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→Brazed Joints
=== Brazed Joints===
Despite optimized brazing parameters non-wetted defect areas in the brazejoint cannot be avoided completely. These wetting defects can mostly be tracedto voids caused by flux inclusions in the braze joint area. Depending on theshape and size of the joint areas, the portion of the fully wetted joint is between65% and 90%. In its final use in switching devices a joint area of 80% isconsidered good or excellent if the individual void size does not exceed 5% ofthe joint area. Frequently wetted joint areas >90% with voids <3% can beobtained.
Evaluation of the quality of the joint can be performed either by destructive ornon-destructive methods.
====Destructive Testing====
====Non-Destructive Test Methods====
Typically the non-destructive testing of braze joints requires more elaborate testequipment. Besides this such test methods have limitations regarding theshape of the contact tips and/or carriers. The prevalent methods are ultrasoundtesting and X-ray analysis.
*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. Fig. 3.15 shows an example of different braze qualities for a Ag/SnO<sub>2</sub> contact tip brazed to a copper carrier and illustrates the position and size of void areas as well as the final joint quality.<br />
