A review of board level solder joints for mobile applications

Solders based on Sn-Ag alloys are susceptible to microstructural coarsening during storage or service, resulting in evolution of joint properties, and hence reliability, over time. Coarsening can occur during static aging, and even faster during thermo-mechanical cycling (TMC). The kinetics of coarsening may also depend on the scale of the joint. These effects lead to evolution of the mechanical properties of the joint over time, as well as spatial variations of property within the joint. Therefore, accurate prediction of joint properties during service or storage requires a quantitative understanding of coarsening under both isothermal and TMC conditions, and incorporating these in constitutive laws. This paper discusses the kinetics of coarsening in Sn-Ag based solders, and presents a rationale for joint-scale dependence of coarsening. The impact of coarsening on creep and fracture properties of joints under drop conditions are also presented.

Microstructural coarsening in Sn-Ag-based solders and its effects on mechanical properties

The built-in stress test (BIST) is extensively used for diagnostics or identification of failure. The current version of BIST approach is focused on reactive failure detection and provides limited insight into reliability and residual life. A new approach has been developed to monitor product-level damage during shock and vibration. The approach focuses is on the pre-failure space and methodologies for quantification of failure in electronic equipment subjected to shock and vibration loads using the dynamic response of the electronic equipment. Presented methodologies are applicable at the system-level for identification of impending failures to trigger repair or replacement significantly prior to failure. Leading indicators of shock-damage have been developed to correlate with the damage initiation and progression in shock and drop of electronic assemblies. Three methodologies have been investigated for feature extraction and health monitoring including development of a new solder-interconnect built-in reliability test, FFT based statistical-pattern recognition, and time-frequency moments based statistical pattern recognition. The solder-joint built-in-reliability-test has been developed for detecting high-resistance and intermittent faults in operational, fully programmed field programmable gate arrays. Frequency band energy is computed using FFT and utilized as the classification feature to check for damage and failure in the assembly. In addition, the Time Frequency Analysis has been used to study of the energy densities of the signal in both time and frequency domain, and provide information about the time-evolution of frequency content of transient-strain signal. Closed-form models have been developed for the eigen-frequencies and mode-shapes of electronic assemblies with various boundary conditions and component placement configurations. Model predictions have been validated with experimental data from modal analysis. Pristine configurations have been perturbed to quantify the degradation in confidence values with progression of damage. Sensitivity of leading indicators of shock-damage to subtle changes in boundary conditions, effective flexural rigidity, and transient strain response have been quantified. Explicit finite element models have been developed and various kinds of failure modes have been simulated such as solder ball cracking, package falloff and solder ball failure. This allows the physical quantification of solder ball crack damage in the form of confidence values and provides a damage index that can be utilized for the health monitoring of solder interconnects in an electronic assembly.

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Statistical Pattern Recognition and Built-in Reliability Test for Feature Extraction and Health Monitoring of Electronics under Shock Loads

Structural damage to ball grid array interconnects incurred during vibration testing has been monitored in the prefailure space using resistance spectroscopy-based state space vectors, rate of change of the state variable, and acceleration of the state variable. The technique is intended for condition monitoring in high reliability applications where the knowledge of impending failure is critical and the risks in terms of loss of functionality are too high to bear. Future state of the system has been estimated based on a second-order Kalman Filter model and a Bayesian Framework. The measured state variable has been related to the underlying interconnect damage in the form of inelastic strain energy density. Performance of the prognostic health management algorithm during the vibration test has been quantified using performance evaluation metrics. The methodology has been demonstrated on leadfree area-array electronic assemblies subjected to vibration. Model predictions have been correlated with experimental data. The presented approach is applicable to functional systems where corner interconnects in area-array packages may be often redundant. Prognostic metrics including α - λ precision, β accuracy, and relative accuracy have been used to assess the performance of the damage proxies. The presented approach enables the estimation of residual life based on level of risk averseness.

Prognostics Health Management of Electronic Systems Under Mechanical Shock and Vibration Using Kalman Filter Models and Metrics

In this paper, the feature extraction for health monitoring based on optical measurements of transient-strain from digital image correlation (DIC) in conjunction with ultra high-speed imaging has been investigated. Full-field measurement of transient strain have been made in various board assemblies subjected to shock in various orientations. Feature-extraction for health monitoring of leadfree area array architectures based on statistical pattern recognition has been presented. Previous researchers have measured the transient-dynamics of board assemblies with high-speed imaging in conjunction with high-speed image analysis for measurement of relative displacement, angle, velocity, and acceleration [Lall 2006, Che 2006], high-speed data-acquisition systems with discrete strain gages [Lall 2004, 2005, Liang 2005] and with accelerometers for measurement of transient acceleration [Dunford 2004, Goyal 2000, Seah 2005]. Degradation in confidence value gives a leading indication of component failure. Package architectures examined include-flex ball-grid arrays, tape-array ball-grid arrays, and metal lead-frame packages. Statistical pattern recognition techniques including, mahalanobis- distance approach, wavelet packet energy decomposition, and time-frequency (TFA) techniques have been investigated for system identification, condition monitoring, and fault detection and diagnosis in electronic systems. Explicit finite element models have been developed and various kinds of failure modes have been simulated such as solder ball cracking, package fall off and solder ball failure. Models developed include, smeared property models, Timoshenko-beam models, and explicit sub-models. Explicit finite-element models have been correlated with experimental data. The presented approach does not depend on continuity and therefore does not need daisy-chained devices for detection of failure.

Feature extraction and health monitoring using image correlation for survivability of leadfree packaging under shock and vibration

Electronics may be subjected to shock, vibration, and drop-impact during shipping, handling and during normal usage. Measurement of transient dynamic deformation of the electronics assemblies during the shock and vibration can yield significant insights in understanding the occurrence of failure modes and the development of failure envelopes. Failure-modes include solder-joint failures, pad cratering, chip-cracking, copper trace fracture, and underfill fillet failures. Previous researchers have measured the transient-dynamics of board assemblies with high-speed imaging in conjunction with high-speed image analysis for measurement of relative displacement, angle, velocity, and acceleration [Lall 2006, Che 2006]. In addition, high-speed data-acquisition systems with discrete strain gages have been used for measurements of transient strain [Lall 2004, 2005, Liang 2005] and with accelerometers for measurement of transient acceleration [Dunford 2004, Goyal 2000, Seah 2005]. Development of accurate models requires better understanding of full-field strain deformation in board assemblies. In this paper, the use of digital image correlation (DIC) with ultra high-speed imaging has been used for full-field measurement of transient strain in various board assemblies subjected to shock in various orientations. Measurements have been taken on both the package and the board side of the assemblies. Accuracy of high-speed optical measurement has been compared with that from discrete strain gages. Package architectures examined include flex ball-grid arrays, tape-array ball-grid arrays, and metal lead-frame packages. Explicit finite-element models have been developed and correlated with experimental data. Models developed include, smeared property models, Timoshenko-beam models, and explicit sub-models. The solder strains have been computed from the explicit finite element models for life prediction in shock.

High Speed Digital Image Correlation for Transient-Shock Reliability of Electronics

In this paper, the feature extraction for health monitoring based on optical measurements of transientstrain from digital image correlation (DIC) in conjunction with ultra high-speed imaging has been investigated. Full-field measurement of transient strain have been made in various board assemblies subjected to shock in various orientations. Feature-extraction for health monitoring of leadfree area array architectures based on statistical pattern recognition has been presented. Previous researchers have measured the transient-dynamics of board assemblies with high-speed imaging in conjunction with high-speed image analysis for measurement of relative displacement, angle, velocity, and acceleration [Lall 2006, Che 2006], high-speed data-acquisition systems with discrete strain gages [Lall 2004, 2005, Liang 2005] and with accelerometers for measurement of transient acceleration [Dunford 2004, Goyal 2000, Seah 2005]. Degradation in confidence value gives a leading indication of component failure. Package architectures examined include-flex ball-grid arrays, tape-array ballgrid arrays, and metal lead-frame packages. Statistical Pattern Recognition Techniques including, mahalanobisdistance approach, wavelet packet energy decomposition, and time-frequency (TFA) techniques have been investigated for system identification, condition monitoring, and fault detection and diagnosis in electronic systems. Explicit finite element models have been developed and various kinds of failure modes have been simulated such as solder ball cracking, package fall off and solder ball failure. Models developed include, smeared property models, Timoshenko-beam models, and explicit sub-models. Explicit finite-element models have been correlated with experimental data. The presented approach does not depend on continuity and therefore does not need daisy-chained devices for detection of

Keynote Presentation Feature Extraction and Health Monitoring using Image Correlation for Survivability of Leadfree Packaging under Shock and Vibration

In this paper, a design-envelope approach based on optical feature extraction techniques has been investigated for drop and shock survivability of electronic packaging has been presented for 6-leadfree solder alloy systems. Solder alloy systems investigated include, Sn1Ag0.5Cu, Sn3Ag0.5Cu, Sn0.3Ag0.7Cu, Sn0.3Ag0.7Cu0.1Bi, Sn0.2Ag0.7Cu0.1Bi- 0.1Ni, 96.5Sn3.5Ag. Previously, digital image correlation (DIC) has been used for measurement of thermally-induced deformation and material-characterization. In this paper, DIC has been used for transient dynamic measurements, and optical feature extraction. Board assemblies have been subjected to shock-impact in various orientations including the JEDEC zero-degree drop and the vertical free-drop. Transient deformation has been measured using both digital image correlation and the strain gages. Measurements have been taken on both the package and the board side of the assemblies. Accuracy of high-speed optical measurement has been compared with that from discrete strain gages. Package architectures examined include-flex ball-grid arrays, tape-array ball-grid arrays, and metal lead-frame packages. Explicit finite-element models have been developed and correlated with experimental data. Models developed include, smeared property models, Timoshenko-beam models, and explicit sub-models. The potential of damage identification and tracking for various solder alloys has been investigated. Data on identification of damage proxies for competing failure mechanisms at the copper-to-solder, solder-to-printed circuit board, and copper-to-package substrate has been presented. Design envelopes have been developed based on statistical pattern recognition. The design-envelope is intended for component integration to ensure survivability in shock and vibration environments at a user-specified confidence level.

Design Envelopes and Optical Feature Extraction Techniques for Survivability of SnAg Lead-free Packaging Architectures Under Shock and Vibration

Electronics may be subjected to shock, vibration, and drop-impact during shipping, handling and during normal usage. Measurement of transient dynamic deformation of the electronics assemblies during the shock and vibration can yield significant insights in understanding the occurrence of failure modes and the development of failure envelopes. Failure-modes include solder-joint failures, pad cratering, chip-cracking, copper trace fracture, and underfill fillet failures. Previous researchers have measured the transient-dynamics of board assemblies with high-speed imaging in conjunction with high-speed image analysis for measurement of relative displacement, angle, velocity, and acceleration. In addition, high-speed data-acquisition systems with discrete strain gages have been used for measurements of transient strain and with accelerometers for measurement of transient acceleration. Development of accurate models requires better understanding of full-field strain deformation in board assemblies. In this paper, the use of digital image correlation (DIC) with ultra high-speed imaging has been used for full-field measurement of transient strain in various board assemblies subjected to shock in various orientations. Measurements have been taken on both the package and the board side of the assemblies. Accuracy of high-speed optical measurement has been compared with that from discrete strain gages. Package architectures examined include-flex ball-grid arrays, tape-array ball-grid arrays, and metal lead-frame packages. Explicit finite-element models have been developed and correlated with experimental data. Models developed include, smeared property models, Timoshenko-beam models, and explicit sub-models. The solder strains have been computed from the explicit finite element models for life prediction in shock.

D. Iyengar

Papers

Feature extraction and health monitoring using image correlation for survivability of leadfree packaging under shock and vibration

High Speed Digital Image Correlation for Transient-Shock Reliability of Electronics

Keynote Presentation Feature Extraction and Health Monitoring using Image Correlation for Survivability of Leadfree Packaging under Shock and Vibration

Design Envelopes and Optical Feature Extraction Techniques for Survivability of SnAg Lead-free Packaging Architectures Under Shock and Vibration

High Speed Digital Image Correlation for Transient-Shock Reliability of Electronics