Daimler HighTechReport: The Fascination of Technology - Issue 02/2008 - PART X
OFFICIAL PRESS RELEASE
Stuttgart, Nov 25, 2008
Electronics Quality: Reliability Can Be Planned - The Risk Management team closely monitors hardware quality
It’s easy to fool lay people with probability questions. Walter Unger is good at this too. “Imagine a device whose modules have a failure rate of just one or two in a million,” he says. “Does that sound reliable to you?” Most visitors immediately fall into the trap, answering unsuspectingly that such a device must have an extremely high level of reliability and quality.
But that’s not Unger’s opinion: “Depending on its equipment options, an E or S-Class vehicle from Mercedes-Benz contains between 50 and 60 electronic control devices, which in turn consist of as many as 15,000 modules. If you multiply that by the large number of vehicles driving with these modules on the road, you’ll see that even with a module failure probability in the ppm zone, theoretically a failure could occur in one of the vehicles at any given moment.”
Says Axel Willikens, head of Electric/Electronic Hardware Technology at Daimler Research and Advanced Engineering: “This is the challenge being addressed by the Risk Management project, in which we search for fault causes that individually occur extremely rarely. However, because of the complexity of automotive electronic systems in combination with the high unit volumes involved, such defects have a major impact on the quality and reliability of our vehicles.”
Interdisciplinary approach The multi-disciplinary team of engineers in the Risk Management project support colleagues from passenger car, van, and commercial vehicle development departments throughout the entire product creation process. Such support includes everything from evaluating new technologies that are being used for the first time in the automotive industry to assisting with mass production and assembly operations. It also involves helping with the search to determine the causes of defects in vehicles that have already been delivered. If, despite all the care taken by Daimler engineers, a previously undiscovered defect should occur in a customer’s vehicle, staff need to take action immediately to identify and eliminate the problem.
The team is multi-disciplinary in the sense that it covers the entire range of hardware expertise - from materials science and circuit technology to analyses of the component design and the quality assessment of production processes. One thing the team has to do is draw up test plans in such a manner as to ensure that the complete series of tests includes all examinations relevant to quality and reliability. Team members also need to have a detective-like intuition, as well as sophisticated measuring and testing equipment to uncover extremely well hidden weak spots in a component. It’s also clear, however, that the team of 20 members or so obviously doesn’t have the manpower to ensure the hardware reliability of every component developed for every Daimler brand and model. In fact, the team has no intention of taking this responsibility away from the relevant development departments. Instead, it focuses on tricky cases where developers aren’t sure if they’ve been asking all the right questions, or where they encounter puzzling defects whose causes can’t initially be isolated with certainty.
Evaluating new technologies Sometimes the conditions that lead to hardware failure are created before an electronic device physically exists. For this reason, reliability analyses begin long before lab prototypes or series components are produced. Instead, they start with studies to determine whether a new technology is even suited for tough everyday vehicle applications to begin with. Lithium-ion batteries, for example, have proved their worth for quite some time in mobile electronic devices such as laptops, digital cameras, and cell phones. Plans at Daimler now call for this powerful battery type to be used in vehicles as well (see article on page 32). However, just because a certain type of battery has functioned flawlessly for years in MP3 players and gone through perhaps hundreds of charging cycles doesn’t necessarily mean it will work reliably in a vehicle. For example, consumer electronics are generally designed for narrow temperature ranges. After all, no one is going to run their MP3 player at a temperature of -40 degrees Celsius. In certain situations, vehicles must be able to function properly at such a temperature, however - not to mention the +85 degrees Celsius maximum that vehicle electronic systems need to be able to withstand without any problems.
Heat and cold, and sharp fluctuations between the two, are not the only environmental influences that impact automotive electronic systems, however. Dampness also needs to be considered, as do the vibrations a moving vehicle is exposed to.
That’s why Willikens believes that the evaluation of new technologies is a very important early step for effective risk management: “The development of hybrid and fuel cell drives has created new areas, like high-voltage electronics, that automakers need to examine. Our job here is to define a component’s stress profile as precisely as possible; otherwise, nasty surprises will be inevitable,” he says. Stress profiles define the extreme environmental parameters that a module and a complete electronic component may be exposed to chemically, thermally, and mechanically. Clearly, such stresses could trigger component failure in the event of insufficient robustness. The most important aspect to consider here is that in many cases, it’s not the intensity of one individual stress factor that causes the failure but instead the concurrence of several separate factors.
Eliminating errors at the conceptual stage Risk Management is also responsible for taking measures at the electronic component design stage that lay the foundation for its reliability later on. Willikens and his team consistently emphasize the importance of this to the developers. Says Unger: “It’s completely natural for developers to focus primarily on how a component should function. But just as interesting as the question of what a component can do is the question of how reliably it can do it.”
Two steps are required in this phase of the risk management process. The first involves examining each component module to determine whether in principle it will be capable of withstanding the normal stresses in a vehicle. In practice, this amounts to only using modules that bear the “Approved for Automobiles” seal of quality. In the second step, the specific demands regarding reliability are defined: What types of stresses and environmental conditions will the component be exposed to? How frequently will it be in operation, and for how long at a time? These are questions that have to be asked, because the end of the process must result in a customized test plan that ensures the specific test set will adequately test all the stresses that can arise. According to Unger, many years of experience here have led to the development of a standard kit consisting of 22 individual tests that have proved themselves over time in terms of reliability. Not all of these tests always have to be used, however. Conversely, it’s sometimes advisable to check particularly critical stress loads in a supplemental test stage.
The type of component will also influence the nature of the tests. Willikens’ team sets the bar very high for safety-critical components, for example. Here, the test plan is designed in such a manner as to reflect 15 years of automobile operation, whereas ten years is considered sufficient for non-safety components. In the case of mechatronic components, test sets for the electronic modules are designed in line with the anticipated service life of the mechanical parts.
A critical look at structural design The third stage of the risk management process is reached when the developer or component supplier has structurally designed the component and built initial lab prototypes. Both the circuit design and the prototype are thoroughly examined here. Among other things, lab prototypes undergo stress tests to determine whether they actually meet Daimler’s reliability standards. “This testing phase is extremely important because if a design error isn’t caught here but instead after series production of the component has begun, eliminating it can prove to be a very expensive affair,” says the Risk Management team’s materials specialist, Jürgen Freytag. “Because in such a situation, series production would have already started, things would have to be put right under tremendous time pressure.”
Achilles’ heel production Practical experience with automotive electronic systems has shown that most hardware failures are caused by quality fluctuations, or even inadequate production quality. Freytag estimates that this aspect accounts for roughly 70 percent of all hardware problems. The two other causes - excessive stress and use of the wrong materials - are responsible for 20 and ten percent of such failures, respectively. As a result, these factors are much less of a problem, according to Freytag. “That’s why we also take an extremely close look at production processes with colleagues from the quality assurance departments at the respective divisions,” says Willikens. And, as Freytag adds, “Sometimes, production problems result from changes that initially appear only marginal, such as a transfer of semiconductor packaging production from the U.S. to the Far East.”
From the road to the microscope The worst defects are those that don’t become apparent until after thousands of vehicles are on the road. This results in breakdowns that not only annoy customers but also have a double negative effect on automakers, as they damage a manufacturer’s reputation and increase warranty and goodwill costs. The expertise of the Risk Management team is especially in demand here, and its members act in these cases as expert appraisers who coordinate communication between the affected departments within the Group and at the supplier companies. Deciding who is at fault is just one of the goals here, although it’s one that can have huge consequences - for example, if it’s determined that a supplier production problem is responsible for the component failure. Even more important, however, is the analysis of the cause of the error, since nothing can be done to fix the problem until the reason for its occurrence can be identified with certainty. According to Willikens, the somewhat tricky role the team plays here has so far been accepted by all parties without any conflicts - and he views this as a clear indication that his people are accepted as objective “error detectives,” so to speak. “In the end, it’s not us who’s making the call; it’s the results of our analyses, and you simply can’t argue with the facts they produce,” he says.
“We search for fault causes that individually occur extremely rarely."
Axel Willikens, head of Electric/Electronic Hardware Technology at Daimler Research
“Failure to catch an error before series production has begun can be expensive.”
Jürgen Freytag, materials researcher on the Risk Management project team
90 sec. with…
Prof. Bharat Balasubramanian
Prof. Bharat Balasubramanian has been the head of Daimler’s Group Research and Advanced Engineering Electric/Electronic, IT, and Process department since March 2006. Balasubramanian has actually worked for the company in various positions since 1977. The 57-year-old engineer is also a lecturer at the Technical University of Berlin, which made him an honorary professor for CAD/CAM and Computational Analysis in 1998.
Automotive electronic components and their software are becoming ever more voluminous and complex. Are defects occurring more frequently as a result? Theoretically, yes. However, we ensure quality at Mercedes-Benz by implementing preventive measures, such as the use of standardized component specifications, systematic change management systems, hardware-in-the-loop test rigs (HIL), and comprehensive testing procedures.
What challenges do you believe Daimler will face in the future when installing E/E components in vehicles for the first time? New E/E components must initially be subjected to systematic assessment analyses that focus on the causes of faults and their effects on vehicle functionality. Experts refer to this as FMEAs. The components must also go through extensive validation.
We ensure the reliability of particularly innovative technologies using functional, stability, and durability tests based on a combination of HIL test rig examinations, component tests, field tests, component maturity assessments, and customer-oriented driving tests.
How exactly has the company - and particularly Research and Advanced Engineering - prepared itself for these additional tasks? We’re currently expanding our expertise in the areas of E/E hardware, E/E software, and reliability technology. In addition, we’ve assumed responsibility for series production in highly innovative fields on behalf of other Group departments, such as Global Parts and Services. Fuel cell system diagnosis is a good example of a highly innovative field in which we are active.
Is the idea of zero-defect electronics in motor vehicles a desirable but unattainable utopia, or is it a realistic possibility for the future? We need to consistently focus our processes, test systems, and safeguarding procedures on the goal of zero defects. Only then will we be able to ensure that highly complex systems achieve a very low probability of failure in the field, and thus achieve the highest levels of customer satisfaction.
What law better describes the behavior of electrical and electronic components in everyday operations: Ohm’s Law or Murphy’s Law? Murphy’s Law always applies in day-to-day reality, while Ohm’s Law is only valid for electric/electronic systems.
Risk management in five steps
The Risk Management project’s electronic component quality control activities cover the entire product development process and don’t end at the factory gates.
1. Evaluating the new
New technologies never before used in automobiles must be thoroughly assessed with regard to their performance under tough everyday conditions.
2. Concept analysis
As early as the component design stage, the foundation must be laid for its reliable functioning in an automobile for up to 15 years.
3. Circuit design
The structural design plan and all lab samples and prototypes are thoroughly tested to determine whether all required specifications have been met.
Most hardware defects are caused by production errors, which is why quality control activities focus on manufacturing processes.
5. Field analysis
Component failures in customer vehicles are not only annoying; they are often also costly. The team’s expertise is therefore especially in demand here.
The visual focus of this article is on photomicrographs of electronic components that show how the Risk Management project team isolates the causes of faults by taking an extremely close look at the materials that make up the component - all the way down to their microscopic structure.
Another aspect of the team’s work consists of stress tests in the lab that take the form of service life and reliability evaluations. These simulate mechanical, thermal, and chemical stresses that electronic components will be exposed to during their long period of use in an automobile. The component or module in question can thus be “aged,” thereby bringing to the fore all possible types of damage, which are then made visible and analyzed under a microscope. HTR online is running a photo feature that highlights the engineering “torture instruments” used for this purpose. Some of these, like the “Shaker,” have harmless sounding names. Others, like the “Temperature Shock Test Cabinet,” sound a little more ominous.
Another report to be found on HTR online describes the special challenges associated with extremely accelerated aging tests designed to reproduce in the lab the stresses encountered by components over a service life of ten or even 15 years on the road.
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