Security for aggressive processes

Durable conductivity sensors for wet chemical surface treatment

From wet chemical plants, where wafers for solar cells are manufactured or printed circuit boards are etched, to electroplating - such production processes require the use of aggressive acids and alkalis.

Therefore, the sensors must meet certain requirements, since common housing materials such as steel or stainless steel are not compatible with aggressive substances like these, which would cause the quick destruction of the materials To safely avoid contamination, ultrapure water requires inert sensors.

The solution lies in sensors for conductivity and flow measurement, with housings made from high-quality plastics such as PVDF or PP.

Robust conductivity sensors for aggressive conditions

Thanks to the high-quality, chemically inert plastic materials deployed and specifically optimised for use in electroplating and wet chemistry, the sensors are ideally suited to be used under aggressive environmental conditions.

Conductive conductivity measuring device for high-quality monitoring of ultrapure water. Source: RENA Technologies GmbH

Systems for wet chemical inline and batch processes

RENA, based in the German town of Gütenbach in the Black Forest, has long been a specialist in production facilities used in wet chemical surface treatment in solar, semiconductor and medical technologies. Its extensive and wide ranging product portfolio can be flexibly applied to a diverse range of manufacturing processes. Functionality, reliability and safety are at the heart of everything RENA does.

The wet-chemical inline and batch processes for solar cell production, for which RENA is the global market leader, are in use worldwide and have been working reliably and safely for many years. This places high demands on the components used. For example, on the sensors that are used for conductivity measurements when distributing demineralised water, or for monitoring heat exchangers during the etching process.

Reliable sensors in robust plastic valve bodies

Wet chemical process downtimes, e.g. for unplanned sensor replacements, must be avoided under all circumstances. Therefore, the equipment manufacturers from the Black Forest region have been putting their trust in our sensor technology contained in robust plastic housings for many years.

RENA uses several inductive and conductive conductivity sensors in its wet chemical surface treatment plants.

Production systems for wet chemical surface treatment in solar technology. Source: RENA Technologies GmbH

Monitoring mixing ratios and cooling water circuits

Inductive conductivity measurement is the preferred method for determining the concentration of acids and alkalis. An alternating current flowing in the primary coil (transmitter) generates an alternating magnetic field. This induces a current in the surrounding ionically conductive medium. The current flow in the medium generates a magnetic field. This in turn generates a voltage and thus a current flow in the secondary coil (consumer) of the sensor. This is a measure of the medium’s conductivity.

Since the conductivity of fluids is significantly dependent on temperature, an additional temperature sensor in the sensor continuously records the temperature of the medium. The temperature’s influence is compensated for via the temperature coefficient (TK value) set in the electronics assembly. Our Type 8228 inductive conductivity meter then provides this measured value to the controller as an interference-free 4... 20 mA signal, which can be easily transmitted over long distances in systems that are often very large.

These measuring devices perform two tasks in the wet-chemical surface treatment plants:

During etching processes, they monitor the cooling water circuit. In the (rare) event of a hole forming in the heat exchanger, for example, twenty percent hydrofluoric acid would penetrate the secondary circuit. Should such an event occur, the conductivity sensors detect the change in concentration and report it to the controller. The controller then automatically switches off the process and thus prevents consequential damage. Another task for the inductive conductivity meters is to monitor the concentration of alkaline textures. Here, ensuring the correct mixing ratios is crucial for maintaining processing quality. The measuring devices operate within a large measuring range - from 100 μS/cm to 2 S/cm, with the resolution at 0.1 μS/cm.

The inductive conductivity meter in the circulation circuit of an etching process. Source: RENA Technologies GmbH

Conductivity measurement in demineralised water

Demineralised water, deionised water or ultrapure water is required for cleaning during wafer production. Its quality is also monitored in the wet chemical plants through conductivity measurement. Since this water’s conductivity is very low, this task is carried out by Type 8222 neutrino conductive measuring devices.

The device’s sensor consists of two electrodes in contact with the medium and a temperature sensor, and they work is a measurement range of 0.05 μS/cm to 10 mS/cm. The measurement signal is also processed directly in the sensor. It is transmitted to the controller as an interference-immune 4...20 mA signal.

The conductivity meters have proven themselves in many applications, and RENA also relies on Bürkert solutions for other sensors that are required for wet chemical machining processes.

Precise inline flow measurement

The Type 8030 inline flowmeter or the Type 8035 inline batch controller are often used for continuous measurements of media supply or leakage monitoring. Both consist of a compact sensor fitting with an impeller and a transmitter. The connection is quick and easy thanks to a bayonet catch. Our sensor fitting system ensures simple and straightforward installation of the devices in all pipelines.

The sensors are suitable for use with flow velocities of 0.3m/s to 10m/s. The housings are made from PVDF or glass fibre-free PP and are completely leak-proof. They are also the perfect choice for use in the aggressive environment of wet chemical plants or electroplating processes.

Inline flowmeters are used to continually measure media supply and to monitor for leakages, e.g. Type 8030 (left) or Type 8035 (right).