There is one other reason for tenting vias, to prevent partial filling of
PTVs with solder. Partial solder fills with voids in the PTV center cause
stress concentrations during the thermal cycling experienced by product in
operational use--however, this is really only a concern for severe use
environments with delta T's of 50oC and up and design lives of 10 years and
longer.

Werner Engelmaier
Engelmaier Associates, Inc.
Electronic Packaging, Interconnection and Reliability Consulting
23 Gunther Street
Mendham, NJ  07945  USA
Phone & Fax: 201-543-2747
E-mail: [log in to unmask]

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