Changes

*Ultrasonic testing <br />This method is based on the disruption of the propagation of sound waves in different media. High resolution modern test systems with graphic print-out capabilities and analytical software are capable to detect even small (<0.5 mm diameter) voids in the braze joint. The portion of the wetted areas is calculated as a percentage of the whole joint area. <xr id="fig:Ultrasound print-out of braze joints"/> <!--(Fig. 3.15) --> shows an example of different braze qualities for a Ag/SnO₂ contact tip brazed to a copper carrier and illustrates the position and size of void areas as well as the final joint quality.<br />

Besides destructive testing for shear force and weld area the non-destructive ultrasound testing of the joint quality is also utilized for welded contact assemblies <xr id="fig:Ultrasonic picture of a weld"/> <!--(Fig. 3.16)-->.

In the preceding sections a multitude of possibilities for the attachment of contact materials to their carriers was described. A correlation of these methods to the switching current of electromechanical devices is illustrated in <xr id="fig:Correlation between Contact Joining Methods and Switching Currents"/> <!--(Tab. 3.2)-->. It shows that for the same switching load multiple attachment methods can be applied. Which method to chose depends on a variety of parameters such as contact material, material combination of contact and carrier, shape of the contact, required number of switching operations and last but not least the required volume of parts to be manufactured.