Sensitivity Surface Analysis Test Process Using Reduced Flying Height
Original Publication Date: 2001-Aug-01
Included in the Prior Art Database: 2003-Jun-18
Disclosed is a manufacturing process to enhance the reliability of the HDD by identifying a method to make the disk Surface Analysis Test more sensitive to certain types of defects by flying the data head at a lower flying height (FHt) than would be used by the customer. The Surface Analysis Test, often referred to as SAT, is used to identify disk defects which would, if written upon, lead to data recovery problems. These regions are then "skipped" and customer data is never written in that location. Certain types of defects, for example, disk asperities, are more easily identified (and then skipped) if the head flies lower than the normal flying height. As an example, one may take advantage of the head response to thermal asperities at the low flying height. This can be achieved through several means: (1) a vacuum system can be attached to the file and with reduced pressure, the flying height of the heads will be reduced in an easily calibrated amount, or (2) injecting a gas with suitable viscosity and density which would replace the air and also reduce the flying height. Helium is an example of such a gas. Identification of small asperities with this technique would allow not only that the defects would be skipped, but it would facilitate restricting customer data from not only the defect, but surrounding areas. This is typical for TAs seen at customer FHt but with this more sensitive technique, padding on more subtle defects would be enabled. In certain cases, disks are rejected for too many asperities. Action would be enabled for better HDD reliability with this more sensitive measurement method.