G.Q. Zhang

Numerical simulation on heat pipe for high power LED multi-chip module packaging

Light emitting diode (LED) as the new light source has the advantages of power saving, environment-friendly, long lifetime and no pollution compared with fluorescent and incandescent lights. But the disadvantage of LED is low light lumen that only 10%~20% input power transform into the light, and 80%~90% into the heat. The junction temperature of LED is so high as to induce the lifetime declining rapidly, luminous decay and reliability decreasing. Therefore, the effective thermal management is very important for the LED light system. In this work, a new packaging architecture the system in package (SiP) configuration is used in the high power LED packaging. The light system consists of nine chips that each chip is 1.2W. Copper/water miniature heat pipe (mHP) is chosen to dissipate heat based on the LED packaging structure and the input power of the system. The principles of the heat pipe are investigated to design and select the structure and size of the heat pipe. Capillary limit and boiling limit of the heat pipe are calculated to determine the maximum heat transfer and verify the design of the heat pipe. The heat pipe is seen as the thermal superconductor in axial, which take the place of the process of the phase exchange in the pipe. The axial thermal resistance of mHP estimated by the net of the thermal resistance is 0.15°C/W approximately. The system level heat and temperature distribution are investigated using numerical heat flow models. In this analysis, 3D finite volume model is developed to predict the system temperature with Icepak which is the professional software to analyze the temperature field of electronics. The result shows that the junction temperature of the source is under 70°C at the natural convection which is satisfied with the requirement of the LED working at under 120°C. It shows that the heat pipe is the effective solution for the LED light application dissipation. For the lower junction temperature, three factors including the height, the thickness and the fin numbers of the heat sink, respectively, are considered to be optimized by DOE (design of experiment). With the simulation results of Icepak, the optimal scheme that the lower junction temperature is 56.7°C obtained by the combination of optimization levels.

Thermal transient analysis of LED array system with in-line pin fin heat sink

In this paper, a 3 W high power LED array system with an in-line pin fin heat sink is designed, fabricated, and investigated for thermal transient analysis. Preliminary finite element simulation is conducted by ANSYS, and LED array average junction temperature is about 40.9°C. In the experiment, electrical test method is used to evaluate the heat dissipation effect of the LED array system. Experiment results show that the system works well. The cumulative thermal resistance of the system is about 6.7K/W, and corresponding LED array average junction temperature is about 40.5°C. It is found that the simulation result is consistent with the experimental result. The error is about 1%. It is also found that, in order to get accurate thermal resistance of every kind of material in the heat flow path, we should analyze the curves of cumulative and differential structure function simultaneously.

Research on heat dissipation of high heat flux multi-chip GaN-based white LED lamp

In this paper, a novel thermal management method of vapor chamber printed circuit board coupled with sunflower heat sink is presented. The finite element method thermal analysis module of a 110 W multi-chip GaN-based white LED lamp is developed by ANSYS parametric design language and user interface design language, the thermal performance of the LED lamp thus can be analyzed more quickly and efficiently. The simulation results indicate that the overall design of the heat dissipation structure of the LED lamp is reasonable and the effect of heat dissipation is effective and satisfactory, the vapor chamber has higher heat transfer ability, and the sunflower heat sink is perfect for the heat dissipation of multi-chip LED lamp. Therefore, VCPCB coupled with sunflower heat sink is a powerful way for heat dissipation of high heat flux multi-chip GaN-based white LED lamps.

Characterization and Modeling of Moisture Absorption of Underfill for IC Packaging

Underfill is a highly particle filled epoxy polymer used in flip chip to fill the gap between the leadframe and die or between die and die. In order to be able to flow in the thin gap, the silica filler particle must have a diameter below 10 mum. This epoxy underfill material mechanically couples the chip and substrate and decreases the stress in the solder joints, therefore enhancing solder fatigue life. Good adhesion between the epoxy underfill and the surface of solder ball, silicon chip, and substrate is necessary to minimize stress in a package. Use of the non-hermetic material does raise a potential concern, i.e. moisture induced interfacial delamination and moisture expansion may cause failure. In this study, moisture absorption and desorption properties were investigated, such as moisture absorption equilibrium weight gain and diffusion coefficients at different temperature and different humidity are tested and characterized, moisture absorption and desorption kinetics are tested and fitted.

The effect of diaphragm on performance of MEMS pressure sensor packaging

MEMS (Micro Electro-Mechanical System) is a technology that offers significant advantages over various microscopic elecromechanical devices. In the field of MEMS products, pressure sensor represents a considerably mature technology and has been extensively used in a variety of applications. Nevertheless, packaging is a key issue among the processes of MEMS manufacture due to the specialty and complexity of MEMS devices. For isolated packaged MEMS pressure sensor, design and fabrication of insulated diaphragm structure is a key factor as it directly affects the accuracy and reliability of packaged pressure sensor. Thermal expansion will emerge among the parts of pressure sensor when working temperature is extremely high. In this paper, finite element method is applied to study the issue on thermal expansion of silicon oil under using flat diaphragm and corrugated diaphragm, respectively. Simultaneously, the volume expansion of silicon oil under using the two diaphragms is calculated. Through comparison, it can be found that the volume expansion of silicon oil under using corrugated diaphragm is less than that when using flat diaphragm along different path. Therefore, conclusion can be achieved that optimization of insulated diaphragm structure will be superior in realization of transmission of pressure almost without loss and relief of additional pressure to the sensor chip induced by thermal expansion of silicon oil.

Thermal analysis and comparison of heat dissipation methods on high-power LEDs

Nowadays LEDs (Light Emitting Diodes) are widely used in many fields. As the fourth generation of lighting sources, LEDs have the advantages of long lifetime, power saving and environment-friendly. In this paper, the thermal variation characteristic of some parameters for two high-power LEDs packaging modules, such as forward voltage, luminous flux, CCT and luminous efficiency, were analyzed experimentally. Moreover, the heat dissipation results of two methods (heat sink with fins and heat pipe with fins) were compared and evaluated in numerical simulation. The experiment data and simulation results demonstrated that high junction temperature of high-power LEDs would decrease luminous efficiency and have other harmful impacts, and heat pipe with fins has better cooling capability than only heat sink. But excellent heat sink design could meet general cooling need for high-power LEDs modules below 15W.

Characterization, modelling, and parameter sensitivity study on electronic packaging polymers

Thermosetting polymers are widely used in electronic packaging. For instance, epoxy molding compound is extensively used as an encapsulant for electronic packages to protect the IC chips from mechanical and chemical hazards. It is well known that molding compounds show not only strong temperature dependent but also time dependent behavior. The thermo-mechanical behavior of these polymer constituents determines the performance, such as functionality and reliability, of the final products. In this paper, experimental characterization was carried out to investigate the time and temperature dependent properties of the selected molding compound. Thermal Mechanical Analysis (TMA) was applied to measure the CTE of the materials. Dynamical Mechanical Analysis (DMA) measurement was performed using temperature and frequency sweep modes. Finite element modeling was conducted on typical QFN (Quad Flat Non-lead) package device. Three material models, i.e., full viscoelastic model, temperature-dependent elastic model (1Hz DMA data) and constant elastic model, are used respectively to describe the behavior of the molding compound. The output responses of the simulations are von Mises stress distribution, package warpage and interlaminar stresses. The results show that the von Mises stress and package warpage are significantly different when considering the EMC as full viscoealstic, temperature-dependent elastic and constant elastic.

A novel soldering method to evaluate PCB pad cratering for pin-pull testing

Abstract The pin-pull test has attracted attention because it can detect a high percentage of laminate cracking failures. In this study, a novel pin-pull test method is proposed to simplify pin soldering and the pin-pull test. The test method utilizes existing tools to perform the soldering and to collect quantitative data on the strength of printed circuit board (PCB) pad. The proposed procedure can be implemented with low cost and be adopted easily using any material or surface mounted technology (SMT) test laboratory. The procedure only requires a common tensile tester with regular copper pins and an external heat element to solder the pin to the pad. The impact of PCB pad design, manufacturing processes (including reflow and rework), thermal cycling, and long-term field usage on pad cratering are explored systematically based on the proposed method. The test result indicates that the high number of traces attached to the pad may significantly increase pad strength such that resistance to pad cratering is improved. Furthermore, pad strength dramatically declines when PCB pads are subjected to thermal stress or are used in the field for long periods.

Fast MSL analysis of microelectronic packages by using equal weight increasing method

With the wide application of microelectronics packaging products in the industry, the chip have been more and more attention in the harsh environment of high temperature, high humidity. Therefore how to rapidly deliver high reliability products to market has been one of the issues of concern in the microelectronics industry. However moisture sensitivity level (MSL) analysis in microelectronics packaging is one of the most time consuming problem. Thus it is important to study the mechanism and method of the analysis of moisture sensitivity and shorten the analysis time. In this paper the fast analysis of microelectronic package MS L is achieved by the approach of an equal weight of water increasing at different conditions by simulation. According to project requirements, the ESOP8 is chosen as experimental device. Further the model is established, which is used to calculate equal moisture weight increase, and 10 to 67 acceleration factors are obtained. The purpose of this paper is to realize MSL the fast reliability evaluation method for microelectronics packaging industry. Finally using ANS YS finite element simulation is for the calculation.

Fast analysis and implementation of microelectronic packaging MSL with equal moisture distribution method

With the rapid development of electronic packaging product design and manufacture, it is one of most concerned problems that how to provide reliable products to the market. One of the most time-consuming problems in the reliability analysis of microelectronic packaging is the problem of conventional heat and humidity sensitivity analysis. The non hermetic package in the microelectronic packaging is affected by the heat and humidity environment, which will lead to the failure during soldering reflow, which seriously affect the microelectronic packaging and assembly. The international electronics industry standardization organization makes a considerable number of standards for heat and humidity problem. But the experiment time is too long and time consuming. Therefore, how to shorten the time of conventional analysis becomes extremely important. This study will establish a new method equal moisture distribution at different pre-conditioning. Different temperatures, different humidity conditions will result in different water saturation and diffusion coefficient. The parameters of the other conditions can be obtained by using the derived formula. According to the requirements of the project, The SOP package is chosen as experimental devices, with the thickness of 1.4mm. Constant temperature and humidity test chamber, reflow soldering machine, ultrasonic microscope SAM300 and electronic balance are used in our experiment instrument. ANSYS software is used to model the structure of the package, such as EMC, underfill, copper and die attach, which are used in the package. Using the finite element method, the distribution of moisture absorption at different pre-conditionings are compared. And 2 to 5 acceleration factors are obtained.