It is my experience that higher Tg materials are better ... but not always.
We have found that there are a few high Tg materials that fail quickly in
assembly or in the field, particularly if they were subjected to sequential
lamination cycles during fabrication. Specifying Tg will not prevent
material problems. Also understand that Tg is not a parameter that is
"written in stone"; Tg can change over time even as PCBs sit on a shelf, but
it is especially variable as a results of process variations in fabrication
and assembly. There are at least five different methods of determining Tg,
all produce numbers that are equally valid, but they typically vary about 20
degrees.
I suggest that you specify specific materials by manufacturer and type.
Lead free assembly is going to prove to be problematic with current
materials, fabrication variables and PCB designs.
-----Original Message-----
From: Gregg Klawson [mailto:[log in to unmask]]
Sent: Monday, August 16, 2004 9:03 AM
To: [log in to unmask]
Subject: [TN] Laminate Tg specifications
What is the best way to specify laminate glass transition temp
(Tg)? These are the types of products we deal with, any recommendations
on what Tg's we should call out? Call them all150C minimum and be done
with it? And what about lead-free processes with higher reflow temps, do
we need higher Tg's?
1.) Standard through-hole 6 to 10 layer wave solder single pass, assume 2x
rework
2.) Standard SM 8 to 16 layer, 2x SM reflow, 1x wave solder palletized, 2x
rework
3.) Complex SM 12 to 24 layers, 2x SM reflow, 1x wave or selective solder,
2x rework
Thanks in advance for your wisdom.
-- Gregg
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