How to Select a High Speed Backplane Connector

These SSDs will need to connect to a backplane to provide high speed data transfer. Here’s how to select high speed backplane connectors for your rack-mount unit.

Once my company received its first backplane job, I had to dive into datasheets to make sure signals wouldn’t be excessively degraded during transmission. High speed backplane connectors make an appearance in a variety of equipment, but they are most prominent in networking equipment built with daughterboard modules. Choosing the right connectors will make all the difference in signal integrity when your system is deployed.

If you’re looking for high speed backplane connectors, you’ll find a variety of form factors, connection counts, and signal integrity graphs in datasheets. For high speed networking and computing interfaces, such as multi-gig Ethernet and PCIe, your best bet is to look at signal integrity data that’s reported in datasheets. Here’s what to look for and how to interpret these data as you select backplane connectors.

Selecting High Speed Backplane Connectors

High speed backplane connectors are typically designed to mate between a vertical on-board connector and a right-angle on-board connector for the daughter card, with differential pairs routed between the connectors. Some high speed backplane connectors are designed as edge connectors. When working with high speed interfaces, signals are often routed as differential pairs with defined differential impedance; high speed backplane connectors are designed to accommodate this value.

• Insertion loss and insertion loss. High speed backplane connector datasheets will often quote signal integrity metrics using insertion loss at a specific frequency. You may see a corresponding return loss graph as well. Insertion loss should (ideally) only be a couple dB out to the rated bandwidth. VSWR or S-parameters may also be available.

• Impedance. High speed backplane connectors are designed to provide matching to a specific impedance out to the rated bandwidth (normally the Nyquist frequency for the relevant data rate, depending on your signaling standard). Many products are specifically marketed for particular signaling standards (e.g., Ethernet), rather than being standard-agnostic. 

• Induced differential crosstalk noise. This is normally quoted as some percentage of the aggressor signal’s voltage level for a specific rise time. Shorter rise times will produce more differential crosstalk. Received differential crosstalk on a victim pair may also be shown as a spectrum in some datasheets.

• Mounting style. Many high speed backplane connectors use through-hole mounting, although surface-mount connectors are available (e.g., edge connectors). 

• Durability rating. This refers to the number of plug/unplug cycles the connector is rated to withstand. Many high speed backplane connectors are rated for 200 cycles.

• Pin arrangement. This is about more than just pinout, which affects how you’ll route signals into the connector. High speed backplane connectors will interleave ground connections between signal pairs to suppress differential crosstalk during operation. Note that, if you require extra shielding between differential pairs, you could ground some pin pairs as needed.

Not all connectors are interchangeable. Connector manufacturers have designed their connectors to mate with specific connectors they sell, which gives you some flexibility in how you arrange your boards. In fact, the right connector combination won’t force you to conform to the typical planar backplane with orthogonal routing; a series of cards can be interconnected orthogonally when you use pairs of right-angle connectors.

Typical high speed backplane connector arrangement for orthogonal boards.

With regards to differential crosstalk, you’ll need to watch how crosstalk is tested and how data is reported in datasheets. Differential crosstalk between pins on a high speed backplane connector is measured with one differential pair as the aggressor and all other pairs in a group as the victims. The largest value for differential crosstalk between any two pairs may be quoted as the value you find in the product summary on a datasheet. Watch for this as you should try to limit differential crosstalk as much as possible, both in the connector and on the board.

High Speed Backplane Connector Options

Two of the three backplane connector options shown below are designed for multi-gig Ethernet as this is a common need in rack-mounted networking equipment. Other backplane connectors for high speed interfaces (e.g., PCIe) will use a different impedance; be sure to check your connector against the intended signaling standards to ensure compatibility. Here are some examples of the connectors you can find from major distributors.

Tyco Electronics, 1934326-1

The 1934326-1 high speed backplane connector from Tyco Electronics is a press-fit connector (through-hole mounting) enabling Ethernet running at up to 10 Gbps data rate. Insertion loss with these connectors is maintained below -2 dB up to 10 GHz with 100 Ohms differential impedance rating (10 columns, 5 pairs per column). The pin arrangement in this connector includes sequenced ground contacts between pairs, which helps suppress differential crosstalk during operation. Maximum operating temperature for these connectors is 90 °C at 500 mA rated current.

1934326-1 high speed backplane connector from Tyco Electronics, from the 1934326-1 datasheet.

TE Connectivity, 2180828-2

The 2180828-2 high speed backplane connector from TE Connectivity provides up to 56 Gbps Ethernet data rate transmission with 100 Ohms impedance and press-fit termination (through-hole mounting). The pinout provides 4 pairs per column (8 columns) with ground shielding providing between pairs (56 ground positions). This provides low loss and less than 1% induced differential crosstalk for signals with 20 ps rise time. Insertion loss is also maintained below -1 dB up to 25 GHz and is flat thereafter. This connector pair is quite rugged with 185 °C maximum temperature at 500 mA rated current.

2180828-2 high speed backplane connector from TE Connectivity, from the 2180828-2 datasheet.

TE Connectivity/AMP, 2298081-1

The 2298081-1 connector from TE Connectivity/AMP provides up to 56 Gbps data transmission at 85 Ohms impedance. This press-fit plug-style connector (through-hole mounting) provides 56 pairs per column and 36 ground positions for shielding. The UL voltage rating for this connector is 80 V, and maximum temperature is rated at 105 °C at 400 mA rated current. Its high UL rated voltage and maximum temperature make it useful in high-speed rack-mount products for industrial applications.

2298081-1 high speed backplane connector photograph and mounting diagram from TE Connectivity/AMP, from the 2298081-1 datasheet.

When you need to select high speed backplane connectors or any other connector for your system, you need the advanced search and filtration features you’ll only find in Octopart’s electronics search engine. Octopart gives you a complete solution for electronics sourcing and supply chain management, and you can access parts data from worldwide distributors for free. Take a look at our connectors page to start searching for the components you need.

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