Recent progresses in science and technology have brought electronic devices closer to our daily life. With respect to the lifecycles of the electronic products, some are expected to have longer life in the important applications, whereas others are used for shorter periods of life. It is remarkable how semiconductor?application marketplaces have expanded and diversified these days. For example, there are handheld terminals which are prone to be replaced frequently, such as cellphones. On the other hand, there are electronic devices which are required long-life durability in the harsh conditions, such as electronic components for automotives.
Most of these electronic products comprise a large number of semiconductor devices without exception. Consisting of many materials (silicon, oxide layers, metal trace materials, dielectrics, etc.) as well as more than one billion transistors and even larger number of contacts, the semiconductor devices including packages that accommodate dice have grown into enormously large-scale systems. The evolution of the semiconductor technology includes the improvement of traces and dielectric layers such as very thin gate dielectric, high-k materials, and Cu/low-k materials, as well as high density packaging technologies including SiP and build-up substrates. Significant progress has been made toward finer patterns, higher integration, higher speed, and less power consumption. The reliability requirements for such complex larger-scale systems are the same as those for the conventional devices or even stringent. In comparison with the mechanical components, the semiconductor devices generally indicate higher reliability. Still the appropriate reliability assurance plans are required in accordance with the applications and purposes of the devices.
On the other hand, the bases of the reliability criteria are not always technically tangible, even though its stress duration or number of stress cycles has already been specified in the qualification program. One of the examples is the stress duration of 1000 hours at the high temperature operation life test or the temperature humidity bias test.
The acceleration test is intended to predict and verify the reliability level. For that purpose, the appropriate acceleration is estimated from the target failure mechanism. Then the relevant test time or stress cycles are determined based on the acceleration factor between the test conditions and the use conditions. As a result of this consideration, the test time or test cycles are in some cases reduced significantly, quite unlike common sense.
The failure mechanisms in the accelerated stress test can be classified into either intrinsic mode or extrinsic mode.