Rigid multi-functional filter assembly

Details Rigid multi-functional filter assembly Rigid multi-functional filter assembly

1999-09-24

2001-05-29

Spitzer, Robert H. (Department: 1724)

Gas separation: apparatus

Solid sorbent apparatus

Plural diverse separating means

C096S139000, C096S147000, C096S152000, C096S153000, C055S385600, C055S502000, C055S519000, C360S097020

Reexamination Certificate

active

06238467

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a device for filtering particulates and vapor phase contaminants from a confined environment such as electronic or optical devices susceptible to contamination (e.g., computer disk drives).
BACKGROUND OF THE INVENTION
Many enclosures that contain sensitive instrumentation must maintain very clean environments in order to operate properly. Examples include the following: enclosures with sensitive optical surfaces, or electronic connections that are sensitive to particulates and gaseous contaminants which can interfere with mechanical, optical, or electrical operation; data recording devices, such as computer hard disk drives that are sensitive to particles, organic vapors, and corrosive vapors; enclosures for processing, transport or storage of thin films and semiconductor wafers; and electronic control boxes such as those used in automobiles and industrial applications that can be sensitive to particles, moisture buildup, and corrosion as well as contamination from fluids and vapors. Contamination in such enclosures originates from both inside and outside the enclosures. For example, in computer hard drives, damage may result from external contaminants as well as from particles and outgassing generated from internal sources. The terms “hard drives” or “hard disk drives” or “disk drives” or “drives” will be used herein for convenience and are understood to include any of the enclosures mentioned above.
One serious contamination-related failure mechanism in computer disk drives is static friction or “stiction”. Stiction results from the increased adhesion of a drive head to a disk while the disk is stationary plus increased viscous drag parallel to the head-disk interface. Newer high density disks are more sensitive to contamination-caused stiction because they are smoother and only thin layers of lubricants are present. Contaminants on the disk change the surface energy and the adhesive forces between the head and disk, which cause stiction. Also, vapors that condense in the gap between the head and disk can cause stiction. In addition to increasing power requirements for spinning up the drive, stiction forces can cause permanent mechanical deformation of the head suspension and gimbal assemblies. The latter have become extremely sensitive to small forces with the introduction of smaller air bearing sliders with lower applied loads, using thinner structural elements in the suspension and gimbal to maintain slider flying heights and attitudes with tremendous precision. Further exacerbating these effects are the newer lower energy, lower torque motors being used in smaller disk drives for portable computers.
Condensation of volatile organic contaminants (VOCs) onto magnetic head and disk surfaces will increase the physical head-medium separation, which will result in signal loss and increased data errors. This is increasingly true as linear bit density continues to rise at a breakneck pace. Accumulation of heavy VOCs on the critical air bearing surfaces of the head slider, through transfer from the much larger disk surface, can cause destabilization of the flying dynamics of the slider as well as significant signal losses. Interaction of VOCs and disk lubricant can lead to chemical degradation of the lubricant, especially during instances of head-disk contact and the accompanying elevated temperatures. This can lead to build-up on the disk surface of viscous, high molecular weight reaction products which are unable to replenish localized regions of lubricant depletion. Other degradation products may be volatile and permanently escape the head-disk interface. These processes can eventually result in elevated wear of head or disk surfaces, increased stiction, higher error rates, and ultimately reduced lifetime for the drive.
Acid gases, which are widely present in pollution and smog as well as industrial environments, can have especially harmful effects on drive reliability if allowed to circulate inside the drive. These compounds will adsorb onto head and disk surfaces and corrode exposed metallic layers via galvanic reaction in the presence of water. They can also be transported by moisture through pinholes in protective coatings on the head and disk. Corrosion typically results in loss of magnetic properties, as well as accumulation of reaction products on critical surfaces.
Another serious contamination-related failure mechanism in computer disk drives is head crashes. Head crashes can occur when particles get into the head disk interface. Newer high density drives have 30 nanometer or less flying heights or spacing between the head and disk during operation and typically have disks rotating 5400 revolutions per minute or greater. Even submicron-sized particles can be a problem, causing the head to crash into the particle or the disk after flying over a particle, bringing the drive to an abrupt failure mode. Particles which do not cause a head crash may still adversely affect data integrity and mechanical reliability of a drive. Small, hard inorganic particles can cause wear of a head or disk, which may result in permanent signal loss, degradation of protective coatings, or further debris generation. Wear of carbon overcoats on the head or disk can accelerate corrosion of sensitive layers through the action of moisture, acid gas contaminants, and elevated interface temperatures. Plowing of small hard particles into the disk surface can create scratches, asperities, or pile-ups of disk material. Current magnetic head technologies, employing magnetoresistive (MR) elements for sensing of magnetic flux emanating from the disk, are highly sensitive to transient temperature excursions as caused by interaction of the head with asperities or adhered particles on the rapidly moving disk. The resulting change in resistance of the MR element may be misinterpreted as magnetic signal, causing data errors. This phenomenon is well known in the industry and is referred to as a thermal asperity.
In addition, disk drives must be protected against a large number of contaminants in the surrounding environment that can penetrate the drive. This is true for drives used in small to medium sized computer systems which may not be used in the typical data processing environment and is especially true in drives that are removable and portable to any environment such as disk drives that are used in laptop computers or in Personal Computer Memory Card International Association (PCMCIA) slots.
Filtration devices to keep particles from entering these enclosures are well known. They may consist of a filtration media held in place by a housing of polycarbonate, acrylonitrile butadiene styrene (ABS), or some other material; or they may consist of a filtration media in the form of a self-adhesive disk utilizing a layer or layers of pressure sensitive adhesive. These devices are mounted and sealed over a vent hole in the enclosure to filter particulates from the air entering the drive. Filtration performance depends not only on the filter having a high filtration efficiency but also on having a low resistance to air flow so that unfiltered air does not leak into the enclosure through a gasket or seam instead of entering through the filter. Such filters work well for particulates of external origin, but do not address the problems from vapor phase contaminants.
Combination adsorbent breather filters to keep particulates and vapors from entering enclosures are also well known. These can be made by filling a cartridge of polycarbonate, ABS, or similar material with adsorbent and securing filter media on both ends of the cartridge. Examples of such filters are described in U.S. Pat. No. 4,863,499 issued to Osendorf (an anti-diffusion chemical breather assembly for disk drives with filter media having a layer impregnated with activated charcoal granules); U.S. Pat. No. 5,030,260 issued to Beck et al. (a disk drive breather filter including an assembly with an extended diffusion path); U.S. Pat. No. 5,124,856 issued to Brown et al. (a unitary filter medium with impregnat

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