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Date: 01-02-17

RESCAR 2.0: To improve robustness of automotive electronics

The Challenge:

50 years ago, electronics in a car was more or less restricted to lighting and ignition. The overall schematic fitted on one sheet and a handful of engineers mastered the related functionality. Nowadays, things have become much more complex. In the application fields power train, safety, comfort and infotainment, thousands of microelectronic chips are designed into a modern car and the embedded software content is measured by hundreds of megabytes.

On top, electric mobility poses further challenges. Revolutionary changes in a car's architecture will have to be implemented. And while today's level of robustness of classical cars has been accomplished over 125 years, at least the same level has to be accomplished within 10-15 years for hybrid and pure electric vehicles.

In effect, the complexity of any electronics in a car directly drives the robustness requirements. Doubling the electronics content simply calls for cutting failure rates of electronic components in half, to maintain the overall quality level. For integrated circuits today, the demand simply is: "zero defect". Even more, the impending change from internal combustion engines to electric motors with the related plethora of innovations seriously exacerbates the situation, as in many cases, we cannot rely on the experience with proven concepts and components any more.

rescar2

The Project RESCAR 2.0:

To address this situation, six partners covering the major stages of the automotive value chain have formed a consortium and set up a research project called RESCAR 2.0. These partners are: AUDI AG, BMW AG (associated project partner), ELMOS Semiconductor AG, Forschungszentrum Informatik (FZI), Infineon Technologies AG and Robert Bosch GmbH. They will be supported by the Fraunhofer-Institute IZM, Berlin, the Fraunhofer-Institute IIS, Dresden, as well as the Universities of Bremen, Dresden, Hannover and Tübingen. The project is coordinated by Infineon Technologies AG. The goal of RESCAR 2.0 is to substantially enhance the robustness of new electronic components for applications in the field of electric mobility. RESCAR 2.0 is funded by the German Authorities (BMBF) with roughly € 6.5 million. The partners will jointly invest about € 13.3 million in this research activity.

Primary Approach:

The fields identified to address the improvement of robustness in RESCAR 2.0 are:

  • Define a robustness metric
  • Set up a development flow to implicitly design-in the specifically required robustness
  • Validate electronic systems with regards to their required robustness by simulation and measurement
  • Identify the critical parameters on component and process level to maintain the robustness within the overall electronic system

The RESCAR approach is built upon the "Robustness Validation" methodology, which was developed on a broad consensus within the automotive industry in 2005 - 2009 and led to the publication of several handbooks1.

The major aspect, which deeply affects all the above points, is how the electronics is used. The approach here is to combine the knowledge of the partners on their various levels along the value chain to better establish robustness targets. The car manufacturer has a clear idea on how electronics is applied. For example, power switches used to fire an airbag may be switched only a very small number of times. Power switches in a bridge to automatically shift gear - especially if used in pulse-width modulation - may be switched millions of times. Many more pieces of information, e.g. temperature, voltage and current profiles, may be of interest. All this information will be collected in a systematic way, thus creating a standardized mission profile. This mission profile is refined and translated along the value chain firstly from car manufacturer to the Tier-1 supplier, which provides the electronic control unit. The next step is from Tier-1 supplier to Tier-2 supplier, responsible for the development and fabrication of microelectronic circuits. On this level, robustness needs to be addressed on the basis of the related microelectronic failure mechanisms. One major challenge of RESCAR 2.0 will be to bridge the gap from how electronics is applied to how this affects potential failure mechanisms. The forward translation maps the application details to the stress applied on the microelectronics, which in turn leads to degradations or complete failures of devices or connections. In contrast to this, the backward translation maps the occurring degradations or failures back to the application level on which their impact can reasonably be assessed.

Robustness Metrics:

We all know that it is difficult to improve a certain level of quality, if there is no undisputed way to measure the level of quality. This also holds for the robustness of electronics. Currently, there are a couple of approaches on the market to assess robustness. One way is to evaluate how far the electronics' ratings and operating ranges can be exceeded with regard to what is promised in the specification or how far the parametric properties of the electronics stay wide inside the specification windows.
Other approaches elaborate on the verification space, which is spanned by temperature, supply voltage, and the many more parameters defining the electronics and the rest of the application. Think for instance about an electric drive train and the related power bridges. Here is a small choice of the parameters (or factors) in question:

Environment:

  • Temperature
  • Supply voltage

Electronics:

  • Switching slew-rate
  • On-resistance of power switches
  • Current measurement op-amp gain
  • Free-wheeling behavior
  • Regulation delays

Mechanical part of drive application

  • Armature inductance
  • Armature resistance
  • Torque constant / backEMF
  • Motor friction and inertia
  • Drive train frictions and inertias
  • Driving load conditions

Easily, we end-up with some 20 parameters or more and all of these parameters have a specification window. This simply means that verification is to be performed in this 20-dimensional space and we need to fully cover this space for a meaningful verification. Robustness could also reflect the quality of coverage of this verification space.

One task of RESCAR will be to evaluate candidates for robustness measures and to select one candidate or a combination thereof.

Design-for-Robustness:

Designing for robustness in the context of RESCAR 2.0 means to translate the electronics' requirements into constraints, which can be maintained and checked in the design software for microelectronic products. This process works for analog as well as digital constraints, though the focus in RESCAR 2.0 will be on analog and mixed-signal functionality. In this way, the requirements compliance and the related robustness is "built-in" rather than "tested-out" of a design. Unfortunately, this does only work for a part of the requirements.

Robustness Assessment by Simulation and Measurement:

When it comes to the assessment of robustness, this can be accomplished on the basis of simulations and measurements. Obviously, these simulations and measurements will go beyond the classical design verification.

One aspect to shed more light on could be to quantify the stress, which is applied on for instance the transistors of a power stage. This can be done taking into account the application and even statistical variations of it. Knowing about the stress, the microelectronics experts devise the related degradations of the devices, which lead to related changes in the device models used for circuit simulation. The resulting behavior could be then simulated.

Measurements can equally be planned to assess robustness. First of all, they need to be carried out to check the simulations results. Moreover, much more experiments can be accomplished in measurements rather than in simulation, as the measurements are typically carried out in real-time.

Those simulations and measurements will have to be done under lots of variations of factors to check out their influence. Tons of simulations or measurements will produce tons of result data for which a data mining approach will be set-up to extract the essence of robustness according to the defined metric.

Conclusion:

The provision of robust electronics at affordable cost will be a major challenge for the foreseeable future. This holds in general for the automotive domain and to an even much higher degree for the very innovative field of electric mobility. RESCAR 2.0 pursues a new approach to address this question. Its results will form a substantial contribution to the big change towards electric mobility in the automotive industry, which we are currently experiencing. This big change will trigger new decisions on winners and losers. Those missing robustness most likely will not be on the winner's side.

 

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Robustness requirements of automotive electronics will be standardized in 'mission profiles' and translated into constraints to be used throughout the design process, validation and test in the whole supply chain

Authored by:

  • Georg Pelz, Principal Design Methodology and Product Modeling, Infineon Technologies AG
  • Julia Lau, Manager Physical Design Methodology & Flow Development, Infineon Technologies AG

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