MICROSTRUCTURE EVOLUTION AND CHARACTERIZATION OF NOVEL SOLDER ALLOYS FOR DEMANDING APPLICATIONS

在2006年实施有害物质限制（RoHS）法规之前，锡铅合金由于其低成本，低熔化温度，优异的润湿性和良好的可靠性，一直是电子工业中主要的焊料合金。自2006年以来，关于什么合金可以取代可靠的锡铅，一直存在着相当大的争论和苦恼。一种由锡、银（3.0%）和铜（0.5%）组成的无铅合金（SAC305）在RoHS过渡期间成为行业标准，因为它具有合理的性能，与其他正在考虑的合金相比熔点低，并且与现有材料和工艺兼容。然而，在接下来的十年里，电子设备被引入了无数的新应用。例如，在汽车应用中，除了基本的开/关开关外，现在还有自动制动控制系统、电子控制减震器、混合动力控制系统和LED照明。随着电子设备种类和密度的增加，它们在确保车辆和乘员安全方面的作用变得非常重要。因此，保证汽车电子设备的性能和可靠性的挑战比以往任何时候都要大。对于这些应用，传统的SAC305或类似的合金具有较差的抗蠕变性能和不稳定的机械性能，是不够可靠的。当暴露在高温和热循环下时，SAC305的微观结构发生了显著的变化，特别是Ag3Sn和Cu6Sn5颗粒的粗化，导致机械性能退化和抗蠕变性能差。因此，电子工业需要一种比SAC合金可靠性更好的新型焊料合金。为了提高SAC合金的可靠性，一些研究人员对Bi， Sb, In, Mn， Ni等合金进行了研究和建议。为了开发一种适用于高温和高要求应用的可靠焊料合金，对SAC-Bi合金进行了进一步改进研究。本课题介绍并研究了一种可靠性较好的新型sac -X焊料合金（X代表合金添加物Bi， Sb, Ni，…）。本项目的主要目的是研究热循环对微观组织演变的影响

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