Clarification of
adhesive interactions in semiconductor packages
can improve reliability of power electronics. In this study, the adhesion
interfaces between the epoxy molding compound and Cu-based lead frames
were analyzed using the density functional theory. A resin fragment
was prepared based on the polymer framework formed in the curing reaction
of epoxy cresol novolac (ECN) and phenol novolac (PN), which are typical
molding materials. The resin fragment was optimized on the surfaces
of Cu and Cu
2
O. We calculated the charge density differences
for adhesion structures and discussed the origin of adhesive interactions.
The ECN–PN fragment’s adhesion to the Cu surface relied
mainly on dispersion forces, whereas in the case of Cu
2
O, the resin bonded chemically to the surface
via
(1) σ-bonds formed between the ECN–PN’s OH group
oxygen and coordinatively unsaturated copper (Cu
CUS
) and
(2) hydrogen bonds between resin’s OH groups and coordinatively
unsaturated oxygen (O
CUS
) located close to to Cu
CUS
, resulting in a stable adhesive structure. The energy required to
detach the resin fragment from the optimized structure was determined
using the nudged elastic band method in each model of the adhesive
interface. Morse potential curve was used to approximate the obtained
energy, and the energy differentiation by detachment distance yielded
the theoretical adhesive force. The maximum adhesive stress was 1.6
and 2.2 GPa for the Cu and Cu
2
O surfaces, respectively.
The extent to which the ECN–PN fragment bonded to the Cu
2
O surface stabilized was 0.5 eV higher than in the case of
the Cu surface.