Topic of the month September 2009

Figure 1: Siemens researches have improved the production of printed circuit boards utilizing chemical nanotechnology. The picture in the front shows the impact of the lotus effect on the wetting behaviour of a technical surface. Source: Siemens AG.

Printed circuit boards are the central core for a wide range of electrical equipments and systems in the high-tech area. Their durable and long term functionality is the indispensable requirement, to guarantee that the particular end devices work solidly. This is of extreme importance concerning the product range of the fairs wire and Tube with
their broad spectrum of branches and their nearly never-ending electrical and electronic applications. Recent findings demonstrate that printed circuit boards still offer a huge potential for technological improvement. Especially engineers from the production area, convince with major innovations, to improve the efficiency and sustainability of the mentioned profile of requirements.

The lotus effect: Soldering with nanotechnology

Researches of the German company Siemens have developed a novel non-stick coating based on chemical nanotechnology that clearly improves the production process of printed circuit boards. By taking advantage of the so called lotus effect the scientists managed to optimize the stencils utilized for printing the rather viscous soldering paste onto the circuit boards. This marketable technology is already being used in various manufacturing processes – persuading with a reliable production of fine soldering structures in a scale of only a few hundred micrometers in size. Additionally, the quality of the circuit boards is improved and the whole production process is optimized, due to the fact, that the coated stencils do not have to be cleaned as often.

Non-stick coatings – creating this kind of property profile – have been known for a long time in various applications. They prevent the wetting of the materials surfaces from liquids or viscous substances by creating defined surface structures or by the use of special coatings like PTFE, for example. But no reliable solution had previously been found for highly viscous materials like solder pastes.

The researches from Siemens Technology in Erlangen use the so called sol-gel process to coat the solder stencils. Starting with a solution containing various molecules, the sol, a stable gel is created via several chemical processes. This gel is then transformed into a solid, adhesive and scratch-resistant coating, which withstands the mechanical stress during the production process of the circuit boards.

Printing the solder paste through a stencil whose internal sides are coated with this method, will demonstrate, that no residue will be found on the stencils, after the board is removed.
This is a significant benefit especially for the production of very small structures addressing dimensions in the region of hundred micrometers edge length, because otherwise insufficient solder paste would have been applied on the circuit board. By using this process it is possible to print high resolution structures precisely, geometrical defined and error-free. The stencil itself stays clean for a long time – roughly 50 soldering cycles.

Fast Control: Failures on large areas

Figure 2: The extremely fast and parallel image processing method developed by Fraunhofer IPM offers data collection and evaluation of huge amounts of device information. It can be used for a quick analysis of small defects like missing solder contacts. © R. Krause/PIXELIO

By using an extremely fast and parallel image processing technique, scientists of the Fraunhofer Institute for Physical Measurement Techniques IPM in Freiburg, manage to record and evaluate huge amounts of picture data in very short time. This method offers the possibility to detect and to define small defects in materials and systems as quick as possible – even on large areas.

Small failures, which are often hard to discover, have a tremendous impact on the production process and of course on the quality and function of products.
One single lacking soldering point, a tiny paint flaw, a minimal geometrical deviation from the
set point or an imprecise positioning define whether a part is “in order” or “waste”.
Because of these facts, many production processes depend on a precise visual inspection, to realize an accurate and reliable visual control. But what can a manufacturer do, if his production line leaves not enough time for an efficient control during the production process? Especially if the possible flaw has to be detected within a short testing phase?

To solve this central problem scientists have developed a camera-based inspection system utilizing an extremely fast and parallel picture processing. The novel inline inspection system is able to record and evaluate up to six pictures per second having a resolution of 16 mega-pixel.

This performance enables a reliable and highly accurate localization of defects, objects or divergences of the set point even in the sub-pixel area. The newly developed inline measurement system is scalable from the sub-micro area up to the meter range and therefore provides a tailor-made control of all kinds of components – surfaces of photovoltaic-devices and integrated circuits are only two examples for the wide range of possibilities and technical relevance. In general the system can be used in every process where small objects, little defects or slight divergences of the set point have to be detected in big amounts of data. This measurement system enables to discover, choose, mark or even count defined objects or defects in the production line, without extending the production period.

Dr.-Ing. Christoph Konetschny
Material- und Nanoexperte

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