Plastic Ball Grid Array Package Research Articles

Study of the effect of crystal orientation on the mechanical response and fatigue life of solder joints under thermal cycling by crystal plasticity

Electronic products are subjected to thermal cycling caused by power cycling in service processes. Owing to the difference in the coefficients of thermal expansion (CTEs) of solder joints and other packaging materials, solder joints suffer from thermomechanical fatigue, and cracks appear at their bonding interfaces. Solder joints are usually a single grain or three grains with Beachball morphology, and their composition is Sn-based Pb-free SAC305 (96.5Sn–3.0Ag–0.5Cu wt.%) solder, which exhibits obvious anisotropic mechanical behavior. This study investigated a thermal cycling simulation of Plastic Ball Grid Array (PBGA) packaging, in which the Anand model was used for solder joints, and the outermost solder joint was found to be a dangerous point. Sub-models were then established for this solder joint with several typical crystal orientations. The effect of crystal orientation under thermal cycling was simulated using thermomechanical crystal plasticity. When the c-axis of Sn crystal was perpendicular to the substrate, the deformation resistance was the largest, and the accumulation of equivalent plastic strain and strain energy dissipation was the slowest; hence, the fatigue life was the longest. As the angle between the c-axis and the substrate decreased, the deformation accumulated faster. When the c-axis was parallel to the substrate, the deformation of the solder joint was the fastest, and thus this joint was the first to fail and had the shortest fatigue life. In addition, the simulation of three grains indicated that orientations and their distributions had an influence on the shear strain accumulation of slip systems and fatigue life.

Mechanical properties of Sn–Pb based solder joints and fatigue life prediction of PBGA package structure

Solder joints are generally the weakest part in electronic packaging structure whose fatigue life depends to a large extent on the durability of solder joints. In pursuit of a balance between environmental protection and soldering performance, commonly used Sn–Pb solder should be modified by adding other chemical elements to reduce Pb content. This work aims to investigate the performance of different solder materials and explore the impact of different electronic package structures. Firstly, tensile experiments are performed on three kinds of solders (Sn–Pb, Sn–Pb–In, Sn–Pb–Bi) to obtain their mechanical behavior, and then the constitutive laws of them are calibrated by Anand model. Additionally, finite element method (FEM) is used simulate the response of plastic ball grid array (PBGA) package structure under thermal cycles, and mechanical variables including deformation, equivalent stress, and equivalent strain are analyzed. Finally, Coffin-Manson and Engelmaier equations are adopted to predict the fatigue life of package structures and the effects of various factors such as solder materials, dimensions of components, and welding quality are further investigated. Results reveal that adding Bi into Sn–Pb solder can make the solder joints have better performance. From the perspective of optimum fatigue life, the plastic package thickness is recommended in the range of 0.8 mm–0.9 mm, the chip thickness is recommended as 0.35 mm, the substrate thickness is recommended to be less than 0.34 mm, and the ratio of stand-off height to solder ball diameter should be controlled between 0.6 and 0.7. According to the prediction, the solder ball diameter is suggested to be 0.54 mm so that fatigue life could reach 194 cycles, and the stand-off height for this package structure is suggested to be 0.36 mm so that fatigue life could reach 123 cycles.

Deformation behaviors of flip chip plastic ball grid array packages subjected to temperature change using moiré interferometry

When the temperature of the package assembly is changed, non-uniform deformation and local stress may occur owing to the different thermal expansion coefficients of the constituent materials, while concentrated thermal stress may cause significant failure. In this study, we carry out an experiment and analysis of the thermal deformation of a flip chip plastic ball grid array package with respect to temperature change. Interference fringe patterns representing the displacement distribution of each temperature stage are obtained using a Moiré interferometry and the bending deformation behavior and the strain of the solder ball are analyzed thereafter. We compare the deformation behavior of a single-sided package assembly and a double-sided package assembly. The effective strain, which significantly affects the failure of the solder ball, is found to be the largest in the solder ball just outside the edge of the chip in the case of the single-sided package assembly. In the case of the double-sided package assembly, the maximum effective strain is found in the solder ball just inside the edge of the chip, with a value approximately 50 % larger than in the case of the single-sided package assembly. Wenn sich die Temperatur eines Gehäuses ändert, kann es aufgrund der unterschiedlichen Wärmeausdehnungskoeffizienten der einzelnen Werkstoffe zu ungleichmäßigen Verformungen und lokalen Spannungen kommen, während konzentrierte thermische Spannungen zu erheblichen Ausfällen führen können. In dieser Studie führen wir ein Experiment und eine Analyse der thermischen Verformung einer Flip-Chip Kunststoffkugel Gitteranordnung in Abhängigkeit von der Temperaturänderung durch. Mit Hilfe der Moiré-Interferometrie werden Interferenzstreifenmuster aufgenommen, die die Verschiebungsverteilung jeder Temperaturstufe darstellen und anschließend werden das Biegeverformungsverhalten und die Dehnung der Lötkugel analysiert. Wir vergleichen das Verformungsverhalten einer einseitigen und einer doppelseitigen Gehäusebaugruppe. Es zeigt sich, dass die effektive Dehnung, die das Versagen der Lötkugel maßgeblich beeinflusst, im Fall der einseitigen Baugruppe in der Lötkugel direkt außerhalb des Chiprands am größten ist. Bei der doppelseitigen Baugruppe ist die maximale effektive Dehnung in der Lötkugel direkt innerhalb des Chiprands zu finden, mit einem Wert der etwa 50 % größer ist als bei der einseitigen Baugruppe.

Prediction on Thermal Cycling Stress of PBGA Package Based on Finite Element Simulation and Machine Learning

As the application environment of Plastic Ball Grid Array (PBGA) package becomes more diverse and severe, higher requirements are placed on the thermal cycling reliability of the PBGA package. The thermal cycling reliability of PBGA package has higher standards. The traditional experimental method has the problems of a long cycle and high costs. In this paper, the thermal cycling stress of the PBGA package is studied based on finite element simulation and machine learning methods. Take the typical PBGA package structure solder ball as the research object, and simulate the solder ball stress value under extreme thermal cycling conditions using the finite element software ABAQUS. The dataset is organized based on the finite element analysis results to establish a machine learning prediction model, which aims to predict the thermal cycling stress of PBGA package rapidly. The result shows that the prediction model established by the Random Forest Regression (RFR) algorithm has better prediction accuracy compared with Multiple Linear Regression (MLR) algorithm and Support Vector Regression (SVR) algorithm, and the Mean Absolute Percent Error (MAPE) is 3.01%, which can provide a new way to predict thermal cycling stress of PBGA packages directly.

Measurement Capability of Laser Ultrasonic Inspection System for Evaluation of Ball-Grid Array Package Solder Balls

Abstract Laser ultrasonic inspection is a novel, noncontact, and nondestructive technique to evaluate the quality of solder interconnections in microelectronic packages. In this technique, identification of defects or failures in solder interconnections is performed by comparing the out-of-plane displacement signals, which are produced from the propagation of ultrasonic waves, from a known good reference sample and sample under test. The laboratory-scale dual-fiber array laser ultrasonic inspection system has successfully demonstrated identifying the defects and failures in the solder interconnections in advanced microelectronic packages such as chip-scale packages, plastic ball grid array packages, and flip-chip ball grid array packages. However, the success of any metrology system depends upon precise and accurate data to be useful in the microelectronic industry. This paper has demonstrated the measurement capability of the dual-fiber array laser ultrasonic inspection system using gage repeatability and reproducibility analysis. Industrial flip-chip ball grid array packages have been used for conducting experiments using the laser ultrasonic inspection system and the inspection data are used to perform repeatability and reproducibility analysis. Gage repeatability and reproducibility studies have also been used to choose a known good reference sample for comparing the samples under test.

Experimental and finite element analysis on determining the fatigue life of pb-free solder joint (Sn-0.5Cu-3Bi-1Ag) used in electronic packages under harmonic loads

Electronic packages that are used these days are exposed to different types of vibration loadings in their usage environment. This vibration exposure can be categorized as harmonic and random vibrations. When reliability assessment of modern electronic systems is considered, vibration loading has an important role to play. One of the biggest challenges facing today is the accurate and rapid assessment of fatigue life under the vibration loading. Conventional solder joints were made of lead-tin alloy. According to many environment legislations and rules, lead is prohibited as an ingredient in the solder alloy. The reason for the prohibition of the usage of the lead is that it poisons the environment. In this study, Sn-0.5Cu-3Bi-1Ag is used as the lead-free solder alloy. Fatigue life prediction of electronic package containing SAC405 is conducted with the aid of vibration testing and Finite element analysis under harmonic vibration loading. A specially designed Plastic Ball Grid Array Package (PBGA) component is mounted on Printed Circuit Board (PCB). It is taken as a test vehicle for the vibration test. The test vehicle is excited by a sinusoidal vibration. The frequency of this excitation equals the fundamental frequency of the test vehicle and it is continued till the component fails. Since the solder balls are very small for direct measurement, Finite Element analysis (FEA) is used for noting down the stresses. The stress versus failures cycles (S-N) curve is made by relating both the stresses on the solder balls obtained and the number of failure cycles from vibration analysis. The fatigue life of the component can be estimated from the generated S-N curve. It is analyzed that the methodology is effective in predicting the component’s life. Hence, the reliability of electronic package can be improved.

Parameterized Anand constitutive model under a wide range of temperature and strain rate: experimental and theoretical studies

The inconsistency of constitutive parameters weakens the rationality and also impedes the application of the Anand model. In this paper, a modified framework of Anand model is proposed and the corresponding parameters are calibrated using two viscoplastic materials, that is, Sn-3.0Cu-0.5Ag and Sn37-Pb63 which are typical die-attach solder alloys in the electronic packaging industry. The stress–strain relationships under a wide range of temperature and strain rate are measured from the uniaxial tensile experiments for both materials by dog-bone specimens. The dependency on strain rate and temperature can be well described by reasonably parameterizing the proposed Anand model. Effects of strain rate and temperature on saturation stresses are emphasized. In order to highlight the necessity to account for strain rate and temperature effects, the plastic ball grid array packaging structures are adopted in the scenario of thermal cycling. Due to variation of strain rate and strain, different stresses are observed among different positions in the packaging structure under the applied cycled temperature field. The wide ranges of strain rate and temperature are satisfactorily described by the proposed Anand model with one set of parameters, rather than using multiple sets of parameters or even multiple types of constitutive models. Lastly, the accumulative plastic strain and stress of two materials are numerically predicted and discussed to reveal the relationship between strength, Young’s modulus and plastic deformation, which shows the proposed parameterized Anand model can be readily utilized for fatigue life estimations of packaging structures under thermal cycling.

Parametric study of warpage in PBGA packages

Plastic ball grid array (PBGA) is one of the most widely used types of chip packages in various electronic devices such as network servers, microcontrollers, and memory devices. As the demand for higher performance electronic devices grows, the I/O densities of PBGA packages are increasing while requiring superior reliability. Warpage induced during the reflow assembly process is one of the crucial factors affecting the thermo-mechanical reliability of PBGA packages; therefore, accurate warpage prediction is an important task for package design processes. In this study, the effects of four geometric factors (the solder bump pitch, package size, molding compound, and substrate thicknesses) of the PBGA package on its warpage are assessed by using parametric finite element analysis. The correlation between PBGA warpage and the four factors is studied using the analysis of variance and the regression method. These results are expected to provide design guidelines for in-house PBGA designers.

Temperature and strain-rate dependent constitutive model for prediction of thermal cycling life

With temperature cycling as the characteristic working environment of aerospace electronic chips, various constitutive models have been proposed to predict the failure problems of solder joints. However, most researchers adopted only a set of constant parameters to describe the solder joint material properties throughout the temperature cycles, which is obviously unreasonable concerning the possible wide range of working temperature. In fact, with the changing temperature and strain rate, some material parameters will correspondingly evolve as observed in the experiments. In this paper, the framework of the Anand constitutive model is adopted to verify the effect of material parameters of different temperatures and strain rates on the mechanical properties of materials under the scenario of temperature cycling. The lead-containing solder alloy 63Sn37Pb material that is most widely used in aerospace is selected as the solder material for the interconnection structure. In addition, a typical plastic ball grid array (PBGA) packaging structure is used to analyze the influence of the constitutive model parameters on the PBGA thermal fatigue life. Based on experimental data, seven sets of constitutive model parameters with different temperatures (-55°C~125°C) under a region of low strain rate (1×10-4/s) were employed to compare the mechanical properties of the material under temperature cycling. The sensitivity analysis of material parameters is performed and the underlying mechanism are also explained so that the present study can promote the optimization of the constitutive model in numerical simulations in practice.

Study on Delamination Between Polymer Materials and Metals in IC Packaging Process.

The electronic package interconnects electronic signals from one area to another and package delamination is a serious problem in the configuration of materials. This study focused on decreasing the delamination of the low-profile fine pitch ball grid array (LFBGA) and plastic ball grid array (PBGA) packages in terms of polymer thermal issue, metal bonding and bonding mechanisms. PBGA and LFBGA are a very common type of packaging processes in the electronics industry. The present study dealt first with delamination of the LFBGA packaging, through characterization and determination of physical and chemical properties such as surface roughness, surface energy, and contact angle. The relationship between surface roughness and delamination was verified through various roughness bonding experiments. In addition, the surface energy was determined by measuring the contact angle after cleaning the metal surface of Cu, Ni and Cr with Ar + O2 gas, and, this gas plasma treatment was applied to enhance the adhesive properties. The compositions of the surface were analyzed through an X-ray photoelectron spectroscopy (XPS). Also, the delamination issue between the corner of the heat sink cap and the epoxy resin was observed for delamination of the LFBGA packaging. Further, this study analyzed the PBGA packaging process through the finite element analysis simulation software ANSYS. To improve the heat sink cap delamination issue of the PBGA, a new chamfer design of the corner seat was streamlined to decrease the stress value and delamination. Besides, the simulation results demonstrated that the stress value reduced after increasing the shoulder length. The results implicate that the stress value is inversely proportional to the shoulder width and the chamfer radius. This study demonstrated that the optimization in design was able reduce the delamination phenomena in configuration material.

Completely in situ and non-contact warpage assessment using 3D DIC with virtual patterning method

Recently, advanced experimental mechanics have been developed using optical techniques for measuring 3D deformations of objects in industries. Especially, Moire systems and 3D DIC (digital image correlation) were competing in characterizing warpage behaviors of electronics package under thermal loading with consideration of manufacturing process, which is accompanied by elevated temperatures. Both techniques conventionally require various surface treatments either physically or chemically, which involves contaminations on measuring objects. Additionally, excessive surface treatment results in reduction of measurement accuracy. Thus, in this study, truly in situ and non-contact 3D DIC method is developed using virtually generated speckle pattern. A commercial DLP (digital light processing) projector together with devised collimate lens system is used to project proper image of speckles on surface of specimen. The collimate lens system fully controls size of speckle image on such small area of electronics package. The feasibility of 3D DIC with virtual pattern is validated, and warpage characterization of PBGA (plastic ball grid array) package (15 mm × 15 mm) is successfully demonstrated.

Dynamic digital fringe projection technique for measuring the warpage of unpainted PBGA packages and boards

A crucial factor for ensuring the reliability of chip packages is the measurement and control of warpage. The warpage of chip packages, printed wiring boards (PWBs), and PWB assemblies (PWBAs) are typically measured by moire techniques (i.e., shadow moire, laser fringe projection, and digital fringe projection), which have noncontact, full-field, and high-resolution capabilities. The application of moire techniques typically involves spraying a mist of reflective paint on the surface of a sample to ensure the uniformity of surface reflectance and to obtain better fringe image contrast and better sinusoidal waveforms in the fringe patterns for the measurement process. However, since painted samples may no longer be re-used, the process of spray painting is not suited for inline inspection; a new technique for measuring warpage without painting is required. In this research, a dynamic digital fringe projection (DDFP) technique for measuring the warpage of unpainted plastic ball grid array (PBGA) packages and boards was developed. The DDFP technique dynamically determines proper fringe intensity distributions for PBGA packages and PWBs and uses them to produce a better fringe image contrast and better sinusoidal waveforms without painting. Experimental results showed that the DDFP technique successfully measures the warpage of PBGA packages and PWBs in unpainted PWBAs accurately.

Contact Resistance of Microbumps in a Typical Through-Silicon-Via Structure

The contact resistance of microbumps in a plastic ball grid array packaging with a through-silicon-via (TSV) structure was characterized. Accordingly, a self-designed TSV daisy-chain circuit was proposed to facilitate the formulation of the measurement paths, and the test samples were made by using a commercialized packaging process to simulate real product behaviors. Using the proposed single model and the complete model for the testing structure, about 25 $\text{m}\Omega $ was measured as the average contact resistance per microbump, and the contact resistance for each microbump was separately extracted between 4 and 60 $\text{m}\Omega $ In addition, decreasing contact resistance due to the annealing effect was observed from two different reliability tests.

Automatic Segmentation Method for Segmenting PBGA Package and PWB Regions During Warpage Measurement of Unpainted PWB Assembly

Among the various warpage measurement techniques, digital fringe projection (DFP) technique is recent trend because of its noncontact, full-field, and high-resolution measurement capabilities for measuring the warpage of chip packages, printed wiring boards (PWBs), and PWB assemblies (PWBAs). When using the DFP technique, reflective painting is generally sprayed on a sample surface to ensure uniform surface reflectance and to obtain better image contrast for the measurement process. However, because painted samples may no longer be reused, and the spray-painting process is not suitable inline, warpage measurement of unpainted chip packages, PWBs, and PWBAs using the DFP technique is required. One of the important tasks for measuring the warpage of unpainted PWBAs is segmentation of the chip package and PWB regions in unpainted PWBA images so that separate warpage of the chip packages and the PWBs can be determined. This paper presents a novel automatic segmentation method, region-growing method (RGM), which segments plastic-ball grid array (PBGA) packages and PWB regions in unpainted PWBA images. The experimental results show that the RGM successfully segments the PBGA package and PWB regions in unpainted PWBA images. The results also show that the RGM can be used in a DFP system to measures the warpage of PBGA packages and PWBs in unpainted PWBAs.

Effect of Electromigration on the Type of Drop Failure of Sn–3.0Ag–0.5Cu Solder Joints in PBGA Packages

Board-level drop tests of plastic ball grid array (PBGA) packages were performed in accordance with the Joint Electron Devices Engineering Council standard to investigate the effect of electromigration (EM) on the drop reliability of Sn–3.0Ag–0.5Cu solder joints with two substrate surface finishes, organic solderability preservative (OSP) and electroless nickel electroless palladium immersion gold (ENEPIG). In the as-soldered state, drop failures occurred at the substrate sides only, with cracks propagating within the interfacial intermetallic compound (IMC) layer for OSP solder joints and along the IMC/Ni–P interface for ENEPIG solder joints. The drop lifetime of OSP solder joints was approximately twice that of ENEPIG joints. EM had an important effect on crack formation and drop lifetime of the PBGA solder joints. ENEPIG solder joints performed better in drop reliability tests after EM, that is, the drop lifetime of ENEPIG joints decreased by 43% whereas that of OSP solder joints decreased by 91%, compared with the as-soldered cases. The more serious polarity effect, i.e., excessive growth of the interfacial IMC at the anode, was responsible for the sharper decrease in drop lifetime. The different types of drop failure of PBGA solder joints before and after EM, including the position of initiation and the propagation path of cracks, are discussed on the basis of the growth behavior of interfacial IMC.

Automatic Segmentation Method for Segmenting PBGA Package and PWB Regions during Warpage Measurement of Unpainted PWB Assembly

Among the various warpage measurement techniques, the digital fringe projection (DFP) technique is recent trend because of its noncontact, full-field, and high-resolution measurement capabilities for measuring the warpage of chip packages, printed wiring boards (PWBs), and PWB assemblies (PWBAs). When using the DFP technique, reflective painting is generally sprayed on a sample surface to ensure uniform surface reflectance and to obtain better image contrast for the measurement process. However, because painted samples may no longer be re-used, and the spray-painting process is not suitable inline, warpage measurement of unpainted chip packages, PWBs, and PWBAs using the DFP technique is required. One of the important tasks for measuring unpainted PWBAs is segmentation of the chip package and PWB regions in unpainted PWBA images so that separate warpage of the chip package(s) and the PWB can be determined. In this paper, an automatic image segmentation method that is used to segment plastic ball grid array (PBGA) package and PWB regions in unpainted PWBA images is presented. Because the patterns such as the copper patterns and traces, and inscriptions on a PWBA can cause measurement errors, the patterns and inscriptions are automatically masked out during the segmentation. The method is experimentally tested by segmenting the PBGA package and PWB regions in three different PWBA samples and measuring the warpage of the PBGA packages and the PWB in an unpainted PWBA.

Parametric Studies of Effects of Solder Bump Pitch, Package Size, and Molding Compound and Substrate Thicknesses on Warpage of PBGA Packages

Plastic ball grid array (PBGA) is one of the most widely used types of chip packages in various electronic devices such as network servers, microcontrollers, and memory devices. As the demand for higher performance electronic devices grows, the I/O densities of PBGA packages are increasing while requiring superior reliability. Warpage induced during the reflow assembly process is one of the crucial factors affecting the thermo-mechanical reliability of PBGA packages; therefore, accurate warpage prediction is an important task for package design processes. In this study, the effects of four geometric factors (the solder bump pitch, package size, and molding compound and substrate thicknesses) of the PBGA package on its warpage are assessed by using parametric finite element analysis. The correlation between PBGA warpage and the four factors is studied using the regression method. These results are expected to provide design guidelines for in-house PBGA designers.

Fatigue Analysis on Thermal Characteristics for PBGA by Using Finite Element Method

The stress and strain of Plastic Ball Grid Array (PBGA) is investigated for reliability evaluation, failure analysis, or manufacturing. A one-eighth model is built to estimate the thermal stress and strain of PBGA under thermal cycling temperature (0°C–100°C). The different 3D elements such as Visco107 and Solid45 were selected for modeling of material 37Sn63Pb and Print Circuit Board (PCB), silicon die, substrate, and Epoxy Molding Compound (EMC), respectively. The results show that the maximum equivalent stress and equivalent plastic strain occur in the second outer solder joint and close to the position of chip. The key solder joint can be obtained and the key node of solder joint is 41402. The results indicate that the integrating 3D model can provide a more comprehensive profile for the thermal investigation of the PBGA package than from using any 2D model. The investigation provides a basis for improving reliability of PBGA product in engineering design.

Thermal fatigue life prediction of solder joints of plastic ball grid array packages

In the present study, the fatigue life of solder joints of plastic ball grid array packages (PBGA) under thermal cycling condition is evaluated using the finite element method. A unified, viscoplastic constitutive model for solder joints of plastic ball grid array packages is employed to improve accuracy of reliability prediction. The constitutive model is then implemented into the commercial finite element analysis software, ABAQUS, to predict the thermo-mechanical behaviour of solder balls in PBGA package subjected to thermal cycling. Damage parameters are obtained from the FEA results and are used to estimate the thermal fatigue life of solder balls. The Coffin-Manson equation is employed. The predicted thermal fatigue lives are discussed in detail.

랜덤진동환경에서 솔더접합부의 인쇄회로기판내 위치에 따른 내구수명 변화 연구

A vibration test coupon is prepared with nine plastic ball grid array packages on a printed circuit board using SnPb solders, and a random vibration test is conducted on the coupon. Life data from the test are analyzed, and it is shown that over the board, life data is location-dependent. For investigating this location dependency, a finite element model is developed and the equivalent stresses, which are defined based on the stress response functions at each node, are investigated. It is shown that one of the corner solder balls has the maximum equivalent stress at a package during the test. Finally, it is demonstrated that the maximum equivalent stress and durability life are inversely proportional.