無鉛銲料與(鎳-釩)基材間之界面反應及錫-鎳-釩相平衡

Interfacial reactions between Pb-free solders and the (Ni-V) substrate and Sn-Ni-V phase equilibria studies

陳志吉(Chih-chi Chen)

指導教授 ： 陳信文

國立清華大學/工學院/化學工程學系/博士(2008年)

摘要

本論文之研究主題為Ni-V合金與無鉛銲料(Pb-free solder)之界面反應及Sn-Ni-V三元系統之相平衡。覆晶構裝(flip chip packaging)是目前最先進之電子構裝技術，Ni-V合金是覆晶構裝最常用之擴散阻障層材料。由於環保意識的抬頭，以無鉛銲料取代錫鉛銲料為大勢所趨。因此，Ni-V合金與無鉛銲料之接合將是電子產品中最常見之銲點(solder joints)結構。
銲點之界面反應與產品可靠度息息相關。本論文探討Ni-V合金與各種無鉛銲料之界面反應，包括Sn、共晶Sn-Cu(Sn-0.7wt.%Cu)與共晶Sn-Ag(Sn-3.5wt.%Ag)。目前文獻上普遍探討的是Ni與無鉛銲料之界面反應，Ni-V合金與無鉛銲料之界面反應的研究十分稀少。雖然Ni-V合金中V含量只有7wt.%，但這並不意味其對界面反應沒有影響。本論文將針對無鉛銲料/Ni-V之界面反應作深入探討。此外，在電子元件中，銲點承受很大之電流密度，電遷移效應不可忽略，故本論文也針對電遷移效應對界面反應之影響作探討。而由於相平衡資訊為探討界面反應所不可缺少，本論文之研究範疇也涵概Sn-Ni-V三元系統之相平衡。
相平衡實驗結果顯示，在250oC下，靠近富錫區之Sn-Ni-V相平衡結果為L(Sn)+Ni3Sn4+V2Sn3三相共存。Ni3Sn4相與V2Sn3相對第三元素幾乎沒有溶解度，L(Sn)相對Ni與V也幾乎沒有溶解度，也沒有形成三元相。V2Sn3相之組成為Sn-34at.%V，與CuMg2之結構相符，應該改寫成VSn2。
界面反應實驗結果顯示，無鉛銲料/Ni-V之界面反應與無鉛銲料/Ni截然不同。當V的添加量為5wt.%以上時，無鉛銲料/Ni-V界面會生成一層Sn-Ni-V之三元相 (T相)，此三元相並非熱力學穩定相，而是在特定條件下，藉由反應生成之介穩定相，其結構為介於非結晶與多晶之間。在固/固反應中，會生成T/Ni3Sn4/T/Ni3Sn4之罕見生成相排列，為兼具「固態非結晶化」(solid state amorphization) 與「生成相交錯排列」(alternating) 雙重特殊性之反應。在液/固反應中，三元相之存在，導致其他生成相，如Ni3Sn4相，剝落至熔融銲料中，並使原來在無鉛銲料/Ni系統中就會剝落的生成相，如Cu6Sn5相，剝落的情況加劇。
500A/cm2電流密度之電流對Sn/Ni-V界面反應之影響與其對Sn/Ni之影響相同，生成相種類沒有改變，但反應速率有改變。在電子流與Sn原子擴散同向之界面，反應速率變快。在電子流與Sn原子擴散反向之界面，反應速率變慢。此結果符合動量轉移理論。
覆晶構裝真正使用之擴散阻障層材料為Ni-V，並非純Ni。既然無鉛銲料/Ni-V之界面反應與無鉛銲料/Ni不同，覆晶構裝產品之可靠度評估必須依據無鉛銲料/Ni-V之界面反應，而非無鉛銲料/Ni之界面反應。

關鍵字

界面反應 ； 鎳-釩 ； 無鉛銲料

並列摘要

Ni-V alloys are frequently used as diffusion barrier materials in the electronic products. As a result, solder/Ni-V joints are often encountered in electronic products. Since Sn is the primary element of most of the electronic solders, Sn-Ni-V is an important ternary material system. However, its phase equilibria information is not available. Interfacial reactions are crucial for the reliabilities of the solder joints. There have been intensive investigations about solders/Ni interfacial reactions, but the interfacial reactions between solders and Ni-V substrates are seldom examined. This study investigates the phase equilibria of the Sn-Ni-V ternary system and the interfacial reactions between solders and the Ni-V substrates. The solders include pure Sn, eutectic Sn-Cu (Sn-0.7wt.%Cu) and eutectic Sn-Ag (Sn-3.5wt.%Ag) solders. The electromigration effect upon solders/Ni-V interfacial reactions is also examined in this study.
Phase equilibria of the Sn-Ni-V system at 250oC were determined both by experimental determination and calculation with CALPHAD method. No ternary equilibrium phase is observed. At the Sn-rich corner, it is a L(Sn)+Ni3Sn4+VSn2(V2Sn3) three-phase region. The ternary elemental solubilities of Ni3Sn4 phase and VSn2(V2Sn3) phase are negligible, and those of both Ni and V in the liquid phase are also very low. The composition of VSn2(V2Sn3) phase is Sn-34at.%V, which is consistent to the structural prototype of CuMg2, and should be accordingly renamed as VSn2.
The interfacial reactions in the solders/Ni-V couples are different from those of solders/Ni. When the V addition is higher than 5wt.%, a ternary meta-stable phase (T phase) is formed. It is an amorphous phase mixing with Ni3Sn4 fine grains. In the solid/solid reactions, unusual T/Ni3Sn4/T/Ni3Sn4 reaction phases were observed in the solders/Ni-V couples. It has two features: solid state amorphization and alternating reaction phases. In liquid/solid reactions, T phase formation makes the reaction phase detachment earlier in comparison with that of Ni substrate. Since Ni-V alloys are the commercial barrier layer materials practically used, and the solders/Ni-V interfacial reactions are different from those in the solders/Ni couples, the reliability assessments of flip chip products should be based on the interfacial reactions of solders/Ni-V.
Electric current with 500A/cm2 density exhibits the same effect upon Sn/Ni-V interfacial reactions as upon those of Sn/Ni. The reaction phases are not altered, but the reaction rate is changed. At the interface where the electron flow and Sn atoms diffusion are co-current, the reaction rate is enhanced. In contrast, at the interface where the electron flow and Sn atoms diffusion are counter-current, the reaction rate is retarded. The result agrees with the momentum transfer theory.

並列關鍵字

interfacial reactions ； Ni-V ； Pb-free solders

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