Metallurgical Reliability Issues in Flip Chip Technology

9987484管这项研究是对机械、化学和电力联合作用下焊点的可靠性进行的系统的基础研究。该项目研究了电子封装技术中最具挑战性的可靠性问题之一。测量了SnPb和无铅焊料从室温到150℃的电迁移。电迁移对界面反应的影响是在焊点界面确定的。还研究了应力对电迁移的影响。研究了这些因素对倒装芯片焊点耐久性的影响。在这些研究的基础上，应该开发洞察力，以实现提高焊点可靠性的有用解决方案。在消费电子产品以及微处理器中，目前的趋势是将硅芯片直接连接到有机基板上。智能卡就是一个很好的例子。它被称为直接芯片连接或倒装芯片技术，其中使用焊料凸块的面积阵列来将芯片连接到基板上。这是一种低成本的工艺，提供了封装高性能芯片所需的大量电引线(超过数千条)。然而，芯片和有机基板之间的热膨胀系数差异很大，导致热应力，这可能会造成严重的可靠性问题。由于衬底的有机性质，需要使用低熔点焊料，如共晶SnPb或共晶SnAg(无铅)合金。这些高锡焊料与芯片表面凸起下的薄膜金属化反应极快，导致机械连接非常薄弱。此外，对于未来的ULSI芯片，焊料凸起的大小可能接近50微米。然后，由于焊料在环境温度附近具有快速的原子扩散率，电迁移成为一个问题。*

9987484TuThis research is a systematic, basic study of the reliability of solder joints undergoing a combination of mechanical, chemical and electrical forces. The project examines one of the most challenging reliability issues in electronic packaging technology. Electromigration is measured in SnPb and Pb-free solders from room temperature to 150C. The effect of electromigration on interfacial reactions is determined at the solder joint interfaces. Also studied is the effect of stress on electromigration. The combined effects are examined on the durability of a flip chip solder joint. On the basis of these studies, insight should be developed that will enable useful solutions to enhancing solder joint reliability. %%%In consumer electronic goods as well as in microprocessors, the current trend is to attach the silicon chip directly to an organic substrate. Smart card is a good example. It is called direct chip attachment or flip chip technology in which an area array of solder bumps is used to join the chip to the substrate. This is a low cost process, which offers the large number of electrical leads (over a few thousands) required for packaging a high performance chip. However, the very large difference in coefficients of thermal expansion between the chip and the organic substrate results in thermal stresses that can create a serious reliability issue. Owing to the organic nature of the substrate, the use of a low melting point solder such as eutectic SnPb or eutectic SnAg (Pb-free) alloy is needed. These high-Sn solders react extremely fast with the under-bump thin film metallization on the chip surface, resulting in mechanically very weak joints. Furthermore, for future ULSI chips, the size of the solder bump could approach 50 microns. Then electromigration becomes a concern since the solder has a fast atomic diffusivity near ambient temperature.***