Hi Peter,
>To comment on sage Werner's suggestions, the reliability of completely
>filling of vias with copper or solderd copper wire depends on the substrate
>material. FR4, for example, has quite a high LCTE in the Z-axis. If the
>holes are solidly filled with metal with a lower CTE, and the boards are
>operating in harsh enviroments with large temperature extremes, there is
>a danger of connections with inner layers being fractured. That's our theory,
>anyway.
A: While it is, of course, true that the CTE(z) of FR-4 PWB--or any other PWB
that has a x,y-CTE-constraining matrix--is high (about 3x the LCTE of the
resin without x,y-CTE-constrains), this does not translate to a higher
propensity of metal-filled PTVs for innerlayer separation (ILS) failures. On
the contrary, the root-cause for ILS is the fact that larger-diameter,
thinner-walled PTVs buckle inwards during high thermal excursions (like a
submarine going too deep) because the resin thermal expansion pressure. If
this inwards-buckling is large enough to cause plastic deformations in the
PTV barrel wall, the innerlayer connections are subjected to tensile stresses
when the resin returns to its former volume on cooling, because the Cu walls
cannot return to its former geometry. The thicker the walls the higher the
hydrostatic pressures have to be for deformation of the PTV barrel to occur.

Werner Engelmaier

---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/html/forum.htm for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------