PCB Design


Custom Backplanes



See also:

Active Backplanes

Standard Backplanes

Boards Design

Schematic Design

Components and Library Management

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What is a custom Backplane?

A custom defined backplane is, as the name suggests, a backplane dedicated to a specific application with its own set of electrical requirements and customized form factor and sometimes even customized connectors. Projects for military, avionics, medical, scientific research, to name the most usual, are known to be based on proprietary specifications. Such a backplane will exhibit little of the industrial standards features, such as form factor, bus, signals definition and connectors. This norm, however, started to change years back. This is due to two major factors that determined these traditional users of custom backplanes to reconsider the options. One is the exacerbated cost of the custom defined components and the associated NREs and minimum quantities coupled with the prominent tendency of the market to make use of the off-the-shelf electronics, such as boards, power supplies, transition modules which are mostly based on and compliant to an industrial standard or another. The other is the increased overall performance of the off-the-shelf components that matches the tough requirements of the mentioned industries where adds the big advantage of these components being extensively tested by the market.

Nowadays the custom backplanes are largely based on industrial standards, like PICMG® or VITA and usually compliancy to these standards is required.  A large portion of the boards used with these backplanes are compliant to a standard or another and thus the same requirement for the backplane.

5-segment, quad bridge, 66MHz, 64-bit, 18-slot CompactPCI backplane


This is a backplane that features one 17 slots-wide, 66MHz, 64-bit CompactPCI bus and a reserved 18th slot, all controlled by one system slot CPU board. The form factor was 6U and access to all slots in the rear was required in order to populate all 18 Rear Transition Modules. A number of proprietary signals were required in the P4 and P5 zone.

Due to the fact that only 5 slots, or loads, are permitted on a cPCI bus segment at 66MHz and a bridge side counts for a load, four bridges were required.

In order to allow for the RTM access in all slots, the PCI-to-PCI bridge pallet boards need to have a low profile such that they do not interfere with the RTM boards.

The four PCI-to-PCI bridges cannot be cascaded due to the latency and timing issues that would render the backplane not functional at 66MHz. The latency and timing issues are solved by adopting a star configuration where the system slot situated at the middle of the backplane is controlling four PCI-to-PCI bridges and each bridge is controlling four peripheral slots with the 18th unused slot attached to one of the four cPCI segments.

The four PCI-to-PCI bridges are placed on two pallet boards, each carrying two of them. The pallet boards plug in the back of the backplane using high density, low profile connectors. Each bridge pallet spans on four slots bringing the signals at the physical location of the first slot of each segment.

Boaeing EDA

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PICMG®2.16 compliant CompactPCI backplane with remote controlled switching between redundant active system slots


The 21-slots, 6U backplane is PICMG 2.16 (packet switching) compliant with 32-bit, 33MHz CompactPCI bridged bus. The 10 peripheral cPCI slots are RTM ready.

The backplane has two system slots but only one of the CPU cards seated in these slots is controlling the cPCI bus at a given time. The two CPU boards update each other through Ethernet links and control 10 peripheral boards through a PCI-to-PCI bridge. If the active CPU board fails or sustains damage, the other CPU will overtake all the functions after a shut sown or a system reset. The cPCI signals between the two system slots and the peripheral slots are routed through CMOS Wide Bandwidth Quad 2:1 Muxes controlled by one external signal driven by the system shelf manager. Elinktron designed the backplane and the low profile pallet board that carries the mux / switching circuitry. The units can be deployed in remote unmanned locations.


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Rigid-Flex-Rigid board for Ethernet and Audio signaling ExampleTitle


The chassis features a front panel that carries 16 circular connectors (see picture) and must swing to the outside in order to allow access inside the chassis. Around 500 mixed analog (audio) and digital signals connect the circular connectors to the backplane in the chassis. The remainder of the pins is assigned to GND and +5V.

Elinktron designed a rigid-flex-rigid board done in 12 layers for the rigid part and 8 layers for the flex. Due to the impedance requirements each signal flex layer refers to a GND layer such that each of the eight flex strips consists of a set of four overlapped dual layer Kapton strips.

Raf flex EDA

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Custom SATA Backplane


The backplane is based on a 3U CompactPCI form factor and features 8 slots, SATA connectors and three slots dedicated for pluggable power supplies.


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