Question 1 — Question 1

R1-A has been operating normally for six months. Over the past two weeks, the base pressure has gradually risen from 0.05 mbar to 0.12 mbar. A rate-of-rise test shows a low but constant rate of 0.02 mbar/min. No maintenance has been performed recently. Which seal failure mode is most consistent with this evidence?

• A. Pinch or cut during installation — the O-ring was damaged when the flange was assembled
• B. Compression set — prolonged compression has permanently deformed the O-ring, reducing its sealing force and allowing a slow, steady gas ingress
• C. Chemical attack — a process gas has degraded the elastomer
• D. Particle contamination — debris on the sealing surface is preventing proper compression

Question 2 — Question 2

A vacuum system is used with an aggressive fluorine-based process gas at temperatures up to 250 degrees C. Standard Viton O-rings are not suitable. Which seal type explains the correct approach for these conditions?

• A. Buna-N (nitrile) O-rings — they are cheaper and more widely available
• B. Silicone O-rings — they have good temperature resistance
• C. Standard Viton with extra clamping force to compensate for chemical attack
• D. CF flanges with copper gaskets — metal seals are impervious to chemical attack and withstand the required temperature

Question 3 — Question 3

On R1-A, the foreline (R1-L-FL) connects R1-V-ISO to R1-P-RP using KF fittings. If this system were intended to achieve UHV performance (base pressure below 10^-8 mbar), what limitation of the current foreline connections would prevent this?

• A. The KF clamps do not provide sufficient clamping force
• B. Thicker O-rings in the existing KF centering rings would be needed
• C. KF connections use elastomer seals, which cannot achieve UHV due to permeation and outgassing limitations — CF flanges with copper gaskets are required for UHV
• D. No limitation — KF fittings work at any vacuum level

Question 4 — Question 4

During a thin-film coating run, the operator notices that the deposited film has a milky, hazy appearance instead of the expected clear optical coating. The chamber base pressure was slightly elevated (0.08 mbar instead of the normal 0.05 mbar). Examination reveals that a plastic cable tie was accidentally left inside the chamber. How does the cable tie explain the coating defect?

• A. The cable tie physically blocked part of the substrate
• B. Under vacuum, the plastic cable tie outgassed hydrocarbon vapour that co-deposited with the coating material, contaminating the film and causing the hazy appearance
• C. The cable tie created a virtual leak that introduced nitrogen into the chamber
• D. The cable tie's colour affected the optical properties of the coating

Question 5 — Question 5

Which of the following materials has the lowest outgassing rate after proper cleaning and surface preparation?

• A. Viton (FKM elastomer)
• B. Aluminium (6061 alloy)
• C. Electropolished stainless steel (Type 316)
• D. PTFE (Teflon)

Question 6 — Question 6

A vacuum system uses both KF and CF connections. The KF connections are on the roughing (foreline) side, and the CF connections are on the chamber and high-vacuum side. What is the engineering rationale for using two different flange standards on the same system?

• A. Cost savings — KF fittings are cheaper, so they are used wherever possible
• B. Availability — CF fittings are hard to find, so they are reserved for critical locations
• C. The roughing side operates at higher pressures where elastomer seal limitations (permeation, outgassing) are negligible, so KF is adequate and faster to assemble. The high-vacuum side requires metal seals to eliminate permeation and enable bake-out for UHV performance.
• D. Aesthetics — CF flanges look more professional on the chamber side

Question 7 — Question 7

An operator assembles a CF flange connection but does not tighten the bolts in a star pattern — instead tightening them sequentially around the circle. The system pumps down but cannot reach its expected base pressure. A rate-of-rise test shows a constant rate. What most likely happened?

• A. The copper gasket was the wrong size
• B. Sequential tightening caused uneven compression of the copper gasket — one side of the knife edge sealed properly while the other side did not fully engage, creating a leak path
• C. The bolts were the wrong material
• D. CF flanges cannot be assembled without special tools

Question 8 — Question 8

On R1-A, the Viton O-ring on R1-V-ISO is observed to appear swollen and has a slightly tacky texture compared to a new O-ring from stock. The system has been used with a process gas that was recently changed. What failure mode does this suggest, and what pattern would be expected in the vacuum data?

• A. Thermal degradation — expect the O-ring to crack and fragment, causing sudden catastrophic leak
• B. Compression set — expect gradual seal deterioration with slowly rising base pressure
• C. Chemical attack — the new process gas is incompatible with Viton, causing the elastomer to swell and soften. Expect an accelerating leak rate that worsens with continued exposure to the gas.
• D. Normal ageing — all O-rings swell over time and this is expected behaviour

Question 9 — Question 9

A technician argues that a vacuum system with a small leak can be compensated by installing a larger pump. The technician reasons that because base pressure scales inversely with effective pumping speed, increasing the pump size would lower the base pressure. Interpret whether this claim is correct.

• A. Correct — a larger pump would lower the base pressure, completely solving the problem
• B. Incorrect — pumping speed has no effect on base pressure
• C. Partially correct but practically poor — increasing effective pumping speed does lower the steady-state base pressure, but the leak still exists and continuously introduces atmospheric contaminants (water, oxygen, hydrocarbons) into the chamber. Eliminating the leak addresses the root cause, whereas a larger pump only masks the symptom.
• D. The relationship between pumping speed and base pressure does not apply when leaks are present

Question 10 — Question 10

The following connections are observed on a vacuum system: the chamber has a large flanged port with a bolt circle and a copper gasket visible between the mating surfaces. The foreline has a smaller connection held together by a single hinged clamp with an O-ring visible in the centering ring. Identify each connection type.

• A. Chamber: ISO-K; Foreline: CF
• B. Chamber: KF; Foreline: ISO-F
• C. Chamber: CF (bolt circle, copper gasket); Foreline: KF (single clamp, centering ring with O-ring)
• D. Both connections are KF — the bolt circle is decorative

Question 11 — Question 11

On R1-A, a rate-of-rise test is performed and shows a constant rate of 0.05 mbar/min. A seal leak is suspected. Which seals on R1-A form the boundary between the isolated chamber volume and atmosphere, making them the most relevant to this observation?

• A. Only the chamber flange O-ring — it is the largest seal
• B. Only R1-V-VENT — it is the most recently operated valve
• C. R1-V-ISO seat seal and the chamber flange O-ring — these are the seals that separate the isolated chamber volume from atmosphere. R1-V-VENT is also a candidate because any leak past its seat would connect the chamber to the vent line and atmosphere.
• D. The pump seals — backstreaming always looks like a leak

Question 12 — Question 12

A technician replaces a CF copper gasket on a chamber port. After reassembly and pump-down, the system reaches the expected base pressure. However, when the system is baked out at 300 degrees C, a leak develops. After cool-down, the leak disappears. What is happening?

• A. The copper gasket melts at 300 degrees C
• B. The bolts loosen at high temperature
• C. Differential thermal expansion — the flanges, bolts, and gasket expand at different rates during bake-out, temporarily opening a leak path. The seal recovers when the system cools because the components return to their original dimensions. This indicates insufficient bolt preload or an incompatible material combination.
• D. The gauge is giving false readings at high temperature

Question 13 — Question 13

In a thin-film coating system, the substrate holder and internal fixturing are made from stainless steel. A new technician suggests replacing them with plastic fixtures to save cost. Why is this proposal unsuitable?

• A. Plastic fixtures are not strong enough to hold substrates
• B. Plastic fixtures are the wrong colour for optical coatings
• C. Plastic fixtures would outgas heavily under vacuum, releasing hydrocarbon vapour that contaminates the coating process. Any organic material inside a deposition chamber compromises the molecular cleanliness required for quality thin-film coatings.
• D. Plastic fixtures would melt immediately under vacuum

Question 14 — Question 14

An O-ring on R1-A is inspected and found to have a small cut on one side. The operator reinstalls it, reasoning that the cut is on the outer edge and "won't be in the sealing zone." Is this reasoning correct?

• A. Yes — only the inner sealing surface matters for vacuum integrity
• B. No — a cut compromises the O-ring's ability to maintain uniform elastic compression. Even if the cut is not directly in the primary sealing zone, it weakens the O-ring structurally and creates a potential leak path. Damaged O-rings should always be replaced.
• C. Yes — as long as the cut is less than 1 mm deep, the seal will hold
• D. It depends on whether the system is high vacuum or rough vacuum

Question 15 — Question 15

The following is observed on a vacuum system: the chamber uses CF flanges with copper gaskets, but the foreline uses KF connections with Viton O-rings. A KF centering ring on the foreline is visibly degraded — the O-ring looks cracked and hard. What is the most likely cause of the O-ring degradation, and what evidence would confirm it?

• A. The O-ring is the wrong size for the centering ring
• B. Thermal degradation — heat from the pump or from a bake-out procedure may have exceeded the O-ring's temperature rating, causing it to harden and crack. Proximity of the KF connections to a heat source, or a history of bake-out procedures, would confirm this interpretation.
• C. The O-ring was installed incorrectly during the last maintenance
• D. Normal wear — all O-rings crack after a few months of use

Question 16 — Question 16

Two rate-of-rise tests are performed on R1-A after replacing a chamber O-ring. Test 1 (immediately after assembly): constant rate of 0.08 mbar/min. Test 2 (after re-tightening the flange bolts): constant rate of 0.01 mbar/min. What do these results tell you about the initial assembly?

• A. The O-ring was defective and self-healed after re-tightening
• B. The initial assembly had insufficient bolt torque — the O-ring was under-compressed and not fully sealed. Re-tightening increased the compression, dramatically reducing the leak. The remaining 0.01 mbar/min should be monitored to determine if it is a residual leak or normal outgassing.
• C. The flange was contaminated and re-tightening cleaned it
• D. Rate-of-rise tests are unreliable immediately after assembly

Question 17 — Question 17

A vacuum system specification calls for "all-metal sealing throughout." What does this requirement mean, and in which applications is it typically necessary?

• A. All structural components must be metal — no glass or ceramic viewports
• B. All vacuum joints use metal gaskets (typically copper in CF flanges) rather than elastomer O-rings. This is required for UHV applications, systems that undergo high-temperature bake-out, and processes sensitive to hydrocarbon contamination from elastomers.
• C. All bolts and clamps must be metal — no plastic hardware
• D. The chamber walls must be at least 10 mm thick stainless steel

Question 18 — Question 18

A colleague presents the following diagnostic argument: "The base pressure on R1-A is 0.12 mbar instead of 0.05 mbar. The O-rings are old. Therefore, the O-rings are leaking and need replacement." Interpret this reasoning using Module 4 evidence discipline.

• A. The reasoning is correct — old O-rings are the most common cause of elevated base pressure
• B. The reasoning is correct because 0.12 mbar is significantly higher than 0.05 mbar
• C. The reasoning is incomplete — it jumps to a root cause without discriminating evidence. An elevated base pressure could be caused by a seal leak, outgassing from contamination, or a conductance restriction. A rate-of-rise test would provide discriminating evidence: constant rate suggests a leak, decreasing rate suggests outgassing. Old O-rings are a plausible hypothesis but not a confirmed root cause without supporting data.
• D. The reasoning is wrong because O-rings never cause base pressure problems

Question 19 — Question 19

A vacuum system design for a thin-film coating application specifies a base pressure of 10^-6 mbar with regular bake-out at 250 degrees C. The proposed design uses a stainless steel chamber with ISO-K flanges and Viton O-rings on all connections. Identify the material/hardware issue with this design.

• A. Stainless steel is not suitable for thin-film coating chambers
• B. The chamber diameter is too small for ISO-K flanges
• C. Viton O-rings cannot survive bake-out at 250 degrees C (maximum approximately 200 degrees C) and their outgassing/permeation would limit the achievable base pressure well above 10^-6 mbar. CF flanges with copper gaskets are required to meet both the temperature and pressure requirements.
• D. ISO-K flanges are never used on coating systems

Question 20 — Question 20

The following evidence has been collected from R1-A:

• A. Base pressure has risen from 0.05 to 0.15 mbar over two months
• B. Rate-of-rise test shows: 0 min: 0.15 mbar, 1 min: 0.20 mbar, 5 min: 0.39 mbar, 10 min: 0.63 mbar (rates: 0.05, 0.048, 0.048 mbar/min)
• C. The chamber was recently cleaned with solvent; the operator reports the chamber "smelled clean" when reassembled
• D. The O-ring on the chamber flange was inspected and appeared to be in good condition
• E. The pump reaches 0.01 mbar when tested independently at the pump inlet
• F. 1st: Pump degradation; 2nd: Seal leak; 3rd: Solvent contamination — discriminated by pump test results
• G. 1st: Seal leak; 2nd: Solvent contamination; 3rd: Pump degradation — discriminated by the O-ring inspection
• H. 1st: Solvent residue contamination (near-constant rate from large volatile source matches the cleaning history); 2nd: Developing seal leak (constant rate, but O-ring visual inspection was normal); 3rd: Pump degradation is eliminated (pump reaches 0.01 mbar independently). Discriminating evidence: repeat the rate-of-rise test after extended pumping — if the rate decreases across cycles, solvent contamination is confirmed (the source depletes). If the rate remains identical across cycles, a leak is more likely (atmospheric source does not deplete).
• I. All three hypotheses are equally likely — cannot be distinguished without RGA analysis

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