T
Ted Wilson
A number of you expressed an interest in the outcome of my search for
an alternative to the solid tantalums that we've had so many problems
with, so here is an update as promised.
Whilst MLCCs looked promising at first, their susceptibility to failure
during soldering and under vibration and thermal stress has effectively
excluded them for our application.
I couldn't find polymer tants at a higher working voltage than 25V, so
the choice came down to either solid polymer aluminiums or Multi-Layer
Polymers. Based on data gleaned from the net, I've opted for MPLs,
subject to us being able to procure them to the requisite spec. These
parts claim to have very low esr, formidable ripple-current rating,
'true' voltage rating that doesn't require derating to achieve
reliability and no aging mechanism.
As I stated earlier, the performance of the tantalums in our
application is dominated by their esr limitations, (110m-ohms), and we
can achieve the required performance in our application with a total
capacitance of only 100uF if the esr of the replacements is
sufficiently low. (Quite an interesting calculation involved to derive
that - peak dV/dt ripple doesn't occur at peak current).
Paktron's 10uF/50V CS4 Capsticks have an esr in the low m-ohms at our
operating frequency and occupy slightly less board area than the
tantalums they are to replace, so we will have room for ten of them to
give the required 100uF. (We shall keep some, if not all, of the
ceramics in parallel to handle the higher frequencies - as I have
already said, we have had very little trouble with them). I've been in
touch with Paktron in the States and they are sending some samples.
On a general note, tantalums have been around for decades and have
always been used for supply filtering/decoupling in the military
environment where significant amounts of capacitance is required, so I
find it somewhat surprising that tantalum manufacturers haven't
sorted out the problems with their reliability by now. The problems we
have fallen foul of can't be peculiar to us, so I hope some of these
discussions have been of benefit to others out there.
Once again, thanks to all who contributed.
Regards
Ted Wilson
an alternative to the solid tantalums that we've had so many problems
with, so here is an update as promised.
Whilst MLCCs looked promising at first, their susceptibility to failure
during soldering and under vibration and thermal stress has effectively
excluded them for our application.
I couldn't find polymer tants at a higher working voltage than 25V, so
the choice came down to either solid polymer aluminiums or Multi-Layer
Polymers. Based on data gleaned from the net, I've opted for MPLs,
subject to us being able to procure them to the requisite spec. These
parts claim to have very low esr, formidable ripple-current rating,
'true' voltage rating that doesn't require derating to achieve
reliability and no aging mechanism.
As I stated earlier, the performance of the tantalums in our
application is dominated by their esr limitations, (110m-ohms), and we
can achieve the required performance in our application with a total
capacitance of only 100uF if the esr of the replacements is
sufficiently low. (Quite an interesting calculation involved to derive
that - peak dV/dt ripple doesn't occur at peak current).
Paktron's 10uF/50V CS4 Capsticks have an esr in the low m-ohms at our
operating frequency and occupy slightly less board area than the
tantalums they are to replace, so we will have room for ten of them to
give the required 100uF. (We shall keep some, if not all, of the
ceramics in parallel to handle the higher frequencies - as I have
already said, we have had very little trouble with them). I've been in
touch with Paktron in the States and they are sending some samples.
On a general note, tantalums have been around for decades and have
always been used for supply filtering/decoupling in the military
environment where significant amounts of capacitance is required, so I
find it somewhat surprising that tantalum manufacturers haven't
sorted out the problems with their reliability by now. The problems we
have fallen foul of can't be peculiar to us, so I hope some of these
discussions have been of benefit to others out there.
Once again, thanks to all who contributed.
Regards
Ted Wilson