FR-4 LAMINATE CHARACTERIZATION / CONTROL

	Printed circuit boards are manufacture with FR-4 laminate, a combination of
epoxy resin impregnated glass cloth.  The bonding agent used to join layers
in a multi layer construction package is called prepreg, glass cloth
impregnated with dry semi polymerized epoxy resin.  The application of heat
and pressure at the lamination process unifies the package into a multi
layer board.

	The printed circuit industry standard for epoxy laminate cure is Tg, the
glass transition temperature of the epoxy resin.  The cured laminate is
heated through two thermal cycles and measured using either DSC or TMA
techniques to determine the delta in Tg  between the two cycles.  If the
delta is small (less than 4 degrees F),  the material is deemed cured since
no additional polymerization occurred.  Tg analysis does not always indicate
how the material will process through subsequent mechanical and chemical
operations.  I am looking for ways to improve and tighten process controls 
over the material aspect of the process,  any comments or recommendations
would be appreciated. 

1.  Are there alternate methods for determination of the state of cure for
epoxy resins ?  Anything from the scientific world ?  Polymer scientists ? 
Resin suppliers ?

2.  Is there a documented procedure to quantify "machine ability" of
materials of this type ?  How can machine ability be quantified ?  How is it
typically determined in other material types ?

3.  Is there a method for quantifying "hardness / softness" of an epoxy
laminate.

4.  What elements within the resin or board manufacturing process will cause
variations in the state of cure or machine ability ?  How can they be
controlled ?

5.  Is there a documented procedure for incoming material inspection to
quantify material dimensional stability other than IPC - TM- 650  2.4.39 ? 
I am familiar with scaled flow and gel testing, but is anyone aware of a
method to quantify growth or shrinkage of laminate before the fact ?  Can
material stress be measured ?


Tony King
Elexsys International Inc. Nashua
603-886-0066
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