BVL Provides Process-Reliable High-Purity Cleaning for Components

During rinsing, it is decided whether high-purity components reach the required cleanliness limits or whether recontamination after cleaning leads to scrap. Three factors are particularly critical: ultra-pure water quality directly at the point of use (particles, organics/TOC, conductivity, pH); minimal carryover between process stages and a clearly defined rinsing strategy; and plant engineering and loop hygiene (suitable materials, well-designed piping and continuous monitoring). 

In high purity component cleaning, cleanliness requirements are more demanding: permissible limits for the chemical composition of the component surface in atomic percent, extremely low outgassing rates and particle freedom in the submicron range.

These requirements result from extreme vacuum conditions in which the components are used, for example in EUV lithography, aerospace, or mass spectrometers for analytical applications. 
In these environments, cleanliness is a system characteristic.

The process chain must be designed to deliver technical cleanliness reliably and to prevent recontamination. Every contact medium must meet the same limits so the specification is not compromised. Otherwise, either the required cleanliness cannot be achieved or the component is re-contaminated after cleaning. 

For ambient air and process air, limit values are generally manageable using cleanroom technology and HEPA/ULPA filtration. 

Process water is often far more challenging. In rinsing, it must not introduce particles or organic residues onto the component otherwise, recontamination and scrap may occur. 

Rinsing is not simply “washing off” cleaner. It is the controlled dilution of the liquid film that is carried over on the component surface with rinse water. Through dilution, remaining contaminants are removed and transported out.

The objective is to reduce contamination concentrations from stage to stage in a defined manner below the relevant limits, both particulate and filmic/organic.

A component can only become as clean as the final rinse allows. 

The decisive factors for high-rinse quality are water quality at the point of use and minimal carryover.

The required water quality depends on the applicable cleanliness requirements. In many cases, ultrapure water is used in the final rinses. 

Water quality is influenced by the quality of municipal feed water. Depending on hardness, conductivity and dissolved salts, pretreatment may be necessary, through activated carbon filtration, particle filtration, manganese removal or iron removal.

Typically, reverse osmosis is then used. Pressure forces water through a semi-permeable membrane, separating low-salt permeate from concentrate.

For the highest demands, further treatment follows via mixed-bed ion exchange or alternatively electrodeionization (EDI), which operates continuously without regeneration 
chemicals. 

Additional stages such as UV treatment for microbial reduction or degassing may be added.

Water quality is defined and monitored using parameters such as conductivity, pH and total organic carbon. 

This is where sophisticated plant engineering is required. It must ensure excellent water quality at the point of use through minimal carryover, appropriate materials and effective loop hygiene. Rinse quality is only as good as the system that carries it.

From the outset, the cleaning system must be designed to minimize carryover. This includes strict separation of media circuits. Each tank has its own piping, filter units and pump. Piping runs should be flow-optimized to prevent residual water from collecting anywhere.

Workpiece carries and racks must be designed to avoid scooping points and unnecessary surface areas where water residues can remain.
In transfer immersion systems, defined overflows and separation baffles between tanks are important. Drip times and vibration of carriers support carryover prevention. In chamber systems, a drain-optimized chamber design, complete draining and chamber cleaning between treatment steps are beneficial. 

Water quality should be monitored directly in the cleaning system, at the point of use, using appropriate sensor technology.

Due to improved compatibility, V4A stainless steels (e.g., 1.4404, 1.4571) should be used instead of V2A. Weld quality must be ensured. Brass should be avoided entirely. PP and PVDF may also be suitable for piping, depending on the application.

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