In the manufacturing of feedthrough capacitors—a core component of EMI filters—the selection of ceramic dielectric material is a critical technical decision. This choice directly determines the performance stability and reliability of the filter in complex real-world environments. The fundamental reason is that the capacitance of a ceramic capacitor changes significantly with ambient temperature, applied voltage, and operating frequency. This capacitance instability directly alters the filter’s insertion loss characteristics, particularly affecting its filter cutoff frequency, which can lead to degraded filtering performance at key noise frequencies.

        When selecting a ceramic dielectric, a fundamental and widespread trade-off exists: dielectric constant is typically inversely related to stability. Ceramic materials with a higher dielectric constant can achieve higher capacitance or smaller component size, but their capacitance also varies more drastically with temperature, voltage, and time—meaning they have poorer stability. The specific factors affecting the dielectric constant are temperature, voltage, frequency, and time (aging).

        The manufacturing of LCA® EMI filters primarily utilizes the following three types of ceramic dielectrics:

1. Ultra-Stable Dielectrics (NP0/C0G):These offer near-perfect capacitance temperature characteristics, with a temperature coefficient of ±0 ppm/°C. Their capacitance remains virtually unchanged with temperature, voltage, and time (no aging effect), and they possess extremely low dielectric loss.
2. Stable Dielectrics (X7R):X7R strikes a good balance between dielectric constant and stability. It exhibits a moderate rate of capacitance change, with capacitance varying no more than ±15% over the -55°C to +125°C range. It has moderate sensitivity to voltage and time (it does experience aging).
3. General-Purpose Dielectrics (Y5V/Z5U):These feature a very high dielectric constant (can exceed 15,000), enabling the highest capacitance in a minimal volume. They are suitable only for applications where high capacitance accuracy and stability are not required.

   ——2018.8.3