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ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 20 NO. 4 16 EDFAAO (2018) 4:16-22

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EARLY LIFE AUTOMOTIVE ELECTRONICS FAILURES AND THEIR ROOT CAUSES Peter Jacob EMPA Swiss Federal Laboratories for Materials Science &Technology Electronics & Reliability Center, Dübendorf, Switzerland peter.jacob@empa.ch

But how far do these condition changes influence the electronics? The following list describes a few typical changes: • New rubber tubes in the engine compartment are isolating—but when street salt becomes attached to them, they become electrostatic dissipative over time. • Noise pulses from electric motor commutators decrease when the carbon contact pads are ground in toward the round shape of the commutator (Fig. 1). • Contact behavior in relays and switches degrades due to vibration, corrosive gases, and fretting or curing. • Corrosion appears and dendrites form within LEDs. • Shorts arise frommetal filaments falling into active electronics.

INTRODUCTION Inautomotive electronics, failures are frequently found that cannot be explained by the failure signatures of the defective devices. In deeper investigations, it turns out that a superimposition of impact factors, which never can be represented by the usual qualification testing, caused the failure. Numerous cases presented the opportunity to be examined in depth, including system-based analysis and failure anamnesis (similar to a complete medical history) in root cause evaluations. This article describes several examples and concludes with general principles for how to proceed with these types of failures. POST FAB STRESS CONDITION CHANGES AND SUPERIMPOSITIONS When a car leaves the factory, operational conditions immediately start to change significantly: • Dirt from the street and environmental dust, humid- ity, and water penetrate into structures, even if they were assumed to be sealed. • Continuous vibrations and mechanical shocks apply. • Outgassing from rubber seals, tires, and plastics find their way into electronic circuits. • Carbon contact pads for numerous electric (servo) motors (for instance, for window lifts, seat or mirror adjustment, or ventilation) begin to form themselves to the round shape of the commutator. • Metal punching burrs peel off and sometimes fall into electronic circuitry, causing shorts. • High thermal cycles impact the sealing of capsuled electronics and optoelectronics, e.g., LEDs. • Radio signals from internal or external data or radio transmissions surround the vehicle.

Fig. 1 Carbon contacts at the commutator of an electric motor. Top: New carbon pieces, planar contact, submitting high level pulses. Middle: After the shape adaption of the carbon pieces to the round collector, the pulse level reduces. Bottom: The pulses can be easily suppressed by a small capacitor.

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