Abstract
To meet the packaging requirements of sapphire in special electronic components, there is an urgent need for a joining process that can realize a good connection between sapphire and dissimilar metals at a low temperature. In this work, the surface of a sapphire substrate was successfully catalytically activated and metallized by an electroless nickel plating process. Moreover, the solderability and interconnection of metallized sapphire with Sn-based solders were evaluated and investigated at 250 °C, and the wetting angle of the Sn-based solders on sapphire on sapphire without and with metallization was 125° and 51°, respectively. The interfacial microscopic morphology and element distribution in the Cu/Sn-Ag solder/sapphire solder joints were analyzed. It was found that the middle solder layer has diffused during the reflow process, inferring good adhesion between sapphire and Cu substrate with the aid of the Ni-P deposition. Thus, a sapphire welding method with a simple process suitable for practical applications is demonstrated.
Highlights
Sapphire has superior optical and mechanical properties, including high melting point, high hardness, strong corrosion resistance and good thermal conductivity, which makes sapphire highly demanded in electronics and scientific instruments [1,2]
The roughness of the polished and smooth surface measured by atomic force microscope (AFM) was 84.0 nm and 1.79 nm, respectively
Ni-P coating can be deposited on the sapphire, indicating that the coarsening solution can react with α-Al2O3 and form enormous micro-holes on the substrates
Summary
Sapphire has superior optical and mechanical properties, including high melting point, high hardness, strong corrosion resistance and good thermal conductivity, which makes sapphire highly demanded in electronics and scientific instruments [1,2]. Sapphire is required to achieve joining with common metals by a simple reflow process. Sapphire is hard to achieve reliable solder joints during the reflow process as it is an Al2O3 single crystal. With the assistance of ultrasonic, the brazing temperature of sapphire solder joints can be greatly reduced. Cui et al used an Al-4.5Cu-1.5Mg alloy as a filling metal to connect sapphire through ultrasonic-assisted hot dipping [5]. Various related researches on sapphire welding have been conducted in the above aspects. They all have shortcomings for electronics applications, including high joining temperature, specific active solder, auxiliary ultrasonic brazing and so on
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