On the Thermal Performance of a Thermally Enhanced FC-PBGA Assembly

• Main Authors: Jie-YuYou, 游傑宇
• Other Authors: Jun-Huang Wu
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/43xwnq

碩士 === 國立成功大學 === 機械工程學系 === 106 === On the Thermal Performance of a Thermally Enhanced FC-PBGA Assembly Jie Yu You Jun-Huang Wu Department of Mechanical Engineering of National Cheng Kung University SUMMARY In this thesis, the three-dimensional finite element analysis using the commercial ANSYS software is performed to study the thermal performance of a thermally enhanced FC-PBGA (Flip-Chip Plastic Ball Grid Array) assembly in both natural and forced convection environments. The thermally enhanced FC-PBGA assembly is a basic FC-PBGA package that is overmolded with molding compound, after which an aluminum heat spreader is adhered to the top of the molding compound and subsequently mounted on a PCB (Printed Circuit Board). The thermal behavior of the assembly is presented, thermal performance is analyzed by considering various design parameters of the aluminum heat spreader, molding compound , adhesive, solder ball , solder bump , PCB , and thermal via. Keyword : Solder ball; FC-PBGA; Thermal performance INTRODUCTION In this thesis, the ANSYS 15.0 is used to study the heat transfer of FC-PBGA by the finite element method, and its heat transfer efficiency is improved by analyzing the Material size. Change the material size including heat spreader, molding compound , adhesive, solder ball , solderbump , PCB and thermal via to perform the parametrize. This thesis study. MATERIAL AND METHOD In this thesis, ANSYS 15.0 finite element analysis software is used to analyze the FC-PBGA structure by the finite element theory. The FC-PBGA assembly is composed of many original materials. The structure contains the molding compound, solder ball, Substrate, adhesive, thermal via, PCB, Substrate Signal, Chip, Copper layer, and heat spreader plate. The assumptions used in the analysis are as follows: 1. Due to the model symmetry, take a quarter of the model to reduce the analysis time.2. There is no deterioration of the material after temperature loading. 3. There is no stress in the initial state of the model, and the residual stress of the assembly process is not taken into account. 4. The symmetrical surface without any displacement. 5. Material is homogeneous and isotropic. 6. Does not consider the effect of gravity caused by the combination. 7. There is no impurities and voids are inside the assembly. 8. The structure itself does not absorb water vapor or the temperature change caused by the Popcorn Effect. RESULTS AND DISCUSSTION To discuss the distance, height ,and radius of solder balls to do temperature analysis and discussion. As shown in Figure 1. it’s effect of solder ball spacing variety on the highest assembly temperature and thermal resistance. It can be found that the smaller the solder ball spacing, the higher the temperature. In contrast, the greater the spacing, the lower the temperature. In general, from the perspective of heat transfer, the smaller the distance between solder balls, the harder it will be for the gap in the middle to allow the air to dissipate the heat to the outside world. Therefore, it is the best when the distance between solder balls is 1.3 mm from the simulation. From the curves in Figure 1., it is found that the impact of solder ball spacing on the natural convection effect, the temperature change is quite large, from 77 °C to 69 °C, mainly forced convection too much influence, resulting in forced convection of tin The ability of the ball to dissipate heat is poor, and it highlights the fact that in natural convection, changes in solder ball pitch have a significant effect on temperature. As shown in Figure 2., for the ball height changes and the maximum temperature and thermal resistance of the assembly. It can be seen from the figure that the change of solder ball height does not change much for the maximum temperature of the assembly, so the solder ball height changes have poor thermal performance. As shown in Fig. 3., it is the change of the center radius of the solder ball and the maximum temperature and thermal resistance of the assembly. The figure shows that the larger the radius, the higher the temperature of the assembly. When doing this simulation, because the solder ball spacing is fixed to 1.3 mm. The higher the center radius, the smaller the gap between the solder ball and the solder ball, which is the main reason for the slight increase in temperature. CONCLUSION Type 3 has the best heat dissipation and wind speed is the dominant cooling parameter. The smaller the solder ball pitch, the higher the thermal resistance. Understanding the changes in solder ball spacing has a high impact on natural convection and highlights the strong influence of forced convection. When the number of PCB layers is 4, 6 and solder ball spacing is 1.3 mm, the heat dissipation effect is the best. The bumps are closest to the wafer. The larger the bump radius, the smaller the thermal resistance; the thicker the bump height, the greater the thermal resistance. The effect of aluminum heat sink width is more significant than thickness, because increasing the width can effectively increase the cooling area of the heat sink. The results of the study found that reducing the gap of the molding compound or increasing the heat transfer coefficient of the molding compound contributes to the heat dissipation of the assembly because both reduce the thermal resistance of the heat transfer path. The width of the molding compound has little effect on the heat dissipation performance of the assembly. The effect of the glue gap is far greater than the effect of the width. The adhesive has little effect on the heat dissipation performance of the assembly, but the larger the thermal conductivity, the smaller the thickness contributes to the improvement of the heat dissipation performance of the assembly. There are thermal vias on both the PCB and the substrate. The heat dissipation capability is best, and the larger the heat sink radius, the smaller the thermal resistance.