Fly height Tester Measurement Error Reduction: Case Study

摘要

Fly height testers are used to measure the spacing between read-write heads from a computer hard drive and a glass test disk. Typical spacing is about 1 μin. (microinch) or 25 nm. This is a dynamic measurement taken when the head is flying above the rotating disk at a surface speed of about 130 ft/s. In early 1997, an engineering team was assigned to explore methods to reduce error in these fly height measurements. The objective was to reduce tester measurement error from 0.07 to 0.04 μin. Measurement error is defined as the total standard deviation (or "sigmal"") determined using a standard format gauge reproducibility and repeatability (GR&R) study. Product standard devia- tions for fly height ranged form 0.10 to 0.25 μin.