One of the reasons people started to tent/plug vias was that it is impossible
to guarantee 100% filling the ALL the vias with solder. 
Partially solder-filled holes have shorter fatigue lives than either
non-solder-filled holes or 100% solder-filled holes. However, for most
applications this reduced fatigue life is of no consequence because even the
reduced fatigue life is much longer than the product life.  Only for severe
thermal cyclic use conditions (deltaT's>~60C) and also depending on the via
construction and quality, is this reduced fatigue life significant.

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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