Investigation Of Characteristics For Adhesive And Bonding Reliability For COG Assembly Under Hygrothermal Conditions

With the increasing demand in higher integration, in/out (I/O) count, power,calculating speed and the lead-free materials, the electronic products are developing towards further miniaturization and green. COG (Chip-on-Glass), as one kind of green and environmental protective assemblies, is widely used in electronic industry. In this dissertation, the characteristics of the adhesive and bonding reliability of COG assembles under hygrothermal conditions are investigated. The main contents of this dissertation are as following.The moisture diffusion characteristics in epoxy system under hygrothermal conditions are investigated by experiments and molecular dynamics simulations. The effects of hygrothermal aging on the epoxy system's properties are studied by thermal mechanical analyzer, thermal gravitational analyzer, uniaxial tensile tests, fractography and computer simulations of the fracture surface patterns. It shows that the moisture diffusion characteristics in epoxy system are dependent on the hygrothermal conditions, aging history and the thickness of the samples; the linear relation is generally valid between the moisture-induced swelling strains and moisture concentrations; the coefficient of moisture expansion increases with the increase of the aging temperature; hygrothermal aging can degrade the mechanics properties and the fracture mechanisms of polymer materials; the ratio of crack velocity to craze or secondary crack velocity can affect the patterns of fracture surfaces.The effects of hygrthermal conditions on the bonding strengths of COG assemblies and the chemical compositions of anisotropic conductive adhesive (ACA) are investigated by macroscopical shear-mode experiments and microcosmic Fourier Transform Infrared Spectroscopy (FTIR) methods. It shows that with the increase of the hygrothermal aging time, the bonding strengths of COG assemblies decrease and the chemical compositions of ACAs subject to the changes, which are relevant to thehydrolysis reaction between the moisture and epoxy system. Additionally, it is found that the interfacial failure modes of COG assemblies are more and more obvious with the hygrothermal aging.One reasonable mechanics model is established by introducing interfacial fracture energy ( Gf -th), which was used to synthetically consider the effects of hygrothermal aging on ACF's properties. It shows that due to the effects of hygrothermal aging, the adhesion interfacial fracture energy gradually decreases. Furthermore, the degradation process of the interfacial fracture energies can be divided into three phases, that is, the primary, secondary and tertiary phases, respectively.