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Understanding the Comparative Tracking Index (CTI) in PCB Design
Release time:
2024-06-15 08:50
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Understanding the Comparative Tracking Index (CTI) in PCB Design
When it comes to PCB manufacturing and design, ensuring safety, reliability, and longevity is paramount. A crucial factor in achieving these aspects is the Comparative Tracking Index (CTI).
What is CTI?
CTI is a critical property for materials used in the electronics industry. It measures the electrical breakdown (tracking) properties of an insulating material used in PCBs. Essentially, CTI quantifies the material's resistance to forming a conductive path on its surface when exposed to high voltages and a contaminated environment.
How is CTI Measured?
The CTI value is evaluated based on a standardized test defined by the IEC 60112. This test involves administering a series of 50 drops of contaminated liquid onto the test material, subjected under progressively increased voltage levels. The CTI value of the material is identified as the maximum voltage at which the material can endure 50 drops without the formation of a conductive path, known as 'tracking', on its surface. Thus, it's worth noting that materials with higher CTI values demonstrate superior electrical insulation performance in resisting electrical breakdown under challenging conditions.
CTI Value and Classification
The CTI value for PCB materials affects their suitability for certain applications, particularly those involving high voltages. Expressed in volts, CTI values categorize materials into different groups:
IEC 60112 Standard Classification:
- Material Group I: CTI ≥ 600V
- Material Group II: 400V ≤ CTI < 600V
- Material Group IIIa : 175V ≤ CTI < 400V
- Material Group IIIb: 100V ≤ CTI < 175V
UL Standard Classification:
- PLC 0: CTI ≥ 600V
- PLC 1: 400V ≤ CTI < 600V
- PLC 2: 250V ≤ CTI < 400V
- PLC 3: 175V ≤ CTI < 250V
- PLC 4: 100V ≤ CTI < 175V
- PLC 5: CTI < 100V
Materials with higher CTI values (600 or more) are considered to have excellent resistance to tracking and are generally suitable for use in high voltage applications. Conversely, materials with low CTI values (less than 100) have poor resistance to tracking and are more prone to electrical failure.
Why is CTI important?
CTI plays a decisive role in determining the minimum distances between conductive parts on a board ( creepage distances) to prevent electrical shorting. A high CTI value allows for shorter distances, potentially leading to a more compact design and better performance in harsh environments.
Applications requiring High CTI
Materials with high CTI values are beneficial in applications where electrical insulation performance is critical. , such as:
- High voltage equipment
- Medical devices
- Automotive electronics
- Aerospace & aviation
- Industrial automation
- Telecommunications hardware
- Lighting application
Conclusion
In the ever-evolving world of electronics, understanding and applying such quality parameters like CTI can be the key differentiator for the success of your product. By leveraging materials with the right CTI values, we can design safer, more reliable, and more efficient electronic products.
Remember, the key to effective and safe PCB design lies in understanding the properties of your materials and how they interact with the intended application of your product.
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