Material properties of anisotropic conductive adhesives (ACAs) and flip chip assembly reliability for chip-on-board (COB) applications

Abstract

Recently, conductive adhesives are being concerned as an interconnection material replacing solder flip chip joints. Conductive adhesives are classified into anisotropic conductive films (ACFs), anisotropic conductive pastes (ACPs), non-conductive films (NCFs), and non-conductive pastes (NCPs) by the form of adhesives and the existence of conductive particles. Among the adhesives, ACFs are most widely used due to its advantages. In past twenty years, ACFs have been being mainly used for liquid crystal display (LCD) packaging as a chip-on-glass (COG) package. Recently, many efforts to apply ACFs to various interconnections including chip-on-board (COB) packages are being carried out. As the usage of flip chip technology using ACFs, to understand flip chip assembly reliability characteristics is very important. ACF flip chip assembly reliability is affected by ACF material properties and flip chip geometry. Therefore, in this thesis, to apply ACFs to COB packages, the relationship between ACF material properties and flip chip assembly reliability was investigated. Subsequently, how the ACF material properties are changed by process parameter, in particular, heating rate was discussed. In addition, the effect of flip chip assembly geometry on flip chip assembly reliability was investigated. Finally, ACF feasibility to COB packages was verified in NAND flash memory applications. At first, chapter 2 discussed the relationship between material properties of polymer adhesive materials such as ACFs, NCPs, and underfills and flip chip warpage behavior. In this chapter, the material property changes of the adhesive materials were investigated. The relationship between the material property changes and warpage hysteresis behavior was also discussed. In the thermo-mechanical analysis (TMA) and dynamic mechanical analysis (DMA), the first thermal cycle (during the TMA and DMA measurements) significantly changed the material properties (dimensional changes and modulus). H...