Selective Laser Remelting of Steel to Suppress Cu Growth in a Subsequent Electroplating Process
Marko Pudas, Ilari Jaakola, Seppo Jarvenpaa and Jouko Vahakangas
A new three-step method has been developed to produce patterned copper on printed circuit boards (PCB) and also to increase flexible circuitry. Firstly, a temporary steel substrate is laser treated by scanning e beam over it. Only those areas of the temporary steel substrate which do not belong to the specified pattern are processed by the laser. Then the patterned temporary steel substrate is immersed in an electrolytic bath and Cu is deposited onto the steel. It was observed that Cu growth could be completely inhibited in those areas processed by the laser. In a third step, the Cu pattern is laminated or peeled-off from the temporary steel substrate, for example by using laminate dielectrics to create a flexible or hard circuitry. The phenomenon preventing copper growth was associated with micro-segregation of Cr and Mo. This created oxidation or micro-surface potential differences.