contamination control

Materials and Processes DivisionESA-ESTEC TOS/QM

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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• ISO-14644-1 (1999) – superseded FED-Std-209)“ Cleanrooms and associated controlled environments”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Contamination control program” superseded Mil-Std-1246C • PSS-01-201 / ECSS Q-70-01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 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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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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• 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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• 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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• 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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• 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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• Particulate Contamination– PFO meter and correlation with cleanliness specifications table


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• 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

contamination control

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