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Sintered silver (SAG) is a widely-used die attach (DA) technology in automotive industry, especially for power modules in electric vehicles (EV) defined by higher power densities. High operation temperatures (> 175°C) are particularly resulting from the application of dies based on wide bandgap semiconductors materials like SiC and GaN. The thermo-mechanical stress resulting from large temperature swings in EV applications fatigues the porous layer of SAG. In order to estimate the reliability of die attach layers physics-of-failure (PoF) based lifetime models are needed. In this study, comparative parametric simulations are used to estimate the influence of geometric factors on the lifetime of the die attach layer. In addition, the state of the art of accelerated fatigue experiments is presented.

Mastectomy is the standard procedure in patients with in-breast tumor recurrence (IBTR) or breast cancer after irradiation of the chest due to Hodgkin’s disease. In certain cases a second breast conserving surgery (BCS) in combination with intraoperative radiotherapy (IORT) is possible. To date, data concerning BCS in combination with IORT in pre-irradiated patients are limited. This is the first pooled analysis of this special indication with a mature follow-up of 5 years. Patients with IBTR after external beam radiotherapy (EBRT; treated in two centers) for breast cancer were included. Patients with previous EBRT including the breast tissue due to other diseases were also included. IORT was performed with the Intrabeam™-device using low kV X-rays. Clinical data including outcome for all patients and toxicity for a representative cohort (LENT-SOMA scales) were obtained. Statistical analyses were done including Kaplan–Meier estimates for local recurrence, distant metastasis and overall survival. A total of 41 patients were identified (39 patients with IBTR, 2 with Hodgkin`s disease in previous medical history). Median follow-up was 58 months (range 4–170). No grade 3/4 acute toxicity occurred within 9 weeks. Local recurrence-free survival rate was 89.9% and overall survival was 82.7% at 5 years. Seven patients developed metastasis within the whole follow-up. BCS in combination with IORT in IBTR in pre-irradiated patients is a feasible method to avoid mastectomy with a low risk of side effects and an excellent local control and good overall survival.

Integration of more functionality and smaller chips into decreasing package volume leads to increasing heat generation. In addition, the use of new compound semiconductors like SiC and GaN require a high thermal conductivity of the interconnect materials. One of the promising solutions is a layer of sintered silver between semiconductor and substrate. The advantages compared to conventional solders are significant. A higher thermal and electrical conductivity in combination with a higher duty temperature due to a higher melting point should enhance the reliability of the package. However, even as the large scale commercial usage of the material has been started by the industry recently, many important details of the mechanical properties and the reliability behavior are still unknown. While the thermal properties could be characterized relatively easy and are quite repeatable and stable, the mechanical properties - important for the reliability - are extremely process-dependent and wide-spreading. The hunt for lowest feasible sintering process parameters - such as temperature, time and especially pressure - even amplify that behavior and led to an impasse in some cases. Also their failure mechanisms, to be identified in lifetime investigations, are yet unknown as well as their stability and predictability. In order to enable prolonged function of these interfaces, thermo-mechanical reliability has to be assured. Within this paper, we show the status of silver sintering and the problems regarding mechanical material characterization found in literature. Additionally, we present a guideline for the mechanical acceleration of reliability experiments by isothermal bending tests. Finally a proof of concept by failure analysis will be presented.

Novel concepts in power electronics rely heavily on the availability and processability of new materials and packaging technologies to meet the requirements of increasing performance and reliability at lower form factor, weight and cost. Today’s main technological route for converter modules is still the power die soldered and wire-bonded to a DCB substrate. New applications or semiconductor technologies like e.g. SiC, however, require enhanced thermal management using standard commercial casings within the same, usually very limited thermal budget. This paper is the final of a series of publications dealing with a novel thermal management concept for power electronics enabled by the use of advanced packaging technologies as well as smart handling of power transients, making use of a TEC and a thermal buffer using a low melting BiSn eutectic as phase change material to store excess heat temporarily exploiting the PCM’s enthalpy of fusion. This concept is exemplified on a typical six-pack converter module for industrial applications (4 kW, 1200 Volts) to be integrated into a standard easyPIM casing while being able to cope with overload power pulses. This paper summarises the whole system approach, references back to literature for details finishes the series of papers with the reliability analysis of the buffer technology. Thus, all stages of product development covering design, technology and performance are finally highlighted.

Aluminium is still one of the most important contact metallisations for power electronic chips like MOSFETs or IGBTs. With a large difference in thermal expansion coefficients (CTEs) between aluminium and silicon and the temperatures generated in hot-spots during high power transients, these layers are prone to failure due to thermo-mechanical fatigue. Usually lifetime assessment is done by subjecting dedicated test specimens to standardised stress tests as e.g. active or passive thermal cycling. This paper proposes a novel method for accelerated stress testing and lifetime modelling of thin aluminium films in the high-cycle fatigue regime by isothermal mechanical loading. The proposed novel test method is suggested to complement or replace resource-demanding thermal cycling tests and allow simple in-situ monitoring of failure.

Lifetime (or health) monitoring in modern power electronics & luminaries continuously gains in importance, especially if safety-relevant applications are in the focus. Moreover, technology development of such devices requires fast and if possible continuous assessment of structural integrity. This work proposes a simplification of transient thermal testing (TTA) of LEDs by condensing measurement data analysis into one characteristic value to be stored and compared to successive or previous measurements for damage evaluation. Our custom-built in-situ monitoring system is based on microcontroller (uC) functionalities and can be used as stand-alone solution for reliability testing without any other electronic equipment. For quantitative assessment of measurement system performance we used Luxeon Z LEDs with different thermal interface materials. Pre-calibrated samples were inspected for structural integrity before and after cycling tests by X-Ray inspection. Measurement concept as detection for failure at thermal interface or die attach was qualitatively proven by correlation with structure function evaluation.

The cost and the package size driven size reduction of semiconductors lead to much higher heat generation. Also the use of new high power technologies on the basis of SiC produces is a need for high conductivity of the interconnect materials. Therefore the requirements for mechanical, thermal and electrical properties of interconnect materials increase compared to existing eutectic solder and glue materials. One of the promising solutions is a sintered layer between semiconductor and substrate. Especially from sintered layers one expects very high thermal conductivity and good mechanical properties in the package. Therefore, new materials with advanced behavior exploiting nano-effects have been developed in the last years. However, processes to use such materials as TIM-material for power applications are still to be optimized for e.g. zero pressure processing. So also their failure mechanisms, to be identified in lifetime investigations, are yet unknown as well as their stability. In order to enable prolonged function of these interfaces, thermo-mechanical reliability has to be assured. Dedicated fatigue tests have to be conducted to evaluate lifetime under relevant testing conditions, then failure mechanisms such as delamination or cracking have to be identified, understood and quantitatively condensed into a lifetime model to predict reliability for future designs. Within this paper, we present a guideline for the mechanical acceleration of reliability experiments for end-of-lifetime prognostics as well as the state of the art regarding reliability and mechanical characterization of sintered silver.

SUMMARY The purpose of this study was to report the outcome of radio(chemo)therapy in the curative management of esophageal squamous cell carcinoma (ESCC). We retrospectively analyzed 163 patients with T1-T4, N0-1, M0 ESCC who were treated between January 1988 and December 2006 at the Technische Universitat Munchen. One hundred sixty patients were inoperable due to a poor performance status, comorbidities or locally advanced unresectable disease. External beam radiation therapy (EBRT) was performed with (n= 146) or without (n= 17) systemic chemotherapy. Fifty-four patients received an additional boost with intraluminal brachytherapy (IBT). Surviving patients were followed for a median of 72 months (range 10–173 months). The estimated overall survival (OS) at 2 and 5 years was 27 ± 4% and 11 ± 3%, respectively. Loco-regional recurrence at the primary site was observed in 29% of patients (n= 47). The recurrence-free survival (RFS) at 2 and 5 years was 24 ± 3% and 9 ± 2%, respectively. In multivariate analyses, the ECOG performance status (P= 0.004), 3D conformal (vs conventional) radiotherapy (P= 0.031) and continuous standard fractionation (vs split-course radiotherapy, P= 0.048) were associated with a better OS. Simultaneous chemotherapy (P= 0.49) or IBT (P= 0.31) had no significant impact on survival. Outcome for patients with ESCC is poor. Despite the very unfavorable patient selection (poor performance status, high rate of comorbidities, and advanced disease), long-term survival with radio(chemo)therapy was achieved in about 10% of patients. The introduction of modern treatment techniques/modalities (3D conformal planning/ continuous standard fractionation) might be associated with better outcomes.

Within this paper, we present a guideline for the mechanical acceleration of reliability experiments for end-of-lifetime prognostics of metal based die attach materials. First, we used an advanced hybrid nano-effect sintered silver layer as interface between die and substrate which has very good electrical and thermal conductivities. Two pairs ofexperiment/simulation are scheduled. An isothermal mechanical 3-pt bending experiment to induce fatigue the specimens rapidly as well as a thermal induced strain fatigue by thermal chamber for validation. The manufactured specimens are designed to be used for both. With a FEM of this subsystem to simulate the failure parameter which is the accumulated von Mises strain, lifetime modelling can be performed.

The generation of meaningful lifetime-models is a serious and time-consuming challenge throughout the field of packaging. Wherever different materials are joined, the CTE mismatch will usually lead to thermo-mechanical fatigue due to the temperature cycles during the usage of the system [1–3]. As a result, the fatigue of interconnections is the limiting factor for reliability of electronic systems [4]. Usually lifetime investigations are executed as active or passive thermal cycles using the final systems with fixed amplitudes. The main objective is rather the validation that the system will exceed a minimum threshold than the developing of a full lifetime-model. Detailed investigations are often bypassed due to time and financial limitations not realizing the future benefits of a lifetime-model, i.e. by gaining understanding of failure mechanisms and the possibility to predict them by modelling [5–9]. Especially for interfaces based on new developed and mostly insufficiently examined materials like sintered (porous) or composite with their predicted time-depending or highly anisotropic behavior, more detailed experiments are necessary to understand the physics of failure. Such results are required for the technology developing and optimization of fatigue behavior. Therefor more experiments with samples of different technology-parameters as well as different amplitudes or load-regimes are necessary to examine the stability of failure mechanisms and the damage accumulation. New concepts to conduct such lifetime investigations faster are urgently needed [5]. The idea presented in this paper is to show a suitable method to substitute lengthy thermal cycling tests by results obtained by rapid isothermal fatigue tests at different temperatures and how to establish a correlation between both of them. For now, samples based on galvanically deposited copper are used as common reference-material. Based on physics of failure principles, the applicability and viability of such a concept then is evaluated and discussed. In conclusion, this work shows a approach for a significant acceleration of the design for reliability procedure in system integration. It is based on the now possible rapid generation of a lifetime model by thin metal layer samples which are easily manufacturable with the same technology as the thermal cycling test (TCT) samples and should show the same failure mechanism. Detailed investigations are still needed to confirm an applicability of the method also to other metal layers used in the electronic packaging industry.

This paper proposes a guideline for the mechanical acceleration of end-of-lifetime prognostics of metal based die attach materials. As a such, we used first an advanced nano-effect sintered silver layer as interface between die and substrate which has very god electrical and thermal conductivities. Two pairs of experiment/simulation are scheduled. An isothermal mechanical 3-pt bending experiment to induce fatigue the specimens rapidly as well as a thermal induced strain fatigue by thermal chamber for validation. The manufactured specimens are designed to be used for both. With a FEM of this subsystem to simulate the failure parameter which is the accumulated von Mises strain, lifetime modelling is possible.

This paper proposes a guideline for the mechanical acceleration of end-of-lifetime prognostics of metal based thermal interfaces. As die attach material, we used an advanced nano-effect sintered silver layer as interface between die and steel substrate which has very good electrical and thermal conductivities. Two types of experiments/simulations are scheduled. A mechanical 4-pt bending experiment to cause the specimens to undergo fatigue failure rapidly as well as a thermal strain induced fatigue by thermal cycling for comparison. The manufactured specimens are designed to be used for both. With a Finite Element (FE)-model it is possible to simulate the accumulated von Mises strain as failure parameter to generate a lifetime model. Most of the work is currently in progress and results will be delivered soon as full paper.

The lens epithelium is the initiation site for the development of radiation induced cataracts. Radiation in the cortex and nucleus interacts with proteins, while in the epithelium, experimental results reveal mutagenic and cytotoxic effects. It is suggested that incorrectly repaired DNA damage may be lethal in terms of cellular reproduction and also may initiate the development of mutations or transformations in surviving cells. The occurrence of such genetically modified cells may lead to lens opacification. For a quantitative risk estimation for astronauts and space travelers it is necessary to know the relative biological effectiveness (RBE), because the spacial and temporal distribution of initial physical damage induced by cosmic radiation differ significantly from that of X-rays. RBEs for the induction of DNA strand breaks and the efficiency of repair of these breaks were measured in cultured diploid bovine lens epithelial cells exposed to different LET irradiation to either 300 kV X-rays or to heavy ions at the UNILAC accelerator at GSI. Accelerated ions from Z=8 (O) to Z=92 (U) were used. Strand breaks were measured by hydroxyapatite chromatography of alkaline unwound DNA (overall strand breaks). Results showed that DNA damage occurs as a function of dose, of kinetic energy and of LET. For particles having the same LET the severity of the DNA damage increases with dose. For a given particle dose, as the LET rises, the numbers of DNA strand breaks increase to a maximum and then reach a plateau or decrease. Repair kinetics depend on the fluence (irradiation dose). At any LET value, repair is much slower after heavy ion exposure than after X-irradiation. For ions with an LET of less than 10,000 keV micrometers-1 more than 90 percent of the strand breaks induced are repaired within 24 hours. At higher particle fluences, especially for low energetic particles with a very high local density of energy deposition within the particle track, a higher proportion of non-rejoined breaks is found, even after prolonged periods of incubation. At the highest LET value (16,300 keV micrometers-1) no significant repair is observed. These LET-dependencies are consistent with the current mechanistic model for radiation induced cataractogenesis which postulates that genomic damage to the surviving fraction of epithelial cells is responsible for lens opacification.

Years ago already, when “Biochemistry of the brain” became visible by PET, the importance of receptors and transmitters for pathophysiology of EPMS became obvious (1). At the same time methods were developed to study regional cerebral blood flow (rCBF) by SPECT and PET (4,5), providing a possibility to correlate rCBF with data on basal ganglia (BG) dopamine metabolism. In recent years a variety of radiotracers has become available, which allow also transmitter and receptor studies with SPECT (10). The purpose of our study was to correlate BG perfusion based on SPECT obtained with 99mTc-HMPAO (perfusion marker) with those of 123 I-s-CIT (presynaptic dopamine transporter marker) in patients belonging to different diseases with EPMS aiming also to clarify the pathophysiological mechanism of various brain disorders considering also possible consequences for therapeutic decisions, e.g. L-dopa-therapy. This seemed important, as EPMS are frequent neurological problems which can only partially be attributed to classical Idiopathic Parkinson’s Disease (IPD) (7). EPMS can also observed in many other brain disorders (6). Rigidity and/or dyskinesia, tremor, gait abnormalities are also observed in patients with Multiple System Atrophy (MSA), Alzheimer’s Disease (DAT) and — of course — Huntington’s Chorea (HC). Several reports also assume that a dysfunction of the dopaminergic system may be involved in the pathogenesis of the Periodic Movements of Sleep — Syndrome (PMS) and of the Sleep Apnea Syndrome (SAS) (8,9).

The study was aimed at the measurement of effect-depth distributions of intracellularly induced DNA damage in water as tissue equivalent after heavy ion irradiation with therapy particle beams. An assay involving embedding of Chinese hamster ovary (CHO-K1) cells in large agarose plugs and electrophoretic elution of radiation induced DNA fragments by constant field gel electrophoresis was developed. Double-strand break production was quantified by densitometric analysis of DNA-fluorescence after staining with ethidium-bromide and determination of the fraction of DNA eluted out of the agarose plugs. Intracellular double-strand break induction and the effect of a 3 h rejoining incubation were investigated following irradiation with 250 kV x-rays and 190 MeV/u carbon- and 295 MeV/u neon-ions. While the DNA damage induced by x-irradiation decreased continuously with penetration depth, a steady increase in the yield of double-strand breaks was observed for particle radiation, reaching distinct maxima at the position of the physical Bragg peaks. Beyond this, the extent of radiation damage dropped drastically. From comparison of DNA damage and calculated dose profiles, relative biological efficiencies (RBEs) for both double-strand break induction and unrejoined strand breaks after 3 h were determined. While RBE for the induction of DNA double-strand breaks decreased continuously with penetration depth,more » RBE maxima greater than unity were found with carbon- and neon-ions for double-strand break rejoining near the maximum range of the particles. The method presented here allows for a fast and accurate determination of depth profiles of relevant radiobiological effects for mixed particle fields in tissue equivalent. DNA DSB-induction, Strand break rejoining, CHO-K1 cells, Heavy ion therapy beams, Effect-depth distribution. 35 refs., 8 figs.« less

Three different methods of failure analysis on die-attaches are presented and compared in the present work. For this purpose, specially designed samples with thermal test chips on top have been used for a modulated thermal excitation to investigate the underlying die-attach layer by lock-in thermography [1]. The thermoreflectance and the lock-in infrared thermography are thermal and non-destructive methods which still must prove their abilities and reliability in die-attach analysis to find the way into working production lines. The results of both methods have been compared to and verified by the common and widely used scanning acoustic microscopy, which has wide-ranging failure detection abilities but compared to thermographic methods it lacks on production line integration capabilities for 100% in-line inspections.