Download - CONTAMINATION CONTROL
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CONTAMINATION CONTROL
SME-CourseD : Materials
Materials and Processes DivisionMaterials Physics and Chemistry Section
Jaco M. Guyt TOS-QMC
– Topics1 Types of contamination2 Cleaning procedures3 Prevention
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Introduction
• Why contamination control ?– Satellites are operational in orbit - no maintenance after launch
– Sophisticated equipment with higher demands on performance
– Increased mission duration
– Increased reliability is needed
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Part 1 Types of contamination
– Introduction
– Origin of Contaminants
– Requirements
– Verification of requirements
– Handling of contamination problems
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Introduction
• Definition– Any foreign matter– Unwanted deposition on surfaces.
• Contamination effects– On thermal control surfaces - changes and ratios– On solar arrays - decrease on power output– On optical instruments - decrease signal / scattering– In waveguides - Multipaction
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Types of contamination
Organic and Inorganic contamination coming from• Humans - Skin, handling greases/salts, hair, cosmetics• Clothing- Fibres, dust collected in clothing • Materials - Outgassing, solvent extraction, creeping(oil
greases), direct contact, degradation• Vacuum test - Pump oils, chamber history, turbulence at start, venting (lines and gas quality)• Machining - Drilling, abrasion, polishing, cleaning• Transport - Packaging, pressure drop in plane • Space - Pyro-valves, wire cutters, thrusters• Exposure C. R.- Working activities, soldering, air circulation
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Requirements
• Inorganic / Particulate contamination– Airborne
• ISO-14644-1 (1999) – superseded FED-Std-209)“ Cleanrooms and associated controlled environments”
• PSS-01-201 / ECSS Q-70-01 - “Cleanliness and Contamination control”
– Surface contamination • IEST-Std-CC1246D - “Product Cleanliness levels and
Contamination control program” superseded Mil-Std-1246C • PSS-01-201 / ECSS Q-70-01
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Requirements
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Requirements Fed-Std-209E
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Requirements ISO-14644_1
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Requirements ISO-14644_1
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Requirements Mil-Std-1246C
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Requirements Mil-Std-1246C
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Requirements Mil-Std-1246C
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Requirements IEST-STD-CC1246D
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Requirements IEST-STD-CC1246D
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Requirements
• Organic Contamination– PSS-01-201 / ECSS Q-70-01
• exposure in clean room during a continuous period of one week, less than 2.0x10-7 g/cm2
• Exposure in vacuum chamber after a blank test of 24 hours, less than 1.0x10-7 g/cm2
• Project depending, more stringent levels.– ECSS Q-70-02A
• Outgassing requirements of materials. – IEST-Std-CC1246D
• Level AA5 up to level J, what is 10 ng till 25 mg per 0.1m2
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Requirements Mil-Std-1246C
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Requirements IEST-STD-CC1246D
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Verification of requirements
• Organic Contamination– Visual inspection - levels unto 10-6 g/cm2 range– ECSS-Q-70-02 (old PSS-01-702) “Thermal vacuum outgassing
test for the screening of space materials” – PSS-01-705 (ECSS-Q-70-05) “The detection of organic
contamination of surfaces by infrared spectroscopy”– ASTM E1235 “Gravimetric Determination of Nonvolatile
Residue (NVR) in Environmentally Controlled Areas for Spacecraft”
– ESTEC work instructions : contact and immersion test
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Verification of requirements Micro VCM
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Verification of requirementsMicro VCM
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Verification of requirementsMicro VCM
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Verification of requirements
• Acceptance limits PSS-01-702 : TML < 1.0%, CVCM < 0.1%
• Acceptance limits ECSS-Q-70-02A : RML < 1.0%, CVCM < 0.1%
• Micro VCM resultsTML RML CVCM WVR Remarks
A - 1.12% 0.05% 0.01% 1.07% Too high waterB - 0.56% 0.45% 0.23% 0.11% Too high CVCMC - 2.15% 1.01% 0.09% 1.14% Too high TML/RMLD - 9.52% 9.50% 6.17% 0.02% Too high
RML/CVCM
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Verification of requirements
• PSS-01-705 (ECSS-Q-70-05) “The detection of organic contamination of surfaces by infrared spectroscopy”– Identification due to specific absorption of the molecule due to
vibrations and rotations of atoms– Quantification by Lambert/Beers Law relation
Abs. = E * b * CE = Molar Absorption Coefficientb = PathlengthC = Concentration
– Calibration curves for four standards• Paraffin, Di-octylPhthalate ester, Methylsilicone and
MethylPhenylsilicone
Concentration
Abs.
Absorption of sample
Concentration of sample
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Verification of requirements
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Verification of requirements
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Verification of requirements
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Verification of requirements
• Sampling for infrared analysis– Indirect by rinsing surface with solvent and analyse of NVR
– Indirect by wiping surface with tissue and analyse of NVR
– Direct by using infrared transparent windows ZnSe, CaF2
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Verification of requirements
• Particulate Contamination– Airborne Counters - Fed Std 209E– Surface contamination
• Visual inspection, less than 300 ppm• ECSS-Q-70-50, Particle Fall Out measurement• ASTM E1216, Tape lift method • ASTM F312, Counting and sizing particles• ASTM F311, Liquid samples
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Verification of requirementsPFO - meter
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Verification of requirements
• Particulate Contamination– PFO meter and correlation with cleanliness specifications table
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Verification of requirements
• Tape lift method as performed at ESTEC• Define area which needs to be checked• Take Polyethylene transparent tape from 3M Scotch 480• Stick it on a surface of at least 5 x 5 cm• Take with tweezers the 0.45 micron filter paper with grid• Apply the filter paper against the just released tape• Cut excessive tape away • Count particles by Microscope in different size ranges
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Handling of contamination problems
• Define problem and location– Define starting point of problem– Write Non Conformance Report (NCR)– Identification of contamination by analysis– Search for possible sources
• on location• Detailed Material Lists
– Excluding by analysis / search / calculation
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Handling of contamination problems
• Can the problem be solved?
• Can we live with it?
• Will it happen again?
• Can we avoid the risk by preventive actions or adjusting procedures?
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Part 2Cleaning Procedures
• Introduction
• Selection of Cleaning method
• Verification of cleaning efficiency
• Cleaning procedure
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Introduction
• Definition of clean– A contamination level below the acceptance limits or not
detectable with the used method.
• Procedure for cleaning is needed for– Customer - that you are cleaning and how– Personnel - that they know how to clean and what– Sub-contractor - that they know how and what are the
requirements
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Selection of Cleaning method
• Selection should be based on : – Method compatibility with hardware
• ultrasonic, temperature, mechanical scratching– Method efficiency with hardware
• accessibility design– Solvent compatibility with hardware
• corrosion, chemical attack, dissolving, removable– Solvent efficiency for contaminant
• what are you removing, polar/non-polar
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Cleaning methods
• Mechanical cleaning - grinding, brushing, blasting• Detergent cleaning or soap cleaning• Solvent bath / ultrasonic• Chemical cleaning - acids, alkalines and salts• Vacuum bake out• Vacuum cleaner / ionised air• Plasma cleaning• Dry ice• Polymer film• Adhesive
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Verification of cleaning efficiency
• By representative test samples and checked visually or by analysis
• Visual inspection after cleaning
• Check of hardware by taking samples, followed by analysis
• Check performance of hardware and verify against previous tests
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Cleaning procedure
• Should contain description or information about – Hardware– Method, with details about e.g. solvents/duration and flow chart– Restrictions or hazards for hardware or personnel– Requirements– Verification of requirements– Inspection after cleaning– Operators (trained)– Logbook entry
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Part 3Prevention
• Introduction
• Material selection
• Garment
• Potential risks
• Preventive actions
• Contamination control plan
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Introduction
• Prevention is better and cheaper then the cure!!
• Think ahead.
• If you are not sure it will contaminate the hardware? Stop the activity! Because the answer is yes.
• If something can go wrong, it will go wrong.
• Working towards a dead-line is where prevention looses its power.
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Material selection
• Outgassing characteristics– low TML and CVCM – Mass of used material– Location
• Optical applications• Cryogenic• High Temperature
– Long term predictions with VBQC
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VBQC
Vacuum balance
TS5
TS7
TS6
TS8
TS2
TS1
Pumpingsystem
Shroudheater
Shroudcooling
Sample
Referencemass
Condensorplate cooling
QCM platecooling Heater plate
QCMplate
VBQC SYSTEM
Heating systemCooling systemMeasuring devices
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VBQC
0
0.1666666667
0.3333333333
0.5
0.6666666667
0.8333333333
1
0
50
100
150
0 24 48 72 96 120
Outgassing andsample temperature profile
TML (%)
Temperature
TML
(%)
Temperature (ºC
)
Time (h)
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VBQC
0
0.05
0.1
0.15
0.2
0.25
0 24 48 72 96 120
CVCM profile
CVCM at -25ºCCVCM at -50ºCCVCM at -75ºC
CVC
M (%
)
Time (h)
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VBQC
• Results taken out of the Mathematical treatment consist of Accelaration factor, Activation energy, Residence time - Temperature dependency.
• Long term predictions with VBQC data is used within the temperature range of test.
• The TML or CVCM data are fitted period by period with a sum of 6 exponential equations.
With W0.i the variables, affected with the time constant 0,i, which are 50, 20, 5, 1, 0.5 and 0.1 hour.
6
1,0
,01i
t
iieWW
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Garment
• As humans are the main source of contamination, garment should be taken into account from the beginning of the project.
• Depending of the contamination budget allocated to a specific operation, selection of garment can be done
• Storage of garment should be separate from street clothing
• Procedure of dressing should be trained to the personnel
• Regular cleaning of garment by specialised company / quality check
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Potential risks
Potential risks Preventive actions• Thermal vacuum tests Check procedure
– Pumping oils Blank test– Outgassing of materials Check DML– Solar radiation Adequate thermal protection
• Clean room operations Training of personnel– Too many personnel in C.R. Entry form – Unauthorised entry in C.R. Access code for CR / locked– Maintenance in C.R. Check impact, protect items– Violation of dress code Clear signs on doors,training– Dirty activity during AIT Separate from sensitive item
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CONTAMINATION CONTROL PLAN
• Contamination control plan– Preventive
– All requirements are mentioned
– Procedures for delicate handling or testing