不同厚度的錫銀無鉛銲錫與銅、鎳之冶金反應探討

Metallurgical Reactions of Various Thickness of Sn-Ag Solder with Ni and Cu Layer

唐進興(Chin-Hsing Tang)

指導教授 ： 陳智

國立交通大學/工學院/工學院半導體材料與製程設備學程/碩士(2018年)

摘要

當封裝的製程由覆晶(Flip chip)接點進展到3D堆疊整合的微凸塊(Microbumps)時。封裝接點銲錫的高度從約70m 降至約15m，而且微凸塊的尺寸將會持續微縮，將來銲錫的高度還會再下降。冶金反應是否與銲錫凸塊的高度是否有影響是值得探討的。本論文研究不同的SnAg銲錫高度對冶金反應的影響。我們製備銅及鎳為冶金底層，接合不同厚度的SnAg銲錫高度，包含5m、10m、15m 及 20m，做260℃迴銲測試與150℃高溫儲存反應，觀察介面介金屬化合物的厚度，我們發現介金屬化合物的生成厚度與銲錫的厚度沒有明顯的相關。但是觀測到明顯的熱遷移現象，銅原子容易往冷端遷移，造成Cu-Sn介金屬化合物的在冷端的厚度明顯較熱端厚度許多。另外，我們觀測到低銲錫高度很容易造成介金屬化合物橋接，例如在 Cu/5m SnAg/Cu及Cu/5m SnAg/Ni的試片中，接合時迴銲的一分鐘後的初始狀態即觀測到有介金屬化合物橋接的現象，對於對接製程的良率及可靠度會有影響。

關鍵字

微凸塊 ； 錫銀銲錫 ； 介金屬化合物 ； 熱遷移效應

並列摘要

When the packaging industry moves to 3D IC packaging, flip-chip solder joints has been replaced by microbumps for interconnects. The solder height for a flip-chip joint is approximately 70m, and it decrease to about 15 m for a microbump. In addition, the dimension of microbumps will continue to scale down, therefore, the solder height will decrease in the future. However, whether the solder height will affect metallurgical reaction is worthy to investigate.
In this study, we examine the metallurgical reactions of SnAg and Cu or Ni under various solder heights. We fabricated Cu and Ni under-bump-metallization (UBM), and electroplate SnAg solders on them. Then, various solder joints were prepared by jointing the solder bumps on the Cu or Ni UBM. Thus solder joints with 5 m, 10m, 15 m and 20 m thick can be fabricated. Then metallurgical reactions under reflow at 260℃ and solid state aging at 150℃ were performed and thickness of intermetallic compounds was measured. We found that the thickness of the intermetallic compounds was not affected by the solder height. Nevertheless, we observed obvious thermomigration of Cu atoms. Cu atoms migrated toward the cold end, and formed Cu-Sn intermetallic compounds at the Cu/solder interfaces, resulting the thicker Cu-Sn intermetallic compounds on the cold end. In addition, bridging of Cu-Sn intermetallic compounds was observed in the joints with low solder heights. For the Cu/5 m SnAg/Cu and Cu/5 m SnAg/Ni specimens at initial state, the Cu-Sn intermetallic compounds bridged within one minute of reflow. This may cause problems for yield and reliability.

並列關鍵字

Microbump ； SnAg solder ； IMCs ； Thermomigration

參考文獻

[1] D. R. Frear, “Materials issues in area-array microelectronic packaging “ J . Minerals Metals & Materials Society, 51, 3, p.22-27, (1999)

[2] Leila J. Ladani, “Numerical analysis of thermo-mechanical reliability of through silicon vias (TSVs) and solder interconnects in 3-dimensional integrated circuits”. Microelectronic engineering, 87, 2, p.208-215, (2010).

[3] K. Takahashi, et al. , "Current status of research and development for three-dimensional chip stack technology." Jpn. J. Appl. Phys., 40, p.3032-3037, 2001.

[4] C.J. Lin, M.T. Lin, S.P. Wu and F.G. Tseng, “High density and through wafer copper interconnections and solder bumps for MEMS wafer-level packaging “Microsystem Technologies, 10, 6-7, p.517-521, (2004).

[5] T. Fukushima, et al.” Self-assembly technology for reconfigured wafer-to-wafer 3D integration” in Electronic Components and Technology Conference (ECTC), p.1050-1055, (2010).