A technical review of RuO₂ conductive phase materials, Al₂O₃ ceramic substrates, and the resulting performance advantages.

Abstract

HVC's HVR series uses RuO₂ conductive material and 96% Al₂O₃ ceramic substrate to achieve stable high-voltage performance through screen printing and high-temperature sintering. Test data shows TCR of ±15 ppm/°C and VCR of 0.1 ppm/V, making the series a practical alternative to OHMITE thick film resistors.

1. Introduction

High-voltage thick film resistors are widely used in power electronics, medical equipment, and precision instrumentation. As equipment becomes smaller and more demanding, designers need better temperature stability, voltage linearity, and long-term reliability than many traditional options can provide.

This article explains how HVC's HVR series addresses those needs and serves as a compatible alternative to OHMITE products.

2. Materials System

2.1 Conductive Phase Material: RuO₂-based Thick Film Resistor Paste

RuO₂ (ruthenium dioxide) is the core conductive phase in the resistor paste and offers the following benefits:

• Resistivity: Approximately 35 μΩ·cm at room temperature, adjustable through particle size and glass content.
• Thermal Stability: Stable at 850°C sintering temperature without phase transformation.
• Chemical Stability: Resistant to acid and alkali corrosion in harsh environments.
• Conduction Mechanism: Metallic conduction with controllable temperature coefficient.

The resistance of a RuO₂-based thick film resistor can be approximated by:

R = ρ × (L/W) × (1/t)

Here, ρ is sheet resistance (Ω/□), L is resistor length, W is width, and t is film thickness. With laser trimming, ±1% resistance tolerance can be achieved.

2.2 Substrate Material: 96% Al₂O₃ Ceramic

96% alumina ceramic is the standard substrate for this resistor class because it combines electrical insulation with stable mechanical performance.

• Dielectric Constant: εr ≈ 9.0 at 1 MHz
• Dielectric Loss: Low tan δ at 1 MHz.

3. Manufacturing Process

3.1 Screen Printing Technology

RuO₂ paste is printed onto the Al₂O₃ substrate using a 200-325 mesh stainless steel screen.

Typical process parameters:

• Squeegee pressure: 20-30 N
• Printing speed: 50-100 mm/s
• Snap-off distance: 1-2 mm
• Wet film thickness: 25-50 μm

3.2 Sintering Process

Typical sintering profile:

• Heating stage: Room temperature → 850°C at approximately 50°C/min
• Holding stage: 850°C for 60-90 minutes
• Cooling stage: Natural cooling to room temperature

During sintering, the glass phase melts and encapsulates the RuO₂ particles, forming a stable three-dimensional conductive network. Final film thickness is typically 40-50% of the wet film thickness.

4. Electrical Performance Testing

4.1 Temperature Coefficient of Resistance (TCR) Testing

TCR is the relative change in resistance with temperature:

TCR = (R₂ - R₁) / [R₁ × (T₂ - T₁)] × 10⁶ (ppm/°C)

Test range: -55°C to +155°C. HVC HVR measured ±15 ppm/°C, better than the common ±50 ppm/°C industry level.

4.2 Voltage Coefficient of Resistance (VCR) Testing

VCR is the relative change in resistance with applied voltage:

VCR = (ΔR/R) / V × 10⁶ (ppm/V)

Measured VCR is 0.1 ppm/V, showing strong resistance stability under high-voltage loading.

4.3 Long-term Stability Testing

HVC performed a 1000-hour load test according to MIL-STD-202 at rated power and +70°C ambient temperature.

Test results:

• Resistance drift: < ±0.5%
• Visual inspection: No cracks, bubbles, or discoloration
• Voltage withstand test: Passed 1.5× rated voltage

5. Performance Comparison with OHMITE Products

The key benchmark comparison between HVC HVR and OHMITE Slim-Mox is summarized below.

6. Conclusion

HVC's HVR series delivers strong temperature stability and voltage linearity through optimized RuO₂ paste formulation and controlled sintering. It matches or exceeds key OHMITE benchmarks while also offering shorter lead times and flexible customization.

7. OHMITE-to-HVC Model Cross-Reference

The following tables summarize representative HVC replacement options for major OHMITE thick film resistor families.

A. Slim-Mox Series (03)

B. Slim-Mox Series (02)

C. Ultra-Mox Series

D. ARC2 Series

E. MOX Series

Appendix A: OHMITE Standard Models (100+)

Representative OHMITE high-voltage thick film resistor models are listed below for reference.

Appendix B: HVC Model Naming Convention

The naming logic below helps map OHMITE model families to HVC equivalents more clearly.

HVR-[Series]-[Size]-[Resistance]-[Tolerance]-[Power]-[Voltage]

Example: SLIM-MOX10203 → HVR-GXP-102-1M-F-1W-5kV

Appendix C: OHMITE Slim-Mox Models

Representative OHMITE Slim-Mox and Ultra-Mox catalog models are listed below.

Contact & Technical Support

If you need an alternative to OHMITE Slim-Mox, Ultra-Mox, or related series, HVC's engineering team can support model selection and customization.

HVC provides free sample evaluation and manufacturer-level technical support for qualified replacement projects.

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Disclaimer: Parameters herein are for reference only; refer to the latest datasheet and any mutually agreed technical specifications for binding values.