed circuit boards. To facilitate and enhance these mechanical properties, the twist pin will typically be heat treated after it has been fabricated. Heat treating anneals or hardens the beryllium copper slightly and tempers the strands
54
at the bulges
58
, causing enhanced resiliency or spring-like characteristics. It is also typical to plate the fabricated twist pin with an outer coating of gold. The gold plating establishes a good electrical connection with the vias. To cause the gold-plated exterior coating to adhere to the twist pin
50
, usually the beryllium copper is first plated with a layer of nickel, and the gold is plated on top of the nickel layer. The nickel layer adheres very well to the beryllium copper, and the gold adheres very well to the nickel.
The bulges
58
are positioned at selected predetermined distances along the length of the wire
52
to contact the vias
60
in printed circuit boards
62
of a three-dimensional module
64
, as shown in FIG.
4
. Contact of the bulge
58
with the vias
60
is established by pulling the twist pin
50
through an aligned vertical column of vias
60
in the module
64
. The outer strands
54
of the wire
52
have sufficient resiliency when deflected into the outward protruding bulge
58
, to resiliently press against an inner surface of a sidewall
66
of each via
60
, and thereby establish the electrical connection between the twist pin
50
and the via
60
, as shown in FIG.
5
. In those circumstances where an electrical connection is not desired between the twist pin
50
and the components of a printed circuit board, the via
60
is formed but no conductive traces connect the via to the other components of the printed circuit board. One such via
60
′ is shown in FIG.
4
. The sidewall
66
of the via
60
′ extends through the printed circuit board, but the via
60
′ is electrically isolated from the other components on that printed circuit board becaus
Boudreaux Randall J.
Garcia Steven E.
Harden, Jr. James A.
Hofmann David A.
Eley Timothy V.
Grant Alvin J.
Ley John R.
Medallion Technology, LLC
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