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Wong, C. P.

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Author: Lu, Daoqiang × End date: 2009 × Start date: 2000 × search.filters.applied.f.resourcesubtype: Article ×

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    Enhanced Electrical Properties of Anisotropic Conductive Adhesive With $pi$ -Conjugated Self-Assembled Molecular Wire Junctions
    (Georgia Institute of Technology, 2009-09) Zhang, Rongwei ; Li, Yi ; Yim, Myung Jin ; Moon, Kyoung-Sik ; Lu, Daoqiang ; Wong, C. P.
    We have investigated the electrical properties of anisotropic conductive adhesive (ACA) joint using submicrometer- sized ( 500 nm in diameter) silver (Ag) particle as conductive filler with the effect of -conjugated self-assembled molecular wires. The ACAs with submicrometer-sized Ag particles have higher current carrying capability ( 3400 mA) than those with micro-sized Au-coated polymer particles ( 2000 mA) and Ag nanoparticles ( 2500 mA). More importantly, by construction of -conjugated self-assembled molecular wire junctions between conductive particles and integrated circuit (IC)/substrate, the electrical conductivity has increased by one order of magnitude and the current carrying capability of ACAs has improved by 600 mA. The crucial factors that govern the improved electrical properties are discussed based on the study of alignments and thermal stability of molecules on the submicrometer-sized Ag particle surface with surface-enhanced Raman spectroscopy (SERS), providing a fundamental understanding of conduction mechanism in ACA joints and guidelines for the formulation of high-performance ACAs in electronic packaging industry.
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    Development of Conductive Adhesives for Solder Replacement
    (Georgia Institute of Technology, 2000-12) Wong, C. P. ; Lu, Daoqiang
    With the phasing out of lead-bearing solders, electrically conductive adhesives (ECAs) have been identified as an environmentally friendly alternative to tin/lead (Sn/Pb) solders in electronics packaging applications. Compared to Sn/Pb solders, conductive adhesive technology offers numerous advantages. However, this new technology still has reliability limitations. Two critical limitations are unstable contact resistance on non- noble metals and poor impact performance. Our previous study proved that galvanic corrosion is the dominant mechanism for the unstable contact resistance during elevated temperature and humidity aging. The ultimate goal of this study is to develop conductive adhesives with stable contact resistance and desirable impact performance. In this study, effects of purity of the resins and moisture absorption on contact resistance are investigated. Several different additives (oxygen scavengers and corrosion inhibitors) on contact resistance stability during elevated temperature and humidity aging are studied, and effective additives are identified based on this study. Then, several rubber-modified epoxy resins and two synthesized epoxide-terminated polyurethane resins are introduced into ECA formulations to determine their effects on impact strength. The loss factor, tan , of each formulation is measured using a dynamic mechanical analyzer (DMA) and impact strength is evaluated using the National Center for Manufacturing Science (NCMS) standard drop test procedure. Finally, high performance conductive adhesives are formulated by combining the modified resins and the effective additives. It is found that 1) purity of the resins and moisture absorption of the formulation affect the contact resistance stability of an ECA; 2) the oxygen scavengers and corrosion inhibitors can delay contact resistance shift; 3) one of the corrosion inhibitors is very effective in stabilizing the contact resistance; 4) some rubbermodified epoxy resins and the epoxide-terminated polyurethane resins can provide the conductive adhesives with superior impact performance; and 5) conductive adhesives with stable contact resistance and desirable impact performance are developed.
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    A Study of Contact Resistance of Conductive Adhesives Based on Anhydride-Cured Epoxy Systems
    (Georgia Institute of Technology, 2000-09) Wong, C. P. ; Lu, Daoqiang
    Electrically conductive adhesives (ECAs) are an environmentally friendly alternative to tin/lead (Sn/Pb) solders in electronics packaging applications. However, current conductive technology is still in its infancy and limitations do exist. One of the critical reliability issues is that contact resistance of silver flake-filled ECAs on nonnoble metals increases in elevated temperature and humidity environments. The main objective of this study is to investigate the contact resistance behaviors of a class of conductive adhesives, which are based on anhydride-cured epoxy systems. Curing profiles, moisture pickup, and shifts of contact resistance of the ECAs on a nonnoble metal, tin/lead (Sn/Pb), during aging are investigated. Also, two corrosion inhibitors are employed to stabilize the contact resistance. The effects of these corrosion inhibitors on contact resistance are compared. It is found that: 1) this class of ECAs shows low moisture absorption, 2) the contact resistance of the ECAs on Sn/Pb decreases first and then increases slowly during 85 C/85% relative humidity (RH) aging, 3) one of corrosion inhibitors is very effective to stabilize contact resistance of these ECAs on Sn/Pb, and 4) the corrosion inhibitor stabilizes contact resistance through adsorption on Sn/Pb surfaces. From this study, it can be concluded that ECAs based on anhydride cured epoxy systems are promising formulations for electronics packaging applications.