Electronics Packaging for the Space Environment Zach Allen ECEN 5004: Fundamentals of Microsystems...

Electronics Packaging for Electronics Packaging for the Space Environment the Space Environment

Zach AllenZach Allen

ECEN 5004: Fundamentals of ECEN 5004: Fundamentals of Microsystems PackagingMicrosystems Packaging

OverviewOverview

• Introduction

• Overview

• Space: extreme heat and cold

• Packaging considerations for the vacuum of space

• Packaging for the space radiation environment

Space: Extreme Heat and ColdSpace: Extreme Heat and Cold

• Definition of temperature: atomic and molecular motion– It is difficult to give space a “temperature”

• The darkness of space: just a few degrees above absolute zero (2.7 Kelvin)– There are a few stray helium atoms floating

around

Space: Extreme Heat and Cold Space: Extreme Heat and Cold

• Temperature of an earth-orbiting satellite varies considerably– Sunward side: outside surfaces can exceed +140°C– Shadow side: outside surfaces can reach

-150°C– Depending on period of orbit: satellite can see these

temperature extremes several times per day

• Huge challenge for packaging of electronics!– Electronics usually have maximum operating

temperatures of -30°C and +70°C


• PWAs usually packaged within an aluminum or magnesium box– Shields electronics from extreme heat/cold

transitions that outer surfaces of spacecraft experience

– Good conductor of heat between PWAs/spacecraft

– Aluminum: Lightweight (approx. $100,000/lb to put something into Low Earth Orbit)


• Key method of power dissipation on Earth-borne electronics assemblies is convection

• Vacuum – heat dissipation methods:– Conduction: heat transfer from parts to

satellite heat management system– Radiation: heat dissipation method for satellite

thermal management system


• Spacecraft thermal control system– Series of pipes that conduct heat between

different parts of the spacecraft– Heat dissipated through radiators on

spacecraft– Heaters are used in some cases– PWA temperature is controlled to within

operating limits


• NASA: developing the Space Technology 8 mission:– Launch in Feb 2009– High-performance onboard

CPU– Highly efficient solar panels– Ultra lightweight solar mast– “Thermal Loop” heat

management system


• “Thermal Loop” heat management system– Based on loop heat pipe

(LHP) design– Deployable radiators:

radiate heat from both sides

– Flow Regulator prevents heat from being transmitted back to the instruments

– Variable Emmitance Coatings (VEC) change emmitance of radiators and eliminate need for supplemental heaters


• Summary of Spacecraft Thermal Management System:– Heat conducted:

• From parts to boards• Boards to enclosures (usually aluminum)• Enclosures to spacecraft thermal management

system• Radiated into space• Sometimes process happens in reverse (using

onboard heaters)

Packaging Considerations for Packaging Considerations for Vacuum of SpaceVacuum of Space

• “Outgassing” of materials occurs in vacuum– Ambient pressure of space is less than 10-6 Torr (10-9

atm)– Materials actually lose mass (evaporate)– Evaporated materials condense on nearby surfaces

• Biggest risk is optical contamination– Best case: mission success is limited – fuzzy or

blurry images– Worst case: mission failure


• Two main parameters to characterize outgassing– Total Mass Loss (TML) ≤ 1.0% – Collected Volatile Condensable Material

(CVCM) ≤ 0.1%

• Sample of material is vacuum baked at 125°C, 10-6 Torr– End mass compared to initial mass (%TML)– Weight of a clean collector compared to weight of

collector having condensed materials (%CVCM)


Material %TML %CVCM DATA REF

Application MFR CODE

PERVEL ANTISTATIC MAT BLUE

31.79 11.57 GSC11866 MAT PVL

ALUMINIZED MYLAR 100M42 0.13 0.01 GSFC2755 REFLECTOR STC

ANTENNA - OUTER SHELL 0.79 0.04 GSC29965 ANTENNA GSC

AMP CONNECTOR HOUSING (PET) POLYETEHYLENE TEREPHTHALATE

0.30 0.06 GSC28273 CONNECTOR TYO

ARATHANE (URALANE) 5750 WITH 2.5% CABOSIL (1/1 THIN/RESIN )

0.68 0.01 GSC28804 CONFORMAL COATING HUP

ENPLATE DSR 3241 GREEN SOLDER MASK UV CURED

0.94 0.01 GSC20345 SOLDER MASK ENT

ENPLATE DSR-3241 (CR)G GREEN SOLDER MASK

1.92 0.00 GSC24536 SOLDER MASK ENT

Outgassing characteristics of selected materials from:

http://outgassing.nasa.gov/cgi/sectiona/sectiona_html.sh

Space Vacuum – Tin WhiskersSpace Vacuum – Tin Whiskers

• Hair-like crystalline structures that grow from pure-tin surfaces– Typically 1mm in length, 1µm in diameter

• Observed up to 10mm long

– Exact cause is still unknown – physical stress may cause growth:

• Compressive stress from screws or other fasteners• Bending or stretching• Scratches or nicks• Mismatch of CTE between Tin surface and substrate


• Hazard is undesired electrical connections• Whisker bridges gap between two isolated

conductors – two scenarios:– Stable short circuit forms in low voltage, high

impedance circuit (takes more than 50mA to fuse a whisker)

– Metal vapor arc occurs when whisker vaporizes into plasma of highly conductive metal ions

• Can be capable of conducting several hundred amps for several seconds


• Dr. M. Mason and Dr. G. Eng at The Aerospace Corporation performed research on Tin plasma arcs:– Sustained plasmas form at power supply

voltages as low as 4V– Plasma duration increases with power supply

voltage

Space Vacuum – Tin WhiskersSpace Vacuum – Tin WhiskersM. Mason and G. Eng Tin Plasma Arc Experiment Setup

Simulated tin whisker: 25 to 50µm diameter tin wire

Space Vacuum – Tin WhiskersSpace Vacuum – Tin WhiskersM. Mason and G. Eng Tin Plasma Arc Experiment Results

Tin Plasma Arc in Vacuum ChamberTin Plasma Duration vs. Power Supply Voltage

Space Vacuum – Tin WhiskersSpace Vacuum – Tin WhiskersDEC 2005, critical Shuttle Endeavour avionics box failed a test

Tin plated card guides


• NASA experiment to contain Tin Whiskers with conformal (Uralane 5750) coating– Tin plated brass boards used as samples– Half of each sample conformal coated– Varying depths of conformal coating up to 2 mils

thickness– After 2 more than 2 years of storage, Tin Whisker

grew through 0.1 mil thickness conformal coating– After more than 3 years, no whiskers had made it

through 2 mil conformal coating


NASA experiment: Tin Whisker penetrating 0.1 mil thick conformal coating


• Tin Whisker prevention techniques for the packaging engineer– Care in handling of assemblies containing Tin

• Minimize physical stress/scratches

– Conformal coat Tin plated surfaces with conformal coating of greater than 2 mils

– Ensure all Tin plating has a minimum lead content of 3%

Space Radiation EnvironmentSpace Radiation Environment

• Single Event Effects– Caused by heavily ionized cosmic rays and high

energy protons– Single Event Upset (SEU)

• Soft errors such as bit flips• Not harmful to hardware

– Single Event Latchup• Can cause device to draw more than specified current• Usually requires power reset to device

– Displacement Damage• High energy particle displaces an atom from its crystal lattice• Permanently alters electrical properties of the device


• Total Ionizing Dose– Cumulative long-term ionizing effect of

protons and electrons– Effects

• Threshold shifts• Increased device leakage (power draw)• Timing changes• Decreased functionality


• Packaging Considerations– Aluminum plate

• Blocks high energy electrons, low energy protons• Not effective against high energy protons

– Tungsten plate• Up to 60% more dense than lead• Used for heavy shielding of parts

– Radiation hardened parts often have redundant gates = more power consumption

ConclusionConclusion

• Packaging of electronics for space environment poses many unique challenges– Keep weight down ($100,000/lb for Low Earth

Orbit)– Electronic assemblies must meet stringent

reliability requirements

Date post:	19-Dec-2015
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Electronics Packaging for the Space Environment Zach Allen ECEN 5004: Fundamentals of Microsystems...

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