Grid Array Research Articles

Study on Reliability of Lead-free mixed BGA Soldering Process for Application of Space-grade PBA

The purpose of this study is to confirm the effect of staking and underfilling for mounting PBGA(Plastic Ball Grid Array) packaged components on satellites. With the goal of developing a process that complies with ECSS (European Cooperation for Space Standardization) standards, the effect of staking and underfilling was analyzed in terms of vibration and thermal properties, and actual test specimens were fabricated and verified. After the environmental test, microsections were performed to confirm whether cracks had actually occurred, and the rate of change in resistance value was confirmed and compared with the analysis results.

Time-Lapse Imaging of Bismuth Precipitation and Coarsening on the Surface of Sn-Ag-Cu-Bi Solder Joints After Thermal Cycling

Abstract Adding bismuth to Sn-Ag-Cu solder compositions can significantly improve reliability in thermal cycling, but there are uncertainties in how bismuth precipitates and coarsens in Sn-Ag-Cu-Bi solders containing > 3 wt.% Bi. Here we apply time-lapse imaging in a scanning electron microscope to study bismuth precipitation and coarsening at room temperature on the polished surface of Sn-2.25-0.5Ag-6Bi ball grid array solder joints after thermal cycling. It is shown that (Bi) precipitates on the surface within 2 h after polishing and then coarsens by a combination of Ostwald ripening, coalescence ripening, and competition between two orientation relationships. Time-lapse imaging revealed that coalescence causes an increase in the local bismuth particle size and the formation of anomalously large (Bi) particles. The accumulation of bismuth on the polished surface increases far beyond the equilibrium volume fraction for this alloy. The bismuth particle size distributions are significantly wider than expected from Lifshitz–Slyozov–Wagner (LSW) theory, that assumes only Ostwald ripening, which is shown to be because coalescence creates anomalously large particles. This study shows the important role of bismuth precipitate coalescence within the coarsening mechanism in Sn-2.25-0.5Ag-6Bi solder joints.

Interpretable data-driven framework for life prediction of homogenous lead-free solder joints in ball grid array packages

Abstract Designing reliable electronic devices depends heavily on the reliability of solder joints. However, due to the ongoing advancement of novel lead-free solder materials, assessing their reliability for various applications, particularly in extreme conditions, often involves costly and time-consuming tests. Multiple factors, including board, package, assembly parameters, solder material properties, and process parameters, all affect the reliability of solder joints. Leveraging the available reliability test data as well as the simulated data, an interpretable data-driven framework is proposed by integrating linear mixed-effects (LME) models and artificial neural network (ANN) with sensitivity analysis to achieve accurate life predictions of solder materials and improve interpretability for understanding new lead-free materials. Multiple linear regression (MLR) and decision tree (DT) models have also been included for comparison. For thermal cycling (TC) tests, ANN, LME, and MLR achieve high prediction accuracy (R-squared values of 88.95%, 91.79%, and 90.07%, respectively), which are approximately 10%, 14%, and 13% higher than DT. Moreover, the interpretation derived from the random effects of LME and the sensitivity analysis of ANN, along with the insights from MLR and DT, successfully extract valuable information about the life of solder materials, which aligns with experimental testing results and empirical physics knowledge. For instance, it is found that the impact of aging duration on reliability depends on the configuration of the tested electronic package. Furthermore, as the temperature range of the TC test increases, the significance of the solder alloy material’s influence on reliability decreases. This reduction in relevance is associated with a transition to the failure mode under more extreme temperature conditions. Therefore, the interpretable data-driven framework not only models the complex relationships among influencing factors and solder joint reliability but also enables understanding the solder joint reliability. This framework can contribute to accelerating the design and adoption of new lead-free solder materials in various electronic applications and utilizing data-driven models to assess the reliability of electronic packages in future research.

Transformer-based neural speech decoding from surface and depth electrode signals

Objective.This study investigates speech decoding from neural signals captured by intracranial electrodes. Most prior works can only work with electrodes on a 2D grid (i.e. Electrocorticographic (ECoG) or ECoG array) and data from a single patient. We aim to design a deep-learning model architecture that can accommodate both surface ECoG and depth (stereotactic EEG or sEEG) electrodes. The architecture should allow training on data from multiple participants with large variability in electrode placements. The model should not have subject-specific layers and the trained model should perform well on participants unseen during training.Approach.We propose a novel transformer-based model architecture named SwinTW that can work with arbitrarily positioned electrodes by leveraging their 3D locations on the cortex rather than their positions on a 2D grid. We train subject-specific models using data from a single participant and multi-subject models exploiting data from multiple participants.Main results.The subject-specific models using only low-density 8 × 8 ECoG data achieved high decoding Pearson Correlation Coefficient with ground truth spectrogram (PCC = 0.817), overN= 43 participants, significantly outperforming our prior convolutional ResNet model and the 3D Swin transformer model. Incorporating additional strip, depth, and grid electrodes available in each participant (N= 39) led to further improvement (PCC = 0.838). For participants with only sEEG electrodes (N= 9), subject-specific models still enjoy comparable performance with an average PCC = 0.798. A single multi-subject model trained on ECoG data from 15 participants yielded comparable results (PCC = 0.837) as 15 models trained individually for these participants (PCC = 0.831). Furthermore, the multi-subject models achieved high performance on unseen participants, with an average PCC = 0.765 in leave-one-out cross-validation.Significance.The proposed SwinTW decoder enables future speech decoding approaches to utilize any electrode placement that is clinically optimal or feasible for a particular participant, including using only depth electrodes, which are more routinely implanted in chronic neurosurgical procedures. The success of the single multi-subject model when tested on participants within the training cohort demonstrates that the model architecture is capable of exploiting data from multiple participants with diverse electrode placements. The architecture's flexibility in training with both single-subject and multi-subject data, as well as grid and non-grid electrodes, ensures its broad applicability. Importantly, the generalizability of the multi-subject models in our study population suggests that a model trained using paired acoustic and neural data from multiple patients can potentially be applied to new patients with speech disability where acoustic-neural training data is not feasible.

Chiplets and Heterogeneous IC Packaging: Building Blocks and Tradeoffs

Chiplets-based IC packages have arrived. This year, many more customers are developing and qualifying their products at Amkor and in the outsourced semiconductor assembly and test (OSAT) and foundry space at large. The rationale for this surge into new multi-die embodiments has been well documented and discussed. In the final analysis, the chiplets approach has become the preferred alternative to large system on chip (SoC) designs. The chiplets approach often permits a better product performance, while lowering total silicon costs. This also enables more transistors in the package than an equivalent SoC, and most importantly, reuse flexibility that reduces time-to-market (TTM) for follow-on products. Heterogeneous IC packages are more expensive than traditional alternatives, for example a single-die Flip Chip ball grid array (FCBGA), but this increase is often offset by lower total silicon cost and the positive time-to-market benefits. However, moving to a heterogeneous approach requires a strong infrastructure to be established for: 1) design, 2) new IC and package structure development and fabrication techniques, and 3) electrical test. IC packaging options to support chiplets have now consolidated into just a few primary constructions that are being developed in the industry and entering early production. These package configurations are much simpler than the now-confusing terminology currently present in the industry. This presentation will review these constructions, simplify their attributes and provide some groundwork for doing the tradeoff analyses during the package construction evaluation and down-selection phase of a project. These higher density integration approaches create modules which integrate the die or chiplets that need ultra fine-line routing for die-die interfaces. Today, these are: (a) modules based on silicon interposers – 2.5D Through Silicon Via (TSV), (b) modules based on High-Density Fan-Out (HDFO) multi-layer redistribution layer (RDL) approaches or (c) modules with bridges. Silicon die can be singular planar devices or combinations using 3D die integration achieved with copper (Cu)-hybrid construction. 1. (c) Bridges (S-Connect) (RDL + Bridge(s)) In Amkor, 2.5D TSV with silicon interposers technology has been in high volume manufacturing (HVM) since 2017. HDFO packaging is internally qualified and currently being qualified for multiple customer products.

Comparison of the Reliability of SAC305 and Innolot-Based Solder Alloy in a Board-Level BGA Package Considering Harmonic and Random Vibration Environment

This paper presents a comparative study of the fatigue life of solder joints in a board-level Ball Grid Array (BGA) assembly. It specifically contrasts the commonly used SAC305 alloy with the advanced Innolot-based solder alloy, recognized for its superior tensile strength. Through Finite Element Analysis (FEA), we simulate and predict the reliability of these solder joints under harmonic and random vibration conditions. Following the JEDEC (Joint Electronic Device Engineering Council) standards, two different board-level BGA assemblies are used for the analysis. In both assemblies, the dimensions of the substrate, molding compound, and solder balls remain identical; only the board dimensions are changed to observe how they affect stress in the solder joints. The results indicate that using Innolot raises the volume-averaged stress levels by more than 25% on larger boards and about 5% on smaller boards compared to SAC305. This increase in stress levels is due to the Innolot alloy having a less significant stiffening effect than SAC305, which results in higher stress levels under the same excitation conditions. While the stress in the Innolot-based solder joint is greater than that in the SAC305 joint under identical excitation conditions, the fatigue life of the Innolot joint is significantly higher than that of the SAC305 joint. The results show that the Innolot-based alloy exceeds the performance of SAC305, and that it is suitable for use as a solder alloy in extreme vibration conditions.

Ball Grid Array Package Intermittent Partial Connection Defect Analysis in DDR4 Data Channel

Ball Grid Array Package Intermittent Partial Connection Defect Analysis in DDR4 Data Channel

Miniaturization Potential of Additive-Manufactured 3D Mechatronic Integrated Device Components Produced by Stereolithography.

Three-dimensional Mechatronic Integrated Devices (3D-MIDs) combine mechanical and electrical functions, enabling significant component miniaturization and enhanced functionality. However, their application in high-temperature environments remains limited due to material challenges. Existing research highlights the thermal stability of ceramic substrates; yet, their reliability under high-stress and complex mechanical loading conditions remains a challenge. In this study, 3D-MID components were fabricated using stereolithography (SLA) 3D-printing technology, and the feasibility of circuit miniaturization on high-temperature-resistant resin substrates was explored. Additionally, the influence of laser parameters on resistance values was analyzed using the Response Surface Methodology (RSM). The results demonstrate that SLA 3D-printing achieves substrates with low surface roughness, enabling the precise formation of fine features. Electric circuits are successfully formed on substrates printed with resin mixed with Laser Direct Structuring (LDS) additives, following laser structuring and metallization processes, with a minimum conductor spacing of 150 µm. Furthermore, through the integration of through-holes (vias) and the use of smaller package chips, such as Ball Grid Array (BGA) and Quad Flat No-lead (QFN), the circuits achieve further miniaturization and establish reliable electrical connections via soldering. Taken together, our results demonstrate that thermoset plastics serve as substrates for 3D-MID components, broadening the application scope of 3D-MID technology and providing a framework for circuit miniaturization on SLA-printed substrates.

Influence and mechanism of ultrafast laser-textured Cu substrate on wetting behavior of SAC305 solder

Influence and mechanism of ultrafast laser-textured Cu substrate on wetting behavior of SAC305 solder

Exploring the extensive movements and home range of one of North America’s most mobile fish: the freshwater drum (Aplodinotus grunniens)

Freshwater drum Aplodinotus grunniens are a unique and ubiquitous freshwater species of the family Sciaenidae. Despite the species’ wide distribution and unique biogeography, life history, and behavior, surprisingly little is known about freshwater drum movement ecology. In this study, we use passive acoustic telemetry tags and a broad-scale gridded receiver array to track the interannual and seasonal movement of freshwater drum tagged in tributaries of the North and South Basins of Lake Winnipeg (Manitoba, Canada). First, tagged freshwater drum had lower survival in the south basin where higher fishing pressure is thought to be a cause of mortality. We found that freshwater drum in Lake Winnipeg are remarkably mobile, with mean monthly movement rates among the highest on record for any freshwater fish. In the spring, fish entered rivers prior to spawning. A few weeks later, most individuals moved into lake habitat where they made extensive lateral movements. Home range and hotspot analysis revealed seasonal and population-specific patterns of occupancy, with elevated densities in lake habitat during the ice-on period and dispersed distributions during open water. Both populations remained almost exclusively in their respective rivers and basins. Homing and site fidelity were apparent, with nearly all fish returning to their original tagging river during each successive spawning season. The results bolster the existing information on freshwater drum movement ecology and may help enhance conservation and management strategies, particularly toward addressing commercial bycatch.

Finite element simulation and experimental study of the coupling acoustic field characteristics of ultrasonic waves with internal defects inside microelectronic packaging

Finite element simulation and experimental study of the coupling acoustic field characteristics of ultrasonic waves with internal defects inside microelectronic packaging

Comparative study of machine learning method and response surface methodology in BGA solder joint parameter optimization

PurposeBall grid array (BGA) package is prone to failure issues in a thermal vibration-coupled environment, such as deformation and fracture of solder joints. To predict the minimum equivalent stress of solder joints more accurately and optimize the solder joint structure, this paper aims to compare the machine learning method with response surface methodology (RSM).Design/methodology/approachThis paper introduced a machine learning algorithm using Grey Wolf Optimization (GWO) Support Vector Regression (SVR) to optimize solder joint parameters. The solder joint height, spacing, solder pad diameter and thickness were the design variables, and minimizing the equivalent stress of solder joint was the optimization objective. The three dimensional finite element model of the printed circuit board assembly was verified by a modal experiment, and simulations were conducted for 25 groups of models with different parameter combinations. The simulation results were employed to train GWO-SVR to build a mathematical model and were analyzed using RSM to obtain a regression equation. Finally, GWO optimized these two methods.FindingsThe results show that the optimization results of GWO-SVR are closer to the simulation results than those of RSM. The minimum equivalent stress is decreased by 8.528% that of the original solution.Originality/valueThis study demonstrates that GWO-SVR is more precise and effective than RSM in optimizing the design of solder joints.

Preparation and Performance Study of Thermally Conductive Silicone Adhesive Applying in Flip Chip Ball Grid Array

A thermally conductive silicone adhesive UB-5715 was prepared using vinyl silicone oil of medium viscosity, hydrogen-containing silicone oil and micron alumina powder. The results revealed that UB-5715 demonstrated superior thermal and mechanical properties. Specifically, its thermal decomposition temperature exceeded 400 °C, the thermal conductivity coefficient surpassed 1.80 W/m·K, the thermal resistance was under 12.0 °C·cm2/W, the shear strength reached achieved was over 5.00 MPa. Meanwhile, after being subjected to uHAST for 384 hours, thermal cycle for 1000 times and heat aging for 1000 hours respectively, UB-5715 still maintained its high thermal conductivity coefficient and mechanical properties. The thermal conductivity coefficient still exceeded 1.70 W/m·K, shear strength still surpassed 5.00 MPa, the tensile modulus remained below 100 MPa, the linear expansion coefficient was less than 160 ppm/°C, and its comprehensive performance met the reliability requirements for advanced packaging process substrates and heat dissipation cover assemblies.

Fatigue life prediction of BGA solder joint of several alloy compositions under an isothermal harmonic vibration

To ensure durable performance and optimal function of electronic components, it is crucial to guarantee their reliability, robustness and goodness of fit. The solder joints used in the BGA (Ball Grid Array) component play an intrinsic role in the reliability of the system. The vibration present in BGA triggers fatigue in solder joints, which raises a major reliability problem in various sectors such as aerospace, automotive and military industries. This study handles the response to a harmonic vibration at three specific temperatures (−40°C, 25°C, and 125°C) for four types of solder alloys in BGA Soldering. Within this framework, predicting the fatigue life of BGA solder joints with various alloy compositions under the influence of an isothermal harmonic vibration emerges as a crucial challenge in the design as well as reliability of modern electronic devices. The investigated solder compositions are SAC105, SAC305, SAC405, and InnoLot. To simulate and analyze the behavior of solder joints, we used the Ansys APDL finite element analysis (FEA). At both 125°C and −40°C, the Von Mises values proved to exceed those observed at 25°C. Likewise, an S-N curve for InnoLot and the different SACs, under a harmonic vibration at 25°C, was fitted using the Basquin power law relationship. As far as the current research work is concerned, an initial comparison was enacted between InnoLot and SAC alloys under an isothermal harmonic vibration, aiming to ascertain the most reliable alloy. The fatigue life under a harmonic vibration loading at 25°C was estimated. The results revealed that under a harmonic vibration at 25°C, the InnoLot solder displayed the longest lifespan, while the SAC105 solder exhibited the shortest fatigue life.

Effect of filer content on the thermal characteristics of underfill materials for Ball-Grid-Array component package

Effect of filer content on the thermal characteristics of underfill materials for Ball-Grid-Array component package

A High-Gain, High-Efficiency Transparent and Flexible Antenna for Vehicular Communication

A high-gain high-efficiency flexible and transparent film antenna in millimeter-wave is proposed in this paper. Comb structure which can be regarded as developed from the grid array structure is employed to mitigate the loss of the feeding network caused by the lossy metal mesh. The gain of the antenna has low sensitivity to the sheet resistance, which is promising in developing large-scale and high-performance transparent antenna. A large-scale ([Formula: see text]@28[Formula: see text]GHz) antenna is designed and fabricated using transparent metal mesh film with sheet resistance of 0.1[Formula: see text][Formula: see text]/sq and a thin PET film substrate. Bending measurement shows the antenna has excellent mechanical flexibility. A peak gain of 15.92[Formula: see text]dBi, radiation efficiency of 65.1%, optical transparency of 84% and 1,000-times bending are obtained. To the best of our knowledge, it is the highest gain and radiation efficiency flexible-transparent antenna reported thus far, which provides a glass-integrated antenna solution for vehicular communication.

Dendrite Growth in Single-Grain and Cyclic-Twinned Sn–3Ag–0.5Cu Solder Joints

The microstructure of electronic solder joints is generated by the solidification of a small volume of bulk undercooled liquid. Here, we study β-Sn dendrite growth in Sn–3Ag–0.5Cu in the specific geometry and nucleation conditions of ball grid array (BGA) solder joints by combining electron backscatter diffraction and imaging of microstructures. It is shown that, while ⟨110⟩\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\langle 110\\rangle$$\\end{document} is the preferred dendrite growth direction, out-of-plane branching and growth with ⟨11W⟩\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\langle 11W\\rangle$$\\end{document} directions are important for allowing dendrites to fan out into the spheroidal volume of BGA joints due to the low symmetry of β-Sn. We find that the crystallographic orientation of β-Sn at the nucleation point plays a strong role in subsequent dendrite growth. In single-grain joints, dendrites are often unfavorably oriented for growth, resulting in different types of zig-zag dendrite growth. In cyclic-twinned joints, it is shown how competitive out-of-plane trunk growth between three dendrite orientations produces {101} boundaries and the characteristic beachball microstructure.

Single-Layer and Wideband Filtering Antenna With Small Footprint Based on Nonuniform Grid Array

Single-Layer and Wideband Filtering Antenna With Small Footprint Based on Nonuniform Grid Array

Analysis of BGA Lead-Free solder joints failure behavior based on thermal shock testing

Analysis of BGA Lead-Free solder joints failure behavior based on thermal shock testing

Enhanced Mechanical Properties with Ag Addition in Electroplated Ni-Sn Solder Joints: Sub-10 Micron Bond Thickness

Keywords: Micro-bump; Microstructure; Intermetallic compounds; Mechanical properties; thermocompression bondingThe advancement of electronic devices has garnered more extensive attention towards three-dimensional integrated circuit (3D-IC) technology due to microbump size reduction and increased power density. Microbumps play an important role in driving the development of this technology, especially in 3D chip-stacking involving multiple reflow processes. The reduction in microbump height spotlights the presence of intermetallic compounds (IMCs). In comparison to traditional ball grid array (BGA) solder joints, microbumps with smaller solder volumes exhibit a predominant fraction of IMCs at solder joints, especially with microbump dimensions potentially shrinking to less than 10 micrometers.The interface reaction within confined spaces has become a critical concern. Mechanical properties will be dominated by IMC properties rather than solder characteristics. In conventional Cu/Sn/Cu solder joints, grain coarsening and prolonged reflowing times, which result in IMC collisions from opposing substrates, forming columnar grains with a uniform orientation, make the solder joint less reliable. Furthermore, the Cu3Sn layer in Cu/Sn/Cu microbumps presents another challenges, indicating the formation of Kirkendall voids, increasing the risk of brittle interface fractures.This study investigates the mechanical reliability and microstructure of two sub-10um sandwiched structures: Cu/Ni/Sn/Ni/Cu and Cu/Ni/Sn-3.5Ag/Ni/Cu. In the 3D-IC manufacturing process, solder joints will experience multiple reflow processing. Different reflow heat treatment process to achieve different fractions of Ni3Sn4 IMCs were performed on both sandwiched structure. Despite the formation of internal voids due to volume shrinkage in Ni/Sn solder joints, the addition of silver in the solder, forming Ag3Sn, effectively fills these voids. The long-time reflowed sample showed outstanding mechanical properties via the addition of silver in solder. In this study, the influence of silver addition on the microstructure and mechanical properties of the overall joints under identical reflow conditions, the fracture path observation after shear test were investigated. The growth mechanism of Ag3Sn and its distribution in the solder would be further explored and addressed. Figure 1