Seunghee Oh

Adhesion improvement of epoxy resin/copper lead frame j oints by azole compounds

The adhesion strength of epoxy resin/copper joints is often very poor, due to the naturally formed copper oxide having a low mechanical strength. To improve the adhesion strength of epoxy resin/copper lead frame joints, copper lead frames were treated with azole compounds as adhesion promoters. The azole compounds used were benzotriazole (BTA), benzotriazole-5-carboxylic acid (CBTA), 8-azaadenine, imidazole, 2-methyl imidazole, urocanic acid, adenine, benzimidazole, and polybenzimidazole (PBI). The dependence of the adhesion strength of epoxy resin/azole-treated copper joints on the structure of the azole compound, the azole treatment time, and the azole treatment temperature was investigated. The surface coverage of azole-treated copper was examined by contact angle measurements, a surface defect test, optical microscopy, and scanning electron microscopy (SEM), and the locus of failure was studied by X-ray photoelectron spectroscopy (XPS). Triazole compounds such as CBTA and 8-azaadenine showed excellent...

Adhesion improvement of epoxy resin/polyimide joints by amine treatment of polyimide surface

Abstract Polyimide (PI) surfaces were modified to improve the adhesion strength of epoxy resin/PI joints by immersing in amine solutions. Adhesion strength of epoxy resin/amine-treated PI joints were measured depending on structure, molecular weight, concentration, treatment time and drying temperatures of amines. There was an optimum drying temperature for maximum adhesion strength after amine-treatment of PI surface. The optimum drying temperature and the maximum adhesion strength increased with increasing the molecular weight of diamines or polyamines. Poly(amic amide) was formed by the reaction of primary amine of diamines and imide group of PI, and the other primary amine of poly(amic amide) reacted with the imide groups of adjacent PI chains to form cross-linked structure. In this way, adhesion strength of epoxy resin/PI joints was improved by reinforcing the weak PI surface layer. Another additional adhesion mechanism could be the chemical reaction of epoxide in the epoxy resin and unreacted amine of poly(amic amide). Adhesion strength decreased at above the optimum drying temperature since poly(amic amide) was imidized. The adhesion mechanisms and existence of optimum drying temperature were investigated using FT i.r., contact angle goniometer, X-ray photoelectron spectroscopy and rheometric dynamic spectroscopy.

Adhesion improvement of epoxy resin to alloy 42 lead frame by silane coupling agents

Three different silane coupling agents were used to improve the adhesion between epoxy resin and alloy 42 lead frame. The adhesion strength and durability of epoxy resin/silane coupling agent-treated alloy 42 joints were investigated. The highest initial adhesion strength, 200 N/m, was obtained with γ-aminopropyltriethoxysilane (y-APS), but durability in a high humidity environment was best with N-,β-(aminoethyl)-y-aminopropyltrimethoxysilane (AAMS). An optimum concentration of the silane coupling agent was determined and thermal stability was studied by thermogravimetric analysis (TGA). Vapor phase deposition of the AAMS silane coupling agent was also employed and compared with dipping of the lead frame in the silane coupling agent solution. Moisture absorption behavior was examined for different silane coupling agents and for different geometries of the joints to resolve the moisture absorption path of joints. The improvement in adhesion obtained by applying a silane coupling agent to the lead frame can...

Development of PCB design guide and PCB deformation simulation tool for slim PCB quality and reliability

In this paper, major concerns from the use of slim PCB are considered and several efforts to solve the trouble are introduced. The critical phenomena by the application of slim PCB are large warpage generated during reflow (soldering) process and large deformation of IC package by external impact environment. Those are due to the low bending rigidity according to the decrease of thickness, and increase the SMD process defect and decrease the drop reliability of IC package mounted on PCB. To solve those issues, various experiment and simulation are performed. First, PCB internal layer material to resist high temperature is investigated. To predict large warpage during reflow process, PCB thermo-mechanical simulation tool is also developed. To increase drop reliability of BGA package, robust design guide for drop impact condition is studied. Last, PCB pad surface finish recently developed is introduced to find the possibility to increase solder joint strength. Based on the material, process and reliability approaches, current PCB deformation level for main board is shown and the optimal PCB design for smaller warpage and larger reliability is obtained.

Drop reliability of glass panel for LCD

In this paper, drop reliability of TFT-LCD panel and module used in digital cameras is investigated since LCD glass failure is one of the most critical quality issues in handheld products. First, three point bending test is performed to evaluate LCD glass quality. The critical force is measured in the bending test even though the data scatter is not small. Second, three point bending simulation is performed by using the critical force obtained from the bending test. For the assessment of glass panel crack, EWK(ESI-Wilkins-Kamoulakos) damage and rupture model is utilized in the bending simulation. Finally, drop impact test and simulation are carried out to verify the drop reliability assessment process for LCD glass panel.

Determination of the molecular assembly of actin and actin-binding proteins using photoluminescence

Actin, the most abundant protein in cells, polymerizes into filaments that play key roles in many cellular dynamics. To understand cell dynamics and functions, it is essential to examine the cytoskeleton structure organized by actin and actin-binding proteins. Here, we pave the way for determining the molecular assembly of the actin cytoskeleton using direct photonic in situ analysis, providing the photoluminescence characteristics of actin as a function of filament length and bundling, without labeling. In experiments for monomeric and filamentous actin reconstituted in vitro, structural forms of actin are identified from the peak positions and intensities of photoluminescence. Actin monomers exhibited small intensity emission peaks at 334 nm, whereas filamentous and bundled actin showed a shifted peak at 323 nm with higher intensity. The peak shift was found to be proportional to the length of the actin filament. With probing structural change of actin in various cells in vivo, our study provides an efficient and precise analytical in situ tool to examine the cytoskeleton structure. It will be beneficial for elucidating the mechanism of various cellular functions such as cell migration, differentiation, cytokinesis and adhesion. Furthermore, our technique can be applied to detect the alterations in the cell cytoskeleton that can occur during many pathological processes.

A modified berman model for the prediction of time-dependent dielectric breakdown (TDDB) characteristics of low-k/ULK interconnect dielectrics from dual-voltage ramp dielectric breakdown (DVRDB) test

We present a modified Berman model that relates breakdown voltage distributions, from dual voltage ramp dielectric breakdown (DVRDB) test, to the distribution of time-to-fail (TTF) during constant voltage stress (CVS) conditions, assuming that dielectric failure behavior under a constant voltage stress follows the square-root E-model. The methodology presented in this work demonstrates a fast and very effective way of extracting the voltage acceleration parameter (i.e., electric field dependence) and predicting TTF under CVS TDDB test conditions. Both low-k (k=3D2.7) and ULK(k<2.5) DVRDB and CVS TDDB data of 45nm and 32nm dielectrics are presented, along with the model predictions and Monte-Carlo simulation results.