Microstructural characterizations of metallized Al2O3 before/after surface treatment and Al2O3/Cu soldered joint

Joining Al₂O₃ ceramics to Cu heat pipes should be conducted at low temperatures since Cu heat pipes may fail at temperatures higher than 320 °C. Due to the poor wettability of low-temperature solder on Al₂O₃ ceramics, it is essential to metallize Al₂O₃ ceramics before joining Al₂O₃ to Cu with a low-temperature solder. Surface metallization of Al₂O₃ has been conducted using Ag-Cu-Ti active metal filler at 900 °C. Microanalysis indicates that an interfacial reaction occurs between the active metal filler and the Al₂O₃, leading to the formation of a Cu₃Ti₃O reaction layer. The metal layer on the surface of Al₂O₃ is primarily composed of Ag (s, s) (solid solution), Cu (s, s) and Ti₂Cu. The polishing treatment of the surface metal layer in metallized Al₂O₃ results in a reduction of the oxide content and contaminants, which subsequently allows joining at low temperature. Low-temperature joining of metallized Al₂O₃ to Cu has been carried out using Sn-Ag-Cu solder at 280 °C. The joining area of the joint includes a Cu₃Ti₃O reaction layer, a metal layer and a solder layer. The solder layer mainly consists of Sn (s, s), Ag₃Sn and Cu₆Sn₅. The Al₂O₃/Cu joint fractures in the solder layer after the shearing test, indicating that the strength of the solder is relatively low. However, the interfacial bonding between the metallized Al₂O₃, solder layer and Cu base material is satisfactory.