Abrading – Abrading process – Utilizing fluent abradant
Reexamination Certificate
2002-04-24
2003-12-02
Nguyen, George (Department: 3723)
Abrading
Abrading process
Utilizing fluent abradant
C451S040000, C451S002000, C451S081000, C451S089000, C134S007000, C134S010000
Reexamination Certificate
active
06656017
ABSTRACT:
BACKGROUND OF INVENTION
The present invention relates generally to the field of cleaning or treating miniature electromechanical device surfaces with cryogenic impingement sprays. More specifically, the present invention relates to the field of environmental control for performing cryogenic spray cleaning processes. Conventional precision cleaning processes using cryogenic particle impingement sprays such as solid phase carbon dioxide require control of the atmosphere containing a treated substrate to prevent the deposition of moisture, particles and other such contaminants onto cleaned surfaces during and following cleaning treatments.
Environmental control is required because of localized atmospheric perturbations created by the low temperatures and high velocities which are characteristic of these impingement cleaning sprays.
For example, snow particles having a surface temperature of −100 F. and traveling through the space between the spray nozzle and substrate are continuously sublimating in transit and upon impact with a substrate surface. This rapidly lowers local ambient atmospheric temperature—causing the contaminants contained therein to condense or “rain-out” of the local atmosphere and onto treated substrate surfaces during or following spray treatments. Moreover, the cleaning spray stream exhibits lower internal pressure than the 3 surrounding atmosphere (Bernoulli Principle) and creates venturi currents adjacent to the flow of the stream. These venturi currents cause the local atmosphere surrounding the stream to collapse into the spray stream above the substrate—thus entraining and delivering a mixture of cleaning spray and atmospheric constituents to the substrate. Finally, static charge build-up and accumulation are common to cryogenic sprays due the dielectric and tribocharging characteristics. This presents two problems—potential device damage from electrostatic overstress (EOS) or discharge (ESD) events and attraction of atmospheric contaminants to treated substrates via electrostatic attractive forces.
Micro-environmental control technology is well established and many techniques have been developed over the years to isolate a process, a substrate or a worker. The purpose of isolation can include protecting workers from toxic chemicals, protecting clean rooms from particles, or protecting delicate processes and substrates from the outside environment, among many others.
There are many examples of techniques to control thermal and electrostatic effects during cryogenic impingement sprays using secondary heated or ionized jets or sprays above the substrate surface and delivered either independently or as a component of the cryogenic spray have been used commercially. In U.S. Pat. No. 5,409,418 and U.S. Pat. No. 5,354,384, both teach direct heated or ionized gas impingement techniques and apparatus for heating, purging and deionizing substrate surfaces.
'384 teaches the use of a heated gas such as filtered nitrogen to provide a pre-heat cycle to a portion of a substrate prior to snow spray cleaning the same portion of said substrate, and a post-heat cycle of same said portion following snow cleaning. This approach relies on “banking heat” into the substrate portion prior to cryogenic spray cleaning by delivering a heated gas stream to a portion of substrate to prevent moisture deposition and adding heat from a heated gas following cryogenic spray treatment. The '384 invention is primarily useful for removing high molecular weight materials such as waxes and adhesive residues from surfaces by partially melting or softening them prior to spray treatment—in essence weakening cohesive energy. However, this approach does not work well for most substrate treatment applications. This is because many materials, or the portions thereof, being cleaned have low thermal conductivity and low mass or because highly thermal conductive materials rapidly lose heat to the sublimating snow during impact. This creates localized cold spots on even a mostly hot bulk substrate, which is the phenomenon for many substrates and surfaces being treated. Examples include ceramics, glasses, silicon and other semi-conductor materials, as well as most polymers. In addition, many electromechanical devices being cleaned are very small—providing no appreciable mass for storing heat. Examples include photodiodes, fiber optic connectors, optical fibers, end-faces, sensors, dies, and CCD's, among many others.
Most significantly, directing a heating spray, or any secondary fluid for that matter, directly at or incident with the substrate surface to be cleaned prior to, during and/or following cryogenic cleaning spray treatments causes the entrainment, delivery and deposition of atmospheric contaminants as discussed above. This necessitates housing the cryogenic spray applicator, substrate and secondary gas jets in large, bulky and complex environmental enclosures employing HEPA filtration and dry inert atmospheres such as taught for example in U.S. Pat. No. 5,315,793, which teaches a fully enclosed environmental chamber containing a snow spray applicator, automation, and thermal control system.
In the '418 invention, an apparatus is taught for surrounding the impinging cryogenic spray stream with an ionized inert gas. Using this invention, it is proposed by that surrounding a stream of solid-gas carbon dioxide with a circular stream of ionized gas and applying the two components to the substrate simultaneously controls or eliminates ESD at the surface during impingement. However, as also with '384 invention above, the '418 secondary stream entrains, delivers and deposits atmospheric contaminants upon the substrate surfaces being treated. Moreover, contact of the ionizing gas with the stream prior to contact with the surface rapidly eliminates ion concentration—highly degrading the performance of such an approach to controlling ESD. Still moreover, using the ionizing spray of '418 independent of the snow spray and which is directed at an angle which is incident to the surface will further re-contaminate the substrate unless, as taught in '793, the entire operation is performed in a controlled HEPA-filtered chamber.
As devices become smaller and their complexity increases, it is clearly desirable to have a improved processing technique, including a method and apparatus, that aids in using environmentally safe cleaning sprays to remove unwanted organic films and particles. It is desirable to have a technique that prevents additional particles and residues from being deposited on critical surfaces during application of said impingement cleaning sprays. The complete environmental control technique should include all of the basic environmental controls of thermal control, ionization control, and providing a dry and particle free cleaning atmosphere, but not negatively impacting the performance of the impinging cleaning spray. From the above, it is seen that a method and apparatus for use with impingement cleaning devices which provides micro-environmental control of precision electromechanical substrates during application that is low-cost, easy to use, adaptable and reliable is desired. As such, there is a present need to provide a method and apparatus for protecting a substrate from atmospheric contaminants and tribocharging effects during application of cryogenic cleaning sprays, and other non-cryogenic jet cleaning impingement sprays, which is low-cost, simple and adaptable to a variety of substrates and applicators. Moreover, there is a present need for an alternative and indirect environmental management process and apparatus whereas the spray applicator and other components are outside of the cleaning zone—thereby not posing a direct contamination threat to the critical substrate surfaces. Still moreover, there is a need for an environmental control process that does not produce a direct impingement spray upon the critical surfaces being cleaned and provides heat, ions and clean-dry atmosphere to the critical surfaces and indirectly removes contamina
Nguyen George
Sonnenschein Nath & Rosenthal LLP
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