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  • 學位論文

碲化鉍系列熱電模組銲料接點之界面反應研究

A study of interfacial reactions in solder joints of bismuth telluride based thermoelectric modules

指導教授 : 廖建能
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摘要


熱電元件組裝是將成對的p型與n型熱電材料以銲料與金屬導線進行連接,並在元件上下兩端外加陶瓷基板以保護元件結構,而熱電材料與金屬導線間的接觸電阻將會嚴重限制微小型或薄膜型熱電元件的效能。本研究探討在迴銲過程中所產生介金屬化合物對熱電材料與導線接點的接觸電阻影響性。我們分別利用兩種不同銲料Sn-4Ag-05Cu和Sn-37Pb將商用p型或n型碲化鉍熱電材料與金屬銅箔進行接著,而實驗結果呈現此兩接點所產生的主要介金屬化合物分別為SnTe及PbxSn1-xTe。接點接觸電阻經量測後約為10-4~10-5 cm2,此數值和在接點的介金屬化合物種類與厚度息息相關。另外實驗結果指出,銻和銅元素在迴銲過程中對介金屬化合物的成長機制有重大且相反的影響性,因此我們利用基本的錫-銻或錫-銅銲料與碲基材反應偶實驗來探討銻或銅元素的影響機制。 實驗結果顯示,在錫-銻銲料與碲基材反應偶中,銻元素的添加大幅加速介金屬化合物SnTe的生成,其成長速率甚至達每分鐘24微米,遠大於在電子封裝中常見化合物的成長速率。隨著增加銻元素的含量,SnTe的成長速率會加快並伴隨著晶粒尺寸的縮小。此表示在化合物內部的錫原子有效傳輸面積將因銻原子不斷排入銲料中而減少,進而改變化合物生長的速率決定步驟,從原先的錫和碲元素界面反應轉為錫原子在化合物層中的擴散。而錫-銅銲料與碲基材反應中發現,僅僅只要0.1wt%Cu添加入純錫銲料中,在液態銲料和碲基材反應界面上會生成一層薄薄的CuTe化合物進而有效抑制SnTe化合物劇烈的生長。CuTe化合物會隨著液態銲料中銅含量增加而由不規則分佈的叢集結構(clusters)轉為層狀結構,且在相同反應時間內,CuTe厚度正比於銅含量的二分之ㄧ次方,此表示CuTe成長為擴散控制機制。另外本實驗以Sn-0.1Cu銲料接著碲化鉍化合物與金屬銅箔,並量測其接觸電阻,數值約為10-5 cm2。經過150 ºC168小時熱處理後,介金屬化合物成長仍然受到明顯的限制,說明CuTe在Sn-0.1Cu/Te反應偶中是個不錯的阻障層。綜合上述結果,我們相信Sn-0.1Cu銲料對於組裝碲化鉍為主的熱電元件是個不錯的選擇。本研究的重要性在於探討碲化鉍材料與銲料的界面反應,並對於適合熱電元件組裝的銲料選擇 提供有效的方針。

並列摘要


Typical thermoelectric modules are made of a number of p- and n-type thermoelements which are jointed to copper conductors by soldering reaction and arranged in a square array between two ceramic plates. Contact resistance of conductors/thermoelements joints may become a serious limitation to the performance of thermoelectric modules with relatively short or thin-film type thermoelements. In this study we have investigated the impact of interfacial compounds on the contact resistivity of bismuth telluride/Cu soldered junctions. Two different solder alloys, Sn-4Ag-0.5Cu and Sn-37Pb, were used to joint both commercial p-type and n-type bismuth telluride onto thin Cu foils. SnTe and Pb1-xSnxTe were identified to be the major interfacial compounds for the Sn-4Ag-0.5Cu and Sn-37Pb soldered junctions, respectively. The contact resistivity measured is around 10-4 ~ 10-5 cm2, which depends on both the thickness and composition of interfacial compounds. Sb and Cu element are observed to have a strong influence but in an opposite manner on growth kinetics of the interfacial compounds during soldering reaction. The mechanisms for Sb and Cu on SnTe growth were explored using a simple solder/Te reaction couple. Addition of Sb element in solder considerably enhances the growth rate of SnTe compound, e.g. 24µm/min for 1wt% Sb addition, that is rarely seen in typical soldering reactions. With increasing Sb content in Sn-Sb solder, the growth rate of SnTe may increase accompanied with the reduction in size of SnTe grains. It indicates that the effective channel area for Sn transport in compound may decrease with the consecutive Sb ejection into solder, and hence the rate-limiting step of SnTe formation will change from Sn/Te reaction to the transport of Sn through the compound layer. A dosage of 0.1 wt% Cu in Sn is capable of suppressing the vigorous Sn/Te reaction effectively by forming a thin CuTe at the solder/Te interface. The CuTe morphology changes from irregular clusters into a layered structure with increasing Cu content. With the same reaction time, the CuTe thickness increases proportionally to x1/2 in the Sn-xCu alloys, suggesting a diffusion-controlled growth for CuTe. The contact resistivity of bismuth telluride/Cu soldered junctions using Sn-0.1Cu alloy were measured to ~ 10-5 cm2. After thermal treatment at 150 ºC for 168 hours, the growth of intermetallic compounds in Sn-0.1Cu/Te couples were still obviously suppressed, indicative of the superior barrier capability for CuTe compound. It is believed that Sn-0.1Cu alloy shall be a good candidate solder for assembly of telluride based thermoelectric modules under the consideration of electrical property and mechanical integrity. This study may be of importance in understanding the interfacial reaction between bismuth telluride and solder, as well as in providing the effective strategy to choose appropriate solder alloys for thermoelectric assembly.

參考文獻


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被引用紀錄


劉祐麟(2012)。Bi-Sb-Te/金屬界面接觸電阻及接觸熱阻之量測與特性分析〔碩士論文,國立清華大學〕。華藝線上圖書館。https://www.airitilibrary.com/Article/Detail?DocID=U0016-2002201315291940

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