Controlling metal corrosion in the precision electronics cleaning process is crucial for ensuring the reliability and lifespan of electronic components. The key lies in balancing cleaning efficiency with metal protection requirements through formulation design, process optimization, and environmental control, thereby avoiding corrosion-induced issues such as poor contact and signal attenuation.
The corrosiveness of aqueous cleaning fluids primarily stems from their pH and active ingredients. Excessively acidic or alkaline cleaning fluids can damage the oxide film or passivation layer on the metal surface, directly inducing electrochemical corrosion. For example, iron-based materials are susceptible to hydrogen evolution corrosion in acidic environments, while copper-based materials may experience oxidation and blackening under alkaline conditions. Common metal substrates used in precision electronic components, such as stainless steel, copper alloys, and gold/nickel plating, vary significantly in their corrosion resistance, necessitating tailored cleaning fluid formulations. Neutral or weakly alkaline aqueous cleaning fluids, by adding organic amines or alcohol ether corrosion inhibitors, can form an adsorption film on the metal surface, blocking contact between the corrosive medium and the substrate.
The selection and formulation of corrosion inhibitors are key technologies for corrosion control. Inorganic corrosion inhibitors such as sodium nitrate and sodium molybdate inhibit anodic reactions by forming an oxide film, but residual crystals may affect delicate structures. Organic corrosion inhibitors such as imidazoline and benzotriazole block corrosion currents through molecular adsorption layers and are more suitable for micron-sized components. Composite corrosion inhibition systems can simultaneously inhibit both anodic dissolution and cathodic hydrogen evolution. For example, combining sodium silicate with sodium gluconate can form a double-layer protective film on aluminum substrates. In actual application, the inhibitor concentration should be optimized based on the metal type, cleaning temperature, and cleaning time to avoid excessive addition, which can reduce cleaning power.
Cleaning process parameters significantly influence corrosion rates. Increasing temperature accelerates the reaction of the active ingredients in the cleaning solution, but temperatures exceeding 60°C may cause the corrosion inhibitor to decompose and become ineffective. Excessive spray pressure can damage the passivation layer on the metal surface, while prolonged immersion time increases the risk of corrosive media penetration. Precision electronics cleaning typically utilizes a staged process: a pre-cleaning stage uses a low-temperature (40-50°C) and low-concentration cleaning solution to remove large contaminants; a main cleaning stage uses a higher temperature (50-60°C) and ultrasonic assistance, but the duration must be strictly controlled within 10 minutes; and a rinsing stage uses deionized water for circulating rinses to prevent residual chloride ions from causing pitting corrosion.
Water quality management is an often overlooked key point in corrosion control. Calcium and magnesium ions in hard water combine with anionic surfactants in the cleaning solution, forming insoluble precipitates that adhere to the metal surface and create localized corrosion cells. Precision electronics cleaning requires deionized water with a conductivity below 10 μS/cm, and the chloride and sulfate ion content in the cleaning bath must be regularly tested. Treating the water source with ion exchange resins or reverse osmosis technology can effectively reduce the impact of water quality on corrosion.
Controlling post-cleaning residues is also critical. Residual surfactants and corrosion inhibitors in the aqueous cleaning fluid can form a conductive film, triggering electrochemical migration and leading to short circuits. After cleaning precision electronic components, a multi-stage rinsing process, combined with compressed air purging and vacuum drying, is required to ensure that residue concentrations remain below the detection limit. For high-reliability applications in aerospace and automotive electronics, post-treatment steps such as plasma cleaning or supercritical CO2 drying are also required.
Material compatibility testing is a prerequisite for formula development. By simulating the contact corrosion of different metal combinations (such as copper-aluminum and steel-gold plating) in cleaning fluids, the optimal corrosion inhibition system can be identified. Accelerated corrosion tests (such as salt spray testing and wet-heat cycling) can predict the corrosion risk of cleaning fluids after long-term use. For special structures such as flexible circuit boards and MEMS sensors, the effect of cleaning fluids on the swelling of adhesives and packaging materials must also be evaluated.
Environmental and safety requirements are driving the development of low-toxic and biodegradable aqueous cleaning fluids. Traditional phosphorus- and nitrogen-containing corrosion inhibitors are being replaced by bio-based inhibitors, such as natural extracts like phytic acid and tea polyphenols. By optimizing the surfactant structure (such as by incorporating branched alkyl glycosides), water-based formulations can reduce metal aggressiveness while maintaining cleaning power.
