鈀含量對銀合金銲線離子遷移之影響

因應金銲線與銅銲線在做為封裝打線接合材料所遭遇到的許多問題，近年來電子產業也開始嘗試使用純銀銲線做為替代材，雖然銀金屬具有最佳的導電率及導熱性質，但是由於銀離子遷移現象所導致電子元件短路失效之問題是純銀銲線一直不被廣為使用的原因之一。由於過去文獻中已證實鈀的添加可以有效抑制銀離子遷移的現象，所以本研究採用合金銲線的概念，利用添加鈀元素對純銀銲線進行改質。隨著半導體製程技術的進步，線寬持續減少，使得導體之間的電場強度增加，進而加速了離子遷移現象的發生，因此離子遷移的影響更是不容忽視。由於離子遷移必須在水氣相當充足的環境下才會發生，所以本實驗採用符合美國材料與試驗協會之F1996標準規範，以水滴法來觀測銀離子遷移的現象。其中為了避免鈀元素因鹵素汙染物而誘發其離子遷移，在實驗溶液上是選擇電阻率為18 MΩ•cm的超純水，如此便可單純地只探討銀離子遷移的發生。利用本實驗所定義之平均離子遷移率公式，可量化鈀含量對銀合金銲線銀離子遷移之影響，將各銀合金線材計算出之結果作比較，可發現平均銀離子遷移率幾乎隨著鈀含量的增加而呈線性下降，而且樹枝狀析出物尺寸也隨之增大。其中純銀銲線擁有最高的平均銀離子遷移率 (10.23 μm/s)，當鈀添加量從2 wt.%增加至6 wt.%時，平均銀離子遷移率下降10 %至25 %。雖然銀離子遷移的現象早在1930年代即被發現並提出，但先前研究所探討的皆是最早有此現象發生的銀厚膜塊材，且都是在添加10 wt.%以上之高含量鈀的抑制效果。透過本研究可證實在銀鈀合金銲線中添加少量鈀元素 (低於6 wt.%) 時，亦可以有效地減緩銀離子遷移的影響，並且有系統地建立起觀測線材電解離子遷移現象的方式。

關鍵字

離子遷移；打線封裝；銀鈀合金銲線；水滴法試驗；樹枝狀析出物

並列摘要

In response to the problems of Au and Cu bonding wires, the electronic industry have begun to try to use pure Ag wire as an alternative material in recent years. Although Ag has the highest electric and thermal conductivities of all the metallic elements, one of the reasons why it has not been widely used is that Ag-ion migration was found to cause electronic devices to short circuit and fail. Many researches have confirmed that alloying Ag with Pd could inhibit the failure mode of Ag-ion migration, so this study used the concept of Ag-alloy wires which were modified by doped with Pd. With the advancement of semiconductor process technology, the wire pitch have been proceeding to decrease so that the electric field strength between conductors will increase. Thus the impact of Ag-ion migration couldn’t be ignored anymore. Ion migration only occur in an environment of abundant humidity, so this study investigated Ag-ion migration by using the water drop test according to ASTM standard F1996. Selecting the distilled water with electrical resistance of 18 MΩ•cm was to avoid inducing Pd-ion migration by halogen contaminants, so it could just simply discuss about Ag-ion migration. By using the formula of average ion migration rate defined in this study, we can quantify the effect of Pd content on ion migration of Ag-alloy bonding wires, the result shows that the average ion migration rate decrease linearly and the dendrite precipitate size enlarge with Pd content increased. Moreover, it can be seen pure Ag wire had the highest Ag-ion migration rate, 10.23 μm/s. The Ag-ion migration rate of Ag-alloy wires decreased about 10 to 25 % by addition of 2 to 6 wt.% Pd. Although the phenomenon of Ag-ion migration was discovered in the 1930s, all of the previous papers were focused on Ag thick film materials and the high Pd content which were more than 10 wt.%. Through this study, it could prove the effective inhibition of Ag-ion migration in Ag-alloy bonding wires when the Pd content is less than 6 wt.%, and establishing a systematic method to observe the phenomenon of ion migration for bonding wires.

並列關鍵字

ion migration ； wire bonding ； Ag-alloy bonding wires ； water drop test ； dendrite

參考文獻

[2] Hsueh, H. W., Hung, F. Y., Lui, T. S., Chen, L. H., and Chen, K. J., Intermetallic phase on the interface of Ag-Au-Pd/Al structure. Advances in Materials Science and Engineering, 2014. 2014: p. 6.

[3] Wei, T. C., A. R. Daud , Mechanical and electrical properties of Au-Al and Cu-Al intermetallics layer at wire bonding interface. Journal of Electronic Packaging, 2003. 125(4): p. 617-620.

[4] Harman, G., J. Albers, The Ultrasonic Welding Mechanism as Applied to Aluminum-and Gold-Wire Bonding in Microelectronics. Parts, Hybrids, and Packaging, IEEE Transactions on, 1977. 13(4): p. 406-412.

[5] Ratchev, P., S. Stoukatch, and B. Swinnen, Mechanical reliability of Au and Cu wire bonds to Al, Ni/Au and Ni/Pd/Au capped Cu bond pads. Microelectronics Reliability, 2006. 46(8): p. 1315-1325.

[6] Breach, C. D., Wulff, F., and Tok, C. W. , An unusual mechanical failure mode in gold ballbonds at 50μm pitch due to degradation at the Au–Au 4 Al interface during ageing in air at 175° C. Microelectronics Reliability, 2006. 46(2): p. 543-557.

國際替代計量

鈀含量對銀合金銲線離子遷移之影響

全文下載

主題瀏覽