Coated products for surface arc prevention Technical Note 5 Holy Stone 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. Arc Prevention Passed IEEE 802.3 1500VAC or 2250VDC Typical Applications for telecommunication devices(IEEE802.3) in LAN interface, Ballast… Surface arcing phenomenon - + Electric field flux is generated upon applying voltage to the capacitor as shown in Fig. above Typical surface arcing on MLCC’s between termination-to-termination (show in polarized lighting) NPO & X7R Material Content & Characteristic Comparison Item NPO X7R Dielectric Constant 30 ~ 100 I. Resistance >1013 B.D. Voltage 70~80 Vdc/um 40~50 Vdc/um Grain Size < 500nm 900nm ~ 1500nm Ω 2000 ~ 4000 >1011 Ω Grain Size (x8000) Porosity (x1000) -1- • 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. Coated products for surface arc prevention Holy Stone Creepage distance vs. Arc effect Recommend Land Requirement Capacitor Land C Solder Resistor A B Solder Ball 3.2mm Chip (mm) L W 4.6±0.3 2.0 ±0.2 4.6±0.3 3.2 ±0.2 5.7±0.4 2.0 ±0.2 5.7±0.4 2.0 ±0.3 5.7±0.4 5.0 ±0.4 EIA Code 1808 1812 2208 2211 2220 Residual solder will reduce creepage distance and Insulation resistance. A 3.2~3.6 3.2~3.6 4.0~4.6 4.0~4.6 4.0~4.6 Land (mm) B 1.2~2.4 1.2~2.4 1.2~2.4 1.2~2.4 1.2~2.4 C 1.5~1.8 2.3~3.0 1.5~1.8 2.0~2.6 3.5~4.8 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 Item Before High Voltage Testing Comparison Porosity (x1000) P/N: C1808X102K302T v.s. C1808X102K302TO(Coated Product) High Voltage Test After Appearance by after coated product. Failure Rate (% ) 70 60 50 Notmal Type Coated Product 40 30 20 10 0 100 1000 Voltage (Vdc) 10000 • 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. ♣ -2-