添加微量Fe、Co、Ni至無鉛銲料對界面生成物Cu3Sn厚度之影響

The Effects of Minor Fe, Co, and Ni addition to Lead-Free Solders on the Thickness of Cu3Sn at the Interface

王儀雯(Yi-wun Wang)

指導教授 ： 高振宏 ； 鄭紹良

國立中央大學/工學院/化學工程與材料工程學系/碩士(2007年)

摘要

由於鉛污染問題，現今已用無鉛銲料取代鉛錫銲料，但無鉛化製程仍有可靠度上的問題，例如封裝適合性、孔洞的形成等。在銲點Cu3Sn/Cu界面處，我們有時可以觀察到一整排Kirkendall’s voids，這些孔洞的形成是造成產品失效的主要兇手，而由於Kirkendall’s voids只會生長在Cu3Sn介金屬層上，因此，Cu3Sn生長型態與Kirkendall’s voids的形成是息息相關的，本實驗觀察的重點即在於Cu3Sn生長。
為了改善無鉛銲料的品質，減少介金屬Cu3Sn生成，添加微量元素於銲料中將有助於降低Cu3Sn生成厚度，本實驗室先前研究結果發現，添加0.1%的Ni於Sn3.5Ag銲料中，能有效降低Cu3Sn生成。在本研究中，將所添加微量元素的量縮小到0.1%以下，觀察其是否仍具有相同效果。另ㄧ方面，我們也添加Fe、Co兩種微量元素和Ni做比較，本實驗目的為探討添加微量Fe、Co、Ni於銲料中，與Cu墊層進行銲接與熱處理反應時對界面生成物的影響。
實驗結果顯示當我們把微量元素Fe、Co、Ni的使用量縮小的情況下，仍具有抑制Cu3Sn生長，但卻增加Cu6Sn5形成。在160oC下當熱處理時間超過1000小時，在Sn2.5Ag-xNi與Cu墊層反應的試片中，Cu3Sn/Cu界面處有Kirkendall’s voids生長，而由於孔洞生長的位置靠近Cu墊層，因此我們推測在Cu3Sn層裡，Cu原子擴散的速度比Sn原子快；另外，在Sn2.5Ag0.8Cu-xNi與Cu墊層反應的試片中，在銲點界面處並沒有孔洞的生成，本實驗結果推測銲料中Cu含量應是其中ㄧ個控制孔洞生成的因子。
Sn2.5Ag-xNi與Cu墊層反應中，在界面生成物Cu6Sn5上有兩層Ni分佈，靠近銲料端的Cu6Sn5 Ni含量比靠近Cu墊層端的Cu6Sn5 Ni含量多，這是由於在冷卻過程中，銲料中部分Ni回到界面所致；而在Sn2.5Ag0.8Cu-xNi與Cu墊層反應中，界面生成物Cu6Sn5沒有Ni分層情形，因為Sn2.5Ag0.8Cu銲料中本身含有Cu，與Cu墊層銲接時銲料內部生成的Cu6Sn5多，部分的Ni溶解到銲料內的Cu6Sn5中，以致於冷卻過程中，回到界面上的Ni少，才不會有分層的情形。
本實驗之主要目的即是探討Fe、Co、Ni的添加對無鉛銲料與Cu界面反應之影響。研究目標是去深入了解加入第四元素對Cu6Sn5、Cu3Sn、及Kirkendall’s voids生長之影響，進而找出最佳之無鉛銲料合金組成。

關鍵字

微量元素 ； 無鉛銲料 ； 孔洞

並列摘要

Owing to the ban of lead, the conventional lead-bearing solder has been replaced by lead-free solder. The drive for lead-free solders in the microelectronics industry presents some reliability challenges. Examples include package compatibility, creep, and Kirkendall’s voids. Along the Cu3Sn/Cu interface, we can find a series of Kirkendall’s voids. These Kirkendall’s voids were the true culprit responsible for the weakening of the interface. It is widely accepted that the formation of these Kirkendall’s voids is related to the growth of Cu3Sn.
In order to promote the quality of lead-free solder, minor elements addition can reduce the Cu3Sn thickness. Recently, our research group showed that a 0.1 wt.% Ni addition to SnAg could reduce the Cu3Sn thickness during the solder/Cu reaction. We want to extend this past result to find out the minimum level of Ni addition that still retains this beneficial effect. In addition, we will also investigate whether the elements, Fe, and Co will have a similar effect. The objective of this study is to investigate the effects of minor Fe, Co, and Ni on the soldering and aging reactions between lead-free solders and Cu.
The experimental result shows that the presence of Ni can in fact reduce the growth rate of Cu3Sn but increase the formation of Cu6Sn5. Moreover, the presence of Fe and Co can have the some effect. We can find the Kirkendall’s voids in the reaction between Sn2.5Ag-xNi (x=0~0.1wt. %) and electroplated Cu at 160 oC for excess 1000 hr. The observation of Kirkendall’s void formation near the Cu3Sn/Cu is direct evidence of Cu diffusion since we can use the voids to serve as diffusion markers. On the side, we didn’t find voids in the reaction between Sn2.5Ag0.8Cu-xNi (x=0~0.1wt. %) and electroplated Cu. The growth of voids is complicated. We consider that the Cu concentration in the solders is the factor to control the void formation.
In the Sn2.5Ag-xNi solders, the addition of Ni also produces two distinct Cu6Sn5 regions at the interface. The outer region contains more Ni, and the inner region contains less Ni. Cooling conditions changed the Ni content of the Cu6Sn5 formed at the interface. Besides, the Sn2.5Ag0.8Cu-xNi solders didn’t have two different Ni content in the Cu6Sn5. This is because there are more Cu6Sn5 precipitated in the Sn2.5Ag0.8Cu-xNi than in Sn2.5Ag-xNi solders. A part of Ni could be dissolved in the Cu6Sn5. Therefore, a few Ni could come back to interface.

並列關鍵字

Cu6Sn5 ； Cu3Sn ； minor elements ； Kirkendall’s voids

參考文獻

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[GAO] F. GAO, T. Takemoto, and H. Nishikawa, “Effects of Co and Ni addition on reactive diffusion between Sn-3.5Ag solder and Cu during soldering and annealing”, Materials Science Engineering, p.39, 2006.

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