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Development Of A Particle Sampling Roller


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This material is presented as an example of work I\'ve done. The information has been previously published and is presented here in a low detail format.

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Development Of A Particle Sampling Roller

  1. 1. Development of a Particle Sampling Roller’ Note, this information has been previously disclosed in papers presented at CleanRooms East and to the IEST. It is presented here in a low-detail format as an example of prior work performed by Jerry Ernst who developed the specifics of this tool and test methods.
  2. 2. Introduction <ul><li>Polymer contact cleaning rollers are well known in conveyance and printing industries. A hand held sampling roller was developed by the author to provide a quick and easy means of characterizing surface cleanliness in an industrial controlled environment. The resulting tool can be used by production personnel for a quick visual scale evaluation, or can be used by technical personnel to collect particles for counting and/or identification. </li></ul>
  3. 3. <ul><li>Lab testing of various materials lead to the identification of a number of roller characteristics including: </li></ul><ul><li>Base polymer formulation </li></ul><ul><li>Hardness (Shore A) Resiliency </li></ul><ul><li>Residual compounds </li></ul><ul><li>Surface finish </li></ul><ul><li>Stability over time </li></ul><ul><li>Particle collection efficiency in the required range (10 to 1000 micrometers) </li></ul>
  4. 4. Testing particle collection efficiency <ul><li>The most challenging attribute is particle collecting efficiency (PCE). Initial tests involved simply rolling over a smooth dark dusty surface to see how well the roller cleaned the surface, the ‘answering machine test.’ Many rollers failed even this simple test. </li></ul>
  5. 5. <ul><li>The final test involved the deposition of particles using a fluid bed aerosol generator, centered between 11 and 20 microns. The goals in developing a test were: </li></ul><ul><li>Provide enough challenge to measure differences in whole numbers, not decimal points. </li></ul><ul><li>Be able to resolve subtle difference between roller conditions. </li></ul><ul><li>Be able to give consistent repeatable results </li></ul><ul><li>Be able to test the ‘seeded’ test substrate, then carry the substrate around the room, turn it over and back, and then re-scan it and be within 5% of the original ‘seeded’ count. </li></ul>
  6. 6. <ul><li>The final test method met all goals. Variables have to be carefully controlled to give repeatable results including: </li></ul><ul><li>Substrate material </li></ul><ul><li>Substrate cleaning method </li></ul><ul><li>Substrate surface charge </li></ul><ul><li>Lab temperature and humidity </li></ul><ul><li>Particle composition </li></ul><ul><li>Fluid bed parameters, such as air flow, deposition time and pattern </li></ul><ul><li>The efficiency test is able to differentiate between like polymers from different vendors, rollers of different surface finishes, and the same roller in a clean or particle laden conditions. </li></ul>
  7. 7. Sampling Roller Selection <ul><li>Having the ability to measure PCE, a suitable material was identified that had a high efficiency, was very durable, and left minimal residue as determined by analytical means. X-ray analysis after cleaning a glass plate with this material showed no residue, however testing at the Lawrence Livermore National Ignition Lab was able to detect very low residuals; at the time the lowest levels they had seen from any roller. </li></ul>
  8. 8. Applications of the Sampling Roller: <ul><li>Using a small roller to sample a larger area concentrates debris for easier characterization </li></ul><ul><li>Particles can be transferred to blank cleanroom label material for a visual evaluation (pass/fail after facility cleaning) </li></ul><ul><li>Particles can be released onto clear tape for microscopic scanning and counting </li></ul>