It is well known that the reliability of a hard disk drive is affected by both the temperature and humidity inside a hard disk drive. At high temperature and humidity, the slider's air bearing can lose lift, which decreases its flying height and increases the probability of contact between the read-write head and the rotating disk surface. Also, when the temperature decreases rapidly from a high temperature in a very humid situation, water vapor within the hard disk drive may condense on sensitive elements of the hard disk drive, such as the read-write head, slider and/or one or more of the disk surfaces.
The prior art shows several examples of three approaches to minimizing these effects. The first approach is to seal the hard disk drive, so that water vapor leaks in very slowly. A second approach is to include a water absorbent material or desiccant inside the hard disk drive to collect any incoming water vapor, which is thought to maintain internal humidity at a low level. These two approaches do increase the time it takes for the internal water vapor level to rise when such hard disk drives are exposed to environments with high water vapor pressure, where both the temperature and relative humidity are high.
However, there are problems with these approaches. Given enough time in an environment with high water vapor pressure, a hard disk drive using these approaches will be overcome by the abundance of water in its surroundings and what was useful before now makes things worse. For example, should the temperature inside such a hard disk drive rise, the desiccant will now release its stored water into the interior of the hard disk drive, causing the air bearing to lose lift, again, decreasing its flying height and increasing the probability of contact between the read-write head and the disk surface it accesses. Should the inside temperature decrease rapidly, the water vapor will tend to condense because the desiccant has a rate limit of absorption.
There is a third prior art approach, which is to make sure a hard disk drive is not sealed, but supports easy and rapid mass transfer between interior of the hard disk drive and its outside environment. This approach responds quickly to changes in external temperature and humidity, which is useful as the outside temperature and humidity decrease rapidly. However, such hard disk drives run into problems when exposed to high external temperatures and humidity, in that the interior soon has high temperature and humidity, causing the internal water vapor pressure to rise, the slider flying height to decrease and the probability of read-write head contact with a disk surface to increase.
What is needed are mechanisms and operating methods that can readily adapt to changes in the outside environment of a hard disk drive to minimize its interior water vapor pressure.