A simplified process for flip-chip attachment of a chip to a substrate is
provided by precoating the chip with an encapsulant underfill material
having separate discrete solder columns therein to eliminate the
conventional capillary flow underfill process. Such a structure permits
incorporation of remeltable layers for rework, test, or repair. It also
allows incorporation of electrical redistribution layers. In one aspect,
the chip and pre-coated encapsulant are placed at an angle to the
substrate and brought into contact with the pre-coated substrate, then the
chip and pre-coated encapsulant are pivoted about the first point of
contact, expelling any gas therebetween until the solder bumps on the chip
are fully in contact with the substrate. There is also provided a
flip-chip configuration having a complaint solder/flexible encapsulant
understructure that deforms generally laterally with the substrate as the
substrate undergoes expansion or contraction. With this configuration, the
complaint solder/flexible encapsulant understructure absorbs the strain
caused by the difference in the thermal coefficients of expansion between
the chip and the substrate without bending the chip and substrate.
