The scientists at Fraunhofer IFAM tested various joining processes for their suitability for the efficient use of copper conductors as contacting elements. Various soldering, forming, adhesive, welded and assembled connections were compared. The joining process also had to meet the following requirements: environmentally friendly process (e.g. no use of substances harmful to health or the environment), minimum effort (no pretreatment or intermediate process steps), series production possible, joining temperature should correspond to thermal class H (max. 180°C) of the insulation class according to DIN EN 60085 and the joining should take place in the installed state, i.e. the coils are already mounted on the sheet metal package.
The results of the extensive investigations show that solid phase joining processes meet the high requirement profile. If the joining temperature is kept below 300°C, as a rule no mixed phases are produced and the joint has a low electrical resistance with sufficient strength. Detailed investigations with regard to strength and contact resistance have shown that joining by ultrasonic welding can be regarded as very promising. This process meets the requirements and offers great potential for further technology optimization. The two-dimensional tool arrangement allows the two contact partners to be joined with very good joining properties. Depending on the application, an optimization with regard to strength and formation of intermetallic phases can be achieved by varying the process parameters, with almost constant electrical resistance.
More information: https://www.ifam.fraunhofer.de/en.html