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Microbus Minimal passive backplane / bridge PCB for Eurocards DIN41612 2 slot 3U 8HP

Introduction

I have originally designed this bridge / backplane for a few of my projects, but this turn out so well that I have now posted all schematic, gerber files and documentation to fellow enthusiast such as yourself. Perhaps (and I hope) content in this obscured corner of interwebs will inspire you to start your own projects.

Eurocard is a European standard format for printed circuit board (PCB) cards that can be plugged together into a standard chassis sub-rack which, in turn, can be mounted in a 19-inch rack. The chassis consists of a series of slotted card guides on the top and bottom, into which the cards are slid so they stand on end, like books on a shelf. At the spine of each card is one or more connectors which plug into mating connectors on a backplane that closes the rear of the chassis.

Eurocards system in general is enormously versatile and convenient way to create any kind of project where high functionality, reliability and ruggedness are required. System uses standardized mechanical dimensions and quality connectors. Eurocards PCB's come in many sizes (wikipedia article). This is a single height, most common size 3U single height card. I have also designed other 3U passive backplanes if you require different sizes tailored to your project. More about Microbus (wikipedia article).

Design of my backplane PCB was inspired by ECB Mini Backplane from RetroBrew Computers Wiki. I definitely recommend going through their webpage!

You can use this backplane free standing on table or fit in industry standard 3U subrack, however Z rais is required to install in subrack. Backplane was designed according to standard mechanical values, therefore connectors mechanical positions match perfectly PCB guide rails with front panel Eurorack should you decide to use this solution. Standardized card size is 3U height with 2 slots for 4HP cards (8HP 3U) and will fit into a half width 19" 40TE 3HE standardized subrack. I'm using this with standard 160mm depth cards, but you can use whatever fits in your rack (100,160,240mm).

Design overview

PCB Card has been primary designed as:
■ Ideal use low cost solution for simple projects or as a testing jig.
■ Standalone 2-slot backplane card to basically connect two cards outside the rack configuration, for example single board computer and additional periphery.
■ As a bridge card to bridge two backplanes in daisy chain array configuration. For daisy chain / bridge configuration use male connectors and solder them to the back side.

Main design features:

Backplane PCB has been designed to be very flexible and can be used with variety of industry standard signal connections:
■ Signal traces - (passive termination) are not terminated nor have determined pinouts apart from PWR and GND connectors allowing you to configure the backplane to exactly match the requirements of the system. Each pin is bussed across the board, allowing you using row B as GND guard rails thus minimising crosstalk on rows A and C.
■ Power connectors - No facility for power connectors, however you can fit power connector via one of the eurocards cards or use capacitor footpring C1-C2 as power connector.

■ Two separate power rails and one single ground plane available. (Vcc, GND, GND, Vdd).
■ No facility for power connectors, however you can fit power connector via one of the eurocards cards or use capacitor footpring C1-C2 as power connector.
■ Capacitor footprint 7.62mm for the silky smooth DC line and outstanding high-frequency noise suppression
■ Rack mounting holes are not electrically connected
■ Footprint supports off the shelf standard DIN 41612C 96/64pin Eurocard connectors or 2x32, 64pin PCB edge connectors.
■ Multiple backplanes can be placed in sub-rack side by side without loss of slot space

These boards look absolutely gorgeous in standard green solder mask if you go for that standard industrial look. I can advise you where to buy connectors. however you can use any standard off shelf connectors which you can pretty puch purchase anywhere.

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EDA preview

click on pictures to enlarge



3d render v1.22

PCB design layout

Specs

Board Type: Backplane
Board Material: FR4-Standard Tg 130-140C Epoxy Glass Composite
Layers: Double sided
PCB Colour: Green colour solder mask, white silk screen lettering
Surface Finish: Lead free HASL-RoHS
External size: 35 x 99 mm
Board Thickness: standard 1.6mm
Pitch: 2.54mm connectors (100.00 mils)
Connector hole matrix: 96 DIN 41612C compatible / PCB edge card connector 2x32 / 64pin compatible
Hole size: 1.00mm
Mounting holes: Standard pitch 3U subrack mount
Board Connector / Footprint: DIN 41612 2 slot x 96pin or 2x32pin 64 / 96 Pin connector, you can also fit 64pin edge connector in. Power connector is via one of the cards or use capacitor (C1-C2 as power connector). Card is double voltage ready. (Vcc, GND, GND, Vdd).
Copper Thickness: 35um
Card weight: 15g

Bill of materials

Identifier		Value	Qty	Notes
Printed Circuit Board		35 x 99 mm 2 slot Microbus backplane	1	v1.2
Hardware		M2.5 x 10 mm screw	4
Hardware		M2.5 nut	4
Connector	E1,E2	DIN41612 connector, type C, Vertical, 3 rows 32 pins wide	2	DIN41612_C_3x32_Female_Vertical_THT Documentation (20 MB)
Connector	E1,E2	DIN41612 connector, type C, Vertical, 3 rows 32 pins wide	2	DIN41612_C_3x32_Male_Vertical_THT Documentation (20 MB) In bridge configuration, solder connectors to back of PCB
Connector	E1-E2	Female DIN 41612 64pin 2x32pin right angle connector	2	2nd alternative use
Connector	E1-E2	2x32pin 64pin PCB edge right angle connector 0.1" pitch	2	3rd alternative use
Capacitor	C1,C2	C_Disc_D4.3mm_W1.9mm_P5.00mm	2	THT
Connector, power	C1, C2	PinHeader_2.54mm:PinHeader_1x03_P2.54mm_Vertical	2	Use for or Dual V power input via backplane

Assembly instructions and notes

■ Gerber files contain " WayWayWay" to the silk layer. You can specify a location of the order number, select the "Specify a location" option when you place an order. Only if you order via PCBWay.
■ If you will use PCB backplane as rack mount: - install molex connectors, resistors, LED's and pin headers to the back side, otherwise components won't fit due to Z rails.
■ If you will use PCB backplane as table top or custom mount: - install all components to front side. Use standoffs or rubber feet to electrically isolate from surface.
■ Use M2.5 screws and nuts to hold DIN connectors in place, these don't need to be fitted to achieve strong mechanical connection however
■ Use a temperature-controlled soldering station and quality solder. Take care not to leave solder bridges as any short circuit will most likely lead to failures
■ Use capacitor footpring C1-C2 for Dual V power input via backplane, use 2x 1x03 0.1" dupont pin header, pull out middle pin.
■ Ground is common for both power rails, E1-E2 DIN connector holes are mechanical and are not connected to ground.
■ In daisy chain configuration use male connectors DIN41612_C_3x32_Male_Vertical_THT, solder on back side of PCB.

Schematic

File type	File name	File size	Last modified
PCB schematic for 2 slot bridge / backplane v1.0	schematic_backplane2_v10.pdf	223 kB	14/04/2021
PCB schematic for 2 slot bridge / backplane v1.22	Same schematic as v1.0
Microbus backplane pinout, v1.0	microbus_pinout_v10.jpg	383 kB	19/01/2024

Design Files

File type	File name	File size	Last modified
PCB layers v1.2	pcblayers_backplane2_v12.pdf	141 kB	22/01/2022
PCB layers v1.22	pcblayers_backplane2_v122.pdf	152 kB	27/08/2022
Gerbers 35 x 99 mm, 2 Layer FR4, v1.1	gerbers_2backplane_v12.zip	95 kB	22/01/2022
Gerbers 35 x 99 mm, 2 Layer FR4, v1.22	gerbers_2backplane_v122.zip	91 kB	27/08/2022
Solder paste stencil	Not available for this project	-	-

Photographs

click on pictures to enlarge
gerber files and photographs may vary, v1.21 pictured

Versions and revisions

This section lists the project version and revision history.

v1.22

■ EDA layers ammended
■ EDA 3D model created
■ Various silkscreen updates

v1.21

■ Various silkscreen updates
■ Various copper layer updates
■ C1, C2 footprint updates

v1.2

■ Various silkscreen updates

v1.1

■ Added bypas capacitors C1, C2
■ Various silkscreen updates
■ Various cosmetic updates
■ Added 45° chamfered corner edges

Last page update: 19 January 2024

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