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Clearance measurement at every POR (power on reset) by touch down only under limited temperature conditions

IP.com Disclosure Number: IPCOM000222196D
Publication Date: 2012-Sep-24
Document File: 2 page(s) / 61K

Publishing Venue

The IP.com Prior Art Database

Abstract

The fly heights of each individual magnetic heads are calibrated by touch down test in the manufacturing process of hard disk drives (HDD). So basically, every heads have proper fly heights, that is, not too high, not too low. However, considering various conditions in the field HDD usage, clearance check by touch down test at every power on process (POR) has potential to improve HDD reliability. The main issue of touch down test at every POR is the additional time it takes. This article offers the solution for the issue.

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  Clearance measurement at every POR (power on reset) by touch down only under limited temperature conditions

[Problem]

Touch down test at every POR takes addtional time before HDD operation is
ready.

As POR time is strictly limited, it is difficult to add touch down to every POR process.

[Solution]

Therefore, do touch down only under cold conditions.

At nominal and high temperature conditions, the fly heights of each individual magnetic heads are reliable because they are calibrated by touch down test in the manufacturing process.

Furthermore, delta-fly-height measurement by read back signal (harmonic sense) has higher accuracy under nominal and hot conditions than that under cold condition.

Only under cold condition, the accuracy of delta-fly-height measurement is not sufficient and we need alternative method.

The minimum fly height point under low temperature may differ from that under other conditions. It often generates non-linearity (Fig. 1).

On the other hand, only under cold conditions, extra time consumption may be allowed because of low probability thorough the product life.

Fig. 2 shows the POR process flow.

[Effect]

Improve clearance control accuracy and resulting reliability, with minimum performance impact

[Fig. 1]

Head fly height

Nominal & high temperature : head fly heights are relatively linear

Calibrated in manufacturing process: reliable

Cold temperature, non-linearity often seen

Moreover, it is not calibrated

0

30

Temperature 60

1


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