Understanding the Influence of Copper Nanoparticles on Thermal Characteristics and Microstructural Development of a Tin-Silver Solder

This paper presents and discusses issues relevant to solidification of a chosen lead-free solder, the eutectic Sn-3.5%Ag, and its composite counterparts. Direct temperature recordings for the no-clean solder paste during the simulated reflow process revealed a significant amount of undercooling to occur prior to the initiation of solidification of the eutectic Sn-3.5%Ag solder, which is 6.5 °C, and for the composite counterparts, it is dependent on the percentage of copper nanopowder. Temperature recordings revealed the same temperature level of 221 °C for both melting (from solid to liquid) and final solidification (after recalescence) of the Sn-3.5%Ag solder. Addition of copper nanoparticles was observed to have no appreciable influence on melting temperature of the composite solder. However, it does influence solidification of the composite solder. The addition of 0.5 wt.% copper nanoparticles lowered the solidification temperature to 219.5 °C, while addition of 1.0 wt.% copper nanoparticles lowered the solidification temperature to 217.5 °C, which is close to the melting point of the ternary eutectic Sn-Ag-Cu solder alloy, Sn-3.7Ag-0.9Cu. This indicates the copper nanoparticles are completely dissolved in the eutectic Sn-3.5%Ag solder and precipitate as the Cu₆Sn₅, which reinforces the eutectic solder. Optical microscopy observations revealed the addition of 1.0 wt.% of copper nanoparticles to the Sn-3.5%Ag solder results in the formation and presence of the intermetallic compound Cu₆Sn_5. These particles are polygonal in morphology and dispersed randomly through the solder matrix. Addition of microsized copper particles cannot completely dissolve in the eutectic solder and projects a sunflower morphology with the solid copper particle surrounded by the Cu₆Sn₅ intermetallic compound coupled with residual porosity present in the solder sample. Microhardness measurements revealed the addition of copper nanopowder to the eutectic Sn-3.5%Ag solder resulted in higher hardness.     

2000年—2001年磁性功能材料研究和应用新进展

综述了磁性功能材料研究和应用在2000年－2001年间的新进展，其内容包括：（1）自旋电子学；（2）Bi-Fe氧化物的磁性；（3）稀有和稀土金属垂直磁记录材料；（4）新的多层膜磁性材料；（5）磁浮列车。     

CoCrPtNb／CrTi／C多层膜记录介质的制备和性能研究

采用CoCrPtNb四元合金作磁记录介质，并采用多层膜结构（CoCrPt）100-Nbx/CrTi／C／Glass制备玻璃盘基硬盘。实验结果表明：采用适宜厚度的籽晶层与合适组分的底层和磁性层的多层膜结构，即使在室温下溅射，此种薄膜磁记录介质也可得到高达260kA／m的矫顽力；在550℃高温下，经过30min真空退火后，其矫顽力有较大幅度提高，并在Nb含量为2．4％（原子分数）时达到极大值386kA／m，适用于高密度磁记录。同时，也详细分析了磁性层和底层组分、籽晶层厚度以及真空退火对磁记录介质磁性能和微结构的影响。     

磁性材料产业现状与展望

介绍磁性材料的主要品种，如永磁体、软磁体和磁记录介质材料的行业现状及技术进步。     

超高密度磁记录的课题与展望

介绍了超高密度记录的研究开发状况 ,论述了垂直磁记录技术的课题以及采用TMR磁头的、记录密度为Subterabit in2 的记录 读出特性。作为高密度记录所必需的头 盘界面技术 ,提出了接触记录技术的课题 ,还就STM (Scanningtunnelingmicroscopy)存储器论述了未来超高密度技术     

相控阵雷达天线阵面记录回放系统

相控阵雷达广泛应用,其天线阵面对记录回放系统的数据速率要求提升。针对两种传统记录回放系统架构的不足,结合其优点,设计并实现了一种新型的基于FPGA的记录回放系统。该系统设计为板卡的形式,FPGA实现对硬盘的读写操作,采用自定义的文件系统对数据进行管理。经过测试,系统记录速度可以达到292 MB/s,回放速率为340 MB/s。实验结果表明,该记录回放系统性能稳定,通用性好,存储速率满足要求。     

Deformation Dynamics of a Reactive Medium During Gasless Combustion

Deformation during gasless combustion of 5Ti + 3Si and Ti + C samples was studied experimentally. The dynamics of motion of the material in a gasless combustion wave was studied using highspeed video recording (500 frames/sec) with a spatial resolution of the order of 10 m. It was shown that behind the combustion front, the medium was first expanded and then compressed. The dimensions of the expansion and compression zones were determined.     

热敏微胶囊热响应特性研究

将热敏微胶囊作为基本显影单元,影像稳定性和分辨率得到了提高,影像形成速度也更符合数字化成像的要求。本文结合热敏技术、微胶囊技术,将染料前体微胶囊化,制备出粒径在1μm以下的热敏微胶囊。测量了囊壁的玻璃化温度,对显影后的影像进行了对比,测量了不同显影温度下的影像密度,分析了影像密度随显影温度变化的关系。     

电子辐射对渗透和非渗透性客体上指纹信息记录的影响

由于恐怖分子利用邮政系统投寄携带炭疽病毒的邮件,传播病毒,已引起美国政府在邮政系统,选择地利用电子辐射杀死病毒。然而,这种病毒袭击并没有得到有效控制,却使信封内的邮件由于高温辐射,受到损坏。有报道说,由于电子辐射使纸张、珠宝、信用卡、软盘和光盘及其它电子材料受到损害。某些研究已在法庭科学中得到验证。本文介绍辐射过程在渗透和非渗透性客体上,对化学试剂、生物酶记录指纹信息的影响。     

一种简便的无损录波数据压缩方法

利用电力系统大多数波形数据的变化率不大的特点,使用波形的变化率代替实时波形进行存储,缩小数据的表示范围,从而能够以更小的数据表示位数保存原信息,达到数据压缩的效果。由于所有的操作都只是对数据进行重新编码,所以本方法除了有无损数据压缩的特点外,整个压缩和解压的过程也都非常简单,特别适用于嵌入式系统使用。最后的现场数据分析表明,该方法也能够达到不错的数据压缩效果。