熱電模組接點的Co(Ni)/In/Cu界面反應與相關材料系統相平衡探討

Co(Ni)/In/Cu interfacial reactions at the thermoelectric module joints and phase diagrams of their related material systems

楊子慶(Tsu-Ching Yang)

指導教授 ： 陳信文

國立清華大學/工學院/化學工程學系/碩士(2017年)

摘要

熱電模組能夠將熱能轉換成電能，在廢熱的回收上具有好的應用潛力。熱電模組具有許多接點，由於過高的銲接溫度會影響熱電材料的性質，進而降低熱電模組的可靠度，因此低熔點的銲料具有應用價值。過渡液相連接是選擇一種熔點較低的銲料，並在高於銲料熔點且低於基材熔點的溫度下進行接合。銲料會先被融化成液體，並與基材發生液固反應，經過一段時間後，銲料可能與基材反應形成熔點較高的介金屬化合物，或是擴散至基材當中，當反應完全後，液相消失且接點僅存在熔點較高的介金屬相，因此，銦的低熔點特性與良好的機械性質成為主要的研究對象。為了避免熱電模組與銲料直接接觸產生擴散並破壞熱電材料的結構，通常會於銲料和熱電材料之間引入一層Ni或Co作為擴散阻障層，並利用導電性與導熱性佳的Cu作為基板，提升熱電模組的可靠度。因此，本實驗將以Co/In/Cu及Ni/In/Cu的三明治結構作為主要探討的對象，並以熱電材料的應用溫度做為實驗溫度點的依據，包含低溫熱電Bi2Te3(200oC)、中溫熱電AgSb2(350oC)與CoSb3(500oC)，其目的是要了解In/Co、In/Cu、In/Ni、Co/In/Cu以及Ni/In/Cu在200oC、350oC、500oC的界面反應及擴散行為，並針對界面反應速率、液相消失速率、生成相隨時間的演進，以及相生成的種類進行系統性的研究，此外，相圖是基礎的材料知識，對於界面反應十分重要，因此，將會建立Co-In-Cu與Ni-In-Cu的等溫橫截面圖做為材料分析主要的依據。首先，從Co/In/Cu在200oC、350oC與500oC下的界面反應結果中發現，當熱處理溫度為200與500oC時，其二元與三元的界面反應結果在相生成順序並無明顯的差異，且無三元相生成，並在200oC觀察到CoIn3、Cu11In9與Cu11In9+In-rich兩相區，而在500oC觀察到CoIn2、η’-Cu2In、δ-Cu7In3相；然而，在350oC的Co/In/Cu界面反應中發現有一Co2In11Cu7三元相生成，並在350oC的界面反應中觀察到CoIn3、η’-Cu2In、δ-Cu7In3相。接著進行Ni/In/Cu在200oC下的界面反應，發現在二元與三元之間的界面反應在相生成順序也無明顯的差異，僅觀察到Ni3In7、Cu11In9與Cu11In9+In-rich兩相區。然而，繼續探討Ni/In/Cu在350oC下的界面反應，一開始其生成相順序為Ni3In7、Cu11In9與Cu11In9+In-rich兩相區，隨著反應時間拉長，且界面反應發生均質化，其生成相順序轉變為Ni3In7、Cu11In9相與’-(Cu,Ni)2In相。此外，繼續探討Ni/In/Cu在500oC下的界面反應，發現該實驗結果隨著時間有明顯的變化，從一開始的NiIn、Ni5In21Cu24、Ni2In3、η’-(Cu,Ni)2In和δ-Cu7In3相的生成，當反應時間增長，Ni2In3相的消失，並於界面形成Ni5In21Cu24相和η’-(Cu,Ni)2In相的共析結構，當熱處理時間繼續增長，最後得到共析結構的消失且η’-(Cu,Ni)2In及δ-Cu7In3相以堆疊狀的表面形態生成。此外，藉由合併二元參數並繪製三元相圖，在Co-In-Cu系統中，於200oC下的計算結果可得六個三相區；於350oC下的計算結果可得六個三相區；於500oC下的計算結果可得四個三相區，並利用實驗的方法加以確認， 於Co-In-Cu 200oC下的等溫橫截面圖獲得兩個三相區，包含Co+Cu+-Cu7In3與Co+-Cu2In+Cu11In9；於Co-In-Cu於350oC下的等溫橫截面圖獲得兩個三相區，包含Co+Cu+-Cu7In3與Co+-Cu2In+Co2In11Cu7，其中發現有一Co2In11Cu7三元相存在；於Co-In-Cu於500oC下的等溫橫截面圖獲得兩個三相區，包含Co+Cu+-Cu7In3與Co+'-Cu2In+-Cu7In3。在Ni-In-Cu系統中，於200oC下的計算結果可得10個三相區；於350oC下的計算結果可得六個三相區；於500oC下的計算結果可得8個三相區。

關鍵字

熱電模組 ； 過渡液相連接 ； 界面反應 ； 計算相圖 ； 等溫橫截面

並列摘要

There are about sixty percent of energies consumed as waste heat in the process of energy conversion. Therefore, recycling of waste heat is now considered as an important issue of energy. Thermoelectric module can convert heat into electricity directly. The reliability of thermoelectric materials depends on the working temperature of soldering. During heat treatment, intermetallic compound forms and it may affect mechanical property of the joint. In this research, low-melting-point metals are chosen as solder. We observe what intermetallic compound forms at the interface while doing the process of transient liquid phase bonding.
In the research of In/Co interfacial reactions , we only find CoIn3 intermetallic phase formed at 200oC, 350oC and 500oC for 26, 12 and 24 hours, and the thickness of CoIn3 phase are 9 m, 53 m and 80 m, respectively. As we increase the reaction time, the thicknesses of CoIn3 phase is proportional to the square root of reaction time. We can conclude that they are diffusion-controlled. In In/Ni interfacial reactions, Ni3In7 phase is formed at 200oC and 350oC for 24 hours, and its thickness is 31 m and 120 m. Besides, NiIn and Ni2In3 phases are formed at 500oC for 12 hours, and their thickness are 57 m and 39 m, respectively. In In/Ni interfacial reactions at 500oC, the results show that only Ni2In3 phase is formed with shorter reaction time, and NiIn phase is formed when we increase the reaction time above 1 hour. Both of In/Ni interfacial reactions at different temperatures are diffusion-controlled. In In/Cu interfacial reactions, the -Cu7In3 and '-Cu2In are formed at 350oC and 500oC for 24 hours and 12 hours, and Cu11In9 and Cu11In9+In-rich are formed at 200oC. There are the same phases at these temperatures when we changed the reaction time. The thicknesses of reaction layer is proportional to the square root of reaction time.
Compare with binary system interfacial reactions, in Co/In/Cu interfacial reactions, there are CoIn3 phase at In/Co side at 200oC and 350oC. it is similar to binary system, but CoIn2 phase is formed at 500oC because of Cu dissolution. At In/Cu side, there are Cu11In9 and Cu11In9+In-rich phase at 200oC, and -Cu7In3 and '-Cu2In are formed at 350oC and 500oC. In Ni/In/Cu interfacial reactions, at In/Ni side, Ni3In7 are formed at 200oC and 350oC. At In/Cu side, there are Cu11In9 and Cu11In9+In-rich phase at 200oC, but there are Cu11In9+In-rich phase at 350oC. when the temperature increasing to 500oC, the NiIn, Ni5In21Cu24, '-Cu2In, and -Cu7In3 are formed. All of Co/In/Cu and Ni/In/Cu interfacial reactions are diffusion-controlled, and we calculate the liquid Indium consumption rate to manipulate thickness of pieces of Indium.
In addition, series of ternary of Co-In-Cu alloys are designed, fabricated and heat-treated at 200oC, 350oC, and 500oC. And new ternary compound are found at 350oC.

並列關鍵字

Thermoelectric modules ； transient liquid phase bonding ； interfacial reactions ； Co-In-Cu and Ni-In-Cu ternary phase diagram ； CALPHAD

參考文獻

[3] G. J. Snyder, E. S. Toberer, Complex thermoelectric materials, Nature Materials, 7 (2008) 105-114.

[4] T. M. Tritt, Thermoelectric materials: principles, structure, properties, and applications, Encyclopedia of Materials: Science and Technology, (2002) 1-11.

[5] A. J. Minnich, M. S. Dresselhaus, Z. F. Ren, G. Chen, Bulk nanostructured thermoelectric materials: current research and future prospects, Energy & Environmental Science, 2 (2009) 466-479.

[6] M. S. El-Genk, H. H. Saber, T. Caillat, Efficient segmented thermoelectric unicouples for space power applications, Energy Conversion and Management, 44 (2003) 1755-1772.

[7] R. Venkatasubramanian, E. Siivola, T. Colpitts, B. O'quinn, Thin-film thermoelectric devices with high room-temperature figures of merit, Nature, 413 (2001) 597-602.