In situ stress monitoring using a stress chip

© Fraunhofer ENAS
Stress chip testboard.
© Fraunhofer ENAS
Evolution of the stresses and propagation of delamination.

The direct detection of thermo-mechanical weak points in microelectronic components and sensor components still poses a major challenge. State of the art in product qualification is still based on the detection of the interconnect failure by monitoring the resistance of daisy chains. Those failures are complete interruption or the increase of the electrical resistance above a given threshold. They may be caused by various geometric, material or process related reasons and may even interact with each other. However, the daisy chains can only signal the failure occurrence. They cannot provide information on the current state of health of the interconnects such as solder joints. For further improvement of the reliability, the ability to gain more information about the root cause of the failure is necessary. The stress sensing system allows measuring the magnitudes and the distribution of mechanical stresses induced in silicon dies during fabrication and testing of electronic packages. The stress sensing system has been successfully used for exploring the curing of adhesives and underfills, soldering processes, active and passive temperature cycling tests, moisture swelling, encapsulation tests and other in situ measurements. In the future, it is planned to use the chip for evaluating the remaining lifetime. Therefore, the whole stress history will be stored on the chip and the time until the failure will be mathematically estimated based on the knowledge of the physics of failure.