Ball Grid Array Solder Joints Research Articles

Thermal fatigue life prediction and intermetallic compound behaviour of SAC305 BGA solder joints subject to accelerated thermal cycling test

PurposeThis study aims to investigate the thermal fracture mechanism of moisture-preconditioned SAC305 ball grid array (BGA) solder joints subjected to multiple reflow and thermal cycling.Design/methodology/approachThe BGA package samples are subjected to JEDEC Level 1 accelerated moisture treatment (85 °C/85%RH/168 h) with five times reflow at 270 °C. This is followed by multiple thermal cycling from 0 °C to 100 °C for 40 min per cycle, per IPC-7351B standards. For fracture investigation, the cross-sections of the samples are examined and analysed using the dye-and-pry technique and backscattered scanning electron microscopy. The packages' microstructures are characterized using an energy-dispersive X-ray spectroscopy approach. Also, the package assembly is investigated using the Darveaux numerical simulation method.FindingsThe study found that critical strain density is exhibited at the component pad/solder interface of the solder joint located at the most distant point from the axes of symmetry of the package assembly. The fracture mechanism is a crack fracture formed at the solder's exterior edges and grows across the joint's transverse section. It was established that Au content in the formed intermetallic compound greatly impacts fracture growth in the solder joint interface, with a composition above 5 Wt.% Au regarded as an unsafe level for reliability. The elongation of the crack is aided by the brittle nature of the Au-Sn interface through which the crack propagates. It is inferred that refining the solder matrix elemental compound can strengthen and improve the reliability of solder joints.Practical implicationsInspection lead time and additional manufacturing expenses spent on investigating reliability issues in BGA solder joints can be reduced using the study's findings on understanding the solder joint fracture mechanism.Originality/valueLimited studies exist on the thermal fracture mechanism of moisture-preconditioned BGA solder joints exposed to both multiple reflow and thermal cycling. This study applied both numerical and experimental techniques to examine the reliability issue.

Shock fatigue damage failure boundary study of BGA solder joints based on shock response spectrum

Multiple shock damage failure of ball grid array (BGA) solder joints is one of the important reasons for reusable spacecraft mission failure. Shock fatigue damage failure boundary of BGA solder joints is proposed based on shock response spectrum (SRS), which can be used to assess the damage failure state. Weibull distribution is employed to characterize the shock fatigue life for a specified SRS. A Bayesian estimation method based on the Bootstrap approach is proposed to estimate Weibull distribution parameters. By using the time-domain load synthesized method based on wavelet and the experimentally validated shock fatigue life model, the shock fatigue life data of BGA solder joints corresponding to different SRS are extended. The variation patterns of the scale and shape parameters with the SRS parameters is analyzed. Then the shock fatigue damage failure boundary based on SRS is determined for a given design life and reliability. The results show that the critical SRS amplitude increase with the rise of the inflection point frequency and the low-frequency slope, respectively. The developed method is expected to provide references for the environment-adaptive design of BGA solder joints in reusable spacecraft.

Optimization of the Boundary Conditions of a Board Level Reliability Test Board to Maximize the Fatigue Life of Ball Grid Array Solder Joints under Thermal Cycling and Random Vibration.

We investigated the screw hole position of a board level reliability (BLR) test board to improve the fatigue reliability of solder joints under thermal cycling and random vibration. We developed a finite element model of a BLR test board and derived the plastic strain energy density and 1-sigma stress, which are the main parameters influencing the fatigue life of solder joints under thermal cycling and random vibration, respectively. We analyzed the correlation between the screw hole position and the main parameters of the fatigue life through sensitivity analysis. By performing multi-objective optimization, we determined the screw hole position that maximizes the fatigue life of solder joints under thermal cycling and random vibration. With the optimal screw hole position, the fatigue life significantly increased under thermal cycling and random vibration compared to the BLR test board with the initial screw hole position.

Bonding Property of Middle Temperature Sn-Ag-Cu Solder Ball Joint of Ball Grid Array Package

Alloying effects of Nickel and Bismuth in SAC solder to achieve mechanical and microstructural evolution were investigated by comparing three different chemical composition of solders. Sn-3.0Ag-0.5Cu (SAC305) is the most commonly used for Pb-free solder and solder balls are based on Sn-Ag-Cu alloy composition. Compositions of solder balls were Sn-3.0Ag-0.5Cu (SAC305), Sn-1.2Ag-0.5Cu-0.05Ni (SAC1205N) and Sn-Ag-Cu-Ni-Bi based solder (SACNB). Organic solderability preservative (OSP) surface finished substrate, ball grid array (BGA) package arranged by 300 ㎛ diameter solder ball and Type 4 solder paste were used. Solder ball shear test of the BGA package was conducted before the reflow soldering. Board level package bonding process was carried out by hot air reflow soldering. Void content of the BGA solder joint was investigated after soldering. The microstructure evolution before and after thermal cycle test (TCT) was observed using scanning eletron microscopy (SEM) and energy dispersive spectroscopy (EDS). After TCT, intermetallic compound (IMC) refinement and solid solution strengthening effects of Bi element addition were observed in the solder matrix, and also any segregation of Bi element was not founded. Based on these result, it was found that the solder joint reliability of the middle and low temperature solder joints was improved.

Effect of gamma irradiation on microstructural evolution and mechanical properties of SnPb eutectic solder joints

Eutectic SnPb ball grid array (BGA) solder joints were exposed to 60Co source gamma irradiation at a dose rate of 1 Gy(Si)/s from 0, 50, 100, 150 and 200 h in air. The effects of gamma irradiation on the microstructure evolution and mechanical properties of the solder joints were investigated. After irradiation, β-Sn and Pb on the surface of the solder joint was oxidized to SnO2, PbO and PbO2, and an oxide layer covered with Cu oxide was formed on the surface of the solder joint. The formation process and mechanism of the oxide layer were analyzed. Sn and Pb depletion holes and Cu depletion areas appeared on the solder joint surfaces after various irradiation time. SnO2 nanocrystals and Sn wrinkles appeared in the FIB specimen after irradiation. After 200 h of irradiation, the melting temperature of the SnPb eutectic solder alloy decrease, and the shear force value of the solder joint first increase and then decrease.

Enhancing ball grid array (BGA) component design and reliability using a novel reliability-based design optimization (RBDO) methodology

In industry and research areas, the importance of reliable and optimally designed BGA components has remarkably grown. To tackle this challenge, we elaborated an innovative approach that optimizes of the BGA’s structure. By adopting the RBDO method, we assess the geometric design variables of the BGA component and determine the optimal variables that promote the structure’s efficiency level. Our approach considers technical and economic feasibility, ensuring an optimal design of the BGA solder joints. This work rests upon coupling Ansys and MATLAB software. The current paper reports our investigation’s results, highlighting our approach’s benefits and potential for practical applications.

A novel shock life model for BGA solder joints based on evolutionary power spectral density

Multiple shock damage of Ball grid array (BGA) solder joint is one of the important reasons for space mission failure. A novel shock life model is proposed for BGA solder joints to evaluate its life under shock loads based on the evolutionary power spectral density (EPSD). Considering the bandwidth and non-Gaussian features of the stress signals during different stages, the shock stress response was treated as a non-stationary and non-Gaussian stochastic process. EPSD of the shock stress response is derived in matrix form based on wavelet transforms. The weight coefficient and non-Gaussian damage factor are proposed to describe the influence of the bandwidth and non-Gaussian characteristics of shock response on fatigue damage, respectively. The damage values of different stress stages were calculated by weight coefficient and corrected using non-Gaussian damage factor. Then the shock life model is proposed based on damage accumulation theory. Tests for the BGA solder joints shock life were conducted, and the result shows that the proposed model is feasible. Therefore, the developed method in the paper is expected to provide reference for the prediction of BGA solder joint shock life in aerospace engineering.

Thermomigration-induced failure in ball grid array solder joint under high current stressing

Thermomigration-induced failure in ball grid array solder joint under high current stressing

TEM and EBSD characterization revealing the recrystallization process occurring in the Sn-3.0Ag-0.5Cu Ball Grid Array solder joints during thermal cycling

TEM and EBSD characterization revealing the recrystallization process occurring in the Sn-3.0Ag-0.5Cu Ball Grid Array solder joints during thermal cycling

Optimal performance and cost-effective design of BGA solder joints using a deterministic design optimization (DDO) under real operating conditions

Users of electronic devices expect efficiency, affordability, and long service life. From this perspective, the optimization of their performance while reducing costs is paramount. The objective of this paper is to find the best compromise between minimizing the volume and thus cost, and preserving the efficiency of the component. This work is based on coupling the finite element model on Ansys with an optimization algorithm on MATLAB. First, fatigue analysis tests were simulated to determine the geometric design variables' sensitivity, having an impact on the service life, then these variables are incorporated into the Deterministic Design Optimisation (DDO) loop. This efficient approach is used to identify the optimal configuration of the BGA (Ball Grid Array) component to increase operational life and efficiency under electro-thermomechanical conditions. The elaborated method constitutes a great impetus for electronic industries and researchers to successfully find the best combination of cost reduction and performance increase, allowing improved design.

Characterising Solder Materials from Random Vibration Response of Their Interconnects in BGA Packaging

Solder interconnection in electronic packaging is the weakest link, thus driving the reliability of electronic modules and systems. Improving interconnection integrity in safety-critical applications is vital in enhancing application reliability. This investigation qualifies the random vibration response of five essential solder compositions in ball grid array (BGA) solder joints used in safety-critical applications. The solder compositions are eutectic Sn63Pb37 and SnAgCu (SAC) 305, 387, 396, and 405. Computer-aided engineering (CAE) employing ANSYS finite element analysis and SolidWorks software is implemented in this investigation. The solder Sn63Pb37 deformed least at 0.43 µm, followed by SAC396 at 0.58 µm, while SAC405 deformed highest at 0.88 µm. Further analysis demonstrates that the possession of a higher elastic modulus and mass density culminates in lower solder joint deformation. Stress is concentrated at the periphery of the solder joints in contact with a printed circuit board (PCB). The SAC396 solder accumulates the lowest stress of 14.1 MPa, followed by SAC405 at 17.9 MPa, while eutectic Sn63Pb37 accrues the highest at 34.6 MPa. Similarly, strain concentration is found at the interface between the solder joint and copper pad on a PCB. SAC405 acquires the lowest elastic strain magnitude of 0.0011 mm/mm, while SAC305 records the highest strain of 0.002 mm/mm. These results demonstrate that SAC405 solder has maximum and SAC387 solder has minimum fatigue lives.

Effect of gamma irradiation on microstructural evolution and mechanical properties of Sn3Ag0.5Cu solder joints

Sn3Ag0.5Cu (SAC305) Ball Grid Array (BGA) solder joints were exposed to 60Co source gamma irradiation at a dose rate of 1 Gy(Si)/s from 0 to 200 h in air. The effects of gamma irradiation on the microstructure evolution and mechanical properties of the solder joints were investigated. β-Sn interacted with O2 in the air and was oxidized to SnO2 on the solder joint surface after gamma irradiation. The oxidation initiated at the corners of the solder joint/pad interface, extended to the entire solder joint/pad interface, and finally occurred at the solder joint matrix. Microcracks usually grow around SnO2/β-Sn interfaces. The interaction of gamma rays with β-Sn and SnO2 is the primary reason for solder joint oxidation. Gamma irradiation generated atomic vacancies, breaking bonds, and dangling bonds in β-Sn and SnO2 crystals through the Compton Effect, which promoted the physisorption and chemisorption of O2 on their surfaces, as well as the oxidation of β-Sn and growth of SnO2. The interaction between the gamma irradiation and solder joints can be divided into two stages. SnO2 was nucleated at lattice defects induced by the interaction between gamma rays and β-Sn crystals in the first stage. The growth of the SnO2 nuclei resulting from a large number of crystal defects in SnO2 and the potential difference between SnO2 and the β-Sn surface induced by the Compton Effect occurred in the second stage. According to the differential scanning calorimetry (DSC) analysis, the melting temperature of the SAC305 solder alloy decreased with increasing irradiation time. According to the nanoindentation test results, with an increase in irradiation time, the microhardness of the solder joints first increased, then decreased, and finally increased again.

Research on thermal fatigue failure mechanism of BGA solder joints based on microstructure evolution

SAC305 (Sn-3.0 %Ag-0.5 %Cu) BGA (ball grid array) solder joints were subjected to thermal cycling. As the number of thermal cycles increased, the thickness of IMCs (intermetallic compounds) increased accordingly. The interface evolutions of the BGA-chip and BGA-PCB (printed circuit board) interfaces were different. On the chip side, the main component of the IMCs was (Cu,Ni)6Sn5, which might form a fine network crack structure with the Ni layer under thermal stress. On the PCB side, Pb particles and the IMC Cu6Sn5 showed a weak ability to coordinate the relative deformation. Grain boundary cracks were easily generated at the BGA-PCB interface and developed into transcrystalline cracks, leading to a high failure rate.

Effect of heat shield locations on rework-induced thermal management in ball grid array solder joint

This study investigated the effectiveness of heat shield placement locations during the rework process to avoid thermal and mechanical damage to adjacent ball grid array components and their solder joints on double-sided printed circuit board assembly. Three types of heat shield placement locations were used: sample X, individual heat shield placement on adjacent components of the rework location; sample Y, a U-shaped, and sample Z, a square-shaped heat shield placed respectively at the heat source location. The dye and pull test results, infrared thermography, and temperature measurements were analysed to understand the relationship between the location of the heat shield and solder joint damage during rework. Heat shield placement at the heat source location on the reworked component can reduce the peak temperatures on the adjacent rework component locations by up to 8.18%. The peak temperatures of the centre and corner of the BGA component can be maintained below 195 °C and 210 °C, respectively to improve the adjacent rework component locations' solder joint quality by reducing solder joint damage by more than 50% solder cracks. This is useful for thermal management during rework involving high-density ball grid array component placements on double-sided printed circuit board assembly.

Process dependence and nucleus models of β-Sn grains in SAC305 freestanding solder balls and BGA solder joints

• Relationship between β-Sn grain morphology and process parameters was studied systematically. • Two nucleus models were proposed to explain the formation of β-Sn morphologies. • Relationship between spatial position of nucleus models and β-Sn orientation was established. • Large θ angle β-Sn grains were theoretically and experimentally proved to have a formation probability higher than 77 %. Due to the anisotropy characteristic of β-Sn grain, the microstructure and orientation of Sn-based solder joints are closely related to the reliability of the solder joints. In this paper, the effects of cooling rate and solder ball size on β-Sn morphology and orientation in Sn-3.0Ag-0.5Cu (SAC305) freestanding solder balls and SAC305/Cu ball grid array (BGA) solder joints were firstly investigated to reveal the process dependence of β-Sn grain features. Three dominant solidified morphologies, i.e., interlaced & beach ball-like grains with three orientations, multiple twin grains with three orientations and single grain with one orientation, were found in the solder balls/joints. Solder ball size showed more significant impact than cooling rate on the morphologies that interlaced & beach ball-like grains and multiple grains were mainly presented in small sized solder balls/joints (≤ 400 μm) and single grain was mainly presented in large sized solder balls/joints (≥ 700 μm). These three solidified morphologies were nucleated and developed from two nucleus model. That is, the interlaced & beach ball-like grains and multiple twin grains morphologies were attributed to {101} nucleus model, while the single grain morphology was attributed to single grain nucleus model. Regardless of whether the solder balls/joints nucleated and solidified based on the {101} or single grain nucleus model, large θ angle β-Sn grains were proved to have a formation probability higher than 77 % both theoretically and experimentally, and this formation probability had little relationship with interfacial Cu 6 Sn 5 grains, cooling rate and solder ball size.

Survey on Fatigue Life Prediction of BGA Solder Joints

With the development of science and technology, consumers’ requirements for various electronic devices present a trend of more diverse functions and thinner bodies. This makes integrated circuits mounted in electronic products and their packaging more vital to satisfying the above requirements. Ball grid array (BGA) packaging is widely used in the field of microelectronic manufacturing industries due to its multiple I/O volumes and excellent electric characteristics. However, due to environmental loads such as vibration and impact during its production and application, defects inevitably emerge in BGA solder joint defects, which will lead to the failure of electronic products. This article summarizes the state-of-the-art research on the factors, analysis methods, and models for the fatigue failure of BGA chips. After rigorous discussions concerning this research, some theoretical suggestions are provided for BGA packaging in reliability analysis and the establishment of evaluation standards.

A study on the effects of electrical and thermal stresses on void formation and migration lifetime of Sn3.0Ag0.5Cu solder joints

PurposeThe purpose of this study is to investigate the effect of electrical and thermal stresses on the void formation of the Sn3.0Ag0.5Cu (SAC305) lead-free ball grid array (BGA) solder joints and to propose a modified mean-time-to-failure (MTTF) equation when joints are subjected to coupling stress.Design/methodology/approachThe samples of the BGA package were subjected to a migration test at different currents and temperatures. Voltage variation was recorded for analysis. Scanning electron microscope and electron back-scattered diffraction were applied to achieve the micromorphological observations. Additionally, the experimental and simulation results were combined to fit the modified model parameters.FindingsVoids appeared at the corner of the cathode. The resistance of the daisy chain increased. Two stages of resistance variation were confirmed. The crystal lattice orientation rotated and became consistent and ordered. Electrical and thermal stresses had an impact on the void formation. As the current density and temperature increased, the void increased. The lifetime of the solder joint decreased as the electrical and thermal stresses increased. A modified MTTF model was proposed and its parameters were confirmed by theoretical derivation and test data fitting.Originality/valueThis study focuses on the effects of coupling stress on the void formation of the SAC305 BGA solder joint. The microstructure and macroscopic performance were studied to identify the effects of different stresses with the use of a variety of analytical methods. The modified MTTF model was constructed for application to SAC305 BGA solder joints. It was found suitable for larger current densities and larger influences of Joule heating and for the welding ball structure with current crowding.

Factors Controlling the Defect Formation in Cu-Sn Micro Joints in 2.5D and 3D Interconnects

The Cu-Sn reaction upon soldering has been thoroughly studied and the sporadic formation of Kirkendall voids within the intermetallic bonds between ball grid array (BGA) or surface mount technology (SMT) solder joints and Cu pads has been demonstrated as well-known concern. However, in the realm of ever developing device miniaturization, there is very limited information on the impact of space confinement on the dynamics of the Cu/solder joint interface. It is known that no voiding has been found in solder joints with high-purity Cu but this phenomenon presents itself, albeit to a different extent, when the joint is realized with electroplated Cu. Also, it is believed, that the voiding propensity in the Cu3Sn intermetallic compounds (IMC) is more likely to be higher in micro joints than in BGA/CSP scale (macro) joints for a given quality of electroplated Cu. Along with that it has been shown that the IMCs on Cu surfaces seem to grow much faster when the solder becomes very thin, and this is accompanied with a greatly enhanced risk of Kirkendall void nucleation.The emphasis of this work is on understanding the voiding behavior within the intermetallic bonds of Cu-Sn micro joints (5 – 30 µm) with the eventual goal of learning how it can be controlled or prevented. Our systematic studies have corroborated the association of voiding with the incorporation of small concentrations of impurities resulting from organic additives degradation during the Cu electroplating as already illustrated for macro joints. Our results also show lack of any voiding not only in macro- but also in micro joints when the interconnection is realized with high purity Cu, likely because no organic impurities are present in sufficient amount to prompt defect nucleation and growth. Our research further demonstrates that the IMC growth rate varies with factors and parameters such as solder volume to pad area ratio, solder composition, pad finish, initial assembly process parameters, subsequent heat treatments, and specifics of the further thermomechanical history, thus impacting differently the overall voiding level. Following this lead, the analysis of micro joints subjected to different synthetic and processing treatments clearly demonstrates the propensity for voiding to be substantially higher, for a given quality of electroplated Cu, in very small solder joints (5 – 30 µm), such as those found in 3D assemblies, unlike in macro joint counterparts. The risk and severity of voiding in these thinner joints is confirmed to depend on the type and amount of incorporated organic impurities in the electroplated Cu. Therefore, in the present report we show how the bath additive chemistry and various Cu electroplating parameters play a systematic role in the type and quantity of impurity incorporation, and thus the propensity for voiding. Approaches to control the electroplating Cu quality in a way that leads eventually to void-free micro joints are also discussed.

Validation of the Critical Strain-Based Methodology for Evaluating the Mechanical Safety of Ball Grid Array Solder Joints in a Launch Random Vibration Environment

Abstract To overcome the limitations of Steinberg's theory for evaluating the mechanical safety of the solder joints of spaceborne electronics in a launch random vibration environment, a critical strain-based methodology was proposed and validated in a previous study. However, in order to apply the critical strain-based methodology to mechanical design of spaceborne electronics with high confidence, its effectiveness must be validated under various conditions of the package mounting locations and the first eigenfrequencies of a printed circuit board (PCB); achieving this validation is the primary objective of this study. For the experimental validation, PCB specimens with ball grid array (BGA) packages mounted on various board locations were fabricated and exposed to a random vibration environment to assess the fatigue life of the solder joint. The effectiveness of the critical strain-based methodology was validated through a comparison of the fatigue life of the packages under test and to the margin of safety, which was estimated using various analytical approaches.

Thermal fatigue life of ball grid array (BGA) solder joints made from different alloy compositions

As temperature cycling drives fatigue failure of solder joints in electronic modules, characterisation of the thermal fatigue response of different solder alloy formulations in BGA solder joints functioning in mission-critical systems has become crucial. Four different lead-free and one eutectic lead-based solder alloys in BGA solder joints are characterised against their thermal fatigue lives (TFLs) to predict their mean-time-to-failure for preventive maintenance advice. Five finite elements (FE) models of the assemblies of the BGAs with the different solder alloy compositions are created with SolidWorks. The models are subjected to standard IEC 60749–25 temperature cycling in ANSYS mechanical package environment. Plastic strain, shear strain, plastic shear strain, and accumulated creep energy density responses of the solder joints are obtained and inputted into established life prediction models – Coffin Manson, Engelmaier, Solomon and Syed – to determine the lives of the models. SAC405 joints have the highest predicted TFL of circa 13.2 years, while SAC387 joints have the least life of circa 1.4 years. The predicted lives are inversely proportional to the magnitude of the areas of stress–strain hysteresis loops of the BGA solder joints. The prediction models are significantly not consistent in predicted magnitudes of TFLs across the solder joints. With circa 838% variation in the magnitudes of TFL predicted for Sn63Pb37, the damage parameters used in the models played a critical role and justifies that a combination of several failure modes drives solder joints damage. This research provides a technique for determining the preventive maintenance time of BGA components in mission-critical systems. It proposes developing a new life prediction model based on a combination of the damage parameters for improved prediction.