Flux activators are chemical additives used in Solder Paste and Fluxes to remove oxides from metal alloys and improve solderability. These activators chemically react with the oxide layer on the metal surface via acid-base or reduction reactions. Organic carboxylic acids react with metal oxides to form soluble metal carboxylate salts and water.
The resulting salts or volatile compounds are either dissolved in the flux medium or vaporized during heating. Soluble salts and metal carboxylates become suspended in the flux medium during soldering. At soldering temperatures (200-250°C), many of these acids thermally decompose via a process called “outgassing.” The weak organic acids, solvents, and other functional additives vaporize
When the outgassing path is blocked by bottom-terminated components (BTCs) such as QFNs, DFNs, or large-pad BGAs, the trapped flux volatiles can’t escape during reflow. The low standoff gap seals off channels that allow the volatiles to outgas. This results in wet, pliable, and deliquescent flux residues that underfill the bottom termination.
Active flux residues trapped under BTCs can cause corrosion, electrical leakage, voids, delamination, and thermal inefficiency. The flux residues from three different solder pastes failed under harsh climatic conditions, as shown in the figures below.
Surface Insulation Resistance (SIR) testing evaluates the long-term reliability of electronic materials and processes by exposing circuits to controlled temperature, humidity, and electrical bias to identify potential failure mechanisms caused by electrochemical reactions. SIR assesses production process chemistries, such as solder masks, fluxes, pastes, and wire, as well as assembly processes, including reflow, SMT parameters, and cleaning methods.
High-temperature and humidity aging tests simulate years of service in days, providing critical insights into material integrity and reliability. With tailored test profiles, SIR testing helps predict service life, ensuring quality and durability in electronic assemblies.