Hyo Soo Lee

Analysis on thermal resistance of LED module with various thermal vias

Light Emitting Diode (LED) has been already familiar that is used as lighting sources of general electronic devices and various displays. LED has many advantages such as long life, low power consumption and high reliability. In the future, as alternative to fluorescent lighting, it is sure that LED in lighting products is expected to receive much attention. However, the components related with advanced LED packages or modules have been issued on the heat from LED chip. And the LED chip is still being developed to the high power devices which are generating more heat. In this study, we investigated the variation of thermal resistance in LED modules embedded with thermal via. Through the analysis of thermal resistance with various test vehicles, we could obtain the concrete relationship between thermal resistance and structure of thermal via.

The Dependence of PET Layer on the Thermal Stability of PET-ITO Substrate for Mobile Electronics

The PET-ITO substrate has been usually applied to many flexible applications such as selectively conducting films, flexible printed circuit, display panels, interconnections, terminals, etc., where the PET-ITO substrate has a main role to enhance the performance in the components of touch screen panels, solar cell panels and so on. Today’s flexible technology is issued on forming fine pattern, pattern alignment and mass-productivity on PET-ITO substrates, which is strongly related to thermal shrinkage and expansion of the substrate[1~5]. We investigated in this study the thermo-mechanical behavior of PET-ITO substrate using a thermo-mechanical analyzer (TMA) in order to analyze thermal strain with varying temperature.

Fabrication and Properties of a Combined Structural Cu Sheet for Interconnect Material

In this study, it was aimed to develop a novel interconnect material simultaneously possessing high electrical conductivity and strength. Combined structural Cu sheets were fabricated by forming the high electrical conduction paths of Ag on the surface of high strength Cu alloy substrate by damascene electroplating. As a result, the electrical conductivity increased by 40%, while the ultimate tensile strength decreased by only 20%. When the depth of Ag conduction path was deep, fracture zone ratio as well as roll-over zone increased.

Grain Size Dependence of Tensile Properties in Cu-Sn Thin Foils (Experimental Study)

This study was carried out to investigate the effects of grain size on mechanical properties in Cu-Sn foil with a thickness of 30 um. The grain size was varied from approximately 7 um to 50 um using heat treatment at 773 K for 2 h to 24 h in a vacuum atmosphere. Tensile test was carried out at room temperature with strain rate of 1mm/min. Typical yield drop phenomenon was observed. Mechanical properties were found to be strongly affected by microstructural features including grain size. The yield strength and tensile strength gradually decreased with increasing the grain size. The strain to fracture also decreased by grain growth. These results could be explained by not only the grain size dependence of yield strength but also the ratio of thickness to grain size dependence of yield strength.

Process Dependence of Microstructure and Mechanical Properties for Al-Fe Based Bulk Alloys

In this work, a comparative study of the microstructure and mechanical properties of Al-8Fe based bulk alloys fabricated by three different rapid solidification methods and subsequent hot extrusion was carried out. Spray forming, gas atomization, and melt spinning methods were used as techniques for rapid solidification having various cooling rates. Equiaxed grains containing Al-Fe, Al-Fe-(Mo, V), and Al-Zr phase particles were characterized. The yield strength of the melt spun and extruded specimen was estimated to approximately 800 MPa at room temperature, a value which is roughly 1.5 times higher than that obtained for the atomized and extruded specimen and roughly 2.5 times higher than for the spray formed and extruded specimen. The higher strength of the melt spun and extruded specimen originated from a finer microstructure compared to the atomized and extruded specimen and the spray formed and extruded specimen.

Tensile Behavior of Rolled and Annealed Copper Thin Foils

Tensile properties of rolled and annealed copper thin foils were investigated based on the grain size and thickness. Yield strength was higher in the thinner foil than in the thicker foil at as-rolled state. Difference of yield strength between the thinner foil and the thicker foil becomes small at annealed state. Tensile strength was higher in the thinner foil than in the thicker foil at as-rolled state, but it was reversed at annealed state. Strain to fracture or elongation increased with increasing thickness in the annealed state. A knife edge type of fracture was characterized in both the as-rolled state and the annealed state. A higher tensile strength and strain to fracture of the annealed thicker foil was attributed to the higher number of grains per thickness. From this work, it was concluded that mechanical properties of thin foils were dependent upon the number of grains per thickness.

Microstructure and Hardness Property of Internally Oxided AgCdO Alloy

Microstructure and hardness property of AgCd alloy internally oxided at 973K for 1 h - 24 h with O2 atmosphere of 3 atm was investigated. Band typed CdO phase was formed at grain boundaries, and particle typed CdO phase was formed at grain interior. In this alloy, it was found that oxygen adsorpted at surface diffuses to interior through grain boundaries, and it subsequently diffuses into grain interior during internal oxidation. No Ag exduation was found in this alloy. The thickness of oxidized layer increased with increasing holding time at given temperature. Hardness of the oxidation zone was 125 ± 5 Hv, which value is higher two times than that of the oxidation free zone. The higher hardness of oxided region than the oxidation free zone was attributed to the dispersion strengthening by CdO particles.

Thermal Resistance and Heat Dissipation of LED PCB with Thermal Vias

Light Emitting Diode (LED) has been already familiar that is used as lighting sources of general electronic devices and various displays. LED has many advantages such as long life, low power consumption and high reliability. In the future, as alternative to fluorescent lighting, it is sure that LED in lighting products is expected to receive much attention. However, the components related with advanced LED packages or modules have been issued on the heat from LED chip. And the LED chip is still being developed to the high power devices which are generating more heat. In this study, we investigated the variation of thermal resistance in LED modules embedded with thermal via. Through the analysis of thermal resistance with various test vehicles, we could obtain the concrete relationship between thermal resistance and structure of thermal via.

Effectiveness of Residual Stress on Forming Copper Patterns of Printed Circuit Board

The effectiveness of residual stress on forming copper patterns of printed circuit board was investigated during applied thermal conditions. Generally, the electrolytic copper foil showed a compressive residual stress about -54MPa as received, which easily caused to form copper patterns irregularly. We verified the compressive residual stress was relaxed with applying thermal conditions under 200°C for a few hours. And also, we observed that the compressive residual stress of copper foil tended to be relaxed, constant, and compressive again during heating times at each temperature. The relationships between residual stress and etching factor of copper pattern were analyzed in this works.

Variation of Heat Dissipation Properties of LED Packages with Thermal Vias

Light emitting diode (LED) has been largely used in industry of consumer electronics such as cell-phones, PDAs, and computers. Since all light sources convert electric power into radiant energy and heat, LED also does the same with an increase of its power. Generally, it only converts 15~25% of electric power into visible light; the rest of the power, 75~85%, is converted into heat. This excess heat should be conducted away from the LED die to circuit boards or heat sinks since heat affects directly performance of the LED. The piled heat in LED products brings color shift and reduces light output very rapidly. Furthermore, the lifecycle of LED products shorten if the heat problem continues. In order to prevent LED products from these negative effects, effective thermal resistance paths need to be achieved so that LED products let the heat conduct from the LED to the outside such as printed circuit board. In this research, optimization studies on thermal-via is to be performed. The 1W and 3W LED assembled printed circuit board with 16 different via designs is set up to measure its temperature for 4 hours in a real time. It was obtained by this work that the optimized thermal via was very effective to dissipate the heat from the LED.