Flux Cleaning is Essential

PCBA cleaning (called flux cleaning or defluxing) is extremely effective in solving or preventing problems caused by flux residue.

Use of high-density mounting of components on PCBAs is accelerating, and in these cases even a small amount of flux residue may cause electrical isolation losses affecting signal integrity.  In these cases, flux cleaning is required.

Fig. 1 – BSE SEM image showing residual solder flux and tin-salts on the surface of the board between the solder lands.

Cleaning, specifically flux cleaning or defluxing, is highly effective in addressing and preventing issues caused by flux residue. Flux residue can lead to various problems such as increased electrical conductivity on the board surface, increased risk of corrosion, and compromised reliability of electronic components.

Fig. 2 – Flux residue spans nearly 100% of the isolation space between signals.

When low-residue or no-clean flux is used, there are cases where the flux cleaning process is omitted. However, in fields where high reliability is required, such as automotive modules and space-related equipment, the flux residue cleaning process is essential to avoid the problems described above.

Fig. 3 – No-clean solder flux residue on PCBA surface between component pads.

Ionic cleanliness refers to the measure of ionic contamination present on the surface of a material or component, typically in the field of electronics manufacturing. It quantifies the amount of electrically conductive ions, such as chloride, sulfate, and other residues, that are left behind after manufacturing processes like soldering, flux application, or cleaning.

Ionic contamination can occur due to various factors, including the use of fluxes, soldering materials, handling processes, and environmental conditions. These ionic residues, if not properly controlled or removed, can have detrimental effects on the reliability and performance of electronic devices.

To assess ionic cleanliness, a common method is to measure the electrical conductivity of an extracted solution from the material or component. This is typically done using techniques like ion chromatography (IC) or resistivity of solvent extract (ROSE) testing. The results are expressed as the concentration of ionic species, typically in units of parts per million (ppm) or micrograms per square centimeter (μg/cm²).

Standards such as the IPC-TM-650 and MIL-STD-2000 provide guidelines and specifications for acceptable levels of ionic contamination in different electronic assemblies or components. These standards help manufacturers ensure that the ionic cleanliness requirements are met to maintain the reliability and functionality of the final products.

Overall, the goal is to ensure optimal performance, reliability, and longevity of electronic devices by addressing flux residue, maintaining adequate ionic cleanliness levels, and mitigating the impact of moisture. Adhering to industry standards and manufacturer guidelines is essential in implementing effective cleaning processes to meet the specific requirements of different applications and sectors.

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