Dongwook Kim

Bio: Dongwook Kim is an academic researcher from University of California, Irvine. The author has contributed to research in topics: Soldering & Intermetallic. The author has an hindex of 11, co-authored 22 publications receiving 387 citations. Previous affiliations of Dongwook Kim include University of California & Intel.

Improved Drop Reliability Performance with Lead Free Solders of Low Ag Content and Their Failure Modes

Abstract: Solder joint reliability of lead free solders (Sn-Ag-Cu) in drop testing has been an issue in mobile and handheld electronics. Since lead free solders have lower drop performance compared with Pb-Sn solders, many efforts have been reported to improve solder joint reliability with various lead free solders. In this study, standard JEDEC drop reliability tests were performed for a CSP (chip scale package) prepared with two different compositions of lead free solders (SAC405 alloy: Sn-4Ag-0.5Cu and SAC105 alloy: Sn-1Ag-0.5Cu). Lead free solders were assembled on substrates with a Au/Ni surface finish. It was seen that SAC 105 alloy solder demonstrated better drop reliability compared with SAC405 alloy solder and failure analysis conducted to understand the differences in failure modes & drop reliability performance.. The fundamental cause of improved drop reliability performance of SAC 105 solders and the advantages of using low Ag content SAC lead free solders for microelectronic devices is discussed. Finally, a finite element model was developed and validated with failure analysis to investigate the high stress concentration distribution and failure mode in solder joints for drop test stress conditions.

Article comprising metal oxide nanostructures and method for fabricating such nanostructures

Abstract: This invention discloses novel field emitters which exhibit improved emission characteristics combined with improved emitter stability, in particular, new types of carbide or nitride based electron field emitters with desirable nanoscale, aligned and sharped-tip emitter structures.

Aligned and open-ended nanotube structure and method for making the same

Abstract: Aligned and open-ended nanotube structures, methods for making the same, and devices including open-ended nanotubes. An aligned and open-ended nanotube structure which is free of catalyst particles at top ends, the aligned and open-ended nanotube structure having an uneven open-end height with local protruding portions. A method of opening an end of a nanotube including a catalyst particle including sputter etching the nanotube to remove an amorphous layer, bend the nanotube to one side, open a hole in the nanotube, and cause detachment of the catalyst particle.

Evaluation of High Compliant Low Ag Solder Alloys on OSP as a Drop Solution for the 2nd Level Pb-Free Interconnection

Abstract: Low Ag content alloys (Sn1.2Ag0.5Cu) with or without Ni doping on Cu organic solderability preservative (OSP) were evaluated as a high G drop solution to Sn4.0Ag0.5Cu with Ni/Au surface finish for the mobile electronics. Three key points are studied in this paper. First, the effect of increasing compliance of alloy was studied. High compliance and high plasticity energy dissipation effectively toughened the crack tip and prolonged the time to reach the critical stress for the fracture. Second, the effect of Ni doping to the interfacial phase formation was studied. The substitution of Ni for Cu effectively suppresses growth kinetics of intermetallic compounds (IMCs) and makes the IMC layer thin. Finally, reliability tests were conducted to evaluate thermomechanical and high G drop resistance of low Ag alloys with Cu OSP surface finish. Overall, low Ag content alloy systems enhance high G shock resistance significantly without sacrificing thermomechanical performance.

Fluxless Flip-Chip Solder Joint Fabrication Using Electroplated Sn-Rich Sn–Au Structures

Abstract: A fluxless flip-chip bonding process in hydrogen environment using newly developed Sn-rich Sn-Au electroplated multilayer solder bumps is presented. Cr/Au dual layer is employed as the plating seed layer and the underbump metallurgy (UBM). This UBM design, seldom used in the electronic industry, is explained in some details. To realize the fluxless possibility, proper intermetallic growth over the composite structure is needed. In this connection, we like to point out that it is much harder to achieve fluxless bonding using Sn-rich Sn-Au design than the familiar Au-rich 80Au20Sn eutectic design. This is so because Sn-rich Sn-Au alloys have numerous Sn atoms on the surface that can get oxidized easily while the Au-Sn eutectic alloy at thermal equilibrium consists of only Au5Sn and AuSn compounds. Intermetallic nucleation and growth mechanism of sequential electroplating of Au over thick Sn layer is studied with scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction method (XRD). It is found that Au-Sn intermetallic forms as Au is plated over the Sn layer and acts as a barrier that prevents the oxidation of the inner Sn layer, making fluxless possibility a reality. It is found that the SnAu intermetallic compounds are randomly distributed in the Sn rich joint making the joint strong. The resulting joints contain few voids as examined by an SEM and a scanning acoustic microscope (SAM) and have a remelting temperature of 217degC-222degC. The plated Sn-Au solder bumps on silicon with 50 mum in height are flip-chip bonded to borosilicate glass substrate. This new fluxless flip-chip bonding process is valuable in many applications where the use of flux is prohibited

Systems and methods for nanowire growth and harvesting

Abstract: The present invention is directed to systems and methods for nanowire growth and harvesting. In an embodiment, methods for nanowire growth and doping are provided, including methods for epitaxial oriented nanowire growth using a combination of silicon precursors. In a further aspect of the invention, methods to improve nanowire quality through the use of sacrifical growth layers are provided. In another aspect of the invention, methods for transferring nanowires from one substrate to another substrate are provided.

Methods for Preparation of Graphene Nanoribbons From Carbon Nanotubes and Compositions, Thin Films and Devices Derived Therefrom

Abstract: Methods for producing macroscopic quantities of oxidized graphene nanoribbons are disclosed herein. The methods include providing a plurality of carbon nanotubes and reacting the plurality of carbon nanotubes with at least one oxidant to form oxidized graphene nanoribbons. The at least one oxidant is operable to longitudinally open the carbon nanotubes. In some embodiments, the reacting step takes place in the presence of at least one acid. In some embodiments, the reacting step takes place in the presence of at least one protective agent. Various embodiments of the present disclosure also include methods for producing reduced graphene nanoribbons by reacting oxidized graphene nanoribbons with at least one reducing agent. Oxidized graphene nanoribbons, reduced graphene nanoribbons and compositions and articles derived therefrom are also disclosed herein.