在現代微電子製造中由於印刷電路板和晶片元件厚度的下降以及封裝體接點數不斷增加且間距不斷減少，倘若封裝體本身翹曲量太大或是在連接各元件的過程產生過大的翹曲量變化，印刷電路板(printed circuit board, PCB)高溫迴銲的過程中翹曲變形會使錫球附著困難，將會造成電子系統內部電信、電力傳輸上的問題。因此，封裝體翹曲變形的分析與控制是發展新技術的重點之一。
分析封裝翹曲方法除了實驗量測外，大多使用有限元素模擬，而模擬之正確與否通常與模型中材料行為之假設有直接關係。過去高分子封裝材料例如環氧樹脂封膠與玻纖基板之本構模型大多以彈性考慮，但隨著高溫迴銲製程對平坦化要求的提高，高溫翹曲模擬預測之準確度要求也隨之提高。為正確的模擬高溫下的翹曲行為，封裝結構中之高分子材料必須考慮其黏彈性本構行為。
在本論文中為正確描述高分子材料之黏彈本構模型行為，首先用拉伸與扭轉動態機械分析分別求得楊氏儲存模數與剪力儲存模數，再經過模數轉換得時間域下的體積與剪切鬆弛模數以作為有限元素分析中之黏彈模型。然而由於實驗中量測結果可能存有誤差，導致模數轉換後得到不合理的材料行為，因此，本論文發展出一套材料行為擬合最佳化方法，在材料特性滿足理論限制條件下，求得近似於實驗結果的合理材料函數。為驗證此近似材料黏彈性本構模型之正確性，本論文使用有限元素法來模擬封裝體在升降溫中熱機械所造成的翹曲行為並與陰影疊紋法(shadow Moiré)實驗結果相互比對，結果發現以此方法所建立高分子材料黏彈性模型可正確預測封裝體翹曲行為。

In this thesis, the viscoelastic behaviors of epoxy molding compound (EMC) and laminate substrate are characterized, and the corresponding constitutive models are developed and implemented in finite element simulations to predict warpage evolution of an overmolded ball grid array (BGA) package. Storage modulus mastercurves measured by using dynamic mechanical analyses (DMA) under either cyclic tension or torsion loads were first converted to the relaxation moduli in the Laplace-Carson transform domain by using approximation formula. The transformed Young’s and shear relaxation moduli were then curve fitted by using an optimization procedure with restriction to ensure physically admissible time-dependent Poisson’s ratio. Bulk and shear relaxation moduli were then obtained from the fitted moduli and inverse transformed to the time domain. The numerical finite element model that considers the viscoelastic constitutive behaviors of EMC and substrate was applied to simulate warpage during the surface mount solder reflow process and compared to experimental shadow Moiré measurements. It was found that the viscoelastic model based warpage prediction agrees well to experimental results; while the conventional elastic model based prediction does not.

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