Power bus bar for providing a low impedance connection between a first and second printed circuit board

The present invention provides a reliable high current connector for connecting the ground and power planes of a first PCB to the ground and power planes of a second PCB. The power bus bar is comprised of a first conductive structure having a first and second surface, a second conductive structure having a first and second, and an inner insulative structure positioned between the first surface of the first conductive structure and the first surface of the second conductive structure. A fastening means, inserted through openings in the conductive structures, provides a secure, low resistance electrical connection from the first or second conductive structure of the bus bar to the electrical traces of the PCB. The high dielectric constant of the insulator provides distributed capacitance between the first conductive structure and the second conductive structure, lowering the AC impedance. The bus bar design mounts both above and below each PCB and increases mechanical strength and spatial efficiency compared to previous bus bar designs.

BACKGROUND OF THE INVENTION 
Usually power is routed from one printed circuit board assembly (PCA) to 
another printed circuit board assembly using a direct printed circuit 
board (PCB) to printed circuit board connection using board mount 
connectors. Although board mount connectors provide easy assembly, they 
typically require significant board space. Not all geometry constraints 
allow for a direct board to board connection. In some cases, the power 
requirements and geometric constraints of the PCA to PCA connector can be 
made using a cable/connector or bus bar solution. 
Existing solutions which utilize a cable/connector solution for connecting 
a first PCA to a second PCA include: plastic molded connectors attached to 
cables which plug into mating connectors on either PCA and uninsulated 
metal power pins that can be placed on each PCA and then connected by 
receptacles at the ends of the wire. Electrical connection between the 
cable mechanism and the PCA is typically made using a mating connector 
which is soldered to the PCA. A problem with the aforementioned 
cable/connector solutions is that they have a relatively high electrical 
impedance. The cable/connector impedance includes the impedance at the 
interface between the wire and the first connector, the impedance of the 
interface between the wire and the second connector, and the impedance 
inherent in the wire itself. A further problem with prior cable/connector 
solutions is that they can be difficult to assemble for high current 
applications since high current applications typically require a large 
wire thickness. The large wire thickness makes the cable/connector 
solutions difficult to manage in a limited space. 
A second solution for electrically connecting a first PCB to a second PCB 
is a power bus bar. FIG. 1A shows a top view of a conventional bus bar 100 
used to electrically connect a first printed circuit board (not shown) to 
a second printed circuit board (not shown). FIG. 1B shows a side 
cross-sectional view of a conventional bus bar of the power bus bar shown 
in FIG. 1A. The bus bar 100 shown in FIGS. 1A and 1B is comprised of a 
first electrically conductive structure 120 and a second electrically 
conductive structure 122. The first electrically conductive structure 120 
is connected to the power plane of both the first and second printed 
circuit boards. The second electrically conductive structure 122 is 
connected to the ground planes of both the first and second printed 
circuit boards. 
Referring to FIG. 1A, the first and second electrically conductive 
structures 120, 122 are physically located on the same plane and are 
placed side by side so that the sidewalls of the first and second 
electrically conductive structures 120, 122 and are separated by a 
predetermined distance 126. A first insulative layer is placed on the top 
surfaces of the first and second electrically conductive structures 120, 
122. A second insulative layer is placed beneath the first and second 
electrically conductive structures. The second insulative layer typically 
has adhesive properties to solidify the positioning of the first and 
second conductive structures 120, 122 thus preventing movement. Electrical 
contact between the conductive structures and the PCBs is made by securing 
each conductive structure to an electrical contact of the PCB. Compared to 
the cable/connector solution, electrical resistance is decreased. However, 
because the first and second structures are placed side by side in the 
same plane, the inductance of the bus bar structure is relatively high. 
Further, it is desirable to further minimize the geometric requirements of 
the bus bar connector. 
A spatially efficient, reliable high current connector for connecting the 
ground and power planes of a first printed circuit board to the ground and 
power planes of a second printed circuit board is needed. 
SUMMARY OF THE INVENTION 
The present invention provides a reliable, high current connector to a 
printed circuit board or printed circuit board assembly. In the preferred 
embodiment of the present invention, the bus bar is used for electrically 
coupling the ground and power planes of a first printed circuit board to 
the ground and power planes of a second printed circuit board. The bus bar 
is spatially efficient and minimizes the amount of space needed to make an 
electrical connection between the first and second printed circuit boards. 
Further, the present invention provides a low impedance, reducing voltage 
drops and improving the transient response of the system. 
The power bus bar is comprised of a first conductive structure having a 
first and second surface, a second conductive structure having a first and 
second surface, and an insulative structure positioned between the first 
surface of the first conductive structure and the first surface of the 
second conductive structure. The first end of the first conductive 
structure and a first end of the second conductive structure form a first 
contacting structure. A similar contacting structure is formed by the 
second end of the first conductive structure and the second end of the 
second conductive structure. The first surface of the first contacting 
structure electrically couples to a first electrical contact on a first 
plane (typically the power plane of a first printed circuit board) and a 
second surface of the contacting structure electrically couples to a first 
electrical contact on a second plane (typically the ground plane of the 
first printed circuit board). The first surface of the first contacting 
structure is typically at a different height and is generally parallel to 
the second surface of the first contacting structure. 
In the preferred embodiment, both the first and second conductive 
structures include a first opening at the first end of both the first and 
second conductive structures and a second opening at the second end of 
both the first and second conductive structures. A first fastening means, 
preferably a screw, is inserted through both the first opening of the 
first conductive structure and the first opening of the second conductive 
structure. Similarly, a second fastening means is inserted through the 
second opening of the first conductive structure and the second opening of 
the second conductive structure. A screw provides a high pressure contact 
which provides a secure, low resistance electrical connection from the 
first or second conductive structure of the bus bar to the electrical 
traces of the PCB. Further, resistance of the bus bar according to the 
present invention has a reduced resistance at the board interface because 
of (1) the high pressure contact created by the screw fastener and (2) the 
ample contact area. 
The first conductive structure and second conductive structure form a low 
impedance transmission line at high frequencies. The high dielectric 
constant of the insulative structure provides distributed capacitance 
between the first conductive structure and the second conductive, lowering 
the AC impedance and thereby improving the transient response. Further, 
compared to the bus bar described in FIG. 1, the present invention makes a 
large current loop which increases radiated emissions. The form factor of 
the present invention reduces the magnetic loop area of the power 
connection which reduces radiated emissions and susceptibility. Reducing 
the radiated emissions of the power connection improves the transient 
response of the power distribution system. 
Compared to the prior bus bar design which electrically couples to a PC 
board at multiple electrical contact points on a single plane, the bus bar 
design according to the present invention mounts both above and below each 
printed circuit board. The prior design of having two connectors mount on 
a single plane is problematic since it increases the surface area needed 
to make an electrical connection to the PCB. Having a connector 
electrically couple both above and below (making electrical contact on a 
both a first plane and on a second plane) of the printed circuit board 
reduces the assembly time and manufacturing costs by reducing the number 
the fasteners required. Further, the connector mount configuration 
according to the present invention strengthens the thickness of the bus 
bar by increasing its thickness by 50%, thus providing for a more stable 
mechanical design. Because of the increased thickness of the bus bar, the 
width of the bus bar may be decreased further increasing the spatial 
efficiency of the design. 
A further understanding of the nature and advantages of the invention 
described herein may be realized by reference to the remaining portions of 
the specification and drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 2A shows a cross-sectional view of the power bus bar 200 according to 
the present invention before insertion of a fastening means and before 
insertion of the printed circuit boards. The power bus bar 200 is 
comprised of a first conductive structure 210 having a first surface 212 
and a second surface 214, a second conductive structure 216 having a first 
surface 218 and second surface 220, and an inner insulative structure 222 
positioned between the first surface 212 of the first conductive structure 
210 and the first surface 218 of the second conductive structure 216. 
In the preferred embodiment, the first and second conductive structures 
210, 216 are electrically conductive elongate structures having a length 
greater than its width or thickness. Typically, the length of the bus bar 
varies widely and is dependent on the distance between the two printed 
circuit boards. The width of the bus bar is typically in the range of 5 to 
40 mm and the thickness of the bus bar is typically in the range of 0.2 to 
2.0 mm. The required length, width, and thickness of the bus bar is 
dependent on the amount of current that is required to be carried by the 
bus bar. 
The first and second conductive structures 210, 216 of the bus bar 200 are 
preferably constructed of 1/2 hard copper. Since the first and second 
conductive structures 210, 216 are made of solid, formed 1/2 copper, the 
bus bar structure holds its shape well, making assembly easy. The bus bar 
200 is constructed by laminating two pieces of blanked and formed copper 
(the first and second conductive structures) together using insulation 
(the inner insulative structure). Although not required, in an alternative 
embodiment an insulator 223 is adhered to portions of the second surfaces 
214, 220 of the first and second conductive structures 210, 216. 
The bus bar 200 is typically used to connect the ground plane 224 and power 
plane 226 of a first printed circuit board 228 to the ground and power 
planes 234, 232 of a second printed circuit board 236. After PC board 
insertion, the first conductive structure 210, the outer bus bar, is 
electrically coupled to the power plane 226 of the first PCB 228 and the 
power plane PCB and brings power in. After PC board insertion, the second 
conductive structure 216, the inner bus bar, is typically electrically 
coupled to the ground plane 224 of the first PCB 228 and the ground plane 
234 of the second PCB 236 and is the electrical return. 
The first and second conductive structures 210, 216 form a low impedance 
transmission line at high frequencies. Thus, in the preferred embodiment, 
the inner insulative structure 222 has a high dielectric constant, 
preferably in the range of 1 to 100. The configuration of the present 
invention, two conductive structures 210, 216 separated by an inner 
insulative structure, provides distributed capacitance between the first 
and second conductive structures, lowering the AC impedance of the system. 
Typically an adhesive is used to adhere the inner insulative structure 222 
to the first surface of the first conductive structure and the first 
surface of the second conductive structure. 
Further, the connector mount configuration according to the present 
invention strengthens the part compared to the power bus bar 100 shown in 
FIG. 1, by increasing the bus bar thickness by 50% or more by adding a 
second conductive structure 216 and an inner insulative structure 222 to 
the bus bar. Increasing the thickness of the bus bar provides a more 
stable mechanical design. Because of the increased strength, the width of 
the bus bar may be decreased, further increasing the spatial efficiency of 
the design. 
Referring to FIG. 2B shows an expanded view of the first contacting 
structure 242 shown in FIG. 2A. The first end 238 of the first conductive 
structure 210 and a first end 240 of the second conductive structure 216 
form a first contacting structure 242. A similar contacting structure 244 
is formed by the second end 246 of the first conductive structure 210 and 
the second end 248 of the second conductive structure 216. The first 
surface 250 of the first contacting structure 242 electrically couples to 
a first electrical contact 252 on a first plane (typically the power plane 
of a first printed circuit board) and a second surface 254 of the first 
contacting structure 242 electrically couples to a first electrical 
contact 256 on a second plane (typically the ground plane of the first 
printed circuit board). The first surface 250 of the first contacting 
structure 242 is typically at a different height and is generally parallel 
to the second surface 254 of the first contacting structure 242. 
The second end 246 of the first conductive structure 210 and a second end 
248 of the second conductive structure 216 form a second contacting 
structure 244. The first surface 250 of the second contacting structure 
244 electrically couples to a first electrical contact 258 on a third 
plane (typically the power plane of a second printed circuit board). A 
second surface 254 of the contacting structure electrically coupling to a 
first electrical contact 259 on a fourth plane (typically the ground plane 
of a second printed circuit board). Typically, the first surface 250 of 
the second contacting structure 244 is at a different height and is 
generally parallel to the second surface 254 of the second contacting 
structure 244. 
In the embodiment shown in FIGS. 2A-2C, the power bus bar 200 further 
includes a fastening means 260 at the end of the contacting structures 
242, 244. The fastening means 260 is used to apply pressure to the first 
contacting structure 242, the pressure applied to the fastening means 260 
forces the first surface of the first contacting structure towards the 
second surface of the first contacting structure. In the embodiment shown 
in FIG. 2A, the fastening means includes a screw. 
Referring to FIG. 2C shows an isometric view of the bus bar 200 according 
to the present invention. A first opening 262 is located at a first end 
238 of the first conductive structure 210 and a second opening 268 is 
located at a second end 246 of the first conductive structure 210. 
Similarly, a first opening 264 is located at a first end 240 of the second 
conductive structure 216 and a second opening 266 is located at a second 
end 248 of the second conductive structure 216. Preferably the central 
axis of the first opening 262 of the first conductive structure 210 is 
aligned with the central axis of the first opening 264 of the second 
conductive structure 216 and the central axis of the second opening 268 of 
the first conductive structure 210 is aligned with the central axis of the 
second opening 266 of the second conductive structure 216. 
In the embodiment shown in FIGS. 2A-2C, a first electrically insulative 
washer 270, typically a shoulder washer, is positioned over the second 
surface 214 of the first conductive structure 210. The opening of the 
first electrically insulative washer 270 is positioned so that at least a 
portion of its opening is positioned over the first opening 262 of the 
first conductive structure 210. Preferably the central axis of the first 
electrically insulative washer 270 is aligned with the central axis of the 
first opening 262 of the first conductive structure 210. Similarly, a 
second insulative washer 274 having an opening is positioned over the 
second surface of the first conductive structure 210, the second 
insulative washer 274 is positioned so that at least a portion of its 
opening is positioned over the first opening 268 of the first conductive 
structure 210. Preferably the central axis of the second electrically 
insulative washer 274 is aligned with the central axis of the second 
opening 268 of the first conductive structure 210. Typically an adhesive 
is used to adhere the insulative washers 270, 274 to the first and second 
conductive structure 210. 
Although the embodiment shown in FIG. 2 shows an insulative washer, any 
insulative structure which prevents the screw (typically a conductor) from 
electrically contacting both the first and second conductive structures 
could be used. For example an insulating sleeve could be used in 
combination with the screw or alternatively a nylon screw could be used. 
What is important is that the metal fastening means be electrically 
insulated from at least one of the electrical contacting surfaces. 
In the preferred embodiment of the bus bar 200, a nut or threaded fastener 
280 permanently pressed into the second surface of both the first end and 
the second end of the second conductive structure 216. Permanently 
pressing the threaded fastener 280 to the second conductive structure 216 
both reduces the electrical resistance of the bus bar and reduces 
fabrication costs and time, since the assembler is no longer required to 
put on a threaded fastener. However, permanently pressing the threaded 
fastener is optional. In an alternative embodiment, a nut could be used on 
the other side of the screw to secure the screw. Further, it is not 
required that the fastening means on both ends of the bus bar be 
identical, for example, in one embodiment a screw could be inserted into 
the openings at the first end of the first and second conductive 
structures and a different fastening means, such as a rivet, could be used 
to fasten the second end of the first and second conductive structures. 
The bus bar 200 is typically used to connect the ground and power planes of 
a first printed circuit board to the ground and power planes of a second 
printed circuit board. FIG. 2A shows a side cross-sectional view of the 
bus bar according to the present invention before insertion of a fastening 
means 260 and before insertion of the printed circuit boards 228, 236. 
Electrical connection from the bus bar 200 to each of the PCBs 228, 236 is 
made by sliding each PCB 228, 236 into the space between the first and 
second surfaces of the contacting structures and then fastening the bus 
bar 200 to the PCB 228, 236. For the type of fastening means 260 shown in 
FIG. 2, a screw is positioned through openings 262, 264, 266, 268 of the 
bus bar and openings in the first and second printed circuit board 228, 
236. 
In embodiment shown in FIG. 3, the printed circuit boards are fastened to 
the bus bar assembly using a screw 260. FIG. 3 shows a side 
cross-sectional view of the bus bar 200 according to the present invention 
after insertion of the printed circuit boards 228, 236 and after insertion 
of the fastening means 260. The power bus bar 200 shown in FIG. 3 is used 
for electrically coupling a first electrical contact 252 on a first plane 
of the first printed circuit board 228 to a first electrical contact 258 
on a first plane of a second printed circuit board 236 and for 
electrically coupling a first electrical contact 256 on a second plane of 
a first printed circuit board 228 to a first electrical contact 259 on a 
second plane of a second printed circuit board 236. 
A fastening means 260, preferably a screw, is inserted through both the 
first opening of the first conductive structure 210 and the first opening 
of the second conductive structure 216. Similarly, a fastening means is 
inserted through the second opening of the first conductive structure 210 
and the second opening of the second conductive structure 216. After the 
screws 268 are inserted through the openings of the conductive structure 
the pressure is adjusted. In general, contact resistance can be reduced by 
increasing the pressure created by the fastening means. 
A screw 260 provides a high pressure contact which provides a secure, low 
resistance electrical connection to the first or second conductive 
structure 210, 216 of the bus bar to the electrical contacts of the PCB. 
Further, resistance of the bus bar according to the present invention has 
a reduced resistance at the board interface because of the high pressure 
contact created by the screw fastener 260. 
Although in the preferred embodiment screws are used, other fastening means 
may be used. For example, a rivet or some sort of clamping mechanism may 
be used. The important criteria for the fastening means is that it provide 
sufficient pressure to make good electrical contact to the first structure 
and the second structure. 
Further, if the space between the first and second surfaces of the 
contacting structure is precisely made to be approximately the width of 
the PCB or slightly less than the width of the PCB, the contacting 
structure may provide sufficient mechanical pressure to provide a good 
electrical contact. Applicant believes a problem associated with this 
alternative bus bar configuration is that it requires a more precise fit, 
potentially increasing the manufacturing costs of the bus bar. Further, 
the alternative bus bar which does not use a fastening means to secure the 
electrical connection, is less mechanically stable and more susceptible to 
a loss of electrical connection since it provides a friction fit as 
opposed to a high pressure contact, however a spring contact would be 
needed. In this alternative embodiment of bus bar, insulative washer 
structures, openings in conductive structures and fasteners are typically 
eliminated since no longer necessary to provide a high pressure contact. 
Although increase in cost for more precise fit, manufacturing and assembly 
cost is decreased due to elimination of insulative washer structures, 
openings in conductive structures and screws. 
Referring to FIG. 4 shows an alternative contacting structure for the power 
bus bar shown in FIGS. 2, and 3A-3C. In the alternative embodiment, the 
two contacting structures are different. In the embodiment shown in FIG. 
4, the first contacting structure 242 is modified while the second 
contacting structure remains the same. Although the first contacting 
structure is modified in the embodiment shown in FIG. 4, in an alternative 
embodiment the second contacting structure is modified and the first 
contacting structure is unchanged. 
In the alternative embodiment shown in FIG. 4, the first contacting 
structure is modified so that electrical connection to a first and second 
voltage plane (typically ground and power plane) are in the same plane. In 
the embodiment shown in FIG. 4, the first end of the first conductive 
structure and a first end of the second conductive structure form a first 
contacting structure. However, in contrast to the first contacting 
structure 242 shown in FIGS. 2A-2C and FIG. 3, the first surface of the 
first contacting structure for electrically coupling to a first electrical 
contact on a first plane, and a second surface of the contacting structure 
for electrically coupling to a second electrical contact on the first 
plane. 
Preferably the modified contacting structure connects the power plane and 
ground planes of a first printed circuit board to the ground and power 
terminals of a power supply. In this alternative embodiment, the power bus 
bar electrically couples a first electrical contact on a first plane of a 
first printed circuit board to a first terminal and a first electrical 
contact on a second plane of a first printed circuit board to a second 
terminal. The power bus bar is comprised of a first conductive structure 
having a first surface and a second surface; a second conductive structure 
having a first surface and a second surface, and an inner insulative 
structure positioned between the first surface of the first conductive 
structure and the second conductive structure. 
It is understood that the above description is intended to be illustrative 
and not restrictive. For example, the bus bar has two ends and statements 
made with respect to a first end of the bus bar are typically applicable 
to the second end of the bus bar and statements made with respect to the 
first conductive structure are typically applicable to the second 
conductive structure. Further, although the current description is made 
with respect to connection between a first and second printed circuit 
boards, the present invention may be used to connect multiple printed 
circuit boards or printed circuit board assemblies. Further, the printed 
circuit board or printed circuit board assembly may be any inner 
insulative structure with conductive traces. The scope of the invention 
should therefore be determined not with reference to the above 
description, but instead should be determined with reference to the 
appended claims, along with the full scope of equivalents to which such 
claims are entitled.