Non volatile response to keeping electronics clean

18 September 2009

Jade Bridges
Jade Bridges

One company making a big splash at Productronica this year is Electrolube who is using the show to launch its latest range of non-VOC products. Tim Fryer talked to the company’s R&D Manager Jade Bridges about the the VOC market.

Tim Fryer: Could you quickly recap on what VOCs are and why they are considered bad for the environment?

Jade Bridges: Volatile Organic Compounds or VOCs are carbon based compounds which vaporise easily at room temperature. They contribute towards the formation of ground-level ozone via the photochemical interactions of VOCs (‘pre-cursors’) and nitrogen oxides. Ground-level ozone is a major component of smog and can have many detrimental effects on the environment, in particular, damaging forests and vegetation. In addition, VOCs when not managed properly can also cause health problems. Over exposure causes them to act as irritants and in worst cases carcinogens.

Tim Fryer: What is the current status of European legislation regarding VOCs?

Jade Bridges: The EU Solvents Emissions Directive states that a VOC is “any organic compound having at 20°C a vapour pressure of 0.01kPa or more, or having a corresponding volatility under the particular conditions of use.” It covers defined operations such as the manufacture of coatings, coating activities (such as PCB conformal coating) and surface cleaning. The threshold limit value for solvent emissions can be found in Annex IIA of the Solvents Emissions Directive, where the quantity is defined by the activity. Manufacturers whose consumption of solvent falls below the appropriate threshold limit, fall outside the scope of the directive. Occupational exposure limits (OELs) in the workplace will still be apparent, however. It is therefore clear that both the manufacturer and end user of conformal coatings are affected by the Solvents Emissions Directive.

Tim Fryer: Are ‘low-VOCs’ permissible and if so what are the limits?

Jade Bridges: There is no standard definition of a ‘low-VOC’. Anything which contains reduced levels of VOCs could be described as a low-VOC as could a material with very low volatility. It is not clear from the statement ‘low-VOC’ whether harmful emissions are still an issue and in most cases, significant air pollutants may still be emitted by the use of such materials. The EU Solvents Emissions Directive classifies a VOC by its vapour pressure; any material above the specified value is classed as a VOC. There is sometimes some confusion as certain materials are exempt from VOC regulations depending on the legislation that is being referred to. It is important that the correct legislation is identified for the location in which VOCs are used and that the description provided by chemical suppliers is also investigated by location. For example, what is exempt in USA may not be exempt in Europe.

Tim Fryer: What have VOCs been used for in the electronics manufacturing environment and what advantages have VOCs had over non-VOC equivalents.

Jade Bridges: Traditionally, VOCs have been used for conformal coating and cleaning applications. The properties of a conformal coating stem from the selected base resin and the various additives included, optimising the performance of the cured coating. Organic solvents are used to dissolve the base resin and reduce viscosity to bring the coating within a workable range. As such, the coating dries by a simple solvent evaporation and in some cases can be further heat or moisture cured to initiate cross linking, further enhancing the coating properties. Solvent based conformal coatings are extremely versatile and can be applied in many ways, such as dipping, spraying and brushing. By simply adjusting the solvent level the viscosity of the coating can be tailored to the required application method. In addition, solvents or VOCs are used for many different cleaning applications during PCB manufacture.

Until recently, there has been a reluctance to change to alternative products, for a number of reasons:

• Change required alterations to production procedures and equipment

• Solvent based materials were very well established

• Alternatives did not have all the answers

Electrolube's new non-VOC products
Electrolube's new non-VOC products

• Lack of knowledge and implementation of alternative products

• Fewer low solvent or solvent-free products on the market

However, there are now non-VOC products available as part of the Electrolube NVOC range that do not suffer from these issues. The NVOC range has been designed to fit in with current processes without the requirement for major alterations or additional equipment. The range has also been tested to the requirements of many international standards. In addition, viscosity control is much easier without solvents evaporating from the material and rapidly changing the viscosity, wastage is much lower as the 100% solids materials means that the coating can spread further and finally, the effect on human health and the environment is vastly reduced.

Tim Fryer: Of the applications you mention, cleaning is interesting in that it largely went out of fashion after the Montreal protocol banned CFCs. Are current PCBs so complex that and so fine pitch that they have to be cleaned to prevent faults? Is cleaning now back in fashion?

Jade Bridges: Cleaning applications were never really ‘out of fashion’ as it is an essential process required at different stages in PCB manufacturing. The purpose of cleaning is to ensure good surface resistance and prevent current leakages which lead to PCB failure. This developing market sees modern and future electronics getting smaller and smaller and the requirement for high performance and reliability is stronger than ever.

Many manufacturers are turning to ‘no clean’ processes, implying that cleaning is not required after soldering. In the ‘no clean’ process, rosin and activator are not removed prior to the next process, such as coating or encapsulating of the PCB. 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. It can therefore be stated that even with advances in new technologies, such as ‘no clean’ fluxes, cleaning is still an essential multi-stage process within the electronics industry. Finally, there are also cleaning stages required for the removal of coatings and adhesives when re-work is necessary and for the cleaning of actual components and for maintenance of the production line.

Tim Fryer: Are there now non-VOC based cleaners that can clean efficiently enough to meet this demand?

Jade Bridges: Yes, there are many products available that offer superior cleaning. The Electrolube Safewash range is a well established water-based cleaning range, designed as an environmentally friendly alternative to CFC-based materials.

Tim Fryer: Do they have environmental side-effects as well (the parallel being the banning of lead in solder was arguably more damaging to the environment when taking into account the mining, mineral processing and energy requirements of Pb-free solder compared to the traditional tin/lead equivalent)?

Jade Bridges: No, in particular, water-based cleaners are biodegradable, they do not require high energy consumption for manufacture and they can be disposed of relatively easily depending on the contamination involved. Solvent-based materials are also a vast improvement over the traditional CFC-based materials, however, due to the impact of VOC emissions discussed earlier, their use should be monitored.

Tim Fryer: The other main application area you mentioned was conformal coating. Same question – are there now non-VOC replacement materials that can match the performance of the VOC-based products?

Dispensing conformal coatings
Dispensing conformal coatings

Jade Bridges: Yes, there are materials available and as discussed the Electrolube NVOC range offers equivalent and in some cases superior performance to its solvent-based alternatives, without the need for costly investment or changes to production procedures. There are many benefits available by switching from a VOC-based to a non-VOC replacement which will be relevant across a wide range of applications. Specific benefits can be discussed in more detail for individual applications based on the current process and materials in use.

Tim Fryer: One of the perceived problems with conformal coating is that certain substances can leach out of the coating, or the coating can degrade over time, to effect the circuit it is meant to be protecting. Have the new products got a track record to demonstrate that they are safe and stable.

Jade Bridges: Substances leaching out of coatings is usually associated with silicone migration and the low molecular weight siloxane phenomena. Many solvent-free, 100% solids materials, offered as alternatives are silicones. However, the Electrolube NVOC range is silicone-free and therefore avoids potential issues involving silicone migration. The NVOC range is a result of substantial development and utilises novel chemistry to provide 100% solids, moisture cure coatings. The formulation provides a low viscosity material which undergoes a complex chemical reaction upon exposure to atmospheric moisture, ‘locking’ all materials into the cured coating.

Additionally, the use of ageing tests, such as those apparent in many industry standards can be carried out to establish the performance of the coating after a certain period of conditioning. Other testing can be carried out to identify the performance of coatings in accordance with particular standards which would highlight any performance issues after only a few simple tests.

Tim Fryer: Some of the main applications for conformal coatings are in harsh environment applications like military and automotive – do the new products need to have necessary military approvals and if so do they have them?

Jade Bridges: Standards are an ideal way to quantify the performance of a coating as they contain many specifically designed tests, identifying the performance of a material for various applications. The tests incorporated in different standards can vary but they are commonly designed around a similar theme. It is therefore important to be aware of the different standards available and which ones are most applicable to the final application. Electrolube have tested and achieved excellent results with the NVOC range across a vast array of international standards, including IPC, MIL, IEC and UL specifications and are currently investigating the most appropriate approval process for the majority of application requirements.

Tim Fryer: Do the new non-VOC materials need more/less curing time and are there any issues with the dispensing equipment required for their use?

Jade Bridges: Electrolube’s NVOC range is extremely versatile in its curing process. Providing there is sufficient humidity in ambient conditions, the coating will cure at a similar rate to solvent-based equivalents. However, if a faster cure speed is required, the process can be accelerated by increasing humidity and temperature therefore achieving touch dry times of less than 10 minutes and full cure properties in less than 20 minutes. The cure is uniform throughout the board and therefore no ‘pockets’ or uncured materials will be present after these short processing times, unlike UV-cure alternatives which suffer from shadow areas. Humidity can be increased by humidity generators or by simple inclusion of deionised water beakers into the curing ovens, again showing the flexibility of the material. As the coating contains no solvents, there is no requirement for a standing time at room temperature to allow the solvents to ‘flash off’. Once applied, the coating can be cured immediately at elevated temperatures without any detrimental effects.

The NVOC range has also been tested and used in a variety of selective spray equipment with excellent results. This includes film, swirl and atomising applicators. This again demonstrates the flexibility of the range, particularly as the standard NVOC conformal coating can be used in all three types of applicator. A higher viscosity version is also supplied where a thicker material is required for dispensing. There are no issues with using the product in a wide variety of equipment and there are no specialist requirements for storage or use, making it a true VOC-based alternative. There are no other solvent-free alternatives that offer such versatility in application and cure.

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