CTI Comparison in PCB Materials: Guide to Safer & High-Voltage Boards

1. What is CTI?
2. CTI Classification
3. CTI Testing (IEC 60112)
4. CTI Comparison: Material Performance
5. Why CTI Matters in PCB Design
6. How to Select the Right CTI Material
7. Conclusion
8. FAQs

1. Introduction to CTI (Comparative Tracking Index)

The Comparative Tracking Index (CTI) is a critical property of PCB (Printed Circuit Board) materials, defining their resistance to electrical tracking. Electrical tracking refers to the formation of conductive paths due to prolonged exposure to electrical stress and environmental contaminants, which can lead to short circuits, material degradation, and electrical failure.

CTI is measured in volts (V) and determines the insulation performance of PCB substrates. A higher CTI value means greater resistance to electrical tracking, enhancing safety, durability, and reliability in high-voltage and high-humidity environments.

This article explores CTI classifications, testing methods, material comparisons, and industry applications to help PCB designers and PCB suppliers choose the right material for their projects.

---

2. CTI Classification and Standards

The CTI value of PCB materials is classified according to the IEC 60112 standard, which measures a material’s ability to withstand electrical tracking. The classification levels are as follows:

Key Insights:

CTI ≥ 600V (Class 0) is ideal for high-voltage applications such as medical devices, aerospace electronics, and industrial control systems.

CTI 400V – 599V (Class 1) is commonly used in automotive and industrial PCBs, where exposure to harsh conditions is frequent.

CTI 250V – 399V (Class 2) is suitable for standard consumer electronics, where lower electrical stress is expected.

CTI below 250V can lead to premature electrical failure and should be avoided for high-reliability circuits.

---

3. CTI Testing Method: IEC 60112 Standard

The Comparative Tracking Index (CTI) test follows the IEC 60112 standard, which determines the breakdown voltage of PCB base materials when exposed to moisture and contaminants.

Testing Process:

1. Sample Preparation: A PCB material sample is prepared according to IEC 60112 specifications.

2.Electrode Placement: Two electrodes are placed on the material, spaced 4 mm apart.

3.Contaminant Application: A conductive contaminant (usually ammonium chloride solution) is applied between the electrodes.

4.Voltage Increment: A step voltage increase is applied to the material until electrical tracking occurs.

5.Failure Identification: The highest voltage at which the material resists tracking is recorded as the CTI value.

This method accurately determines the tracking resistance of different PCB base materials under real-world conditions, ensuring safety and reliability.

---

4. CTI Comparison: PCB Material Analysis

The CTI value can vary significantly depending on the type of PCB material used. Below is a comparison of common PCB substrate materials:

Observations:

FR4 materials show a wide CTI range (175V – 600V), making high-CTI FR4 the preferred choice for high-voltage PCBs.

Polyimide materials have a lower CTI value compared to FR4 but excel in high-temperature environments.

Ceramic PCBs offer the highest CTI rating (≥ 600V), making them ideal for power electronics and RF circuits.

CEM-1/CEM-3 materials have lower CTI values, making them less suited for high-reliability applications.

---

5. Why is CTI Important in PCB Design?

CTI is crucial in high-voltage and high-reliability PCBs for the following reasons:

✅ Prevents Electrical Failure: A high CTI value reduces the risk of short circuits caused by moisture, contamination, and voltage stress.

✅ Enhances PCB Durability: Materials with higher CTI ratings ensure longer lifespan and improved reliability in harsh environments.

✅ Ensures Compliance with Industry Standards: High CTI materials meet IEC, UL, and IPC safety regulations, crucial for automotive, medical, and industrial electronics.

✅ Optimizes PCB Performance in Harsh Conditions: Applications in power electronics, aerospace, and outdoor environments benefit from high CTI materials due to their superior insulation and stability.

---

6. Selecting the Right CTI Material for Your PCB

Choosing the appropriate CTI-rated material depends on the application, voltage requirements, and environmental conditions.

Application	Recommended CTI Material
Consumer Electronics (Smartphones, Laptops)	Standard FR4 (CTI ≥ 250V)
Automotive Electronics (ECU, Sensors, ADAS)	High-CTI FR4 (CTI ≥ 600V)
Medical Devices (MRI, ECG, Implants)	Ceramic PCB (CTI ≥ 600V)
Industrial Control Systems	High-CTI FR4 or Polyimide (CTI ≥ 400V)
Aerospace & Defense	Polyimide PCB (CTI ≥ 400V)
Power Electronics & High-Voltage Circuits	Ceramic or Metal Core PCB (CTI ≥ 600V)

---

7. Conclusion: Why CTI Matters in PCB Manufacturing

CTI plays a critical role in PCB material selection, influencing electrical insulation, durability, and reliability. While standard FR4 is sufficient for low-voltage applications, materials such as high-CTI FR4, ceramic, and polyimide are essential for high-voltage applications in industries like automotive, medical, aerospace, and power electronics.

For high-quality, high-reliability PCB manufacturing, it is essential to choose materials with an appropriate CTI rating to ensure electrical safety, longevity, and optimal performance.

SQPCB offers express PCB solutions featuring high-CTI materials, ensuring compliance with industry standards for automotive, industrial, and power applications. Contact SQPCB for expert PCB manufacturing services tailored to your specific needs.

Frequently Asked Questions (FAQ)

What is the importance of CTI in PCB manufacturing?
CTI helps ensure that a PCB material can withstand electrical tracking, preventing electrical failure and ensuring reliability in harsh conditions.

How is CTI measured in PCB materials?
CTI is measured by applying a voltage across a material and gradually increasing it until electrical tracking occurs. The highest voltage that the material can withstand without tracking defines its CTI value.

What CTI rating is needed for automotive PCBs?
Automotive PCBs typically require high-CTI FR4 materials with a CTI rating of ≥ 600V due to the exposure to harsh environments and high electrical stress.

Can low-CTI materials be used in consumer electronics?
Yes, for consumer electronics where electrical stress is lower, materials with a CTI rating between 250V and 399V, such as standard FR4, are typically used.

What is the best PCB material for high-power applications?
Ceramic PCBs are ideal for high-power applications due to their excellent insulation and thermal properties, with a CTI rating of ≥ 600V.