近年來，先進電子封裝技術以疊構晶片的方式生產高階電子產品，同時為了降低銲接溫度產生之問題，進而發展出以Sn-Bi合金系統為主流的低溫銲料。然而電子產品在長期使用下，於高於室溫之環境中，亦會使低熔點合金產生相變化行為，因此Sn-Bi合金雖具有良好前景，但由於Sn-Bi之間不互溶，導致在元件和基板之銲接界面處有Bi析出之狀況，從而增加銲接點斷裂的風險。
本研究中將添加Cu元素於Sn-Bi合金，利用真空熔煉法製備Sn-(40-x)Bi-xCu合金塊材，x分別為0、0.5、2.5、5、15、20，針對其晶體結構、微觀結構及機械性質之變化探討，接著將此合金系統導入銲接製程，觀察在不同迴銲及時效熱處理條件下，銲接接點之界面反應行為。
首先在Sn-Bi合金中，由於Sn與Bi彼此不互溶，經XRD分析結果為獨立Sn、Bi相峰值；在微觀結構上則以層狀結構散佈。接著隨著不同Cu含量加入後，於XRD結果指出於在Cu含量0.5 wt%添加時，繞射角度30°開始出現Cu6Sn5相峰值，意謂少量之Cu添加就能夠促進Cu-Sn化合物生成，並且以條狀散佈於Sn-Bi合金之中，本身作為異質成核點，促進Bi之高成核密度，成核成長的過程中彼此競爭，進而縮小Bi之尺寸；另外透過Cu-Sn化合物生成而有析出強化之效果，Sn-40Bi由平均硬度為24.93 HV，當Cu含量上升至20 wt%時，合金整體硬度上升至63.13 HV，有助於提升合金之機械性質。
在經過時效熱處理後，探討界面處之介金屬化合物(Intermetallic Compound, IMC)成長與抑制Bi於界面處分佈之表現。日前業界之IMC厚度標準以1~5 µm為宜，因此以含0.5 wt% Cu以下之銲料落於此範圍內，另外界面處富Bi相的分佈，在經時效處理後有大幅成長的趨勢，含2.5 wt% Cu以內之銲料其Bi面積佔比小於Sn-Bi銲料；綜合以上兩者表現來說，以0.5 wt% Cu添加於Sn-Bi銲料，儘管Cu元素的添加使得IMC的厚度隨之上升，但是透過Cu-Sn化合物析出在Sn-Bi銲料與Cu基板連接之界面，減少Bi於界面析出，進而降低Bi之粗大化引起的界面脆化，並保持界面之完整性。

In recent years, advanced electronic packaging technology produces high-end electronic products by stacking chips. In order to reduce the problem of high soldering temperature, Sn-Bi alloy system have been developed. However, the long-term use of electronic products above room temperature will cause low melting point alloys occur phase change. Although Sn-Bi alloys have good prospects, the precipitation of Bi at the interface will increase the risk of solder joint fracture.
In this study, Cu element will be added into Sn-Bi alloy. First, the Sn-(40-x)Bi-xCu alloy bulk was prepared by vacuum melting method. The changes of alloy crystal structure, microstructure and metallurgical diffusion behavior would be discussed. Then, the alloy system was introduced into the soldering process, and the interface reaction behavior of the solder joints was observed after different reflow and aging conditions.
Sn and Bi are immiscible with each other. XRD analysis results show the peaks of independent Sn phase and Bi phase. We observed the layered structure in microstructures. With adding Cu content of 0.5wt%,XRD results indicated the Cu6Sn5 phase peaks at the diffraction angle of 30°, which means that a small amount of Cu addition can promote the formation of Cu-Sn compounds. These compounds are in the shape of strips and act as a heterogeneous nucleation point, which promotes the high nucleation density of Bi . High nucleation density of Bi competes with each other in the process of grain growth, which reduces the size of Bi. Due to the precipitation strengthening of Cu-Sn compounds ,the average hardness of alloy increases from 24.93 HV to 63.13 HV when the Cu content increases to 20 wt% .
After aging, the growth of IMC at the interface and the inhibition of Bi distribution at the interface would be discussed. In terms of IMC thickness performance of the industry standard is from 1 to 5 µm. The solder containing less than 0.5 wt% Cu meets the industry standard. The distribution of Bi-rich phase at the interface has a tendency to grow significantly, and the growth rate of Bi containing 2.5 wt% Cu is lower than the Sn-Bi solder. Therefore, adding 0.5 wt% Cu into Sn-Bi solder can reduce the interface embrittlement and maintain the integrity of the interface.

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