In this study, the adhesive interaction between gold and epoxy resin is theoretically investigated. These materials make up crucial components of a wide range of electronic devices. The objectives of the study are (1) to elucidate the bonding mechanism between epoxy resin and a realistic gold surface, and (2) to obtain a device-design guideline for superior adhesion, thus reducing the bonding breakage that may potentially cause device failure. Die pad surfaces used in chip attachment methods for microelectronics are usually fabricated using an electrolytic plating technique. This technique involves ionic gold solutions like K[Au(CN) 2 ]. The combined theoretical and experimental studies previously carried out by the authors have revealed that the CN − counteranion of the gold cation has a high affinity for gold and is likely to remain on the realistic gold surface generated by plating. However, the cyano group content on the surface of the plated gold is still unknown. Therefore, gold surfaces embedded with cyano groups with various coverages are constructed. The effect of the varying coverage of the cyano groups on the adhesion strength is inspected using firstprinciples density functional theory calculations. As the number of cyano groups on the surface increases, the direct interaction between the gold surface and the epoxy resin is hindered, but the hydroxy and amino groups in the epoxy resin and hardener form more hydrogen bonds with the cyano groups adsorbed on the surface. It is found that the surface with intermediate cyano coverage (about 33%) yields the highest adhesive strength.

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.

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