T
Terry Moreau
Guest
SMD packaged ceramic resonators from ECS are showing up electrically
leaky in from one of the in/out terminals to the central ground
terminal. This is causing a full inventory re-work and even a field
recall of over 1,000 finished assemblies. Serious and expensive
problem to say the least. It's looking like water/solvent has gotten
into a good percentage of these SMD resonators. Specifically its ECS
part#ECS-SR1-4.00 . The electrical leakage appears to be affected by
dc bias voltage (increasing leakage current the longer any DC bias
voltage is applied for, while the leakage reduces almost to nothing if
the DC bias is removed and the part is let to stand for several
hours). Seems to me to behave like a sort of electrolysis type of
conduction.
I'm aksing if anyone has any experience with this problem with anyway,
that they can share.
Best theories so far are:
1. Solder profile is too hot or for too long and ceramic SMD package
seal is compromised. Susequent water wash flux removal is letting
flux laden water into the resonators delicate internals where some
closely spaced electrode metalization path air gaps are being filled
with party conductive ionize solution. The solution evaporates and
super saturates down to a "goo" where it never completely dries out to
a non-conductive state. Compounded by the fact that the resonator is
on a board that gets conformal coated. Trapped moisture is then
sealed in!
3. The water wash cycle is too long and/or the board is not
sufficiently dried and/or gets conformal coated before it's completely
dried. The porosity of the ceramic is enough to let some moisture
into the resonator internals where it straddles electrodes and
provides an electrically leaky conduction path.
2. The solvent in the conformal coating (hexamethyldisiloxane) is
either attacking the ceramic package seal material, or is simply over
time diffusing into the partially porous ceramic package? Again,
collecting/depositing inbetween small spaced internal electrodes and
provide an electrically leaky conductive path.
The resonator is used in a typical +5V CPU oscillator circuit with
about 500K feedback resistor internal to the CPU. Leakage spec for
the part are > 100Meg ohms at 10volts, however I get anywhere from 4K
to 4Meg ohms leakage at 2.5Volts.
I never get the problem on a fresh resonator out of the tape/real
package.
The problem is showing up in about 10% of boards and it may be
anything from days to months of operation before the leakage level is
bad enough that the CPU oscillator dies.
Short term I've halted production and ordered rework of all boards to
switch to a different resonator from a different from a more trusted
manufacturer in the more proven thru-hole package and to be done by
hand so it's outside of oven reflow, water-wash, and conformal coat
process.
Looking for further ideas and info on this type of problem at this
point?
leaky in from one of the in/out terminals to the central ground
terminal. This is causing a full inventory re-work and even a field
recall of over 1,000 finished assemblies. Serious and expensive
problem to say the least. It's looking like water/solvent has gotten
into a good percentage of these SMD resonators. Specifically its ECS
part#ECS-SR1-4.00 . The electrical leakage appears to be affected by
dc bias voltage (increasing leakage current the longer any DC bias
voltage is applied for, while the leakage reduces almost to nothing if
the DC bias is removed and the part is let to stand for several
hours). Seems to me to behave like a sort of electrolysis type of
conduction.
I'm aksing if anyone has any experience with this problem with anyway,
that they can share.
Best theories so far are:
1. Solder profile is too hot or for too long and ceramic SMD package
seal is compromised. Susequent water wash flux removal is letting
flux laden water into the resonators delicate internals where some
closely spaced electrode metalization path air gaps are being filled
with party conductive ionize solution. The solution evaporates and
super saturates down to a "goo" where it never completely dries out to
a non-conductive state. Compounded by the fact that the resonator is
on a board that gets conformal coated. Trapped moisture is then
sealed in!
3. The water wash cycle is too long and/or the board is not
sufficiently dried and/or gets conformal coated before it's completely
dried. The porosity of the ceramic is enough to let some moisture
into the resonator internals where it straddles electrodes and
provides an electrically leaky conduction path.
2. The solvent in the conformal coating (hexamethyldisiloxane) is
either attacking the ceramic package seal material, or is simply over
time diffusing into the partially porous ceramic package? Again,
collecting/depositing inbetween small spaced internal electrodes and
provide an electrically leaky conductive path.
The resonator is used in a typical +5V CPU oscillator circuit with
about 500K feedback resistor internal to the CPU. Leakage spec for
the part are > 100Meg ohms at 10volts, however I get anywhere from 4K
to 4Meg ohms leakage at 2.5Volts.
I never get the problem on a fresh resonator out of the tape/real
package.
The problem is showing up in about 10% of boards and it may be
anything from days to months of operation before the leakage level is
bad enough that the CPU oscillator dies.
Short term I've halted production and ordered rework of all boards to
switch to a different resonator from a different from a more trusted
manufacturer in the more proven thru-hole package and to be done by
hand so it's outside of oven reflow, water-wash, and conformal coat
process.
Looking for further ideas and info on this type of problem at this
point?
about 'ceramic resonators gone electrically leaky?', on