溫度循環試驗對晶圓級擴散型封裝之可靠度影響

Abstract

晶圓級擴散型封裝是未來主要的封裝技術之一，可實現任何數量的內部連接與標準的線寬間距，並且可以有效整合縮小化晶片封裝尺寸。本文實驗利用完成擴散型封裝的單顆成品，直接進行前處理以及溫度循環試驗，次數各為250、500 Cycle，觀察不同材料間熱膨脹係數影響的界面差異性以及無鉛銲錫層的冶金反應，並試圖找出推球機制和推球強度之關係，進而對可靠度作評估及改善。實驗研究結果發現，在高冷卻速率下 (每秒3.44℃)，Inside ball 推球平均值會下降約20%，Outside ball下降約26%。而在低冷卻速率下(每秒2.19℃)，Inside ball會下降約18% ，Outside ball則下降約17% 。推球斷裂面都只有 Mode 2 (Pad lift) 現象產生，且未有任何 Mode 1 (Ball Shear) 現象發生。而造成Mode 2的主要原因為製程中熱應力影響，導致界面劣化以及推球值下降，可藉由降低冷卻速率的方法，讓推球強度有效提升約 20% ~ 40% 左右。

Fan-out Wafer Level Package is the upcoming future packaging technology. FO-WLP has the potential to realize any number of interconnects with standard pitches at any shrink stage of the wafer node technology. The purpose of this thesis was investigated in reliability test of Pre-condition & TCT 250/500 cycles with finished FO-WLP product. Interface observed differences and solder layer metallurgical reaction between the different coefficient of thermal expansion. And trying to figure out the relationship between the shear mode and shear strength. Experiment results showed that the shear strength of the inside ball decreased about 20% the mean for high cooling rate (3.44℃/sec), the outside ball about 26%. The shear strength of the inside ball decreased about 18% the mean for low cooling rate (2.19℃/sec), the outside ball about 17%. Only one mode2 (Pad lift) of FO-WLP shear mode was found after reliability test and no any mode1 (Ball shear) phenomenon. Mode 2 is caused mainly due to the thermal stress on the process leading to the deterioration of interface and the decrease in the shear strength. The low cooling rate of solder reflow process allow to improve the shear strength about 20% to 40%.