Passives for Automobiles: A Brief Look at What it Means to be AEC-Q200 Qualified

I realized recently, while reading a press release about an AEC-Q200 qualified part, one that met the Automotive Electronics Council requirements for components suitable for harsh automotive environments, that it was taken for granted that we all basically understood what this set of requirements was all about. That we didn’t have to think too much about it when specifying AEC-Q200 -compliant products for systems such as infotainment, engine control, air bags, lighting, etc.

In essence all that our mind absorbs in these cases was the fact that a supplier said its passive component was AEC-Q200 qualified, so that’s good enough for us and we can go on with the business of designing systems and sub-systems without really appreciating what this means, or what passing these tests involve.

But maybe we should know a little more. So let me start from the beginning.

The Automotive Electronics Council (AEC) is an organization based in the US that sets qualification standards for the supply of components in the automotive electronics industry. The idea of creating the AEC occurred at a JEDEC meeting in the summer of 1992. Following subsequent meetings work began on Q100 (Stress Test Qualification for Integrated Circuits). The initial release of AEC Q100 was presented to IC suppliers in June, 1994. Following this initial start, qualification specifications for other part categories were developed: AEC -Q101 for discrete parts (transistors, diodes, etc.) and AEC-Q200 for passive components such as capacitors, inductors, etc.

The Q200 tests recognize that demands placed on passive components in an automotive environment relate to a very high resistance to temperature and vibration and to protection against short circuiting. Recognition is given to the fact that temperature conditions in automobiles can vary greatly, with the most demanding locations being in the engine, transmission and brake systems. Engine and transmission temperatures are typically less than 200°C, but some of the wheel-mounted components can reach 250°C. Consequently, the appropriate component needs to be selected not just for the application in question—automotive-- but for a specific function and location, too. AEC recommends that car parts be classified for the engine area and the passenger area based on the intended location of use, and because the intrinsic heat requirements of these parts are different, different test temperatures are recommended.

Large and rapid temperature changes also can occur when components are mounted on a PCB, and this can induce stress as a result of different material CTE (Coefficient of Thermal Expansion) rates. The difference in material (PCB, ceramic, solder) expansion rates can induce cracks within components that cause them to electrically fail.

For all of these reasons there are five temperature range grades defined in AEC-Q200:

Grade 0: Minimum/maximum temperature range is -50°C to +150°C. Applicable parts include flat chip ceramic resistors and X8R ceramic capacitors

Grade 1: -40°C to +125°C (mostly under hood applications). Parts include capacitor networks, resistors, Inductors, transformers, thermistors, resonators, crystals and varistors, all other ceramic and tantalum capacitors.

Grade 2: -40°C to +105°C (mostly passenger compartment applications). e.g., aluminum electrolytic capacitors.

Grade 3: -40°C to +85°C film capacitors, ferrites, R/R-C networks and trimmer capacitors

Grade 4: 0°C to +70°C: (non-automotive)

Qualification of the device to its minimum temperature grade allows the supplier to claim the part as "AEC qualified" to that grade and all lesser grades. Qualification to temperatures less than the minimum specified above would allow the supplier to claim the part as "AEC qualified" at the lower grade only.

It is well accepted that the AEC-Q200 specification includes the most stringent stress tests for passive components, which are tested and audited to a much greater extent than for other commercial applications, primarily with respect to stability under high temperatures and temperature changes, resistance to humidity, mechanical stress (shock, vibration, board flex) as well as brazeability and solderability under challenging conditions.

AEC tests are mostly based on test conditions of JEDEC and MIL-STD, adding some new test methods. Here is a brief table of the tests and test conditions involved:

Among capacitors, the most frequent used in the automotive segment is the MLCC (multi-layer ceramic capacitor). While extremely reliable, they do have a high mechanical sensitivity to bending forces. This can cause cracks, which usually ends in reductions to resistance values all the way to short circuit, with the risks that implies (fire, for example). With more stringent requirements from the automotive industry for additional component robustness-- many components may be subject to severe flexing and vibration when used in under the hood automotive applications-- a growing number of MLCCs with enhanced mechanical strength and AEC-Q200 certification are available, ensuring that electrical integrity is maintained while external forces are being applied to the component.

Even electronic components that are as simple as resistors must satisfy the severe demands of automotive applications, including long-term stability, pulse resistance, and resistance to harmful gases. Suitable applications for AEC-Q200 qualified resistors include electronic controls, electric and hybrid electric vehicle battery management, and dc/dc converter applications.

Of course the AEC standard is only one of many worldwide that affect suppliers of passive components. Since safety is top priority for electronic components, international safety standards have been developed such as IEC 60384-14 (a world standard) and its U.S., equivalent UL 60384-14. Part of IEC 60384 applies to capacitors and resistor-capacitor combinations which will be connected to an AC mains or other supply with nominal voltage not exceeding 1 000 Vac or 1 000 Vdc and with a nominal frequency not exceeding 100 Hz. One example of the difference between the IEC and AEC standard is in temperature cycling. The IEC 60384-14 standard requires that capacitors pass five full cycles over the complete operating temperature range. In contrast, the AEC standard requires a minimum number of 1,000 temperature cycles.

Finally, parts that pass the AEC tests are seen as qualified, high quality components that can be used in critical environments; therefore, basically, there is no need for conducting other component level tests. Indeed, if you read spec sheets you’ll know that suppliers go out of their way to caution engineers not to use non-AEC products in any automotive power train or safety equipment (including battery chargers for electric vehicles and plug-in hybrids). Usually the language is something along these lines: “Only products clearly stipulated as "for Automotive use" in the parts catalog should be used for automobile applications such as power train and safety equipment.”