So Anchoring barrel wall is not recommended on higher Tg/Td laminate
systems due to Cu CTE...
Could I get a copy of that White paper? I'm interested in the cause
effect also...
We have seen similare problems arise from trace/pad interface and
fracturing. If what you say is good for Barrel, this may also have
limits that are being exceeded. Our conventional wisdom is to teardrop
or filet the interface from Annular ring to Trace, to help with the
migration of a mechanical fracture.
Will this logic still apply?
LoHst and Confused...
-----Original Message-----
From: Werner Engelmaier [mailto:[log in to unmask]]
Sent: Wednesday, August 02, 2006 5:23 PM
Subject: Re: Barrel to Laminate Adhesion loss
Hi Richard & All,
Actually, the higher occurrances of hole wall separation and trace
separation
are not so much caused by more lateral stresses, but the different
thermal
and mechanical properties of SAC solders.
To understand what is happening, one really needs to understand what the
whole damage process causing hole wall separation [sometimes also called
resin
recession] and inner-layer separation [also called post separation or
trace
separation.
(1) On heating the resin expands-because of the glass fiber
reinforcement it
is prevented to expand in x/y and thus expands in z at nearly 3-times
its
thermal expansion without the glass reinforcement]; there is an
exception to this- the resin also tries to expand into the volume
occupied by the PTH, and is of
course, to some degree at least, prevented from doing so by the Cu
barrel
plating.
Thin Cu plating and/or large separation between inner-layer land
[serving as
anchors] encourage larger bulging inwards of the Cu with plastic
deformation
of the Cu.
(2) On cooling, the resin contracts to its former volume-if the Cu is
plastically deformed to a significant degree, it cannot do so: the
result=>hole wall
separation, and near the surface in connection with land rotation
inner-layer
separation.
(3) For SnPb solders the Solidus is 183C; thus, Solidus - Tg
(183-170C)~13C. For SAC solders the solidus is 217C; thus, Solidus - Tg
(217-170C)~47C. The consequence is that the delta-T after solder
solidification is about
4-times larger for SAC-solders, over which the high above Tg-thermal
contraction
acts-and this also holds the Cu back to its former position: the result
=>more
hole wall separation, and inner-layer separation.
Pretty straight-forward when you think about.
Werner
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