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ESD UNDER OPERATION Mechanically experienced car technicians know that electrical shocks may occur—even through rubber gloves—when sandblasting rusty metal parts. Each time particles or liquids are sputtered, electrostatic charge separation takes place and high voltage is generated. Striking visual examples include lightning at volcano exhausts (Fig. 2) and Kelvin generators. [1,2] In a car, such situations frequently occur within the engine and gear box, where oil is sputtered at high speed in the presence of many sensors (e.g., Hall or pressure sensors), which are electrically on. If an electrostatic discharge (ESD) strike happens, the leakage path opened will be under the full short current from the power supply, which means that the failure path will suffer artefactual burning and show a typical electrical overstress (EOS) signature in later failure analysis. CMOS circuitry is especially affected by this phenom- enon, because in the case of ESD (or extremely high exter- nal E-fields), both nFET and pFET channels may open at the same time, thus opening direct Vdd-Vss short paths. This has even been observed in modern car electronics when lightning strikes close to an operating vehicle— creating numerous EOS signatures in several electronic components. If the car had been in a parked position and electrically off, the failures would have been significantly less. If the electric field froma lightning strike opens both nFET and pFET channels for only a short time, it doesn’t matter as long as the CMOS circuitry is in the off state and not electrically powered. The next example describes a constructionweakness. Returns of fairly new cars were observed, usually at a mileage of less than 10,000 km. Within the engine control unit, amixed signal device controlling a sensor unit failed. The semiconductor device clearly generated an EOS sig- nature. At first, a sound failure anamnesis indicated that the returns came from countries without a speed limit and after the control unit was repaired, the failure never occurred again. Inspection revealed that the unit had beenmounted between rubber tubeswithout any ground connection. A contactless electrostatic voltage probe was used to measure the charge of the unit’s metal case (Fig. 3). At a speed of less than about 150 km/h, no failure was observed, but at faster runs, suddenly high charge was measured—above the 3kV limit of the instrument. This voltage was generated by the unit’s extremely high air/petrol drop flow speed. Due to the missing ground (GND) connection, the high voltage directly arrived at the mixed signal device and killed it within a short time. After

• Partial memory loss occurs due to noise and EMI within the onboard supply system. EARLY LIFE FAILURE EXAMPLES Following are some more detailed examples of early life failures. CROSS TALKING In this first example, about 100-200 electric motors are evaluated. Many of them are classic DC motors with carbon contacts to the commutator as described previ- ously. If they send inductive pulses into the power line, these pulses can be coupledwithin the cable tree feeding the signal lines. If the inductance behind is at a high level, for example, in the engine’s starter motor or themagnetic switch for it, the inductive responsemight become critical to sensitive electronics, even with capacitive coupling. In addition to this coupling, electromagnetic interference (EMI) also needs to be considered in a modern car, with special attention given to tire pressure measurement. For such measurement, independent radio frequency (RF) transmitters are mounted within the tires, sending small pulse RF signals to an onboard receiver. In many cases, this transmission is done within industrial, sci- entific, and medical (ISM) frequencies, very often in the 433MHz ISMband; this band iswithin the busy 70-cmham radio frequency band and close to other 70-cm users as taxi transceivers and those from fire brigades, police, and ambulance services. If these µW-signals have to compete with neighboring high power signals of licensed radio amateurs (around50W) or other transmitters, interference or destruction of the highly sensitive receiver can occur. Therefore, a careful considerationof interference suppres- sion measures is mandatory for modern cars.

ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 20 NO. 4

Fig. 2 Volcanic eruption of the Sakurajima volcano. Elec- trostatic charge is generated by separation of par- ticles. Courtesy of Martin Rietze.

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