Hi Barbara,
You did not indicate where, in relation to the PTH/PTV innerlayer
connections, and when, after what processing steps, these fractures in the
traces have occurred. Therefore, I can not give you an indication of the
damage mechanism(s) and root cause of failure. However, it is quite clear
that the inner layer copper foil has inadequate ductility for the loading
conditions your boards have been subjected to. I would suspect however, that
your inner layer foils are CF-E1 (Standard Electrodeposited Copper Foil as
per IPC-150), which can have an elongation as low as 2%. While this does not
happen very often, problems have occurred with other clients of mine, when
such Cu foil from the lower end of the 'acceptable' quality spectrum are used
in applications for which the average in the quality spectrum just suffices.

Werner Engelmaier
Engelmaier Associates, Inc.
Electronic Packaging, Interconnection and Reliability Consulting
23 Gunther Street
Mendham, NJ  07945  USA
Phone & Fax: 973-543-2747
E-mail: [log in to unmask]

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