I don't believe the undercut you described has much to do with the
propagation of cracks between the mask and underlying material. If
delamination is propagating like that, then you have inherently poor
adhesion between the mask and the substrate. The tape peel test is the
universal standard for this, and the information the board vendor is
giving you indicates that this is not the issue at all. I guess you
need to get pictures from the board vendor showing what he's talking
about. If, indeed, the only thing coming off on the tape is the
minuscule overhangs due to the double developing, then I doubt this will
cause a problem, unless this overhang is more than about 20 microns.
And that kind of overhang would be hard to believe unless the mask is
real thick.
Wayne Thayer
>>> [log in to unmask] 9/26/2006 2:02:34 pm >>>
It's possible, depending on how adhered the mask is. My thought was not
so
much on the undercut entrapping anything; however, once the adhered
mask
began to separate from the glass of copper (at whatever stage), then
it
would allow for entrapped 'stuff' at this newly formed pocket or
space.
This of course could happen during assembly (from pre-clean to
post-clean)
and while in use (environmental conditions, humidity, dust, dirt,
etc).
Franklin
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Kevin Glidden
Sent: Tuesday, September 26, 2006 12:52 PM
To: [log in to unmask]
Subject: Re: [TN] Over-developed Soldermask
Franklin,
The concern of the undercut trapping residues or contaminants is an
interesting point and one that I had not considered. Would that not
also be
a concern during the initial soldering / cleaning steps that the flux
residues could get trapped in the undercuts?
Thanks!
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