The presence of measling is generally not considered a defect.  The
laminate fabricators test to IPC-4101, which is basically a thermal
cycle on a 12x12 sample of etched laminate - testing for any
visual/mechanical changes that could indicate a structure issue.

The presence of measles on a PCB should be qualified by the an
additional thermal stress (550f/10s) to the effected area and ensure the
measles do not propagate.  If propagation is evident, then the
subsequent thermal excursions in assembly will worsen the condition.
Either way, the presence of measles if generally either an issue with
the base materials or a management of the thermal cycling process during
solder coating/assembly.  Heavier copper cladding increase the
propensity for measling as the CTE mismatch of the package creates
stress to the reinforcement of the laminate.    

In our process we check for propagation and any reduction in design
spacing below 50% or the minimum circuit spacing in tighter areas where
the 50% rule is to close. 




Jeffrey Bush
Director, Quality Assurance and Technical Support

                          76 Technology Drive - POB 1890
                             Brattleboro, Vermont 05302-1890
                                Tel. 802.257.4571.21 Fax. 802.257.0011
                                    [log in to unmask]
                              http://www.vtcircuits.com	



-----Original Message-----
From: Richard Kraszewski [mailto:[log in to unmask]] 
Sent: Wednesday, August 11, 2004 12:41 PM
To: [log in to unmask]
Subject: [TN] IPC Test methods for measeling of laminate


Can any one tell me what the appropriate IPC test methods would be
measeling of FR4 laminate?  I understand there is a float test of some
sort.
 
 
Rich K  / KEDS

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Search the archives of previous posts at: http://listserv.ipc.org/archives
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