र125,000 crores approximately). According to a study by the Export-Import Bank of India (Exim Bank), it is estimated to exceed $150 billion (र750,000 crores approximately) by 2015 and is growing at a Compounded Annual Growth Rate (CAGR) of over 25%. Exports of electronic goods are expected to touch $15 billion (र75,000 crores approximately) by 2013-14, an estimate by the Ministry of Commerce and Industry. It is growing in sectors like commercial software, telecommunications, electronics, instrumentation, positioning & networking systems, Consumer Electronics and Industrial Electronics.
The industrial cleaning requirement is therefore projected to grow complemented with advancements in cleaning technologies like Ultrasonic Cleaning, High Pressure Cleaning, Aquastorm, Plasma and Water based Surfactant Technology.
The purpose of cleaning, specifically within the rapidly expanding electronics industry, is to essentially improve product lifetime, increase the reliability of assemblies and allow coating and encapsulating operations to be carried out efficiently. More so as cleaning is still an essential multistage process within the electronics industry. Says Nanjunda Swami, Production Manager, Easun Reyrolle Ltd, Bangalore, a company into electronic fault finding, conformal coating removal and diagnostic testing for complex electronic systems, “All our electronics components and Printed Circuit Boards (PCBs) cleaning are done through Ultrasonic Cleaning at the sub contractor’s end before soldering and after soldering. Another stage of ant- static or anti-tarnish cleaning by liquids is done inside the manufacturing unit for PCBs.”
He further explains that Ultrasonic cleaning is used for cleaning of PCBs after the soldering process in the Electronics industry. Although many chemicals are available, no-clean flux is used for better results. The cleaning process depends on the quantity which is why manual brushing is used if the quantity is small but the cleaning solution remains the same. These are tailor-made solutions and no detergents are used. High pressure cleaning is used in the assembly area, while vacuum cleaner is used to avoid dust in the room.
Besides, Easun Reyrolle Ltd is also using automatic compressor systems for varnishing. Nanjunda explains, “The electronic components are varnished so that components does not get tarnished by humidity and other environmental conditions.
“Chemicals are available in the market as anti-tarnish PCBs conformal coatings with acrylic or silicon base. Kaiser Fluids Inc. is the manufacturer and exporter of anti-static cleaning in Electronics industry.”
Water based Surfactant Technology is also in use in the industry for heavy contaminants, which are removed by detergents and water with the help of this technology.
Cleaning – a multi-stage process
There are many stages where cleaning is required; prior to stencilling and soldering in order to remove contaminants from the many previous production stages; after stencilling to remove excess adhesive, and after soldering to remove corrosive flux residues and any excess solder paste.
Such residues, along with any other unwanted elements collected due to the missing cleaning stage, could cause issues with adhesion and possibly affect the performance of the protecting media applied.
Trends in cleaning
There are many applications for cleaning, all of which depend on the type of equipment available. Whether it be ultrasonic, spray under immersion or dishwasher type application, identifying the correct water-based cleaner for a specific job is essential. Says Laxmikant, Production Manager, Innovlite India Pvt Ltd, Bangalore, “Ultrasonic cleaning is applicable in most large scale units of the electronics industry.”
There are, however, technologies which do not complement Ultrasonic Cleaning. Hemanth Bapat, DGM, Manufacturing, BPL Techno Vision Pvt Ltd, “Surface Mount Technology is used in our manufacturing facility, in which the components are mounted directly onto the surface of PCBs through Reflow Soldering. Electronic components get soldered without leaving any trace of flux. There is, therefore, no requirement left for Ultrasonic Cleaning or any cleaning after the soldering.”
Raghu, Production Manager, Avalon Technologies Pvt Ltd (Sienna Corporation), Chennai, said Aquastorm is a versatile, high-performance cleaning system designed to optimize the PCB cleaning process while minimizing overall cost. This cleaning is used for the water soluble process. It looks like a lengthy oven and has three or two wash chambers depending on the requirement.
Ultrasonic Cleaning is the other type of cleaning applicable for the PCBAs to remove the residues. These are available in different frequency ranges and the normal cleaning agent for this is the Isoproponal Alcohol (electronic grade).
Cleaning Audit
PCBs are subjected to thorough inspection by Automated Optical Inspection (AOI). This is to check excess Lead in the soldering area or dry soldering. Floor mats are checked to ensure anti-static properties through the meters.
There are two main categories of cleaner currently available, solvent based and water based. Traditionally, solvent based cleaners such as 1,1,1-trichloroethane and 1,1,3- trichlorotrifluoroethane dominated the market; however, due to their ozone depleting potential, they have been replaced by a more diverse range of solvent cleaners. This category is now typically divided into three sub-sections; flammable solvent cleaners, non-flammable solvent cleaners and non-flammable halogenated solvent cleaners such as HFCs and HFEs. All three types have their advantages and disadvantages but overall solvent cleaners can be described as fast evaporating, single stage cleaners. However, they require specialist equipment and extraction to protect against toxicity and other possible hazards.
Laxmikant said, “Cleaning of the PCBs is done manually by alcohol IPA in our units. Flux contaminants and regular rosin flux is removed using Industrial Grade IPA. Hygiene and cleanliness of the factory is maintained through regular mopping.”
Founded in 2005, Innovlite is one of India’s Green Business pioneers with a track record in technology-based innovation that contributes to a clean and healthy environment.
Analytical methods for cleaning
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A common method of determining the degree of ionic contamination is to measure Resistivity of Solvent Extract (ROSE), also known as Solvent Extract Conductivity (SEC). The theory of ROSE is that as the concentration of ions in a solution increases, the resistivity decreases. Simple automated versions of ROSE testing, the Omega Meter, Ionograph or ZeroIon, are used by a number of electronic assembly houses for quality control testing.
Maintaining Standards
The industry standard, IPC-TM-650, employs a solution of isopropanol and deionised water to extract the contaminants whilst the meter measures the change in conductivity. This type of testing is widely accepted and offers rapid results but can be restrictive. Originally designed to test residues from traditional rosin based fluxes and utilise a cheap, readily available solvent (IPA), the scope of this method is now somewhat outdated and may not alert users to possible changes resulting in non-soluble residues.
The change in accepted cleanliness levels also highlights the development of the cleaning industry. Traditionally for the CFC-113 type cleaners mentioned earlier an accepted limit of 1.56μg/cm2 (10μg/in2) equivalent NaCI is detailed as per ANSI/J-STD-001. Today, most assemblies are now achieving well below this level, typically in the region of 0-1μg/in2. This method is also only capable of measuring ionic contamination and cannot define exactly where or what that contamination is.
Two further methods provide valuable data are the measurement of Surface Insulation Resistance (SIR) and Ion Chromatography (IC). The former involves measuring the change in electrical current over time via an interleaved comb pattern PCB and is typically performed at elevated temperatures and humidity levels. The presence of contamination lowers the insulation resistance of the material between the conductors. The latter, Ion Chromatography (IC), is a newer method for cleanliness evaluation which can be used for identifying and quantifying specific ionic species that are present on an electronic device.
The test method details a specific list of ionic residues which can be removed by specific media. Subsequent analysis of the fluid can separate, identify and quantify the residue. Substrate handling and preparation are critical for this method making it particularly expensive and time consuming. Therefore, it is not used for general quality control purposes but as a more specific analytical technique.
The type of cleaner chosen depends widely on the manufacturing conditions. Whether solvent based or water based technology is chosen, the correct application method and set up is imperative in order to achieve successful cleaning. Many specifications have been outlined for cleanliness evaluation; IPC TM-650 is the industry standard. It details methods for many of the cleaning tests described above, giving precise guidelines for analysis. It is clear that some methods are costly and rather time consuming, however they can provide extremely accurate data on the type, location and quantity of the residue. Other, less intense methods can be employed for fast, efficient quality control.
Cleaning equipment market
Industrial cleaning tanks available in the market provide ultrasonic cleaning power for large, small and delicate items. The price of these tanks brings ultrasonic cleaning within the budgets of small and medium sized businesses. Made from stainless steel, the tanks range in size from 1.3l to 13l, with the transducers generating between 50W and 400W of ultrasonic power. Heaters built in to the larger models enhance the cleaning performance, while the stainless steel basket and rack protects and permanently suspends the items being cleaned. Each unit features a 30 minute timer and LCD display. The unit heats the liquid inside the tank to a maximum of 70°C.
Using just water or a cleaning solvent, the ultrasonic sound waves agitate the liquid to such a force that contaminants are lifted from the surface of the items within a matter of minutes. Ultrasonic cleaning will attack previously impenetrable agents such as limescale, mould and bacteria from the surfaces of items.
In yet another form of cleaning, Hydroxide solution is used for Tungsten cleaning, which helps in removing graphite from Tungsten wire for units manufacturing Cathode & Heaters for TV Picture Tubes & CRT’s.
Plasma processing
Plasma processing is also gaining popularity due to its environmenta
Plasma activation effectively raises surface energies and ensures good wettability. This in turn promotes more complete flow of resins onto almost all low energy polymer materials, including PTFE, silicone rubber and Kapton®. Plasma processing makes polymer surfaces bondable by the reactive chemistry present in the plasma. New chemical functional groups are formed with strong chemical bonds to the bulk of the plastic allowing both aqueous based solutions and adhesives to wet into every crevice of the material. This results in improved bonding, with increases of up to 50 times the strength of the traditional bond not uncommon.
Plasma processing enables the cleaning of residual organics at the molecular level on materials such as glass, metals, plastics, polymers or composites prior to bonding, potting, printing, marking, painting or labelling. It can also be used on PCB’s prior to metallization, where plasma de-smear and etch-back of PCB’s allows for the smear left on via walls after drilling to be removed.
Challenges
The Electronics industry today finds a challenge in the usage of electronic grade IPA, which is used for cleaning of fluxes and other residues from the PCBAs. As of today the industry is looking for a cleaning agent which will avoid the white patches on the boards. When IPA reacts with the flux, it leaves a white patch at the solder joints though it’s not bad it’s definitely indicating an ineffective cleaning.
In summary, selection of the most suitable cleaning process, which provides the required level of cleanliness, is the key to ensuring maximum reliability at minimum cost. Experts point out that this can be accomplished through combining the most advanced cleaning technologies in an energy-efficient design.
Water based cleaners
Water-based cleaners tend to be much more complex than their solvent based counterparts. They utilise surfactant technology to assist the removal of contaminants from a PCB by reducing the interfacial tensions and suspending or emulsifying them in solution. Alternatively, water-based flux removers work by saponification, neutralising the flux acids.
The only major disadvantage of water-based cleaners is that they require multiple stages to complete the cleaning process, including a two-stage rinse process and a final drying stage. Finally, there is also a newer type of surfactant-free water based cleaner. Based on glycols, these cleaners combine the advantages of water based and solvent based cleaners with only minimal rinsing required.