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Electronics Packaging for the Space Environment . Zach Allen ECEN 5004: Fundamentals of Microsystems Packaging. Overview. Introduction Overview Space: extreme heat and cold Packaging considerations for the vacuum of space Packaging for the space radiation environment.

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electronics packaging for the space environment

Electronics Packaging for the Space Environment

Zach Allen

ECEN 5004: Fundamentals of Microsystems Packaging

overview
Overview
  • Introduction
  • Overview
  • Space: extreme heat and cold
  • Packaging considerations for the vacuum of space
  • Packaging for the space radiation environment
space extreme heat and cold
Space: 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 cold1
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
space extreme heat and cold2
Space: Extreme Heat and Cold
  • 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)
space extreme heat and cold3
Space: Extreme Heat and Cold
  • 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
space extreme heat and cold4
Space: Extreme Heat and Cold
  • 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
space extreme heat and cold5
Space: Extreme Heat and Cold
  • 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
space extreme heat and cold6
Space: Extreme Heat and Cold
  • “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
space extreme heat and cold7
Space: Extreme Heat and Cold
  • 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 vacuum of space
Packaging Considerations for Vacuum 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
packaging considerations for vacuum of space1
Packaging Considerations for Vacuum of Space
  • 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)
packaging considerations for vacuum of space2
Packaging Considerations for Vacuum of Space

Outgassing characteristics of selected materials from: http://outgassing.nasa.gov/cgi/sectiona/sectiona_html.sh

space vacuum tin whiskers
Space 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
space vacuum tin whiskers1
Space Vacuum – Tin Whiskers
  • 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
space vacuum tin whiskers2
Space Vacuum – Tin Whiskers
  • 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 whiskers3
Space Vacuum – Tin Whiskers

M. Mason and G. Eng Tin Plasma Arc Experiment Setup

Simulated tin whisker: 25 to 50µm diameter tin wire

space vacuum tin whiskers4
Space Vacuum – Tin Whiskers

M. Mason and G. Eng Tin Plasma Arc Experiment Results

Tin Plasma Duration vs. Power Supply Voltage

Tin Plasma Arc in Vacuum Chamber

space vacuum tin whiskers5
Space Vacuum – Tin Whiskers

DEC 2005, critical Shuttle Endeavour avionics box failed a test

Tin plated card guides

space vacuum tin whiskers6
Space Vacuum – Tin Whiskers
  • 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
space vacuum tin whiskers7
Space Vacuum – Tin Whiskers

NASA experiment: Tin Whisker penetrating 0.1 mil thick conformal coating

space vacuum tin whiskers8
Space Vacuum – Tin Whiskers
  • 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 environment
Space 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
space radiation environment1
Space Radiation Environment
  • Total Ionizing Dose
    • Cumulative long-term ionizing effect of protons and electrons
    • Effects
      • Threshold shifts
      • Increased device leakage (power draw)
      • Timing changes
      • Decreased functionality
space radiation environment2
Space Radiation Environment
  • 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
conclusion
Conclusion
  • 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