No Clean fluxes are a hot topic, because No Clean fluxes are fluxes of type L or, depending on the test result, M, and their residues do not necessarily have to be removed from the soldered assemblies. Such fluxes, which are classified according to DIN EN 61190-1-1 or J-STD-004, are generally completely uncritical with regard to corrosion behavior, halogenide content and surface insulation resistance of the flux residues remaining on the assembly. Both the DIN EN 61190-1-1 and J-STD-004 standards are currently the standards with the appropriate requirements for soft solder fluxes for high quality solder joints in electronic assembly. However, these test methods represent a flux for the wave soldering process.
The standards and associated test methods do not deal with flux residues on assemblies that have not undergone a thermal process, such as selective or manual soldering. Unfortunately, there is no current and official standard with more specific requirements that addresses this process issue. For this reason, flux manufacturers have developed and introduced in-house tests to provide a better indication of the suitability and recommendation of a flux for a particular process.
These in-house tests have more demanding test criteria, such as steam reactions, climatic conditions, e.g. higher temperatures and humidity, which means that they can give a reliable statement about the behaviour of a flux. Thus, No Clean fluxes, which are qualified according to the in-house tests of Emil Otto, for example, always pass the DIN EN 91190-1-1 (J-STD-004) standard. The situation is different with the standard DIN EN 6119-1-1 (J-SDT-004). The No Clean fluxes qualified according to this standard do not always pass the in-house tests for selective or manual soldering.
On the basis of these internal tests, it can be proven that even if flux residues are found, which are not thermally contaminated, the assembly is safe. Unfortunately, there is no colore detection of flux residues, but only reagents that react to a part of the contained substances of a common flux. However, these also react to similarly products containing these substances, which only provides information about the presence of such substances, but not whether flux residues are present and thus whether the assembly needs to be cleaned or not. This proof is therefore unsuitable for providing reliable evidence of the safety of fluxes and flux residues.
Do you have questions regarding this matter?
Your contact person: Markus Geßner
company: Emil Otto