Reliability assessment of a plastic encapsulated RF switching device

In this study the degradation and reliability of a plastic encapsulated RF switching device were assessed by comparing several lots of a device that came directly off the assembly line to several other lots which had been subjected to accelerated stress testing. Comparisons of the structure, die and wirebonds were based on the results of examinations using optical microscopy, X-ray analysis, scanning acoustic microscopy, environmental scanning electron microscopy and wire bond pull tests.     

Comparisons of instabilities in scaled CMOS devices between plastic and hermetically encapsulated devices

Scaling down of transistor cell sizes causes some instabilities in CMOS devices under high temperature or high humidity bias stress, especially in plastic encapsulated devices. On CMOS test transistors with various kinds of the passivation layer, accelerated reliability tests have been conducted in this study. As a result of tests, it has been found that devices with a phosphosilicate glass passivation layer show remarkable threshold voltage shifts, which depend on the gate length, compared with devices with a silicon-nitride passivation layer, in both plastic and ceramic encapsulated devices. This paper describes characteristics of the shift, passivation, and packaging effects on the shift and modeling of the shift mechanism.     

Ruthenium and tungsten as contact materials in hermetically plastic sealed telecom- and signal-relays

Palladium is the most frequently used contact material for telecommunication and signal relays. Good contact resistance stability and material transfer characteristics make it the most often used. The strong variation of the palladium price in recent years has made it necessary to look for alternatives. The development of gas-tight plastic sealed relay housings, which keep the gas filling inside the relay for a long time, e.g., more than 10 years for nitrogen and more than 100 years for sulfur-hexafluoride, allows nonprecious metal contact materials to be used, as an inert atmosphere can be kept for the entire life of the relay. Tests were performed with gold covered tungsten and ruthenium contacts mounted in a standard telecom relay filled with N/sub 2/ or SF/sub 6/. Although the contact resistance was always measured with dry circuit conditions applied, no relevant increase was observed during all electrical endurance tests. The ruthenium as well as the tungsten layer with a thickness of only 5 /spl mu/m withstood endurance tests at maximum loads at 30 W. As only minimum contact erosion and material transfer occurred, no contact sticking or bridging was observed. Overall the switching performance of tungsten and ruthenium is similar to PdRu10. As PdRu10 has superior performance especially when operating in an SF/sub 6/ atmosphere, the properties of Ru and W in N/sub 2/ as well as in SF/sub 6/ are at least comparable with all contact materials in current use. Gas-tight plastic sealed relay housings offer the advantages of hermetically sealed housings at an affordable cost.     

Reliability evaluation of plastic encapsulated parts

This work compares the failure rates of several families of plastic encapsulated microcircuits (PEMs) using both field and test data (test data are converted to device failure rates for field conditions using common acceleration equations) and Mil-Hdbk-217 calculations. Calculated failure rates are obtained from the Mil-Hdbk-217F for both plastic encapsulated and ceramic hermetic class-B microcircuits. Comparisons show that the results from Mil-Hdbk-217 are misleading and that the US military and Government part-selection methods should not be burdened by this -217 methodology     

Reliability of plastic ball grid array package

The reliability of plastic ball grid array (PBGA) package is studied for different materials. The reliability of the PBGA packages using conventional Bismaleimide-Triazine type PWB and our original product PWB that is made of high Tg epoxy resin is evaluated. The PBGA package using our original PWB has a feature of lower warpage for the package, and has similar performance regarding the thermal cycling stability and the endurance during reflow soldering as compared with the PBGA using the conventional PWB. The endurance during reflow soldering for each PBGA is JEDEC STD Method A112 level 3. In order to improve the endurance during reflow soldering, not only PWB materials but also other factors are investigated. As a result, the molding compound with the property of low moisture absorption and the die attach material with the properties of high adhesion strength and fracture strength are effective to improve the endurance property during reflow soldering. The package crack mechanism during reflow soldering is briefly described as follows     

Reliability assessment of multiple-agent cooperating systems

Multiple agent systems are being increasingly used in real-time applications, safety-critical systems, etc. Many of these applications have soft real-time constraints and imprecise correctness criteria for the output value. A principal characteristic of such systems is the tradeoff between using an efficient but less accurate strategy and a sophisticated but more time-consuming strategy. This paper develops methods for assessing the reliability of these systems in terms of the timeliness and accuracy of the output, to aid decision making. Two commonly used coordination structures, parallel and pipeline, are used. Some adaptive schemes are proposed, i.e., strategies can be selected dynamically by agents at the run-time according to the input encountered in order to enhance the reliability of the system. The applicability of this approach is demonstrated by a practical multimedia client-server example     

Reliability modeling and assessment of the Star-Graph networks

The reliability of the Star Graph architecture is discussed. The robustness of the Star Graph network under node failures, link failures, and combined node and link failures is shown. The degradation of the Star Graph into Substar Graphs is used as the measure of system effectiveness in the face of failures. Models are provided for each of the failure and re-mapping modes evaluated herein, and the resilience of the Star Graph to failures is emphasized. This paper defines failure of a Star Graph as being when no fault-free (n - 1)-substars remain operational and the intermediate states are defined by the number of (n - 1)-substars that remain operational. A powerful tool (re-mapping) is introduced in which the number of operational (n 1)-substars can be maintained for longer periods, thus improving the overall MTTF (mean time to failure). For comparison the results of a similar reliability analysis of the hypercube is shown. The comparisons are considered conservative due to the failure model used herein for the star graph. One might apply re-mapping to hypercubes; while it would improve the overall MTTF of hypercubes, the hypercubes would still have an appreciably poorer performance than star graphs     

Reliability assessment from fatigue micro-crack data

Micro-cracks are generally defined to be cracks less than 1 mm in length, which propagate under cyclic stresses until they grow large and cause failure in an item (e.g. component or structure). This paper proposes a method of using data on `fatigue micro-crack growth in a material' to predict its reliability. It is increasingly important to model such cracks effectively, Their growth properties, which differ in several respects from larger cracks, are discussed. The paper develops a hierarchical model for the propagation of micro-cracks in a material. This stochastic model attempts to model the dependence of growth on local conditions, varying throughout the material, that causes variation in growth rates across the specimen. Given the model, data on micro-crack growth are used to compute posterior distributions of model parameters, from which a predictive distribution for reliability can be calculated. Computation of the posterior distributions is by Gibb's sampling and kernel density estimation. The methodology is illustrated with two data sets, one simulated and the other from a cast-iron specimen. Some possibilities for further work are presented     

Reliability assessment for MIMO detection and its application

We propose a reliability assessment (RA) for multiple input and multiple output (MIMO) detection at the receiver, which can assess whether the output of MIMO detection is reliable or not. First, an analytical formula of the RA is derived to assess the reliability of the receiver's output, a simplified RA is also proposed and a complexity-reduced method is further given by adjusting the threshold of RA, with some potential performance loss compared to the original method. Next we develop a combined detector with simple receiver, advanced receiver and RA module as follows: (1) the initial estimate of transmit symbols is obtained by the simple receiver, assessed by RA in the RA module; (2) if the estimate satisfies the RA, we consider the estimate as the final result; otherwise, the estimate will be through the advanced receiver for further improvement. Finally we give two practical cases of combined detection and run Monte Carlo simulations to confirm the analysis and the efficiency of our proposed combined detection.A key contribution of this paper is a simple analytical formula used to assess whether the detection result is reliable or not at the receiver, which can help the combined detection to sufficiently utilize the output of the simple detection, and estimate part of transmit symbols only using the simple receiver instead of the advanced receiver with negligible performance loss.     

A critique of the Reliability Analysis Center failure-rate-modelfor plastic encapsulated microcircuits

As the use of plastic encapsulated microcircuits (PEM) has escalated in the electronics industry, especially in applications in which “mission” success must be accomplished at “any cost”, some researchers have proposed reliability models to predict their failure rates or mean times-to-failure. One organization that took on such a challenge was the US Dept. of Defense (DoD) Reliability Analysis Center (RAC). Despite its admirable aims, the model has inherent limitations which result in unrealistic predictions, which could negatively affect parts selection, environmental management and logistics support. This paper presents an analysis of the model developed by the RAC     

Reliability assessment and hygroswelling modeling of FCBGA with no-flow underfill

In the flip-chip ball grid array (FCBGA) assembly process, no-flow underfill has the advantage over traditional capillary-flow underfill on shorter cycle time. Reliability tests are performed on both unmolded and molded FCBGA with three different types of no-flow underfill materials. The JEDEC Level-3 (JL3) moisture preconditioning, followed by reflow and pressure cooker test (PCT) is found to be a critical test for failures of underbump metallization (UBM) opening and underfill/die delamination. In this paper, various types of modeling techniques are applied to analyze the FCBGA-8×8 mm on moisture distribution, hygroswelling behavior, and thermomechanical stress. For moisture diffusion modeling, thermal-moisture analogy is used to calculate the degree of moisture saturation in the multi-material system of FCBGA. The local moisture concentration along the critical interface, e.g. die/underfill, is critical for delamination, because the moisture weakens the interfacial adhesion strength, generates internal vapor pressure during reflow, and induces tensile hygroswelling stress on UBM during PCT. The results of moisture distribution can be used as loading input for the subsequent hygroswelling modeling. The magnitude of hygroswelling stress acting on UBM is found to be greater than the thermal stress induced during reflow, both in tensile mode which may cause the UBM-opening failure. Underfill with lower saturated moisture concentration (C_sat) and coefficient of moisture expansion (CME) are found to induce lower UBM stress and has better reliability results. Molded package generally has higher stress level than unmolded package. Parametric studies are performed to study the effects of no-flow underfill materials, package type (molded vs. unmolded), die thickness, and substrate size on the stresses of UBM during reflow and PCT.     

Reliability and availability assessment of storage area network extension solutions

Reliability is one of the key performance metrics in the design of storage area network extensions as it determines accessibility to remotely located data sites. SANs can be extended over distances spanning from hundreds to thousands of kilometers with optical or IP-based transport networks. The network equipment used depends on the storage protocol used for the extension solution. The present article provides analytical models developed for the calculation of long-term average downtimes, service failure rates, and service availability that can be achieved as a function of hardware/software failures, software upgrades, link failures, failure recovery times, and layer 3 protocol convergence times.     

光纤碳密封涂覆的工艺研究

碳密封涂覆光纤具有良好的耐疲劳性能,以及抗氯损性能,在军事及通信领域内有着重要的应用前景。本文简单介绍了碳密封涂覆光纤的研究进展,以及其应用前景,并主要分析了碳密封涂覆光纤的工艺影响因素。     

Reliability assessment with amalgamated data via theexpectation-maximization algorithm

A solution is given to the problem of estimating reliability indicators in a context of crude data arising in an industrial study devoted to the reliability assessment of electronic calculators used in modern airplanes. The authors introduce the concept of amalgamated data and develop an expectation-maximization algorithm to obtain a maximum likelihood estimator of the reliability function and the cumulative failure intensity associated with the lifetime of calculators     

Reliability evaluation of plastic packaged devices for long life applications by THB test

The reliability of transistors, bipolar and CMOS integrated circuits encapsulated in different types of plastic packages was investigated by using the 85°C/85% R.H. test with applied bias and the results compared with a long term operating life test. Particular attention was devoted to pointing out the influence of technology, process control and working conditions on device reliability and failure mechanisms.In micropackaged transistors the importance of surface passivation in protecting the devices against gold corrosion was forcused, while the need of good process control was confirmed by the results of the test on micropackaged linear integrated circuits.In dual-in-line CMOS integrated circuits silicon nitride and polymide give, in general, a superior protection, but good results were obtained also with normal P-glass passivation when a clever arrangement of layout design rules was adopted. Results obtained exhibit a significant improvement in the reliability of plastic packaged devices, with the best figures showing no failures after 15,000 hours at 85°C/85% R.H. test with bias.     

Reliability assessment of principal point estimates for forensic applications

Although quite recent as a forensic research domain, computer vision analysis of scenes is likely to become more and more important in the near future, thanks to its robustness to image alterations at the signal level, such as image compression and filtering. However, the experimental assessment of vision-based forensic algorithms is a particularly critical task, since they cannot be tested on massive amounts of data, and their performance can heavily depend on user skill. In this paper we investigate on the accuracy and reliability of a vision-based, user-supervised method for the estimation of the camera principal point, to be used in cropping and splicing detection. Results of an extensive experimental evaluation show how the estimation accuracy depends on perspective conditions as well as on the selected image features. Such evidence led us to define a novel visual feature, referred to as Minimum Vanishing Angle, which can be used to assess the reliability of the method.     

Reliability assessment of delamination in chip-to-chip bonded MEMS packaging

The bond layer is often the weakest link in the reliability of chip packages in the integrated circuit (IC) industry. Micro-electrical-mechanical systems (MEMS) packages are no exception to this trend. This paper presents a nondestructive methodology for determining delamination in chip-to-chip bonded MEMS. Experimental methods are used to determine the adhesive layer strength in samples subjected to environmental testing, and the reliability of the bonding layer is investigated. A simulation is performed using inputs from scanning acoustic microscopy, and simulation model results are correlated with the experimental die shear measurements to establish the validity of the nondestructive methodology for determining adhesive layer strength.