碲化鉛熱電塊材與銅電極間填料接合之擴散阻障效應及界面性質研究

Abstract

熱電材料能利用它的材料特性將熱能與電能互相轉換，在廢熱回收方面極具發展潛力。然而，熱電元件製作成模組過程中，在熱電材料與電極間的接合技術和防止元素擴散上是一大挑戰。本研究使用中溫段的PbTe和PbAgTe熱電材料，以電鍍方式沉積Ni擴散阻障層來防止元素擴散，並且透過SnAgTi銲片於真空度2×10-2 torr及溫度400℃的條件，持溫20分鐘與銅電極進行真空軟銲接合。另一方面，以PbTe熱電材料搭配AgCuTi銲片，於580℃真空環境下持溫一小時與銅電極進行固態擴散接合。最後將各成功接合的實驗試片，分別進行300℃至500℃的短時效測試與微觀組織觀察及電性量測。 實驗結果顯示，上述實驗條件可將PbTe/Ni/SnAgTi/Cu與PbAgTe/Ni/SnAgTi/Cu兩種系統成功接合，並且均可在300℃持溫30分鐘時效條件下，維持良好的接合界面情形。以及PbTe/Ni/AgCuTi/Cu系統亦依上段實驗參數下接合成功，更可在時效溫度高達500℃時，並持溫30分鐘下保持良好界面狀態。另外，於25℃環境溫度下，在PbTe/Ni/SnAgTi與PbAgTe/Ni/SnAgTi/Cu系統所測得的電阻值，均隨著時效處理溫度提高而上升。然而，在PbTe/Ni/AgCuTi系統所測得的電阻值，則是隨著時效處理溫度提高而下降。Thermoelectric materials featuring the advantage of energy interconvertibility between heat and electrical energy shows a great potential on the application of waste heat recovery. However, the element inter-diffusion between thermoelectric materials and electrode during bonding process is a major challenge for module production. In this study, Ni diffusion barrier was deposited by electroplating on intermediate-temperature PbTe and PbAgTe thermoelectric materials to prevent the element diffusion. The bonding process for SnAgTi filler and copper electrode was carried out at 400℃ for 20 minutes under vacuum with a pressure of 2×10-2 torr. On the other hand, the high-temperature AgCuTi filler was also used for the investigation of solid-state diffusion bonding at a high temperature of 580℃for 1 hour under vacuum. Finally, the bonding samples were evaluated by short-time aging test and electrical measurement over the temperature range from 300℃ to 550℃. The cross-sectional structure was observed by scanning electron microscope. The experimental results demonstrate that the stack of PbTe/Ni/SnAgTi/Cu and PbAgTe/Ni/SnAgTi/Cu can be successfully bonded below 450℃. These samples with appropriated bonding conditions also maintain good bonding stability at an ageing temperature of 300℃ for 30 minutes. Another bonding stack of PbTe/Ni/AgCuTi/Cu even obtained a well-bonded interface with increasing aging temperature up to 500℃ for 30 minutes. Besides, it is worth to note that the interface resistance for the bonding structure of PbTe/Ni/SnAgTi/Cu and PbAgTe/Ni/SnAgTi/Cu raised with increasing aging temperature. On the contrary, the PbTe/Ni/AgCuTi/Cu structure based on diffusion bonding approach shows a reverse trend that was evident in a lowered interface resistance with relevant increase in aging temperature.