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Glossary of Disk / Substrate Industry Terms

  • Disk Drive and Slider Arm assembly

The purpose of this glossary is to create common usage and understanding among disk and substrate uses and interested groups.   This glossary is also useful for training persons entering the disk drive industry.
The scope of this glossary is limited to disks and substrates.
IDEMA D2-91, Specification for Substrates for Rigid Disks.
1. ADHERED GLASS - Small transparent glass particles adhered or fused to the glass surface.
2. AIRLINE (Glass) - An elongated gaseous inclusion.
3. ALLOY - Name given to metal mixtures composed of several elements. Aluminum alloys use a system of four digits to identify particular compositions, the first digit indicates the alloy group, 5xxx indicates a magnesium bearing aluminum alloy, 6xxx indicates a magnesium and silicon aluminum alloy.
4. AMP-TURNS - Used in the interface process of controlling the coupling of magnetic field to or from a magnetic layer relative to the recording head signal output.
5. BLISTER (Glass) - A bubble in glass greater than .030" in length. A gaseous inclusion. May be open at surface.
6. BOW - The measure of curvature relative to a perfectly flat disk. MILS or MICROINCHES per linear distance are its units.
7. BOW (Glass) - A term more properly applied to glass tubing; for sheet glass see Warp.
8. BREAK-THROUGH - The physical void of material between two holes or adjacent voids.
9. CAMBER (Glass) - A slight convex curve of a surface; for sheet glass see Warp.
10. CHECK - A fissure in the glass which does not extend through the thickness of the material.
11. CHIP - Region of material missing from the surface or edge of a substrate material. This defect does not pass through both sides. See — INDENT.
12. CHIP (Glass) - A depression or irregularity on the surface caused by the unintentional removal of glass (as in flaking).
13. CIRCUMFERENTIAL - Points of reference which are equidistant from an axis of rotation.
14. CIRCUMFERENTIAL LINES - Visual circular lines (scratches) on the surface of the substrate after the final finish.
15. CLEANLINESS - A term used to describe the degree of particulate contamination or foreign material allowable on a part or laboratory environment.
16. COMET - The visual pattern created by thickness variations in an epoxy media spun on a disk.
This pattern occurs if the surface is not perfectly smooth or if a particle of solid material rest on the surface during spinning.
17. CONCAVE - Surface area which has a depression relative to the immediate surrounding area. (ID depressed with respect to OD).
18. CONVEX - The opposite of concave, having a protrusion relative to the surrounding area. (ID protruding with respect to OD).
19. CORD - A narrow inhomogeneous band of glass having a different refractive index than the surrounding glass.
20. CORROSION - Destructive chemical deterioration of a metal by reaction with its environment. Corrosion in disks occurs at thin film interfaces (substrate to thin film, thin film to thin film or thin film to environment).
21. CRACK - A fissure in the glass extending through both surfaces and body of the material.
22. CRUSH (Glass) - A lightly pitted area resulting in a gray appearance, usually the result of the abrasive action of a glass chip between two sheets of glass.
23. CUT-OFF - The term given the length of a sinewave whose amplitude is transmitted with 75% of its actual height. The selection of a cut-off length determines which feature of the profile is regarded as roughness and therefore constitutes thoroughness profile.
24. DEFECT, PROTRUDING - Asperities, particles, contamination, or foreign debris above the surface of substrates.
25. DEVITRIFICATION - The process by which glass returns to its non-glassy state. The glass is said to have “devitrified.”
26. DIAMOND TURNED - Micromachining operation using a diamond cutting tool to obtain a microscopic finish.
27. DIGS - Pulled out surface micro-structure caused by burnishing, polishing or other process machining.
28. DINGS - Marks left on disk surface due to physical mishandling.
29. DIRT (Glass) - Foreign material which contaminates the glass surface.
30. DOUBLE DISK GRIND - The process of surface polishing a substrate using two polishing wheels counter rotating.
31. DRAW LINES - A surface irregularity or waviness caused during glass fabrication.
32. DUB-OFF - A lesser degree of chamfer, slight rounding of the intersection of two surfaces.
33. EDGE-BREAK - The physical deformation which occurs at the edge area when material is cut, sheered and punched. The edge usually has a raised deformation.
34. ELECTROLYTE - A solution that will conduct an electric current. Chemically a compound whose water solution will conduct an electric current. Acids, bases, and salts are electrolytes.
35. ELECTROLYTIC - Chemical action of or having to do with an electrolyte.
36. EPOXY COATING - Pertains to the magnetic layer spun on top of a substrate. Epoxy coating describes the polymetric material in which the magnetic particles and alumina are suspended.
37. FLARE (Glass) - Cutting fin or projection on a score cut edge.
38. FLAT BAKE - The process of clamping a stack of substrates between two massive rigid plates under extreme pressure then subjecting the assembly to an elevated temperature. The assembly is allowed to cool slowly to stress relieve the disks and flatten them after rough machining.
39. FLY-CUT - Machinist term of process used to cut the substrate blanks to rough dimension.
40. GASEOUS INCLUSION - Void in the body of the glass as a result air or reaction gases from the melt becoming trapped in the solidifying glass.
41. GAUSS - The unit of magnetic induction or magnetic flux density in the SI system — equivalent to one maxwell per square centimeter. NOTE: The earth’s magnetic field is approximately 0.3 to 0.5 gauss
42. HARDNESS - The resistance to plastic deformation of a locally stressed substance. The hardness of metals is called out as BRINELL or a ROCKWELL hardness number representing different measurement methods by permanent impression in the material made by an indenter.   Higher numbers represent higher resistance of the surface to indentation by inference to wear or abrasion.
43. HAZE - The