In a message dated 05/31/2000 11:46:36 AM Central Daylight Time,
[log in to unmask] writes:

<< Good Morning TechNet,

 I have a couple of questions on a couple of SMT parts.

 The First part is an aluminum electrolytic chip cap(wet cap)(SMT D Case).
 Does anyone know of any problems with these if used on the top side of the
 board?

 The Second part is a ceramic chip cap in a 1812 package. Again this part is
 on the top side of the board. Is the size of the part and the thermal
 coefficient difference great enough to cause solder joint cracking?

 Thanks in advance to all you SMT component experts!

 Ken Bloomquist >>

Hi Ken!

Having both these components on the topside of the board is recommended. The
Electrolytic can't be wave soldered in the first place anyway, but it is
possible to wave solder the 1812 ceramic cap...not recommended, but possible.
I've built many assemblies on FR4 PCB's with both these type parts, and
really haven't had many issues. But I know with the larger electrolytics I've
had to get special feeders that had a deeper channel because of the height.
I've also had people mistake the colored band (that's usually painted on the
top of the part) as meaning the same thing as the band on a regular tantalum
capacitor, which it AIN'T. The band on tantalums is the positive end but on a
electrolytic it's the negative end.

1812's are more prone to fractures. It's recommended to keep them away from
board edges, tooling holes, test points, etc....anywhere there's going to be
a risk from board flexure.

Here's a web link to a online book about electrolytic capacitors that has
more information than you ever wanted to know about electrolytic capacitors:

http://www.faradnet.com/deeley/book_toc.htm#toc

-Steve Gregory-

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