Underfilling n. : The filling below or beneath; the under part of a building.

Example:
Is there an easy way to add ATF to 1990 Maxima?

Taxonomy
underfills, flip chip, assembly, troubleshooting, SMT Magazine, assembly process, strategies, Reflow, encapsulants, capillary flow, vibration, shock, dropping, trauma, flex, FlipChips, Latest additions, solder.

Defination from the web:
Underfilling. Latest additions on this page. Troubleshooting Underfill Void Elimination. Advanced Packaging ... This article presents an alternative to fully underfilling components to protect them from vibration, shock and dropping trauma. (added on 21-Mar-2004) ...