Abstract
Due to the combined advantages of low cost, good soldering properties, and appropriate melting temperature range, novel Sn8Zn3Bi1Mg active solder was developed for direct soldering of transparent conductive oxide (TCO) ceramic targets with oxygen‐free copper at 200°C in air. The TCO specimens have aluminum‐doped zinc oxide (AZO) and zinc oxide (ZnO) ceramics. The direct soldering process was performed without the need for flux or pre‐metallization of the two transparent conductive oxides. The microstructure, phase constitution, melting characteristics, and soldering properties of the Sn8Zn3Bi1Mg active solder were investigated. The liquidus temperature of the Sn8Zn3Bi1Mg active solder was 198.6°C, which was very close to the binary Sn‐Zn eutectic temperature of 198.5°C. The effect of temperature on the bonding strength of the solder joints was evaluated. The shear strengths of AZO/Cu and ZnO/Cu joints soldered with Sn8Zn3Bi1Mg active solder were 10.3 and 7.5 MPa at room temperature, respectively. Increasing the temperature from room temperature to 180°C reduced the bonding shear strengths of AZO/Cu and ZnO/Cu joints to 3.3 and 3.7 MPa, respectively.
Highlights
Transparent conductive oxide (TCO) layers such as indiumtin-oxide (ITO), aluminum-doped zinc oxide (AZO), and zinc oxide (ZnO) are widely applied in optoelectronic devices such as huge touch panels, flat-panel displays, photovoltaics, electrically heatable glass, opto-electrical interfaces, and circuitry [1]
Among the multiple methods of depositing TCO thin film layers onto desired substrates, such as evaporation, spray pyrolysis, chemical vapor deposition, sol-gel, and sputtering, magnetron sputtering is the most attractive technique because of its good reproducibility, high deposition rate, and best deposition results in terms of the conductivity and transparency of thin film layers [2, 3]. e backing plate provides electrical conductivity and heat transfer, and it supports the target material during sputtering to keep the target from falling off and to avoid cracking of the brittle ceramic target. us, the ceramic sputter target must be bonded to copper backing plates of high conductivity. e integrity of the bond between the sputtering target and the backing plate is critical to the performance of the sputtering
Cross-sectional SEM micrographs of the bonding interfaces of AZO/Cu and ZnO/Cu joints joined with the Sn8Zn3Bi1Mg active solder at 200°C are shown in Figures 4 and 5, respectively. ose figures demonstrate the good wettability of the active filler metal and satisfactory bonding interfaces both between AZO and copper and between ZnO and copper. e copper dissolved irregularly to form a thin intermetallic compound layer with a thickness of about 0.5 μm at the solder/copper interface. e energy dispersive X-ray (EDS) analysis indicated that the composition of the intermetallic layer was Cu : Sn 41.1 : 58.9, which corresponds to the c-Cu5Zn8 IMCs
Summary
Lung-Chuan Tsao ,1 Cheng-Kai Li ,2 Yu-Kai Sun ,3 Shih-Ying Chang ,2 and Tung-Han Chuang 3. Due to the combined advantages of low cost, good soldering properties, and appropriate melting temperature range, novel Sn8Zn3Bi1Mg active solder was developed for direct soldering of transparent conductive oxide (TCO) ceramic targets with oxygen-free copper at 200°C in air. E TCO specimens have aluminum-doped zinc oxide (AZO) and zinc oxide (ZnO) ceramics. E liquidus temperature of the Sn8Zn3Bi1Mg active solder was 198.6°C, which was very close to the binary SnZn eutectic temperature of 198.5°C. e effect of temperature on the bonding strength of the solder joints was evaluated. E shear strengths of AZO/Cu and ZnO/Cu joints soldered with Sn8Zn3Bi1Mg active solder were 10.3 and 7.5 MPa at room temperature, respectively. Increasing the temperature from room temperature to 180°C reduced the bonding shear strengths of AZO/Cu and ZnO/Cu joints to 3.3 and 3.7 MPa, respectively
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