無電鍍純鈀應用於印刷電路版表面處理上之研究

The Application of Electroless Pure Palladium Deposition for Surface Finishing on Print Circuit Boards

陳帛佑(Po-You Chen)

指導教授 ： 萬其超 ； 王詠雲

國立清華大學/工學院/化學工程學系/碩士(2009年)

https://doi.org/10.6843/NTHU.2009.00264

摘要

Our study is to develop an alternative surface finishing process to mitigate the drawback of traditional gold film finishing processes for PCB industry. This alternative process is to plate an electroless pure palladium layer directly onto the copper substrates in PCBs. It can decrease the cost and complicacy of the existing process.
We first develop an electroless pure palladium bath at first. This bath comprises palladium dichloride as palladium source, ethylene diamine or sodium citrate as complexing agent and sodium fomate as reducing agent.
According to UV-vis spectra, the pH of ethylene diamine will affect its complex ability. If we adjust the pH of ethylene diamine to acidic condition, the ethylene diamine will have weaker complexing ability due to the potonated amine group. Therefore, we can obtain electroless palladium deposition mainly by immersion. If we keep the pH of ethylene diamine at strong basic condition, we will obtain a strong PdCl2-ethylene diamine complex after adding PdCl2. Therefore, we can obtain electroless palladium deposition mainly by autocatalytic reduction.
In addition, the stability of sodium citrate system is better than ethylene diamine system. The mole ratio of palladium ions to sodium citrate is most stable at 1 to 50. If we adjust the pH to 6 or 8 with NH4OH, we will get stronger PdCl2-sodium citrate complex than with NaOH. This is because the ammonia water, NH4OH, also has complexing ability due to its amine group, but NaOH cannot complex palladium. The activity of this pure electroless bath system is higher in slightly acidic condition. We can get the best deposits at pH=6 and T=65℃.
The result of XRD shows that electroless palladium film for sodium citrate system is a polycrystalline film. But pure activation palladium film is very thin, so that the intensity of Pd is weaker and Cu signal is evident. The wire-bonding ability test shows that the pulling force for electroless palladium film is almost larger than 6 cN. This result passes the criteria in industry.

關鍵字

無電鍍鈀沉積 ； 表面處理 ； 甲酸鈉 ； 檸檬酸鈉

並列摘要

我們的研究主要是在於開發一項替代性的表面處理製程，以改善印刷電路板工業上傳統金薄膜之表面處理製程的缺失。這項替代製程為：在銅基板上直接沉積一層無電鍍純鈀，其可以達到降低製程成本以及複雜度的目的。
　　為了檢視這項製程的效果，首先我們必須發展出一個可用的無電鍍純鈀鍍液。此鍍液的組成為：以氯化鈀作為鈀沉積層的來源，以乙二胺或檸檬酸鈉作為錯合劑，並且以甲酸鈉作為還原劑。
　　由紫外－可見光譜的結果顯示，乙二胺本身的pH值對於他的錯合能力有很大的影響。如果我們把乙二胺調至酸性條件下，其質子化的胺基會使他對鈀離子的錯合能力降低。因此我們可以鍍出以置換反應為主的鈀鍍層。但如果我們把pH值保持在乙二胺原本的強鹼性條件下，則會有乙二胺－鈀離子的強錯合物產生。因此我們可以得到以自催化還原反應為主的鈀鍍層。
以檸檬酸鈉作為錯合劑的鍍液系統相較於乙二胺系統有較好的穩定性，而鈀離子與檸檬酸鈉間的最佳比例為1:50。如果我們用氨水把鍍液的pH值調到6～8，則能到較強的檸檬酸鈉－鈀離子錯合物。但若用氫氧化鈉來調整pH則無額外的錯合效果。這是因為氨水分子中所含的胺基也有錯合能力的緣故。而由實驗顯示，此系統之純還原鍍鈀液在pH=6以及65℃.時會有最好的浸鍍活性。
由XRD的結果顯示，檸檬酸鈉系統的無電鍍鈀層為一多晶薄膜。但由於純置換的活化鈀層厚度太薄，因此鈀的訊號很弱而銅的訊號明顯。此外，打線能力測試結果顯示其拉力幾乎都大於6 cN，可通過工業上的評量標準。

並列關鍵字

Electroless Palladium Deposition ； Surface Finishing ； Sodium Formate ； Sodium Citrate

參考文獻

[2] Masaru Kato and Yutaka Okinaka, Some Recent Developments in Non-Cyanide Gold Plating for Electronics Applications.

[3] E. J. M. O’Sullivan, Fundamental and Practical Aspects of the Electroless Deposition Reaction,

[5] F. H. Reid and W. Goldie, Gold Plating Technology, Electrochemical Publications, Scotland (1974)

[7] Alison Winlow, Surface Finishing (2003)

[8] U.S. Environmental Protection Agency, Implementing Cleaner Printed Wiring Board Technologies: Surface Finishes, Washington (2000)