Development of a high curing latency no-flow underfill with self-fluxing ability for lead-free solder interconnects

Tin-lead solders have been used as joining materials in the electronics industry for many years. As present there are great concerns about the potential harm of lead-containing solders to human beings and many efforts have been made to remove the lead from the electronics packages. However, there is no no-flow underfill currently on the market that is compatible with the lead-free solder. In this study, a new no-flow underfill for flip chip bumped with lead-free solder has been developed based on a curing agent and catalysts with high curing latency. The curing agent itself has the fluxing ability, so the need of extra flux is eliminated. Compared with the underfill for lead-containing solder, the new underfill has a higher curing temperature, compatible with the melting profile of lead-free solder. The wetting compatibility of the underfill with the lead-free solder has been studied by wetting experiments. The material properties of the underfill have been investigated using DSC, TGA, TMA and DMA. The results show that the newly developed underfill material has the potential to be used in lead-free interconnects.     

黄河下游断流对策探讨

经分析认为，黄河下游频繁发生断流的主要原因在于黄河下游两岸的引水规模超过节灌溉季节黄河上游来水量的承受能力，破坏了黄河下游原来的生态环境状况。为此提出解决黄河断流问题的对策；必须在对黄河水资源及其可开发利用和程度作进一步核算的前提下，按照国务院分水方案，严格控制引黄灌区的进一步扩大；开展有关龙羊峡、刘家峡、三门峡、小浪底“四库”联调运用的研究，以增加枯水季节对黄河下游的供水能力；进一步加强领导，协     

Preventing buoyancy-driven flows of two Bingham fluids in a closed pipe – Fluid rheology design for oilfield plug cementing

The mechanically unstable situation of a heavy Bingham fluid resting on top of a light Bingham fluid in an inclined closed-ended pipe can be stabilised if the fluids have sufficiently large yield stresses. This paper focuses on determining the yield stresses that are sufficient to keep the fluids statically stable for a given fluid density difference, pipe diameter and pipe inclination. The results are applicable to a broad class of practically observable flows. This situation provides an idealised model for the oilfield process of plug cementing.     

填充不流动胶的倒装焊封装中芯片的断裂问题

用断裂力学方法和有限元模拟分析了填充不流动胶芯片断裂问题 .模拟时在芯片上表面中心预置一裂缝 ,计算芯片的应力强度因子和能量释放率 .模拟表明 ,由固化温度冷却到室温时 ,所研究的倒装焊封装在填充不流动胶时芯片断裂临界裂纹长度为 12 μm,而填充传统底充胶时为 2 0 μm.模拟结果显示芯片断裂与胶的杨氏模量和热膨胀系数相关 ,与胶的铺展关系不大 .焊点阵列排布以及焊点位置也会影响封装整体翘曲和芯片断裂 .     

不流动性半固化片压合白斑的思考

介绍了利用不流动性半固化片在制作刚挠板压合过程中产生白斑的原因,通过对不同条件下（不同敷形材料、表面不同线路图形分布、不同压合压力、不同半固化片张劐不流动性半固化片的压合实验发现,不流动性半固化片的压合与普通半固化片无论是从压合辅材、压合压力及压合模型上来说者研艮大不同。最后通过之前的实验分析,提出了不流动性半固化片的压舍模型。     

Functional no-flow events and their identification in the Lower Yellow River

Based on the understandings of the relationship between the river runoff and the primary functions of the Yellow River, this paper advances the concept of functional no-flow event that is different from the zero-discharge event occurring in the river. Factors reflecting the characteristics of functional no-flow events were analyzed and the criteria describing severity levels of the events were given from the cluster analysis with the measured data from 1950 to 1999. The results show that the severity level is subject to the critical water demand for river ecosystem protection. Using two critical water use demand scenarios for the Yellow River proposed by the authors and the Yellow River Water Conservancy Commission, different severity levels of functional no-flow events are identified. In addition, the differences between the zero-discharge and the functional no-flow events are discussed.     

论黄河断流问题

由于近年来黄河年径流量小，上下游用水量较多，水沙调控不协调，造成黄河下河道连年断河、河床淤积，洪水位抬高，防洪能力降低。指出黄河断流和防洪都有重要的，必须同时考虑，并提出增加黄河调水量、节约用水、减少黄河泥沙、优化小浪底水库调度运用、利用干流水库调水流调沙、整治下游河道、全河统一调度等一系列解决黄河下游河道断流和减少下游河道淤积的对策。     

倒装芯片封装技术概论

高密度电子封装正朝着小型化、高I/O密度、更好的散热性和高的可靠性方向发展,传统引线键合技术已经无法满足要求。先进的倒装芯片封装技术由于具有较高的单位面积内I/O数量、短的信号路径、高的散热性、良好的电学和热力学性能,在电子封装中被广泛关注。底部填充胶被填充在芯片与基板之间的间隙,来降低芯片与基板热膨胀系数不匹配产生的应力,提高封装的稳定性。然而,流动底部填充胶依赖于胶的毛细作用进行填充,存在很多缺点。为了克服这些缺点,出现了非流动底部填充胶,以改善倒装芯片底部填充工艺。文章回顾了倒装芯片封装技术的发展,阐述了流动和非流动底部填充胶的施胶方式和性质。     

1997年黄河下游断流情况分析

１９９７年，由于黄河流域降雨、径流量较常年明显偏少，水资源从矛盾十分突出，黄河下游同 有资料记录以来断流量为严重的一年，利津站于２月７日开始断流，截止到１２月３１日，断流１３次，共计２２６ｄ与有记录以来的历史资料比较，呈现出断流开始时间最早、恢复地流时间最晚、断流河段最长、断流次数最多，断流时间最长等特点，另外，黄河中游各主要支流控制站亦多数出现断游戏呈接近断流其中华县站出现有资料记录以来的首次断