Hi
Dan,
I've seen this same
problem many years ago from other manufacturers of ceramic capacitors as
well. The bottom line is that these big ceramics are not great in
low-noise analog filter circuits. Since this application only represents a
small percentage of the total use of these components, the manufacturers don't
consistently check for this problem. This may not be what you want to
hear, but the only long-term solution I found was going to film caps for this
application.
Regards,
Seth Goodman
Goodman Associates,
LLC
tel 608.833.9933
fax 608.833.9966
Fellow TNers,
Wanted to see if any one else has
experienced this.
We are using a 1uF
X7R 1206 of this particular cap and using the recommended reflow profile for
the solder paste. The test is to ground one end of the cap and measure the
noise level from the other end through a 330kohm impedance circuit. What we
have seen is that after the PCB is reflowed and tested, the noise level is at
some specific amplitude. We can then re-solder the cap by hand and the noise
level will drop an order of magnitude. The reflow soldering appears to be good
- nice fillet, wetting, structurally sound. We were speculating if perhaps the
termination ends of the cap were disconnecting internally during the reflow
(CTE problems) and that the hand soldering is somehow connecting it back. I
have noticed that the recommended reflow profile of the cap specifies a much
shorter liquidous time than what the paste profile requires. This could also
be the problem. I have not yet been able to speak with the component
manufacture to get ! their opinion.
Sorry for the lengthy message and thanks for your feedback,
Danny