ABSTRACT:In order to develop easily peelable dicing tapes from diced wafers, UV curing of various pressuresensitive adhesives (PSAs) was studied. After UV irradiation, the adhesive strength of a PSA composition including a diacrylourethane oligomer (UDA) decreased drastically compared with other compositions. Because of network formation via UV irradiation, this composition had a greater volume contraction that might yield microvoids at the interface between the adhesive and the wafer, resulting in the loose adhesion. Its storage modulus increased up to about 1000 times that before UV curing, which was due to the crosslinking of the UDA component. It was suggested that the increased crosslinking density and the high internal coagulant energy of the UDA backbone structure caused a remarkable decrease of the adhesive strength. Furthermore, it was ascertained that the UV-irradiated UDA adhesives left few residual deposits on the wafer released from the tape.
To facilitate the fabrication of a reliable stacked package for a semiconductor, UV/heat dual curing of adhesives was investigated. The formulated adhesives contained acrylic monomer and epoxy resins. First, UV curing was conducted on the acrylic monomer, followed by heat curing. It was found that UV-curable acrylic monomers affected the adhesive's properties, e.g., adhesion, water absorption, and viscoelasticity. As the acrylic monomer, neopentylglycol diacrylate (NPGDA), trimethylolpropane triacrylate (TMPTA), dipentaerythritol hexaacrylate (DPHA), and tricyclodecanedimethanol acrylate (TCDDA) were used to investigate the effect of functional group numbers and structure. As a result, an acrylic monomer that has two functional groups with a rigid moiety (TCDDA) showed acceptable properties as adhesives for the fabrication, and thus a UV/heat-curing adhesive has been successfully developed.
ABSTRACT:In an attempt to control the adhesive properties of acrylic copolymer-based pressure-sensitive adhesives, a series of multifunctional acrylate monomers were added and UV cured. The adhesive compound with a difunctional monomer had increased peel strength after UV curing. On the other hand, the compound with a tri-or more functional (polyfunctional) monomer had markedly decreased strength after UV curing. Those adhesives containing any polyfunctional monomer also showed much higher storage modulus than an adhesive containing a difunctional monomer. The greater volume contraction of UV-cured polyfunctional monomer suggested microvoids at the interface between the adhesive layer and the adherent, resulting in poor strength. Estimated values of the peel strength of UV-cured adhesives according to the theoretical equations proved that the strength is approximately inversely proportional to the elastic moduli.
Aliphatic unsaturated polyesters (UPEs) mixed with N,N-diethylaminoethyl methacrylate (DEAEMA) were convertible by electron beam irradiation to soft solids of high peeling strength. Double bond conversions, gel contents, molecular weight distributions, and crosslinking densities of the irradiated mixtures were studied in comparison with those of UPE-vinyl acetate mixtures, which gave very low peel strength on irradiation. The latter system started gel formation even at earlier stages of irradiation and had higher cross-linking densities as a result of copolymerization between polyester and monomer double bonds. In contrast, the UPE-DEAEMA system exhibited slow gel formation with predominant conversion of monomer double bonds, indicating formation of graft copolymers. This system also had lower crosslinking densities than the other system. Therefore, it was concluded that the pressuresensitive adhesive nature of the electron-beam-cured UPE-DEAEMA mixtures could be attributed to the formation of flexible graft polymers entangled in a loosely crosslinked network.
Thermal curing of adhesive films was investigated to facilitate the fabrication of a reliable bonding for semiconductors. The formulated adhesive films contained acrylic polymer, epoxy resins, phenol resin, and an imidazole derivative that was the catalyst for curing the epoxy resins with phenol resin. The solubility, thermally latent characteristics, mechanical and adhesive properties of 2-methylimidazole/boron trifluoride (2MZ/BF3), and 2MZ/aluminum trisacetylacetonate (AlAC) were investigated. It was found that 2MZ/BF3 and 2MZ/AlAC had excellent solubility in adhesive materials and they had excellent latent characteristics as thermal curing catalysts for epoxy resins, whereas conventional catalysts (2MZ and 2-phenyl-4, 5-dihydroxymethylimidazole (2PHZ)) could not achieve both excellent solubility and thermally latent characteristics. The mechanical and adhesive properties of the post-thermal-cured adhesive film that contained 2MZ/ BF3 or 2MZ/AlAC were comparable to those of the postthermal-cured adhesive films that contained conventional catalysts.
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