Bonding mechanism between aluminum nitride substrate and Ag-Cu-Ti solder

The bonding mechanism between aluminum nitride (AlN) substrate and silver-copper-titanium solder was studied. The AlN surface was bonded to the solder with the TiN intermediate layer containing free Ti and Al, produced at the interface between the AlN substrate and the solder. There were garnet phases consisting of aluminum oxide and yttrium oxide partially existed on the AlN substrate surface and these were also bonded to the solder. It was observed that the interface between the garnet phases and the intermediate layer had the highest bonding strength of all the regions. The reasons for variations in bonding strength of a copper plate to AlN substrate were also investigated, focusing on the differences in the preparation procedures of the AlN surface. The adhesion strengths of the copper plate were higher for samples using as-fired AlN substrates than those of lapped ones. This was attributed to the existence of a large amount of the garnet phases and no mechanical damage on the as-fired AlN surface, while the lapped AlN surface had a small amount of the garnet phases and was damaged mechanically