Control of Ag electro chemical migration is crucial for long–term reliability of electrical components in high–voltage applications. In this work, Cu was bonded onto an AlN substrate at temperatures between 650 °C and 950 °C for 1 h using a Ag free Cu–P–Sn–Ni brazing filler metal with Ti as an active metal addition. The interfacial structure between the Cu and the AlN and the mechanical properties of the bond were both investigated. Three different phases which contain Ti and O were observed during the growth process of the Cu/AlN interfacial reaction layer: an amorphous P–Ti–O phase, an amorphous Ti–O phase and rutile, TiO2. The most stable Cu/AlN interfacial structure occurred when rutile was present, and where a particular orientation relationship with AlN was observed: TiO2 (101)//AlN (0001), TiO2 [010]//AlN [11 2 ¯ 0]. The probability of Cu/AlN interfacial fracture decreased as the bonding temperature was increased. Cu/AlN interfacial fracture was completely suppressed above 850 °C where rutile was the dominant phase at the Cu/AlN interface.