SPP FIELDS MEP PEER REVIEW17 JULY 2013 slide 1 of x 1
SPP FIELDS MEPMain Electronics Package
PEER Review
Bill [email protected]
UCB/SSL17 July 2013
MAVEN PFDPUFlight Unit
SPP MEPBaseline Design
SPP FIELDS MEP PEER REVIEW17 JULY 2013 slide 2 of x 2
MEP Peer Review Overview
• Requirements• MAVEN Heritage • Mechanical Overview• Thermal Considerations• Dynamics Approach and Analysis• Status and Schedule
SPP FIELDS MEP PEER REVIEW17 JULY 2013 slide 3 of x 3
MEP Requirements
• Provide Packaging for 9 different Board Assemblies in common box– LNPS1, LNPS2, MAGo, MAGi, RFS/DCB, DFB, AEB (2x), TDS
• Modular box arrangement that allows individual boxes to be built up independently and taken apart a/r
• Design/Coordinate/Fab Box Frames with responsible groups
• .060” thick Aluminum walls for Radiation Shielding • One plane mounting interface to Spacecraft• Adequate Structure Integrity (Strength, Dynamics)• Provide optimal thermal path to Spacecraft
SPP FIELDS MEP PEER REVIEW17 JULY 2013 slide 4 of x 4
MEP Challenges
• Provide common module for different boards • Differing functions, connectors, and organizations
(SSL/LASP/MN/GSFC)• Box will be located in hot environment, must get heat out
of box as much as possible (Thermal environment: baseline 75 C)
• Modular Frames must fit well together into final structural/thermal package
• Provide optimal thermal path to get heat out of boxes• All frames must be in-plane for proper interface to
Spacecraft Panel• Mass is limited• Column Grid Arrays require conformance to Steinberg /
LASP requirements
SPP FIELDS MEP PEER REVIEW17 JULY 2013 slide 5 of x 5
MAVEN Design Heritage
6x Skewers
Top EMI Shield over Card-Card Harnesses
S/C Bracket
Box Vents
Connectors on 3 sides of box
MAVEN Electronics Box• 11 Separate Cards sharing common Frame
details• Bolted to S/C Bracket on one Box face
Box Size: 8.1” Wide x 6.2” Tall x 9.3” Long
SPP FIELDS Electronics Box• 9 Separate Cards sharing common Frame
details• Bolted to S/C on one Box face
FIELDS MEP is modeled on MAVEN PFDPU
10x Attach feet to S/C(every other Frame)
(no shear panels)
Box Size: 9.4” wide x 6.5” Tall x 8.0” long
2x Skewers
SPP FIELDS MEP PEER REVIEW17 JULY 2013 slide 6 of x 6
MEP Typ Box Frame Assy
Frame
Instrument Connectors
Spacecraft Connectors
Mounting Surface to Spacecraft
Intrabox Connectors
6 x Skewers
Screws and Custom Inserts at PCB perimeter
SPP FIELDS MEP PEER REVIEW17 JULY 2013 slide 7 of x 7
Box Machined Open Frame
Box Frame walls .060”
Multiple PCB attach screws to Frame to increase PWB stiffness and provide good thermal conduction path
Machined 6061 T6 Al Alloy Machined Frame.85” Pitch (Frame to Frame)
Feet for attachment to S/C
Identical Open Frame Design for all Boxes except LNPS• LNPS to be 5-sided box• LNPSs mounted at stack
ends
6X Skewers (#8 Threaded Rod)
SPP FIELDS MEP PEER REVIEW17 JULY 2013 slide 8 of x 8
Upright Boxes bolted to S/C Bracket
S/C Attach Surface
Individual Frames bolted together with 6X skewers
Detail showing Frame Interlocking
Features
Volume for Intrabox Cables
SPP FIELDS MEP PEER REVIEW17 JULY 2013 slide 9 of x 9
Card Assembly Overview
EMI ShieldAl Alloy, 1/32”
Frame6061 T6
Custom SSL threaded insert soldered to PCB(provided by SSL)
SPP FIELDS MEP PEER REVIEW17 JULY 2013 slide 10 of x 10
Electronics Board Layout Control Drawing
SPP FIELDS MEP PEER REVIEW17 JULY 2013 slide 11 of x 11
Daughter Board Details
• DB Module to be designed/built by SSL• Large Chip (RJEX4000 CCGA) at Center• Used on DCB, TDS, DFB
Custom threaded tool thru threaded inserts applies gentle force at corners to remove DB from MB
4X Custom Tools
SPP FIELDS MEP PEER REVIEW17 JULY 2013 slide 12 of x 12
Connectors Fastening
• APL desirement: allow changeout of connector jackposts w/o taking entire box apart late in the flow
• Solution: replace OTS nuts with custom nutplates• Separate design for D-Connectors and MDM Connectors
UCB Custom Connector Nutplate
• Easier than nuts to assemble
• no need to get wrench to hold nuts during jackpost torquing
• Standoffs can be removed one-by-one
D-Connector
OTS Jackposts
Blind hole to indicate Spiralock direction side of part
Spiralock tapped holes
SPP FIELDS MEP PEER REVIEW17 JULY 2013 slide 13 of x 13
MAVEN PFDPU Thermal Design
• S/C environment is hot—testing at 75 C• Boards screwed to Frames (may be bonded if required) at
perimeter• 2X Screws at PCB center to EMI shield w/ integral posts• Attachment frame wet mounted to S/C (TBC)• Aluminum black anodized outside surfaces to radiate to
S/C
S/C
S/C
S/C
PCB screwed to EMI Shield (2x)
SPP FIELDS MEP PEER REVIEW17 JULY 2013 slide 14 of x 14
Thermal Considerations: Center of PCB
• EMI Shield with integral posts to PCB• provide conductive path from center of PCB• Shield screwed to Frames at perimeter
Screws at perimeter to frame
Integral Posts at Center (fastened to PCB)
SPP FIELDS MEP PEER REVIEW17 JULY 2013 slide 15 of x 15
Thermal Modeling: Center Rib Tradeoff
• Trade Study on Electronics Board performed– With Center Frame Rib– Without the Frame Rib– With integral standoff on EMI shield
• Model: AEB Board, heat load of 1.17 W, 2 x 2 oz Cu Layers
Conduction (W/K)
ΔT (°C)
W/O Rib 0.26 4.4
W/ Rib 0.30 3.9
W/ Shield 0.31 3.8
SPP FIELDS MEP PEER REVIEW17 JULY 2013 slide 16 of x 16
PWB Thermal Design
• Consider entire heat path• Component To Board
– All components dissipating more than 50 mW should be looked at by thermal engineer
• Thermal / Ground / Power Planes– Board dissipated power needs to travel to the frame via conduction in
thermal (or ground) planes, then to the frame• Board Mounting to Box
– Need a good path from thermal planes to standoffs / box lip / wedge locks etc
SPP FIELDS MEP PEER REVIEW17 JULY 2013 slide 17 of x 17
MEP FEM Dynamic Analysis
• Requirements– Project: First Natural Frequency > 100 Hz– Steinberg Design: First Natural Frequency separation of 2X between
individual PCB Assys and Entire Box
SPP FIELDS MEP PEER REVIEW17 JULY 2013 slide 18 of x 18
FEM Analysis: Preliminary Runs
• PCB/Spacers/EMI Shield Assy
• Fixed at Perimeters (to Frame)
• Fn=195 Hz
• Entire MEP Box Assy• (PCBs/Frames)• Fixed at Attach Feet (to S/C)• Fn > 600 Hz
Preliminary FEM Runs Encouraging• Fn > 100 Hz• Separation of 2X between PCB
and Overall Structure • More detailed analysis required
• With completed LNPSs design
• Vibration testing of Prototype frames will confirm test results
SPP FIELDS MEP PEER REVIEW17 JULY 2013 slide 19 of x 19
MEP Status and Schedule
• July 2013– Baseline Design Completed
• PCB sizing, connector locations, component heights, wall thicknesses, Frame details• PCB Layout ongoing at this time by responsible groups
– LNPS work ongoing---not completed– FEM Analysis ongoing----first runs completed
• August 2013– Finish Frames design– Finish LNPS design– Complete FEM Analysis– Start Fab of Frames
• September 2013– Prototype Vibration Test of MEP Box
• Verify Dynamics analysis– Finish thermal design– Finish Design Details
• November 2013– Instrument PDR