an increase of soldering top temperature by some 30 Centigrades, or a
slight increase in humidity absorption (0.01 %), does that motivate such
a dramatic extension of bake out procedure? Is it proven bytests or is
it an assumption based on maths? I can't see the reason to increase bake
out to +150 Centigrades. Why not keep the ordinary std temperature and
extend the oven time?
Inge

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Fox, Ian
Sent: den 24 augusti 2007 08:53
To: [log in to unmask]
Subject: Re: [TN] Baking out board moisture


Typical values for Novolac cured materials eg IS410/415, PCL370HR, are
declared by the manufacturers to be between 0.15-0.3%, ie bridging the
gap between polyimide and traditional FR4. If you are processing at Pb
free temps then bakeout becomes much more important than it is at
traditional SnPb levels. We usually bake 4hrs at 125degC with no impact
on ENIG solderability

Regards
Ian Fox

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Hernefjord Ingemar
Sent: 24 August 2007 07:03
To: [log in to unmask]
Subject: Re: [TN] Baking out board moisture

"higher" says nothing, they should be more precise.Here are some
examples on moisture absorption:

ISOLA      std FR-4 Tg130 :  0.2  %
GE         std GETEK Tg180:  0.12 %
Polyclad   BT-Epoxy       :  0.2  %
Nelco      PI             :  0.35 %
GIL        GML 1000       :  0.02 %
nn         PTFE           : <0.01 %
nn         Cyanate Ester  :  0.3  %
Taconic    all products   : <0.01 %
Rogers     Ro group       : <0.1  %
Rogers     RT/duroid      : 0.015 to 0.6 %
Rogers     TMM            : 0.010 to 0.16 %
Arlon      DiClad         : < 0.1%
Metclad    all products   : < 0.08 %

Would be interesting to know why your Tg170 has higher moisture
absorption and also how much higher in percentage.

Inge


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Rob Strecker
Sent: den 23 augusti 2007 20:04
To: [log in to unmask]
Subject: [TN] Baking out board moisture

Hi All,

We are having an issue with boards delaminating post oven (oven profiles
are good).  We brought the issue up with our PCB manufacturer and they
said "The absorption of moisture on Tg170 laminate (Lead Free) is higher
than Tg130 laminate." Their corrective action is to increase the bake
time of the inner layer as well as additional drying process of 60min at
150oC before packing.  I am concerned with regards to the high bake
temperature and what it will do to our ENIG finish.  This is also the
recommendation they have given us to bake our existing stock before
running.  Could this reduce the solderability of our boards?  I know
with Tin finishes you would definitely have a problem with the Tin
degrading.  One other odd thing about this is we have been soldering
lead free for about 2 years now and started seeing issues in Jan of 07.

 

Rob Strecker 

 


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