Hi Ioan,
You automotive environment is the harshest [short of down-hole drilling] for
electronic assembliies--just look at the millions of SUVs GM has to recall
because of solder joint failures. In a harsh environment, any voids in via solder
fill creates stress risers and thus reduce reliability. What would work for
many years in a telecom environment would fail quickly in an automotive
under-hood environment. The life ratio for unfilled vias is about a factor of 1000.
Thus, in your environment I would not allow any voids in solder-filled vias;
voids in polymeric fills of vias are not very important.
And, as Robert pointed out, solder joint reliability degradation mmay be even
more important.

Regards,
Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL  32174  USA
Phone: 386-437-8747, Fax: 386-437-8737
E-mail: [log in to unmask], Website: www.engelmaier.com

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