Research on Thermal Analysis of Iris Recognition Module Package Structure

A physical model is presented that describes mechanisms for operating-equipment junction-to-ambient thermal resistance in excess of a typical component manufacturer's data-sheet value by as much as a factor of four under constant cooling conditions. The model accounts for the discrepancy between system thermal performance of a package and data-sheet thermal resistance value which are not accompanied by qualifying data in the form of junction-to-header thermal resistance, board temperature rise over ambient, convection coefficient, mounting sensitivity, and power dissipation. The eight constants used to predict inherent increases in package thermal resistance when going from the data-sheet-specified operating conditions to the excess-value conditions are described. These constants and procedures for obtaining them are given for dual in-line packages (DIPs), pin-grid arrays (PGAs), small-outline transistors (SOTs), and plastic leaded chip carriers (PLCCs). >

In this paper, the thermal performance analysis and optimization of the package of a specific multi-heat source power device is carried out. Firstly, the finite element analysis software ANSYS Icepak is used as a tool to build a simplified model of the array type multi-power device package module. Secondly, the impact of five variable parameters on thermal performance of multi-heat source power devices is analyzed. These parameters are chip size, chip power consumption, die attach material, packaging material, package size. Finally, through the orthogonal test analysis method, the junction temperature and thermal resistance of the package are selected as the test indexes, and five parameters are selected as the orthogonal test factors to analyze the influence of the five parameters on the thermal performance. The results show that the thermal conductivity of the die attach material is most significant regardless of the package junction temperature or thermal resistance. By summarizing the influence of various factors on the thermal performance of power devices, the suggestions for optimizing the thermal performance of multi-heat source power devices are proposed. The results obtained have important guiding significance for the thermal performance optimization of power devices.

Constructal design of I-shaped high conductive pathway for cooling a heat-generating medium considering the thermal contact resistance

In this paper, the effects of eutectic voids in bonding area on the thermal resistance and light output power of flip-chip ultraviolet light-emitting diode (UV-LED) devices have been studied by experiments in detail. It has been demonstrated that the eutectic voids effectively influenced the thermal resistance, the junction temperature, and the light output power of the UV-LEDs. The UV-LEDs with lower eutectic voidage exhibited a superior thermal performance based on the thermal resistance analysis. The thermal resistance was greatly reduced by 48% and the junction temperature by 3.5 °C as the driving current was 800 mA when the eutectic voidage decreased from 30% to 3%. As a consequence, a maximal enhancement of 13.3% of light output power was obtained when the LED was driven by a current of 1500 mA. These results confirmed that a better performance of eutectic flip-chip UV-LED can be obtained with lower eutectic voidage for the reason that the thermal resistance and junction temperature can be decreased effectively.

Study on thermal conductivity of cement with thermal conductive materials in geothermal well

Experimental Study on the Thermal Performance of Rice Straw-Mortar Composite Materials

The optical performance and reliability of High power light emitting diode (HP-LED) devices can be affected by the junction temperature, while thermal resistance is one of the main factors which influence the p-n junction temperature, especially for the thermal spreading resistance. So, Thermal analysis was conducted by differential structure functions combining with finite element analysis and calculation of thermal spreading resistance of HP-LED devices. The results show that thermal spreading resistance plays an important role on total thermal resistance of LED devices. The thermal spreading resistance shows a declined and then increased trend with the increase of substrate thickness; the contact area between the heating source and substrate is the main factor which influences thermal spreading resistance; It is beneficial to decrease the thermal spreading resistance when contact area ratio be increased. Thermal-convection resistance becomes the main factor that influences total thermal resistance of HP-LED devices with the changing of substrate bottom area, while the influence of thermal spreading resistance is weak. The eccentric distance between chip and substrate plays a distinct impact on thermal spreading resistance and junction temperature. The results of finite element simulation are in good agreement with calculation of thermal spreading resistance.

The optical performance and reliability of High power light emitting diode (HP-LED) devices can be affected by the junction temperature, while thermal resistance is one of the main factors which influence the p-n junction temperature, especially for the thermal spreading resistance. So, Thermal analysis was conducted by differential structure functions combining with finite element analysis and calculation of thermal spreading resistance of HP-LED devices. The results show that thermal spreading resistance plays an important role on total thermal resistance of LED devices. The thermal spreading resistance shows a declined and then increased trend with the increase of substrate thickness; the contact area between the heating source and substrate is the main factor which influences thermal spreading resistance; It is beneficial to decrease the thermal spreading resistance when contact area ratio be increased. Thermal-convection resistance becomes the main factor that influences total thermal resistance of HP-LED devices with the changing of substrate bottom area, while the influence of thermal spreading resistance is weak. The eccentric distance between chip and substrate plays a distinct impact on thermal spreading resistance and junction temperature. The results of finite element simulation are in good agreement with calculation of thermal spreading resistance.

The effect of organic–inorganic interfaces on the thermal conductivity of composite materials was studied by evaluating thermal conductive resistance at the organic–inorganic interfaces experimentally. Polymer layers were sandwiched between thin ceramic plates to produce multilayer stacked samples. Through the comparison between the thermal conductivities of the multilayer stacked materials and those of single component materials for both polymers and ceramics, the thermal resistance at the interface between a polymer and a ceramic plate was evaluated. The results suggest that the contribution of thermal resistance becomes significant for actual composite materials because of the increase in the number of interfaces. The results also demonstrate that organic modifications of an inorganic surface could effectively reduce interfacial thermal resistance. The control of interfaces seems to be effective for improving the thermal conduction property of composite materials.

In recent high power LED applications, metal core PCB (MCPCB) has replaced FR4 PCB in order to achieve greater heat dissipation ability. However, the low thermal conductivity of dielectric and other complicated structures in MCPCB has not supported to maintain junction temperature in safe level when LED is operated at higher power. The challenge is to identify and synthesize high thermal conductivity materials and thin dielectric layers that would favour the usage of MCPCB as a better heat dissipation elements for high power LEDs. This research is focused on developing such thermal substrates with enhanced thermal conductivity at a low cost for mass production. Variety of thin films especially metal oxides and also nitrides as dielectric material (with high thermal conductivities) have been researched rigorously, as these materials could be synthesized as thin films and also as thick films. As a result, the total thickness of thermal substrates could be reduced and hence lower thermal resistance is achievable. In this paper, two different kinds of materials such as ZnO (thick film) and B-AlN (thin film) have been synthesized by two different methods such as screen printing followed by co-precipitation method and chemical vapor deposition using bubbler technique respectively. As an outcome of this research, ZnO thick film was screen printed on Al substrates and cured at low temperatures (125°C) which is low as compared with current curing temperature (>350°C). The screen printed substrates was used as thermal substrates to replace the glassy dielectric material (current practice in industries) of low thermal conductivity. The performance of such thermal substrates were tested using commercial LEDs which has shown a low thermal resistance for pure ZnO thick films with a thickness of 25μm. As observed low thermal resistance with ZnO thick film, the junction temperature of the LED was reduced noticeably. ZnO thick film is also having good reflectivity and can be considered as reflective substrates in electronic packaging. Low curing temperature of the proposed ZnO dielectric paste will also lead to low cost fabrication and mass production of the product. In addition to the above, B-AlN thin film (400 nm) was also deposited by CVD method using gas bubbler on bare Al substrates to improve the performance of thermal substrates (prototype) and compared with commercial MCPCBs. Improved performance of LED was achieved with high value in lux for B-AlN thin films deposited thermal substrates, low thermal resistance and high difference in junction temperature (ATj = 13°C) in comparison with MCPCB. Overall, ZnO thick film and B-AlN thin film deposited Al substrates has been proposed as an alternative to replace commercially available thermal substrates, in place of MCPCBs and FR4s.

Experimental investigation on thermal performances of SMD LEDs light bar: Junction-to-case thermal resistance and junction temperature estimation

In this paper, package-level thermal modeling of the embedded micro-wafer-level-packaging (EMWLP) package has been performed to extract the parametric trends for thermal design guidelines of an eccentric single active die embedded alongside an integrated passive device (IPD), as shown in Fig.1 (with optional heat sink as a cooling solution). Exploratory thermal resistance modeling of an embedded two-die-stack has also been conducted. The effect of the mold compound used in the thermal models is further considered under the following parameters: mold thickness and thermal conductivity (0.4 W/mK to 2.5 W/mK). The effects of heat spreaders and heat sinks on the package thermal resistance are also studied, with due consideration paid to the above mold parameters. Furthermore, experimental characterization has been conducted to validate the package-level simulation for the single active die model, conforming to the JEDEC JESD 51-2A Thermal Measurements in Natural Convection standard. Finally, simulation results for a general system-level thermal modeling in both cellphone as well as laptop systems are also performed. Thermal management solutions for both scenarios, such as thermal vias and heat spreaders, are studied, with an optimal cooling solution proposed.

With the continual increase in cooling demand for microprocessors, the microelectronics industry has been increasingly focused on the development of thermal solutions. Thermal Interface Material (TIM) plays a key role in reducing the thermal resistance of packaging and the thermal resistance between the electronic device and the external cooling components. Nano-TIM, a new type of thermal interface material, was developed to improve the heat dissipation of electronic devices. This paper describes work undertaken to research the reliability of Nano-TIM. Pull tests were used to investigate the shear strength of samples with Nano-TIM of different thicknesses coalesced between two PCBs with Sn coating made under different pressure. Scanning Electron Microscopy (SEM) analysis techniques were used to determine the morphology of the shear fracture section after pull tests and observe the structure of the cross section of Nano-TIM coalesced between two PCBs with Sn coating.

Thermophysical Properties of Building Materials are Considered to have high importance in predicting building thermal performance, calculating thermal loads inside building, and optimizing the use of a building and insulating materials. Due to the lack of measurements of local building materials properties, designers and air- conditioning engineers have no choice but to use the published foreign data, which probably leads to inaccurate predictions of thermal loads and may give a false thermal performance. At the same time, it leads to an over-designed capacity of air- conditioning systems that lead to increased energy consumption in the building. Thus, it is clear that it was important to conduct this research to evaluate the thermal conductivity and thermal resistance of Iraqi building materials. The number of the local building materials were listed, and specimens were collected from their sites, factories, and suppliers such as bricks, stones, concrete products, gypsum, etc. Those samples were dimensioned to the specific size required when a measurement was conducted by the Hot Wire method. All measurements were carried out at room temperature. The relationship between thermal conductivity, density, moisture content, and pressure for a number of materials was Studied. A comparison between the measurements of the Iraqi building materials and results published in the ASHRAE, CIBS Guide, Australian Specifications, and Jordanian Specifications was made. However, the availability of such data is important for the climatic design of buildings, thermal load calculations for air- conditioning, and choosing the insulating materials.

<div class="htmlview paragraph">Power hybrids are particularly well suited for application in transportation systems because they combine a high level of functionality with low weight, size, and cost in a single electronic package. They are easy to interface with the system's logic, minimize electrical resistance and voltage overshoots, often incorporate protective circuits, allow easy fault detection and replacement, and can be largely technology transparent. An example of such a power hybrid package suitable for automotive applications was recently developed by GE and has been given the MO-55 designation by JEDEC.</div> <div class="htmlview paragraph">The power hybrid is discussed in terms of package electrical resistance, thermal resistance, both transient and steady state, and reliability, particularly corrosion protection and solder fatigue. Modeling, including finite element analysis, is applied to analyze heat flow and thermal interactions. In particular, the effect of various heatsinking and heatspreading approaches is given. Thus, the problem of choosing a heatspreader can be reduced to a simple tradeoff between chip area, the heatspreader thickness, and the heat transfer coefficient to the heat-sink. Generalized curves allow an easy assessment of heatsinking options.</div> <div class="htmlview paragraph">Highly Accelerated Stress Testing (HAST) allows a rapid assessment of corrosion resistance of the power hybrid construction approach toward damp heat under electrical bias. The thin aluminum metallization on the semiconductor chips and the bond wires are particularly vulnerable. Finally, solder fatigue is also strongly influence by the environmental conditions.</div>