A PCB Surface Finish for the 21st Century

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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.