Lifetime modeling of cyclically, thermo-mechanically stressed components

Thermal loads dominate the causes of failure of electronic components with more than 50 %. The cyclic thermal loads electrical components are exposed to due to climatic conditions or intrinsically because of their functionality lead to thermo-mechanical stresses on the substrate, connection and component due to the high material mix of the assembly. Fraunhofer IKTS uses the following approaches:

• Lifetime modeling by means of suitable test specimens
• Accelerated ageing
• Damage progress monitoring using XCT
• In-situ resistance measurement technology

Customer and product requirements play a key role in the design of test specimens for accelerated ageing to align the damage mode with the actual assemblies. In addition, boundary conditions for test specimen monitoring and damage progress analysis are considered. The initial 100 % inspection of the test specimens using automatic optical inspection (AOI) and X-ray-based void analysis reduces the error band of the subsequent service life model and avoids time-consuming interpretation of the results.

The damage progression analysis can be carried out using micro X-ray Computer Tomography (micro-XCT) in addition to conventional methods such as the shear test or microsection. Compared to other analysis methods, the main advantage is the visualization of the damage in three-dimensional solder contact. In addition, the test specimen can be returned to the accelerated ageing test after the damage progress has been analyzed and tested again later. Monitoring the test specimens over their life cycle in this way enables a significant reduction in the number of test specimens while at the same time significantly increasing the information content.

Another method of test specimen monitoring is in-situ monitoring. Thanks to special hardware and software components adapted for end-of-life tests, we are able to monitor the test specimens live during accelerated ageing. One application example is monitoring the change in electrical resistance (∆R < 2 mΩ) of the solder contacts of 0 ohm resistor components. Up to 460 channels are currently available for this purpose, which can be expanded if required.