現今工業上有許多需要降低熱預算的材料與製程，如三維積體電路構裝會因翹曲現象導致良率降低，而低溫銲料正是降低熱預算的方法之一。過去常用的低溫銲料無法解決目前所遇到的低熱預算問題，故本實驗試圖開發新低溫合金銲料，跳脫以往利用Sn為基底的銲料，純粹利用In與Bi兩種金屬為本實驗的合金銲料。根據相圖上的共晶點，選用33In67Bi (wt.%)與68In32Bi (wt.%)，透過DSC分析得知此兩種不同比例銲料之熔點，再利用高於熔點30 oC的溫度下，將銲料迴焊於Cu基材上，分別進行多次迴焊，並且於不同溫度的狀況下退火，利用SEM分別觀察迴焊後與熱退火後的界面形貌，再利用EPMA與同步輻射之XRD與GIXRD分別鑑定介金屬化合物及銲料中的生成相。
於33In67Bi/Cu之反應偶中，生成之介金屬化合物的厚度非常薄，生長速度緩慢；此外，經由EPMA與GIXRD的分析可知，銲料中分成Bi-rich相與InBi兩相，而介金屬化合物為Cu2In。
於68In32Bi/Cu之反應偶中，其介金屬化合物比33In67Bi/Cu系統中稍厚，但其生長速度也不快，甚至長到固定厚度後將會停止生長，成為一自體擴散阻障層，鑑定可知銲料中的相為BiIn2與In-rich相，介金屬化合物的相為CuIn2與Cu11In9兩相，低溫下會偏向生成CuIn2，高溫之下會偏向生成Cu11In9。

In the semiconductor industry, low thermal budget is a critical topic. A low thermal budget is achieved by using a polymer substrate, a molecular machine, and 3D integration technology, which are associated with a low glass transition point, low decomposition temperature, and severe warpage, respectively. In conventional assembling technology, low-melting-point solder is an extremely economical solution for a low thermal budget. However, low-melting-point solder used in industry cannot solve the aforementioned problems. According to two eutectic points in an In-Bi phase diagram, solder alloys with the compositions 33In-67Bi wt.% and 68In-32Bi wt.% were selected in this study. Both alloys were reflowed on a Cu substrate 1, 3, 5, and 10 times at a temperature that was 30 oC higher than each melting point. To investigate the intermetallic compounds (IMCs) and phase formation in diffusion couples, samples treated with one reflow cycle were aged at different temperatures. The microstructural evolution and phase formation of two diffusion couples (33In67Bi/Cu and 68In32Bi/Cu) were observed through scanning electron microscopy, X-ray diffraction, electron probe microanalysis, and grazing incidence X-ray diffraction at the National Synchrotron Radiation Research Center.
In the 33In67Bi/Cu system, the rate of IMC growth at the interface was quite low. The phase of the IMCs was identified to be Cu2In, and those in the solder were determined to be Bi-rich and InBi phases.
The IMC growth rate of the 68In32Bi/Cu system was higher than that of 33In67Bi/Cu. After long-term reflow, IMCs that formed at the interface of 68In32Bi/Cu served as a self-diffusion barrier so that the thickness of the IMCs would not increase. The phases of the IMCs that formed at the interface of the 68In32Bi/Cu diffusion couple were Cu11In9 and CuIn2, and the phases formed in the solder were In-rich and BiIn2 phases. Furthermore, CuIn2 was a metastable phase that could transform to Cu11In9 spontaneously. Consequently, both CuIn2 and Cu11In9 were found at the interface.

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