Enhancing Humidity Robustness of Electronics: Understanding the Crucial Role of Solder Flux Chemistry in Determining Humidity Boundary for Failure

Corrosion issues of electronic devices under humid conditions heavily rely on the cleanliness of Printed Circuit Board Assemblies (PCBAs). Use of no-clean flux during diverse soldering techniques such as wave, selective, and reflow soldering
significantly influence PCBA cleanliness. Residual flux on PCBA poses a threat, causing corrosion failure modes under humid conditions. All flux residues are hygroscopic and, therefore attract moisture on the PCBA surface at different humidity levels depending on the Critical Relative Humidity (CRH) of the ionic component of the residue. Another contribution of residue is to the conductivity of the water film due to the dissolution of ionic residues. Although all solder processes can generate residues, use of liquid fluxes for wave and selective soldering processes make it more adverse from corrosion robustness point of view. Liquid fluxes are used for wave and selective soldering, which is sprayed, therefore producing residues spread over the PCBA surface. Therefore, liquid flux chemistry, especially the ionic part of the flux composition plays a big role in determining the humidity boundary for the PCBA. This paper presents an analysis of large number of PCBA cleanliness-related performance data and effects on corrosion reliability within the framework of descriptive analytics to understand how activator chemistry and chemistry of the flux system play a huge role in determining humidity boundary
for PCBA.