新式抗大氣腐蝕之表面處理層開發並應用於高可靠度元件;Development of Newest Anti-corrosion Surface Finish for High Reliability Devices

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Title:	新式抗大氣腐蝕之表面處理層開發並應用於高可靠度元件;Development of Newest Anti-corrosion Surface Finish for High Reliability Devices
Authors:	曾讚憲;Tseng, Tsan-Hsien
Contributors:	化學工程與材料工程學系
Keywords:	大氣腐蝕;金屬表面處理層;車用電子元件;電化學分析;無電鍍製程;化鈷金錫
Date:	2019-08-26
Issue Date:	2019-09-03 12:36:22 (UTC+8)
Publisher:	國立中央大學
Abstract:	鑒於空氣汙染日益嚴重，許多酸性汙染物溶於水氣後破壞建築物、電子元件等。現今印刷電路板常用之表面處理層，如化鎳金(ENIG)、化銀(ImAg)與化錫(ImSn)等已不敷使用在高可靠度電子元件，故須開發新式表面處理層。本研究利用鈷系無電鍍金屬層作為新式表面處理層，分別有化鈷(EC)與化鈷金錫(ECIGS)，並比較商用化鎳金、化錫等表面抗大氣腐蝕之能力。在日常大氣腐蝕中，以含硫氣氛為影響最嚴重之因素，故本研究利用不同濃度之二氧化硫氣體通入自製氣密瓶中模擬含硫氣氛並將試片置放於其中，此外，為加速腐蝕反應的發生，實驗溫度設定為80 oC及相對溼度為100% RH。通過48與120小時的曝氣實驗分析表面處理鍍層的抗腐蝕能力，並藉由分析表面腐蝕物推測各鍍層之腐蝕機制。經過濃度為15 ppm放置48與120小時後，各試片皆無明顯腐蝕物產生，故本研究將濃度提升至1500 ppm並一樣放置48與120小時。在曝氣48小時後，化鎳金表面產生大量腐蝕物，化鈷錫表面出現些許腐蝕物，而化錫表面無明顯腐蝕物產生，化鈷表面僅出現些許裂痕。當曝氣時間提升至120小時後，化鎳金與化鈷表面分別產生大量氣泡狀與片狀腐蝕物，化錫與化鈷錫表面也些許產生花瓣狀腐蝕物，經元素分析後發現表面僅化鈷錫沒有出現與銅相關之腐蝕物，藉此推斷在此環境下化鈷錫具有最佳的抗腐蝕能力。為了探討各試片之電化學特性，將各試片浸入0.5 M硫酸水溶液後，進行Tafel。結果顯示在硫酸環境下，ECIGS都具有最好的穩定性。經過電化學動力學計算電子轉移係數後，EC最不容易在具正過電位下發生氧化反應，故新研發之ECIGS具有良好抗腐蝕之特性，並具有應用於提升高可靠度元件之耐候性潛力。;Amounts of corrosive gas affect the reliability of electronic devices. In order to prevent corrosion reaction on automobile printed circuit broads (PCBs), surface finish is adopted to protect the surface of PCBs. In this investigation, PCBs were coated several metallic thin films on the surface, such as electroless nickel immersion gold (ENIG), immersion tin (ImSn), electroless cobalt (EC), and electroless cobalt immersion gold immersion tin (ECIGS). The air-tight clave, pumping the SO2 gas, was utilized to explore the anticorrosion capability and the corrosion products for samples. The concentration of SO2 gas was either 15 or 1500 ppm at 80 oC for 48 and 120 h. The humidity was processed with 100% relative humidity (RH) to confirm the water-film on the surface. Negligible corrosion products formed on the surface after 15 ppm SO2 for 48 and 120 h. The multiple corrosion products formed and covered whole sample on the ENIG surface after 1500 ppm SO2 for 48 h. At the same condition, corrosion products some grew on the ECIGS surface. In addition, slight corrosion products formed on the ImSn and EC after 1500 ppm SO2 for 48 h. When exposed time increased to 120 h, the corrosion products covered whole the ENIG and EC samples. Additionally, Cu signals was observed on the corrosion products for ENIG, ImSn, and EC but not on the ECIGS. The surface finishes also were investigated by electrochemical analyses such as Tafel test. According to Tafel curve, ECIGS was stable coating in this investigation. The results of transfer coefficient showed that reduction reaction dominated when EC sample immersed in the 0.5 M H2SO4. The ECIGS exhibited the effective anticorrosion capability for high reliability device in this investigation.
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