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.

Determination of Anand Parameters From Creep Testing of SAC305 Solder Joints

Solder Joints are among the most vulnerable components within electronic packages, and solder joint fatigue is regarded to be one of the major methods of electronic package failure. The prediction of solder joint reliability is thus of great importance and most finite element packages utilize the Anand Viscoplastic Model to model the mechanical behavior of the solder joint material. In this work, 3 × 3 arrays of SAC305 solder joints of roughly 750 μm in diameter were reflowed in between two FR-4 printed circuit boards to create a sandwich structural sample. These samples were then subjected to creep testing in shear at various temperatures (T = 25, 50, 75, 100 °C) and stress levels (τ = 5, 10, and 15 MPa). A set of specially designed fixtures was used to grip the solder joint specimens. The nine Anand model constants were then extracted from the creep data. The Anand model predicted creep response curves were then compared with the experimental creep measurements to determine the accuracy of the model. The Anand model predictions were found to match the measured data very well over a wide range of temperatures and stress levels.

Additive Fabricated Compliant Interconnects: Design, Fabrication and Reliability Effects

Electronics packaging development is greatly dependent on the magnitude of interconnect and on-chip stress that ultimately limits the reliability of electronic components. Thermomechanical strains occur because of the coefficient of thermal expansion mismatch from different conjoined materials being assembled to manufacture a device. To curb the effect of thermal expansion mismatch, studies have been done in integrating compliant structures between dies, solder balls, and substrates. Initial studies have enabled the design and manufacturing of these structures using a photolithography approach which involves an increased number of fabrication steps depending on the complexity of the structures. This current study involves the fabrication of these structures using a different approach, utilizing additive manufacturing that reduces the number of fabrication steps required to obtain compliant geometries, while also providing a platform for unique compliant structures. This paper discusses the method of fabrication and analyzes the properties and effects of these interconnect structures on a die. Structural finite element thermal cycling simulations between −40 to 125°C show about a 115% increase in the solder joint fatigue life. Additionally, fabricated test structures created directly on a PCB were experimentally characterized for compliance using a micro-indenter tester, showing a mechanical compliance range of 265.95 to 656.78 μ/N for selected design parameters to be integrated into a test vehicle.

Influence of the Applied Load on the Creep Behaviour of Tin-Silver-Copper Solder

During the life cycle of an electronic printed circuit boards (PCBs), the cold solder joints formation between the component and PCB are a failure mode that happen commonly. This phenomenon is related to solder joint fatigue and is attributed mainly to the mismatch of the coefficients of thermal expansion (CTE) of component-solder-PCB assembly. With today’s solder joint thickness decreasing and increasing working temperatures, among others, the stresses and strains due to temperature changes are growing, leading to limited fatigue life of the products. In this way, once as fatigue life decreases with increasing plastic strain, it is important to study creep occurrence, especially during thermal cycles. In this work, a dynamic mechanical analyser (DMA) was used to study the influence of different applied load and temperature on the creep behaviour of the solder during a sequence of cycles. For these tests, different SAC405 alloy samples were produced, all in the same processing conditions. Creep tests were made on three-point-bending clamp configuration, isothermally at 303, 323 and 348 K, under three separate applied load of 3, 5 and 9 MPa. The results show that creep rate has an important decrease from the 1st to the following applied creep cycles. This behaviour occurs for all the tested loads and temperatures. Results, also, show that the main creep mechanisms changes, from a diffusion base type, for low load and different temperatures, to a dislocation glide-climb type for an applied load of 9 MPa and temperatures from 303 to 348 K. Experimental determined n exponent for the tested conditions allows the correlation between creep mechanisms and experimental parameters (applied load and temperature).

Modeling of Underfilled PBGA Assemblies Using Both Viscoelastic and Elastic Material Properties

In microelectronics packaging industry, polymer based materials are used extensively. These polymer materials show viscoelastic behavior when subject to time dependent loads or deformations. The viscoelastic behavior highly depends on both temperature and time. In many cases, these viscoelastic properties are often neglected due to saving computational cost or unavailability of full characterization of the viscoelastic properties. To make accurate predictions of packaging mechanical behavior and reliability, it is important to accurately characterize the viscoelastic behavior of mold compounds, underfill encapsulants, adhesives and other polymers used in electronic assemblies. After characterization, these parameters can be used as input material property data for finite element analysis (FEA) simulations. In this study, both frequency dependent dynamic mechanical analysis (DMA) measurements, and strain and temperature dependent stress relaxation experiments were performed on a typical underfill material in order to characterize its linear viscoelastic behavior. In both cases, a master curve was determined using the assumption of time-temperature equivalence, and Prony series expansions were utilized to model the underfill material relaxation behavior. After that, these viscoelastic underfill material parameters were used in finite element models of underfilled ball grid array packages (Ultra CSP) subjected to thermal cycling from −40 to 125 °C. Separate simulations were also performed using temperature dependent elastic properties for the underfill material. In both cases, the solder joint fatigue life was estimated, and the effects of using viscoelastic properties for the underfill in solder joint fatigue life simulation were investigated.

Probabilistic methodology for reliability assessment of electronic packages

In the mechatronic devices, the finite element analyses are the most used method to determine time-dependent solder joint fatigue response under accelerated temperature cycling conditions, the deterministic analyses are the most used methods. However, the design variables show variability and randomness which will affect the lifetime prediction quality. This paper focuses on solder joint reliability in tape-based chip-scale packages(CSP) with the consideration of uncertainties in material parameters.