Rigid disk surface defect detection and classification

Details Rigid disk surface defect detection and classification Rigid disk surface defect detection and classification

1998-12-10

2001-08-28

Williams, Hezron (Department: 2862)

Electricity: measuring and testing

Magnetic

Magnetic information storage element testing

C360S025000, C714S042000

Reexamination Certificate

active

06281676

ABSTRACT:

FIELD OF THE INVENTION
The invention pertains to the detection of defects on data surfaces of rigid disk drives and more particularly to the detection and classification of defects to first determine whether a threshold number of defects has been exceeded and secondly, determine the type of damage by examining the occurrence and location of defect clusters.
BACKGROUND OF THE INVENTION
In the highly competitive disk drive industry, there is a continuing effort to reduce cost including the manufacturing cost, but not at the expense of reliability and quality. A vital element of the testing to assure quality, performance and reliability is the disk surface analysis to assure the flatness necessary to permit transducer heads to fly over the surface at a height of 1.8 microinches as well as evaluating the magnetic integrity of the data storage tracks.
Surface analysis testers, like the harmonic ratio flyheight (HRF) test, have been a common test procedure. The HRF glide testing is used to detect the presence or absence of mechanically protruding surface defects that interfere with the head/slider. The HRF test is effective, but requires expensive external testers that are typically placed in the manufacturing clean rooms. The HRF process samples every Nth track, called here subsampling, and determines the presence or absence of protruding defects. The subsampling used for HRF is typically every 30th to 40th track with the subsampling period less than the minimum rail width on a slider. The HRF test is an expensive low bandwidth instrumentation system that requires separate manual handling of each disk drive. Due to the smaller air bearings of future sliders and increased rotational velocity, rail contact time with a protruding defect is much shorter and the signal suggesting a defect is much shorter. This means that the HRF system needs a much higher bandwidth for reliable detection, which will make the HRF system even more expensive. Further, the thermal response of the current state of the art magnetoresistive (MR) heads can not be used since future very high speed disk drive recording bandpass channels are AC coupled with lower edge frequency set to about 5 MHz which effectively blocks the thermal response. Accordingly, a surface analysis test method is sought that will replace the HRF based method without sacrificing the reliability and quality of the disk drives being produced while lowering cost.
SUMMARY OF THE INVENTION
The present invention provides a quick, reliable, and low cost disk drive surface analysis method that is in-situ to the drive. The method of the invention quickly scans each disk surface of a hard disk drive for major clusters of defects followed by a classification of the defect clusters to determine whether they were caused by mechanical contact or not. The algorithm is simple enough to permit storage in the drive microcode. The method is not limited to manufacturing, but can also be used, for example, as a post shipping test for identifying surface damage that may have occurred during transportation, or by the user to determine the disk surface integrity status of the disk drive at any time. Thus the method can be used in manufacturing to decide if disk surface damage is caused by merge or demerge damage, system integrators can find whether surface damage was caused during shipping and the user can learn whether an accidental event caused any serious disk surface damage.
The in-situ surface analysis test method or self-glide test (SGT) searches for large clusters of surface defects rather than individual surface defects. It also determines whether the clusters have cylindrical adjacency (collateral damage) for drives with two or more data surfaces to suggest the presence of handling damage or assembly damage. Large clusters of surface defects are commonly associated with protruding defects. The SGT uses information similar to the information stored in the listings obtained during a surface analysis test (SAT). Once a cluster is found, the generalized error measurement facility (GEM) in the recording channel can conduct HRF-like measurements over the defect for additional verification.


REFERENCES:
patent: 4498146 (1985-02-01), Martinez
patent: 5935261 (1999-08-01), Blachek et al.
patent: 363317748A (1988-12-01), None

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