散热密集孔爆板分层改善探讨

随着电子产品应用技术的不断更新以及功能的完善,板件的散热性能要求越来越高,因此大量的散热密集孔设计应用于印制线路板,由此带来散热密集孔分层的问题。本文通过对密集散热孔裂纹区域的分析、研究,对VIP散热密集孔设计、钻孔参数、烘烤参数进行了试验验证,并提出了散热密集VIP孔爆板分层改善的方向。     

塑封组件可靠性测试中加速浸润方法的研究

在对塑封集成电路进行封装可靠性评估中,预处理过程是必经的步骤,其中的浸润测试通常在非加速条件下进行,耗时较长。在市场竞争日趋激烈的环境下,企业迫切需要缩短新产品的可靠性验证时间。针对JEDEC(电子器件工程联合委员会)和JEITA(日本电子信息技术协会)标准中涉及到的三种加速浸润条件,以组件在非加速条件下(JEDECLevel3和JEITARankE)潮气的穿透力、吸收量及由此产生的失效为参照,确定在加速条件下,组件达到同样的潮气吸收量并产生相类似的失效所需的时间;同时应用有限元分析的方法进行建模和计算,并与实际的测量结果比较验证。     

加速浸润方法在塑封可靠性分析中的应用

在对塑封集成电路进行封装可靠性评估中,预处理过程(precondition)是必经的步骤。其中的浸润测试(soak)通常在非加速条件下进行,其耗时较长。在市场竞争日趋激烈的环境下,企业迫切需要缩短新产品的可靠性验证时间。文章针对JEDEC(电子器件工程联合委员会)和JEITA(日本电子信息技术协会)标准中涉及到的三种加速浸润条件,以组件在非加速条件下(JEDEC Level 3和JEITA Rank E)潮气的穿透力、吸收量及由此产生的失效为参照,确定在加速条件下,组件达到同样的潮气吸收量并产生相类似的失效所需的时间。同时应用有限元分析的方法进行建模和计算,并与实际的测量结果比较验证。     

渗碳体分解对高碳钢丝分层的影响

根据拉丝过程中渗碳体分解的观点,并通过实验数据,对高碳钢丝发生分层现象进行研究。当钢丝中铁素体的最高碳原子分数超过1%,钢丝就会发生分层;高碳钢丝的渗碳体在因拉拔而温度升高的表层附近及拉丝后的片层间距小的区域更易分解;拉拔加工导致的强度不均匀性增大是发生分层的主要原因。     

脱粘裂纹扩展诱发热障涂层陶瓷层温度场演变与烧结行为研究

目的 研究等离子喷涂热障涂层(APS-TBCs)内部脱粘裂纹尺寸对陶瓷层温度场与烧结行为的影响.方法 采用有限元模型研究不同尺寸脱粘裂纹对其上方陶瓷层温度场变化规律的影响,并通过梯度热循环试验对裂纹上方陶瓷层烧结行为进行研究,采用扫描电子显微镜(SEM)分析陶瓷层表面和断面的组织形貌,并使用图片法对裂纹上方陶瓷层不同区域的孔隙率进行分析.结果 裂纹上方陶瓷层温度变化区域的面积取决于裂纹尺寸,且最高温度始终位于裂纹中心的上方陶瓷层表面,随着裂纹宽度向两端依次递减,其对应的上方温度依次递减.在本试验条件下,随着脱粘裂纹尺寸的增加,涂层厚度方向的最高温度以线性形式增加,裂纹尺寸每增加0.5 mm,其上方陶瓷层同一位置处的温度增加约30℃,且最高温度区域随之增大.裂纹长度超过3 mm时,在脱粘裂纹热阻效应下,裂纹上方陶瓷层区域的温度升高.裂纹越长,上方陶瓷层整体温度提升越高,不仅导致陶瓷层发生相变和烧结的区域增大,还使得相变和烧结速率升高.不同梯度热循环次数下,陶瓷层表面和内部均出现了数量和长度不等的脱粘、垂直裂纹,烧结面积逐渐增大.脱粘裂纹长度为4 mm时,其最大宽度约40μm.结论 脱粘裂纹上方陶瓷层温度变化以表面最高温度处为中心向四周呈放射性递减.越靠近陶瓷层表面,层状组织信息越少,相应区域的孔隙率越小,烧结和相变程度逐渐增加,使涂层发生脱落失效的可能性进一步增加.     

Interlayer delamination and adhesion of coextruded films

Efforts to evaluate interlayer adhesion of coextruded films are often hampered by the inability to initiate delamination. On the other hand, interlayer delamination was often noticed at cut or trimmed edges of coextruded films. In this study, a test method was developed by first initiating delamination by uniaxial stretching and then measuring interlayer adhesion by peel test. Delamination was initiated by uniaxial stretching under controlled conditions for samples with double‐neck geometry. The double‐neck geometry was designed to create a specimen for the subsequent 180° peel test. Peel force was used to quantify interlayer adhesion of coextruded films based on polycarbonate and its copolymers. With this two‐step technique, coextruded films with peel force as high as 5300 N/m or 30 lb./in. were quantified. In addition, effects of copolymer composition and coextrusion processing condition on interlayer adhesion of these coextruded films were clearly demonstrated. A great deal of variation of interlayer adhesion across film surface was also revealed. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3901–3909, 2004     

New Adhesion Promoters for Copper Leadframes and Epoxy Resin

New primer molecules have been synthesized to increase the adhesion strength between a copper leadframe and an epoxy molding compound in microelectronical devices. The coupling agents were preliminarily chemisorbed at the surface of copper plates via special binding groups like thiol, disulfide, ethylene diamine and phthalocyanine. Binding to the epoxy resin was performed via an hydroxyl group. Linear hydrocarbon spacers with various chain lengths connected the copper- and epoxy-binding groups. The self-assembled layers of the organic coupling agents at the metal surface were characterized by X-ray photoelectron spectroscopy. Thermogravimetric analysis was used to study the coating with respect to its corrosion oxidation inhibition. Shear tests clearly indicated that the coupling agents increase adhesion strength and are stable even in extreme humidity and thermal conditions in analogy to IPC-Level-1 pretreatment. Thus, delamination of the microelectronical packages was prevented.     

Thermoplastic Sizing of Carbon Fibres in High Temperature Polyimide Composites

Thermoplastic sizing of various carbon fibres has been evaluated as a means of controlling the microcracking resistance, transflexural strength (TFS), and thermo-oxidative stability (TOS) of PMR-15 matrix composites. Four different fibre/thermoplastic size combinations were selected for this study, based on their higher TOS than appropriate controls. Data are presented for the transverse microcrack (TVM) density/inch, and the subsequent delamination of [0,90]_4s laminates induced by thermal cycling (-196 to 350°C for 20 cycles). Results for composite TFS, conditioned TFS (after heating in air at 350°C), and TOS (350°C and 316°C) are also reported. One fibre/thermoplastic size combination gave both good microcracking resistance, and significantly improved TOS, in composite when compared with current commercially-available material.     

A holistic mathematical modelling and simulation for cathodic delamination mechanism – a novel and an efficient approach

This paper addresses a holistic mathematical design using a novel approach for understanding the mechanism of cathodic delamination. The approach employed a set of interdependent parallel processes with each process representing: cation formation, oxygen reduction and cation transport mechanism, respectively. Novel mathematical equations have been developed for each of the processes based on the observations recorded from experimentation. These equations are then solved using efficient time-iterated algorithms. Each process consists of distinct algorithms which communicate with each other using duplex channels carrying signals. Each signal represents a distinct delamination parameter. As a result of interdependency of various processes and their parallel behaviour, it is much easier to analyse the quantitative agreement between various delamination parameters. The developed modelling approach provides an efficient and reliable prediction method for the delamination failure. The results obtained are in good agreement with the previously reported experimental interpretations and numerical results. This model provides a foundation for the future research within the area of coating failure analysis and prediction.     

Mechanics of the indentation test and its use to assess the adhesion of polymeric coatings

The indentation test provides a simple means by which the adhesion of coatings can be qualitatively assessed. On the way to establishing a quantitative measurement of the adhesion strength of coatings and films, it is important that the mechanics of this test are clearly understood. To investigate the influence of factors such as the coating thickness, the indenter radius, and friction during the test, numerical simulations of the indentation of a typical polymeric coating, polymethylmethacrylate (PMMA), bonded to a rigid substrate were conducted by using the finite element method. The stress generated during the indentation test were obtained by employing an accurate constitutive model of the elastic-viscoplastic behaviour of the polymeric coating under consideration. The results of this analysis illustrate the effects of the factors mentioned above on the deformation of the coating during indentation, its confinement, and interfacial shear, and the normal, shear, and hoop stress distributions occurring during indentation. These results provide insight into the possible failure mechanisms operative during the indentation of thin coatings and the important effects of the coating thickness during such tests.