# Patent

## Title
Disk drive with slow acting desiccant

## Abstract

A disk drive includes a disk drive enclosure and a disk rotatably mounted to and within the disk drive enclosure. A desiccant canister is in fluid communication with the disk drive enclosure. The desiccant canister includes a canister housing and a desiccant material within the canister housing. The desiccant canister includes a water absorption restriction that limits a steady-state hourly water absorption rate of the desiccant to not exceed 2% of the desiccant's total capacity for water absorption.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority to provisional U.S. Patent Application Ser. No. 61/813,458, filed on Apr. 18, 2013, which is hereby incorporated by reference in its entirety.


BACKGROUND
Information storage devices are used to retrieve and/or store data in computers and other consumer electronics devices. A magnetic hard disk drive is an example of an information storage device that includes one or more heads that can both read and write to a spinning disk media, but other information storage devices also include heads—sometimes including heads that cannot write.
Disk drives may be hermetically sealed, for example so that an alternative gas (e.g. helium) can be retained within the disk drive. In such hermetically sealed disk drives, humidity that enters during manufacture may be trapped inside thereafter. Such humidity may condense at reduced temperatures, causing undesired water particles or droplet within the disk drive. Even in non-hermetically sealed disk drives, the disk drive reliability may be enhanced by control of humidity within the disk drive enclosure, since such humidity may otherwise adversely affect the head/disk interface. For example, disk drives have been manufactured with internal desiccant materials within, to reduce the accumulation of moisture and the risk of water particles or droplets reaching the head/disk interface.
However, during disk drive manufacture, there is often a period after installation of a desiccant material into the disk drive, but before finally sealing the disk drive enclosure. During that period, the desiccant material may be degraded by humidity in the manufacturing environment (e.g. clean room moisture absorption by the desiccant). Hence there is a need in the art for a means to preserve a desiccant material for a longer period during the disk drive manufacturing process.



BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a top perspective exploded view of a disk drive capable of including an embodiment of the present invention.
FIG. 2 is a side perspective view of a desiccant canister according to an embodiment of the present invention.
FIG. 3 is a top perspective view of a desiccant canister according to an embodiment of the present invention.
FIG. 4 is a top exploded perspective view of a desiccant canister according to an embodiment of the present invention.



DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
FIG. 1 is top perspective exploded view of a disk drive 100 according to an embodiment of the present invention. The disk drive 100 includes a disk drive base 102 and a disk drive cover 104 that together comprise a disk drive enclosure. The disk drive 100 further includes a spindle 166, rotatably mounted on the disk drive base 102, for rotating at least one disk 162 that is mounted on the spindle 166. In certain embodiments, disk drive 100 may have only a single disk 162, or alternatively, two or more disks. The disk drive 100 also includes a head stack assembly 164 pivotably mounted to the disk drive base 102 for positioning one or more read or write heads over a respective surface of the disk 162.
In the embodiment of FIG. 1, the disk drive cover 104 includes a canister opening 110, although in an alternative embodiment the canister opening may instead be disposed in the disk drive base 102. The disk drive 100 includes a desiccant canister 120 (e.g. a canister formed from a hard plastic material) containing a desiccant material such as silica gel, activated carbon, calcium sulfate, calcium chloride, and/or montmorillonite clay. FIG. 1 shows that after assembly the desiccant canister 120 is at least partially disposed within the disk drive enclosure 102,104.
The desiccant canister 120 may include internal and/or external features described herein so that the rate of water vapor absorption (relative to the desiccant's total capacity for water absorption) is slowed. For example, in certain embodiments, the desiccant canister 120 includes a water absorption restriction that limits a steady-state hourly water absorption rate of the desiccant to not exceed 2% of the total capacity for water absorption of the desiccant material within. In this context, the steady-state hourly water absorption rate may be consistently estimated or measured after any initially high transient water absorption rate has passed, in an environment in which the relative humidity is held at approximately 80%.
In certain embodiments where freedom from temporal limitations in the manufacturing process is even more important, the water absorption restriction may preferably but not necessarily limit the maximum steady-state hourly water absorption rate of the desiccant to not exceed 0.20% of the total capacity for water absorption of the desiccant material. Note also that the scientific definition of water (i.e. H2O) is contemplated herein, according to which “water” need not be in liquid form. For example, H2O vapor in humid air is considered “water” herein.
In the embodiment of FIG. 1, a hermetic seal 130 covers the external surface 122 of the desiccant canister 120, and is externally adhered to the cover 104 of the disk drive enclosure. In the embodiment of FIG. 1, the hermetic seal 130 optionally is a disk drive cover seal that is also adhered to the external surface 122 of the desiccant canister 120, and may optionally also be adhered to an external surface of the disk drive base 102. In certain embodiments, the hermetic seal 130 preferably includes a metal foil laminated with an adhesive layer.
In certain embodiments, the rate of water vapor absorption by the desiccant in the canister 120 is slowed by a diffusion hole in the canister 120 that faces into the disk drive enclosure 102,104 (and is in fluid communication with the disk drive enclosure 102,104). In certain other embodiments, the rate of water vapor absorption by the desiccant in the desiccant canister 120 is slowed by a barrier to the desiccant—e.g. a pressure sensitive adhesive (PSA) polymer layer, with a finite clearance between its periphery and an interior surface of an opening in the canister, to allow diffusion around the barrier. The barrier may also be a semi-permeable polymer membrane or carbon layer that does not need such a peripheral clearance to permit diffusion around it or therethrough.
FIG. 2 is a side perspective view of a desiccant canister 200 according to an embodiment of the present invention. In the embodiment of FIG. 2, the desiccant canister 200 includes a canister housing 202, and a desiccant material 210 within the canister housing 202. The desiccant material 210 defines a total capacity for water absorption. The desiccant canister 200 also includes a plurality of diffusion paths 204 that permit but limit a steady-state hourly water absorption rate of the desiccant material 210. The diffusion paths 204 do this by allowing limited diffusion from the outside environment past a barrier 234 (e.g. a pressure sensitive adhesive polymer layer) within an opening in the canister housing 202 that faces into the disk drive enclosure.
Specifically, in the embodiment of FIG. 2, the diffusion paths 204 create local regions of increased finite clearance between the outer periphery of the barrier 234 and an interior surface (within the opening) of the canister housing 202 to allow and limit diffusion from the external environment around the barrier 234. In certain embodiments, the diffusion paths 204 (in conjunction with the barrier 234) preferably limit the diffusion such that the steady-state hourly water absorption rate of the desiccant material 210 does not exceed 2% of the total capacity for water absorption of the desiccant material 210. In the embodiment of FIG. 2, the desiccant canister 200 also includes an optional adsorbant layer 220 (e.g. carbon), and includes an optional gas-permeable membrane 232 over the opening in the canister housing 202 that faces into the disk drive enclosure. For example, an expanded polytetrafluoroethylene (EPTFE) filter fabric may be used as the gas-permeable membrane.
FIG. 3 is a top perspective view of a desiccant canister 300 according to an embodiment of the present invention. In the embodiment of FIG. 3, the desiccant canister 300 includes a canister housing 302, and a desiccant material 310 within the canister housing 302. The desiccant material 310 defines a total capacity for water absorption.
In the embodiment of FIG. 3, the canister housing 302 includes an opening 320 therethrough, which acts as a water absorption restriction. The opening 320 preferably faces into the disk drive enclosure, so that the desiccant canister 300 is in fluid communication with the disk drive enclosure. In the embodiment of FIG. 3, the opening 320 is optionally cylindrical, with a diameter that is preferably but not necessarily in the range of 0.25 mm to 2 mm. In certain embodiments, the opening 320 preferably limits diffusion therethrough, such that the steady-state hourly water absorption rate of the desiccant material 310 does not exceed 2% of the total capacity for water absorption of the desiccant material 310.
FIG. 4 is a top exploded perspective view of a desiccant canister 400 according to an embodiment of the present invention. In the embodiment of FIG. 4, the desiccant canister 400 includes a canister housing 402, and a desiccant material 410 within the canister housing 402. In certain embodiments, the canister housing 402 may comprise a hard plastic material that preferably but not necessarily has a thickness in the range of 0.5 mm to 5 mm. In the embodiment of FIG. 4, the canister housing 402 includes an opening 404 that faces into the disk drive enclosure, so that the canister 400 is in fluid communication with the disk drive enclosure.
In the embodiment of FIG. 4, the desiccant material 410 comprises a solid monolith of desiccant material 410, which may be coated by a semi-permeable barrier layer that permits but limits a steady-state hourly water absorption rate of the desiccant material 410. For example, the semi-permeable barrier layer may be a semi-permeable polymer film or a latex paint having a thickness in the range of 10 microns to 100 microns.
In the embodiment of FIG. 4, the semi-permeable barrier layer on the desiccant material 410 serves as a water absorption restriction, limiting the water diffusion therethrough, such that the steady-state hourly water absorption rate of the desiccant material 410 does not exceed 2% of the total capacity for water absorption of the desiccant material 410. In the embodiment of FIG. 4, the desiccant canister 400 also includes an optional adsorbant layer 420 (e.g. carbon), and includes and an optional gas-permeable membrane 432 over the opening 404 in the canister housing 402. For example, an expanded polytetrafluoroethylene (EPTFE) filter fabric may be used as the gas-permeable membrane. In alternative embodiment, the desiccant material 410 may not need to be coated with a semi-permeable polymer film or a latex paint, because the optional adsorbant layer 420 may also serve as the water absorption restriction. In such an embodiment, if the optional adsorbant layer comprises activated carbon, it may have a thickness that is preferably in the range 0.3 mm to 2 mm.
In various embodiments described herein, water vapor absorption by the desiccant cartridge is advantageously limited to a substantial and non-zero but reduced rate, so that the desiccant cartridge can be exposed to a normal external manufacturing environment without becoming saturated for a practical period during disk drive assembly, yet thereafter still absorb moisture from the internal environment of the assembled disk drive quickly enough to control the humidity within the disk drive (e.g. during the useful life of the assembled disk drive).
In the foregoing specification, the invention is described with reference to specific exemplary embodiments, but those skilled in the art will recognize that the invention is not limited to those. It is contemplated that various features and aspects of the invention may be used individually or jointly and possibly in a different environment or application. The specification and drawings are, accordingly, to be regarded as illustrative and exemplary rather than restrictive. For example, the word “preferably,” and the phrase “preferably but not necessarily,” are used synonymously herein to consistently include the meaning of “not necessarily” or optionally. “Comprising,” “including,” and “having,” are intended to be open-ended terms.

## Claims

1. A disk drive comprising:
a disk drive enclosure;
a disk rotatably mounted to and within the disk drive enclosure; and
a desiccant canister in fluid communication with the disk drive enclosure, the desiccant canister including:
a canister housing;
a desiccant material within the canister housing, the desiccant material defining a total capacity for water absorption, and
a water absorption restriction that limits a steady-state hourly water absorption rate of the desiccant material to not exceed 2% of the desiccant material's total capacity for water absorption.

2. The disk drive of claim 1 wherein the desiccant canister is in fluid communication with the disk drive enclosure by the canister housing including an opening that faces into the disk drive enclosure.

3. The disk drive of claim 2 wherein the canister housing is at least partially disposed within the disk drive enclosure.

4. The disk drive of claim 2 wherein the opening in the canister housing is the water absorption restriction.

5. The disk drive of claim 4 wherein the opening is cylindrical with a diameter in the range of 0.25 mm to 2 mm.

6. The disk drive of claim 2 wherein the water absorption restriction comprises a pressure sensitive adhesive (PSA) polymer layer that has an outer periphery and that is disposed within the opening in the canister housing, the outer periphery of the PSA polymer layer being disposed with a finite clearance from the opening in the canister housing, said clearance allowing water absorption between the PSA polymer layer and the opening in the canister housing.

7. The disk drive of claim 1 wherein the canister housing comprises a hard plastic material having a thickness in the range of 0.5 mm to 5 mm.

8. The disk drive of claim 1 wherein the water absorption restriction comprises a semi-permeable barrier layer.

9. The disk drive of claim 8 wherein the semi-permeable barrier layer comprises a semi-permeable activated carbon layer having a thickness in the range of 0.3 mm to 2 mm.

10. The disk drive of claim 8 wherein the desiccant material comprises a solid monolith of desiccant material, and the semi-permeable barrier layer is a coating on the solid monolith of desiccant material.

11. The disk drive of claim 10 wherein the coating comprises a semi-permeable polymer film or a latex paint, having a thickness in the range of 10 microns to 100 microns.

12. The disk drive of claim 1 wherein the steady-state hourly water absorption rate of the desiccant material does not exceed 0.20% of the desiccant material's total capacity for water absorption.

13. A desiccant canister for a disk drive, the desiccant canister comprising:
a canister housing;
a desiccant material within the canister housing, the desiccant material defining a total capacity for water absorption, and
a water absorption restriction that limits a steady-state hourly water absorption rate of the desiccant material to not exceed 2% of the desiccant material's total capacity for water absorption.

14. The desiccant canister of claim 13 wherein the desiccant canister includes an opening for water absorption.

15. The desiccant canister of claim 14 wherein the opening in the canister housing is the water absorption restriction.

16. The desiccant canister of claim 15 wherein the opening is cylindrical with a diameter in the range of 0.25 mm to 2 mm.

17. The desiccant canister of claim 14 wherein the water absorption restriction comprises a pressure sensitive adhesive (PSA) polymer layer that has an outer periphery and that is disposed within the opening in the canister housing, the outer periphery of the PSA polymer layer being disposed with a finite clearance from the opening in the canister housing, said clearance allowing water absorption between the PSA polymer layer and the opening in the canister housing.

18. The desiccant canister of claim 13 wherein the canister housing comprises a hard plastic material having a thickness in the range of 0.5 mm to 5 mm.

19. The desiccant canister of claim 13 wherein the steady-state hourly water absorption rate of the desiccant material does not exceed 0.20% of the desiccant material's total capacity for water absorption.

20. The desiccant canister of claim 13 wherein the water absorption restriction comprises a semi-permeable barrier layer.

21. The desiccant canister of claim 20 wherein the semi-permeable barrier layer comprises a semi-permeable activated carbon layer having a thickness in the range of 0.3 mm to 2 mm.

22. The desiccant canister of claim 20 wherein the desiccant material comprises a solid monolith of desiccant material, and the semi-permeable barrier layer is a coating on the solid monolith of desiccant material.

23. The desiccant canister of claim 22 wherein the coating comprises a semi-permeable polymer film or a latex paint, having a thickness in the range of 10 microns to 100 microns.