為滿足使用者的需求，消費性電子產品，愈來愈講究輕薄短小之可攜特性與多功能，以致3D電子構裝為之因應而生，即將晶片作薄化處理並以堆疊晶片型式於一封裝體中，以整合單種或多種晶片，來節省封裝所占空間及晶片開發時間以快速反應市場的需求。本文研究懸臂式疊晶之打線接合性以提供設計準則。
打線接合已經是一個很成熟的技術，一般的打線接合研究，多在支撐物的支撐下進行，所以在打線過程中晶片(鋁墊)與銲針是相對固定不動的，然而因為是懸臂結構，晶片在懸臂區域為沒支撐的狀況，當打線接合力作用時，晶片會下沉撓曲；又因DAF為黏彈性材料在與晶片接合下拘束條件會引發潛變效應使撓曲隨時間之延長而更下沉，並使超音波震盪能量無法完整的傳輸至金鋁接合面，導致共晶不良，推球值無法達到品質要求。
為了得到懸臂疊晶結構的設計準則，首先利用接合力、振動功率與接合時間，為打線接合的三個參數設計實驗方法，並用推球值(>18g)來驗證懸臂疊晶的打線接合特性。在確定好的接合參數下以有限元素法預估懸臂端點下沉撓曲量，以對應出可作業之範圍(有效懸臂長度)，在晶片厚度為100um下，接合力25g、振動功率43~50DAC及接合時間20ms下，二層疊晶與三層疊晶的總懸臂長度設計規範分別為1.2mm與1.75mm(前懸臂+後懸臂，且前懸臂≧後懸臂)。

Portable electrical products are trended to light、thin、short and merge more functions into a single package. To reduce the required space for packages and developed time for chips, 3D electronic packages are evolued to meet the requests of market.
This paper focuses on the bondability of overhang stacked die and then provides a design rule for stacking. Actually, Wire Bonding is a mature technology and most of the studys are under a supporting structure during bonding. Threrfore, the chip(Al pad) is fixed relative to the capilly, however for overhang structure, the chip has no supporting at overhang area, the chip is sunk and deflected due to bonding forces applied. More over, under the bond constraints of chip with viscoelastic DAF, the DAF creep effect will make more downward deflection. As a result, the ultrasonic energy can not be fully transferred to the Au-Al interfaces to make sufficient eutectic join.These bad qualities are exposed by the ball shear test.
Using bond force、bond power and bond time as three parameters of bondability, the experiment methods are designed, performed and then verified by the ball shear test(>18g). With good three parameters of bondability obtained, FEM is employed to simulate the chip deflection at overhang edge and then to determine the workable range (effective overhang length). For 100um chip thickness, the design rule for the total overhang length of 2-stacked die and 3-stacked die are 1.2mm and 1.75mm (front overhang + back overhang, front overhang length≧back overhang length)

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