1. Mechanical Discussion
8/16/2017
Joshua Held, Mechanical Engineer, Facebook
Yueming Li, Thermal Engineer, Facebook
John Fernandes, Thermal Engineer, Facebook
Jia Ning, Hardware Engineer, Facebook

2. Current Mezz 3.0 Concepts Option 13 7 8 15 Option 7a Option 7d8 A1 15 B1
Option 7a
Option 7d
IC on back of PCB

3. Comparison of Concepts
Option 7
Option 13
Option 14
Small Size
78x110
74x110
Small Area
8580
8140
Large Size
98.3x167.6
118x110
Large Area
16475
12980
Expansion Direction
Back
Side
Connector Style
Mezz
Edge (.6mm pitch)
PCB Orientations
Horizontal
Horizontal/Vertical
Installation
In Chassis
Front/Rear Panel
Installation Action
Parallel to Front/Rear Panel
Parallel to Front/Rear Panel with side slide
Perpendicular to Front/Rear Panel
Hot Swap No
Yes
EMI Containment for Serviceability
High Difficulty
Medium Difficulty
Low Difficulty

4. Option 14 Configuration Large Smart NIC with Straddle
Straddle Connectors
Chassis Face
Smart NIC Module
Snap in card guides both sides
Large Smart NIC with Straddle

5. Option 14 Variants Small NIC Right Angle (upper left)
Small NIC Straddle
Large Smart NIC Straddle (upper right)
Large Smart NIC Right Angle
Small NIC Straddle in large chassis slot (lower right)

6. Top/Bottom Component Placement
Option 14 Details
Available Space
PCB Size
Top/Bottom Component Placement
Routing Inner Layers
Small Size
74x110
70x104
Large Size
118x110
114x104
2mm card guide keep out
- 4mm to width (card guide)
- 6mm to length (edge connector)
2mm card guide keep out
Request to community
Share ideas/thoughts on PCB sizing? We’ve had a few requests to lengthen option 14 PCB to ease routing congestion between gold fingers, ASIC, and QSFPs.
In regards to large smart NIC form factor. Is this enough usable space for expected configurations?

7. Option 14 Details
Note – In right angle connector case, current connectors only provide 2.25mm of vertical clearance from NIC bottom to MB top.
FB requesting connector manufactures to meet PCIE standard clearance.

8. Next Steps
Investigating use of latch for injection and ejection. This would make removal tool-less as well as increase the amount of faceplate cutouts, more airflow.
Mating force of 1.6mm edge connectors in Large Smart NIC module (option 13 and 14) is in the realm of 84N, which is significant. Under investigation.
Possible integration of EMI shielding into faceplate designs.
Ongoing work with thermal team to verify thermal impact of mechanical changes.