Re: Capacitors Question?

Chuck Harris
 

All SMD aluminum electrolytics are made that way. It keeps
the rubber seal's as far as possible from the oven heat. The
plastic lead forming boots are made from a high temperature
withstanding, thermally insulating plastic material.

They even keep the aluminum cans bare, and mill colored
(white) to take advantage of aluminum's high reflectivity
at IR (heat) wavelengths... they reflect most of the heat
from the oven rather than get hot... Just like you do by
putting aluminum foil strips around a pie crust's edge
to prevent burning...but this only works so well. Keep
the heat on too long, or too hot, and it will cause a
big problem.

What kills most SMD using manufacturers is their desire to
do all of the soldering in the ovens. Even big stuff like
CAT5, USB, DB15's, HDMI, and power connectors.

They get themselves in a bind where if they want the big
stuff to get hot enough to make a good solder joint, they
have to let the little stuff, like SMD electrolytics get
too hot. They get away with it most of the time, but the
parts are damaged, and start to leak during the product's
lifetime.

The proper way to do oven soldering of large parts is to
either do them first, before installing the smaller more
thermally sensitive parts, or do them last, and put an
aluminum heat reflecting cover over the sensitive parts
before you do the oven pass for the big stuff...

But, this amounts to extra hand work, and extra passes
through the oven, and they want things to be cheap.

In my experience, the corrosive electrolyte formulations
do not end up in SMD electrolytic capacitors. Because of
all of the extra steps required to add the plastic cup
and lead forming hardware, it just isn't worth it to
shave a few microcents off by using fake electrolyte.
Even the small size of the aluminum cans puts them out
of reach of the scam artists...

The same is not true of radial leaded electrolytic caps.
They can be built on manufacturing machines that were made
in the 1960's. There is a lot of cheap surplus component
manufacturing equipment out there to enable cheating in
radial leaded capacitor manufacture.

The companies that get fooled are buying parts that are
odd name brands, and much, much cheaper than the usual
name brands. They know, they just don't care.

-Chuck Harris

Dave Casey wrote:
What about the many SMD electrolytics which are just radial electrolytics
anchored in a base with their leads bent over and cut really short?

Dave Casey

On Tue, Mar 6, 2018 at 3:25 PM, Chuck Harris <cfharris@...> wrote:

Not to put too fine a point on my nitpicking, but
AFAIK, the capacitor plague applied only to radial
leaded, low ESR electrolytic capacitors, not to
SMD electrolytic capacitors.
...

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