MICROSTRUCTURE EVOLUTION AND CHARACTERIZATION OF NOVEL SOLDER ALLOYS FOR DEMANDING APPLICATIONS

在2006年有害物质限制(RoHS)法规实施之前，锡铅合金因其低成本、低熔化温度、良好的润湿性和良好的可靠性而成为电子工业中的主要焊料合金。自2006年以来，关于什么合金将取代可靠的锡铅，一直存在相当大的争论和痛苦。在RoHS过渡期间，一种由锡、银(3.0%)和铜(0.5%)组成的无铅合金(SAC305)因其合理的性能、较低的熔点以及与现有材料和工艺的兼容性而成为RoHS过渡期间的行业标准。然而，在接下来的十年里，电子设备被引入了无数新的应用领域。例如，在汽车应用中，除了基本的开关外，现在还有自主制动控制系统、电子控制减震器、混合动力控制系统和LED照明。随着电子设备的种类和密度不断增加，它们在确保车辆和乘员安全方面的作用变得非常关键。因此，挑战是要保证汽车电子产品的性能和可靠性比以往任何时候都更大。对于这种应用，传统的SAC305或类似合金具有较差的蠕变抗力和不稳定的机械性能，不够可靠。在高温和热循环条件下，SAC305的组织发生了显著的变化，特别是Ag3Sn5和Cu6Sn5颗粒的粗化，导致力学性能下降，抗蠕变性能变差。因此，电子工业需要一种比SAC合金更可靠的新型焊料合金。为了提高SAC合金的可靠性，用铋、锑、铟、锰、镍等元素进行合金化。一些研究人员已经对此进行了研究并提出了建议。为了开发一种适用于高温和苛刻应用的可靠的焊料合金，对SAC-Bi合金的进一步改进进行了研究。在这个项目中，一种新的SAC-X焊料合金(X代表合金化添加的铋、锑、镍等)具有较好的可靠性，并对其进行了介绍和研究。本项目的主要目的是研究热循环对组织演变的影响。

Prior to the implementation of Restrictions on Hazardous Substances (RoHS) regulations in 2006, Sn-Pb alloyshad been the predominant solder alloy in electronic industry due to their low cost, low melting temperature,excellent wettability and good reliability. Since 2006 there has been considerable debate and distress over whatalloy would replace dependable Sn-Pb. A Pb-free alloy made up of tin, silver (3.0%) and copper (0.5%)(SAC305) emerged as the industry standard during the RoHS transition because of its reasonable performance,low melting point compared to other alloys under consideration and compatibility with existing materials andprocesses. However, in the ensuing decade, electronic devices have been introduced in a myriad of newapplications. For example, in automotive applications, in addition to basic on/off switches, there are nowautonomous brake control systems, electronically controlled shock absorbers, hybrid power control systemsand LED lighting. With the increasing variety and density of electronic devices, their role to ensure the safetyof the vehicle and occupants becomes very critical. Therefore, the challenge is to guarantee the performanceand reliability of car electronics is greater than ever. For such applications the traditional SAC305 or similaralloys with poor creep resistance and unstable mechanical performance are not sufficiently reliable. Whenexposed to high service temperatures and thermal cycling, SAC305 undergoes significant microstructurechange, specifically, the coarsening of Ag3Sn and Cu6Sn5 particles, which leads to degradation of mechanicalproperties and poor creep resistance. Therefore, the electronics industry needs a new solder alloy with betterreliability than SAC alloys. To improve reliability of SAC alloys, alloying with Bi, Sb, In, Mn, Ni et al. hasbeen studied and suggested by some researchers. In order to develop a reliable solder alloy for high temperatureand demanding applications, further improvement of SAC-Bi alloy has been studied. In this project a newSAC-X solder alloy (X represents alloying additions Bi, Sb, Ni,...) with better reliability is introduced andstudied. The main objective of this project is to study effects of thermal cycling on the microstructure evolution