My understanding of the term 'glass transition' is, that FR4 behaves like
glass up to a certain temperature. Maximum usable temperature is 10deg C to
15deg C below Tg, as I have learned the costly way.
Volkmar
Best regards
Volkmar Huss, C.I.D.
> -----Original Message-----
> From: Brooks,Bill [SMTP:[log in to unmask]]
> Sent: Friday, April 22, 2005 8:22 PM
> To: [log in to unmask]
> Subject: Re: [DC] IPC-4101
>
> Actually Chris, the Glass does not melt.
>
> I'm not sure why they refer to the rapid expansion of the epoxy/glass
> board
> in the z-axis as the Tg or 'glass transition' phase of its properties but
> they do... Maybe someone more into the properties of the materials can
> expand on that one for me... I believe the more epoxy there is the more
> it
> expands... the glass is fairly stable material and comes in different
> diameters of the filaments in the weave of the fiberglass cloth. Varying
> from very coarse to very fine... The resin content affects the Tg, to the
> best of my knowledge, as well as the DK of the material too.
>
>
> I agree with you that for a designer the 'maximum useable temperature' is
> really what we want to know... A nice chart indicating that in plain
> language would make it simpler for most of us. In the mean time, good
> design practice tells me 'pay attention to the lowest number' and the
> design
> should be okay.
>
> Great thoughts Chris, maybe they will stir some activity related to this
> Tg
> specification issue and how it is published.
>
> Best regards,
>
>
>
> 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 10:54 AM
> To: (Designers Council Forum); Brooks,Bill
> Subject: IPC-4101
>
>
> Hi-
>
> In IPC-4101, why is a temperature range specified rather than a rated max,
> like components? Is melting the glass ever a desirable thing? If not,
> wouldn't it be less confusing to just specify IPC-4101/21 at 110C MIN? Who
> needs a guarantee that the glass will melt at 150C? In bare board fab, do
> you sometimes need to T the G?
>
> If that's a stupid question, tell me why. Good designers aren't afraid to
> be slapped with the facts, and neither am I ;-/
>
> I see the range and think I can get that material rated at 110C or 150C
> and
> maybe some points between.
>
> -Chris
> <NITPICK>
> P.S. If Tg could be as low as 110C, a fair-to-middlin' designer would
> make
> sure the board never SEES 110C...
> </NITPICK>
>
>
>
>
>
> "Brooks,Bill"
>
> <[log in to unmask]> To:
> [log in to unmask]
> Sent by: DesignerCouncil cc:
>
> <[log in to unmask]> Subject: Re:
> [DC] High Temperature Environment
>
>
> 04/22/2005 12:02 PM
>
> Please respond to
>
> "(Designers Council
>
> Forum)"; Please respond to
>
> "Brooks,Bill"
>
>
>
>
>
>
>
>
>
>
>
> 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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