多晶片模組主要是以分離晶片方式，將系統所需的各種晶片，放在同一個模組中，盡量減少系統中晶片的間隙，以縮短晶片間信號的延滯，有效的節省空間、提高性能速度、降低功率消耗、節省封裝乃至於整個模組的成本。而多晶片模組由許多元件所組成，當模組受到溫度循環變化的負載，由於各元件材料因熱膨脹係數的不一致而導致構裝結構變形，進而造成錫球產生疲勞破壞，因此本文主要以高計算效能之多晶片模組為探討對象，考慮受到溫度循環變化的負載，探討各元件材料及幾何對疲勞可靠度的影響。

　　本研究所考慮的多晶片構裝結構含有散熱片、熱黏膠、晶片、底填膠、結構黏膠、基板、印刷電路板及Sn3.5Ag無鉛錫球，利用ANSYS有限元素分析軟體建立三維條狀模型進行分析，同時考慮簡化模型計算與分析，將晶片與基板間的底填膠與錫球的部分結構，以等效平板代替。在無鉛錫球材料行為方面，採用多線性等向硬化模式，並以葛拉佛拉-阿瑞尼阿斯數學模式描述無鉛錫球潛變行為模式。其他材料皆以彈性模型描述之。本文所考慮的溫度循環變化範圍為-40℃～125℃，各循環的高低溫持平時間各為5分鐘、升降溫時間各為10分鐘；因此，每循環為30分鐘。本文利用有限元素計算最外側錫球(基板與印刷電路板間)之變形、應力與應變及遲滯曲線等機械行為之變化情形，並將等效應變範圍值代入Coffin-Manson計算公式中，以預估錫球之疲勞壽命。為有效進行有限元素分析，先建立參考模型(全域精細網格模型)，接著導入Hybird模型簡化分析的複雜度，並與參考模型之分析結果進行比較，以評估Hybird模型的效率及分析結果的精確性。

　　在本文中考慮基板厚度、基板熱膨脹係數、散熱片寬度、散熱片厚度、散熱片熱膨脹係數、印刷電路板厚度、晶片厚度、結構黏膠熱膨脹係數、結構黏膠厚度、大晶片尺寸與小晶片尺寸等因子，進行單一因子分析以評估各因子對封裝結構疲勞壽命的效應。接著，將上述各因子以田口品質設計，建立直交表進行實驗，並經誤差統合，找出最佳化的參數組合，並有效改善多晶片構裝之可靠度。

　　由單一因子分析結果顯示，藉由降低基板熱膨脹係數、減小基板厚度、減小印刷電路板厚度、增加晶片厚度、增加散熱片熱膨脹係數、增加散熱片厚度、增加散熱片寬度或增加大晶片尺寸，皆能有效提高多晶片模組疲勞壽命，其餘因子對多晶片模組疲勞壽命的影響性並不大。最後，利用田口品質設計所得最佳製程參數之構裝體疲勞壽命為1310次，而原始製程參數設計之構裝體疲勞壽命為165次，疲勞壽命約提昇7.94倍，因此有效改善多晶片模組之可靠度。

　　Multichip module (MCM) mainly is a mode of discrete chips needed in the system and assembled in a module in order to shorten the distance among chips and reduce the signal delay so that to save space, enhance the speed of performance, decrease the power dissipation and cut down the cost of package or even entire module. A multichip module package consists of various components, when it is under a temperature cycling load, due to the mismatch of coefficients of thermal expansion (CTE) of components, the package tends to deform and lead to fatigue failure of solder joints. Therefore, this paper focused on a MCM model of high speed computation under a temperature cycling load to investigate the effects of component’s material and geometry on the fatigue life of 96.5Sn3.5Ag lead-free solder joints in a MCM assembly.

　　A MCM model consists of an assembly of heat spreader, thermal adhesive, chip, underfill, structural adhesive, substrate, printed circuit board and 96.5Sn3.5Ag lead-free solder joint. Applying finite element analysis software, ANSY, a 3-D finite element sliced bar-like model for solder joint reliability is constructed. Furthermore, in order to simply numerical simulation of the model, an effective substitution for solder joints/underfill between the chip and the substrate is adopted turning the complex geometry to a simple isotropic layer. To describe the material behavior of lead-free solder, multilinear isotropic hardening and Garofalo-Arrhenius creep model were used in plastic analysis and creep analysis respectively, but other components are assumed to be linear elastic. The temperature history consists of temperature fluctuating cycles between -40℃ and 125℃. It dwells at high temperature or low temperature for 5 minutes. the package is heated from room temperature to 125℃ in 10 minutes and then cooled down to -40℃ for 10 minutes. Each cycle totals 30 minutes. This paper computed the deformation, stress, strain and hysterisis curve of the outermost solder joint (between substrate and PCB) by finite element analysis. The equivalent strain range is substituted into Coffin-Mansion formula to estimate the fatigue life of solder joint. For efficiently running numerical simulation, firstly, a reference model (global fine mesh model) was constructed, and then followed a Hybrid model for a simpler simulation. Finally, a comparison of two results proceeded to evaluate efficiency and accuracy of simulation result of Hybrid model.

　　The single-factor experiment was adopted to predict the impact on the fatigue life of MCM by following factors: the control factors are thickness of substrate, CTE of substrate, width of heat spreader, thickness of heat spreader, CTE of heat spreader, thickness of PCB, thickness of chip, CTE of structural adhesive, thickness of structural adhesive, size of large chip, size of small chip. Finally, the Taguchi Method was applied to obtain an optimal parameter combination to improve the reliability of MCM package.
　　
　　The results of single-factor study showed that by reducing the value of the CTE of the substrate, substrate thickness, PCB thickness as well as by increasing chip thickness, heat spreader width, CTE of the heat spreader, heat spreader thickness and large chip size will increase the solder fatigue life. On the other hand, the other factors have no significant effect on the solder fatigue reliability.
Finally, the optimal design from Taguchi Method optimized the fatigue life of 1310 cycles, but the original design had much less fatigue life of 165 cycles, the optimal design had 7.94 folds on the fatigue life over the original design, far improving the reliability of MCM module package.

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