碲化鉍熱電系統之無鉛銲點界面反應與無電鍍沉積擴散阻障層之研究

Studies on interfacial reactions of lead-free solder joints and electroless deposited diffusion barriers in the Bi2Te3-based thermoelectric system

邱俊暐(Chun-Wei Chiu)

指導教授 ： 王朝弘

國立中正大學/工學院/化學工程學系/碩士(2014年)

摘要

熱電元件是由大量之P-N型熱電對所構成，利用軟銲技術將其連結，以Bi2Te3之熱電材料系統最為普遍，而P、N型熱電基材則分別摻雜Sb與Se於Bi2Te3中，即Bi0.5Sb1.5Te3與Bi2Te2.7Se0.3。由於Sn合金銲料與熱電基材反應之生成相成長速率極快，常於銲料與基材之間電鍍Ni作為擴散阻障層。
本研究將使用Bi2Te3系統之熱電晶粒作為基材，與Sn、Sn-58wt%Bi銲料進行固/固及液/固界面反應。P型基材和Sn或Sn-Bi銲料進行固/固界面反應，其SnTe相成長速度皆快於N型反應偶。在液/固反應中，Sn分別與垂直c軸及平行c軸方向之熱電基材進行反應，發現P型反應之SnTe相受到基材方向性影響較為明顯，N型反應偶則無顯著變化。本研究也探討反應相成長動力學，在固/固及液/固反應中，Sn與Sn-Bi系統之反應相皆以擴散控制成長，只有P型反應在液/固反應下為反應控制。
本研究也模擬真實熱電模組之銲點，在銲料與基材之間中導入Ni-8.5wt%P及Co-4.5wt%P阻障層，並進行一系列之界面反應。加入Ni-P層之固/固反應，銲料與P型基材反應明顯受到抑制。在N型反應中，一旦Ni-P層消耗完畢，Sn將穿透Ni-Sn-P層，並使基材側NiTe相發生相轉變及生成SnTe及BiTe相。探討其液/固反應，無論是P型或N型基材，在短時間與Sn反應將因熱膨脹應力而導致Ni-P層剝離，使得SnTe相生成並快速增厚。Co-P鍍層與P、N型基材反應之生成相總厚度成長極慢。加入Sn銲料反應後，Sn將與Co-P層快速反應生成CoSn4相。P型反應偶在熱處理一段時間後，CoSn4轉變成Co(Sn,Sb)3相並於基材側生成SnTe相，而N型則生成CoSn4/Co-Sn-P/SnTe/BiTe之結構。對於液/固反應而言，CoSn4相快速生成並往銲料飄散，基材側反應相隨之生成。
此外，本研究將利用無電鍍Co-W-P合金於在Cu基材上，並與Sn及Sn-3.0wt%Ag-0.5wt%Cu(SAC305)進行反應。Sn與Co-W-P之固/固反應於界面處生成層狀CoSn3相與Co-Sn-P相，而SAC305則生成(Cu,Co)6Sn5相於CoSn3相外側。在液/固反應，在反應初期生成Co-Sn及Co-Sn-P介金屬相，隨時間增加，兩系統中的Co-Sn相往液相銲料中飄散。當Co-W-P鍍層消耗完後，銅快速擴散至銲料中，使銲料中Co-Sn飄散相轉變成(Cu,Co)6Sn5相，在界面處Co-Sn-P三元相顯著增厚且生成相當厚的孔洞狀Cu6Sn5相。最後界面處Co-Sn-P相整層往銲料剝落，同時Cu6Sn5相大幅增厚。

關鍵字

無電鍍沉積 ； 擴散阻障層 ； 熱電材料 ； 界面反應 ； 無鉛銲料

並列摘要

Thermoelectric (TE) devices consist of many pairs of p- and n-type semiconductor elements, which are interconnected electrically by soldering technology. Bi2Te3-based alloys are the most popular thermoelectric materials. Sb and Se are usually alloyed to Bi2Te3-based alloys for p- and n-type, respectively, i.e., Bi0.5Sb1.5Te3 and Bi2Te2.7Se0.3. Ni is frequently used as a diffusion barrier to prevent the fast IMC growth.
In this research, we studied the solid/solid and liquid/solid reactions between Sn-based solders (Sn or Sn-58Bi) and Bi2Te3-based thermoelectric materials. The SnTe growth rate of p-type couples were larger than the n-type. For the liquid-state aging, Sn reacted with TE substrates with two different directions (⊥c-axis or //c-axis), we found that the IMC growth of the Sn/p-type substrate reaction couple was anisotropic. The growth kinetics were also investigated. For the solid-state reactions, the growth is parabolic for p- and n-type reactions. For the liquid-state reactions, the growth of the p-type reaction is linear, and the n-type case followed a parabolic law.
This study also simulated the solder joints of the thermoelectric device, using the electroless deposition of Ni-P or Co-P as a diffusion barrier between Sn and TE substrates. In the Ni-P system, the reaction was inhibited significantly between solder and p-type material. For the n-type cases, Sn diffused through the Ni-Sn-P layer when the Ni-P barrier was depleted, the NiTe phase occurred phase transformation in substrate side, and the SnTe and BiTe phases were formed. During the liquid reaction, the Ni-P layer was peeled off from the interface due to thermal expansion stress, resulting in the fast IMC formation.
For the Co-P cases, Sn fast reacted with the Co-P layer and formed the CoSn4 phase. After an aging period of the p-type reaction, the metastable CoSn4 phase was transformed to Co(Sn,Sb)3 phases and the SnTe was formed in substrate side. In the solid/solid reaction of n-type, the CoSn4/Co-Sn-P/SnTe/BiTe structure was found. Both the p- and n-type liquid/solid reactions, the CoSn4 and Co-Sn-P phases were formed, and massive spallation of the CoSn4 phase occurred.
In addition, the electroless Co-W-P was deposited on Cu substrate, and reacted separately with Sn or SAC305. The layer-structured CoSn3 phase and Co-Sn-P IMC were formed at the interface between Sn and the Co-W-P layer, while the (Cu,Co)6Sn5/CoSn3/Co-Sn-P structure was observed for using the SAC305 solder. In the liquid-state reactions, the Co-Sn and Co-Sn-P phases were formed in the initial stage. With the reaction proceeding, the Co-Sn phase was spalled into the liquid-state solder. When the Co-W-P was depleted, Cu fast diffused into the solder and the Co-Sn spalling phase transformed into (Cu,Co)6Sn5. The Co-Sn-P ternary phase grew thicker obviously, and a thick porous-structured Cu6Sn5 phase was formed at the interface. Finally, the Co-Sn-P layer was peeled off and the Cu6Sn5 thickness grew significantly.

並列關鍵字

diffusion barrier ； thermoelectric material ； interfacial reaction ； electroless deposition ； lead-free solder

參考文獻

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