Abstracts by Session

Session C: Power Electronics - Packaging
Tues   15:30 – 16:10 Golta Khatibi PoF based accelerated testing

The trend in competitive electronic manufacturing industry is cost reduction and shorter-time-to-market while maintaining the high-quality standards of the products. Qualification of the devices is based on active or passive thermal cycling reliability tests to simulate their typical application in an accelerated manner. Further acceleration of thermal stress tests by increasing the temperature or excessive time reduction is limited due to physical characteristics of the devices and may result in unrealistic failure modes.
Recently accelerated mechanical fatigue testing (AMT) has been proposed as an alternative rapid tool for evaluation of electronic. The basic idea is replacement of thermal stresses by equivalent mechanical stresses. Dedicated test set-ups are designed to induce fatigue failure in the weak sites of the devices and to reproduce the failure modes occurring during the operation. Increasing the testing frequency allows to obtain lifetime curves in a very short time. This talk provides exemplary studies of the application of AMT for interconnects, joints and thin film stacks in semiconductors with a brief discussion on the advantages and limits of the proposed methods.

Tues  16:10 – 16:30 Oliver Schilling
Generation and Charcaterization of Condensation Phenomena in Power Modules

This presentation introduces and validates a measurement technique to detect and quantify condensation in a power module by means of a stray-field capacitor sensor. We apply this sensing technique to investigate the hypothetical use case of a railway application, which triggers measurable condensation on the silicone gel surface of the power module. Using this as a reference, we introduce the concept of combining a cyclic chamber profile with a thermal mass. It is shown that the thermal mass has a significant impact on the thermal profile of the device under test (DUT) and on the observed condensation. The paper explains how the railway use case can be simulated by optimizing the test configuration, and how a validation of power modules with respect to condensation conditions can be achieved.

Tues  16:30 – 16:50 Jakob Willner Development and Application of a New Weathering Setup for Investigation of Polymer Degradation in Harsh Environments
The semiconductor industry is a highly demanding application field for polymers, where they find use as insulation or encapsulation materials. As semiconductor devices have to be operable in ambient conditions, polymer coatings are utilized to protect sensitive components from environmental influences such as corrosive gases (H2S, SO2), increased temperatures and humidity. The development and optimization of such materials with enhanced properties requires weathering equipment for controlled exposure, as well as methods for investigating the effects that the exposure causes on the exposed materials.
For that purpose, a weathering setup with a special cell design has been developed, to provide electrical contact to each specimen, while gas composition, relative humidity and temperature can be adjusted. Laser Ablation – Inductively Coupled Plasma – Mass Spectrometry (LA-ICP-MS) allows the depth-resolved analysis of the sulfur uptake from corrosive gases, whereas Laser-Induced Breakdown Spectroscopy (LIBS) data is evaluated to describe polymer degradation. The results lead to a better understanding of the tested polymer materials and the influence of certain environmental conditions.
Tues  16:50 – 17:10 Nando Kaminsky Humidity Driven Degradation in Power Semiconductor Devices

Housings of modern semiconductor modules are not at all hermetic. Humidity can intrude and together with the high electric fields all kinds of humidity driven degradation mechanisms can be triggered. For lifetime prediction the dynamics of the respective mechanisms need to be modelled precisely. Accelerated testing is the method of choice, though it introduces some uncertainty. However, more crucial is the precise knowledge about the mission profile of the devices, which usually requires comprehensive field measurements. Unfortunately, even if all these prerequisites are available, the lifetime prediction is not perfectly matching reality. An example of converters in wind turbines shows that the power semiconductor devices fail much more frequently than predicted: Either the failure mechanisms observed in the lab are not the relevant ones, or contamination is accelerating the degradation or the power devices are not the root cause of the failure but just a secondary effect.

Tues  17:10 – 17:30 Gerald Dallmann
Analysis of packaging materials for power devices- some new developments
Power Modules like inverters are widely used in E-mobility and Solar applications. They are often exposed to harsh environmental conditions such as extreme and rapidly changing temperatures, condensing humidity as well as corrosive gas exposure by environmental contamination. The standard qualification procedure of microelectronic devices does not cover these effects sufficiently. In-depth knowledge of qualification and application failures is required to find the root cause mechanisms. Properties and impurities of packaging materials are often involved in these mechanisms. Some general material test procedures defined for other applications are presented in this talk as well as new techniques developed specifically for some of the main materials used in current power modules (hard mold compound and silicone material as soft mold). The work was partly funded by the EU in the Power2Power project.
Tues  17:30 – 17:50 Elisabeth Giebel Investigation of element enrichment in silicone gels used to encapsulate inverter modules for renewable power generation

The focus of this study is to investigate the enrichment of impurities within silicone gels protecting power electronic modules during application. For this purpose, the power modules of three photovoltaic (PV) string inverters installed at different locations and after an operation time of 7.5 years were compared with modules tested in a continuous condensation test and the respective reference modules. Impurities found in the silicone gel will be correlated to possible sources, such as polymer housing, electronic components or from environment