Cleanliness in the submicrometer and atomic percent range

March 30, 2022 - 12:00pm
For integration into clean rooms the ultrasonic ultrafine cleaning systems are fitted out in compliance with the applicable cleanroom class. Photo credit: UCM / Gebr. Brasseler

In many industries, new and enhanced products lead to high cleanliness specifications. Due to changed manufacturing, joining and coating technologies and more stringent regulatory specifications, there are stricter requirements for particulate and film-type part cleanliness. 

To reach these values in series production in a process-reliable and efficient way, not only do cleaning and drying processes meet demands and suited system technology, but also software implementation and cleaning environment must be adapted accordingly. 

These ultrasonic ultrafine cleaning systems are specifically dimensioned for the application on hand. Their various treatment stations can be flexibly accessed so that defined processes can be prioritized. Photo credit: Philips Medical Systems
 These ultrasonic ultrafine cleaning systems are specifically dimensioned for the application on hand. Various treatment stations can be flexibly accessed and process prioritized. Photo Philips Medical Systems 

Whether production equipment for the semi-inductor industry, biotechnology, laser and sensor technology, devices for measuring and analysis technology, components for accumulators and fuel cells, optical systems or metal cutting tools, the requirements for performance and reliability are extremely high. This not only leads to high demands in terms of production precision of the parts, but also their cleanliness. For medical technology products such as implants, instruments, cannulae and endoscopes, particulate and film-type contamination from manufacturing processes is an essential criterion due to regulatory specifications. 

Moreover, there is a trend for miniaturization and functional integration with smaller and more complex components. These developments entail that particulate cleanliness specifications in the micrometer and even nanometer ranges as well as stringent requirements regarding residual thin-film contamination must be met by more and more industry sectors. Depending on components and applications, outgassing rates for organic substances and residual moisture may also have to be met, as well as limit values down to the atomic percent range when it comes to surface analyses for residues of prohibited substances. For the production of these miniaturized components there is also an evolution towards ever-larger integrated manufacturing modules. This also creates new challenges for the cleaning processes and the machine systems required to implement them.

The result is a series of demanding parts cleaning tasks across the complete manufacturing chain. As a supplier of future-oriented complete solutions, SBS Ecoclean Group of companies covers the whole range of precision and ultrafine cleaning. This enables them to adapt cleaning processes, their control software as well as the machinery and ambient conditions to the requirements and applications on hand. 

The right system concept 

By combining wet chemical and low-pressure plasma cleaning methods for ultrafine degreasing in a single machine, the surface characteristics required for downstream coating or bonding are efficiently achieved. Photo: Ecoclean
By combining wet chemical and low-pressure plasma cleaning methods for ultrafine degreasing in a single machine, the surface characteristics required for downstream coating or bonding are efficiently achieved. Photo: Ecoclean

For the selection of a suitable cleaning system for a specific task, the first thing looked at is whether the system is to be used for pre-cleaning, intermediate cleaning or final cleaning. Depending on the use and cleanliness specifications to be achieved, the solution may be a chamber or multi-tank immersion machine, a flexible ultrasonic multi-tank machine based on standardized modules, or a customized ultrasonics-based ultrafine cleaning system. 

The cleaning chemicals, and the optimal process technologies such as spraying, high-pressure fluid application, immersion, ultrasonic or megasonic treatment, plasma cleaning, injection flood wash, pulsated pressure cleaning (PPC) as well as passivation/preservation as required, are also specifically chosen for the application and the contaminants.  

Cleaning processes and systems for ultra-high cleanliness 
The design of customized ultrasonic multi-chamber systems and processes for ultrafine cleaning applications is the core competence of Switzerland-based UCM AG. Key factors to be considered are the material and geometry of the parts to be cleaned, the type and quantity of contaminants, the particulate or film-type cleanliness specifications, and, where applicable, permitted outgassing rates and maximum acceptable residues of prohibited substances in the atomic percentage rate. 

Another important aspect is the selection of suitable cleaning chemicals and wash fluid, for example, reverse osmosis water or deionized water. The materials and manufacturing methods used to build the cleaning system and automatic transport system are also selected with the prevention of dirt build-up, recontamination and cross-contamination already in mind. Outfitting with cleanroom grade components and interfacing with clean rooms are also possible. 

Standard equipment installed in precision and ultrafine cleaning systems is multifrequency ultrasonic systems that offer flexible adjustment of ultrasonic frequency and intensity to the requirements of different parts to be cleaned. With parts that present complex geometries, capillary structures or porous surfaces, such as sintered metal components or additive manufactured components, the PPC method comes into play. Features such as multi-side overflow in all wash and rinse tanks as well as the immersion/spray rinse technology specially developed for ultrafine cleaning systems contribute to the reliable meeting of severe cleanliness specifications. 

The decision on which parts are taken to which wash and rinse tanks as well the part-specific process parameters such as temperatures, ultrasonic output and frequency, the intensity of PPC, dwell time in the various wash and rinse tanks, are defined during the process development phase. Depending on the complexity and heat absorption capacity of the parts, drying is mostly done using infrared or vacuum technology. The resulting part-specific cleaning programs are stored in the machine controller. The software-controlled implementation of the cleaning sequence plays a decisive role in this context. It ensures among other things that the specified dwell times in wash and rinse tanks are precisely observed, and that prioritized sequences - e.g. for fragile parts - can be programmed. 

The best system and process solution from a cleanliness and economic efficiency point of view can be determined through cleaning trials with original parts in Ecoclean’s and UCM’s Precision Cleaning Technology Centers.

Related Glossary Terms

  • centers


    Cone-shaped pins that support a workpiece by one or two ends during machining. The centers fit into holes drilled in the workpiece ends. Centers that turn with the workpiece are called “live” centers; those that do not are called “dead” centers.

  • micrometer


    A precision instrument with a spindle moved by a finely threaded screw that is used for measuring thickness and short lengths.