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Wong,
C. P.
Wong,
C. P.
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ItemMoisture Absorption in Uncured Underfill Materials(Georgia Institute of Technology, 2004-06) Wong, C. P. ; Luo, ShijianThis paper presents a systematic study on moisture absorption in uncured underfill based on epoxy cured with acid anhydride [methylhexahydrophthalic anhydride (MHHPA)] and epoxy cured with non-acid anhydride curing agent. The influence of absorbed moisture on curing properties, thermomechanical property, and adhesion property of underfill after curing has been investigated. For epoxy cured with non-acid anhydride, the moisture absorption is low, and the absorbed moisture has no significant effect on the properties of cured underfill materials. For epoxy cured with acid anhydride, the moisture absorption before curing can be more than 2.0%, and the absorbed moisture can affect the properties significantly. The absorbed moisture can catalyze the curing reaction between acid anhydride and epoxy. The glass transition temperature of the cured samples is reduced after the underfill absorbs the moisture before curing. The adhesion strength decreases dramatically after the underfill absorbs the moisture before curing.
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ItemSurface Property of Passivation Layer on Integrated Circuit Chip and Solder Mask Layer on Printed Circuit Board(Georgia Institute of Technology, 2003-10) Wong, C. P. ; Luo, ShijianAdhesion of underfill to passivation layer on integrated circuit chip and solder mask layer on printed circuit board is critical to the reliability of an underfilled flip chip package. In this study, the surface properties of solder mask and four passivation materials: benzocyclobutene (BCB), polyimide (PI), silicon dioxide (SiO₂)and silicon nitride (SiN) were investigated. A combination of both wet and dry cleaning processes was very effective to remove contaminants from the surface. The element oxygen, introduced during O₂plasma treatment or UV/O₃treatment, led to the increase of the base component of surface tension. X-ray photoelectron spectroscopy (XPS) experiments confirmed the increase of oxygen concentration at the surface after UV/O₃treatment. Wetting of underfill on passivation and solder mask was slightly improved at higher temperatures. Although UV/O₃ cleaning and O₂plasma treatment significantly improved the wetting of underfill on passivation materials, they did not improve adhesion strength of epoxy underfill to passivation. Therefore, the wetting was not the controlling factor in adhesion of the system studied.
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ItemThermal and Mechanical Characterization of ViaLux™ 81: A Novel Epoxy Photo-Dielectric Dry Film (PDDF) for Microvia Applications(Georgia Institute of Technology, 2001-09) Wong, C. P. ; Dunne, Rajiv Carl ; Sitaraman, Suresh K. ; Luo, Shijian ; Estes, William E. ; Periyasamy, Mookkan ; Coburn, JohnMultilayered high density interconnect (HDI) processing on organic substrates typically introduces warpage and residual stresses. The magnitude of the warpage and the residual stresses depends on, among other factors, the processing temperatures and the thermomechanical properties of the dielectric and substrate materials. In this work, a prospective epoxy-based dielectric material for such sequentially built up (SBU) high density- interconnect printed wiring boards (HDI-PWB) is considered. The polymer is a photo-dielectric dry film (PDDF) material called ViaLux™ 81, which exhibits a complicated curing behavior due to the long lifetime of the cationic photoinitiators generated by ultraviolet (UV) exposure. The objectives of this work are 1) to conduct differential scanning calorimetry (DSC) experiments and develop a cure kinetics model; 2) to develop a cure shrinkage model based on thermal and chemical shrinkage experiments; 3) to determine the thermomechanical properties of partially and fully cured Vialux™ 81 dry film. All of these experimental characterizations are necessary to select suitable process parameters and to obtain a consistent product with the desired physical and mechanical properties.
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ItemStudy on Effect of Coupling Agents on Underfill Material in Flip Chip Packaging(Georgia Institute of Technology, 2001-03) Wong, C. P. ; Luo, ShijianCoupling agents are widely used in order to improve the adhesion property of underfill. In this study, three different silane coupling agents, two titanate coupling agents, and one zirconate coupling agent were added into an epoxy underfill material. Their effects on the flow behavior and curing profile of the epoxy underfill were studied with a rheometer and a differential scanning calorimeter (DSC), respectively. The thermal stability of the cured underfill material was studied with a thermogravimetric analyzer (TGA). A thermal mechanical analyzer (TMA) and a dynamic mechanical analyzer (DMA) were used to measure the coefficient of thermal expansion (CTE), the glass transition temperature (T[underscore g]), and the storage modulus ( T′). In addition, the adhesion of the underfill on benzocyclobutene (BCB) passivated silicon die and polyimide passivated silicon die was measured through die shear test. The effects of aging in an 85 ℃ /85% relative humidity chamber were also studied through moisture absorption test and die shear test.
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ItemEffect of UV/Ozone Treatment on Surface Tension and Adhesion in Electronic Packaging(Georgia Institute of Technology, 2001-03) Wong, C. P. ; Luo, ShijianSurface tension of material surfaces and interfaces is an important parameter that affects wetting and adhesion. Surface tension can be divided into three components: Lifshitz–van der Waals component, acid component, and base component. In this study, the three-liquid-probe method was used to investigate the surface tension and its three components of various surfaces of electronic packaging materials: benzocyclobutene (BCB) passivation, FR-4 board, polyimide board, and alumina board. When UV/ozone was employed to treat the surfaces, the surface tension increased, and the base component increased the most. The change in surface tension due to UV/O3 treatment decayed with time after the treatment. The difference in surface tension between untreated and treated surface became smaller with the increase of time after UV/O3 treatment. Different substrates showed different rate of decay in surface tension change. Among the surfaces studied, BCB passivation showed the fastest decay after treatment, while alumina showed the slowest decay. The contact angles of several liquid underfill materials on BCB passivation and their surface tension before and after curing were also measured. It was found that the wetting was not the controlling factor in adhesion of the system investigated.
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ItemStudy on Effect of Carbon Black on Behavior of Conductive Polymer Composites with Positive Temperature Coefficient(Georgia Institute of Technology, 2000-03) Wong, C. P. ; Luo, ShijianConductive polymer composites showing large positive temperature coefficient (PTC) are made of semi-crystalline polymer as an insulator and a conducting filler, whose concentration is close to the critical volume fraction. In this study, the resistivity and PTC behavior of high density polyethylene (HDPE) filled with different carbon blacks were studied. Among those composites, N660 carbon black filled PE showed the greatest PTC behavior. Carbon black with large particle size, small surface area and small amount of aggregated structure leads to large amplitude of PTC transition (defined as the ratio of maximum resistivity to the resistivity at 25 ℃). The great PTC behavior is due to some microscopic mechanism under the macroscopic thermal expansion of polymer matrix during melting of polymer crystal.