Analysis of Material Selection for High-Voltage Power Supplies in Exposure Machines

The high-voltage power supply is a core component of exposure machines, directly determining the precision of lithography and equipment stability. Material selection, as the foundation of high-voltage power supply design, requires comprehensive consideration of electrical characteristics, thermal management, environmental adaptability, and long-term reliability. This article professionally analyzes the key points of material selection for high-voltage power supplies in exposure machines.
Core Elements of Material Selection
High-voltage power supplies for exposure machines typically need to provide a stable DC output ranging from thousands to tens of thousands of volts, with requirements for low ripple, high precision, and fast response. Material selection must prioritize insulation performance, voltage resistance, thermal stability, and high-frequency characteristics. For instance, insulating materials must meet a dielectric strength of over 30 kV/mm to resist breakdown risks under high-voltage electric fields; semiconductor devices should select wide-bandgap materials (e.g., silicon carbide) to reduce high-frequency switching losses and enhance temperature tolerance.
Semiconductor Materials: Balancing Silicon-Based and Silicon Carbide
Silicon-based diodes (e.g., fast recovery diodes) remain mainstream in industrial frequency scenarios due to mature technology and low cost. However, their reverse recovery time (trr) generally exceeds 1μs, leading to increased switching losses in high-frequency applications. Silicon Carbide (SiC) diodes break through with their wide-bandgap characteristics: reverse recovery charge (Qrr) approaches zero, voltage resistance can reach up to 20kV, and junction temperature tolerance can reach 200°C. In the high-frequency switching power supplies of exposure machines, SiC devices can significantly reduce losses, though their higher forward voltage drop may increase conduction losses. Selection should be based on system frequency: when frequency exceeds 100kHz or ambient temperature is above 150°C, SiC solutions should be prioritized; for industrial frequency or cost-sensitive projects, silicon-based solutions can be retained, but with a 30% voltage redundancy margin.
Packaging Technology and Insulating Materials
Packaging is the first line of defense for the reliability of high-voltage power supplies. It requires balancing the contradictions between insulation, heat dissipation, size, and voltage resistance:
• Ceramic packaging (e.g., alumina or aluminum nitride) is suitable for high-voltage modules due to high thermal conductivity and insulation strength, but requires increased copper pad area to optimize heat dissipation.
• Epoxy resin potting can increase the PCB creepage distance but may aggravate heat accumulation; the multi-layer glass passivation process enhances voltage resistance to 12kV under miniaturization conditions by adding PN junction passivation layers.
• Insulating material selection: Cross-linked polyethylene (XLPE) is the preferred choice for high-voltage cable insulation due to its high dielectric strength (≥30 kV/mm), excellent mechanical strength, and aging resistance. Silicone rubber, while offering higher temperature resistance (up to 230°C), has lower dielectric strength (20-25 kV/mm) and higher cost, making it suitable only for extreme temperature environments.
Thermal Management Materials
Losses in high-voltage power supplies cause temperature rise, affecting performance and lifespan. Thermal management requires focus on:
• Heat dissipation substrates: Aluminum nitride (AlN) ceramic substrates are used, with thermal conductivity up to 170-200 W/mK, much higher than alumina, though at a higher cost.
• Thermal interface materials: High thermal conductivity grease or phase change materials should be selected to ensure efficient heat transfer to heat sinks.
• Three-dimensional thermal simulation: Thermal models must be established during the design phase to ensure junction temperature is controlled below 120°C, as every 10°C increase in temperature may double the reverse leakage current.
System-Level Selection Suggestions
High-voltage power supplies for exposure machines need optimization for specific working conditions:
• Voltage gradient distribution: In multi-stage series structures, the consistency of the reverse leakage current of diodes must be matched. Measurements show that a 1% deviation in leakage current can lead to a voltage distribution offset of >15%, requiring the introduction of voltage equalizing resistors or active balancing circuits.
• Dynamic surge tolerance: Simulating the lamp box start-up scenario, it is necessary to ensure devices can withstand short-term surge currents (e.g., 100A/10ms), with a forward voltage drop drift of less than 5%.
• Environmental adaptability: Exposure machines may operate in high-humidity or contaminated environments, requiring IP67 protection level packaging and validation of insulation degradation through accelerated aging tests (e.g., 1000-hour test at 85°C/85%RH).
Conclusion
Material selection for high-voltage power supplies in exposure machines is a multi-objective optimization process, requiring a balance among material characteristics, packaging technology, thermal management strategies, and cost. With the maturation of wide-bandgap semiconductor technology, silicon carbide devices and high-performance insulating materials (e.g., XLPE) will become key to improving the precision and reliability of exposure machines. In the future, material innovation will focus on higher voltage resistance, lower losses, and better thermal stability to meet the demands of exposure technology towards higher precision.