• 1. GENERAL INFORMATION
• 1.1 System Introduction
• 1.2 General Specifications of J3 and J5/J6 Backplanes
• 1.3 Terminology
• 1.4 Module and Transition Module Layout for Compatibility with Custom Backplanes
• 2. BACKPLANE MECHANICAL DIMENSIONS
• 2.1 Backplane dimensions
• 2.2 Connector Placement - General
• 2.2.1 Connector Placement - DIN 41612 (0.100" pitch) connectors
• 2.2.2 Connector Placement - Hard Metric (2.0 mm pitch) connectors
• 2.2.3 Connector Placement - backplane thickness control
• 3. Drill and Soldermask Information
• 4. Connector Part Number Information
• 4.1 VME Board Connectors
• 4.2 Subrack Backplane Connectors
• 4.3 Transition Module Connectors
• 4.4 VME Extender Connectors
• 4.5 Transition Module Extender Connectors
• 4.6 Shields
• 4.7 Shrouds
• 5. Signal Routing
• 5.1 Layer stacking
• 5.2 High speed signal traces
• 5.3 Low-speed private buses
• 5.4 Power Distribution
• 6. Appendix: Useful Ancilliary Information

SVX II Silicon Strip Detector Upgrade Project

Readout Electronics for Beam Test

Guidelines for Custom J3 Backplanes

--PRELIMINARY--

December 6, 1996

John T. Anderson

Document # ESE-SVX-961126 

1. GENERAL INFORMATION

1.1 System Introduction

1.2 General Specifications of J3 and J5/J6 Backplanes

1.3 Terminology

The custom backplane is the printed circuit board which is mounted parallel to the main backplane in the system. The custom backplane has fixed-board connectors in it which have pins pointing in both directions. The fixed-board connectors are mounted from the component side of the backplane, which is the Module side - that is, towards the front of the subrack. On the rear or Transition Module side, a spacer is placed between the custom backplane and the connector shroud, which is a plastic body that slips onto the pins of the fixed-board connector and makes the Transition Module side of the fixed-board connector look like the Module side of the fixed-board connector. Free-board connectors are mounted on Modules and Transition Modules, and they plug into the fixed-board connectors. This is shown in Figure 1.

1.4 Module and Transition Module Layout for Compatibility with Custom Backplanes

Connector layout dimensions for 9U x 400 mm Free Board Modules are defined in VME64x 9U x 400 mm Format Draft Standard, VITA 1.X-199x, Draft 0.6, dated 20 October 1996. This document may be found on Fermilab’s ESE department Web server at ftp://eseserver1.fnal.gov/pub/vme-p/9ux400/V64_9U_0_6_2.doc. The basic spacing information, taken from that document, is provided here as Figure 3.

2. BACKPLANE MECHANICAL DIMENSIONS

2.1 Backplane dimensions

• Height: 128.7 +0.0/-0.3 mm (5.067" +0.0/-0.012")

• Width: (N * 5.08)-0.3 mm, +0.0/-0.2 mm, where ‘N’ is the number of horizontal pitches (4 HP per slot). For a 21-slot backplane, the width is then

[(4 * 21) * 5.08] = 426.72 mm +0.0/-0.2 mm (16.800" +0.0/-0.012")

• Thickness: 2.362 mm nominal (0.093" ), maximum 4.45 mm (.175") 

2.2 Connector Placement - General

2.2.1 Connector Placement - DIN 41612 (0.100" pitch) connectors

Holes for the DIN41612 connector are placed on a rectilinear 0.100" (2.54 mm) grid. The placement of the holes relative to the mounting holes does not change between 3-row (96-pin) and 5-row (160-pin) DIN 41612 connectors. The mounting hole is always aligned with respect to the ‘B’ row.

Mounting holes are placed along the backplane according to a spacing rule stated in IEEE 1101.1. Horizontal pitch lines are defined which are co-linear with the mounting hole lines. The first horizontal pitch line (that is, the first connector mounting hole) is located 7.47 mm +0.0/-0.1 mm (0.244" +0.0/-0.004"). Subsequent mounting holes are located 4 HP (20.32 mm / 0.800") to the right of this point.

2.2.2 Connector Placement - Hard Metric (2.0 mm pitch) connectors

This arrangement places the ‘z’ row of the connector in the leftmost slot (slot 1) off the edge of the backplane. The ‘z’ row centerline is 7.47 mm - 1.85 mm - (3 * 2.0 mm) = -0.38mm, or 0.38 mm past the left edge of the backplane. Thus, the designer must choose one of two options:

1. Use only the 5-row hard metric connector in slot 1 or

2. Follow rule 10.2 of IEEE 1101.1 and increase the 7.47 mm dimension by 5.08 mm to 12.55 mm, making the backplane a little wider between slot 1 and the edge than is normally done.

Either choice is acceptable but the designer must be most careful to insure that the connectors are all properly aligned to the horizontal pitch lines when the backplane is made wider than normal. Failure to do so will result in a backplane where all the connectors are at the proper spacing to each other, but are all offset with respect to the subrack mechanics. The proper procedure to follow is to lay out the horizontal pitch lines and reference all measurements to the pitch lines, not to the board edge. The designer must also insure that if choice (2) is taken, the backplane does not press against the inside surface of the subrack side mounting plate.

Hard metric connectors do not require mounting holes as the pin count is sufficiently high that the press-fit retention force is sufficient to hold the connector in the backplane during insertion and removal. 

2.2.3 Connector Placement - backplane thickness control

DIN 41612 connectors such as J2 and J3 have a different seating plane than hard metric connectors such as J0, J5 and J6. Figures 6 & 7 show the necessary dimensions. Different manufacturers make different shroud base thicknesses; insure that the combination of the shroud and spacer selected match the placement dimensions shown. Also, some manufacturers (e.g. ERNI) sell a single piece shroud/spacer combination, others (e.g. AMP) sell separate shroud and spacer parts which must be combined. As the hard metric connectors can tolerate a much wider range of over-insertion than the DIN 41612 parts, custom backplanes should be designed such that DIN 41612 connectors define the seating plane of the Transition Module, not the hard metric connectors. This insures that the DIN 41612 connectors are always fully mated.

3. Drill and Soldermask Information

DIN 41612 connectors are customarily designed to use a 0.040 inch ±.003 inch (1mm +.09 mm - .06 mm) press-fit hole. 2mm hard metric connectors normally use a 0.7 mm ± .02 mm hole (0.6 mm ± .05 mm after plating). Sufficient pad size should be used to insure a stable pad after drilling for plating. Note that the small pitch of the 2mm connectors probably requires a smaller-than-normal anti-pad on copper layers to insure that signals can be routed between the pins. This anti-pad consideration should also be noted when routing power planes on Modules and Transition Modules to insure sufficient copper connection from J0 power and ground pins to the planes of the Module.

All custom backplanes should use a soldermask on both outer surfaces of the backplane. 

4. Connector Part Number Information

4.1 VME Board Connectors

2) 2 mm refers to connectors made or IEC 1076-4-101, Level 2. 

4.2 Subrack Backplane Connectors

4.3 Transition Module Connectors

4.4 VME Extender Connectors

4.5 Transition Module Extender Connectors

4.6 Shields

2) Connector with integral shield 

4.7 Shrouds

2) Optional side latch assemblies are available.

3) Requires 352130-2 spacer. 

5. Signal Routing

5.1 Layer stacking

5.2 High speed signal traces

Calculation of stripline and microstrip impedance is relatively straight-forward. For microstrip and side-couple striplines, formulae for impedance calculations are found in The MECL System Design Handbook from Motorola, publication number HB205. Copies of the most frequently used graphs within that book are found in the Appendix at the rear of this document. For broadside-coupled striplines the calculation is more laborious. A good start is found in Stripline Circuit Design by Harlan Howe, Jr., part of the Artech House microwave series. This latter book is available in the Fermilab Library. A couple of nomographs from this book are copied in the Appendix, plus a chart of estimated broadside-coupled stripline impedances for a relatively common configuration. The reader should be aware that the chart given in the Appendix for broadside-coupled impedance is only good for one particular set of layer spacing. 

5.3 Low-speed private buses

5.4 Power Distribution

In those cases where a private terminated bus is implemented on the custom backplane, only one Module slot should be allowed to provide the power for those terminations. If multiple Modules are allowed contact to the power or ground pins, ground loops are created which adversely affect the operation of the system. 

6. Appendix: Useful Ancilliary Information

Note: This graph is only an approximation, and is only good for broadside-coupled striplines with the layer spacing and trace width as given. Changing either the layer thickness between strips or the layer thickness from strip to ground plane will result in different curves. Zoo is the impedance to use for non-biased, differentially-driven lines terminated in a single resistor across the pair (what one normally thinks of as the characteristic impedance). Zoe is the impedance from either line to ground and is used for systems that drive both lines with currents flowing in the same directions with all return current flowing in the ground planes - thus, the impedance seen by any common-mode portion of the signal.