Influence of the grain boundary phase on the mechanical strength at aluminum nitride substrate surfaces

The influence of grain boundary phases on the mechanical strength at alumin um nitride (ALN) substrate surfaces, after a wet chemical process, was stud ied using AIN substrates doped with 2 wt% CaO or 4 wt% Y2O3. Mechanical str ength was measured by pin pull-off, pin bending tests and Vickers hardness measurements, Test specimens were obtained by the processes of lapping, pol ishing, thin-film metallizing, photoengraving, plating, and brazing, The te st results showed that the mechanical strength at the surface of Y2O3-AlN s ubstrates was higher than at CaO-AlN surfaces, where it was under the adhes ion strength between the metallization layer and the AIN substrate. The mec hanical strength at the surface of the CaO-AlN substrate was lost during pa tterning and plating. This was accompanied by an important weight loss in H NO3 and K2O . n(B2O3) aqueous solution, due to dissolution of the grain bou ndary phase, The reason for the difference in the mechanical surface streng th of AIN substrates after patterning and plating is that the CaO-AlN grain boundary phase dissolves in the chemical solution in the process more easi ly than the Y2O3-AlN grain boundary phase. The Y2O3 -AlN substrate showed u nchanged pin pull-off and bending strength even after thermal cycling (1000 cycles) and 1000 h of a pressure cooker test. Although the CaO-AlN grain b oundary phase seemed to cover all the grains, thermal conductivity was only slightly affected, because the grain boundary film was very thin.