Hyung-Pil Park

New dummy design and stiffener on warpage reduction in Ball Grid Array Printed Circuit Board

Abstract Printed Circuit Board (PCB) warpage increases as thickness decreases and ultimately is attributed to CTE mismatch and thickness geometry of the components. Recently, a thin Ball Grid Array (BGA) PCB has been developed due to the advantages like high electrical translation speed with low signal noise. Large warpage severely limited by BGA PCB performance leads to reliability issues modes such as crack and delamination between interconnection components. This is why a dummy design on a BGA PCB and metal stiffener on a Flip Chip (FC) BGA PCB warpage are analyzed experimentally. At the first step, new dummy design in BGA PCB (BoC type) is proposed to reduce warpage. The new dummy design is shaped as a bar. Results of the statistical experimental analysis show PCB warpage using the new dummy design is significantly reduced compared to the use of a PCB with a conventional dummy design. Furthermore, the new dummy design decreases PCB warpage by about 67%. These results signify that the stiffness of the BoC PCB is improved by the new dummy design because the bar-shaped Cu pattern in the dummy acts as a rigid bar stiffener. At the second step, metal stiffener effect is studied to reduce coreless FCBGA PCB warpage. Coreless FCBGA PCB, coreless FCBGA package, and specimens with non-symmetric structure are considered to determine metal stiffener effect on warpage. The experimental results show that metal stiffener has high stiffness, and it seems very effective on reducing average and standard deviation of coreless PCB warpage.

A Study on the Void Formation in Residual Wall Thickness of Fluid-Assisted Injection Molding Parts

In fluid-assisted injection molding, the distribution of the residual wall thickness on the inside and outside of the curved area is different, and void is formed due to the effect of the shrinkage on the outside where the residual wall thickness is thicker. The shrinkage that takes place in the residual wall is affected by the rheological changes in the polymer caused by temperature change and also by the thermal properties of the penetration fluid. In this study, the different effects on void formation in residual wall during fluid-assisted injection molding were analyzed, and water and silicone oil that had different thermal properties were used for the fluids. For this, heat transfer analysis and injection molding analysis were conducted. The void formation occurred due to the different temperature distribution and volumetric shrinkage in the direction of the residual wall in the curved area with a hollow section. It was also found that the void formation in the curved area decreased in the case of silicone oil compared to the case of water from simulation and experiments.

Development of Metal Plate with Internal Structure Utilizing the Metal Injection Molding (MIM) Process

In this study, we focus on making a double-sided metal plate with an internal structure, such as honeycomb. The stainless steel powder was used in the metal injection molding (MIM) process. The preliminary studies were carried out for the measurement of the viscosity of the stainless steel feedstock and for the prediction of the filling behavior through Computer Aided Engineering (CAE) simulation. PE (high density polyethylene (HDPE) and low density polyethylene (LDPE)) and polypropylene (PP) resins were used to make the sacrificed insert with a honeycomb structure using a plastic injection molding process. Additionally, these sacrificed insert parts were inserted in the metal injection mold, and the metal injection molding process was carried out to build a green part with rectangular shape. Subsequently, debinding and sintering processes were adopted to remove the sacrificed polymer insert. The insert had a suitable rigidity that was able to endure the filling pressure. The core shift analysis was conducted to predict the deformation of the insert part. The 17-4PH feedstock with a low melting temperature was applied. The glass transition temperature of the sacrificed polymer insert would be of a high grade, and this insert should be maintained during the MIM process. Through these processes, a square metal plate with a honeycomb structure was made.

Experimental and Numerical Investigation of the Effect of Process Conditions on Residual Wall Thickness and Cooling and Surface Characteristics of Water-Assisted Injection Molded Hollow Products

Recently, water-assisted injection molding was employed in the automobile industry to manufacture three-dimensional hollow tube-type products with functionalities. However, process optimization is difficult in the case of water-assisted injection molding because of the various rheological interactions between the injected water and the polymer. In this study, the boiling phenomenon that occurs because of the high melt temperature when injecting water and the molding characteristics of the hollow section during the water-assisted injection process were analyzed by a water-assisted injection molding analysis. In addition, the changes in the residual wall thickness accompanying changes in the process conditions were compared with the analysis results by considering water-assisted injection molding based on gas-assisted injection molding. Furthermore, by comparing the cooling characteristics and inner wall surface qualities corresponding to the formation of the hollow section by gas and water injections, a water-assisted injection molding technique was proposed for manufacturing hollow products with functionality.

A Study on the sealing Characteristic of Automobile Waterproof Connector

Abstract Liquid silicone rubber(LSR) has been applied to various products such as electronic devices owing to its excellent thermal and chemical resistance. Hyperelastic materials, however, have properties distinguished from generalmetal materials. Hyperelastic materials show elastic behaviors in the range of large deformation in which load has the nonlinear relation with deformation. In addition, they have characteristics of nonlinearity, incompressibility, in large scale. On account of such characteristics, there are many difficulties in design and production using these materials. In this study, the load-deformation relation obtained from tension and compression tests was applied to finite element analysis in order to design waterproof connectors for automobiles. Furthermore, the effectiveness of thefinite element analysis was confirmed by comparing the results of analysis with those of performance tests. Key Words : Hyperelastic material, Liquid silicone rubber, Sealing, Waterproof connector