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Microbus Passive backplane for Eurocards DIN41612 12 slot 3U 48HP

Introduction

I have originally designed this backplane for a few of my projects (Rubidium frequency standard and Z80 Micro Computer), but this turned out so well that I have now posted all schematic, gerber files and documentation to fellow enthusiasts such as yourself. Perhaps (and I hope) content in this obscured corner of the 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 Extended Backplane-12 from RetroBrew Computers Wiki. I definitely recommend going through their webpage!

Design overview

You can fit this card in industry standard 3U DIN subrack or Eurorack without Z rail (however the card will also work with Z rail to a limited extent). Backplane PCB was designed according to standard mechanical dimensions, therefore connectors' mechanical positions will match perfectly with PCB guide rails with front panel Eurorack should you decide to use this solution. Standardized card size is 3U height with 12 slots for 4HP cards (48HP 3U) and will fit into a full width 19" 84TE 3HE standardized subrack. I'm using this with standard 160mm depth cards, but you can use whatever fits in your rack (100,160,240mm).

Main design features:

Backplane PCB has been designed to be very flexible and can be used with large variety of industry standard power and 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 minimizing crosstalk on rows A and C.
■ Power connectors - 2x 4pin power (Molex) connector with 5.08mm pitch, M4 screw terminal or cable with blade receptacle pushed onto 6.3mm Faston terminals. Footprint silkscreen on front and back side allowing connectors to be fitted on both sides. All M4 screw terminal footprint are also accepting 6.3mm faston terminals.

■ Two separate power rails and one single ground plane available. (Vcc, GND, GND, Vdd).
■ Supply voltages provided via dedicated power connectors facilities: - 2x 4pin Molex power connector 5.08mm pitch (up to 5A), M4 screw terminal or 6.3mm faston terminals for very high loads (for example if you using TTL logic)
■ Capacitor footprint 7.62mm for the silky smooth DC line and outstanding high-frequency noise suppression
■ Linking/separation of digital and chassis GNDs by means of 0 Ohm / R / C link (Footprint R7)
■ Rack mounting holes can be electrically connected
■ Utility for load resistor, polarity diode and capacitor (for old power supplies that require minimal load) and polarity diode.
■ Footprint for R and LED power status on board and dupont connectors to connect chassis power status LED's.
■ Footprint supports off the shelf standard DIN 41612C 96/64pin Eurocard connectors or 2x32, 64pin PCB edge connectors.
■ Multiple backplanes can be placed side by side without loss of slot space

Backplane can also be extended with 2 slot bridge connector card to create a daisy chain array of backplanes if required. You can literally make any kind of project and scale it up as much as you wish.

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 v1.4

PCB design layout

Specifications

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: 242x128mm
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 12slot x 96pin or 2x32pin 64 / 96 Pin connector, you can also fit 64pin edge connector in. Power connector is via standard 2X 4pin MOLEX 5.08mm / 200mil connector. Card is double voltage ready. (Vcc, GND, GND, Vdd).
Copper Thickness: 35um
Card weight: 120g

Bill of materials

Identifier		Value	Qty	Notes
Printed Circuit Board		242 x 128 mm 12 slot Microbus backplane	1	v1.1
Hardware		M2.5 x 10 mm screw	24
Hardware		M2.5 nut	24
Connector	E1-E12	Female DIN 41612 96pin 3x32pin right angle connector	12
Connector	E1-E12	Female DIN 41612 64pin 2x32pin right angle connector	12	2nd alternative use
Connector	E1-E12	2x32pin 64pin PCB edge right angle connector 0.1" pitch	12	3rd alternative use
Connector, power	U1, U2	Molex 15-24-4745 THD male 4pin (5.08mm) 0.2" pitch	2
Connector, power		M4 Screw terminal	12
Connector, power		6.3mm Faston terminal	4
Capacitor	C1-C22	Capacitor_THT:C_Disc_D3.0mm_W1.6mm_P2.50mm	22
Resistor	R1, R2	1k THD 0.5W	2	VCC rail
Resistor	R3, R4	3.3k THD 0.5W	2	VDD rail
LED	LED1,LED2	RED THD Dia 3.0mm_P2.50mm	2
Connector		PinHeader_2.54mm:PinHeader_2x02_P2.54mm_Vertical	1	THT

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.
■ Please note, that PCB is connected via ground chassis plane on Z rail. If you don't desire to connect ground chassis and prefer to connect via molex connectors, then cut little GND xxx trace on top left corner on back side of PCB.
■ 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, thse 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

Schematic

File type	File name	File size	Last modified
PCB schematic for 8 slot backplane v1.0	schematic_backplane_8-10-12.pdf	687 kB	03/01/2022
PCB schematic for 8,10,12 slot backplane v1.4	schematic_backplane_8-10-12_v14.pdf	368 kB	25/08/2022
PCB schematic for 8,10,12 slot backplane v1.41	schematic_backplane_8-10-12_v141.jpg	1373 kB	19/01/2024
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 v1.1	pcblayers_backplane12_v11.pdf	510 kB	03/01/2022
PCB layers v1.4	pcblayers_backplane12_v14.pdf	450 kB	26/08/2022
Gerbers 242 x 128 mm, 2 Layer FR4, v1.1	gerber_backplane12_v11.zip	680 kB	03/01/2022
Gerbers 243 x 129 mm, 2 Layer FR4, v1.4	gerber_backplane12_v14.zip	582 kB	26/08/2022
Gerbers 243 x 129 mm, 2 Layer FR4, v1.41	gerber_backplane12_v141p.zip *	557 kB	14/01/2023
Solder paste stencil	Not available for this project	-	-

* gerber file is generated for PCBWay fabrication, but should work with other manufacturers.

Photographs

click on pictures to enlarge
v1.41 pictured


v1.3 pictured

v1.41 pictured


back side with ATX piggyback PCB attached

Versions and revisions

This section lists the project version and revision history.

v1.41

■ Amended molex connector
■ Minor silk screen updates

v1.4

■ Amended connector positions and hole sizes
■ Footprint for 0 Ohm / R / C link
■ Added mounting holes for ground link
■ Various silkscreen and cosmetic updates
■ Various design layout updates

v1.2, v1.3, v1.31

■ Added molex connector, screw faston terminals
■ Revised VDD, VCC power and GND planes
■ Capacitor footprint changed
■ Revised bigger plane for VDD and VCC
■ Added load resistor, polarity diode and capacitor

v1.1

■ Various cosmetic updates
■ Various silkscreen updates.
■ Added margin about border of PCB
■ Redesigned LED and resistors to fit better

v1.0

■ Prototype

Last page update: 21 January 2024

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