Research

1) “ Measuring mechanical behavior of components as a function of temperature using moire and shadow-moire interferometry” Dr. James Pitarresi and Brian D Roggeman

Parts tested include a wide array of PBGAs,CBGAs, TSOPs, QFPs, Flip chip devices, CSPs and WLCSPs, as well as portions of printed circuit boards and fully assembled devices. During the ongoing research, advances and improvements were made to the processes of both moire and shadow-moire interferometry systems. Also, the development of a high-g shock machine began and testing of populated motherboards was done at relatively high accelerations.

2) “ Shock testing and modeling of mounted components ” Dr. James Pitarresi and Brian D Roggeman

3) " Characterization of thermo-mechanical behavior of Pb-free Ceramic Column Grid Array (CCGA) package using Moiré Interferometry " Dr. S.B. Park and Rahul Joshi

The thermo mechanical behavior of the ceramic lead-free copper column grid array (CuCGA) package has been characterized under accelerated thermal cycling using high sensitivity moiré interferometry and compared with conventional ceramic tin-lead column grid arrays (CCGA). Unlike tin-lead columns, where the failure occurs at the column near the top of the solder fillet and through the thickness of the column, in the CuCGA, the failure is found to occur first in the solder fillet along the periphery of the copper column that propagates along the boundary of the column and solder fillet. The accumulated plastic deformation per cycle is bigger in tin-lead columns compared to the copper columns. A deformation mechanism is provided to explain the nature of this failure.

4) " A Proper Life Projection of Organic Flip Chip Package through Power Cycling " Dr. S.B. Park and Izhar Ahmed

The applicability of accelerated thermal cycling (ATC) for organic packages was reevaluated. Conventionally, fatigue life is obtained empirically through accelerated thermal cycling (ATC) since it is assumed to simulate worse case condition in all the packages. In reality, an assembly is subjected to Power Cycling i.e. non-uniform temperature distribution with chip as the only source of heat generation. This non-uniform temperature and different coefficient of thermal expansion (CTE) of each component makes the package deform differently than the case of uniform temperature in case of organic packages. In this work, a proper power cycling (PC) analysis scheme was proposed and conducted to predict solder fatigue life of organic flip chip package. Numerical simulations were performed by combination of computational fluid dynamics (CFD) and finite element analyses (FEA). CFD analysis was used to extract transient heat transfer coefficients while subsequent thermal and structural FEA was used to grade the relative fatigue life. Heat generation and heat transfer coefficient from CFD was applied as thermal boundary conditions for extracting transient nodal temperature loads. Fatigue Life Prediction showed that Power Cycling simulates more severe condition than ATC for certain Organic Packages.

5) "The Role of Intermetallics in Electromigration in Solder Bumps for Lead Free Solder Structure and Its Solder-Pad Combination" Dr. S.B. Park and Ganesh Iyer

It is attempted to quantify the role of intermetallics for the electromigration in flip chip solder interconnects (C4). Intermetallics are formed at the interface of solder and metallic pad where they serve as metallic bonding agent. For the transition to the Pb-free solder interconnects, electromigration is one of the prime reliability concerns. It is observed that some flip chip solder interconnect fails earlier than the estimated time to failure. It is explained by the effect of intermetallics formed by solder and different matching pad metallurgies. This paper quantifies the role of the intermetallics in the time to failure for a system. A series of experiments are being conducted to determine the current exponent and activation energies of the Black’s equation for different solder and pad metallurgy combinations. Two test structures are proposed. The first test structure was made to study the role of the intermetallics and the second structure was made to characterize the pure solder’s electromigration.

6) " Study on the phase change of solder in CSP with lead-free solder during 2 nd level packaging " Dr. S.B. Park and Dr. Chung

The lead-based solders such as eutectic or high-Pb solder have been used to provide electrical continuity and structural member between chip and substrate. The lead-based solders have the advantages of the low melting point and the variation of melting point according to the ratio of lead. However, the use of lead should be decreased sooner or later due to the environmental regulation, etc. The use of lead-free solder causes several problems in manufacturing of electronic packaging. Among those, the most severe phenomenon is that the phase of lead-free solid solder in CSP(Chip Scale Package) can be changed to liquid during 2 nd level packaging(system packaging) because the difference of melting point between lead-free solders is insignificant. Since the metals extremely expand when they are heated up to the melting point, the high pressure is applied to the surrounding material and may cause the crack at the interface between chip or substrate and underfill. Thereafter, the underfill is detached from chip or substrate and a short circuit can happen. In this study, the effects of volume expansion of solder will be numerically simulated by using ANSYS, and the crack propagation caused by the pressure of liquid metal will be implemented. The material characteristics such as creep and CTE of solder will be obtained by experimental tests. Furthermore, the desired material property or the spacing of solder will be investigated for safe electronic packaging. From this study, the obstacle related to the electronic packaging with lead-free solder will be removed.

7) " Development of a methodology for service life prediction of aircraft parts " Dr. S.B. Park and Dr. Chung

All the structural components of a mechanical system have life time and should be repaired before that time in order to operate the whole system. Specially, the maintenance and the accurate prediction of service life are very important in the fields of aircrafts. Therefore, a durability analysis methodology will be developed for predicting the durability of critical control points in this study. For this, the literature survey will be performed for the essential procedures of durability and fatigue analyses, and the concepts of fracture and damage mechanics will be studied. The loading and boundary conditions representing the real environment will be investigated by changing many variables. The methodology will be verified by comparing with the service life obtained by other programs. After the methodology is established, it will be applied to the parametric study for a new design with increased life.

8) " Reliability issues of the Lead free solder in during reflow " Dr. S.B. Park and Zhenming Tang

Our research is focused on the reliability issue of Pb free solder during reflow process. . The component of solder bumps between chip and substrate is SAC (Sn-Ag-Cu), have a melting temperature of 217 degree Celcius. The solder balls between substrate and PCB have the same component as solder bumps. In order to stick substrate and PCB together, whole package is heatedabove 217 degree Celcius in oven. So solder bumps will be melted during heating and the volume of solder ball will expand. The expansion of solder bumps is much more than that of under fill material ‘Epoxy’. The expansion may induce some reliability problems. So it is important to find out phase change phenomena and research how much the volume expands from solid to liquid. So we are trying to model this phase change phenomena. First, an experiment is set up, which is used to observe the metal volume expansion from solid to liquid. From the experiment, CTE (coefficient of thermal expansion) of liquid metal and volume via temperature picture are obtained. Second, FEA method is used to analyze solder balls in liquid state and the structure of chip and substrate.

9) " The Package Of Underwater Detection Devices And Its Deployment By Airdrop " Dr. S.B. Park and Xiping Huo

The package is designed to house underwater detection devices and to be employed to the deployment by airdrop. Since the detection devices are employed for underwater detection purpose, their packaging must be hermetic. The hermetic package prevents the diffusion of moisture and water vapor through its walls. And the hermetic package significantly increases the long term reliability of electronic components performance. On the other hand, the detection devices are used to detect the nuclear radiation. And they are deployed into the place that it is difficult to reach by the ordinary way. So they are normally located as desired by aircraft. When the packages enter the water during airdrop, they might be damaged by water impact. So the deployment techniques are adopted to protect the device from the damage of the water impact.