Brian,
I think perhaps you are confusing measles with weave exposure. Measles are
entirely enclosed within the laminate and not exposed to contaminants. Weave
exposure, on the other hand, is a removal of resin from the laminate surface
(e.g. by excessive soldermask stripping) leading to exposed glass fibers,
and definitely should be rejected due to the risk of capillary uptake of
contaminants/moisture as you said.
Tim Reeves

> ----------
> From:         Brian Ellis
> Sent:         Wednesday, February 2, 2000 3:58 AM
> Subject:      Re: Measling
>
> Kelly,
>
> I'm 100% with you on this. Measling is due essentially to too little resin
> at the fibre
> "bumps", because either it was squeezed out too much during pressing or
> there has been
> a chemical attack of the resin, baring the fibres. The real problem with
> real measles
> is that chemicals can enter the fibre structure by capillary action, after
> which
> anything can (and does) happen. Overheating pads is not a cause for
> measles but, sure
> as God made little green apples, it can cause one helluva lot of other
> problems. This
> is why we put thermal breaks in ground and power planes, just to reduce
> this risk.
>
> Brian
>
> "Kelly M. Schriver" wrote:
>
> > Whoops!!  Help me with this one, guys!!   Measling, by definition,
> occurs
> > only at the intersection of two fiber bundles within the lamina.
> > Accordingly, it cannot occur in the same plane as the metal foil of that
> > laminate layer.   The size of a measle is self limiting by the structure
> of
> > the glass (or fiber) bundles.  Further, one measle cannot join with an
> > adjacent measle or become a running fault in the laminate.
> >
> > Crazing and delamination, however, can occur in the same plane as the
> metal
> > foil, and can become large running or bridging faults.  I've seen
> numerous
> > cases of crazing which were misdiagnosed as measling.
> >
> > Many of the publications, such as WS6536, MIL-STD-2000 and others failed
> to
> > recognize this charactaristic about measles vs other internal laminate
> > faults, leading to a few misconceptions.  I have seen no indication of
> test
> > data, other than some specialized high power applications which suggests
> > that real bona fide measles are a reliability problem.
> >
> > Regards - Kelly
> >
> > -----Original Message-----
> > From: rampinc <[log in to unmask]>
> > To: [log in to unmask] <[log in to unmask]>
> > Date: Tuesday, February 01, 2000 6:39 PM
> > Subject: Re: [TN] Measling
> >
> > >Rick,
> > >
> > >Be careful. Measling can be a source of reliability problem when it
> bridges
> > two
> > >conductors. Measling becomes 'A' type defect ( Critical function
> -causing
> > rejection)
> > >when two conductors of different polarity are bridges. If glass fibers
> > become visible
> > >in a measled spot, that is also a cause for concern.
> > >
> > >Send  pictures of measled board for further discussion if you like.
> > >
> > >"Howieson, Rick" wrote:
> > >
> > >> IPC states measling is not cause for rejection. Anyone out there know
> > >> where I can get supporting data that documents testing performed to
> come
> > >> to this conclusion? All help is appreciated.
> > >>
> > >> Rick Howieson
> > >> http://www.gt-corp.com
> > >>
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