My fear was that, per what you were saying Bill, I'd have to specify /24 to
guarantee a Tg above 110C. I'm sure /24 costs more than /21.
I just talked to Tom Newton at IPC, and to paraphrase: It's perfectly
acceptable to specify IP-4101/21 with a minimum Tg of 135C (you should also
specify that the Tg is measured in the same way).
So... if you want FR4 with a Tg above 110C but below 150C, you don't have
to specify /24 to be sure you get it. You can further refine your call-out
of /21 by adding a more specific Tg requirement. A good designer saves
money when he can.....
So, I can rest this weekend....
"Brooks,Bill"
<[log in to unmask]> To: [log in to unmask]
Sent by: DesignerCouncil cc:
<[log in to unmask]> Subject: Re: [DC] IPC-4101
04/22/2005 03:55 PM
Please respond to
"(Designers Council
Forum)"; Please respond to
"Brooks,Bill"
This is a great topic for conversation Chris.. (you made me go look it up).
By definition Tg is "the temperature at which an amorphous polymer or the
amorphous regions in a partially crystalline polymer, changes from being in
a hard and relatively brittle condition to being in a viscous, or rubbery
condition."
The term "glass transisiton" has nothing to do with the glass reinforcement
used in the printed circuit board.
The thermal expansion characteristics of FR4 in the x and y axis is only
16-19 ppm (parts per million) but in the Z-axis it's 50-85 pmm!
The type of resin used has a big affect on the Tg characteristics. Epoxy
E-glass, Multifuntional Epoxy, High Performace Epoxy, Bismalaimide
Triazine/Epoxy, Polyimide, Cyanate Ester... they all have varying
performance characteristics... almost all are better than standard FR4.
Jack's comment about Td is very interesting. I have only heard of this
characteristic with respects to lead free soldering temps and how they
affect the material. There is just so much to learn in this area... I am
still trying to get good data on the issues.
The Tg is really an indicator of via barrel cracking in 2 sided and
multilayer boards and the Td, .... well, I am really still trying to get my
arms around that one. I am not sure what sort of decomposition they are
talking about and what the failure modes are...
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: Chris Ball [mailto:[log in to unmask]]
Sent: Friday, April 22, 2005 12:30 PM
To: [log in to unmask]
Subject: Re: [DC] IPC-4101
Rodney/Bill-
OK, Tg isn't when the glass melts. Thanks. ..."expand on that one for
me"... heh heh...
Exceeding the rated Tg sounds like a thing to avoid rather than achieve. So
again, why the range on the spec if not that you can specify a target
within it?
I've submitted the question to IPC directly and will report back the
official response.
Preparing to stand corrected,
-Chris
"Brooks,Bill"
<[log in to unmask]> To:
[log in to unmask]
Sent by: DesignerCouncil cc:
<[log in to unmask]> Subject: Re:
[DC] IPC-4101
04/22/2005 02:22 PM
Please respond to
"(Designers Council
Forum)"; Please respond to
"Brooks,Bill"
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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