MLCC Arc Prevention – Hi-Pot Testing
When performing Hi-pot tests on ceramic capacitors, various factors (temperature, moisture, relative pressure, termination creepage distance, and PCB layout…etc.), can affect surface arcing potential. This surface arcing becomes more of a factor in high dielectric constant materials such as X7R and Y5V Holy Stone has developed an arc prevention solution for MLCC products.
Surface arcing phenomenon
NPO & X7R Material Content & Characteristic Comparison
- Different grain sizes result in differing grain densities after the sintering process.
- Because NPO grain sizes are thinner & longer, than X7R, the resulting structure is tighter
and more dense, especially due to porosity differences between NPO & X7R.
- Greater surface porosity will entrap more dust and moisture.
- When voltage, specifically high voltage, is applied, the surface porosity will readily attract electrical charge. When the applied voltage is increased and reaches the inception voltage, electrical arcing will occur.
Creepage distance vs. Arc effect
Recommend Land Requirement
The metal-to-metal distance could affect the arcing phenomenon. Therefore, the above land layout is recommended to minimize arcing potential in high voltage capacitors.
Coating solution for surface arcing prevention
To prevent surface arcing due to surface porosity in X7R capacitors, an insulated gel (high insulation material) process is introduced to provide a smooth and less porous surface. The following tests describe the difference between coated & non-coated products.
Surface Handling Comparison
High Voltage Testing Comparison
P/N: C1808X102K302T v.s. C1808X102K302TO (Coated Product)
- The coating will “fill-in” the X7R surface porosity and provide a smooth surface that minimizes the arcing potential.
- The Hi-pot endurance level will increase ~ 1000Vdc after coating for individual and on-board hi-pot test.
The hi-pot test voltage will be increased by 1000Vdc for X7R coated products. Due to the inherent reduced porosity of NPO capacitors, the coating process is typically not required. However, Holy Stone can apply the same coating solution for both NPO and X7R capacitors.