Definitions for "Underfill"
In flip chip applications, the material injected under the die after testing to ensure reliability. This material is particularly important for flip chips mounted on substrates with different CTEs than silicon, such as FR-4 and some ceramics.
Encapsulant material typically deposited between a flip chip device and substrate used to reduce a mismatch in CTE between the device and the substrate.
Encapsulant material typically deposited between a flip chip device and substrate to reduce a mismatch in thermal expansion coefficients.
In injection molding, failure to fill the mold completely.
An underfilled cooling system will suffer from air entrainment and will experience rapid corrosion and rusting of metal components as coolant will not protect those areas with which it has no contact. A cooling system should be routinely examined to maintain the proper fill level.
A depression on the weld face or root surface extending below the adjacent surface of the base metal.