NEW BURNISH HEAD TECHNOLOGY
Original Publication Date: 2004-Jan-16
Included in the Prior Art Database: 2004-Jan-16
Burnish is a necessary but very critical process step used for media finishing technology. Burnish is being used to eliminate contamination as well as tiny asperities on the disk surface of the finished media. Cross over from non-critical to critical burnish is pretty small. Critical (aggressive) burnish does have the high probability to create debris, which could cause later on head fly ability and reliability problems. The burnish head is kind of touching the disk surface. In case of "bad" edges on head level the burnish head also could cause surface damages like scratches etc.. An extended study, see below, has shown, that the edges of the burnish head should be improved and optimized due to 5-waviness and smooth surface roughness requirements. The study also showed, that the modified heads (edge blend) increased Yield by two digits at least.
NEW BURNISH HEAD TECHNOLOGY
The burnish head, having several pads (here 6) on slider ABS side (see picture below), is been tracked across the media surface using low RPM (1000 - 1500 rpm) only. The pads are touching the surface and are supposed to knock off tiny asperities and clean from contamination.
The head does have a regular roll, required due to head/media interface, to prevent from damages during head load/unload.
The burnish head view below shows the 6 pads which are having the media surface contact and are rubbing the surface. In case of sharp edges at the pads, it is obvious, that media surface damages, like scratches etc., can be caused.
The pad shapes themselves (triangle, oval or rectangular) seem to have no impact on the burnish performance.
The study has found, that conventional burnish heads need significant improvement to be able to satisfy finished media surface requirements. One result of the study is, that the conventional burnish heads are to be classified having "bad" sliders. The so called good sliders require a much better quality of edge blending of all 6 pads on the ABS. Also the slider quality has to be improved concerning chips, cracks, protrusion above the ABS and thousands of loose slider-substrate-particles all over the slider and even on the ABS. Sharp edges certainly can cause during surface contact chips, cracks and particles. Therefore focus has to be to improve edge blending, but the head supplier also should improve outgoing quality due to above listed criteria. Edge blending will also reduce protrusion significantly, which improves head/media burnish interface. Basically the pad edges should be changed as shown in the schematic below:
To improve the pad edges specific machining have to be used to realize appropriate blending. In case of the study an ion mill process had been applied to
achieve round edges. Any other type of machining can be used, as long as appropriate edge blending is achieved. The edge scans below show first a so called "bad" head with sharp edges and bad burnish performance. The second scan shows an optimized edge blended pad with perfect shape and burnish performance.
The study has also shown, that the edge rounding should be within a certain range to achieve...