The investigation of various properties on Sn-8.5Zn-0.5Ag-0.1Al-xGa solder with different Ga content

• Main Authors: Nai-Shuo Liu, 劉乃碩
• Other Authors: K. L. Lin
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/80647898881844382881

博士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 95 === This study investigated the addition of Ga to improve the properties of Sn-Zn series Pb-free solders. Our laboratory had been awarded the patent of Sn-8.55Zn-0.5Ag-0.45Al-0.5Ga solder. But the role of Ga in solder was not understood clearly. Therefore, this work investigated the effect of Ga on thermal, mechanical and wetting properties of Sn-Zn-Ag-Al containing solders. The microstructure of Sn-8.5Zn-0.5Ag-0.1Al-xGa (x=0.05~2wt%) solder consists of needle Zn-rich phase and dendritic AgZn3 compound distributed in the Sn matrix. The addition of Ag results in the conversion of the eutectic structure. The results of EPMA analysis indicated that Ga dissolves in Sn matrix as well as in Zn-rich phases, while Al may segregate at grain boundary of β-Sn. The results of DSC (Differential Scanning Calorimetry) analysis reveal that the increase in the Ga% from 0.05% to 2% will lowers the solidus temperature of the solder from 197oC to 183oC and expand the two phase region as well. It is noteworthy that a shoulder can be seen in the DSC curve at higher Ga contents, indicating the formation of hypoeutectic structure. The results of mechanical test showed that with an increase in Ga content up to 1wt% will improve the average tensile strengths and total elongation of the solder. Yet, the total elongation of solders drops from 42% to 20% when Ga content increases from 1 to 2wt%. The facture surface morphology indicates that all the specimens exhibit a ductile dimple pattern. The investigation of wetting behavior indicates that wetting time and wetting angle decreased while the wetting force increases with an increase in Ga content. The intermetallic compounds formed at the interface after wetting experiment were Al4.2Cu3.2Zn0.7, Cu5Zn8 and AgZn3 in the solder of lower Ga contents, while the CuZn5 forms between Cu5Zn8 and AgZn3 when the composition of Ga approaches 0.5wt%. The aging treatment at 150℃ converts the Al4.2Cu3.2Zn0.7 and CuZn5 compound to Cu5Zn8. The AgZn3 was decomposed and Ag dissolves in Cu5Zn8 after aging for 1000 hours. Addition of Ga into the solder also increases the thickness of Cu5Zn8 compound. Long time aging results in the formation of voids and consequently cracks between IMC and solder. The results of Thermogravimetric Analysis under O2 atmosphere at 250°C show that an increase in Ga content enhances the oxidation resistance of Sn-8.5Zn-0.5Ag-0.1Al-xGa lead-free solders. The cross sectional investigation of solder surface with the aid of focus ion beam (FIB) shows that the thickness of oxidation layer was about 30~100 nm. The oxidation layer was found to be porous at low Ga content. The surface oxide layers were further examined by Auger electron spectroscopy (AES) and thin-film XRD to show that the oxide layer formed was ZnO with the segregation of Al and Ga.