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For better health conditions

Filtration and extraction of dangerous fumes in electronics
For better health conditions

More attention is being paid in the electronics manufacturing to healthy work areas for employees. People can be exposed to dangerous fumes that occur during production or repair in many situations. It is important to indicate recognizable examples of daily work, where fumes appear and how these can be extracted with the appropriate equipment.

Peter Strikwerda, export manager, Filtronic, Lidköping

In daily work on the electronics production floor and repair shop, noticeable situations that normally are unhealthy to operators who carry out the process go undetected. The fumes which occur at soldering, conformal coating, gluing or at the removal of those materials can be present in such small amounts that they are not perceivable, but they exceed the levels accepted. Due to more strict labor rules and environmental demands, this calls for suitable actions.
Working areas
Major electronic production plants have special rules for certain areas in their plants to make them special working areas. Think about ESD safety rules. Normally, a specification regarding the conditions in that environment applies to these areas. Air conditioning and more frequent air recirculation through a central system will give these zones a good working climate, though these measurements are not good enough when dangerous or toxic fumes appear even under normal working activities. It becomes very hard measuring those fumes to get acceptable figures due to the volume of such a working area. But the operator with his or her nose rightat the spot of the fume source does geta much higher dose in the inhaled airthan will be measured in the area on average.
The fumes are extracted by a central air supply system and come into a unit that has to ‚clean‘ the air stream. Unfortunately, those systems have not been designed for this task of removing chemical particles from the polluted air. Moreover, the fumes follow the airflow and appear somewhere else in the building. More than shifting the problem will not be the case with these central air conditioning systems. The correct way is the removal directly at the source of the fume occurring, with a system that meets the correct specifications.
Daily situations
The operational method within a factory or repair shop determines the way the fumes are removed. Such an extraction can be provided by a high-vacuum or a low-vacuum system. The first solution is suitable for removing fumes through small tubes (tip extraction) with a high air speed, while the second deals with large volumes of air at lower speed (arm or hood extraction). The difference of both systems determines the vacuum motor and the usage of accessories.
When we look to the entire process of PCB assembly, we will see a number of different stages. First, the manufacturing of the bare PCB with the etching and coating, followed by solder paste printing, assembly and the soldering process. Finally, we have the attachment of cabling or installing the boards into housings or equipment. A repair or rework shop adds to this chain.
During the manufacturing of the bare PCB, we can meet different chemicals among which are mainly etching liquids and coatings. Taking in account the volume of the air, we can only use low-vacuum extraction systems with high processing capacities. Fumes occurring here are acetates and cyanides.
The next stage, the assembly, primarily reflects the use of SMT adhesives, contact glues, etc. These materials all release a kind of isocyanides at handling, which is extremely dangerous even in small quantities.
After this, the soldering process follows where we find the main fume elements consisting of the residues of PCB base material and the solder and flux itself – for example aldehydes, alcohol, organic base materials, lead, etc. At heating of flux, these fumes are released, and the quantity depends upon the type of flux being used. New in the process are the fluxes based on water. The fumes of these fluxes have yet to be determined, and it is also important knowing how toxic and dangerous these materials will be.
Following soldering, the application of cabling and eventually conformal coating of the PCB take place during the final assembly. With cabling, stripping, pre-tinning of the cable ends and soldering of them to connectors or terminals by hand, etc. may be necessary. This manual work is often hard to do automatically. This means that an operator is very close to the process, especially in case of manual soldering with a hand iron. Here, different fumes mentioned above will appear in various combinations. Additionally, in the rework or repair shop, all aspects of an entire production process will appear, but on a smaller scale. Moreover, flux residues must be removed by hand or conformal coatings by other means (heated tools, for example) for testing and eventually desoldering components. Isocyanides and formaldehydes together with alcohol will be released during these steps.
Health aspects
To indicate the importance of fume extraction, a small explanation of the most important health aspects are necessary. Very often, too many production managers neglect the harmful influence of hazardous fumes. While in Scandinavia, liability due to occupational asthma in electronics manufacturing is accepted, and is seen on the same level as asbestos exposure, there are still many companies, for example in the UK, not taking care of fumes the correct way in electronics. (In this respect, it would be very interesting to look at remote operations of multinational firms or contract manufacturers in developing countries.) Not that we are far away from claims due to occupational asthma. In Scandinavia, a company has been sentenced paying a lifetime pension to several employees with an additional fee for the financial compensation of health problems. With equality in European aspects, we can expect the same in other countries.
Fumes are inhaled by the operator’s breathing organs (nose, throat and lungs), and then wander into the blood circulation system. First symptoms of exposure are a lack of smell, irritation of throat and eyes, serious headaches and dizziness. Major effects of occupational asthma can be contributed to the isocyanide parts in the airflow, while the isopropyl alcohol causes dry, cracked skin, headaches and dizziness. Flux forms up after heating aliphatic aldehydes (formaldehyde), and gives reason for operator’s complaints of running nose or eyes, and a soar throat with loss of taste and smell. Not to forget, even when their analysis takes a lot of time and is costly: these different toxins being stored in liver and other organs. Apparently, they can lead to very serious health problems, and eventually to inability to work and an early death. Therefore, there are more than enough reasons for responsible caring for non-toxic workspaces.
Asthma can be defined as a condition characterized by recurrent attacks of increased resistance to airflow in the lungs, partially or completely reversible, either spontaneously or as result of treatment. Most important symptoms are breathlessness, coughing, wheezing and tightness of the chest. Compare it to a small plastic tube that has been narrowed even further. The airflow still will come through it, but it takes a longer time, and in addition the airflow will become noisy. Occupational asthma occurs after exposure to fumes at the working area. The symptoms will disappear more or less when the operator leaves the working area for a longer period.
Biological allergens are reasonably well understood (grain, flour, hops, birds, animals, insects, different sort of dusts, etc.), but industrial chemicals are underestimated very much in their effects. The most prominent product which is indicated as the main cause for occupational asthma is isocyanate. This chemical appears in fumes when heating up polyurethane coatings such as of transformer wires or conformal coatings and so on.
Occupational asthma is treated by many doctors as bronchitis and medicated as such. There is a latent period between first exposure and the onset of symptoms. This is the period required for sensitization, it averages four years in the electronics industry, but may actually vary from a few months up to 16 years. The sensitizing agents in the workspace therefore have usually been in use a longer time before any symptoms develop.
There are three reaction patterns to an occupational agent:
• Immediate asthmatic reaction (starts within minutes of exposure and lasts 1 to 2 hours)
• Late asthmatic reaction (starts some hours after exposure and continues up to a maximum of 6 to 18 hours afterwards)
• Recurrent asthmatic reactions (a single exposure may also lead to continuing symptoms for days or even weeks)
There are cases known of employees showing asthmatic reactions in an office building where they were working three floors above the electronics manufacturing floor. This is an effect due to a central air recirculation system without sufficient filtering methods.
Filter efficiency and lifetime
A fume extraction/filtering system consists of different parts. Most important for such a fume extraction system are the vacuum motor, filter concept, control and the enclosure. At the beginning, we mentioned the working principles of high and low-vacuum systems, and that application of one of these depends upon the method used. However, clearly, the filter concept in both of those systems is similar.
The filter concept dominates the efficiency of a system, especially when it affects the removal of hazardous fumes and not simple moving airflow. Therefore, a filter consists of two key elements: the medium used for filtering the gases, and the contact time of the gas with the filtering medium.
The filtering medium of a solution removing fumes in electronics production can be made up of activated carbon or a mixture of activated carbon with purafil (potassium permanganate). Activated carbon solely reduces the lifetime of a gas filter to a short time even to only a few hours. By processing, the filter becomes rapidly saturated and needs to be exchanged. The efficiency of such a system is far from being within an acceptable time frame. The second option is the mixture of both mentioned materials. Purafil is a product that regenerates the absorbed gases from the activated carbon. By a chemical reaction, the gases are converted to salt, brown stone and water. The filter has a noticeably longer lifetime, compared to an activated carbon filter. Lifetimes are reported of from six up to nine months‘ usage, depending of course of the fumes load.
But the medium itself is not the only object influencing the efficiency of a filter. Such a medium must have the capability of removing the gases sufficiently from the airflow through the filter. This depends also on the so-called contact time with the filter medium. The minimum value for contact time is 0.3s in the gas filter. This value can be calculated easily by taking some measurements from the gas filter (height, width, surface, airspeed or volume). This will determine the efficiency of the filter, or the limits of the maximum airflow.
When we have revealed the efficiency of a gas filter, we can set-up some other features of a filtering system. Lifetime of a filter depends upon the capability of overcoming a certain pressure drop over the filter (indicated in mmwp) before the filter clogs up. The higher this value, the longer the lifetime. At present, it is the only method indicating the lifetime of a gas filter. All industrial filter systems only display the lifetime expected of the micro filter by means of measuring the pressure drop.
The most difficult particles to catch are those with a diameter of 0.3mm. For indication of the efficiency of a filter used for those submicron particles, these constituents are measured according to a DOP standard. A good filter should at least catch 99.997% of the particles of 0.3mm. Any smaller or larger size will be caught much more easily.
Also taken into account must be the complete assembly of the filter. A perfect system first has a micro filter to collect the submicron particles from the airflow. Then follows the gas filter, and after this there is a dust filter removing particles that come from the gas filter in the airflow. There are of course filtering systems with another concept, but they do have some disadvantages. For example, a gas filter in front of a micro filter results in a fast-clogged gas filter, or a gas filter in a bond-molded form after the dust filter, or an impregnated-mat type will give a too short contact time with the filter medium.
Useful tips
With the application of some useful tips, a filtering system can be made more efficient. The airflow for arm or hood ex-traction should at least have a speed of0.5 m/s. This causes gas molecules not to go up into the air but to follow the stream within the system. With tip extraction, airspeed of 20l/min has to be realized for effective operation.
Also, the nozzle or intake of a system has to be placed as close as possible to the work area. This will result in the coanda-effect: A vacuum will be formed due to the draft of the airflow over the surface, and provides better extraction results even at low speeds.
All fume extraction systems have to be documented and certified in terms of efficiency by independent labs for gas filtering and ESD-safety issues. Some suppliers mention that their filters are operating according specifications, but these are only the manufacturer’s claims, not necessarily verified by neutral experts.
Zusammenfassung
In der Elektronikfertigung entstehen trotz aller umweltschützenden Maßnahmen unerwünschte Dämpfe, Partikel sowie Abdampfungen leichtflüchtiger Lösemittel. Die sehr weitgehende Beseitigung solcher toxischen Stoffe, sowohl bevor sie in die Umwelt gelangen als auch zu den Mitarbeitern, sollte in Europa eigentlich Minimal-Konsensus sein, andernfalls können erhebliche Schäden an Gesundheit und Umwelt auftreten – mit dramatischen Folgen.
Résumé
Malgré toutes les mesures prises pour protéger l’environnement, la fabrication d’électronique produit des vapeurs, particules et émanations de solvants très volatils indésirables. L’élimination aussi poussée que possible de ces substances toxiques avant qu’elles n’affectent aussi bien l’environnement que le personnel devrait faire l’objet en Europe d’un consensus minimal faute de quoi des dommages considérables pour la santé et l’environnement sont à prévoir, avec les conséquences dramatiques qui en découlent.
Sommario
Nella produzione di componenti elettronici, nonostante tutti i provvedimenti di protezione ambientale, vengono generati indesiderati vapori, particelle ed evaporazioni di solventi volatili. La necessità di eliminare su ampio fronte tali sostanze tossiche dovrebbe essere chiara a tutti in tutta Europa, in caso contrario possono generarsi danni sia alla salute umana che alla natura – con conseguenze drammatiche.
Current Issue
Titelbild EPP EUROPE Electronics Production and Test 11
Issue
11.2023
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