Solder Joint Reliability Risk Estimation by AI-Assisted Simulation Framework with Genetic Algorithm to Optimize the Initial Parameters for AI Models

Solder joint fatigue is one of the critical failure modes in ball-grid array packaging. Because the reliability test is time-consuming and geometrical/material nonlinearities are required for the physics-driven model, the AI-assisted simulation framework is developed to establish the risk estimation capability against the design and process parameters. Due to the time-dependent and nonlinear characteristics of the solder joint fatigue failure, this research follows the AI-assisted simulation framework and builds the non-sequential artificial neural network (ANN) and sequential recurrent neural network (RNN) architectures. Both are investigated to understand their capability of abstracting the time-dependent solder joint fatigue knowledge from the dataset. Moreover, this research applies the genetic algorithm (GA) optimization to decrease the influence of the initial guessings, including the weightings and bias of the neural network architectures. In this research, two GA optimizers are developed, including the “back-to-original” and “progressing” ones. Moreover, we apply the principal component analysis (PCA) to the GA optimization results to obtain the PCA gene. The prediction error of all neural network models is within 0.15% under GA optimized PCA gene. There is no clear statistical evidence that RNN is better than ANN in the wafer level chip-scaled packaging (WLCSP) solder joint reliability risk estimation when the GA optimizer is applied to minimize the impact of the initial AI model. Hence, a stable optimization with a broad design domain can be realized by an ANN model with a faster training speed than RNN, even though solder fatigue is a time-dependent mechanical behavior.

Testing and analysis of solder joint reliability for BGA assembly under flexural loading

The solder joint reliability for BGA (Ball Grid Array) assembly is becoming a more concerned issue as these packages are featuring higher density interconnections, multiple functionality and higher speed combined with smaller size. The traditional test methods for second level PCBA (Printed Circuit Board Assembly) mechanical reliability monitor the electric resistance changes of Daisy chains in the test samples under 4-point bending. The method has been documented by Interconnecting and Packaging Electronic Circuits and Joint Electronic Devices Engineering Council in PC/JEDEC 9702 standard. The effectiveness of the test has been questioned when applied to the new lead-free soldered packages. Due to the failure mode shift from solder joinicopper pad interface cracking in Tin-lead PCBAs to pad-cratering cracking in leadfree packages, the electrical continuity monitoring becomes ineffective in detecting the interconneCt failure. On the other hand, the strain gauges recorded PCB strains during bend tests show little increase that would be indicative of an onset failure. This project applies Fiber Bragg Grating (FBG) strain sensors to detect the pad-cratering failure. FBO have been employed widely in different areas of engineering due to its advantages of small size, light weight and high sensitivity. In this project the FBG sensors are laid to the vicinity of the BGA substrate comers. By detecting and recording the solder joint fracture induced strain release, the onset of pad-cratering is explicitly revealed. The study has demonstrated that the FBG sensors are much more sensitive than electric resistance strain gauges in detecting the substrate strain release in BGA assembly 4-point bend testing due primarily to the sensor's much smaller geometric size. By placing the sensors very close to the comer solder joints, the new test obtains accurate strain information related to the first solder joint cracking. Furthermore, the recorded strain release enables the detecting, understanding and analysis of the critical load of the solder joint fracture, the brittle and ductile fractures and related strain relaxation phenomenon during the PBGA flexural loading, etc.

Testing and analysis of solder joint reliability for BGA assembly under flexural loading

The solder joint reliability for BGA (Ball Grid Array) assembly is becoming a more concerned issue as these packages are featuring higher density interconnections, multiple functionality and higher speed combined with smaller size. The traditional test methods for second level PCBA (Printed Circuit Board Assembly) mechanical reliability monitor the electric resistance changes of Daisy chains in the test samples under 4-point bending. The method has been documented by Interconnecting and Packaging Electronic Circuits and Joint Electronic Devices Engineering Council in PC/JEDEC 9702 standard. The effectiveness of the test has been questioned when applied to the new lead-free soldered packages. Due to the failure mode shift from solder joinicopper pad interface cracking in Tin-lead PCBAs to pad-cratering cracking in leadfree packages, the electrical continuity monitoring becomes ineffective in detecting the interconneCt failure. On the other hand, the strain gauges recorded PCB strains during bend tests show little increase that would be indicative of an onset failure. This project applies Fiber Bragg Grating (FBG) strain sensors to detect the pad-cratering failure. FBO have been employed widely in different areas of engineering due to its advantages of small size, light weight and high sensitivity. In this project the FBG sensors are laid to the vicinity of the BGA substrate comers. By detecting and recording the solder joint fracture induced strain release, the onset of pad-cratering is explicitly revealed. The study has demonstrated that the FBG sensors are much more sensitive than electric resistance strain gauges in detecting the substrate strain release in BGA assembly 4-point bend testing due primarily to the sensor's much smaller geometric size. By placing the sensors very close to the comer solder joints, the new test obtains accurate strain information related to the first solder joint cracking. Furthermore, the recorded strain release enables the detecting, understanding and analysis of the critical load of the solder joint fracture, the brittle and ductile fractures and related strain relaxation phenomenon during the PBGA flexural loading, etc.

Improving the Solder Joint Reliability Prediction Accuracy for Quad Flat No Lead Packages

This paper discusses the modeling approach used in improving the solder joint reliability prediction for Quad Flat No Lead (QFN) packages. A new power equation fatigue prediction model was developed based on the accumulated creep strain energy density from FEA (finite element analysis) simulation and the corresponding actual experimental result in terms of solder characteristic life of different QFN packages. The new curve fitted fatigue life correlation equation was then used in the solder joint reliability modeling together with the use of a hyperbolic sine constitutive model for lead-free solder. The model prediction using the new curve fitted equation was compared with the result from using the equation previously published. Based on the results, the new curve-fitted life prediction equation was able to improve the accuracy of solder life prediction. This study shows that solder joint reliability prediction could be improved by developing a prediction model based on actual data and consistent FEA modeling considerations in terms of methodology, material model and properties.

Thermal Cycling Test and Simulation of Fan-Out Chip-Last Panel-Level Packaging for Heterogeneous Integration

In this study, the reliability of the solder joints of a heterogeneous integration of one large chip (10 × 10 mm) and two smaller chips (7 × 5 mm) by a fan-out method with a redistribution layer-first substrate fabricated on a 515 × 510-mm panel is investigated. Emphasis is placed on the thermal cycling test (−55°C Δ 125°C, 50-min cycle) of the heterogeneous integration package on a printed circuit board (PCB). The thermal cycling test results are plotted into a Weibull distribution. The Weibull slope and characteristic life at median rank are presented. At 90% confidence, the true Weibull slope and the true 10% life interval are also provided. A linear acceleration factor is adopted to map the solder joint reliability at the test condition to the solder joint reliability at an operating condition. The failure location and failure mode of the PCB assembly of the heterogeneous integration package are provided and discussed. A nonlinear, time- and temperature-dependent 3-D finite element simulation is performed for the heterogeneous integration PCB assembly and correlated with the thermal cycling test results.