Young-Eui Shin

Intermetallic compound layer formation between Sn–3.5 mass %Ag BGA solder ball and (Cu, immersion Au/electroless Ni–P/Cu) substrate

The growth kinetics of intermetallic compound layers formed between eutectic Sn–3.5Ag BGA (ball grid array) solder and (Cu, immersion Au/electroless Ni–P/Cu) substrate by solid-state isothermal aging were examined at temperatures between 343 and 443 K for 0–100 days. In the solder joints between the Sn–Ag eutectic solder ball and Cu pads, the intermetallic compound layer was composed of two phases: Cu6Sn5 (η-phase) adjacent to the solder and Cu3Sn (ε-phase) adjacent to the copper. The layer of intermetallic on the immersion Au/electroless Ni–P/Cu substrate was composed of Ni3Sn4. As a whole, because the values of the time exponent (n) are approximately 0.5, the layer growth of the intermetallic compound was mainly controlled by a diffusion-controlled mechanism over the temperature range studied. The growth rate of Ni3Sn4 intermetallic compound was slower than that of the total Cu–Sn(Cu6Sn5+Cn3Sn). The apparent activation energy for growth of total Cu–Sn(Cu6Sn5+Cu3Sn) and Ni3Sn4 intermetallic compound were 64.82 and 72.54 kJ mol−1, respectively.

Dynamic modeling for resin self-alignment mechanism

Abstract A new self-alignment process using surface tension of resin material was developed to realize a low-temperature, fluxless, and cost-effective alternative alignment process for the future assembly of electronic and optoelectronic systems. In this new self-alignment process, we achieved self-alignment capability by using 3-dimensional pads to form the positioning boundary, and by mounting chips in the opposite direction. This process releases the force acted on liquid bumps, even when using resin material, which has been known not to possess self-alignment capability because of its low surface tension. As the viscosity of the resin material is considerably higher than that of the solders, the restoring force resulting from its low surface tension must be larger than the resistance force resulting from its high viscosity. In this paper, we propose a new passive alignment mechanism using the surface tension of a resin material and a comprehensive mathematical model in order to enhance understanding of the self-alignment behavior of resin. Moreover, we conducted a scaled-up experiment to calibrate and verify the models accuracy. It has been proved that resin self-alignment behavior is totally different from the oscillatory motion of solder alignment. This shows that the motion is aperiodic, regardless of the initial conditions of the system, such as an overdamped system due to the low surface tension and high viscosity characteristics of resin material.

The Influences of Residual Stress on the Frequency of Ultrasonic Transducers with Composite Membrane Structure

Arrayed ultrasonic sensors based on the piezoelectric thin film (lead-zirconate-titanate : Pb (Zro.52Tio.48) O3) having composite membrane structure are fabricated. Different thermal and elastic characteristics of each layer generate the residual stress during the high temperature deposition processes, accomplished diaphragm is consequently bowing. We present the membrane deflection effects originated from the residual stress on the resonant frequencies of the sensor chips. The resonant frequencies(fr) measured of each sensor structures are located in the range of 87.6-111 kHz, these are larger 30–40 kHz than the resultant frequencies of FEM. The primary factors offr deviations from the ideal FEM results are the membrane deflections, and the influence of stiffness variations are not so large on that. Membrane deflections have the effect of total thickness increase which sensitively change thefr to the positive direction. Stress generations of the membrane are also numerically predicted for considering the effect of stiffness variations on thefr.

The Study on Thermal Shock Test Characteristics of Solar Cell for Long-term Reliability Test

Abstract ―This study has been performed Thermal Shock test for analyze the cause of Power drop in PV(Photovoltaic) Module. Thermal Shock test condition was performed with temperature range from -40℃ ~ 85℃. One cycle time is 30min. which are consist of low and high temperature 15min. each other. The test was performed with total 500cycles. EL, I-V were conducted every 100cycle up to 500cycles. Mono Cell resulted in 8% Power drop rates in Bare Cell and 9% in Solar Cell. In the case of Multi Cell resulted in 6% Power drop rates in Bare Cell and 13% in Solar Cell. After Thermal Shock test, Solar Cells Power drop resulted from surface damages, but in the case of Bare Cells Power drop had no surface damages. Therefore, Bare Cells Power drop was confirmed as according to leakage current increase by analysis of Fill Factor after Thermal Shock test. Also, Solar Cells Power drop rates are higher than that of Bare Cell because of surface damages and consuming electric power increase. From now on, it should be considered that analyzed the reasons of Fill Factor decrease and irregular Power drop in PV module and Cell level using cross section, various conditions and test methods.

A study on μBGA solder joints reliability using lead-free solder materials

In this study, the numerical prediction of the thermal fatigue life of a μBGA (Micro Ball Grid Array) solder joint was focused. Numerical method was performed using the three-dimensional finite element analysis for various solder alloys such as Sn-37%Pb, Sn-3.5%Ag, Sn-3.5%Ag0.7%Cu and Sn-3.5%Ag-3%In-0.5%Bi during a given thermal cycling. Strain values obtained by the result of mechanical fatigue tests for solder alloys, were used to predict the solder joint fatigue life using the Coffin-Manson equation. The numerical results showed that Sn-3.5%Ag with the 50-degree ball shape geometry had the longest thermal fatigue life in low cycle fatigue. A practical correlation for the prediction of the thermal fatigue life was also suggested by using the dimensionless variable γ. Additionally Sn-3.5Ag-O.75Cu and Sn-2.0Ag-0.5Cu-2.0Bi were applied to 6X8μBGA obtained from the 63Sn-37Pb Solder. This 6X8μBGA were tested at different aging conditions at 130°C, 150°C, 170°C for 300, 600 and 900 hours. Thickness of the intermetallic compound layer was measured for each condition and the activation energy for their growth was computed. The fracture surfaces were analyzed using SEM (Scanning Electron Microscope) with EDS (Energy Dispersive Spectroscopy).

Mechanical strength and fracture mode transition of Sn-58Bi epoxy solder joints under high-speed shear test

The shear force and failure behaviors of the Sn-58Bi epoxy solder joints with various surface finishes under the high-speed shear test were investigated. The relationships between the shear speed, shear force, and fracture mode are elucidated in this study. The shear force of the Sn-58Bi solder joints increased with increasing shear speed, mainly due to the high strain-rate sensitivity of the solder alloys. Brittle interfacial fractures were more easily achieved at higher shear speed in the high-speed shear test. This result was discussed in terms of the relationship between the strain-rate of the solder alloy, the work-hardening effect, and the resulting stress concentration in the interfacial regions. The fracture mode changed from ductile solder fracture to brittle interfacial fracture with increasing shear speed. On the other hand, the different surface finish materials did not affect the shear force and fracture mode of the Sn-58Bi solder joints under high-speed shear loading.

Reliability of Fine-Pitch Flip-Chip (COG) Bonding with Non-Conductive Film Using Ultrasonic Energy

This study evaluated the reliability of fine-pitch, flip-chip bonding with ultrasonic energy and non-conductive film (NCF). The surface treatment was carried out with H2SO4 before flip-chip bonding (FCB). The electro-plated Cu bumps on the Si wafer and Cu-coated glass substrate were prepared for chip on glass (COG). The ultrasonic bonding was carried out, with and without NCF, under optimum bonding pressure and time. The mechanical properties were tested by die shear testing. The reliabilities of COG with and without NCF were evaluated with thermal shock testing, humidity and temperature (HT) testing, and high temperature storage (HTS) testing after FCB. The contact resistances of COG were evaluated for electrical reliability. To determine the variation in the initial value of the contact resistance of the flip-chip bumps according to the bonding method, the bonded interface of each sample was analyzed with scanning electron microscopy (SEM).

Development of a Visual Monitoring System for Deformation Measuring of Welded Members and its Application

Recently, in the loading tests for steel members, the deformation value is measured by calculating a distance of both cross-heads. This measuring method encounters a test error due to various environmental factors, such as initial slip, etc.. Especially, in the case of welded members, the non-uniform deformation behavior in welded joints is observed because of the effect of welding residual stress and weld metal. This is mainly responsible for a test error and a loss of the reliability for used test instruments. Therefore, to improve the accuracy and the applicability of measuring system, it is necessary to employ a visual monitoring system which can accurately measure the local and overall deformation of welded members. In this paper, to accurately measure a deformation of welded members, a visual monitoring system (VMS) was developed by using three-dimensional digital photogrammetry. The VMS was applied to the loading tests of a welded member. The accuracy and the applicability of VMS was verified by comparing to the deformation value measured by a test instrument (MTS-810). The characteristics of the behavior near a welded joint were investigated by using VMS.

A Study on The Characteristics of Solar Cell by Thermal Shock test

In this study, The report analysed the characteristics of power drop in solar cell through thermal shock test. The solar cells were tested 500 cycles in lowest temperature and highest temperature by thermal shock test on ironbound conditions, that excerpted standard of PV Module(KS C IEC-61215). The result of the efficiency analysis through measure of I-V, efficiency of Cell decreased from 13.9% to 11.0% and decreasing rate was 20.9% after test. The result of the surface analysis through EL, solar cell has damage of gridfinger and ribbon joint. Cell cracks were founded in damage of cells through cross section of solar cells. Also, Fill factors were decreased from 72.3% to 62.0% after thermal shock test and decreasing rate is 11.8%. therefore, Yearly power drop is aggravated with facts that cell crack, damage of surface and power loss of cell by change of I-V characteristic curve with decreasing of parallel resistance.

Study on the Long-term Reliability of Solar Cell by High Temperature & Humidity Test

In this study, The report analysed the characteristics of power drop and damage of surface in solar cell through high temperature and humidity test. The solar cells were tested during the 1000hr in temperature and 85% humidity conditions, that excerpted standard of PV Module(KS C IEC-61215). An analysis of the cell surface through EL(Electroluminescence), the cell has partly change of surface in yearly. Single-crystalline Solar cell efficiency is decreased from 17.7% to 15.6% and decreasing rate is 11.9%. On the other hand, Poly-crystalline Solar cell efficiency is decreased from 15.5% to 14.0% and decreasing rate is 9.3%. A comparison of the fill factor for analysis of electro characteristic in yearly, Single-crystalline Solar cell efficiency is decreased from 78.7% to 78.1% and decreasing rate is 4.7%. On the other hand, Poly-crystalline Solar cell efficiency is decreased from 78.1% to 76.7% and decreasing rate is 1.8%. Single-crystalline has more bigger power drop than poly-crystalline by the silicon purity and silicon atom arrangement. Also, FF decreasing rate has more bigger drop than efficiency decreasing rate for the reason that the damage of surface by exterior environmental factor is the more influence in cell than other reason that is decreasing FF by damage of p-n junction.