Thermal deformation measurement of the solder joints in electronic packages using electron moiré method

In this paper, electron moiré method is used to measure the thermal deformation of electronic packages. In order to observe the electron moiré fringe, a holographic grid was replicated on the cross section of the BGA type package at 150°C. This grid was fabricated on a glass plate using a moving point holographic system, and was replicated to measured area at high temperature. Under SEM, the holographic grid(specimen grid) and a programmed electron beam scan(master grid) interfere and form electron moiré patterns. The shear strain measurement technique using electron moiré method is described. Using the electron moiré method, the shear strains in the different solder joints were measured and analysed. Some useful results were obtained.     

Wavelet-based approach for ball grid array (BGA) substrate conduct paths inspection

The aim was to detect boundary defects such as open, short, mousebite and spur on ball grid array (BGA) substrate conduct paths using machine vision. The 2-D boundaries of BGA substrate conduct paths are initially represented by the 1-D tangent curve. The tangent angles were evaluated from the eigenvector of a covariance matrix constructed by the boundary coordinates over a small boundary segment. Since defective regions of boundaries result in irregular tangent variations, the wavelet transform was used to decompose the 1-D tangent curve and capture the irregular angle variations. A boundary defect can then be easily located by evaluating the wavelet coefficients of the 1-D tangent curve in its high-pass decomposition. The proposed method is invariant with respect to the rotation of the BGA substrates and does not require prestored templates for matching. Real BGA substrates with various boundary defects were used as test samples to evaluate the performance of the proposed method. Experimental results show that the proposed method achieves 100% correct identification for BGA substrate boundary defects by selecting appropriate wavelet basis and decomposition level.     

一种新型共轭接枝聚合物的合成及性能

将微波辐射合成的苯代三聚氰胺(BGA)-均苯四酸二酐(PMDA)体系的PAA与TDI-对位取代苯胺衍生物反应,通过改变TDI-对位取代苯胺衍生物的对位取代基来合成具有不同电子效应的侧链端基的接枝聚合物.用红外及核磁共振的测试方法对聚合物的结构进行表征.接枝聚合物具有较强的三阶非线性光学响应和较强的荧光性能.考察了侧链端基电子效应对聚合物三阶光学非线性极化率系数和荧光行为的影响.     

Modified gamma correction method to enhance ball grid array image for surface defect inspection

BGA (Ball Grid Array) surface defect detection requires faster and more accurate methods for semiconductor industry applications. Traditionally, the BGA inspection used gray-scale images. However, the solder pad, wiring and gray scales shown in images depict little variance. Therefore, when the threshold value is poorly set or the contract rate is insignificant, BGA detection may fail to segment an object. This research proposes a modified methodology that uses Gamma correction for image enhancement. Three-color bands were applied to a modified Gamma correction algorithm (i.e. RGB) to better separate the high and low image contrasts. Better results were obtained by dividing the image into background and foreground portions using the Gamma correction. As a result, the proposed method improved the contrast value by 52.09%. After the images were enhanced and segmented, the compactness and internal holes were calculated as features for classification. The results showed that classification correctness was 96.43%. The proposed method used a 640?×?480 pixel image, performing complete defect detection 0.3 seconds faster than the traditional enhancement method, which requires 1?second. The research results provide an effective solution for the detection and classification of the BGA surface tin ball defect problem.     

The ‘IMC rings’ growth mechanism in Sn–Ag–Cu solder ball and NiAu-plated BGA ball pad

Due to environmental pollution concerns, the law says the lead (Pb) inside electronics devices must be eliminated. Lots of lead-free materials have been introduced and been used for electronic products and Sn–Ag–Cu (SAC) is one of most popular lead-free representatives and has been used in high-volume production. The most popular IC packages, BGA packages which have higher I/O counts, and better thermal and electrical performance than lead-frame type packages, use solder balls of SAC for lead-free applications to connect with printed circuit boards. A particular phenomenon, so-called ‘IMC rings’, is only observed on BGA solder ball pad surfaces after the SAC solder balls are mounted on BGA ball pads which are plated with NiAu. It has not been found in either eutectic solder or Sn–Ag solder welding on plated NiAu pads. No significant evidence exists to show that ‘IMC rings’ degrade the strength of solder joints or cause earlier failures in mechanical tests. ‘IMC rings’ appear to be an inevitable outcome after the SAC is soldered onto a plated NiAu ball pad. This study is to find the growth mechanism of ‘IMC rings’ on the ball pad which is created between SAC ball and plated NiAu pad during solder ball temperature reflow. The design of the experiment and data have been discussed.     

Electrical properties and interfacial reaction of BGA package with underfill

This study evaluated the electrical properties and interfacial reaction of the ball grid array (BGA) packages with various underfills under thermal shock and isothermal aging conditions. The BGA packages were composed of two surface finishing materials on the bottom substrate, viz. bare Cu and electroless nickel-immersion gold (ENIG). The thickness of the intermetallic compounds (IMCs) formed at the interface between the solder and substrate increased with increasing number of thermal shock cycles and isothermal aging times. Also, the growth rate of the IMCs during the isothermal aging condition was faster than that during the thermal shock condition. The electrical resistance of the BGA package with the underfill was lower than that of the BGA package without the underfill under thermal shock condition. The electrical resistance of the underfill with silica particles was lower than that of the underfill without silica particles.     

Noncontact electrical test of a ball grid array substrate that uses the electro-optic probing technique

A new technique for testing a ball grid array (BGA) package substrate that uses the electro-optic (EO) probing technique is investigated. This technique can detect open circuits in the BGA substrate with a high spatial resolution. An experimental setup that uses an EO probe tip made of LiNbO3 crystal is reported along with the measurement results from a real BGA substrate.     

In situ fiber-optic oxygen consumption measurements from a working mouse heart.

Luminescence-based imaging-fiber oxygen sensors (IFOSs) were utilized for the in situ measurement of oxygen consumption from intact perfused mouse hearts. IFOSs were fabricated using a technically expedient, photoinitiated polymerization reaction whereby an oxygen-sensitive polymer matrix was immobilized in a precise location on an imaging fiber's distal face. The oxygen-sensing layer used in this work comprised a transition metal complex, Ru(Ph2phen)3(2+), entrapped in a gaspermeable photopolymerizable siloxane membrane (PS802). The transduction mechanism was based upon the oxygen collisional quenching of the ruthenium complex luminescence; detection was performed utilizing an epi-fluorescence microscope/charge coupled device imaging system. IFOS measurements from working mouse hearts were validated through concurrent, blind, ex situ blood gas analyzer (BGA) measurements. The BGA and IFOS methodologies were utilized successfully to measure oxygen concentrations in aortic and pulmonary artery perfusates from the working mouse heart before and after isoproterenol administration. Coupled with coronary-flow measurements, these data were used to calculate myocardial oxygen consumption. Regression analysis of measurements of myocardial oxygen consumption showed that there was a strong correlation between the values generated by the BGA sampling and those obtained via in situ IFOS methods. To our knowledge, this research represents the first report of in situ fiber-optic sensor monitoring of oxygen content from the intact, beating mouse heart.     

板级跌落冲击载荷下无铅焊点形状对BGA封装可靠性的影响

焊点高度和焊盘尺寸相同情况下,分析焊点形状（桶形、柱形、沙漏形）对BGA封装在板级跌落冲击载荷下可靠性的影响。根据不同焊点形状建立3种3D有限元模型,采用Input-G方法将加速度曲线作为数值模型的载荷输入,对BGA封装件在板级跌落冲击载荷下的可靠性进行分析。结果表明：在跌落冲击过程中,在0.1ms左右PCB板出现最大弯曲变形;焊点形状对BGA封装件在跌落冲击过程中的可靠性有较大的影响;以最大剥离应力作为失效准则对三种焊点进行寿命预测, 沙漏形焊点的平均碰撞寿命值最大,其次是柱形焊点,桶形焊点最小,表明沙漏形焊点在跌落测试中表现出较好的抗跌落碰撞性能。     

Ball grid array (BGA) substrate conduct paths inspection using two-dimensional wavelet transform

The objective of this paper is to implement two-dimensional wavelet transform (2-D WT) in the detection of mousebite, spur, open, and short defect candidates on ball grid array (BGA) substrate conduct paths. Once the defect candidates are located, traditional BGA substrate inspection algorithms can further detect true defects among these suspicious defects. Therefore, the scope and effort during the inspection stage can be significantly reduced. The binary BGA substrate image is processed that shows only conduct path boundaries, which are decomposed directly by 2-D WT. Then, the inter-scale ratio from the wavelet transform modulus sum (WTMS) across adjacent decomposition levels for the edge pixels on BGA substrate conduct path boundaries is calculated. Since irregular edges in a small domain can preserve much more wavelet energy, an edge pixel is considered as an abnormal one or a defect candidate if its inter-scale ratio is less than a predefined threshold. The proposed approach is template-free and easy to implement, so it is suitable for small batch production. Real BGA substrates with synthetic boundary defects are used as testing samples to evaluate the performance of the proposed approach. Experimental results show that the proposed method is able to capture all the true mousebite, spur, open, and short defects without any missing errors by appropriate wavelet basis, decomposition level, and image resolution.     

Preparation of insulated metal substrate for MBGA package

An anodizing technique was employed to prepare insulated metal substrates (IMS) for BGA package in this study. The insulating anodic films of aluminum that were chosen as the substrate were studied with different anodizing processes. A multiple-anodizing process improved the characteristics of IMS, including insulating and thermal performances. BGA packages were achieved on the IMS through electroless plating, electroplating, and photolithography methods.     

Approach on Thermal Strain Behaviour of PBGA Solder Joints

Abstract: The aim of this study was to provide a systematic method to analyse and test the thermal strain behaviour of plastic ball grid array (PBGA) solder joints in electronic packaging. Based on the structural, thermal and physical properties of the PBGA sample, the thermal strain test was developed to measure the strain distribution at the surface of the bismaleimide triazin (BT) substrates and the printed circuit board (PCB) surface under thermal cycling, at the temperature range of 0 to 100°C. The experimental results show that the changing trends of strain in the BT and PCB surfaces were approximately the same during the thermal cycling. Comparison between the experimental results and simulation illustrates the validity of the experimental test and finite element modelling results. It builds a basis for future work for evaluating the design and reliability of the BGA packaging.     

Fatigue failure of pb-free electronic packages under random vibration loads

The electronic equipment are used in several fields like, automotive, aerospace, consumer goods where they are subjected to vibration loads leading to failure of solder joints used in these equipment. This paper presents a methodology to predict the fatigue life of Pb-free surface mounted BGA packages subjected to random vibrations. The dynamic characteristics of the PCB, such as the natural frequencies, mode shapes and damping ratios were determined. Spectrum analysis was used to determine the stress response of the critical solder joint and the cumulative fatigue damage accumulated by the solder joint for a specific duration was determined.     

A meso-scale damage evolution model for cyclic fatigue of viscoplastic materials

This study presents an approach to predict the degree of material degradation and the resulting changes in elastic, plastic and creep constitutive properties of viscoplastic materials, during cyclic loading in micro-scale applications. The objective of the study is to address the initiation and growth of homogeneous meso-scale damage, in the form of distributions of micro-cracks and micro-voids, due to cyclic, plastic (rate-independent inelastic) and creep (rate-dependent inelastic) deformations in viscoplastic materials and to evaluate the resulting changes in the effective meso-scale elastic, plastic and creep constitutive properties. An energy partitioning damage evolution (EPDE) model is proposed to describe the viscoplastic damage evolution. Development of the EPDE model constants is then demonstrated for a Pb-free solder, based on cyclic fatigue test data. Application of the EPDE model is demonstrated for solder joint fatigue during thermal cycling of a ball grid array (BGA) electronic assembly. A 3D viscoplastic finite element analysis is conducted, and damage evolution is modeled using a successive initiation (SI) technique reported earlier by the authors. In this approach, the local (meso-scale) material properties are progressively degraded and highly damaged sections of the macro-scale structure are ultimately eliminated, using the EPDE model. Prediction of damage initiation and propagation is presented both with and without property updating, for comparison purposes. The analysis shows that the EPDE model can realistically capture the softening observed during cyclic loading.     

Improving the reliability of ball grid arrays under random vibration by optimization of module design

Abstract

In this work, three different arrangements of circuit board in an electronic device were designed and the effects of random vibration frequencies on the reliability of ball grid arrays (BGA) in these arrangements were evaluated. The failure criterion in solder balls was the root mean square of peeling stress exerted during the dynamical loadings. According to the finite element method (FEM) results, the uttermost stress concentration was generated at the interface of printed circuit board (PCB) and the solder balls. It was also revealed that the increase of input power spectral density (PSD) decreased the fatigue life of solder joint in all the arrangements. Considering the arrangements of circuit boards, it was found that the maximum domain of peeling stress had a minimum effect on the solder balls when the heat sinks were away from the packages. The microstructural characterization of critical zone in solder balls indicated that with the increase of maximum peeling stress, the crack initiated and propagated along the interface.     

Bending strength of adhesive joints in microelectronic components: Comparison of edge-bonding and underfilling

The bending strength of underfilled and edge-bonded ball grid array (BGA) microelectronic packages assembled on printed circuit boards (PCBs) was compared using double cantilever beam (DCB) specimens. All specimens with fillets of the same size and shape failed at the same load, with cracks initiating and propagating within the PCB. This was consistent with measurements of the crack initiation strain energy release rate for PCB interfacial failure, which was significantly smaller than that of cohesive failure within the adhesives. Finite element analysis (FEA) indicated that the stress state in the PCB near the PCB-fillet interface in both underfilled and edge-bonded specimens was only a function of the adhesive fillet size and shape, and independent of the extent of the adhesive layer between the PCB and the BGA, and independent of the adhesive mechanical and thermal properties over the broad range of properties of the tested adhesives. This explained why decreasing the fillet curvature in edge-bonded specimens produced a significant increase in the joint strength. The crack path in the PCB of the edge-bonded specimens was found to change with the adhesive cure temperature; however, this had a negligible effect on the failure load.     

Detrimental angle range between c axis of Sn crystal and electron flow for the electromigration reliability of ball grid array devices

With the rapid development of miniaturization and high integration for electronic components, the increasing current density and Joule heat put a great challenge on the electromigration (EM) reliability. In this study, four kinds of surface finishes were adopted in ball grid array (BGA) structure in order to compare their EM reliability performance. Interfacial microstructure evolution during EM test was observed by scanning electron microscopy equipped with energy-dispersive spectroscopy. When surface finish of hot-air solder leveling and organic solderability preservative were adopted, two IMCs, i.e., Cu₃Sn and Cu₆Sn₅ were formed at the Cu/SnAgCu interface. When electroless nickel immersion gold and electroless nickel electroless palladium immersion gold were used, only (Cu, Ni)₆Sn₅ was formed. Moreover, crack was found on the cathode with Ni-free surface finish. However, it was also noticed that not all the cathodes with Ni-free surface finish would fail even under the same test condition. In order to find out the hidden factors influencing the EM reliability, electron back-scattered diffraction analysis was conducted. According to the statistics, the grain orientation of Sn crystal played a decisive role on the EM reliability, especially when the transgranular migration took a major part along the diffusion path. Detrimental angle range between c axis of Sn crystal and electron flow was calculated as smaller than 45°. It was because the angles influenced the migration rate of atoms, further determined the initiation of cracks. This study reveals a hidden dominant factor of EM reliability, which also gives insights for analyzing EM reliability and improving overall reliability of BGA devices.

     

Life Prediction of Ball Grid Array Soldered Joints under Thermal Cycling Loading by Fracture Mechanics Method

［1］J.J.Wang, M.F.Lu, D.Q.Zou and S.Liu: IEEE-CPMT(B), 1998, 21, 79. ［2］Y.H.Pao, E.Jih and V.Siddapureddy: J. of Electronic Packaging, 1996, 118, 235. ［3］H.U.Akay, N.H.Paydar and A.Bilgic: J. of Electronic Packaging, 1997, 119, 228. ［4］D.J.Xie, Y.C.Chan and J.K.Lai: IEEE-CPMT(B),1996, 19, 669.     

Nondestructive analysis of interconnection in two-die BGA using TDR

Nondestructive analysis (NDA) is one of the most important tasks that is performed during the industrial characterization of integrated circuits (ICs) because even a tiny defect or failure in the IC packages could be disastrous from the standpoint of quality control. To detect an interconnection failure in IC packages, a time-domain reflectometry (TDR) analysis system was developed. An open-end fixture (OEF) was employed to detect the rapid rise of edge signals from the package and to monitor them under the two parameters of time interval and reflection voltage. We developed a simple and effective electrical NDA system based on the TDR technology that can evaluate the interconnection of ball grid array (BGA) packages. The TDR-measurement results can determine both the failure location and type based on the aforementioned parameters for a two-die BGA package.     

板级跌落碰撞下无铅焊点的有限元分析

为了预测跌落碰撞下球栅阵列(BGA)封装中无铅焊点的失效,采用ABAQUS软件来模拟跌落碰撞过程中焊点的应力分布.首先建立圆形电路板(PCB)组件的有限元模型,接着用模态试验和有限元模拟相结合的方法确定有限元模型的边界条件和PCB的阻尼参数,然后运用ABAQUS有限元软件模拟PCB组件从三种高度下跌落碰撞过程中BGA封装中无铅焊点的拉应力分布.结果表明:封装最外圈四个拐角焊点的拉应力最大,最大拉应力出现在焊点靠近封装的一侧.由此预测最外圈拐角的焊点最易失效,焊点失效的位置在靠近封装一侧.