Deformation Of Printed Circuit Board Research Articles

Advanced utilization of 3D digital image correlation for thermal and impact reliabilities of electronics components

PurposeThis paper aims to present an adaptation of digital image correlation (DIC) to the electronics industry for reliability assessment of electronic packages. Two case studies are presented: one for warpage measurement of a micro-electro-mechanical system (MEMS) package under different temperature conditions and the other for the measurement of transient displacements on the surface of a printed circuit board (PCB) assembly under free-fall drop conditions, which is for explaining the typical camera setup requirement and comparing among different boundary conditions by fastening methods of PCB.Design/methodology/approachDIC warpage measurements on a small device, such as a MEMS package, require a special speckle pattern. A new method for the creation of speckle patterns was developed using carbon coating and aluminum evaporative deposition. To measure the transient response on the surface of a PCB during a free-fall impact event, three-dimensional (3D) DIC was integrated with synchronized stereo-high speed cameras. This approach enables the measurement of full-field displacement on the PCB surface during a free-fall impact event, contrary to the localized information that is obtained by the conventional strain gage and accelerometer method.FindingsThe authors suggest the proposed patterning method to the small-sized microelectronics packages for DIC measurements. More generally, the idea is to have a thin layer of the dark or bright color of the background and then apply the white or black colored pattern, respectively, so that the surface has high contrast. Also, to achieve a proper size of speckles, this paper does not want to expose the measuring objects to high temperatures or pressures during the sample preparation stage. Of course, it seems a complicated process to use aluminum evaporator, carbon coater and electroformed mesh. However, the authors intend to share one of the solutions to achieve a proper pattern on such small-sized electronic packages.Originality/value3D DIC technique can be successfully implemented for the measurement of micro-scale deformations in small packages (such as MEMS) and for the analysis of dynamic deformation of complex PCB.

Heat transfer enhancement by flexible printed circuit board's deformation

Flexible printed circuit board (FPCB) has started replacing rigid PCB in some electronic application. However, the deflection and heat transfer of FPCB caused by flow and thermal are far more crucial compared to rigid PCB. In the current study, effects of flow and thermal induced deflection were coupled in real time. The numerical modelling was executed using FLUENT and ABAQUS, coupled online by Mesh-based Parallel Code Coupling Interface (MpCCI). The numerical findings have been validated with experimental results. Rigid PCB with same thermal properties of FPCB has been compared. The findings showed that the deflection of the FPCB does help to increase the heat transfer of the PCB. Furthermore, models with different power of heat sources along with various Reynolds numbers (Re) had been studied. The results exhibited that the magnitude and the trend lines' pattern of deflection divided by characteristic length changes according to thermal power. It indicates both flow and heat have significant effect to the deflection and Nusselt number (Nu) of FPCB. Therefore, flow and thermal should be coupled at the same time for more realistic FPCB simulation under flow environment in operating condition.

Realistic warpage evaluation of printed board assembly during reflow process

Purpose – This paper aims to develop an estimation tool for warpage behavior of slim printed circuit board (PCB) array while soldering with electronic components by using finite element method. One of the essential requirements for handheld devices, such as smart phone, digital camera, and Note-PC, is the slim design to satisfy the customers’ desires. Accordingly, the printed circuit board (PCB) should be also thinner for a slim appearance, which would result in decreasing the PCB’s bending stiffness. This means that PCB deforms severely during the reflow (soldering) process where the peak temperature goes up to 250°C. Therefore, it is important to estimate PCB deformation at a high temperature for thermo-mechanical quality/reliability after reflow process. Design/methodology/approach – A numerical simulation technique was devised and customized to accurately estimate the behavior of a thin printed board assembly (PBA) during reflow by considering all components, including PCB, microelectronic packages and solder interconnects. Findings – By applying appropriate constraints and boundary conditions, it was found that PBA’s warpage can be accurately predicted during the reflow process. The results were also validated by warpage measurement, which showed a fairly good agreement with one and another. Research limitations/implications – For research limitations, there are many assumptions regarding numerical modeling. That is, the viscoplastic material property of solder ball is ignored, the reflow profile is simplified and the accurate heat capacity is not considered. Furthermore, the residual stress within the PCB, generated at PCB manufacturing process, is not included in this paper. Practical implications – This paper shows how to calculate PBA warpage during the reflow process as accurately as possible. This methodology helps a PCB designer and surface-mount technology (SMT) process manager to predict a PBA warpage issue and modify PCB design before PCB real fabrication. Practically, this modeling and simulation process can be easily performed by using a graphical user interface (GUI) module, so that the engineer can handle an issue by inputting some numbers and clicking some buttons. Social implications – In a common sense manner, a numerical simulation method can decrease time and cost in manufacturing real samples. This PCB warpage method can also decrease product development duration and produce a new product earlier. Furthermore, PCB is a common component in all the electronic devices. So, this PCB warpage method can have various applications. Originality/value – Because of an economic advantage, the development of a numerical simulation tool for estimating the thin PBA warpage behaviour during reflow process was attempted. The developed tool contains the features of detailed modeling for electronic components and contact boundary conditions of the supporting rails in the reflow oven.

Coupling effects of mechanical vibrations and thermal cycling on reliability of CCGA solder joints

The microstructures and crack propagation behavior of CCGA (ceramic column grid array) solder joints after sinusoidal vibration loading, random vibration loading, and thermal cycling test have been discussed in this study. The failure mechanism of solder joints was analyzed using an experimental method and finite element analysis. It was found that the failed solder joints mainly distributed at the peripheral area in the solder column arrays and the crack initiation was mainly caused by mechanical vibrations. The deformation of PCB (printed circuit board) introduced by mechanical vibrations brought the outermost solder columns in CCGA devices with significant stress concentration and induced the initiation of cracks. Furthermore, cracks propagated during the process of mechanical vibrations and thermal cycling. The cracks propagated rapidly and the solder joints finally failed. The structure of the PCB holder was improved to relieve the vibration response from the peripheral joints. No visible crack was found in the solder joints after the same mechanical vibrations and thermal cycling test. The reliability of solder joints have been greatly improved with the new PCB holder.

Optimum design of printed circuit board to reduce deformation in reflow process by a global optimization method

A printed circuit board (PCB) is a laminated composite made of circuit and insulator layers. The PCB is heated in a furnace in order to mount electronic devices. This process is called a reflow process. The PCB deforms in the reflow process by gravity and thermal expansion difference of materials. The mechanical properties of the layers of the PCB are modeled based on the micro mechanics of composites. In addition, the relationship between stress and strain of the PCB is modeled by using the laminated composite theory in order to estimate deformation of the PCB. A design optimization problem is defined so that the area ratios of copper in the circuit layers and the ratios of thickness increase in the insulator layers are determined to decrease the PCB deformation. A penalty is introduced into the objective function so that the cost of design change is minimized. Because the consideration of the less design change results in some sets of local optimum values of design variables, a global optimization method is adopted. Several optimization examples clarify features of the optimum PCB designs with small deformation and less design change. The validity of the optimum design is verified by an experiment.

多層基板の熱変形挙動の予測およびそのパッケージの反り解析への適用

In electronic packages such as a BGA package, decrease of package warpage in the temperature range where the package is used is a key issue in order to enhance the reliability of solder connection and to reduce the number of defective packages. If we can predict the package warpage accurately in the design stage of electronic packaging by using a simulation method, we can make use of such a prediction to enhance the reliability of electronic packaging. We need the material properties of silicon chip, molding resin and printed circuit board (PCB) used as a substrate to predict the package warpage. Among them, PCBs have multi-layered structures, and each layer has a complicated structure such as fine and high density wiring pattern. In the present study, we propose a method for predicting the thermal deformation of PCB using a finite element viscoelastic analysis, in which the complicated structure of each layer in PCB is taken into account. The apparent coefficient of thermal expansion (CTE) for PCB calculated from the proposed method is compared with the experimental results to show the effectiveness of the proposed method. Furthermore, it is shown that the warpage of a package consisting of a silicon chip and a substrate (PCB) can be predicted using the apparent CTE of PCB.

Modal analysis of board-level electronic package

The reliability of board-level electronic package subjected to drop impact is one of the most concerned issues. After drop impact, the Printed Circuit Board (PCB) experiences free vibration which leads to the deformation of PCB, hence the failure of solder joints. The free vibration is dependent on the inherent parameters of PCB. So it is necessary to study the inherent parameters of board-level package. Modal analysis is a common way to characterize the inherent dynamic parameters of a system. By modal analysis, we can understand the inherent vibration features of board-level package system. In this paper, the theoretical vibration model of the JEDEC standard PCB assembled with three Chip Size Packages (CSPs) is performed. Then the results of theoretical analysis are validated by that of finite element analysis (FEA) and modal test. A series of modal parameters are obtained during the modal analysis such as the mode shapes, the natural frequencies and the damping ratios. These parameters are useful for studying the dynamic response of PCB and the strain rate of solder joints during drop test. The Modal Assurance Criterion (MAC) value is used to validate the correlation between two modal shapes obtained from two different modal parameters estimation methods during modal analysis. The MAC value is computed for the first two order mode shapes, indicating the high correlation between the experimental and predicted (including theoretical and FE results) mode shapes.

Optimum Design of Printed Circuit Board for Warp Reduction in Reflow Process

A printed circuit board (PCB) is equipped with electronic devices. PCB is a laminate composite made of copper and resin. Electronic circuit in PCB is made of copper. PCB is heated in a furnace in order to fix electronic devices. This process is called a reflow process. PCB deforms in a reflow process by thermal extension difference between copper and resin. An analytical model was proposed to calculate deformation of PCB. Laminate mechanical model and micro mechanical model were used in the modeling. Area of copper circuit pattern was optimally decided in order to minimize PCB deformation. The analytical model and the method of feasible direction were used in the optimization. Upper and lower limits of copper area decided by circuit design were taken into consideration in the optimization.

Statistical analysis for test lands positioning and PCB deformation during electrical testing

The goal of this research is to develop a systematic, accurate and robust method for printed circuit board (PCB) positioning evaluation in the testing fixture. Theoretical analysis and experimental observation of tolerance distribution in bed-of-nails fixture were involved. Actual deformation of PCB (translation, rotation and deflection) could be obtained based upon a proposed model. The combined accuracy of the test lands positioning (false failure rate) were estimated by the Weibull distribution. All data processing was finished by MATLAB. Results will be helpful for evaluation of the minimal size of the PCB test lands and modification of the testing fixtures.

3-Dimensional graphic image representation of holographic microscopical displacement pattern by using cubic spline function

Abstract For quantitative measurement of microscopical displacement of an object surface due to thermal stress, the holographic pattern measuring system (HPMS) has been developed by the authors, which is combined both the techniques of holographic interferometry and graphic image processing. In this measuring sytem, a cubic spline function was applied to get the 3-dimensional graphic image patterns of the distribution of the displacement. The displacement is calculated from the interferometry fringe pattern, and the system was applied to deformation analysis of printed circuit board (PCB) due to thermal stress. The PCB deformation was expresed by 3-dimensional graphic image. A smooth curve could be obtained from rather less number of sampled data of interferometry fringe.

International quality control—cooperation in an overview : J. M. Juran. Quality Prog. p. 14/15 (July 1979)

The goal of this research is to develop a systematic, accurate and robust method for printed circuit board (PCB) positioning evaluation in the testing fixture. Theoretical analysis and experimental observation of tolerance distribution in bed-of-nails fixture were involved. Actual deformation of PCB (translation, rotation and deflection) could be obtained based upon a proposed model. The combined accuracy of the test lands positioning (false failure rate) were estimated by the Weibull distribution. All data processing was finished by MATLAB. Results will be helpful for evaluation of the minimal size of the PCB test lands and modification of the testing fixtures.