Giovanni Nicoletti

Reliability Failures in Small Optocoupling and DC/DC Converter Devices

In power electronics, often control and power part are at different electric potentials. Thus, electrically isolated coupling of them is performed by optocoupling devices. Also, isolating DC/DC converters are in use. While such systems are dedicated for high reliability application, weak points within these small components generate problems to the system reliability. The paper outlines most common weakness, as optocoupling internal LEDs, packaging problems and hybrid components in use at their electrical limits

Reliability and wearout characterisation of LEDs

Abstract LEDs play a key role as an active element in electronic circuitry – for example in optocouplers. Their life time strongly depends on the operation conditions. Degradation usually starts by the generation of both reverse and forward bias direction pinpoint leakage paths. When the resistance of such a path becomes lower than the regular operational resistance in forward direction, it will start to act as a bypass. Then, reduced and inhomogeneous emission is the first degradation indicator. The paper describes degradation mechanisms and their characterisation.

Surface electrostatic damage by microprocess robotic machines: diagnosis and reliability, process auditing, and remedies

Electrostatic discharge (ESD) is generally known as a discharge phenomena via device pins. Many precautions have been taken against ESD, mostly considering workplace protection, pad protection structures. However, electrostatic events, originating from robotic semiconductor wafer- and device-processing seems at least a problem of similar severeness, which has not been considered enough, yet. This paper describes electrostatic mechanisms in most common assembly process tools, how to do diagnostics on devices and tool auditing. Auditing experiences are listed and hints how to improve tool-related ESD are described

Failure causes generating aluminium protrusion/extrusion

Abstract Aluminium protrusion/extrusion are frequent failures, which are responsible for severe short damage in semiconductor devices. Unfortunately, the mechanisms results also frequently as an artifact of many other high-current failure signatures as EOS, which makes root cause investigations sometimes rather difficult. To overcome the problem, most frequent root causes for aluminium protrusion/extrusion are shown and discussed in this paper. This information combined with the individual device process- and testing history helps to conclude to the failure root cause. The authors evaluated and reviewed related case studies of their own practice resulting in following root causes for aluminium protrusions and extrusions: laser-induced damage, ESDFOS, application-related EOS, thermal cycling, thermomechanical mismatch in stacked devices, ultrasonic-induced damaging, micro-Si-particles in chip-pick&place and surface-pressure-induced damage, as for instance when doing copper-wirebonding.

Device decapsulated (and/or depassivated) – Retest ok – What happened?

Abstract One of the very first steps to enter into physical device failure analysis is the device decapsulation. In some cases, an additional depassivation follows to give access to contact needles for internal probing. However, it happens from time-to-time that the device has been cured from its failure behaviour. Such cases often end as non-conclusive analysis result. Our principle investigations and results, however, will help to understand the mechanisms and allow in many “hopeless” cases to draw useful conclusions on the root causes. These are linked in most cases to metal related failures. Besides the “classical case” of touching bond wires, typical root causes are metal filament shorts in the nanometer-order-of magnitude, which can be removed easily by mechanical and/or chemical effects of any delayering procedure. Surface metal shorts may also be generated by bump metal or pad-interface-metallisation-redeposition onto the passivation surface and by metal residue-related recombinations of trimming fuses. In both latter cases, nanometer metal films short-circuit neighbouring pads or fuses in trimming-fuse-arrays. This paper describes these and some second-order mechanisms in detail, which sometimes let the chip recover after decapsulation and/or depassivation.

Recovering contacting interfaces in packaging and in semiconductor devices: Mechanisms and how to handle them in analysis

Several analysis cases reported contact problems on both device and packaged level. However, they recovered upon the attempt to electrically verify them. Further analysis showed that this recovery can be achieved through extremely low ESD effects. Recovery mechanisms and important precautions will be further discussed in order to avoid sudden disappearance of recoverable opens.

Reading distance degradation mechanisms of near-field RFID devices.

In case of operation distance degradation, frequently RFID chips are extracted from their tags and electrically/physically analysed. However, manifold mechanisms based on interaction effects between package and device, exist. This paper examines and highlights these mechanisms, giving also valuable hints for the failure analyst.

Humidity-induced semiconductor device electrical reliability failures: Mechanism and wafer-level risk evaluation/ electrical screening-test proposal

Automotive semiconductors are frequently exposed to humidity- if penetrating, a high-ohmic film at the chip surface connects pins to various voltage levels, if they arenpsilat pull up/down protected. Since latest integration combines different technologies/voltage levels, such films trigger destructive malfunctions. A wafer-level test, high ohmically short-circuiting all existing pins to first maximum, then minimum voltage, should eliminate such design-induced reliability risks.

Design and reliability aspects of multilevel metal large-scale power line layouts in ULSI-ICs

Integration of both extremely small-dimensioned metal lines and large-dimensioned metal structures may cause reliability problems due to thermomechanical stress between the intermetal dielectric and the multi-level-metalization. The paper reports a case study and shows a problem solution approach: due to thermomechanical mismatch of aluminum and Si-oxide, metalization processing should not be used for both small and large structures. This may cause cracks and generate intermetallic shorts as a reliability problem.