Dong-Ok Kwak

Anisotropic viscoelastic shell modeling technique of copper patterns/photoimageable solder resist composite for warpage simulation of multi-layer printed circuit boards

In this study, the warpage simulation of a multi-layer printed circuit board (PCB) was performed as a function of various copper (Cu) patterns/photoimageable solder resist (PSR) composite patterns and their anisotropic viscoelastic properties. The thermo-mechanical properties of Cu/PSR patterns were obtained from finite element analysis (virtual test) and homogenized with anisotropic composite shell models that considered the viscoelastic properties. The multi-layer PCB model was simplified based on the unit Cu/PSR patterns and the warpage simulation during the reflow process was performed by using ABAQUS combined with a user-defined subroutine. From these results, it was demonstrated that the proposed anisotropic viscoelastic composite shell simulation technique can be successfully used to predict warpage of multi-layer PCBs during the reflow process.

Development of Reliability Verification System for Robust Package Design

To achieve design for reliability (DFR), a reliability verification system (RVS) was developed. Package level and board level reliabilities were predicted by the developed system automatically and the design for six sigma (DFSS) was achieved. Process server and database server were developed. FEM mesh was generated automatically by well-organized builder, simulation conditions were assigned by standardized procedure, and reliabilities were calculated by developed life models. All data related to the simulation were managed by database system. High quality simulation was carried out easily and quickly. Robust package design was achieved by design optimization using the RVS.

Warpage Simulation of a Multilayer Printed Circuit Board and Microelectronic Package Using the Anisotropic Viscoelastic Shell Modeling Technique That Considers the Initial Warpage

In this paper, the warpage simulation of a high-density multilayer printed circuit board (PCB) for solid-state disk drive (SSD) and microelectronic package was performed using the anisotropic viscoelastic shell modeling technique. The thermomechanical properties of various copper patterns were homogenized with the anisotropic shell model, which considered their viscoelastic properties. Then, warpage simulations of an SSD PCB unit/array and a full microelectronic package were performed; these simulations accounted for the initial warpage that occurred during fabrication using ABAQUS combined with a user-defined subroutine. Finally, it was demonstrated that both the maximum warpage and the remaining residual warpage of the full microelectronic package can be accurately predicted.

Characterization of Wire Bondability on Overhang Structured Chip in Multi Chip Package

Characteristics of wire bonding on the overhang structured chip were investigated in this study. During the wire bonding process, chip crack and bondability were severe factors for thin wafer bonding. Chip crack was investigated by chip strength test and parametric study was performed by changing bonding parameters, constant velocity, force, and power. Bondability was measured for 500, 700, and 1000 mum overhang length. Bonding strength was tested by ball shear test method. 700 mum overhang showed better performance than 500 mum. 1000 mum overhang showed very low bondability. Bonding characteristics were observed by numerical FEM method. Nonlinear dynamic analysis was performed. Unstable contact pressure and shear stress were observed between ball and metal pad. Noise of reaction force was increased with overhang length.

Bi-directional homogenization equivalent modeling for the prediction of thermo-mechanical properties of a multi-layered printed circuit board (PCB)

Warpage of multi-layered printed circuit boards (PCB) during the reflow process is a serious problem which affects the reliability of solder ball connections between the PCB and the mounted semi-conductor packages in electronic devices. It is essential to predict the warpage of the PCB accurately; however, the complicated copper patterns in multi-layered PCBs render a full modeling analysis impossible due to the excessive computing time required. To overcome this problem, we have developed analytical equations of three Cu patterns (line, square, and grid) for the application of thermo-mechanical properties simply by equivalent modeling of Cu patterns. In the proposed equations, the effect of thermo-viscoelastic properties as well as the influence of surrounding layers such as woven glass fabric/BT (bismaleimide triazine), composite laminate (BT core), and photoimageable solder resist (PSR) were considered. To verify the developed equations, vibration tests based on the wave propagation approach were performed at various temperatures. Good agreement was observed between the equivalent model and the experimental results.