Bongtae Han

Advanced iterative algorithm for phase extraction of randomly phase-shifted interferograms

An advanced random phase-shifting algorithm to extract phase distributions from randomly phase-shifted interferograms is proposed. The algorithm is based on a least-squares iterative procedure, but it copes with the limitation of the existing iterative algorithms by separating a frame-to-frame iteration from a pixel-to-pixel iteration. The algorithm provides stable convergence and accurate phase extraction with as few as three interferograms, even when the phase shifts are completely random. The algorithm is simple, fast, and fully automatic. A computer simulation is conducted to prove the concept.

Characterization of hygroscopic swelling behavior of mold compounds and plastic packages

Hygroscopic swelling behavior of mold compounds is analyzed by a novel experimental procedure using a whole-field displacement technique. Large variation in moisture content at the virtual equilibrium state is observed, while the coefficient of hygroscopic swelling is shown to not vary significantly. An investigation on an actual package is also performed to determine the hygroscopic swelling mismatch strains at the chip/mold compound interface. The results are compared with the thermal expansion mismatch strains at the same interface and reveal much higher hygroscopic swelling mismatch strains. The hygroscopic strains must be considered for reliability assessment when a package is subjected to environments where the relative humidity fluctuates.

Physics-of-Failure, Condition Monitoring, and Prognostics of Insulated Gate Bipolar Transistor Modules: A Review

Recent growth of the insulated gate bipolar transistor (IGBT) module market has been driven largely by the increasing demand for an efficient way to control and distribute power in the field of renewable energy, hybrid/electric vehicles, and industrial equipment. For safety-critical and mission-critical applications, the reliability of IGBT modules is still a concern. Understanding the physics-of-failure of IGBT modules has been critical to the development of effective condition monitoring (CM) techniques as well as reliable prognostic methods. This review paper attempts to summarize past developments and recent advances in the area of CM and prognostics for IGBT modules. The improvement in material, fabrication, and structure is described. The CM techniques and prognostic methods proposed in the literature are presented. This paper concludes with recommendations for future research topics in the CM and prognostics areas.

Moiré Methods for Engineering and Science — Moiré Interferometry and Shadow Moiré

Moire interferometry and shadow moire are extraordinarily versatile and effective methods for determining in-plane and out-of-plane displacement fields, respectively. The basic concepts are reviewed for both methods, topics on practice and analysis are addressed, and numerous examples of important applications are presented.

THERMAL STRESSES IN MICROELECTRONICS SUBASSEMBLIES: QUANTITATIVE CHARACTERIZATION USING PHOTOMECHANICS METHODS

Several optical methods for in-situ displacement measurement are presented as a tool to characterize thermomechanical behavior of microelectronics subassemblies. Features and recent developments of the methods are reviewed and applications to diverse problems are illustrated to demonstrate wide applicability of the methods. The whole-field displacement information, with various sensitivity and resolution scales, is ideally suited for the deformation study of a broad range of problems in microelectronics packaging. The methods are mature and they can be practiced routinely. More applications are anticipated.

On Moisture Diffusion Modeling Using Thermal-Moisture Analogy

Thermal-moisture analogy schemes for a moisture diffusion analysis are reviewed. Two schemes for practical applications are described using the governing equations of heat and mass diffusions: (1) direct analogy and (2) normalized analogy. The schemes are implemented to define valid domains of application. The results corroborate that the direct analogy is valid only for single-material systems, but the normalized analogy can be extended to multimaterial systems if thermal loading conditions are isothermal, spatially as well as temporally.

Advanced Thermal-Moisture Analogy Scheme for Anisothermal Moisture Diffusion Problem

We propose an advanced thermal-moisture analogy scheme to cope with the inherent limitations of the existing analogy schemes. The new scheme is based on the experimentally observed unique hygroscopic behavior of polymeric materials used in microelectronics; i.e., the saturated concentration is only a function of relative humidity regardless of temperature. A new analogy formulation based on the modified solubility is presented and the scheme is implemented to investigate its accuracy and applicability. The results from a simple case study corroborate that the advanced scheme can be used effectively for package assemblies subjected to general anisothermal loading conditions.

Development of real time/variable sensitivity warpage measurement technique and its application to plastic ball grid array package

Far infrared Fizeau interferometry (FIFI) and shadow moire with enhanced sensitivity (SMES) are developed for real time warpage measurement of microelectronics devices. The methods are implemented in a compact apparatus that is based on a computer controlled environmental chamber. The apparatus combines the two methods to provide unique capabilities of thermally induced warpage measurement with variable sensitivity, ranging from 5.3-100 /spl mu/m. The methods are employed to document warpage of plastic ball grid array packages subjected to various thermal cycles.

On the design parameters of flip-chip PBGA package assembly for optimum solder ball reliability

An experimental investigation of the warpage of a flip-chip plastic ball grid array package assembly is presented and a critical deformation mode is identified. The experimental data, documented while cooling the assembly from the underfill curing temperature to -40/spl deg/C, clearly reveal the effect of the constraints from the chip and the PCB on the global behavior of the substrate. The constraints produce an inflection point of the substrate at the edge of the chip. An experimentally verified three-dimensional (3-D) nonlinear finite element analysis proceeds to quantify the effect of the substrate behavior on the second-level solder ball strains. An extensive parametric study is conducted to identify the most critical design parameter for optimum solder ball reliability.

Inverse Method to Determine Elastic Constants Using a Circular Disk and Moiré Interferometry

We propose an inverse method, using a circular disk in diametrical compression, for the simultaneous determination of two elastic constants,E andv, from a single displacement map. Moiré interferometry combined with the phase-shifting technique provides a full-field displacement field. An overdeterministic approach using the least-squares method is implemented to fit the experimentally determined displacements to the theoretical solution. An implementation guideline is provided, considering the effects of accidental rigid-body motions, random noise and imperfect position of the origin. Accuracy and repeatability of the proposed method are verified experimentally.