Solders of fortune…

Solders of fortune…Electronics manufacturers are on track for healthier solder practiceas the choice of solders and fluxes gets ever greater. Paul Gregg sniffs out the details
Electronics manufacturers are faced with an almost impossible choice when it comes to selecting the right solders and fluxes for their process. Vendors claim that these products hold the key to improved production, as well as meeting health and environmental standards.
Lead-free solders have raised considerable interest in the industry, because of the perceived threat of lead poisoning. One particular cause for concern is what happens to quantities of discarded PCBs when they are dumped in landfill sites. There is always the possibility of the lead becoming soluble and finding its way into ground water, and contaminating drinking water.
Unfortunately there is no single alloy that has all the properties of tin/lead and that can be used as an ideal replacement. Most alternatives have a drawback or a cost penalty. Developments in no-clean fluxes have been more successful, particularly reducing the solids’ content, which allows manufacturers to produce boards that have low residues.
The health hazards are associated with the resin-based fluxes are primarily due to the naturally derived residue that occurs. Inhalation of the fumes produced at the soldering stage can be overcome by turning to no-clean fluxes. These normally contain two to three per cent solids, while resin-based flux usually contains 30 to 50 per cent solids.
While the solids content is low in no-clean type fluxes, they do contain acids, alcohols and other types of solvents that can be equally as dangerous to inhale. “For this reason”, said a spokesman for soldering and desoldering systems specialist, Pace Europe, “employees should be protected from exposure to these substance by the use of fume extractors”.
In order to help engineers get to grips with legislation on fume extraction requirements, and how to comply with the law, Hi-Tech UK is hosting a series of free one-day seminars throughout the year. The subject of fume extraction will be the focus of attention of a number of companies at this week’s Nepcon Electronics exhibition in Birmingham.
However, there is little information at present on the chemical composition of no-clean flux fumes. Further research has to be conducted in order to identify and quantify these by-products, in order to fully understand the seriousness of exposure to vapours given off by volatile organic compounds (VOCs). What the suppliers are offering
To help meet industry concern, Multicore Solders has brought out a resin-free solid flux that has been developed to meet the stringent legislation on VOC emissions. The Ecosol 105 product excludes all rosins, modified rosins, and their derivatives.
Ecosol 105 accurately imitates the behaviour of rosin-based cored solder wire flux. This means that in addition to appearing visibly the same, for example in its colour, it also provides high activity, fast and sustained soldering on copper and brass. But it features a distinctive low odour that differentiates it from rosin-based products.
Tests undertaken by Cobar BV in Holland, show that VOC-free fluxes can be used successfully with no additional change to the production process. However, the preheat temperature needs to be increased by 20 per cent overthose used for alcohol-based fluxes.
Consequently, Cobar has developed a flux solution that acts as a compromise between the alcohol-based fluxes and complete VOC-free solutions. The company’s low VOC flux is made up of approximately 30 per cent water and 70 per cent alcohol. It is currently undergoing tests in Sweden.
Warton Metals says that it’s environmentally friendly solder wire can help cut down occupational asthma, because the Omega product contains no resin, pine oil or other naturally occurring derivations from the pine tree. Tests carried out in accordance with the proposed limits of “Methods for Determination of Hazardous Substances” (MDHS 83), confirmed that the fumes produced were rosin-free.
The wire is available in solder alloys including 63/37, 62S, and lead-free 96S. It can also be obtained in wire gauges, ranging from 10 to 32swg. The Omega solder wire passes the copper mirror corrosion and surface insulation requirements of Bellcore TR-NWE-000078 and J-STD-004.
With the increasing application of stencil printing for the production of smaller surface mount board sizes, there has been a wider application of no-clean solder pastes. These pastes have the advantage of being able to provide the fine-line definition required, as well as being easier to handle, often in cartridge form.
Their binder compound is exclusively based on synthetic polymer chemistry, that have low residues and excellent adhesive properties after reflow, and long stencil life. Cobar says that its no-clean solder pastes have the approval of Siemens Technology Centre in Berlin.
Tests performed on stencil printers using Cobar’s no-clean solder pastes showed that stencil life of over 24 hours was achievable. When used on a machine such as a DEK 265, print speeds of up to 150mm/s were achievable, with fine line definition down to 0.3mm pitch.
Developed as an alternative to solder paste, Epoxy Technology says that its silver filled epoxy does not flow when subjected to heat or dry out during processing. It has been developed specially for stencil printing, and the two- component epoxy comprises 100 per cent solids. It contains no solvent or thinners that can dry out during processing.
The product (EPO-TEK E2101) has a volume resistivity of 0.0001 to 0.0004 ohms/cm, and adhesion to silicon wafers, glass, and metals is claimed to be excellent. Curing can be achieved at 150 degrees C in one hour, 175 degrees C in 15 minutes, and instantly at higher temperatures.


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