RP090 -
Characterization and Use of Polyfluorosiloxanes in Automotive
Applications, Motorola Inc., Anthony Polak
ABSTRACT
Polysiloxanes
are routinely used in the semiconductor industry as die encapsulants.
Thermal analysis, NMR, ion chromatography, and dielectric spectroscopy
was used to characterize these polymers. The dielectric loss
spectrum was found to be directly related to the long term
electrical stability of the encapsulated die, and was also
found to be a more sensitive technique for determining the
concentration of electronically active impurities than GC/MS,
and ion chromatography.
Dielectric spectroscopy
was also used to study the diffusion of acids, and water through
these polymers. While the solubility of acids and water in
these materials is low, their diffusion constants are high,
on the order of ten to the minus four sq.cm./s. In addition,
the interaction of the encapsulant with the Si3N4 passivation
used on the die surface was found to have an effect on the
long term stability of the device. This is believed to be due
to the formation of a conductive layer at the Si3N4/polymer
interface which ultimately forms a leakage path between the
bond pads, or into the Si3N4 passivation layer.
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