晶圓級封裝形式WLCSP(Wafer Level Chip Scale Package)，由於其尺寸較小可提高產品之聚集度，已逐漸成為未來發展的趨勢。其中連結錫球與晶片二者間之多層金屬薄膜(Under Bump Metallurgy簡稱UBM)，對產品的好壞具有決定性之影響力。另外傳統上所使用之含鉛錫球中鉛的含量，會對環境及人體健康造成危害，各先進國家莫不積極尋找無鉛之替代材料。
本研究乃將著手以無鉛錫球含UBM材料之WLCSP封裝模式，建構在含雙層微盲孔(Micro-via)之增層(Build-up)電路板上，利用有限元素分析法ANSYS6.0之軟體，在熱循環負荷下進行計算模擬，以瞭解整體封裝結構之變形、微盲孔及錫球應力應變及遲滯曲線之變化和壽命預估等機械行為。其間分別採用多線性等向硬化( Multilinear isotropic hardening ) 、黏塑性(Viscoplasticity)及葛拉佛拉-阿瑞尼阿斯潛變模式(Garofalo-Arrhenius creep model) 等三種不同材料性質理論，以分析錫球並比較其差異。
透過本計畫之完成，希望能提供業界對無鉛錫球及UBM材料之應用更深一層的認識，有利於自然環境的保護，並縮短開發時間，提升產品的競爭力。

The wafer level chip scale package (WLCSP) has increasingly become popular due to its wafer-sized compact package. In the WLCSP, the under bump metallurgy (UBM) which connects the solder joint and the chip, is crucial for the package reliability. Additionally, the lead contained in conventional solder joints is adverse to environments and human health, so that many countries are seeking lead-free solder-material for replacement.

This study focuses on the WLCSP with lead-free UBM solder joint mounted on the build-up electric board with double-layered micro-via. Finite element analysis ANSYS 6.0 is used for simulations under thermal cycling to investigate the deformations of entire package, micro-via and the changes of stress-vs.-strain hysterisis curve for solder joints. The fatigue life prediction is also included. Three material property theories are adopted, such as viscoplasticity, multilinear isotropic hardening and Garofalo-Arrhenius creep model, to analyze solder joins and compare the differences between results.

The complication of this study could give some suggestion to manufacturers the application of lead-free solder joint and UBM, urge them to pay attentions to environmental protections, and furthermore shorten the development period to enhance the competitiveness.

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