Understanding the interaction between silver and lead-free solders in order to develop new solder alloys

在玻璃上印刷导电轨道是汽车工业等领域的一项重要技术，在汽车工业中，银浆被用来为加热的挡风玻璃制造轨道。在玻璃上印刷导电轨道也是一些光伏系统(太阳能电池板)制造的关键部分。点火后，这样的导电网络需要一个电气连接才能运行，这是通过焊接实现的。以前，使用的焊料合金含有铅，但意识到这种金属的健康和环境问题导致了无铅焊料的配方(如基于锡-银-铜系统的SAC焊料)。虽然这避免了使用铅的风险，但获得的连接强度还不够可靠，对于继续使用这项技术来说，更好地了解问题并找到解决方案是至关重要的。在本项目中，我们将探索现有技术的基本行为，以进一步了解所看到的问题的关键来源；这些问题包括连接区域中微裂纹的形成和焊接后的残余应力，这两者都会导致连接强度降低。我们将制作并显微检查不同焊料和银粉之间产生的接头，以首次充分了解发生的相互作用及其对接头强度的影响。然而，了解这个问题只是第一步。利用我们所获得的知识，我们将设计新的银浆组合物来缓解这些问题。这些新型合金将在实验室和试生产规模上进行生产和加工，从而使按照行业标准方法生产的合金得到验证。这项工作将包括通过他们位于英国牛津郡Sonning Common的技术中心与工业合作伙伴Johnson Matthee plc(一家在贵金属技术方面拥有独特专业知识的全球科学和化学品公司)密切合作，以进行工业试验。

The printing of electrically conductive tracks on glass is an important technology in areas such as the automotive industry, where silver pastes are used to create the tracks for heated windscreens. The printing of conductive tracks on glass is also a key part of the manufacture of some photovoltaic systems (solar panels). After firing, such conductive networks need an electrical connection in order to operate, which is achieved by soldering. In former times, the solder alloys used contained lead, but realisation of the health and environmental concerns with this metal have led to the formulation of lead-free solders (such as SAC solders, based on the tin-silver-copper system). While these avoid the risks of using lead, the joint strength achieved is not reliably high enough, and it is critical for continued use of this technology that the problem is better understood, and that a solution is found.In this project we will explore the fundamental behaviour of the existing technology further to understand the key origin of the problems seen; these include microcrack formation in the joint region, and residual stresses after soldering, both of which contribute to reduced joint strength. We will fabricate and microscopically examine the joints produced between different solders and silver powders, to fully understand for the first time the interactions occurring and how they impact on the joint strength. Understanding the problem is just the first step however. Using the knowledge we gain, we will design new silver paste compositions to mitigate the problems. These novel alloys will be produced and processed at laboratory and trial scales, leading to validation of the alloy produced in accordance with industry standard methods. The work will involve close collaboration with the industrial partner, Johnson Matthey plc (a global science and chemicals company, with unique expertise in precious metals technology) through their technology centre in Sonning Common, Oxfordshire, UK and other sites, to trial the technology industrially.