Michael H. Azarian

Sensor Systems for Prognostics and Health Management

Prognostics and health management (PHM) is an enabling discipline consisting of technologies and methods to assess the reliability of a product in its actual life cycle conditions to determine the advent of failure and mitigate system risk. Sensor systems are needed for PHM to monitor environmental, operational, and performance-related characteristics. The gathered data can be analyzed to assess product health and predict remaining life. In this paper, the considerations for sensor system selection for PHM applications, including the parameters to be measured, the performance needs, the electrical and physical attributes, reliability, and cost of the sensor system, are discussed. The state-of-the-art sensor systems for PHM and the emerging trends in technologies of sensor systems for PHM are presented.

Nanoindentation, microscratch, friction and wear studies of coatings for contact recording applications

Abstract A nanoscale monolithic slider-suspension produced by photolithography is used for contact recording. The contact pad consists of a multilayered structure consisting of SiC, amorphous hydrogenated carbon (a-C:H), Al203, Si, and CoNbZr films. In this study, we have compared hardness, Youngs modulus of elasticity, and scratch resistance or adhesion of various coatings deposited on a single-crystal silicon wafer by nanoindentation and microscratch techniques and friction and wear performance by sliding against a diamond tip and sapphire ball in reciprocating mode. SiC coatings exhibit the highest hardness, about 27 GPa, and the highest elastic modulus, about 255 GPa. Microscratch data indicate that SiC and a-C:H coating exhibit the highest resistance to scratching or debonding from the substrate. During scratching, an Al203 coating deforms like a ductile metal rather than like a ceramic. Si and CoNbZr coatings exhibit ploughing of the tip into the sample surface and debris generation right in the beginning of the scratch. SiC coatings exhibit the best wear performance against a diamond tip as well as a sapphire ball. For comparisons, we also made mechanical property measurements on bulk materials used in conventional recording: NiZn ferrite, Al203-TiC, and SiC (under development). The bulk Ni-Zn ferrite sample was found to be damaged by grain pull-out during scratching even at a low load of 3 mN. Bulk Al203-TiC exhibits unexpected ploughing of the sample right from the beginning of the scratch. Bulk SiC did not exhibit any signs of significant damage up to a normal load of about 15 mN. Overall comparison of mechanical properties of bulk materials and coatings suggest that SiC is the most desirable coating in the contact pad for low wear. An SiC coating is also recommended as an overcoat for thin film magnetic disks.

Motor Bearing Fault Detection Using Spectral Kurtosis-Based Feature Extraction Coupled With K -Nearest Neighbor Distance Analysis

Bearing faults are the main contributors to the failure of electric motors. Although a number of vibration analysis methods have been developed for the detection of bearing faults, false alarms still result in losses. This paper presents a method that detects bearing faults and monitors the degradation of bearings in electric motors. Based on spectral kurtosis (SK) and cross correlation, the method extracts fault features that represent different faults, and the features are then combined to form a health index using principal component analysis (PCA) and a semisupervised k-nearest neighbor (KNN) distance measure. The method was validated by experiments using a machinery fault simulator and a computer cooling fan motor bearing. The method is able to detect incipient faults and diagnose the locations of faults under masking noise. It also provides a health index that tracks the degradation of faults without missing intermittent faults. Moreover, faulty reference data are not required.

Early Detection of Interconnect Degradation by Continuous Monitoring of RF Impedance

Traditional methods used to monitor interconnect reliability are based on measurement of dc resistance. DC resistance is well suited for characterizing electrical continuity, such as identifying an open circuit, but is not useful for detecting a partially degraded interconnect. Degradation of interconnects, such as cracking of solder joints due to fatigue or shock loading, usually initiates at an exterior surface and propagates toward the interior. At frequencies above several hundred megahertz, signal propagation is concentrated at the surface of interconnects, a phenomenon known as the skin effect. Due to the skin effect, RF impedance monitoring offers a more sensitive and reproducible means of sensing interconnect degradation than dc resistance. Since the operation of many types of electronic product requires transmission of signals with significant frequency components in the gigahertz range, this has the further implication that even a small crack at the surface of an interconnect may adversely affect the performance of current and future electronics. This paper demonstrates the value of RF impedance measurements as an early indicator of physical degradation of solder joints as compared to dc-resistance measurements. Mechanical fatigue tests have been conducted with an impedance-controlled circuit board on which a surface mount component was soldered. Simultaneous measurements were performed of dc resistance and time domain reflection coefficient as a measure of RF impedance while the solder joints were stressed. The RF impedance was observed to increase in response to the early stages of cracking of the solder joint while the dc resistance remained constant. Failure analysis revealed that the RF impedance increase resulted from a physical crack, which initiated at the surface of the solder joint and propagated only partway across the solder joint. A comparison between RF impedance and event detectors was made to compare their respective sensitivities in detecting interconnect degradation. These test results indicate that RF impedance can serve as a nondestructive early indicator of solder joint degradation and as an improved means for assessing reliability of high-speed electronics.

Using a reliability capability maturity model to benchmark electronics companies

Purpose – This paper seeks to introduce a set of key practices that can be used to assess whether an organization has the ability to design, develop and manufacture reliable electronic products.Design/methodology/approach – The ability to design, develop and manufacture reliable electronic products is defined in the paper in terms of a reliability capability maturity model, which is a measure of the practices within an organization that contribute to the reliability of the final product, and the effectiveness of these practices in meeting the reliability requirements of customers.Findings – The paper presents a procedure for evaluating and benchmarking reliability capability. Criteria for assigning different capability maturity levels are presented. The paper also presents a case study corresponding to reliability capability benchmarking of an electronics company.Originality/value – The paper provides a set of practices for evaluating and benchmarking reliability capability.

Prognostics of Failures in Embedded Planar Capacitors using Model-Based and Data-Driven Approaches:

This paper presents the application of model-based and data-driven approaches for prognostics of failures in embedded planar capacitors. An embedded planar capacitor is a thin laminate that serves both as a power/ground plane and as a parallel plate capacitor in a multilayered printed wiring board. These capacitors have gained importance with an increase in the operating frequency and a decrease in the supply voltage in electronic circuits since they can enable miniaturization of electronic circuits as well as improved electrical performance. In next generation electronic circuits, embedded planar capacitors will be crucial in communication, automotive, military, medical, and space applications. The capacitor laminate used in this study consisted of an epoxy-barium titanate nanocomposite dielectric sandwiched between Cu layers. Three electrical parameters, capacitance, dissipation factor, and insulation resistance, were monitored in situ during testing under elevated temperature and voltage-aging conditions. The failure modes observed were a sharp drop in insulation resistance and a gradual decrease in capacitance. An approach to model the time-to-failure associated with these failure modes is presented in this paper. Further, a data-driven technique known as the Mahalanobis distance method is also investigated for early detection of these failures.

Prognostics of ceramic capacitor temperature‐humidity‐bias reliability using Mahalanobis distance analysis

Purpose – This paper seeks to present a prognostics approach using the Mahalanobis distance (MD) method to predict the reliability of multilayer ceramic capacitors (MLCCs) in temperature‐humidity‐bias (THB) conditions.Design/methodology/approach – Data collected during THB testing of 96 MLCCs were analyzed using the MD method. In the THB tests, three parameters (capacitance (C), dissipation factor (DF), and insulation resistance (IR)) were monitored in situ. A Mahalanobis space (MS) was formed from the MD values of a set of non‐failed MLCCs. MD values for the remaining MLCCs were compared with an MD threshold. Data for MLCCs which exceeded the threshold were examined using the failure criteria for the individual electrical parameters to identify failures and precursors to failure.Findings – It was found that the MD method provided an ability to detect failures of the capacitors and identify precursors to failure, although the detection rate was not perfect.Research limitations/implications – It was observ...

Reliability of Printed Circuit Boards Processed Using No-Clean Flux Technology in Temperature–Humidity–Bias Conditions

Printed circuit board (PCB) specimens containing three different IPC-B-25 test structures were exposed to temperature-humidity-bias conditions in order to evaluate the effects of no-clean flux chemistry, conductor spacing, voltage bias, and test environment on surface insulation resistance (SIR). Comb patterns on the PCBs were coated with a eutectic (63Sn/37Pb) solder applied by a hot air solder leveling and processed by using no-clean aqueous-based and rosin-based fluxes. The SIR failure rate with rosin-based no-clean flux was observed to be greater than that with aqueous-based no-clean flux. This was explained by the more corrosive nature of the flux residues and the larger concentration of hygroscopic weak organic acids in the rosin-based flux residues. A characteristic of the SIR failures for PCBs processed with rosin-based flux was a series of intermittent SIR drops, which could severely affect the reliability of electronic assemblies. It was hypothesized that flux residues combined with adsorbed moisture from the environment form an acidic medium, occasionally breaking through the tin oxide passivation layer on the electrodes. Penetration of the passivation layer combined with conductive flux residues bridging the electrodes caused the resistance to decrease, and rehealing of the passivation layer resulted in the intermittent behavior. Conductor spacing was observed to represent a factor in the electrochemical migration process that is independent of electric field. Since conductor spacings in electronic products continue to decrease, the experimental results support recommendations to replace 25-mil (0.64-mm) comb structures on industry standard test boards with those having smaller spacings, below 12.5 mil (0.32 mm), that accurately reflect the greater risk for SIR drops of todays higher density assemblies.

Analysis of Solder Joint Failure Criteria and Measurement Techniques in the Qualification of Electronic Products

The specification of a failure criterion for solder joints is an important element in the qualification of an electronic product. A common approach to reliability testing is to monitor electrical resistance during the testing. The techniques employed for resistance monitoring and data acquisition will determine whether information regarding transients or long-term drift is captured by the measurement. This paper reviews and assesses the failure criteria used in industry and academia, focusing on three key attributes: resistance threshold, duration of resistance change, and frequency of changes. An experimental study on thermomechanical fatigue of ball grid array package solder joints was performed to compare measurement techniques and failure criteria.

Surface Insulation Resistance of Conformally Coated Printed Circuit Boards Processed With No-Clean Flux

Printed circuit board (PCB) specimens containing three different IPC-B-25 test structures were exposed to temperature/humidity/bias conditions in order to evaluate the effects of conformal coating, conductor spacing, voltage bias, flux chemistry, and test environment on surface insulation resistance (SIR). Results indicate that conformal coatings improve reliability, provided that sources of contamination on the PCB and within the coating are minimized. The presence of fibrous contaminants within the coating represented a preferential medium for moisture adsorption and ion transport, leading to accelerated reduction of SIR. In the absence of contamination, PCBs with conformal coatings were found to be less susceptible to SIR degradation than uncoated PCBs, with silicone providing better protection than urethane, and acrylic providing the least protection of the three coating materials evaluated. Conductor spacing was observed to represent a factor in the electrochemical migration (ECM) process independent of electric field, indicating that updated test structures are required to predict reliability of todays high-density assemblies. The SIR failure rate with rosin-based no-clean flux was observed to be greater than that with aqueous-based no-clean flux. A higher failure rate was also observed for tests conducted at 40 degC/93% RH than for 85 degC/85% RH. Due to the more rapid evaporation of weak organic acids in the flux residues at higher temperatures, test results obtained at 85 degC/85% RH will not accurately predict reliability at lower temperatures for PCBs processed using no-clean flux. PCB specimens were exposed to temperature/humidity/bias conditions in order to evaluate the effects of conformal coating, conductor spacing, voltage bias, flux chemistry, and test environment on reduction of surface insulation resistance. Results indicate that, in the absence of contamination, conformal coatings improve reliability