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Attachment Method for a Highly Reliable, Low IR Drop Bolted Bus Bar Interface to a Printed Circuit Board

IP.com Disclosure Number: IPCOM000015029D
Original Publication Date: 2001-Nov-09
Included in the Prior Art Database: 2003-Jun-20
Document File: 3 page(s) / 45K

Publishing Venue

IBM

Abstract

The power requirements in high-end processor backplanes created a distribution problem. These backplanes required efficient distribution of 1700 Amps at 1.2V to four 3.4 inch X 3.4 inch multi-chip module sites through six 1/2 oz. copper planes with 30 mV or less voltage drop from the common sense point. The distribution system was also required to have low inductance to minimize the decoupling capacitance required on the backplane to absorb high frequency switching noise in the power system. The magnitude of the design point was complicated further by wiring constraints and physical obstructions from logic card connectors and L3 memory modules. These restrictions resulted in a bus bar pad design that was 0.38 inches X 3.0 inches. An illustration of the pad is shown in Fig. 1.

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  Attachment Method for a Highly Reliable, Low IR Drop Bolted Bus Bar Interface to a Printed Circuit Board

    The power requirements in high-end processor backplanes created a distribution problem. These backplanes required efficient distribution of 1700 Amps at 1.2V to four 3.4 inch X 3.4 inch multi-chip module sites through six 1/2 oz. copper planes with 30 mV or less voltage drop from the common sense point. The distribution system was also required to have low inductance to minimize the decoupling capacitance required on the backplane to absorb high frequency switching noise in the power system. The magnitude of the design point was complicated further by wiring constraints and physical obstructions from logic card connectors and L3 memory modules. These restrictions resulted in a bus bar pad design that was 0.38 inches X 3.0 inches. An illustration of the pad is shown in Fig. 1.

Note: Fig. 1 only shows the general long rectangular shape. In reality, the pads come in pairs since the bus bar is a two layer laminated design. The close proximity of ground to the voltage on the bar helped to reduce the inductance and overall impedance of the power system.

Due to wiring constraints in the bus bar area as well as the number of vias required to support the current from the pad to the inner planes, only three holes could be tolerated to hold the bus bar to the pad on the backplane as can be seen in Fig. 1. This invention, however, could be used over longer bus bars that would utilize more attach...