Eltville, 04.08.2015
Soldering is one of the most important process steps in today's connection technology. Solders are metal alloys that have a lower melting point than the base metals in the contact surfaces of the printed circuit board and the component. Once the solder has melted, it forms a contact with these base metals. This requires the application of heat. The solder must be melted and the base metals must absorb enough heat to ensure the flow of solder.
The base metals and the solder are oxidized on their surface by atmospheric oxygen and environmental influences. These oxides interfere with the melting behavior and the structure of the joint layer. Fluxes must be used to prevent this. Fluxes are substances or mixtures that are able to reduce oxides to metals and prevent reoxidation. The surfaces of the base metal and the solder become metallically bright. This state can be maintained in the soldering process thanks to the flux. The melting and flow of the solder is significantly improved and the connection zones can form well.
With the further development of electronics, the fluxes also had to be constantly adapted. Initially, the PCBs had a very simple structure and the conductor spacing was sometimes quite large. The standard solder used was the eutectic tin-lead solder. The fluxes had a high solids content to safeguard the soldering process. It was often applied using a foam fluxer. Avoiding flux residues was not of major importance.
With the increasing use of electronic components in many areas of industry, printed circuit boards became more delicate and spray fluxing became established in system technology. Smaller track spacings brought the issue of flux residues and their behavior on the finished assembly into focus, as this could lead to corrosion, oxidation and destruction of the solder connections. The risk of short circuits caused by flux residues increased enormously due to the packing density on the PCBs. Future fluxes still had to provide reliable soldering with a lower solids content.
The ban on the use of lead and other hazardous substances as a result of the RoHS Regulation, which came into force on June 1, 2006, marked a turning point in electronics production. Alternative lead-free solders melted at about 30-45°C higher temperatures than solders containing lead. Their chemical-physical behavior was more difficult, as these solders reacted very sensitively to the lowering of the temperature. These temperature drops could be partly caused by the circuit board itself. This meant that the soldering process had to be adapted. The solder wave temperature was increased by 10-20 °C and the preheater had to introduce more heat into the PCB to prevent the solder flow from stagnating. The fluxes had to correspond to these process changes. This meant that they had to become more thermally stable and actively dissolve the oxides and prevent reoxidation even at higher temperatures.
Parallel to the switch to lead-free alloys, the flux residues remaining on the PCB were evaluated more and more critically. This resulted in detailed requirements for the fluxes. Remaining flux residues should only have a low corrosion potential and a high surface resistance. Halide-free formulations, labeled as L0 according to DIN EN 61 191-1-1, offered the best conditions for this.
In the run-up to the lead-free changeover, Emil Otto developed a new flux series based on synthetic resins and a combination of activators that possessed the properties required in the lead-free process. The GSP series with the products "GSP-2533/RX" and "GSP-2533/RX/OVAP" was also used in the BFE (lead-free soldering) working group for numerous tests and was found to be good. These products quickly found their way into the industry and are still used there today. In the course of further development and improvement of the long-term behavior, the product group "S-250" with the fluxes "S-250/FRO" for spray fluxing and "S-250/FR" for foam fluxing was then also developed on the basis of synthetic resin. It is characterized by very good soldering properties and high cleanliness (residue behavior) and has proven itself in industry. Both series are halogen-free and classified as L0.
With the increase in mixed assemblies, high packing densities and ever smaller components, the process performance of solder, system technology and flux has been further advanced. As a result, the use of selective soldering processes is currently on the increase. In this process, the thermal load only occurs in the sections of the PCB that are to be soldered. The flux wetting is spatially limited and the solder supply is very precisely controlled. This process also requires special fluxes in order to make optimum use of the creep properties and to counteract possible corrosion on the PCB. With the selective soldering fluxes "RS-4004", "SD-35" and "HR/D-110", products specially designed for the selective soldering process are available in accordance with the above-mentioned criteria.
Growing environmental awareness and occupational safety issues are further areas that are leading to changes in fluxing agents. The industry is considering replacing the traditional solvent alcohol in fluxes. The alcohols ethanol and isopropanol are standard solvents and can ignite at 12°C if an ignition source is present. This poses considerable risks during transportation and handling.
On the customer side, production and warehouse employees must be specially trained in handling these products and companies must comply with strict framework conditions and laws during transportation and storage. This leads to a massive amount of additional work on the part of the manufacturer and the customer, which in turn leads to considerable additional costs. As an alternative, water-based solvent-based fluxes have therefore been developed. These are non-flammable, do not release CFCs, are absolutely safe to handle and transport and are now commonly used in industrial electronics production. The water-based fluxes "WB-35/SOX/DT" or "WB-35/EK 1405" are representative of this group. Emil Otto accompanies the customer on site during the changeover process.
The Emil Otto company, founded in Magdeburg in 1901, has been involved in the development and manufacture of fluxing agents since its foundation. Initially, the focus was on soldering and brazing fluxes for the metalworking sector in industry and trade, but from the 1970s onwards it shifted to electronic fluxes. All the aforementioned developments have helped to shape Emil Otto's products. Today, Emil Otto can offer a range of fluxes that covers all wave soldering areas in the field of alcohol-based and water-based electronic fluxes. In addition, specific solutions are offered for selective soldering, iron soldering and other special cases. Fluxes for cable assembly and strand tinning have also been developed and successfully launched on the market.