The strength of a join between a ceramic and an associated non-ceramic is determined using an ultrasonic microscope. A converging ultrasonic beam (B) is radiated against a point (P) on a surface of the ceramic (1), said point being a predetermined distance away from the join (3) between the ceramic (1) and the associated non-ceramic (2). Data on the intensities of interference waves at respective predetermined varia­tions of the relative distance between a probe (5) of the ultrasonic microscope and the ceramic (1) are col­lected. The residual stress at the point is calculated on the basis of the cycle of echo intensities of the interference waves for the respective predetermined variations of the relative distance. The strength of the join is then determined on the basis the residual stress.