In this paper, the grain orientation evolution of Pb-free solder joints during thermomechanical fatigue (TMF) was characterized quantitatively using in-situ electron backscattered diffraction (EBSD) observation, which was an effective way to clarify the mechanism of recrystallization. The results showed that the grain orientation evolution of solder joints was significantly affected by the anisotropy of β-tin grains. Recrystallization behavior of a solder joint during TMF was very sensitive to the location of grain boundaries and orientations in the joints. Substantial stress could build up at grain boundaries in real joints in micro-electronic applications under thermomechanical stress, leading to premature failures. Also, slip systems were clarified playing an important role in recrystallization and could be used to predict the subgrain and recrystallized grain formation. While it was conventional cognitive, tricrystals were less likely to develop cracks during TMF and had longer lifetime than single-crystal joints. However, for the tricrystal joint with particularly undesirable orientations, it was clarified that (1 0 1)[1 0 \(\bar{1}\) ] and (1 0 1)[\(\bar{1}\) 0 1] silp systems were activated in tricrystals and premature failures occurred with the internal stress caused by anisotropic thermomechanical responses.

以北京工业大学节约型校园节能监管体系示范项目建设为背景,着眼于校园建筑低压配电系统的节能增效需求,从变电所参数监管系统的系统架构、功能特点等方面对该系统进行介绍,并对其在校园建筑节能监管方面的应用效果进行讨论.

This study quantitatively characterized the grain orientation evolution of Sn3.0Ag0.5Cu ball grid array (BGA) solder joints subjected to thermomechanical stress using electron backscatter diffraction (EBSD). Further polishing of the as-reflowed solder joint cross sections was avoided after thermal shock treatment to accurately analyze the underlying mechanism of recrystallization. No previous reports have been presented on this topic because of the inability to conduct pattern indexing due to cross-sectional contamination after thermomechanical fatigue. The results show that the pre-existing low-angle boundaries in the as-reflowed joints tend to gradually increase in misorientation and that low-angle boundaries inhomogeneously increase mainly by the cross-slip and climb of dislocations. Recovery tends to occur at the pre-existing low-angle boundaries in the as-reflowed joints and the regions in the solder joints near the package interface composed of a single grain, and there is a partial release of stored energy prior to recrystallization. However, the residual stored energy remains sufficiently high to induce subsequent recrystallization in the deformed solder alloy after subgrain formation. The transition process from subgrains to recrystallized grains is continuous, and subgrains appear before the formation of recrystallized grains in the Pb-free solder joints subjected to thermomechanical stress. The orientations of the small recrystallized grains separated by the low-angle boundaries evolve from the initial orientations by subgrain rotation. Additionally, the subgrain rotation behavior of Pb-free solder joints was investigated in terms of the rotation axis and angle. The results show that there is typically a single rotation axis for each subgrain in the early stages of recrystallization. This finding confirms the interrelationship between the activated β-Sn slip systems and the process of recrystallization in Pb-free solder joints.

In this paper, the grain orientation evolution of Sn3.0Ag0.5Cu ball grid array (BGA) solder joints under thermomechanical stress was characterized quantitatively using electron backscatter diffraction (EBSD). Further polishing of the cross-sections of as-reflowed solder joints was avoided after thermal shock treatment to accurately analyze the underlying recrystallization mechanism (no previous reports on this topic exist because of the inability of pattern indexing due to cross-section contamination after thermomechanical fatigue). The results showed that subgrains appeared before the formation of recrystallized grains in Pb-free solder joints under thermomechanical stress, and the orientations of the small recrystallized grains separated by high-angle grain boundaries evolved from the initial orientations via subgrain rotation. The localized recrystallization produced fine grains and grain boundary sliding in the solder joints during thermal shock treatment. Additionally, slip systems played an important role in recrystallization and could be used to predict the subgrain and recrystallized grain formation. Avoiding further polishing of the cross-sections of as-reflowed solder joints during thermal shock treatment is an effective method to accurately investigate the recrystallization behavior and grain orientation evolution (as a function of the subgrain and recrystallized grain rotation behavior) of Pb-free solder joints.

高校后勤改革是我国高等教育改革的重要内容,高校后勤改革必须在现代大学制度的框架下有序推进.当前,高校后勤改革面临诸多困难和挑战,高校应当将后勤改革纳入到完善现代大学制度的整体改革中,加强后勤自身建设,处理好高校后勤改革、发展、稳定三者的关系.

伴随着经济的高速发展,我国资源相对不足,与经济高速发展和人民群众日益增长的物质文化生活需要之间矛盾愈加突出.节约资源,合理利用资源势在必行.以科技为先导,用科技促节能,运用远程监管系统实施能源监管,实现能源信息化控制,是未来时期我国能源管理的大趋势.我校2010年9月启动能源信息化建设,取得了初步成效,下面简要介绍一下我们的做法.

Improving the reliability of solder joints is an urgent issue to guarantee the quality of surface assembly products. The size of components and pitches on the circuit board differs from each other which leads to the size of solder joints variation one by one. In this study, the size effect of solder powder on Sn-3.0Ag-0.5Cu solder joints in high density LED display packaging was investigated. The microstructure and shear stress of the solder joints were observed as-reflowed and after different thermal cycling period conditions. The study suggested that the type 3 solder joint had good reliability and mechanical property than others. So the type 3 Sn-3.0Ag-0.5Cu solder powder was recommended the best to package this high density LED display.

分别用Sn37Pb钎料和Sn3Ag0．5Cu钎料组装高密度LED灯板，试验观察了焊后和老化后焊点的显微组织，测试了焊点的抗剪强度．结果表明，Sn3Ag0．5Cu焊点的金属间化合物层明显大于Sn37Pb焊点，但都在合格范围内，不会造成脆断，且其JB—Sn初品晶粒被网状共晶物包覆的特殊结构使其抗剪强度明显大于Sn37Pb焊点；老化后，两组焊点的抗剪强度均有所减小．虽然无铅焊膏代替Sn37Pb焊膏是电子工业界的发展的必然趋势，但是利用无铅焊膏组装小尺寸、高密度LED组件需要更精确的回流工艺．

X-ray detection facility was employed to investigate micro voids of the Sn37Pb and Sn3.0Ag0.5Cu solder joints in high density LED packages under as-reflowed and isothermal aged conditions.The micro voids inside the joints were observed,the sizes of which were measured.The results show that the area ratio(micro voids area/solder joints area) between 10%-25% of the micro voids inside the Sn3.0Ag0.5Cu solder joints is about 25.5%,which is slightly higher than the 23.5% inside the Sn37Pb solder joints,and is obviously less than the 31.4% after isothermal aging.The area ratios of the micro voids inside the Sn3.0Ag0.5Cu and Sn37Pb solder joints are all within the acceptable range(25%),but the Sn3.0Ag0.5 Cu solder joints are easier to form the micro voids after reflowing.

节能减排战略决定了信息技术能力在资源节约中的作用。为全面引入节能机制,提高能源监测、资源整合及共享程度,北京工业大学把建设节能监测平台,作为资源科学管理、科学利用和可持续发展的重要举措,基于校园网络建设了"能源监控系统",将水、电等能源进行远程管理——既物联网。努力提升节能减排管理水平,为建设数字化节约型校园提供基础保证。

Construction of key Disciplines in colleges and universities has important effect on improving technological innovation,knowledge innovation and innovative personnel training of higher education.Local university is the significant part of higher education system,of which planning and construction of key disciplines not only has essential effect on universities themselves,but also plays a role in promoting and supporting the social construction and economic development of the local area and even the whole country.This paper which takes Beijing University of Technology as an example analyzes the development of national key disciplines,key disciplines and key constructing disciplines of Beijing and key disciplines construction projects in 211 Project.And the paper lists the main achievement of construction of key disciplines in Beijing university of technology and gives some suggestions for its faster and stronger development.

Uniform droplet spraying technique was employed to fabricate the BGA balls.Silicone oil and peanut oil were employed as cooling mediums.When temperatures of cooling mediums were 150,200 and 250 ℃,influences on the sphericity and the surface quality of Sn-3.0Ag-0.5Cu solder balls were studied,and the microstructure of the solder balls was investigated.The results demonstrate that with silicone oil and peanut oil as cooling mediums,the optimal sphericities of solder balls can be obtained when the temperature of cooling medium is 200 ℃,those are 92.2% and 98.2%,respectively.In addition,the increased temperature of the cooling medium can improve the surface quality of solder balls.The suitable the super cooling of the cooling medium,the more the hypoeutectic phases can be filled into β-Sn dendrites.Accordingly,the improvements on surface quality of solder balls can be achieved.

<正>为积极落实建设节约型社会的基本国策,国家发改委、教育部、北京市教委提出了"建设节约型学校","节能减排学校行动"的工作部署,高校后勤作为学校各项资源的管理和服务保障部门,建

In the present work, the creep strain of solder joints is measured using a stepped load creep test on a single specimen. Based on the creep strain tests, the constitutive modeling on the steady-state creep rate is determined for the Cu particle-reinforced Sn37Pb-based composite solder joint and the Sn37Pb solder joint, respectively. It is indicated that the activation energy of the Cu particle-reinforced Sn37Pb-based composite solder joint is higher than that of Sn37Pb solder joint. In addition, the stress exponent of the Cu particle-reinforced Sn37Pb-based composite solder joint is higher than that of the Sn37Pb solder joint. It is expected that the creep resistance of the Cu particle-reinforced Sn37Pb-based composite solder joint is superior to that of the Sn37Pb solder. Finally, the creep deformation mechanisms of the solder joint are discussed.

Reinforced Ag nanoparticles were incorporated into Sn-0.7Cu matrix composite solder by a mechanical means in order to improve the creep properties of the solder matrix. The creep-rupture life was studied of Sn-0.7Cu solder joints and composite solder joints reinforced with Ag nanoparticles at different temperatures and applied stresses. Stress exponents and creep activation energy were calculated for Ag nanoparticle reinforced Sn-Cu matrix composite solder joints at different temperatures and stress levels. Steady-state creep constitutive equation of the composite solder joint was established. Results show that at different temperatures and stresses, Ag nanoparticles reinforced Sn-Cu composite solder joints have higher creep rupture life and creep activation energy than Sn-0.7Cu solder joints. It indicates the creep resistance of the composite solder joint with 1 vol% Ag reinforcement addition is better than that of Sn-0.7Cu solder joint.

<正>随着后勤社会化改革"市场提供服务、学校自主选择、政府宏观调控、行业自律管理、职能部门监管"新型后勤保障体系的逐步建立,高校后勤市场相继开放,师生对后勤服务需求不断提高,市场竞争日趋激烈,高校后勤面临一个自身发展的问

为了使材料加工专业人才更好地适应经济发展和社会需求,材料加工专业教学必须注意授课方式的改革,加强实践训练,突出创新能力和创新意识的培养,形成"以学强学"的良性循环;同时应将教学计划同国际材料加工工程师培训课程结合起来,拓展学生未来的就业及发展空间。

In this paper,some common problems in current bilingual teaching were analyzed. Besides,some approaches that could enhance the quality of bilingual teaching were suggested based on practical experiences of bilingual teaching.Those approaches were put forward according to five fields,such as,enhancing understanding,strengthening the quality of teaching,improving skills,creating circumstances and standardizing the management.

PurposeThe purpose of this paper is to investigate the creep properties of Sn‐0.7Cu composite solder joints reinforced with optimal nano‐sized Ag particles in order to improve the creep performance of lead‐free solder joints by a composite approach.Design/methodology/approachThe composite approach has been considered as an effective method to improve the creep performance of solder joints. Nano‐sized Ag reinforcing particles were incorporated into Sn‐0.7Cu solder by mechanically mixing. A systematic creep study was carried out on nano‐composite solder joints reinforced with optimal nano‐sized Ag particles and compared with Sn‐0.7Cu solder joints at different temperatures and stress levels. A steady‐state creep constitutive equation for nano‐composite solder joints containing the best volume reinforcement was established in this study. Microstructural features of solder joints were analyzed to help determine their deformation mechanisms during creep.FindingsThe creep activation energies and stress exponents of Ag particle‐enhanced Sn‐0.7Cu lead‐free based composite solder joints were higher than those of matrix solder joints under the same stress and temperature. Thus, the creep properties of nano‐composite solder joints are better than those of Sn‐0.7Cu solder joints.Originality/valueThe findings indicated that nano‐sized Ag reinforcing particles could effectively improve the creep properties of solder joints. A new steady‐state creep constitutive equation of nano‐composite solder joints was established. Deformation mechanisms of Sn‐0.7Cu solder and nano‐composite solder joints during creep were determined.

<正>随着我国经济体制改革的逐步深入,高等教育面向日益发展完善的社会主义市场经济,经历着内容广泛而意义深刻的变革过程。高等工科教育由于与社会生产经济活动密切相关,受经济体制变革、产业结构调整和新的科技发展的触动而发生着变化。面对不断变化的新形