Wave transmission lines and networks – Coupling networks – With impedance matching
Reexamination Certificate
2001-12-26
2004-03-02
Pascal, Robert (Department: 2815)
Wave transmission lines and networks
Coupling networks
With impedance matching
C333S034000, C333S247000, C257S775000, C361S777000, C174S261000
Reexamination Certificate
active
06700457
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present inventions relate to circuit boards, more particularly, to impedance compensation for circuit board breakout regions.
2. Background Art
Circuit boards, such as printed circuit boards (PCBs), have chips (integrated circuits or die) on one or both sides of the circuit board. The chips are typically protected by a package. A variety of connection approaches may be used to make connections between the PCB, package, and die. The interface of the PCB with the package often has a circuit board breakout region where the traces from package balls are more densely populated for a small length prior to fanning out on the PCB. This may be used to interface the larger PCB physical features with the smaller package features.
A typical prior art approach is illustrated schematically in FIG.
1
. Referring to
FIG. 1
, a system
10
includes a packaged chip
14
supported by a PCB
16
. Packaged chip
14
includes a die
22
and an associated package
20
. Support
24
is a portion or portions of package
20
that supports traces. For ease of illustration, die
22
is shown on an edge of package
20
, but that is not required in actual use. Die
22
has die bumps
26
of which die bumps
26
A,
26
B,
26
C,
26
D,
26
E, and
26
F are illustrated. Die bumps
26
are an interface between package traces
30
and internal circuitry of the die. Package
20
has package balls of which package balls
36
A,
36
B,
36
C,
36
D,
36
E,
36
F,
36
G, and
36
H are illustrated. Package traces
30
couple corresponding die bumps
36
and package balls
26
. For example, package trace
30
A couples package ball
36
A to die bump
26
A, package trace
30
B couples package ball
36
B to die bump
26
B, etc.
PCB traces
40
are positioned on PCB
16
. Examples of PCB traces
40
include traces
40
A,
40
B,
40
C,
40
D,
40
E, and
40
F. PCB traces
40
from PCB
16
couple to corresponding package balls
36
. For example, PCB trace
40
A couples to package ball
36
A, PCB trace
40
B couples to package ball
36
B, etc. PCB
16
includes multiple layers and different ones of traces
40
may be in different layers of or on the same layer of PCB
16
and can change layers through vias.
A PCB breakout region
38
is a region in which PCB traces
40
connect to package balls
36
. There is a relatively small amount of space for traces
40
to connect to package balls
36
when compared with the amount of space on PCB
16
for traces
40
to be positioned. Generally, there is a higher density of traces
40
in breakout region
38
than outside breakout region
38
. Density refers to the number of portions of traces that are included in a unit area. With a higher density of traces, there may be a greater danger of problems such as cross-talk. One way to allow the higher density in breakout region
38
while reducing cross-talk or similar problems is to have traces
40
be narrower inside breakout region
38
than outside. For example, section
40
A
2
of trace
40
A is narrower than is section
40
A
1
of trace
40
. Traces
40
are illustrated as fanning out at different angles, but this is shown to illustrate a lower trace density, not to show an actual fan-out. The actual position of traces in the fan-out may be different than that illustrated.
The impedances Zo of the narrower portions of traces
40
in breakout region
38
(e.g., trace section
40
A
2
) are greater than those wider portions outside breakout region
38
(e.g., trace section
40
A
1
). This presents an impedance discontinuity to signals propagated through this region, which is not desired. Impedance discontinuities can create unwanted reflections, thereby slowing the speed at which signals can be reliably switched. Merely as an example, the impedances of traces
40
may be 50 ohms outside breakout region
38
, but increase to 60 ohms where PCB traces narrow inside breakout region
38
. Package traces
30
may be 50 ohms again.
A package breakout region
32
refers to a region in which package traces
30
connect to die bumps
26
. The density of package traces
30
may be generally lower between PCB breakout region
38
and package breakout region
32
than in either PCB breakout region
38
or package breakout region
32
. Although package traces
30
are narrower than PCB traces
40
, the impedance of package traces
30
may be the same as PCB traces
40
where other dimensions such as the distance between the trace and ground plane are also scaled.
The impact of an impedance discontinuity increases as the frequencies of signals on the traces increases.
REFERENCES:
patent: 5184095 (1993-02-01), Hanz et al.
patent: 5194833 (1993-03-01), Dougherty et al.
patent: 5880657 (1999-03-01), Dorschky et al.
patent: 6366466 (2002-04-01), Leddige et al.
patent: 6518663 (2003-02-01), James et al.
U.S. patent application, pending, Ser. No. 09/724,634, filed Nov. 28, 2000 to Michael W. Leddige et al.
David M. Pozar, “Microwave Engineering”, John Wiley & Sons, Inc. Second Edition, 1998. pp. 276-297.
Theodore Moreno, “Microwave transmission design data”, Sperry Gyroscope Company, 1958. pp. 50-54.
J.C. Slater, “Microwave Transimmion”, McGraw-Hill Book Company, Inc., 1942. pp. 42-45.
McCall James A.
Shykind David N.
Stahlberg Steven M.
Aldous Alan K.
Intel Corporation
Jones Stephen E.
Pascal Robert
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