Evaluation of Smear and Its Effect on the Mechanical Integrity of Plated Through Hole-Inner Plane Interface in Thick Printed Wiring Boards

2000 ◽  
Vol 123 (1) ◽  
pp. 6-15 ◽  
Author(s):  
R. Venkatraman ◽  
K. Ramakrishna ◽  
K. Knadle ◽  
W. T. Chen ◽  
G. C. Haddon
Keyword(s):  
Failure Analysis ◽  
Stress Analysis ◽  
Failure Mechanism ◽  
Stress Testing ◽  
Large Strain ◽  
Peel Test ◽  
Stress Tests ◽  
Printed Wiring Boards ◽  
Element Analysis ◽  
Plated Through Hole

In multi-layer printed wiring boards (PWBs), electrical connections between different layers are accomplished with plated through holes (PTHs). The reliability of the PTH barrel and the PTH-inner plane (IP) connection depends not only on the design but also on the conditions of manufacturing and assembly processes of the board. The concerns associated with manufacturing arise from drilling which heats up and smears the surrounding epoxy onto the copper inner plane surfaces and also from subsequent chemical hole-clean operations which desmear the drilled holes. Good adhesion of the PTH copper to the desmeared PTH wall and to the copper inner planes is important for the reliability of the PTHs during assembly and field service. PWB coupons consisting of resin-glass bundle areas as well as resin filled clearance areas surrounding the PTH have been considered for a series of experiments and tests. On these coupons, accelerated stress tests and failure analysis of the PTHs at the end of these tests have been conducted. An elasto-plastic finite element analysis of the PTH strains for a temperature excursion of 102°C has been carried out for signal PTHs without and with IP connections. A peel test, using a micro-mechanical tester, has also been carried out to assess the adhesion of PTH copper to different regions along the drilled hole. All of the testing techniques have been supplemented by suitable analytical techniques for studying the distribution of smear on the copper inner planes. A birefringence technique to estimate the temperature of the hole wall during drilling has been described. All of the fails observed during stress testing are in the form of cracks in the PTH barrel, the plane of the crack being perpendicular to the barrel axis. The cracks are localized near the glass bundle-resin rich interface. It has also been observed in the failure analysis that the PTH/IP connections are not susceptible to failure during the accelerated stress testing conditions considered. These observations are also supported by the results of stress analysis. The results of stress analysis show that the interior clearance holes show higher strains than those closer to board surfaces, suggesting that the PTH barrel failure is likely to occur at the clearance hole and that the likelihood of failure at the interior clearance holes is higher than those closer to the PWB surfaces. The results of the peel test reveal that in the glass bundle-resin regions, the adhesion along the PTH wall is determined by the mechanical interlocking between the plated copper and the glass bundles and is relatively insensitive to desmear operations. However, adhesion in the resin-rich areas is a strong function of the desmear operation, which enhances the adhesion of the PTH to the resin. Finally, it is shown that the birefringence technique may be used effectively to estimate the drilling temperature and, hence, the degree of smearing and PTH quality. It is concluded that while smear may play an important role in the failure of PTHs in PWBs, for thick packaging boards with high aspect ratio PTHs, the predominant failure mechanism is less likely to be smear related. Such a failure mechanism would be preceded by failure in the PTH barrels as a result of the large strain concentrations imposed at specific locations within the cross-section.

Experimental Analysis of Thermal Cycling Fatigue of Four-Layered FR4 Printed Wiring Boards

1994 ◽  
Vol 116 (2) ◽  
pp. 76-82 ◽  
Author(s):  
Tsung-Yu Pan ◽  
Ronald R. Cooper ◽  
Howard D. Blair ◽  
Thomas J. Whalen ◽  
John M. Nicholson
Keyword(s):  
Thermal Cycling ◽  
Electrical Resistance ◽  
Crack Model ◽  
Electronic Packages ◽  
Printed Wiring Boards ◽  
Element Analysis ◽  
Mechanics Model ◽  
Plated Through Hole ◽  
Thermal Cycling Fatigue ◽  
Factor Interactions

Long-term reliability of electronic packaging has become a greater challenge as a result of ever increasing power requirements and the decreasing size of electronic packages. In this study, the effects of three variables on plated-through hole (PTH) design have been investigated on the thermal cycling fatigue lives in four-layered printed wiring boards (PWB’s). These three variables were evaluated at two levels each: (a) hole size (0.030 and 0.040 in.), (b) internal pad (presence or absence), and (c) epoxy-plugged holes (plugged or unplugged). The electrical resistance was measured on 40 test boards with 23 design of 8 daisy-chain PTH nets each. Full factorial analysis and analysis of variance indicate that all three factors had significant influence on PTH fatigue life, but no two-factor or three-factor interactions were found. Metallurgical analysis reveals that the failure mechanism is barrel cracking near the internal pad. This mechanism has been illustrated by a finite element analysis in this study and correlated by a SEM stereoimaging analysis in the literature. The increase of electrical resistance with thermal cycles correlates well with an analytical barrel crack model. The crack length in each net at specific cycles is calculated, but fails to match predictions from a fracture mechanics model.

Failure Analysis of Weld Repaired Turbine Rotor

2004 ◽  
Author(s):  
Fred V. Ellis ◽  
Blaine W. Roberts
Keyword(s):  
Weld Metal ◽  
Failure Analysis ◽  
Stress Analysis ◽  
Failure Mechanism ◽  
Turbine Rotor ◽  
Weld Bead ◽  
Design Stage ◽  
Weld Repair ◽  
Fracture Appearance ◽  
Product Forms

The first stage of an IP turbine rotor failed after approximately eight years of service. The rotor had been weld repaired using a 360 degree all weld metal buildup. The rotor material was specified as ASTM A-470 Class 8, 1Cr-1Mo-1/4V forging material, and the weld metal was Modified 9Cr-1Mo known as Grade 91 in the wrought product forms. The weld repair procedure used a controlled weld bead deposition process to refine the grain size of the HAZ. A failure analysis was performed including metallurgical examination and stress analysis. For the failure analysis, the primary features of interest were the fracture appearance, cracking/failure location, and failure mechanism. The fracture appearance was “lack of fusion” where the fracture surface nominally conforms to the weld bead shape. The primary cracking and failure was located at the fusion interface of the weld repair. The failure mechanism was creep rupture. Based on the thermal and stress analysis, the probable root cause of failure was improper location of the weld fusion line during the design stage. Both the operating stress and temperature were higher than design. The operating temperature was higher than the design temperature because of the lower cooling of the rotor experienced in service than predicted. Thus, the HAZ was located at a radial position having higher than allowable temperatures and stresses for the creep weak HAZ.

Residual Photoresist Identified as Cause for Frequency-Dependent Signal-to-Noise Failure After Autoclave Stress Testing

1999 ◽  
Author(s):  
Martin J. McVeigh
Keyword(s):  
Failure Analysis ◽  
Failure Mechanism ◽  
Failure Mode ◽  
High Speed ◽  
Stress Testing ◽  
Signal To Noise ◽  
Analysis Techniques ◽  
Dependent Signal ◽  
Voltage Swing ◽  
Maximum Voltage

Abstract A case history is presented for the failure analysis of a 0.5u CMOS A/D converter in which high fallout occurred after autoclave stressing. The observed failure mode of degraded signal-to-noise distortion (SINAD) ratio (measured in dB) was found to affect devices within a specific bandwidth centered around 5MHz. From a circuit designer’s viewpoint, an explanation for this unique failure mode did not readily present itself. Yet, using straightforward failure analysis techniques, involving laser ablation of photoresist and selective etching of passivation, the specific failing circuit block was isolated. Crosssectional analysis, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) found evidence of residual photoresist at topography related voids in the nitride passivation layer. The photoresist reacts with moisture in the autoclave, resulting in increased capacitance at minimum-spaced top layer metal lines. This failure mechanism correlates with the observed maximum SINAD degradation around 5MHz: at this frequency the signals along the affected metal lines are at their maximum voltage swing. This failure mechanism is potentially an issue for any similar high-speed, high-resolution designs.

Case Study in Fault Isolation of a Metal Short for Yield Enhancement

2010 ◽  
Author(s):  
Sarven Ipek ◽  
David Grosjean
Keyword(s):  
Failure Analysis ◽  
Failure Mechanism ◽  
Photon Emission ◽  
Fault Isolation ◽  
Yield Enhancement ◽  
Analysis Technique ◽  
Laser Signal ◽  
Signal Injection ◽  
Microscopy Techniques

Abstract The application of an individual failure analysis technique rarely provides the failure mechanism. More typically, the results of numerous techniques need to be combined and considered to locate and verify the correct failure mechanism. This paper describes a particular case in which different microscopy techniques (photon emission, laser signal injection, and current imaging) gave clues to the problem, which then needed to be combined with manual probing and a thorough understanding of the circuit to locate the defect. By combining probing of that circuit block with the mapping and emission results, the authors were able to understand the photon emission spots and the laser signal injection microscopy (LSIM) signatures to be effects of the defect. It also helped them narrow down the search for the defect so that LSIM on a small part of the circuit could lead to the actual defect.

Unique Autoclave Stress Induced Failure Mechanism

2005 ◽  
Author(s):  
John Butchko ◽  
Bruce T. Gillette
Keyword(s):  
Corrosion Rate ◽  
Grain Boundary ◽  
Failure Analysis ◽  
Failure Mechanism ◽  
Metal Corrosion ◽  
Corrosion Mechanism ◽  
Reliability Testing ◽  
Process Change ◽  
Transistor Reliability ◽  
Pass Through

Abstract Autoclave Stress failures were encountered at the 96 hour read during transistor reliability testing. A unique metal corrosion mechanism was found during the failure analysis, which was creating a contamination path to the drain source junction, resulting in high Idss and Igss leakage. The Al(Si) top metal was oxidizing along the grain boundaries at a faster rate than at the surface. There was subsurface blistering of the Al(Si), along with the grain boundary corrosion. This blistering was creating a contamination path from the package to the Si surface. Several variations in the metal stack were evaluated to better understand the cause of the failures and to provide a process solution. The prevention of intergranular metal corrosion and subsurface blistering during autoclave testing required a materials change from Al(Si) to Al(Si)(Cu). This change resulted in a reduced corrosion rate and consequently prevented Si contamination due to blistering. The process change resulted in a successful pass through the autoclave testing.

Investigation of High Frequency Failures on a 0.35μm CMOS IC

1999 ◽  
Author(s):  
Alan Kennen ◽  
John F. Guravage ◽  
Lauren Foster ◽  
John Kornblum
Keyword(s):  
Failure Analysis ◽  
Failure Mechanism ◽  
Integrated Circuit ◽  
Metal Layer ◽  
Ion Beam ◽  
Stress Test ◽  
Design For Test ◽  
Interface Failure ◽  
Serial Interface ◽  
High Impedance

Abstract Rapidly changing technology highlights the necessity of developing new failure analysis methodologies. This paper will discuss the combination of two techniques, Design for Test (DFT) and Focused Ion Beam (FIB) analysis, as a means for successfully isolating and identifying a series of high impedance failure sites in a 0.35 μm CMOS design. Although DFT was designed for production testing, the failure mechanism discussed in this paper may not have been isolated without this technique. The device of interest is a mixed signal integrated circuit that provides a digital up-convert function and quadrature modulation. The majority of the circuit functions are digital and as such the majority of the die area is digital. For this analysis, Built In Self Test (BIST) circuitry, an evaluation board for bench testing and FIB techniques were used to successfully identify an unusual failure mechanism. Samples were subjected to Highly Accelerated Stress Test (HAST) as part of the device qualification effort. Post-HAST electrical testing at 200MHz indicated that two units were non-functional. Several different functional blocks on the chip failed electrical testing. One part of the circuitry that failed was the serial interface. The failure analysis team decided to look at the serial interface failure mode first because of the simplicity of the test. After thorough analysis the FA team discovered increasing the data setup time at the serial port input allowed the device to work properly. SEM and FIB techniques were performed which identified a high impedance connection between a metal layer and the underlying via layer. The circuit was modified using a FIB edit, after which all vectors were read back correctly, without the additional set-up time.

Failure and Stress Analysis of Cu TSVs Using GHz-Scanning Acoustic Microscopy and Scanning Infrared Polariscopy

2015 ◽  
Author(s):  
Ingrid De Wolf ◽  
Ahmad Khaled ◽  
Martin Herms ◽  
Matthias Wagner ◽  
Tatjana Djuric ◽  
...  
Keyword(s):  
Failure Analysis ◽  
Stress Analysis ◽  
Rayleigh Waves ◽  
Acoustic Microscopy ◽  
Scanning Acoustic Microscopy ◽  
Through Silicon Vias ◽  
Stress Anisotropy ◽  
Silicon Vias ◽  
Ic Technology ◽  
Detection Of Defects

Abstract This paper discusses the application of two different techniques for failure analysis of Cu through-silicon vias (TSVs), used in 3D stacked-IC technology. The first technique is GHz Scanning Acoustic Microscopy (GHz- SAM), which not only allows detection of defects like voids, cracks and delamination, but also the visualization of Rayleigh waves. GHz-SAM can provide information on voids, delamination and possibly stress near the TSVs. The second is a reflection-based photoelastic technique (SIREX), which is shown to be very sensitive to stress anisotropy in the Si near TSVs and as such also to any defect affecting this stress, such as delamination and large voids.

scholarly journals Stress testing reveals gaps in clinic readiness of image-based diagnostic artificial intelligence models

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Albert T. Young ◽  
Kristen Fernandez ◽  
Jacob Pfau ◽  
Rasika Reddy ◽  
Nhat Anh Cao ◽  
...  
Keyword(s):  
Artificial Intelligence ◽  
Real World ◽  
Stress Testing ◽  
Operating Characteristic ◽  
Characteristic Curve ◽  
Skin Lesions ◽  
Stress Tests ◽  
Performance Metric ◽  
Intelligence Models ◽  
Artificial Intelligence Models

AbstractArtificial intelligence models match or exceed dermatologists in melanoma image classification. Less is known about their robustness against real-world variations, and clinicians may incorrectly assume that a model with an acceptable area under the receiver operating characteristic curve or related performance metric is ready for clinical use. Here, we systematically assessed the performance of dermatologist-level convolutional neural networks (CNNs) on real-world non-curated images by applying computational “stress tests”. Our goal was to create a proxy environment in which to comprehensively test the generalizability of off-the-shelf CNNs developed without training or evaluation protocols specific to individual clinics. We found inconsistent predictions on images captured repeatedly in the same setting or subjected to simple transformations (e.g., rotation). Such transformations resulted in false positive or negative predictions for 6.5–22% of skin lesions across test datasets. Our findings indicate that models meeting conventionally reported metrics need further validation with computational stress tests to assess clinic readiness.

Finite Element Analysis of Drum on the New Type Self-Driven Towing Machine for Cable

2011 ◽  
Vol 55-57 ◽  
pp. 664-669
Author(s):  
Jin Ning Nie ◽  
Hui Wang ◽  
De Feng Xie
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Stress Analysis ◽  
Compressive Stress ◽  
Wire Rope ◽  
Ansys Software ◽  
Element Analysis ◽  
Structure Improvement ◽  
Improvement Measures ◽  
New Type

According to the situation that the dual-friction drums on the new type towing machine lack stress analysis when designed, the safety is difficult to test and verify. The pull of wire rope in various positions was derived and calculated, so both compressive stress and tangent friction force generated by the pull of wire rope were calculated. The result made by ANSYS software demonstrates the safety of the left drum which suffers from larger loads, structure improvement measures are put forward for the drum.

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