In the manufacturing process of precision discs, precise control of track spacing is a core element ensuring stable data read/write operations. Its achievement relies on precise coordination throughout the entire process, from master disc preparation to mass replication. The master disc preparation stage requires the construction of a high-precision track template using lithography and photolithography. Lithography uses a photomask to transfer a pattern to a photoresist layer, which, after development, forms a microstructure matching the target track spacing. Photolithography selectively etches areas not covered by the photoresist using a high-energy light source (such as synchrotron X-rays or alternative sources), forming nanoscale trenches with aspect ratios hundreds of times. During this process, the pattern accuracy of the photomask, the resolution of the photoresist material, and the stability of the etching parameters collectively determine the initial accuracy of the master disc's track spacing. Any minute deviation will be amplified to the final product during replication.
The master disc cleaning and installation stages must eliminate surface impurities and mechanical stress to prevent track spacing distortion due to contamination or deformation. The cleaning process uses an ultra-clean environment and precision chemical reagents to ensure the master disc surface roughness is below the nanometer level. During installation, a laser positioning system achieves micrometer-level alignment to prevent track distortion caused by installation deviations. For example, the coaxiality error between the master die and the casting equipment must be controlled within an extremely small range; otherwise, the track spacing will exhibit periodic fluctuations during the replication process.
The casting and demolding processes utilize electroforming technology to achieve high-precision transfer of the master die pattern. Metal ions in the electroforming solution are directionally deposited onto the surface of the master die under the influence of an electric field, forming a metal mold complementary to the grooves of the master die. During this process, parameters such as the composition, temperature, and current density of the electroforming solution must be precisely controlled to avoid uneven deposition layer thickness or internal stress accumulation. Non-contact separation technology is used during demolding to prevent friction between the mold and the master die, which could damage the track edges and affect spacing accuracy. For example, one company significantly improved the consistency of track spacing by optimizing the electroforming solution formula and reducing the surface roughness of the mold.
The casting inspection stage uses high-resolution inspection equipment to perform a full-size scan of the track spacing. Laser interferometers and atomic force microscopes can achieve nanometer-level measurement accuracy. By comparing the deviation between the actual spacing and the design value, qualified molds are selected. For example, one inspection standard requires that the track spacing fluctuation range be limited to an extremely small tolerance; exceeding this range will cause laser head tracking failure. Furthermore, dynamic testing simulates actual read/write scenarios to verify the stability of the track spacing under high-speed rotation, ensuring that the data error rate during batch replication is below the standard.
In the batch replication stage, the injection molding process achieves large-scale reproduction of the track spacing through precise mold and process parameter control. Parameters such as mold temperature, injection pressure, and cooling rate must be matched with material properties to prevent track deformation due to uneven shrinkage. For example, one company uses a gradient curing process, extending the UV curing time to increase the hardness of the protective layer and reduce track deformation during high-speed rotation. Simultaneously, the injection molding machine's high-precision positioning system ensures the alignment accuracy of the mold cavity during each injection, avoiding the cumulative impact of repeated positioning errors on the track spacing.
The quality inspection system ensures track spacing accuracy through multi-dimensional parameter monitoring. A laser power meter measures signal amplitude fluctuations, requiring them to be controlled within an extremely small range to prevent read/write errors due to uneven energy; a metallographic microscope detects track texture depth errors, ensuring they are less than the standard value to avoid crosstalk during laser head jumps. Furthermore, accelerated aging tests simulate extreme environments to verify the stability of track spacing during long-term use. For example, damp heat cycling tests require that the light attenuation rate of the reflective layer of the optical disc does not exceed a certain percentage of its initial value under high temperature and humidity conditions, preventing spacing changes due to material aging.
The precision control of track spacing in precision discs is the result of the cross-integration of materials science, optical engineering, and precision manufacturing. From the nanoscale pattern construction in master disc preparation to the optimization of process parameters for batch replication, and then to multi-dimensional verification of quality inspection, each step must be standardized to micrometer or even nanometer precision. As optical storage technology develops towards higher densities, the precision control of track spacing will face even more severe challenges, requiring continuous innovation in testing technologies and processes to meet the extreme demands of future data storage for reliability and stability.
