Information

MLCC Arc Prevention – for Hi-Pot Testing
Typical Applications for telecommunication devices(IEEE802.3) in LAN interface, Ballast…
Due to the open and porous nature of
the surface of the X7R dielectric,
moisture and/or dirt which will have a
lower resistance than the dielectric
grains, can become entrapped in the
surface. Dirt can also include any flux
residues as a result of the soldering
process. This dirt/flux as well as
becoming entrapped into the surface
will, in itself, attract additional moisture
onto the surface thus reducing the
surface resistance and the voltage at
which arcing occurs. Surface arcing or
flashover at worst can cause equipment
failure during isolation testing and, in
addition, will leave a carbon track on the
surface which can lead to eventual
failure of the capacitor.
Typical surface arcing on X7R MLCC is from termination-to-termination
(shown in polarized light)
NP0 & X7R Material Characteristic Comparison
Item
Item
NP0
NP0
X7R
X7R
Dielectric Constant
Dielectric Constant
30 ~ 100
30 ~ 100
2000 ~ 4000
2000 ~ 4000
I. Resistance
I. Resistance
>10
>10
13
13
Ω
ΩΩ
Ω
Ω
ΩΩ
Ω
>10
>10
11
11
Ω
ΩΩ
Ω
Ω
ΩΩ
Ω
B.D. Voltage
B.D. Voltage
70~80
70~80
Vdc
Vdc
/um
/um
40~50
40~50
Vdc
Vdc
/um
/um
Grain Size
Grain Size
< 500nm
< 500nm
900nm ~ 1500nm
900nm ~ 1500nm
Grain Size
Grain Size
(x8000)
(x8000)
Porosity
Porosity
(x1000)
(x1000)
• The different grain shape and size will lead to
different grain density after sintering.
• The grain size of NP0 dielectric is smaller than
that of X7R resulting a denser and less porous
structure.
•Surface porosity will trap dirt, flux and moisture
causing the surface resistance to dramatically
decrease.
• Low surface resistance will cause the arcing
voltage to reduce, possibly leading to failure of the
capacitor or equipment during isolation testing.
•Using the Holy Stone Arc Prevention coating
effectively makes the surface of X7R dielectric
similar to that of NP0.
Arc Prevention
A
rc Prevention
Passed IEEE 802.3
150
0VAC or 2250VDC
Increases
voltage at
which arcing
occurrs
Coated Products for Surface Arc Prevention
Holy Stone
- 60 -
Holy Stone h
as developed an Arc Prevention
coating process that coats the surface of the
dielectric without encroaching onto the termination
material. This coating makes the surface of the
dielectric non porous and prevents moisture and dirt
becoming trapped thus reducing the surface
resistance and the arcing voltage of the capacitor. It
has been shown that the arcing voltage can be
increased by up to 65% on soldered parts by using
the Holy Stone Arc Prevention Coating.