Accelerated testing for electro-migration

In earlier work it was recommended that accelerated tests, using elevated currents, be used to evaluate the performance of contact designs using materials that may be susceptible to electro-migration. This is necessary since it was found in earlier work that the type of self-diffusion in some cases had a major impact on time to failure. Since the type of diffusion is generally not known in advance, it is necessary to design tests that assume electro-migration can occur. In the present work, previously developed degradation models are used to analyze the effects of elevated currents on degradation due to both electromigration and stress-relaxation. Simulations were conducted on several cases using silver contacts. The results show that running tests for specific times at elevated currents can provide minimum estimates for acceleration parameters such as the self-diffusion activation energy, Q. The latter estimates of Q were used in subsequent simulations at normal operating conditions to estimate a minimum limit on time to failure. This approach is recommended to provide guidance in developing accelerated tests, as it was concluded that this approach should work in principle. However, additional work is recommended to evaluate the impact on time to failure due to various factors such as other susceptible contact materials, force, hardness and surface roughness.