| 摘要: | 摘 要 含鉛銲料如PbSn eutectic 一直是微電子工業最主要、最常用的銲料。但歐盟最近提議將在2008年起禁用含鉛銲料，日本各大電子公司如Panasonic、Fujitsu等公司也計畫在2002年前後主動的改換製程至無鉛系統。一般均認為此次改用無鉛的趨勢是無可避免且勢必在幾年內完成。過去十餘年來，產學界一直試圖尋找能夠直接替代(Drop-In Replacement) PbSn eutectic 的無鉛銲料，但一直無法找到完全令人滿意的替代品。最近因為改用無鉛銲料的時程實在十分緊迫，美國工業組織NEMI已達成共識，將以SnAgCu系列銲料來取代PbSn eutectic 銲料在reflow上的應用。目前文獻中有關SnAgCu的各項性質資料十分缺乏，本計畫之主要目的即是探討SnAgCu無鉛銲料與基材表面處理層(Surface Finish)之反應。 由於SnAgCu系列銲料有很多不同組成，而以何種組成為最理想，目前並無定論。因此本研究將探討Ag、Cu濃度對界面反應之影響，藉以了解就反應而言Ag、Cu之理想組成。而目前Au/Ni是最常用的surface finish，目前也使用在多種覆晶之金屬化層上。因此本研究之總目標是去深入了解不同Ag、Cu濃度之SnAgCu與Au/Ni 發生反應時每一階段的現象及其機制。 本研究中BGA構裝基板之墊層為電鍍0.8 mm Au / 6 mm Ni表面處理的型式，錫球銲點的組成為：Sn-3.5Ag、Sn-3.5Ag-0.75Cu、Sn-xAg-0.5Cu ( x=1/3/4 wt.%)、Sn-3Ag-yCu ( y=0/0.3/0.5/0.7/1 wt.%)。在銲接後，並進行180oC，0-2500小時之固態熱處理。在不同的熱處理時間後，測試其剪力強度。 本研究發現SnAgCu銲料中Cu含量的微小差異，會影響迴銲後所產生的介金屬種類與生長形態，也影響銲點的剪力強度。當銲料中沒有Cu時(例如使用Sn-3Ag)，迴銲後在銲點界面處所產生的介金屬是Ni3Sn4。當Cu濃度較高時(例如使用Sn-3Ag-1Cu)，所產生的介金屬則是(Cu1-p-qAupNiq)6Sn5。在經過固態熱處理後，(Cu1-p-qAupNiq)6Sn5下方會多產生一層(Ni1-yCuy)3Sn4。當Cu濃度是0.5 wt.% (例如使用Sn-3Ag-0.5Cu)，迴銲後產生的介金屬是(Ni1-yCuy)3Sn4與(Cu1-p-qAupNiq)6Sn5共同存在界面上。總而言之，隨銲料之Cu濃度的升高，銲接接合物之生長情形將由原先單一、且連續的(Ni1-yCuy)3Sn4層，逐漸轉變為(Cu1-p-qAupNiq)6Sn5與(Ni1-yCuy)3Sn4之混合型式。若Cu的濃度更高時，則銲接接合物將轉變為一連續的(Cu1-p-qAupNiq)6Sn5層。換句話說，隨所採銲料之Cu濃度的不同，則界面上之生成物種類與其生長形態亦有所不同。亦即銲料之Cu濃度的高低，將可直接影響銲接界面之接合物的種類與生長形態。此一結果在工業應用上極為重要，因為界面之介金屬種類，勢必影響到銲點的強度。因此工業界在銲接時，必須極為嚴格監控銲料中Cu濃度，以利生產具一致品質之高強度銲點。而本研究最主要之目的在更進一步探討上述現象之機制。 ABSTRACT Lead-bearing solders, such as the PbSn eutectic, have been used extensively in the microelectronic industry for a long period of time. Recently, the European Union proposed to phase out the lead-bearing solders by January, 2008. Moreover, many major Japanese electronic companies, such as Panasonic and Fujitsu, have decided to switch voluntarily to lead-free processes by the year of 2002. It is generally believed that this lead-free transition is unevitable this time. Past research by the academia and industry indicated that a drop-in replacement for PbSn eutectic is difficult to find, if not impossible. Due to the extremely tight time schedule to go lead-free, the U.S. industry had reached a consensus to use SnAgCu series of solders to replace the PbSn eutectic, despite the fact that the literature for SnAgCu solders is still seriously lacking. The main objective of this proposal is then to study the reactions between such lead-free solders with the Au/Ni surface finish used in the industry. The SnAgCu solders are a series of solders with broad compositions. We propose to study the effect of the Cu concentration on the interfacial reation. The Au/Ni surface finish is the most common and important one for solder pads and bumps in the industry now. Therefore, the overall objective is to study in depth the reactions between the SnAgCu solders with various Cu concentration and the Au/Ni. The contact pads for solder balls on the PBGA substrates used in this study have the 0.8mm-Au / 8mm-Ni surface finish by electroplating. The solder composition, Sn-3.5Ag, Sn-3.5Ag-0.75Cu, Sn-xAg-0.5Cu (x=1/3/4 wt.% ), and Sn-3Ag-yCu (y=0/0.3/0.5/0.7/1 wt.%), were used, and their performances were compared. After reflow, the solder joints were subjected to aging at 180 oC for time up to 2500 hrs. The shear strengths of the solder joints with different aging time were then tested. It was found that the Cu concentration in the SnAgCu ternary solder has a very strong effect on the compound formation and the shear strength in solder joints with the Au/Ni surface finish. When there was no Cu (ex:Sn-3Ag), the reaction product was Ni3Sn4. When the Cu concentration was high (ex:Sn-3Ag-1Cu), the reaction product was (Cu1-p-qAupNiq)6Sn5 right after reflow, and two intermetallic compounds (Cu1-p-qAupNiq)6Sn5 and (Ni1-yCuy)3Sn4 formed after aging at 180oCfor 2500 hrs. When the Cu concentration was 0.5 wt.% (ex:Sn-3Ag-0.5Cu), both Ni3Sn4 and (Cu1-p-qAupNiq)6Sn5 were present near the interface right after reflow, and there was a layer of solder between these two intermetallic compounds. After aging, a layer of (Cu1-p-qAupNiq)6Sn5 over a layer of (Ni1-yCuy)3Sn4 formed at the interface. |
