A PCB Surface Finish for the 21st Century

多年来，基本的PCB制造工艺几乎没有变化，仍然是一系列复杂的操作，涉及光成像，蚀刻，钻孔和层压，使用一系列化学品和大量的水，并产生大量的废水。后续操作之一是对将要焊接组件的铜接触区域进行“表面抛光”。这种表面光洁度可防止铜氧化，如果发生氧化，将损害PCB基板和组件之间的焊点，并导致产品故障。一些用于表面处理的化学品是有毒的，如氰化物，它用于镀金工艺。几年前，人们最初尝试开发类似的涂层，但由于几个原因，这在市场上没有获得牵引力，主要是由于材料含有卤化物，这些卤化物在电子行业被淘汰，而且，在当时，人们对诸如减少用水量之类的环境问题几乎没有真实的兴趣。2要求所有工业对环境更加负责的压力越来越大。因此，人们对不使用水且不产生废物的纳米涂层方法重新产生了兴趣。某些类别的无卤化物材料已被确定为原始纳米涂层的潜在替代品，迄今为止的测试结果令人鼓舞。除了卤化物的问题外，还发现了原始涂层的另外两个关键技术问题，这两个问题将在重新配方中得到解决。在这种应用中使用等离子涂层将大大减少PCB制造中的水和能源消耗，沿着减少二氧化碳排放。在原始材料中观察到一种不寻常的各向异性特性，即z轴电导率，其中一个轴上的每纳米电阻远低于其他两个轴上的每纳米电阻。这是建议的表面处理能够取代金属表面处理的关键，并且需要不受任何配方变化的影响。

The basic PCB manufacturing process has changed very little in over the years, remaining as a complex series of operations involving photo-imaging, etching, drilling and laminating, using a range of chemicals and large quantities of water as well as producing a large amount of effluent. One of the later operations is to apply a 'surface finish' to the copper contact areas where components will be soldered. This surface finish prevents oxidisation of the copper which, if it occurs, will compromise the solder joint between the PCB substrate and the components and leads to product failure. Some of the chemicals used for surface finishes are toxic such as cyanide, which is used in the gold plating process.An initial attempt was made several years ago to develop a similar coating, but this failed to gain traction in the market for several reasons, principally due to the material containing halides which were being phased out in the electronics sector and also, at the time, there was little real interest in environmental issues such as reducing water consumption.There is a growing pressure on all industries to become more environmentally responsible. Consequently, there has been a renewed interest in a nanocoating method that uses no water and produces no waste. A certain class of halide free materials has been identified as a potential alternative to the original nanocoating and test results to date have been encouraging. Apart from the issue of halides, two other key technical issues were identified with the original coating, which will be addressed in the reformulation.The use of plasma coatings for this application will dramatically reduce the water and energy consumption in PCB manufacturing along with a consequent saving in CO2 emissions. Significant cost savings can be achieved with this new technology.An unusual anisotropic property was observed in the original material, that of z-axis conductivity in which the resistance per nanometre is much lower in one axis than in the other two axes. This is key to the proposed surface finish being able to replace metallic surface finishes and needs to be unaffected by any formulation change.