錫2.3銀微凸塊與銅金屬的冶金反應研究

Abstract

由於封裝技術的進步，以微小接點來橋接晶片已是先進封裝的趨勢，而銲錫接點的微縮所帶來微小尺度的問題，是很重要的議題。 本研究分析不同厚度的Sn2.3Ag銲錫與銅金屬墊層反應的影響。在260℃定溫下，迴銲2μm、5μm、9μm與19μm四種不同厚度的銲錫，經過1分鐘、5分鐘、10分鐘、20分鐘與30分鐘的迴銲時間，並用掃描式電子顯微鏡觀察量測Cu6Sn5介金屬化合物的大小。結果發現不同體積的銲錫，對Cu6Sn5介金屬化合物生長沒有影響。 因為錫與銅金屬墊層反應生成介金屬化合物，使剩餘銲錫內之銀濃度上升，增加片狀Ag3Sn生成的可能。2μm厚度的銲錫，在迴銲2分鐘看到大片Ag3Sn析出，而在5μm厚度的銲錫，在迴銲11分鐘後，有68%的機率看到大片Ag3Sn析出。經由理論預測剩餘銲錫內之銀濃度上升到3.5wt.%的迴銲時間，2μm厚的銲錫是1.5分鐘，5μm厚的銲錫是10.2分鐘，也十分符合觀察的結果。 而在150℃高溫儲存測試中，5μm、9μm與19μm三種不同厚度的銲錫，經過100小時、200小時、500小時與1000小時的高溫儲存時間後，最後量測發現不同銲錫體積，對Cu6Sn5與Cu3Sn介金屬化合物的成長，並無影響。

Due to the progress of packaging technology, microbumps has been adapted as the interconnect of advanced packaging. When the interconnect is shrinkage into microbump level, reliability become an important issue. In this study, we study the metallurgical reaction between Cu under bump metallization (UBM) and solder with 5μm, 9μm, and 19μm thickness at 260℃. The reflow time is 1 min, 5 min, 10min, 20min, and 30 min. Plan-view scanning electron microscope was employed to measure the diameter of the interfacial Cu6Sn5 intermetallic compounds (IMCs) after the selective removal of the un-reacted solder. It is found that the solder volume does not have a significant effect on the growth rate of the Cu6Sn5 IMCs. Because the Sn in solder is gradually depleted during the solder reactions, the concentration of Ag in solder increase obviously in the microbumps. Therefore, large precipitation of Ag3Sn may take place. We can observe large Ag3Sn precipitation in 2μm and 5μm solder after 2 and 11 minutes reflow, respectively. The probability of observing a large Ag3Sn IMC is shown that there is 68% chance of finding a large Ag3Sn IMC in 11-min-reflowed sample for 5μm solder. Theoretical calculation indicates that it takes 1.5 min reflow for 2μm solder for Ag concentration to increase to 3.5wt.%; while it is 10.2 min for 5μm solder, which agrees quite well with the experiment observation. For aging test at 150℃, we also measure the thickness of the IMCs and their growth rate. We found that the solder volume does not have a significant effect on the growth rate of Cu6Sn5 and Cu3Sn IMCs.