Improving die attach adhesion on metal leadframes via episulfide chemistry

The objective of this study is to develop a basic understanding and practical approaches to achieve universal adhesion in metal leadframe packages. Universal die attach refers to a single die attach material that has excellent adhesion properties to Cu, Ag and Ni-Pd-Au substrates. Universal adhesion is a key element in achieving "universal die attach", which means that one single die attach can be applied onto different substrates (Cu, Ag and Ni-Pd-Au), all of which are commonly used in metal leadframe packages in semiconductor industry. The most difficult part of achieving universal adhesion is to achieve a good adhesion on Ag and Ni-Pd-Au by conventional adhesion promoters. In this study, a series of episulfide materials were synthesized, where episulfide moieties can be utilized as a latent thiol generator and can be cured in a similar way as epoxides. The adhesion properties of these materials were investigated through formulation testing, dynamic curing studies, surface analysis and fundamental characterization. We found episulfide indeed functioned as an adhesion promoter and improved cohesiveness of die attach adhesive on Ag and Ni-Pd-Au leadframes. The interactions between episulfide and the host resin system, and the stronger interfacial adhesion to metal leadframe by episulfide have contributed to these improvements.