Hi Chris,

I would think that you either specify the material per the IPC spec or you
specify the characteristics you want and let the board shop pick the
material. I'm sure they would prefer the IPC spec to matching the
characteristics, it would make their job easier and less confusing.

So if he says the board will not experience more than a 5 degree rise then
there must not be any hot components on the board or any appreciable current
in the traces...

According to the spec IPC4101/21 is good up to 110 deg C, any higher and
all bets are off. The mix of ratio of glass to resin will give the board
different Tg characteristics, so they give a large range from 110degC to
150degC based upon the material combinations that can fall into this specs
category.

A good design will make sure that the board never sees more than the
110degC... If there are heat generating parts on the surface of the board
then you have to reduce the ambient accordingly so that the surface of the
board never exceeds the minimum Tg of the material. Or you move to a
material with a higher Tg to accommodate the higher temps.

Also a good designer never designs against the minimums or maximums but
gives themselves some margin for tolerances... as I'm sure you already
know... :)

Bill Brooks - KG6VVP
PCB Design Engineer, C.I.D.+, C.I.I.
Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510
_______________________________________
Member of the San Diego Chapter of the IPC Designers Council
Communications Officer, Web Manager
http://dcchapters.ipc.org/SanDiego/
http://pcbwizards.com

-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Friday, April 22, 2005 5:23 AM
To: (Designers Council Forum); Brooks,Bill
Subject: Re: [DC] High Temperature Environment


In this case, Don says he doesn't anticipate even a 5 degree rise above
ambient anywhere...

Is it bad form then to specify IPC-4101/21 with a min Tg of 135C, for
example? I always get hung up on interpreting these spec's. Is any
IPC-4101/21 OK down to 110C, or can you specify where in the range you want
your IPC-4101/21 to fall?

Happy Friday,
-Chris

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