How compact discs are made
Each pit on a compact disc is about 100 nanometers deep, and a laser reads them from underneath.
- stations
- 6
- things upstream
- 60
- raw sources
- 20
- steps from the ground
- 8
The short version
A compact disc is a disc of clear polycarbonate plastic molded with a spiral track of tiny pits. A thin layer of aluminum is deposited over the pits in a vacuum to make them reflective, then a layer of lacquer protects the metal. The label is printed on top. A laser reads the pits from underneath.
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Master the pit pattern
The audio data is encoded and written as a spiral of tiny pits onto a master disc. The master is used to make a metal stamper, the negative of the pit pattern.
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Mold the plastic disc
Molten polycarbonate is injected against the stamper in a clean mold. The plastic hardens in seconds with the pattern of pits pressed into one face, so the stamper can be used again for the next disc.
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Metalize the surface
A thin layer of aluminum, or rarely gold, is deposited over the pits in a vacuum chamber. The metal fills the surface so that light is reflected differently from pits and flat areas.
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Spin on the lacquer
The disc is spun to spread a thin film of lacquer over the metal. The lacquer protects the aluminum, since the reflective layer is on the label side and is only a hair from the surface.
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Print the label
The label is printed on the lacquer by screen or offset printing. The disc is checked on a player that reads the track as it spins.
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Package the disc
Discs are tested, then dropped into plastic cases with printed inserts and wrapped.
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Worth repeating
- Each pit on a CD is about 100 nm deep and 500 nm wide.
- A CD player reads the track with a 780 nm infrared laser focused through the plastic from underneath.
Back to the ground
Follow every input upstream and compact disc starts as these 20 raw sources.
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Sources
Cite this page: "How compact discs are made." Assembly Line, 2026-11-03. https://assemblyline.org/make/compact-disc