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November 1999

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Subject:
From:
"Wolfe, Robert" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 10 Nov 1999 13:13:38 -0500
Content-Type:
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text/plain (87 lines)
Yes,
Also I did not specify anything to do with enviroment , which Richard Wenda
pointed out and rightly so.
The enviroment the device will be in would most definutitly be a deciding
factor in ceramic part size on FR4
with respect to CTE mismatch.
And yes we have also run a 2225 caps on FR4, but as a general DFM rule we
have 
tried to stick to below 1825 for use on FR4. I believe the 2225 ceramic
package is pushing the CTE missmatch.
The IPC has specs 275 or the new 222X series defineing CTE's of common
materials used in boards, caps etc.
Also I would believe any physics book or college site would have more CTE
values.
Bob Wolfe
Executone


Bob,

what you just said interests me. It's an interesting point of view to match
the components and the PCB like this. Can one find CTE compatibility
criteria and data somewhere on the Web?

We are running 2225caps on FR4 with no problem, never seen cracks.

Regards,  Ioan

> -----Original Message-----
> From: Wolfe, Robert [SMTP:[log in to unmask]]
> Sent: Wednesday, November 10, 1999 12:12 PM
> To:   [log in to unmask]
> Subject:      [TN] 1812's on FR4
> 
> Wanner,
> Case size 1825 and larger should not be used on FR4 due to the CTE
> missmatch
> 
> on a ceramic part that large, however the 1812's should be OK. I would not
> look to the FR4 as 
> the problem but look at the Cap vendor and whether the caps have been on
> the
> shelf too long'and moisture has 
> invaded them. They may need to be pre-backed if the later problem is it.
> Again verify with your cap vendor also.
> Bob Wolfe
> Executone
> 
> 
> Wanner Berndard wrote
>         Von:    Matthew Lamkin
> [SMTP:[log in to unmask]]
>         Gesendet am:    Freitag, 25. Juni 1999 09:26
>         An:     [log in to unmask]
>         Betreff:        Re: [TN] FW: What it would be like living in
> Australia
> 
>         Well I don't know about being a joke, but I've saved it as a handy
>         little utility.
>         By selecting it from my start menu I can now turn a PCB that I am
>         working on upside down to view it from another angle.
> 
>         Something that I have occasionally wanted to do. I can remember
> actually
>         going as far as turning the monitor on its side
>         before, just so that I could view something from a different angle
>         without upsetting everything else in the PCB file.... <g>
> Hi technos, we have some problems with 1812 (and also with 1210)
> capacitors
> on FR4 because cracks at the corner. Is there any size limit for SMT cap's
> on FR4 (may be different classed for different application temperatures)?
> Thanks, Bernhard, Zürich

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