Accelerated model for mechanically caused material damage

Description

© Fraunhofer EMFT
Control of concealed solder joints (BGA, PGA, QFN)

In the field of drive systems, press-fit technology presents an interesting alternative to other electrical contacting methods such as solder, screw or crimp connections. The benefits are minimal space requirements, repair capacity and a failure rate which is potentially between ten and hundred times lower. The press-fit procedure creates a touch zone between the pressfit contact and the copper sleeve in the circuit board. As a result of the pressure caused by the deformation of the press-fit contact when it is pressed in, this touch zone forms a gas-tight and corrosion-proof contact zone after about 24 hours. Inside this zone, the free electrons generate attraction forces that connect the two metal surfaces. In this way, a cold weld zone is formed within a few hours.

However, the process can also involve unintentional damage to the component. For example, microrelative movements between the press-fit contact and the copper sleeve in the circuit board, induced by vibrations, can result in fatigue damage or fatigue failure of the cold weld zone. The cold weld zone then disengages as a result of crack formation and crack growth. In collaboration with the Institute of Materials Technology and the Institute of Drive and Automotive Engineering, both at the University of Kassel, Fraunhofer EMFT researchers are working to develop an accelerated model so as to gain a better understanding of these undesired effects.

The Fraunhofer EMFT team is building a test bench to study the microrelative movements described above. The Munich experts also undertake precise electric characterizations of the contact resistance of the cold weld zone. Having conducted a detailed mechanical analysis and simulation, the team at the University of Kassel is involved in developing the accelerated model. The aim will then be to validate the model in the Fraunhofer EMFT labs using a practically oriented press-fit contact/copper sleeve combination featuring surface materials that are of interest from an industry point of view.

Partners

University of Kassel:

  • Institute of Materials Technology
  • Institute of Drive and Automotive Engineering

Funding

The research project is being funded by the AiF (German Federation of Industrial Research Associations) »Otto von Guericke« e.V. (IGF Application No.: N 09826/16, FVA-No. 618 II »Accelerated Models II«).