Tom wrote:

>   The "rehealing" feature with electrolytics relates to the working
>electrolyte in that any faults in the oxide layer will be repaired by
>further anodization. This is a factor is the design of the cap.
>
>   "Self-Healing" refers to metallized caps where a partial discharge
>results in a localized failure of the dielectric which burns away the
>metallized electrode effectively isolating the fault.
>

So, it is reasonable to think that a cap *blasted by an ESD bolt*
can possibly "reheal" by reforming its oxide layer, or may
"self-heal" with the charge blasting the electrode away in a local
area, but leaving intact the rest of the cap surface. (I'm not sure
if your reference to "s-h" & metallized caps applies to aluminum
electrolytics).

I got onto this a few years ago, when consulting with a company
that was using 6805 embedded controllers in industrial icemaker
machines. A really bad ESD, EMI, and inductive switching transient
environment. The controllers were constantly latching up (the
orig design had NO protection on the sense lines at all - would you
believe!). The contractor redesigned the controllers by adding
pi-filters to the sense lines, consisting of 10uF/25v alum
electrolytic right on the "external" pin, then 10K resistor, and
finally .1 uF bypass at the uC pin.

We did some inhouse ESD tests using a 5KV Zap gun, and I was
amazed to discover that the little 25v electrolytics weren't
completely blown off the boards. Leakage increased into the
caps temporarily, but this seemed to diminish after a while.
Thus, I got onto the healing bit.

I also discovered that the small lead spacing on the caps acted
as a spark gap, but still the caps must have been getting blasted
pretty good. All in all, pretty amazing.

Thanks,
- Dan Michaels
Oricom Technologies
http://www.sni.net/~oricom