應用實驗設計法於銅線打線製程之最佳化參數研究

Optimum Design for Cu Wire Bonding Process by Applying DOE Method

徐權邁(Chuan-Mai Hsu)

指導教授 ： 張國華

中原大學/電機資訊學院/工業與系統工程研究所/碩士(2011年)

https://doi.org/10.6840/CYCU.2011.00089

摘要

近年來，因為金價的不斷上漲，封裝產業漸漸導入銅線(Copper wire)代替原有的金線(Gold wire)做為IC原件內部訊號的傳導材料。以材料性能來看，相關資料顯示，銅線在室溫(20oC)之下的電阻率為0.017 micro-ohm-m，同樣在室溫(20oC)下，金線的電阻率則為0.022 micro-ohm-m，因此銅線的導電性比黃金線高出25~30%。此外銅的溫度傳導性也比金線高出25%，用於晶片封裝中，散熱與省電表現自然比黃金來得好。

但是晶圓構造也朝向低電阻值與低介電係數的材料發展，鋁墊層(Al layer)由12k降至8k，甚至Low-K(K值為鋁墊層厚度)，減少電路(metal)堆疊能改善時間延遲效應(R/C delay)，降低功率耗損(power dissipation)及雜訊干擾(cross-talk noise)。

隨著銅線與低k值材料的同時使用衝擊晶片結構的機械強度，熱膨脹系數較高，對於IC封裝製程造成衝擊。裂紋與彈坑，一直是銅線封裝打線製程所遭遇的難題。本研究是以實際生產作業的情況，針對0.8mil銅線與Al layer 8k材料，使用DOE/Minitab的驗證方法，找出最佳化的作業條件，管控與提升封裝打線製程品質，達到品質穩定使銅線/低介電係數材料可大量生產的目標。

根據實驗的結果，增加最初壓合壓力(Initial force)能有效抑制超音波(USG Power)的輸出達到降低裂紋(Crack)發生的機率，同時產生較扁平的銅球而獲得更大的接觸面積來改善推球克數，提升作業性與可靠度。最後，建議縮短放電結球(EFO)時間控制球形大小避免銅球互相橋接問題。

關鍵字

裂紋 ； 彈坑實驗 ； 銅線 ； 實驗設計

並列摘要

The cost of gold has been dramatically increasing, therefore copper wire has been used to replace gold wire as conduction material. Regarding copper wire capability, if atmospheric temperature is under room temperature (about 20 degrees), the copper wire resistivity is 0.017micro-ohm-m. Gold wire resistivity under room temperature is 0.022micro-ohm-m. Comparing copper wire and gold wire electric conductivity, it shows that the copper wire is better than gold by about 25–30%. Besides, copper heat conductivity is better then gold by over 25%. Therefore, if the copper wire replaces gold wire in the assembly process, the heat dissipation and energy efficient performance will be improved.

The material development of the wafer is trying to have electric resistance and low dielectric layer material, it results in that A1 layer is decrease from 12k or 8k and even Low-k. To reduce metal layers can improve the R/C delay problem, lower power dissipation and cross-talk noise.

There is an impact on the IC package resulting from using the copper and low K material. It causes that the whole IC structure strength is getting worse and the coefficient of thermal expansion is getting higher. Crack and Crater have been problems of copper wire bounding process for a long time. Based on the practical product operation, we study the optimal operating situation especially focusing on 0.8mil copper wire and 8k Al layer material. In this thesis, we perform design of experiments(DOE) to study the cause-effect relation in the bonding process and find the optimal operating conditions to stabilize the quality and increase the capacity of production.

Base on experimental results, increasing the initial force can inhibit the USG power and reduce the possibility of bond pad crack; flatter copper ball can increase contact area to allow high ball shear. It can improve the corresponding reliability; Short EFO fire time could control ball size to avoid ball bridge issue.

並列關鍵字

Design of Experiment ； Copper wire ； Bond pad crack. ； Crater test

參考文獻

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