I must be overlooking something or not understanding the construction of tantalum caps.

I have a 12VDC power supply that plugs into a circuit board. This is a lab grade power supply. I have some filter caps sitting there on the DC side consisting of a 100uF 35V SMT electrolytic "can", a 10uF SMT Tantalum 25V in a 3528-21 package, and a 0.1uF 25V in a 0603 package.

On the other side of the caps is a pretty typical circuit consisting of a LDO 5VDC regulator, a 3.3VDC LDO regulator, and a LPC932 micro.

When I power this up, the 10uF tantalum immediatly "blows up". The o-scope never triggers on anything above 12VDC. So, I think...hmmm, I've got some bad caps. So I order two more sets from two different manufacturers. Try them and the same thing happens.

I double checked to ensure the polarity is correct. It is.

I just happened to have some through hole 10uF 16V "dipped" tantalum's laying around so I put that in it's place. It works fine. If I put nothing in it's place, everything works fine.

So, I feel like I must be violating a design rule. Is there some reason why SMT tantalum's cannot be used in power supply filters?

I know the first question is going to be, why do you even need a filter for a DC lab supply, but the answer is that I am using a noisier DC source. I am just eliminating a ball in the air by using a lab grade DC supply.

Thanks for your help,
Bruce