Measurement of Vertical Stiction (Adhesion) Forces in a Head-Disc Interface

One of the applications of the CETR UMT Micro-Tribometer is the precision measurements of pull-off forces. This paper describes a test procedure for the measurement of pull-off forces between magnetic head slider and a disc.

Instrumentation: UMT-series Micro-Tribometer provides precision measurements of forces and displacements, simultaneously in all three directions. It can accommodate specimens of a wide variety of shapes and dimensions.

Experimental procedure: Figure 1 shows the schematic of the pull-off setup. 

Fig. 1. Schematic of the Pull-off test setup

A magnetic disc is positioned on a horizontal stage. A suspension with magnetic head is assembled on the carriage and is brought onto the disc surface by liner vertical motion system. A load sensor provides feedback to the closed-loop vertical motion control, which controls the load. The sensor accurately measures both vertical compressive and tensile loads, as well as horizontal friction forces.

The head rests on the disk surface for 10 minutes under the constant vertical load of 7 cN. 

After rest, the carriage starts lifting up with the vertical speed 0.005 mm/sec. Pull-off force F is determined as the maximum force before the slider is pulled off the disk surface. Figure 2 presents the data for a pull-off test of a so-called 30% head slider from a laser-textured carbon overcoated disk; the pull-off force was found to be 38 cN. 

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Fig. 2. Pull-off force in a head-disc interface

The Micro-Tribometer allows to investigate effects of vertical speed, time of stationary contact (rest), head and suspension design, head and disc materials, lubricant, etc. on vertical stiction (adhesion).