LIGO Document E0900480-v6
- FTIR Testing to Qualify Parts for LIGO UHV Service
The ultimate requirement of = .02 micrograms/cm^2 corresponds to ~ 0.1 monolayers of oil or polymer (assuming a density ~1 g/cm^3 and a molecular size of ~20 angstroms).
The acceptance criteria for pre-bake FTIR results are NVR Level A/20 (or ≤ 0.05 micrograms/cm2) per MIL-STD-1246C or IEST-STD-CC1246D.
If an FTIR is conducted after an air bake, the surface should be at Level A/50 or better or ≤ 0.02 micrograms/cm2
It is not necessary to perform the FTIR sampling both before and after an air bake.
- v6: New section added to group information on when to FTIR: Section 5.1 --
As above, it is preferable to perform the FTIR test prior to an air bake (so that the FTIR results are obtained while, or shortly after, the air bake has been completed). Parts should be held within Vacuum team until FTIR is completed, approved and sign off on the DCC. It is not necessary to perform the FTIR sampling both before and after an air bake
If FTIR is taken off-site from LIGO then the parts should be held at the off-site location (e.g. vendor) until the FTIR is completed, approved and sign off on the DCC. As long as it is confirmed on arrival at a LIGO site (during incoming inspection) that the packaging is intact (then again) it is not necessary to perform the FTIR sampling both before and after an air bake. If there are any concerns about the packaging on arrival (or other issues) the local vacuum lead can request a further sample set to be collected in line with the sampling steps below
V5: Added Hexanes as potential solvent for use, refer to E0900479 (v2 onward) for details on sampling with Hexanes.
V4: For the reasons cited below, we are relaxing the requirements on acceptable NVR level for sampled holes to the following:
v4: For threaded holes the maximum acceptable NVR level is = 1.2 microgram/hole for through holes and = 2.0 microgram/hole for blind holes, both prior to the air bake.
If an FTIR is conducted after an air bake, the acceptance level is = 0.4 microgram/hole for through holes and = 0.7 microgram/hole for blind holes.
v4: Reasons for the change: Our pass rate with the previous criteria was not very high. We had to repeat cleaning on a number of parts. While this is good if we are catching holes which were missed during the cleaning, or other problems such as compromised packaging during shipment, there is evidence that our criteria is just at or below the level achievable with our cleaning processes, both in-house and at AstroPak (our principal contracted precision cleaner). Most significantly, AstroPak took considerable care and spent a great deal of effort in cleaning a recent large SEI plate and yet still failed to achieve the criteria in v3 of this document (when sampled at AstroPak and so not subjected to the shipping environment). See for more detail. For this recent part, the JPL FTIR results were 1.7 micrograms/hole for blind holes and 1.04 micrograms/hole for through holes. Without researching a change to the basic cleaning approach and spending considerably more time and money, it is unlikely that we can achieve better FTIR results.
DCC Version 3.4.1, contact
Document Database Administrators