Flip-chip underfilling with non-conductive photoinitiated adhesives - a new approach

The trend for miniaturisation in electronic equipment is continuing unabated. The increasing complexity of electronic memory components allows for new layout structures and design possibilities which constantly reinforce this trend. As IC capacity rises, new packaging technologies are also gaining steadily in importance, and flip-chip technology has established itself as a marketable and highly efficient technique. When flip-chip technology is used, there is always a need to fill the gap between die and substrate with a resin, also known as an underfill. Due to different coefficients of thermal expansion, stresses appear between bumps and die as well as between bumps and substrate. The underfill minimises or compensates these stresses. Additionally, it ensures the die's mechanical stability on the substrate. This paper presents three different underfiller systems which are cured by three different mechanisms. These completely new and partly unique underfilling materials have been developed on the basis of elastified, single component epoxy resins, and are suitable for a wide range of carrier substrates, offering obvious advantages compared with the systems available on the market at present. Greater attention is paid to those underfills which enable completely new underfilling techniques involving photoinduced pre-activation by light of a certain wavelength and intensity, even without subsequent heat curing. This technology opens up new ways of drastically cutting flip-chip process cost by economising on several process steps.