覆晶構裝受熱循環應力 疲勞壽命之可靠度

Abstract

在以往電子構裝相關研究之文獻中，分析一構裝體受力後之應力、應變及最後所得之壽命經常為一定值，然而實驗或實測所得的結果卻往往具有相當的離散性，而需以韋伯等機率分佈函數來呈現。本研究為了探討此隨機疲勞壽命分佈從何而來的問題，就以下兩種狀況探討之，一為構裝體之元件尺寸因加工誤差而有所變異，另一為疲勞壽命預估公式之參數有所變異。研究方法為在適當隨機考量下，利用有限元素軟體，模擬覆晶構裝體受溫度循環負載，得到等效非彈性應變範圍，再經由壽命預估公式求得構裝體的隨機疲勞壽命及其量化可靠度。研究結果顯示：考慮實際製造所產生的合理誤差範圍下，錫鉛凸塊半徑變異較晶片厚度變異更易影響覆晶構裝體之疲勞壽命變異，而在疲勞壽命預估公式並非一完全確定公式之假設下，構裝體因壽命預估公式參數變異而產生之隨機疲勞壽命分佈現象已不可忽略，我們也進一步發現當預估公式參數的變異係數夠大時，可以光就指數參數變異來探討對構裝體壽命的變異與分佈之影響。並且進一步可以了解就實際面而言，各參數變異對疲勞壽命影響程度的大小為：凸塊>晶片>係數A>係數B。

In study the reliability of electronic packages from mechanics point of view, the analytical of stress and strain obtained from finite element analysis and fatigue life prediction based on a Coffin-Manson equation are always constant values. However, the real outcomes of package life have probability distributions and frequently plotted in Weibull probability papers. In order to find out this contradiction, we suppose two kind of possible causes to investigate. One is the geometric parameters of a flip-chip package are random variables. The other is parameters of the Coffin-Manson equation are also random variables. The method of investigation is using finite element software to simulate a flip-chip package on thermal-cyclic loading. Then the cyclic equivalent inelastic strain range of a certain type of flip-chip package is found, and the fatigue life of the package is determined base on a Coffin-Manson equation. It is found that among different geometric parameters, the radius of solder bump affects the fatigue life of the package the most when considering the actually manufacturing tolerance. Considering parameters of the Coffin-Manson equation are random variables, we found the exponent parameter affects the fatigue life distribution more than the other parameter.