SPP FIELDS MEP PEER REVIEW 17 JULY 2013 1 SPP FIELDS MEP Main Electronics Package PEER Review Bill Donakowski [email protected] UCB/SSL 17 July 2013

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


MEP Peer Review Overview

• Requirements• MAVEN Heritage • Mechanical Overview• Thermal Considerations• Dynamics Approach and Analysis• Status and Schedule


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


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


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


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


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)


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


Card Assembly Overview

EMI ShieldAl Alloy, 1/32”

Frame6061 T6

Custom SSL threaded insert soldered to PCB(provided by SSL)


Electronics Board Layout Control Drawing


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


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


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)


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)


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


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


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


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


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

Documents

SPP FIELDS MEP PEER REVIEW 17 JULY 2013 1 SPP FIELDS MEP Main Electronics Package PEER Review Bill Donakowski [email protected] UCB/SSL 17 July 2013