This paper demonstrates a novel defect localization approach based on EBIRCH isolation conducted from the backside of flip chips. It discusses sample preparation and probing considerations and presents a case study that shows how the technique makes it possible to determine the root cause of subtle defects, such as bridging, in flip chip failures.

A typical workflow for advanced package failure analysis usually focuses around two key sequential steps: defect localization and defect characterization. Defect localization can be achieved using a number of complementary techniques, but electro optical terahertz pulse reflectometry (EOTPR) has emerged as a powerful solution. This paper shows how the EOTPR approach can be extended to provide solutions for the growing complexity of advanced packages. First, it demonstrates how localization of defects can be performed in traces without an external connection, through the use of an innovative cross-sectional probing with EOTPR. Then, the paper shows that EOTPR simulation can be used to extract the interface resistance, granting an alternative way of quantitative defect characterization using EOTPR without the destructive physical analysis. These novel approaches showed the great potential of EOTPR in failure analysis and reliability analysis of advanced packaging.

We report and demonstrate a new methodology for the localization of dielectric breakdown sites in through-silicon via (TSV) structures. We apply a combination of optical beam induced resistance change (OBIRCH) and mechanical/chemical chip deprocessing techniques to localize nm-sized pinhole breakdown sites in a high aspect ratio 3x50 ìm TSV array. Thanks to the wavelength-selective absorption process in silicon, we can extract valuable defect depth localization info from our laser stimulation measurement. After chip deprocessing we inspect and localize the defect site in the dielectric liner using a scanning electron microscope (SEM). We confirm our results and analysis by cross-sectioning a TSV with a focused-ion beam (FIB).

This paper demonstrates a methodology for chip level defect localization that allows complex logic nets to be approached from multiple perspectives during failure analysis of modern flip-chip CMOS IC devices. By combining chip backside deprocessing with site-specific plasma Focused Ion Beam (pFIB) low angle milling, the area of interest in a failure IC device is made accessible from any direction for nanoprobing and Electron Beam Absorbed Current (EBAC) analysis. This methodology allows subtle defects to be more accurately localized and analyzed for thorough root-cause understanding.

This paper introduces a novel sample preparation method using plasma focused ion-beam (pFIB) milling at low grazing angle. Efficient and high precision preparation of site-specific cross-sectional samples with minimal alternation of device parameters can be achieved with this method. It offers the capability of acquiring a range of electrical characteristic signals from specific sites on the cross-section of devices, including imaging of junctions, Fins in the FinFETs and electrical probing of interconnect metal traces.

The bonding at the interface in cold sprayed coating is considered to be a very crucial factor determining its mechanical properties, physical and chemical behavior such as tensile strength, hardness, electrical and thermal conductivities, as well as corrosion resistance. Therefore, in this study the deformation behavior of the particle initial surface is investigated in order to reveal the evolution of free-oxide interface during the high-velocity particle impact in cold spray. The variation of the stress at the interface during the impact is also examined to evaluate the bonding between particle and substrate, and further to predict the bonding strength for the experiments. Results show that the area ratio of the free-oxide interface and the whole interface are 0.52, 0.7 and 0.76, respectively, for the case of copper particle impact at 500 m/s, 800 m/s and 1100 m/s. Moreover, the free-oxide interface in case of 800 m/s is about 3 times as much as that in case of 500 m/s while the free-oxide interface of 1100 m/s is approximately 5 times as much as that of 500 m/s. The compressive stress in the normal direction at the position where free-oxide interface occurs is higher than the yield strength of the material and during the whole impact, the tensile stress is no more than the tensile strength of the material.

This study investigates the formation of ZnNi/Cr 2 O 3 -TiO 2 -CuO-SiO 2 /PTFE composite ceramic coatings by atmospheric plasma spraying and assesses their ability to improve the corrosion, friction, and wear performance of reciprocating parts. The as-sprayed coatings were examined then subjected to a series of tests to evaluate corrosion and fouling resistance. Reciprocating parts that had been coated were relatively intact after 5000 h in a realistic ocean environment. Cyclical changes in coating weights were found to be influenced by the dissolution of oxide films and the accumulation of secondary products. PTFE proved to be an effective sealing agent, reducing mass loss and porosity by approximately 30%.

In this study, metal oxide films were synthesized from an EDTA·Er·H complex by flame spraying. The erbium oxide (Er 2 O 3 ) layers were deposited on stainless steel using N 2 , air, or O 2 as the carrier gas and a H 2 -O 2 mixture as the combustion gas. Test results indicate that the carrier gas has a significant effect on film thickness and porosity and that O 2 is the ideal carrier gas for producing dense metal oxide films.

This paper describes 2 case studies where device characterizations using Atomic Force Probe (AFP) nanoprobing, allow for the localization and verification of design weakness and process variations on the Analog-to-Digital (ADC) block that resulted in degraded device performance and severe yield loss. In these cases, the sensitive resistor structures in the ADC block was impacted due to design pattern density interaction with process fabrication steps. In addition, close collaboration with customer was also essential for quick root cause identification, design and process fix.

A magnesium coating with a low porosity and high microhardness was elaborated using cold spraying. However at present, a poor bonding strength between the coating and substrate limits its application. This paper aims at improving the bonding strength between the coating and substrate using substrate preheating. Aluminum substrates were heated to 100, 200 and 300°C respectively by a flame prior to cold spraying. The results show that substrate preheating can significantly increase the bonding strength. The bonding strength increased from 3.3±0.8 MPa to 11.6±0.5 MPa when the substrate temperature increased from room-temperature to 200°C. The fracture analyses show that the coating fracture occurred within the coating when the substrate was preheated at 200°C.

Several product lots were found to suffer from data retention failures in OTP (one time program) devices. PFA (physical failure analysis) was performed on these devices, but nothing abnormal was observed. Cross-sectional TEM (transmission electron microscopy) revealed no physical defects or abnormal CDs (critical dimensions). In order to isolate the failed layer or location, electrical analysis was conducted. Several electrical simulation experiments, designed to test the data retention properties of OTP devices, were preformed. Meilke's method [1] was also used to differentiate between mobile ion contamination and charge trap centers. Besides Meilke's method, a new electrical analysis method was used to verify the analysis results. The results of our analysis suggests that SiN charge trap centers are the root cause for the data retention failures, and the ratio of Si/N is the key to charge trap center formation. Auger analysis was used to physically check the Si/N ratio of OTP devices. The results support our hypothesis. Subsequent DOE (Design Of Experiment) experiments also confirm our analysis results. Key Words: OTP, data retention, Non-visible defect, AFP, charge trap center, mobile ion.

A previous study indicated that dense thick Cu-4Cr-2Nb coatings could be formed by cold spraying, and the post-spray heat treatment could significantly influence the microstructure and microhardness of the as-sprayed Cu- 4Cr-2Nb coatings. In this study, the tensile strength and fracture performance of the Cu-4Cr-2Nb coatings after annealing were investigated. The vacuum heat treatment was conducted under 10-2 Pa at 850°C for 4 h. Results showed that the heat treatment had a great contribution to the healing-up of the incompleteness of the interfaces between the deposited particles. In addition, the coating microhardness decreased from 156.8±4.6 Hv0.2 for the as-sprayed coatings to 101.7±4.5 Hv 0.2 for the annealed ones. The mean tensile strength of the annealed coatings was approximately 298.8±31.5 MPa compared to that of 45±10.5 MPa for the as-sprayed ones, which results from the partially metallurgically bonded zones between the deposited particles inducing by the heat treatment process.

This study investigates the effect of substrate conditions on supersonic jet flow pattern, particle acceleration and substrate preheating process in cold spraying. Computational fluid dynamic (CFD) approach is employed in the present work to achieve this objective. The simulated results show that substrate diameter has some effects on gas flow regime and thus particle acceleration. When the substrate diameter is smaller than the nozzle exit diameter, the size of the bow shock formed in front of the substrate is rather small, which contributes to increase the particle impact velocity. With increasing the substrate diameter gradually, the flow regime becomes more and more insensitive to the substrate diameter and the pattern becomes uniform. Moreover, the current numerical work also reveals that substrate preheating process can be significantly influenced by substrate thickness. With the increment in substrate thickness, the preheating effect becomes increasingly undesirable and the substrate surface temperature presents a downward trend.

Numerical simulations focused on the impacting behavior of cold-sprayed particles are usually conducted with the Lagrangian method. However, the calculated output is much dependent on the mesh size due to the mesh distortion and/or the element-averaged variables in simulations. While the Eulerian method is attractive to overcome the mesh distortion. In this study, an investigation on the impacting behavior of cold-sprayed particles using the Eulerian formulation available in ABAQUS/Explicit was conducted with typical copper material. The results show that a jet can not be formed at the impacting velocities of 200-300m/s, but a continuous and smooth jet composed of the particle and substrate materials can be formed as the impacting velocity is in the extent of about 300-400 m/s which could be a theoretical value of the critical velocity for a successful bonding. At this velocity extent, the maximum PEEQ almost keeps unchanged accompanying with a temperature fluctuation. In addition, the jet presents discontinuous and the splashing causes the loss of material as the impacting velocity exceeds this velocity extent. Therefore, this model could be also used to predict the critical velocity of other materials besides the copper.

Magnesium coatings were deposited upon aluminum and stainless steel substrates by cold spraying. Three Mg powders with different particle size distributions were used as feedstock. The microstructures of as-sprayed coatings were evaluated by optical microscopy, and scanning electron microscopy. The coating observations show that a main gas temperature has an important effect on the deposition behaviour of particles. Changing the gas temperature from 350°C to 630°C involves an increase of the deposition efficiency from 1.57% to 19.57%. The effects of the particle size distribution and substrate material on the deposition efficiency of particles were also investigated. The results show that the particle size distribution has a significant effect on the deposition efficiency of particles which increases from 19.57% to 59% when the mean particle size decreases from 63 µm to 38 µm under gas temperature of 630°C. However, the deposition efficiency of particles was slightly influenced by the substrate material. In addition to these experimental results, the in-flight particle velocities were simulated by FLUENT software to point out the effects of the gas temperature and particle size distribution.

In this paper, a commercial AZ91D magnesium alloy powder and its mixture with 30 vol.% SiC powder were used to deposit coatings by cold spraying. Two types of converging-diverging nozzles with different cross-sectional shapes were employed. The velocity and temperature of in-flight particles under different operating conditions were simulated using the FLUENT software. The simulated results show that the particle velocity through the rectangular cross-section nozzle is the same with that through the circular one. However, the coating observation shows that the AZ91D coating and its composite could only be deposited using the rectangular cross-section nozzle. The increase of gas temperature has little effect on the coating microstructure, porosity and microhardness. Furthermore, the observation of the composite coating produced under the gas temperature of 600°C shows that the SiC content in the composite is about 23 vol.%. The microhardness of the composite is improved to about 140 HV 0.3 due to the enhancement of SiC particles, compared to that of about 100 HV 0.3 for the AZ91D coating.

Atmospheric plasma-sprayed YSZ thermal barrier coatings (TBCs) are widely used in industrial gas turbine engines to prevent the superalloy blades from failure. The failure of TBCs in service occurs by the spalling of YSZ coating. Crack propagation leading to the failure of plasma-sprayed thermal barrier coatings usually occurs within YSZ coating near the YSZ/Bond coat interface. In the present study, a novel durable TBCs consisting of a YSZ interlayer of the well-bonded interlamellae between the bond coat and conventional YSZ top porous coat was introduced. The YSZ interlayer was deposited at different coating surface temperatures, which resulted in the formation of YSZ with significantly improved interlamellar bonding. The result shows that thermal cyclic lifetime of the novel TBCs with the 20-30 µm thick YSZ interlayer increased by factor of 4 compared with that of the conventional one. The improved thermal cyclic lifetime was attributed to the controlled transition of cracking path from the near YSZ/bond coat interface to YSZ top layer. The effect of thickness of the YSZ interlayer on the lifetime of TBCs was also investigated.

Surface morphology of MCrAlY bond coats is one of the factors that affect the oxidation behavior and the thermal stability of thermal barrier coatings. In the present study, the isothermal oxidation behavior of cold sprayed MCrAlY bond coat was investigated at three surface conditions: as-sprayed, polished and shot-peened conditions. The MCrAlY bond coat with sputters adhered weakly on the surface prepared by low-pressure plasma spraying was also employed. The above four types of surface conditions were employed to investigate the effect of the surface morphologies of MCrAlY (M=NiCo, Ni) bond coats on their oxidation behavior. MCrAlYs with the compositions of Ni20Cr10AlY and Ni23Co20Cr8.5Al5.0Ta0.6Y were employed for bond coat deposition. Cold-sprayed Ni20Cr10AlY exhibited a higher oxidation rate than that of the cold-sprayed Ni23Co20Cr8.5Al5.0Ta0.6Y bond coats. After 10 hrs oxidation, the TGO on the as-cold-sprayed bond coat surface was merely constituted by Al 2 O 3 , while the TGO on the bond coat surface attached with sputters was composed of Al 2 O 3 and spinel. After 500 hrs oxidation, Cr 2 O 3 and porous spinel appeared in the TGO on the two surfaces of as-cold-sprayed bond coat. The growth of Ni/Cr-oxides was attributed to the Al depletion. The content of spinel on cold-sprayed NiCrAlY decreased after shot-peening.

In this research, large gas-atomized copper powder was selected as the feedstock. Some powder was annealed in a vacuum circumstance to avoid to the greatest extent the effect of grain boundaries on the high velocity impact behavior of particles during cold spraying. Some powder was oxidized in a resistance furnace to clarify the effect of surface oxide films. Both the annealed and the oxidized Cu powders were deposited by cold spraying with respect to the single impacts and coating deposition under the same gas condition. In addition, the rebounded copper particles were collected for morphology analysis compared to the adhered particles. The results show that the average size of the rebounded particles is apparently increased compared to the starting powder because of the rebound of the larger particles and the intensive plastic deformation of particles. For the deposited particles, obvious plastic deformation causes the higher hardness of the coatings. The last but not the least finding in this study is the rebounded particles also experienced large deformation and possible shear instability at the impact interfaces.

Thermal conductivity of plasma-sprayed YSZ thermal barrier coatings depends on microstructure and significantly influences the effectiveness of the thermal barrier. In this study, YSZ coatings are deposited by plasma spraying using fused and crushed Y 2 O 3 -ZrO 2 powder. Coating microstructure was modified by substrate temperature, which was varied from room temperature to 880 °C during deposition. The coating microstructure was examined from the fractured cross-section of the deposits to reveal changes in interlamellar bonding due to substrate temperature. The thermal conductivities of the YSZ coating were tested by laser flashing from room temperature to 1300 °C. The results showed that the coating deposited at room temperature exhibited a typical lamellar structure and a thermal conductivity of 1.26 W·m -1 ·K -1 measured at room temperature. With the increase of substrate temperature, the thermal conductivity was increased. The coating deposited at a substrate temperature of 840-880 °C consisted of trans-lamellae long columnar grains and exhibited a value of 1.95 W·m -1 ·K -1 at room temperature. The influence of substrate temperature on thermal conductivity is discussed based on the changes in microstructure observed.