摘 要
本研究利用錫湯與Cu板在270oC擴散達100小時，來探討Cu原子濃度逐漸增加下，無鉛銲料Sn-3.0Ag-0.5Cu-0.2Sb的微結構、濕潤性、機械性質的改變，並作160°C、240小時的熱處理，再利用拉伸試驗來了解不同Cu原子濃度熱穩定性的差異。
實驗結果顯示，錫湯中Cu原子濃度隨著擴散時間而增加，到了擴散時間100小時，Cu原子濃度已達0.933wt%，而Cu的增加會稍微降低熔點並改變固液區間溫差，擴散50小時之錫湯固液區間溫差最大，Cu的增加並不會改變其析出相，仍為Ag3Sn與β-Sn所組成的環狀共晶，但晶粒更細，且Cu6Sn5析出物更多更粗大。
在潤濕行為方面，由於Cu的加入，會使得銲料與Cu的表面張力減小，而能夠降低銲料與Cu板的接觸角，亦能縮短Cu棒與銲料的潤濕時間，而對潤濕力影響雖然不大，但整體而言，使銲料的潤濕行為更佳 。
機械性質方面，隨著Cu原子的加入，析出物變多，析出強化的效果增強，故在硬度與降伏強度有上升的趨勢，到了擴散時間100小時後，降伏強度已由29.16升至35.5MPa，但其破壞模式不受改變，所以伸長率不受影響 ; 但經過160oC、240小時的持溫下，Cu原子濃度越高的銲料，析出物粗大化越明顯，未經擴散之銲料降伏強度由原本的29.16MPa下降至熱處理後的23.62MPa，下降了18.8%，而擴散100小時的試片其降伏強度由35.52MPa下降至20.80MPa，下降率高達41.4%，故Cu原子濃度越高，其熱穩定性越差。
綜合上述所論，雖然Cu原子濃度增加會提升潤濕性、機械性質，但熱穩定性反而變差，故在選用錫銀銅系列無鉛銲料時，必須先考量製程上的條件，若需要長期處於高溫環境，仍以銅含量偏低為適當。

關鍵字:錫銀銅、無鉛銲料、潤濕行為

Abstract
In this study, the liquid of tin and copper plate were diffused at 270oC for 100 hours to investigate micro-structures, wettability and mechanical properties of lead-free solder Sn-3.0Ag-0.5Cu-0.2Sb when the concentration of copper was increased. Besides, the tensile test after 160°C for 240 hours thermal treatment was used to understand the different thermal stability between different copper concentrations.
The results of structure show that the concentration of copper in tin liquid was increased by rising the diffusion time. When the diffusion time up to 100 hours, the concentration of copper was 0.933 wt%. The increasing of copper will reduce the melt point little and change the temperature difference between solid phase and liquid phase. After 50 hours diffusing, temperature difference between solid and liquid was the largest. No matter in what concentration of copper, it still be the circular eutectic microstructure of Ag3Sn and β-Sn but the grain size was finer and the precipitation of Cu6Sn5 were more and coarse.
In wetting behavior, the surface tensile stress of solder-copper interface decreasing by rising copper concentration. The contact angle and wetting time of solder on copper plate decrease too. Summarily, in the study adding copper to the solder can enhance the wettability.
On the mechanical properties, when the Cu atoms increasing, hardness and yield strength were improved due to precipitates increasing. After 100 hours diffusing, the yield stress was improved from 29.16 to 35.5 MPa.
The rupture forms were the same as non-diffusion specimens and the elongation is not varied. After diffusing for 240 hours at 160oC, the concentration of Cu was increasing, the precipitates became coarse and the yield strength was reduced from 29.16 MPa to 23.62 MPa by 18.8 percent. The yield strength of 100 hours diffused sample was reduced from 35.52MPa to 20.80MPa by 41.4 percent. From the results, when the concentration of Cu increase, the thermal-stable properties were worse.
In summary, although the increasing of copper concentration enhance wettability and mechanical properties, thermal stability decreases.The parameters of manufacturer process are very important for lead-free solder. According to the study, if the working environment is on the high temperature, it is the optimum that the copper concentration is lowest in solder.

Key words: Sn-Ag-Cu、lead-free solder、wetting behavior

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