Metallurgical Reliability Issues in Flip Chip Technology

9987484本研究是对在机械、化学和电力共同作用下焊点可靠性的系统、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。电迁移是在室温至150℃的SnPb和无pb焊料中测量的。在焊点界面处测定了电迁移对界面反应的影响。研究了应力对电迁移的影响。研究了这些综合效应对倒装芯片焊点耐久性的影响。在这些研究的基础上，应该开发出能够提高焊点可靠性的有用解决方案。在消费电子产品和微处理器中，目前的趋势是将硅片直接附着在有机衬底上。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，其中一个区域阵列的焊料凸起是用来连接芯片到衬底。这是一个低成本的过程，它提供了大量的电气引线（超过几千）所需的封装高性能芯片。然而，芯片和有机衬底之间热膨胀系数的巨大差异会导致热应力，从而产生严重的可靠性问题。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凹凸下的金属化薄膜反应极快，导致机械上非常脆弱的接头。此外，对于未来的ULSI芯片，焊料凸起的尺寸可能接近50微米。然后电迁移成为一个问题，因为焊料在环境温度附近具有快速的原子扩散率

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.***