電子封裝體掉落之力學分析與可靠度評估

Abstract

一般來說，多數研究者估計電子封裝體所能承受之掉落次數，亦即其衝擊壽命為一定值；然而衝擊試驗結果顯示，此壽命呈現離散的情況。本研究即分別探討電子封裝體尺寸與壽命預估模型中參數之不確定性，對其衝擊壽命的影響。吾人首先利用有限元素軟體，模擬封裝體在錫球直徑變異下，錫球與印刷電路板或晶片間的最大剝離應力值，代入封裝體壽命預估模型後，將衝擊壽命以機率分佈方式呈現，相較於原始封裝體可承受245次掉落次數，若由可靠度函數計算後，其可靠度僅有46.71%，顯示封裝體幾何形狀參數之不確定性會對其壽命造成影響；電子封裝體壽命預估模型為一經驗公式，其中會有誤差存在，吾人接著探討封裝體壽命預估模型中常數項及指數項參數變異，造成衝擊壽命的離散性，並以可靠度方法評估之，結果顯示封裝體各材料參數的不確定性對其壽命具有一定程度之影響。本研究之分析過程與結果應可作為封裝體掉落衝擊壽命之可靠度評估。

Most researchers consider the life of an electronic package subjected to drops is a fixed value. However, drop tests show that impact lives of a random sample of an electronic package usually exhibit certain scatter. Therefore, the impact life had better be described by a random variable. In this study, the influence of geometrical size variation of an electronic package on its impact life distribution and reliability is investigated. The influence of uncertainty of parametric values in the life prediction model is investigated as well. First, finite element analysis is employed to evaluate the maximum peeling stresses of solders of a random sample of an electronic package. The obtained maximum stresses are then substituted into a life prediction model to obtain the distribution of impact lives. The result shows that size variation of electronic packages does affect the life distribution and reliability estimation of the package. Next, the influence of uncertainty of parametrical values in the impact life prediction model is investigated. It is also found that uncertainty of parametrical values affects the variation of impact life and its associated reliability estimation. It is believed that the study can be used for quantitative reliability estimation of an electronic package subjected to drops.