ALLAN WEBBER, RON ELLER, MATT MARUDACHALAM and DHANOOP VARGHESE, Texas Instruments Inc.
FRIEDRICH SCHROEDER, MARKUS WITTMANN and REGINA GROTE, Robert Bosch GmbH
As the automotive industry transitions manufacturing from the cars with combustion engines to electric vehicles (EV), a dramatic increase in the requested power-on hours (POH) required for semiconductor ICs is also occurring. For example, POH would increase from 8,000 to 12,000 POH for traditional passenger cars with combustion engines up to 100,000 POH or higher for commercial EVs with autonomous driving.
Analyzing the suitability of ICs to these newer mission profiles presents a significant industry challenge for the IC suppliers and automotive TIER 1s. The legacy reliability approach of using the Arrhenius equation and performing High Temperature Operating Life (HTOL) stress testing to match extended POH (> 20,000 POH) can give a false assurance of reliability. A more analytic approach is to assess the application-specific use profile against the intrinsic reliability models of semiconductor wear-out mechanisms. This method is called the ZVEI Robustness Validation (RV) process and is described in appendix 7 of AEC-Q100 specification.
However, broader use of the robustness validation process requires an industry-level paradigm shift to more advanced levels of reliability assessment. This will require collaboration between the automotive TIER1 customer and their semiconductor supplier to understand, with more detail than may have been required previously, how the IC will be used and stressed in the end-use application. In consequence, this will better enable the semiconductor supplier to use appropriate intrinsic reliability models to assess the capability of the device for the intended application.
How the automotive industry is redefining vehicle power-on hours
A survey of documented automotive mission profiles is shown in FIGURE 1. A traditional ‘automotive mission profile’ has been the passenger combustion engine, targeted at 8,000-12,000 hours for driving 10% of the time over 15 years.
The driving profile for an EV is similar to that of a vehicle with combustion engine. However, if the semiconductors are active during charging, the charging POH should be added to the driving profile. Autonomous commercial vehicles are still being defined, but some early profiles suggest anything from 80,000 to 170,000 POH.
While charging adds a longer time to the EV profile, the temperature at which charging occurs may be relatively benign from a reliability perspective. Calculations have shown the mission profile for passenger combustion engines (#1 in Fig. 1) to be a harsher load than EV passenger (#3 in Fig. 1) even if the POH is longer because the temperature exposure is lower without heating from the combustion engine block.
#7 Fig. 1 includes also “24×7” mission profiles that capture some application scenarios where the semiconductor IC may be 100% powered on during its application. Some of these “24×7” examples are battery monitoring or connectivity. In these applications, the IC typically stays in quiescent or low power modes at lower operating temperatures over much of the lifetime despite the higher POH exposure.
Click here to read the full article in the November issue of Semiconductor Digest.
