Warpage behavior of LOC-TSOP Memory Package

This paper describes a warpage study on LOC-TSOP memory devices. The main objectives of this study are to evaluate the impacts of epoxy mold compounds on package warpage with different sized dies. It was found that the balance of the bending between the edge side region and the die attach region controls the package warpage. The package tends to bend convex upwards in the edge side region and concave downwards in the die attach region. The various mold compounds were prepared to study the affect on the components, particularly the resin and the filler. It has been shown that the optimum mold compound can be changed according to the inner structure of the LOC-TSOP. The effect of post-mold cure on package warpage was also examined based on the cure rate.     

Research on the reduction of sink mark and warpage of the molded part in rapid heat cycle molding process

Rapid heat cycle molding (RHCM) is a recently developed innovative injection molding technology to enhance the surface quality of the plastic parts without extending the molding cycle. Most of the common defects that occur in the plastic parts produced by conventional injection molding (CIM), such as flow mark, silver mark, jetting mark, weld mark, exposed fibers, short shot, etc., can be well solved by RHCM. However, RHCM is not a nostrum for all the defects in injection molding. Sink mark and warpage are two major defects occurring in RHCM. The purpose of this study is to investigate and further solve the sink mark and warpage of the molded parts in RHCM. To solve the problem of sink mark, a new “bench form” structure for the screw stud on the product coupling with a lifter structure for the injection mold was proposed. The external gas assisted packing was also proposed to reduce the sink mark in RHCM. To solve the problem of warpage, design of experiments via Taguchi methods were performed to systematically investigate the effect of processing parameters including melt temperature, injection time, packing pressure, packing time and also cooling time on the warpage. Injection molding simulations based on Moldflow were conducted to acquire the warpages of the plastic parts produced under different processing conditions. A signal to noise analysis was conducted to analyze the effect of the factors, and the optimal processing parameters were also found out. ANOVA was also conducted to quantitatively analyze the percentage contributions of the processing parameters on the warpage. The verification results show that part warpage can be reduced effectively based on the optimal design results.     

Self-extinguishing epoxy molding compound with no flame-retarding additives for electronic components

A self-extinguishing epoxy molding compound that does not have any flame-retarding additives, such as halogen compounds, has been developed for electronic components. This compound enables the overcoming of environmental issues posed by these flame-retarding additives when compounds containing such additives are burned and disposed of. The molding compound contains phenol aralkyl-type epoxy resin and hardener, both of which include a specific multi-aromatic moiety (biphenylene) in novolac resin structure. The compound extinguished itself after ignition because it formed a stable foam layer on the resin surface during the ignition due to the low elasticity at high temperatures and high pyrolysis resistance of the compound after curing. The foam layer effectively retarded the transfer of heat to the inside during the ignition. Adding silica filler to the molding compound resulted in the synergistic effectiveness of the compound for flame resistance because it increased the foam-layer stability during burning. The molding compound showed other excellent characteristics, including moldability, water resistance, and package reliability. In fact, its resistance to soldering heat, humidity, and high-temperature storage was much better than that of current high-quality epoxy molding compounds containing halogen-type flame-retarding additives.     

Optimization of injection molding process parameters using sequential simplex algorithm

In this study warpage and shrinkage as defects in injection molding of plastic parts have been undertaken. MoldFlow software package has been used to simulate the molding experiments numerically. Plastic part used is an automotive ventiduct grid. The process optimization to minimize the above defects is carried out by sequential simplex method. Process design parameters are mold temperature, melt temperature, pressure switch-over, pack/holding pressure, packing time, and coolant inlet temperature. The output parameters aside from warpage and shrinkage consist of part weight, residual stresses, cycle time, and maximum bulk temperature. Results are correlated and interpreted with recommendations to be considered in such processes.     

Analysis of warpage and shrinkage properties of injection-molded micro gears polymer composites using numerical simulations assisted by the Taguchi method

Microgears containing four cavities and consisting of three different types of thermoplastic materials, namely, the amorphous polycarbonate/acrylonitrile–butadiene–styrene blend (PC/ABS), amorphous polyphenylene–ether/polystyrene (PPE/PS), and crystalline polyoxymethylene (POM) filled with glass fibers were analyzed. Molding parameters such as packing time, cooling temperature, molding and melting temperatures, packing and injection pressures, and fiberglass percentages are the most important factors affecting warpage and shrinkage. Three factors and their interactions were investigated in this case study. The effects of the injection parameters on warpage and shrinkage at different fiberglass percentages and cooling temperatures were analyzed according to the Taguchi method. The minimum values for warpage (0.0051 mm) and shrinkage (2.2886%) were derived from the PC/ABS and PPE/PS composites, respectively. Process efficiency predictions and conformational analyses of the optimal levels for each injection molding parameter were conducted to demonstrate the advantages of the Taguchi analytical method. The highest improvement percentages in the shrinkage and warpage analyses were obtained from the PPE/PS and the PC/ABS, respectively. PPE/PS was the best polymer composite by shrinkage analysis because of its molecular structure and minimum temperature at the flow front range, while the PC/ABS behaved the best in the warpage analysis.     

基于混沌粒子群的微齿轮注塑精密成形翘曲变形分析

目的 针对注塑加工生产的微齿轮运转一段时间后会出现严重变形的问题,对微齿轮注塑精密成形翘曲变形进行分析。方法 基于混沌粒子群建立微齿轮注塑CAE模型,获取曲面全局最优解,在此基础上,计算微齿轮注塑精密成形翘曲收缩率,得到翘曲变形量,同时优化微齿轮注塑精密成形工艺参数,分析微齿轮注塑精密成形翘曲变形情况。结果 将仿真结果与实际试验结果进行对比,得出该分析方法的预测结果与实际翘曲变化趋势完全一致。结论 微齿轮注塑中心位置的翘曲变形量最大,离中心位置越远,翘曲变形量越小。     

Vapor pressure assisted crack growth at interfaces under mixed mode loading

Moisture diffuses into the numerous pores and cavities formed in polymeric molding compounds, at the filler particle–polymer matrix interfaces and at polymer–silicon interfaces of IC packages. During reflow soldering, the rapidly expanding moisture generates high internal pressures within the voids which are comparable to yield strengths of the molding compounds at glass transition temperatures. The combined action of thermal stresses and high vapor pressure accelerates void growth, and ultimately leads to interface delamination and package cracking. In this study, the molding compound is taken to be an elastic–plastic material while the silicon substrate is treated as an elastic material. The extended Gurson model which incorporates vapor pressure as an internal variable is used to characterize the void growth and coalescence process at the interface. When the mode II loading is dominant, high vapor pressure can cause several-fold reduction in the interface fracture toughness.     

A hybrid inverse method for evaluating FC-PBGA material response to thermal cycles

This study proposes a hybrid experimental-analytical inverse method that can be used to evaluate thermomechanical cyclic behavior of flip-chip plastic ball grid array modules and the constituent materials. Treating such a package as an adhesively bonded trilayer plate, the structural formulation follows and modifies an existing analytical model. A phase-shifted shadow moiré method is employed to obtain the package thermal warpage variation in responding to a temperature cycle. By correlating the modeling predicted and the experimentally measured package warpage, the application of the method leads to the determination of those uncertain material parameters including temperature dependent modulus of elasticity and coefficient of thermal expansion of the die attachment and the substrate materials. These parameters are difficult to determine otherwise due to the complexity involving the effect of package processing condition and extremely thin thickness of the adhesive layer. As the values of all material parameters are ascertained, shear and peel stresses in the module adhesive layer can also be evaluated based on the analytical model.     

Prediction of shrinkage and warpage in consideration of residual stress in integrated simulation of injection molding

The accurate prediction of shrinkage and warpage of injection molded parts is important to achieve successful mold design with high precision. In this study, the numerical analysis of shrinkage and warpage of injection molded parts made of amorphous polymers was carried out in consideration of the residual stresses produced during the packing and cooling stages of injection molding. The temperature and pressure fields were obtained from the coupled analysis of the filling and post-filling stages. For residual stress analysis, a thermo-rheologically simple viscoelastic material model was introduced to consider the stress relaxation effect and to describe the mechanical behavior according to the temperature change. The effect of the additional material supply during the packing stage was modeled by assigning the reference strain. The deformation of injection molded parts after ejection induced by the residual stress and temperature change was analyzed using a linear elastic three-dimensional finite element approach. In order to verify the numerical predictions obtained from the developed program, the simulation results were compared with the available experimental data in the literature. In the case of residual stress, it was found that the present simulation results overpredicted the tensile residual stresses at the surface of injection molded parts. However, the predicted shrinkage was found to be reasonable to describe the effects of processing conditions well. Finally, an analysis of the shrinkage and warpage was successfully extended for a part with a more complex curved shape.     

Investigation on the transferability of algorithms for the numerical optimization of cooling channel design in injection molding on metal gravity die casting

The thermal mold design and the identification of a proper cooling channel design are primordial steps in the development of complex molds for injection molding. In order to find a suitable cooling channel system, a lot of effort is needed to avoid part warpage after solidification. In current research, a simulative procedure to optimize the cooling channel layout iteratively is being developed at the Institute of Plastics Processing. These algorithms are transferred to the metal gravity die casting process, which has several similar requirements to the mold. Effectively, the simulation is simplified to a heat conduction problem. Instead of water, high temperature resistant oil is deployed and the casted material is a A356 aluminum alloy instead of semi‐crystalline plastics. The algorithm is adapted to these changed boundary conditions and the calculation of the optimized heat distribution is performed. Aim of this procedure is the construction of a mold producing parts with less warpage than a conventional mold.     

Warpage and Shrinkage Optimization of Injection-Molded Plastic Spoon Parts for Biodegradable Polymers Using Taguchi,ANOVA and Artificial Neural Network Methods

In this study, it is attempted to give an insight into the injection processability of three self-prepared polymers from A to Z. This work presents material analysis, injection molding simulation, design of experiments alongside considering all interaction effects of controlling parameters carefully for green biodegradable polymeric systems, including polylactic acid(PLA), polylactic acid-thermoplastic polyurethane(PLA-TPU) and polylactic acid-thermoplastic starch(PLA-TPS). The experiments were carried out using injection molding simulation software Autodesk Moldflow?in order to minimize warpage and volumetric shrinkage for each of the mentioned systems. The analysis was conducted by changing five significant processing parameters, including coolant temperature, packing time, packing pressure, mold temperature and melt temperature. Taguchi's L27(35) orthogonal array was selected as an efficient method for design of simulations in order to consider the interaction effects of the parameters and reduce spurious simulations. Meanwhile, artificial neural network(ANN) was also used for pattern recognition and optimization through modifying the processing conditions. The Taguchi coupled analysis of variance(ANOVA) and ANN analysis resulted in definition of optimum levels for each factor by two completely different methods. According to the results, melting temperature, coolant temperature and packing time had significant influence on the shrinkage and warpage. The ANN optimal level selection for minimization of shrinkage and/or warpage is in good agreement with ANOVA optimal level selection results. This investigation indicates that PLA-TPU compound exhibits the highest resistance to warpage and shrinkage defects compared to the other studied compounds.     

Notched behavior of prepreg-based discontinuous carbon fiber/epoxy systems

The elastic behavior and failure response of discontinuous carbon fiber/epoxy laminates produced by compression molding of randomly-oriented preimpregnated unidirectional tape is characterized. Commercial applications for this type of material form already exist, such as Hexcel HexMC^®. Complex relationships between unnotched and notched tensile strengths are observed, and show this material to be particularly notch-insensitive. A parametric study on the effect of specimen thickness, width, diameter/width ratio, and hole size yields fundamental information on the behavior of this material.     

基于代理模型和改进遗传算法的注塑翘曲优化

提出一种最小化制品翘曲的注塑工艺参数优化集成方法.以空调柜机顶盖注塑制品开发为例,该方法使用Moldflow软件分析制品的翘曲变形,运用田口方法确定与制品翘曲量密切相关的工艺因素,然后采用响应曲面法(RSM)和改进的精英保留自适应遗传算法(EAGA)相结合的方法,建立主要影响工艺参数与制品翘曲量之间的关系模型,通过对模型寻优以实现对制品翘曲的优化.该方法的适用性在制品的实际生产中得到了验证.     

Tool–part interaction in composites processing. Part I: experimental investigation and analytical model

The ability to process composite structures with a high degree of dimensional control remains a barrier to further implementation of composite materials in commercial applications. Of the numerous types of process induced deformations that occur, the warpage of flat laminates due to tool–part interaction remains a poorly understood phenomenon. This paper presents an experimental study of the effect of process conditions and part aspect ratio on tool–part interaction induced warpage. For a given lay-up and material, part aspect ratio was found to have a much greater influence than autoclave pressure on warpage, while the tool surface condition was not observed to have any significant effect. The results of the study are embodied in an empirical relation, which can be a useful guide to predict laminate warpage over a range of industrially relevant conditions. In addition, a simple analytical model is proposed which agrees well with the experimentally determined relationships. A complementary numerical model is presented in a companion paper.     

塑件翘曲度及其计算方法

参考其它行业中翘曲度的应用,引入了评价注塑制品翘曲变形的翘曲度概念。随后对特征尺寸上的翘曲度、平面上特征的翘曲度进行了详细的阐述,并在构建注塑CAE翘曲变形模拟结果的数据结构基础上,提出了基于注塑CAE翘曲变形模拟结果的翘曲度计算方法。用一实例说明了用平面特征上的翘曲度评价翘曲变形的有效性。     

FDM技术中加热底板样式对翘曲变形的影响研究

针对熔融沉积成型（fused deposition modeling,FDM）过程中存在的典型缺陷--翘曲变形,以加热底板样式为研究重点,对比ANSYS数值模拟结果与成型实验数据,探究普通加热底板与九宫格加热底板对成型件翘曲变形量的影响。在数值模拟过程中,采用生死单元技术建立2种加热底板上成型件温度场模型,再采用热-力间接耦合的方法分析成型件的应力分布,最后得到成型件翘曲变形的位移云图,分析2种加热底板上成型件的翘曲变形量。在进行成型实验时,分别在普通加热底板与九宫格加热底板上打印试件,再进行2种加热底板成型件的4个角点的翘曲变形量的测量。对比2种加热底板上成型件在ANSYS数值模拟与成型实验中的最大翘曲变形量,结果表明：九宫格加热底板相比普通加热底板能更好地减小由成型件残余应力导致的翘曲变形,即在实际打印成型过程中,不需要对3D打印机的生产参数作任何调整,只需要将工作平台处的普通加热底板换为九宫格加热底板则能极大地减小成型件的翘曲变形,有助于得到具有较高质量精度的成型产品,这对提高成型产品质量具有重要的参考意义。     

A 3‐node flat triangular shell element with corner drilling freedoms and transverse shear correction

The formulation, implementation and testing of simple, efficient and robust shell finite elements have challenged investigators over the past four decades. A new 3‐node flat triangular shell element is developed by combination of a membrane component and a plate bending component. The ANDES‐based membrane component includes rotational degrees of freedom, and the refined nonconforming element method‐based bending component involves a transverse shear correction. Numerical examples are carried out for benchmark tests. The results show that compared with some popular shell elements, the present one is simple but exhibits excellent all‐around properties (for both membrane‐and bending‐dominated situations), such as free of aspect ratio locking, passing the patch test, free of shear locking, good convergence and high suitability for thin to moderately thick plates. The developed element has already been adopted in a warpage simulation package for injection molding. Copyright © 2011 John Wiley & Sons, Ltd.     

Experimental study of warpage and shrinkage in injection molding of HDPE/rPET/wood composites with multiobjective optimization

In this paper, injection molding of squared parts with 1.25 mm in thickness, composed of wood plastic composites (high-density polyethylene, recycled polyethylene terephthalate, and wood flour), was done. The warpage and volumetric shrinkage in the parts was determined experimentally with various process conditions (packing time, melt temperature, wood content, and packing pressure). The experiments were done based on Box–Behnken design of experiments. The significance of each parameter and model was evaluated by analysis of variance (ANOVA). ANOVA showed that packing time and melt temperature are the most significant parameters on warpage and wood content is the most significant on volumetric shrinkage. Packing pressure and wood content had no considerable effect on warpage and packing time on shrinkage too. To obtain optimal process conditions for minimum warpage and shrinkage, a multiobjective optimization based on Pareto front was developed. Response surface method was used to find the relationships between input parameters and objective functions, and genetic algorithm presented the Pareto front solutions to determine the optimum solution. It was observed that there was a good agreement between the predicted optimum values and the experiments.     

工艺参数对短玻璃纤维增强PP复合材料注射压力和翘曲变形的影响

采用Moldflow对聚丙烯及其短玻璃纤维增强复合材料的注塑成型过程进行3D模拟分析,基于Taguchi试验设计方法(DOE),采用L16(45)正交矩阵进行试验设计,研究工艺参数对注射压力和翘曲变形的影响。结果表明,纤维含量对注射压力和翘曲变形影响作用较为显著,且存在最佳值;模具温度、熔体温度、保压时间和保压压力对注射压力的影响为单调的线性关系,但其对翘曲变形的影响较复杂。     

Effect of Nano-fillers on the Strength Reinforcement of Novel Hybrid Polymer Nanocomposites

The aim of this article is to investigate the effect of the ratio of fillers, such as multiwalled carbon nanotubes (MWCNTs) and graphene nanoplatelets (GNPs), as well as different matrix stiffnesses, on the tensile strength of epoxy/polyester material. These fillers are added to epoxy/polyester solutions in various ratios and mixed well before molding. Experimental specimens are then made by means of the hot press process and utilizing the same curing and postcuring conditions. To investigate the effect of the matrix stiffness on the mechanical property reinforcement role of MWCNTs and GNPs in the resulting nanocomposites, the variations in the mixture ratios of the epoxy/polyester blend and hardener are considered. The results show that the tensile strength of epoxy/polyester material increases its maximum value by approximately 86.3% with the addition of MWCNTs at a ratio of 1% and increases to 86.8% with the addition of a mere 0.2% ratio of GNPs. The morphologies of the fractured surfaces of the resulting nanocomposites are observed by a scanning electron microscope (SEM). It is expected that the experimental results will lead to the offering of low-cost, high-strength materials for applications in the automobile industry and the manufacturing of household products.