Appeal No. 2007-1530
Application 10/095,112
Pyzik explains that it is not feasible to make thinner disk substrates from
aluminum:
Aluminum disks (the current technology) begin to warp, sag, flutter,
or resonate during handling and use when the thickness of a 95 mm
O.D. substrate is less than 800 pm [sic, µm] or when the thickness of a
65 mm O.D. substrate is less than 635 µm. A goal of computer
companies to produce substrates having a 65 mm O.D. that are about
381 µm thick and 95 mm O.D. substrates that are about 508 µm thick.
(Col. 1, ll. 34-36).
A hard-disk substrate should have high electrical conductivity in order to
prevent write-through, which occurs when the information being written on one
side of the disk potentially harms or destroys data on the opposite side of the disk
(col. 2, ll. 55-58).
Various alternatives to aluminum have been proposed, including glass and
ceramic materials (col. 1, ll. 57-60). While some of these materials have low
material density, high stiffness, high thermal conductivity, high electrical
conductivity (or, low electrical resistivity, which is the inverse of high
conductivity), and good surface texture for receiving a plated layer or sputtered
magnetic media layer, they are unsuitable because they can break when dropped
(col. 1, l. 60 to col. 2, l. 2). Other materials, including silicon carbide, Canasite (a
partially-crystallized glass or ceramic/glass, available from Corning, Inc., under the
trade name MEMCOR), and alumina ceramic also have been found to be
unsatisfactory in various respects (col. 2, l. 66 to col. 3, l. 19).
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