PCBs can be thought of as acting like a nervous system, forming a network that links the microchips mounted on the board and supplies them with power. One of the most important methods of fabricating large PCBs involves the precision electroplating of copper onto the PCB panel immersed in an acidic electrolyte bath.
Electronic components are becoming ever smaller and ever more powerful while at the same time having to be connected with one another in increasingly complex ways. “A printed circuit board today is an extremely complicated three-dimensional structure, that essentially acts like a central nervous system connecting all the various individual components,” explains Professor Frank Mücklich, Professor of Functional Materials at Saarland University and Director of the Steinbeis Material Engineering Center Saarland (MECS). The method typically used for high-precision fabrication of large-surface PCBs is acid copper electroplating, in which the PCB panel is immersed in an acidic solution of copper ions, the electrolyte. A very high electric current flows through the board transporting copper ions in the electrolyte to the surface of the PCB and into the minute holes, known as vias, into which the leads or contact pins of the electronic components will later be inserted. “As a result, the PCB is covered with a uniform extremely thin coating of copper whose thickness is less than one tenth of the diameter of a human hair,” says Mücklich.
The PCB panels are held in solution by acid-resistant titanium PCB plating clamps that guide the current onto the PCB panel. “These clamps have to withstand an enormous amount of electrical energy over an area of only a few square millimetres. The extremely powerful current generates sparks that are similar to a lightning discharge and that damage the clamps by eroding their surface each time the panels undergo plating,” says Mücklich, describing the fundamental problem of modern electroplating systems. The Saarbrücken material scientists examined the damage mechanisms using not only electron microscopy, but also tomographic techniques that allow imaging down to the nano- and even atomic scales. “We came to realise that with spark temperatures of around several thousands of degrees the previous strategy of trying to develop materials with ever greater resistance to these extremely hot and destructive sparks was not going to prove successful,” explains Mücklich.Even the use of very expensive precious metals, such as platinum, only delays but does not stop the onset of damage. Working together with engineers from Atotech, the material scientists and technologists at Saarland University came up with an extremely economical and reliable solution. According to Mücklich: “The new process is similar to the mechanism used to regenerate human skin when wounds heal.”
In their search for more robust materials, the research team also used laser cladding to deposit microscopic layers of different materials onto the titanium contacts. They also employed laser interference structuring techniques to modify the surface of the clamps in an effort to make them more robust. While these techniques certainly improved the properties of the original titanium, the improvements were not sufficient to permanently withstand the enormous stresses to which the clamps are subjected during the PCB electroplating process. “This led us to the idea of using copper as a sacrificial layer that can be continuously replenished during the PCB production process.
The advantages of this approach are that copper is far cheaper than the other materials that had been tested and that it was already present in the system. It was this that ultimately led to the successful conclusion of the research project,” explains Frank Mücklich. In recognition of their efforts, Professor Mücklich, together with research assistants Dominik Britz and Christian Selzner and the project members from Atotech, will receive the Transfer Award, which is conferred by the Steinbeis Foundation and worth up to 60,000 euros, at a ceremony in Stuttgart.Background: The Steinbeis Foundation’s Transfer Award
Friederike Meyer zu Tittingdorf | Universität des Saarlandes
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