而隨著對於電子產品效能的需求，要如何在有限空間內放入更多電子元件則成了現今發展的重點。POP(Package on Package)技術就是一種發展出來的解決辦法，利用已經完成的封裝體(Package)在三維空間(高度)透過回焊將封裝體堆疊，形成三維系統封裝(3D system in Package SiP)，以達到更高密度封裝以及減少尺寸等目的。
本論文使用ANSYS 15.0以有限元素法針對POP探討其熱傳路徑，並透過分析出來的熱傳路徑改善其熱傳效率。構裝體元件包含了基板(Substrate)、錫球(Solder Ball)、晶片(Chip)、封膠(Modling Compound)、散熱孔(Thermal Via)、印刷電路基板(Print Circuit Bpard PCB)。

Parametric Anaysis of POP Thermal Performance
Tzu Hsuan Chou
Jun-Huang Wu
Department of Mechanical Engineering of National Cheng Kung University
SUMMARY
This paper is divided into five chapters. The first chapter includes the introduction of BGA and POP packaging, the literature review. The second chapter is theoretical analysis, including elastic theory analysis, nonlinear convergence criterion, the viscoelastic material mechanics model, heat conduction and thermal convection, heat radiation. The third chapter is the model establishment and analysis, including the establishment of POP body model, modeling analysis process and parameter setting. The fourth chapter is for the results and discussion analysis, including the analysis of POP heat transfer path, different material parameters and structural thickness analysis. The fifth chapter is for the conclusions and future prospects.
Keywords: POP, heat path, POP Thermal Performance
INTRODUTION
In this paper, ANSYS 15.0 is used to study the heat transfer path of POP by finite element method, and its heat transfer efficiency is improved by analyzing the heat transfer path. Substrate components include Substrate, Solder Ball, Chip, Molding Compound, Thermal Via, and Print Circuit Board PCB.
MATERIAL AND METHOD
In this paper, ANSYS 15.0 finite element analysis software is used to analyze the POP structure by finite element theory. The material properties are linear and non-linear materials, and the solution of transient and steady state is obtained.
The assumptions used in the analysis are as follows: 1. The ball is a viscoplastic material; the sealant is a viscoelastic material; the heat sink, the wafer, the substrate and the printed circuit board are linear materials. 2. The package itself has no initial stress, regardless of the process of residual stress process. 3. All contact surfaces are completely intact and have no cracks or impurities inside. 4. The structure itself does not absorb water vapor or the temperature change caused by the Popcorn Effect. 5. Regardless of the gravity effect arising from the quality of the purchased body. 6. Due to model symmetry, a quarter model is used to shorten the time. 7. The symmetry plane is adiabatic and the shear stress is zero.
In this paper, the conditions of analysis include natural convection and forced convection, and the thermal convection coefficient using Ellison's empirical formula for the thermal convection coefficient of small electronic components on a flat plate is used as heat transfer simulation analysis
RESULTS AND DISCUSSTION
In the case of nature convection, less heat of the chip will transfer to the air by convection, most of the heat will transfer from the thermal vias and solder balls to the PCB. The heat of memory chip will go through the innermost of solder balls, then transfers to the lower substrate and PCB by thermal vias. The heat of logic chip will go through thermal vias, then transfers to the PCB by the innermost of solder balls.
We change the materials and structure of substrate and PCB to analyze the influence of cooling efficiency. The KZZ of the substrate is more influential than KXX, because the heat path is down to the PCB. The KXX of the PCB is more influential than KZZ, because PCB is the end of the heat path.
CONCLUSION
It’s important to find the heat path of the POP. If we need to cost down, we can know the significant part to change the material.
1. In the heat transfer, the heat transfer of the wafer after the heat transfer path is mainly through the closest to the wafer of the ball passed to the bottom of the final transmission to the PCB, and then contact the air with the PCB and a large area of convection heat transfer.
2. In the substrate and PCB base material, for the memory chip, the effect of improving the longitudinal heat transfer coefficient of the substrate than the transverse heat transfer coefficient of the effect is more significant. But the lower substrate temperature is higher, and with the end of the heat path (PCB) is closer, and the number of rows of solder balls, and thus the effect of lateral heat transfer coefficient change is more significant.
3. PCB to improve the effect of lateral heat transfer rate than the vertical heat transfer effect is more obvious, because the PCB is the end of the heat path, and then by the large area and the convection heat convection, and because the PCB and the wafer Is not in direct contact, so when the heat dissipation coefficient increases or decreases, the logic chip and memory chip in the same coefficient, the respective temperature change ratio will vary.
4. Because the sealant is in direct contact with the wafer and has 5 faces to the wafer, the effect of improving the heat transfer coefficient is most obvious.
5. The height of the substrate signal layer changes for the logic of the chip is relatively large.
6. PCB thickness of the copper layer, because the PCB and the two wafers is not directly in contact with the logic chip and memory chip image is similar, but the logic of the PCB by the copper layer will be slightly less than the memory chip.
7. For the composition of this paper, the PCB cooling of the 2-layer board is poor, and the heat dissipation to the 4-layer board has reached the limit, the effect is very obvious when the board is increased to 6 layers.
8. Increase the heat sink for the memory chip cooling effect is most significant, the temperature decreased by 2.636%, but for the logic chip is only reduced by 0.2655%.
9. If there is already a heat sink plate, the thickness of the heat sink> viscose coefficient> viscose thickness> heatsink coefficient is compared with the original part of the structure.

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