*Article* **Metallization on Sapphire and Low-Temperature Joining with Metal Substrates**

**Jiajun Fang 1, Qiaoxin Zhang 1, Zhou Luo 1, Wei Huang 1, Zhenyu Liu 1, Zhiwen Chen 2, Xueqiang Cao <sup>1</sup> and Li Liu 1,\***


**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.

**Keywords:** sapphire; surface metallization; deposition mechanism; wettability; low-temperature joining
