Surface Treatment Issues for RF Structure Fabrication

Juwen WangSLAC National Accelerator Laboratory

X-Band Accelerating Structure Review

November, 2014, CERN

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Outline

1. Etching Tests Revisit and Discussion2. Etching Time Studies Using TD24 Cups3. Chemical Treatment Procedure

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Done by R. Kirby, C. Pearson and F. Pimpec in 2002.

1. Etching Tests Revisit and Discussion

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Microbalance Results

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Etch Rate vs. Etch History

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Single-Crystal Diamond Machining

5 seconds metallographic image reveals grains; 10 seconds optical shows grain edges developing; 5 – 10 seconds etching is proper.

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Polycrystalline Diamond Machining

60 seconds mettallographic image reveals grains; 60 -120 seconds optical shows grain edges developing; 45 seconds or little more etching is proper.

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Surface Roughness after Different Etching Time

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Discussion on Amount of Etching

The amount of etching required depends very much on the condition of the machined surface. • A single crystal diamond turned axis-symmetric surface only need the slightest etching.  Its purpose may only be to assist in removing light residues of machining fluids and other light contamination.  • Conventionally machined surfaces by a polycrystalline tool or cells with milling operations, need to be etched more heavily.  In this case the purpose of the etching will be to remove burrs, to etch sufficient material to remove embedded particulates or entrained fluids.

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Discussion on Surface Roughness Change

• Etching and firing the diamond turned surfaces will slightly degrade the surface due to revelation of grain boundaries and the possible creation of etch pits.  • The converse is true for conventionally machined surfaces with >8 micro-inch finishes.  The rougher finishes benefit from etching due the preferential removal of sharp or protruding features, and benefit from firing due to the smoothing effects of recrystallization and surface diffusion.

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2. Etching Time Studies Using TD24 Cups

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2. Etching Time Studies Using TD24 Cups

30 seconds etching time was experimentally decided

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1. Four TD24 cups were chemical etched for 30-second or 60-second, then followed with SEM studies:

• 14R20C: SEM, 60-second etching 11/18, SEM, chemical cleaning 12/2, SEM

• 14R21B: 30-second etching 11/22, SEM

• 14R22B: 30-second etching 12/2, SEM

• 14R23B: 60-second etching 12/2, SEM

3. 30-second etching could completely remove all burrs and large machining defects.

4. 60-second etching produce too deep and too much etching pits.

5. Some contaminations and residues are created and remained on the surface after chemical cleaning procedure, we believe most of them would be burnt out in the heating processes in hydrogen furnaces.

2. Etching Time Studies Using TD24 Cups

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TD24 Structure Assembly

I’d like to confirm the time of heavier etching for TD24 Cups. 30 seconds?

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TD24 Cups before Etching

Machining burrs

Machining burrs

Rough machining surfaces

Particles

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After 30 Seconds Etching

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After 60 Seconds Etching

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For accelerator structure parts with single diamond tuning surfaces:

1. Vapor degrease in 1,1,1 trichloroethane or equivalent degreaser for 5 minutes.2. Alkaline soak clean in Enbond Q527 for 5 minutes at 180ºF.3. Cold tap water rinse for 2 minutes.4. Immense in 50% hydrochloric acid at room temperature for 1 minutes.5. Cold tap water rinse for 1 minute.6. Immense in the following solution for maximum of 5 seconds depending on the surface

finish required: Phosphoric Acid, 75% 21 gallons Nitric Acid, 42º Baume 7 gallons Acetic Acid, Glacial 2 gallons Hydrochloric Acid 12.6 fluid ounces Temperature Room7. Cold tap water rinse for minimum of 2 minutes until the film on part disappears.8. Ultrasonic in DI Water for 1 minute. 9. Ultrasonic in new, clean alcohol for 1 minute. 10. Final Rinse to be done in new, clean alcohol. 11. Hold in clean alcohol in stainless steel containers. 12. Dry in a clean room using filtered N2.

For accelerator structure parts with regular machining surfaces: 6. Immense in the following solution for maximum of 30-60 seconds depending on the

surface finish required:

3. Chemical Treatment Procedure

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1. Vapor degrease in 1,1,1 perculoroethylene or equivalent degreaser for 5 minutes. (Now in use)

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2. Alkaline soak clean in Enprep 527 for 5 minutes at 180ºF.

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3. Cold tap water rinse for 2 minutes.

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4. Immense in 50% hydrochloric acid at room temperature for 1 minutes.

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5. Cold tap water rinse for 1 minute.

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6. Immense in the following solution for maximum of 5 seconds depending on the surface finish required:

Phosphoric Acid, 75% 21 gallons Nitric Acid, 42º Baume 7 gallons Acetic Acid, Glacial 2 gallons Hydrochloric Acid 12.6 fluid ounces Temperature Room

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7. Cold tap water rinse for minimum of 2 minutes until the film on part disappears.

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8. Ultrasonic in DI Water for 1 minute.

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9. Ultrasonic in new, clean alcohol for 1 minute, then final rinse and storage in stainless container.

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11. Hold in clean alcohol in stainless steel containers.

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Ready to ship for brazing or diffusion Bonding

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12. Dry in a clean room using filtered N2

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Ready to move to furnace area