IPC-D-279 EN.pdf - 第137页
NASA Reference publication 1124 tabulates the results of outgassing tests on many materials. T ypical limits on out- gassing are 1.0% maximum T otal Mass Loss (TML), 0.10% maximum V olatile Condensable Material (VCM). Ho…
Appendix O
Aerospace and High Altitude Concerns
O-1.0 INTRODUCTION
Use of Surface Mount Technology for aerospace and high
altitude applications has the same problems that are expe-
rienced with through-hole technology. The problems are as
follows:
• lack of air for convection cooling
• larger thermal excursions
• contamination
• radiation environment
• change in dielectric property of gases with pressure
• lessened gravitation or pseudo-gravitational effects.
The degree which these problems impact the design of sur-
face mount assemblies depends on the precise space envi-
ronment, the purpose of the mission, and the system
design. A detailed analysis may be needed for each PWA to
determine the extent of the problems.
O-2.0 THERMAL DESIGN
At sea level, natural or forced air convection greatly assists
in the cooling of electronic components; however in
un-pressurized compartments, there is little or no air for
convection and additional thermal considerations must be
made. Since radiation is negligible at the temperature of
interest for most SM PWA the only way to remove heat is
by conduction. Many components generate heat which
requires dissipation to prevent excessive junction tempera-
ture; heat removal may be enhanced with thermal materials
placed beneath these components. However, the thermal
material placement must not result in excessive thermo-
mechanical stress on the solder joint and subsequent solder
joint failure by fatigue when the assembly is thermally
cycled. Simulation, analysis and testing is needed to deter-
mine the thermal control measures needed for components
and SM PWA in space.
O-3.0 LARGE THERMAL EXCURSIONS
In addition to the normal thermal issues in packaging
design, the space environment adds a new consideration;
thermal excursions due to the effect of the sun/shade expo-
sure. While exterior surfaces of the spacecraft may be
exposed to 100,000 temperature cycles from −60 to
+120°C, through temperature control, the temperature of
internal regions of the satellite may be limited to a few
temperature cycles of 5°C. In a deep space mission, the
temperature may be as low as −270°C. These differences
are critical in the selection and use of materials and a sys-
tems level as well as a PWA level, thermal analysis is criti-
cal in designing electronic packaging.
The following are a few general guidelines in selecting
materials for wide temperature extremes:
• Exercise caution in using polymeric materials with
glass transition temperatures (T
g
) in the temperature
range of test or use. Material properties change rapidly
and drastically near T
g
.
• Ensure compliant joints and bond lines between mate-
rials with different coefficients of thermal expansion.
Thermally induced stresses may be very large and
cause solder fatigue failures, adhesive bond failures,
crack ceramic and glass materials or permanently
deform metal. Thermal stresses may also be generated
if there are large, although perhaps transient, thermal
gradients from one part to another or within an indi-
vidual part.
• Ensure that metals do not undergo a phase change or a
change of the heat treatment in the temperature range
of interest.
• Ensure that polymers do not crystallize in the tempera-
ture range of interest.
Space applications exposed to severe environments require
packages robust to temperatures in the −55°C to +125°C
range. Hermetic packages may be required to be robust to
life cycle environment which include high relative humid-
ity; under extreme levels of shock and vibration, hermetic
packages (with flying internal leads) are less robust than
plastic encapsulated packages.
O-4.0 CONTAMINATION
Contamination in spacecraft comes in two forms, particu-
late and condensed outgassed vapor. Particulate contamina-
tion may create false stars around the spacecraft by reflect-
ing sunlight causing problems with scientific and
navigational equipment. For some spacecraft missions,
condensed outgassed vapor is a minor concern; for others,
even a monolayer of condensed outgassed vapor is exces-
sive. Condensed outgassed vapor can cloud optical surfaces
causing decreased reflectance of mirrors, degraded clarity
of lenses and reduced solar cell output with subsequent
degraded star tracking capability, possible false data from
spectrum analyzers, and other degraded performance in
optical equipment. The outgassing species of most concern
in a vacuum are compounds which have sufficiently low
molecular weight to volatilize from a warm surface and
condense on cold surfaces. Gases (oxygen, water, and
nitrogen) usually are not a concern because they do not
form permanent contaminating films. The worst sources of
outgassing material are incompletely reacted monomers
and plasticizers found in polymers.
July 1996 IPC-D-279
125
NASA Reference publication 1124 tabulates the results of
outgassing tests on many materials. Typical limits on out-
gassing are 1.0% maximum Total Mass Loss (TML),
0.10% maximum Volatile Condensable Material (VCM).
However the maximums vary depending on factors such as
spacecraft mission, amount of material used, material loca-
tion, and thermal/vacuum testing.
Some conformal coatings outgas significantly, making
them unsuitable for spacecraft. Fluorescent chemicals
added to the conformal coating outgas and may cause prob-
lems where optical clarity is paramount in systems with
lenses, mirrors and viewing ports.
O-5.0 RADIATION ENVIRONMENT
For some orbits and missions, ionizing radiation concerns
play an important design role in component selection and
shielding. The primary sources of radiation in space are
gamma rays from the sun and trapped radiation in the Van-
Allen belt. Radiation has many effects on materials. The
most sensitive materials on spacecraft are the exterior ther-
mal control finishes and IC components. The radiation can
cause damage to ICs in the following forms:
a. Single Event Phenomena (SEP) which include Single
Event Upsets (SEU)
b. Single Event Latchup (SEL)
c. Single Event Gate Rupture (SEGR)
d. Single Event Snapback (SES)
e. Single Event Burnout (SEB) due to Electrical Over-
stress (EOS)
Analysis is needed to determine if radiation control is
required. Radiation control may be accomplished by
increasing shielding thickness, selecting radiation hardened
components or adding error-correction software. Increasing
shielding thickness may be accomplished by increasing the
wall thickness of the electronic enclosure or bonding pieces
of tantalum sheet to the top and bottom of components.
SEP-related failure rates are expected to increase linearly
with the frequency capability of the devices in a system.
Protons as well as cosmic rays are implicated in SEP. The
earth’s proton belt is one region of operation which causes
increased SEP rates. Multiple upsets are not uncommon;
single error correction schemes are inadequate in these cir-
cumstances.
Older radiation-hardened devices are slower and less sus-
ceptible to SEP than are such technologies as very high
speed, very shallow silicon devices, advanced compound
heterostructures such as heterojunction bipolar transistors,
and high speed optoelectronic integrated circuits.
O-6.0 ELECTRICAL PROPERTIES OF GASES
Under high or hard vacuum conditions or at ‘‘high’’ gas
pressures, the Dielectric Withstanding Voltage (DWV) is
higher than at some intermediate pressure. A space-borne
or high altitude system tested satisfactorily on the ground
may also endure the mission satisfactorily but intermit-
tently fail during the launch phase.
O-7.0 GRAVITY (OR LACK OF)
The effects of gravity are greatly lessened at distance far
from massive bodies, such as the earth.
Effects similar to low gravity are found in situations such
as geo-synchronous orbit or in forced flight paths used to
simulate ‘‘weightlessness.‘‘
In these circumstances, the orienting effect of gravity is
lessened and particles can float around. If the particles are
conductive and inside the sealed cavity of an electronic
package, the particle may intermittently or permanently
bridge conductors, causing failure.
Particle Impact Noise Detection (PIND) evaluation is used
with external mechanical excitation (mechanical vibration),
to screen hermetic electronic packages for loose internal,
possibly conductive, particles to reduce this reliability haz-
ard.
Electrostatic forces may cause the particles to adhere to the
surface of the cavity and escape detection.
IPC-D-279 July 1996
126
Appendix P
Technical Acronyms and Abbreviations
ABS* Acrylonitrile Butadiene Styrene
AOI Automatic Optical Inspection
AR Aspect Ratio
ASIC Application Specific Integrated Circuit
BGA Ball Grid Array
CGA Ceramic Grid array
BIST Built-In Self Test
BIT Built-In Test
BITE Built-In Test Equipment
BP Boiling Point
CAD Computer Aided Design
CAE Computer Aided Engineering
CAF Conductive Anodic Filament
CBGA Ceramic Ball Grid Array
CC Conformal Coat(ing)
CCD* Charge Coupled Device
CDR Cumulative Damage Ratio
CFC Chlorofluorocarbon
CIC Copper-Invar-Copper
CLLCC Ceramic Leadless Chip Carrier
CMC Copper-Molybdenum-Copper
CMOS Complementary Metal Oxide Semiconduc-
tor
COG* Capacitor Temperature Characteristic
C
p
* Process (potential) capability index = USL-
LSL/ 6 (estimated process standard devia-
tion)
C
pk
* Process capability index taking into account
two sided specification limits
CPVC* Chlorinated polyvinyl chloride
C-SAM C (-mode) Scanning Acoustic Microscopy
CTE Coefficient of Thermal Expansion
C4* Controlled Collapse Chip Connection
C5* Controlled Collapse Chip Carrier Connec-
tion
DAP* Diallyl phthalate
DC Direct Current
DfA Design for Assembly
DfM Design for Manufacturability
DfR Design for Reliability
DfT Design for Testability
DIP Dual In-line Package
DMF Dimethyl Formamide
DMSO* Dimethyl Sulfoxide
DNP* Distance from the Neutral Point
DRAM Dynamic Random Access Memory
DUT Device Under Test
DWV* Dielectric Withstand Voltage
E
a
Activation Energy (eV)
EIA Electronic Industries Association
EM Electromagnetic
EMC Electromagnetic Compatibility
EMI Electromagnetic Interference
EOS Electrical Overstress
ESD Electrostatic Discharge
ESDS Electrostatic Discharge Susceptibl (e, ility)
ESR Equivalent Series Resistance
ESS Environmental Stress Screening
FEA Finite Element Analysis
FP Fine Pitch
FR Flame Retardent
GAC Grid Array Components
GBL Gamma Butryolactone
geo geo(-synchronous orbit)
HAL Hot Air (Solder) Leveling
HASL Hot Air Solder Leveling
HAST Highly Accelerated Stress Test(ing)
HCFC Hydrochlorofluorocarbon
HFC* Hydrofluorocarbon
IC Integrated Circuit
ICT In-Circuit Test(ing)
IEC International Electrotechnical Commission
IMC Intermetallic Compound
I/O Input/Output (pins, ports, leads)
IPC The Institute for Interconnecting and Pack-
aging Electronic Circuits
IR Infrared
I
SB
Current, Secondary Breakdown
JEDEC Joint Electron Devices Engineering Council
JFET Junction Field Effect Transistor
JTAG Joint Test Action Group
KGD Known Good Die
LCC Leaded Chip Carrier
LLCC Leadless Chip Carrier
LDPE* Low Density Polyethylene
LED Light Emitting Diode
leo low earth orbit
LSSD* Level Sensitive Scan Design (M/S F/F
design)
MC Moulding Compound
MCM Multi-Chip Module
MELF Metal Electrode Face-Bonded
MGM Molybdenum-Graphite-Molybdenum
MIL-HDBK* Military (US) Handbook
MIL-T* Military ( US specifications)
MIR* Moisture Insulation Resistance
MLB Multilayer Board
July 1996 IPC-D-279
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