BASF PCB Special Cleaning Agent (PCB Special Cleaning Solution) Electronic/EL Grade is an acidic, low-foaming aqueous concentrate formulated for removing rosin-based, mildly activated, and water-soluble flux residues from assembled printed circuit boards. The product carries the Electronic/EL Grade designation because the batch-release specification constrains anionic and cationic contaminants that would otherwise compromise high-impedance surface insulation after final rinse. At 20°C, the concentrate exhibits a density of 1.05–1.08 g/cm³, a pH below 1.0, and a closed-cup flash point greater than 100°C, and it contains no intentionally added volatile organic solvent, halogenated solvent, or nonylphenol ethoxylate. In use, the concentrate is diluted to 3–10% v/v with deionized water; the working liquid has a surface tension below 30 mN/m at 45°C, which is low enough to penetrate beneath fine-pitch QFN and flip-chip components with gap heights below 50 µm. The chemistry is an acidic aqueous system, and its wetting and defluxing performance is therefore governed by acid activity, surfactant load, and mass transfer at the solder-flux interface rather than by solvent solvency alone.

Release testing for the Electronic/EL Grade includes ion chromatography of neat product diluted 1:100 w/w in ultrapure water, with integration limits of 0.01 mg/kg for chloride, sulfate, nitrate, and bromide. Typical batch data show chloride at ≤1 mg/kg, sulfate at ≤5 mg/kg, and nitrate at ≤1 mg/kg, while transition metals are held to ≤0.5 mg/kg each as determined by inductively coupled plasma optical emission spectrometry according to ISO 11885:2007. The low cation burden matters because calcium, magnesium, zinc, and iron can form hygroscopic or electrochemically mobile residues that reduce surface insulation resistance under powered humidity testing. The product is filtered through a 0.2 µm rated cartridge during final filling, and non-volatile residue after evaporation at 105°C is controlled to ≤0.05% w/w. These limits are distinguishable from industrial descaler grades, where chloride and sulfate may be orders of magnitude higher and where filtration and cation control are not specified.

The cleaning mechanism on rosin residues involves protonation of abietic acid and dissolution of low-molecular-weight modified rosin esters. Under the acidic conditions of the working bath, this reaction proceeds rapidly at 45°C, but the rate is mass-transfer dependent; spray impingement creates turbulent boundary layers that remove dissolved residues before saturation at the board surface. In contrast, simple immersion in a stagnant bath yields slower cleaning and can deposit residues in low-energy regions of the board. Production-scale inline spray systems therefore rely on nozzle overlap and pressure rather than chemical concentration alone. Increasing concentration above 10% v/v is not recommended because the marginal improvement in rosin removal is small while the corrosion risk to exposed copper and tin increases. Below 3% v/v, acid activity is insufficient for thermally aged no-clean residues, and bath life shortens because the soil-loading capacity of the bath is depleted quickly.

The product’s low-foam profile is measured by a dynamic foam test under recirculation at 45°C, in which the liquid is circulated through a centrifugal pump for 5 min and the foam collapse time after pump stop is recorded. The Electronic/EL Grade is specified to collapse within 30 s at a concentration of 5% v/v. This property prevents false high-level alarms in spray sumps and permits ultrasonic cleaning without the acoustic losses associated with a persistent foam blanket. In inline systems, antifoam addition is not normally required, which is an operational advantage because silicone-based antifoams can deposit films that interfere with conformal coating adhesion. If foam persists due to soil loading, the bath is replaced rather than treated with antifoam, because the soil itself contributes surface-active flux constituents that neutralize the low-foam design.

What separates the Electronic/EL Grade from commodity acidic descalers, alkaline saponifiers, and solvent defluxers?

Commodity acidic descalers based on hydrochloric or sulfuric acid are proton-rich and can remove inorganic tarnish but are not formulated for printed circuit cleaning because their anionic load can exceed 100 mg/kg chloride and sulfate and because their surface tension remains near that of water, limiting penetration under low-standoff packages. Alkaline saponifiers are effective on polymerized rosin residues through ester hydrolysis, but their working pH of 10.5–12.0 requires a neutralizing rinse and gives a different residue signature in ion chromatography. Solvent blends such as isopropanol or modified alcohol mixtures offer rapid drying and low surface tension, but they may require explosion-proof handling and can swell acrylate and silicone conformal coatings. The BASF Electronic/EL Grade operates at a working pH of 2.0–3.0 and removes mildly activated no-clean flux residues without a neutralization step, while its aqueous non-flammable nature simplifies equipment design. The following table compares the cleaning regimes for typical printed circuit assembly defluxing.

In a five-stage inline defluxing machine with a 600 mm wide conveyor and flat-fan spray nozzles, the concentrate is delivered by a diaphragm metering pump into the wash sump at a controlled volume fraction of 3–6% v/v. The wash solution is held at 45°C ±2°C using titanium immersion heaters, and the manifold pressure is maintained at 2.0–3.0 bar. At conveyor speeds from 1.2 m/min to 2.4 m/min across a 900 mm sprayed zone, the wet contact time lies between 60 s and 180 s. This temperature window is critical. At bath temperatures below 40°C, acidic defluxing of thermally aged rosin slows materially, and the increased viscosity of the soil-loaded liquid reduces impingement and drainage. Above 55°C, copper dissolution from exposed edges and test pads accelerates, and some matte tin finishes can become visibly hazed after extended dwell. The bath is therefore controlled within a narrow ±2°C band. The low-foaming character prevents level-sensor drift and pump cavitation in high-velocity spray systems, and dissolved copper is tracked by atomic absorption or ICP-OES. Published data for this specific configuration is limited; the commonly used control limit for copper in bath management is 150 mg/L, above which replacement is initiated to avoid electrochemical interaction with exposed silver conductors and to maintain acid activity.

After the wash stage, the board passes through two counter-current deionized-water rinse stages and a heated air-knife drying section. Final rinse water is maintained at or above 18 MΩ·cm resistivity at 25°C and is monitored continuously by in-line conductivity cells; a final rinse conductivity above 0.5 µS/cm triggers automatic shutdown of the conveyor to prevent uncleaned or partially rinsed boards from leaving the line. Drying air is filtered to 0.01 µm particle retention and supplied at 85–100°C for conventional FR-4 assemblies. For assemblies with low-standoff components below 25 µm gap height, vacuum-assisted drying is specified because capillary retention of rinse water under packages can otherwise leave localized ionic residues that pass the bulk resistivity-of-solvent extract test but fail biased humidity testing.

When bare copper and wire-bondable gold pads demand controlled anion and cation residues after solder paste reflow

For wire-bonding and mixed-technology assemblies, post-cleaning ionic cleanliness is verified by ion chromatography in accordance with IPC-TM-650 2.3.28 and by resistivity of solvent extract in accordance with IPC-TM-650 2.3.25. Individual anion thresholds are often set at ≤0.01 µg/cm² for chloride, sulfate, and nitrate, with total anion content below 0.05 µg/cm². The Electronic/EL Grade is specified in these lines because controlled cation levels in the concentrate prevent calcium, magnesium, and zinc from being deposited during wash and rinse; cationic contamination is separately measured by ion chromatography after 1:100 dilution of the neat product or by ICP-OES. The process alarm for bulk ionic contamination is typically 1.0 µg/cm² NaCl equivalence, with high-reliability assemblies controlled to 0.75 µg/cm² or lower. The rinse water must be free of carbon dioxide breakthrough, because dissolved CO₂ can depress resistivity without indicating ionic contamination from the cleaner. On-line monitoring therefore combines resistivity, conductivity, and temperature compensation at 25°C. The final rinse station uses a polished DI water loop with 0.1 µm final filtration and a recirculation flow rate of at least 10 L/min per 100 L tank volume to prevent stagnant boundary layers on high-aspect-ratio boards.

Surface insulation resistance testing is performed after cleaning on test coupons coated with solder flux and processed through the same wash and rinse recipe. Typical acceptance is no measurable drop below 100 MΩ at 85°C and 85% RH with 50 VDC bias, in accordance with IPC-TM-650 2.6.3.7. The Electronic/EL Grade is qualified for the cleanliness requirement because its controlled anion background does not contribute measurable chloride or sulfate after rinse. However, the ion chromatography and SIR results are valid only if the final rinse water is itself free of ionic contamination; a DI water system with exhausted mixed-bed resin or a damaged reverse-osmosis membrane can introduce chloride and sulfate levels that exceed the cleaner’s own contribution by several orders of magnitude. For this reason, process validation includes a rinse-only blank coupon run to separate board contamination from cleaner contamination and water contamination.

The product is used in batch ultrasonic tanks from 40 kHz to 80 kHz, with ceramic transducers bonded to the tank bottom. In a 100 L tank, the bath is prepared at 5% v/v and held at 50°C ±2°C. Ultrasonic power density is initially limited to 20 W/L to prevent cavitation-induced erosion of thin gold flash on ENIG surfaces and to avoid lifting delicate bond wires. If white residue persists after the first cycle, the acoustic power is increased to a maximum of 35 W/L for a second pass. The cleaner’s low-foaming behavior is operationally significant in ultrasonic systems because a surfactant-rich foam layer attenuates cavitation and can cause transducer heating and uneven acoustic field distribution. After immersion cleaning, the boards are transferred through two cascading DI water rinses with overflow rates of 2.0 L/min and 1.0 L/min, respectively, until the second rinse conductivity remains below 0.5 µS/cm. This process is not recommended for assemblies with bare aluminium housings, zinc-plated fasteners, or silver-frit die attach, because the acidic working solution can corrode those materials.

Compared with BASF general-purpose metal-cleaning formulations, the PCB Special Cleaning Agent Electronic/EL Grade differs mainly in the control of non-volatile residue and the absence of silicate or phosphate builders. General-purpose acidic detergents may contain sodium metasilicate or phosphate corrosion inhibitors that leave hygroscopic films and are therefore undesirable on high-frequency substrates where surface conductivity shifts can alter impedance. The Electronic/EL Grade does not use silicate-based inhibition; instead, its corrosion moderation relies on a low concentration of a non-ionic wetting agent and tight control of the acid activity. This is why the working pH is not driven to the extreme low values seen in commodity acid descalers. The resulting copper etch rate on bare copper test coupons is specified below 0.1 µm/min at 45°C and 5% v/v, although published data for the exact product may be limited and the value should be confirmed on the target surface finish.

For assemblers using no-clean solder paste, a common application sequence is to apply the Electronic/EL Grade only when visual inspection or electrical test detects white residues from reflow. In such cases, the concentrated liquid is diluted to 5% v/v in a batch spray-under-immersion system and the boards are processed for 120 s at 45°C, followed by a 60 s DI-water spray rinse at 2.0 bar. This minimal exposure is intended to remove surface flux without attacking solder mask or organic solderability preservative coatings. On boards with OSP finishes, residue testing is mandatory after cleaning because the acidic liquid can strip a thin OSP layer and expose copper to subsequent oxidation if the rinse and dry steps are not tightly controlled. The product is therefore used on OSP-finished boards only when a final solderability re-test confirms that the finish remains intact or when the board is reflowed again immediately after cleaning.

Impurity profiling, analytical verification, and storage stability of the Electronic/EL Grade concentrate

The concentrate is stored in high-density polyethylene or fluorinated containers at 5–35°C. Storage below 0°C may produce partial crystallisation of inorganic components; the container is warmed to 25°C with gentle recirculation before use, and the product is rejected if any crystalline phase fails to redissolve. Analytical verification of the Electronic/EL Grade uses ion chromatography for chloride, sulfate, and nitrate with method detection limits of 0.01 mg/kg; lead and cadmium are determined by graphite furnace atomic absorption spectroscopy, and transition metals by ICP-OES according to ISO 11885:2007. The release limits are ≤1 mg/kg chloride, ≤5 mg/kg sulfate, ≤0.1 mg/kg lead, ≤0.05 mg/kg cadmium, and ≤0.5 mg/kg each for iron, zinc, copper, and calcium. The product remains stable for 12 months from the date of manufacture in the original sealed container at 25°C. Dilution water must meet or exceed 18 MΩ·cm resistivity; use of tap water or softened water introduces chloride, sulfate, and hardness ions that defeat the low-ionic-residue performance of the grade.

The formulation is not a universal cleaner. For thermally polymerized no-clean residues on high-thermal-mass assemblies, an upstream solvent pre-wipe or higher wash temperature may be required because diffusion of the acidic aqueous phase into crosslinked rosin networks is finite. When component standoff height is below 25 µm, the cleaner cannot be reliably dried by thermal convection alone, so vacuum-assisted drying is specified. The working solution must not be mixed with cationic surfactants or amine-based anti-corrosion additives, because acid-base neutralization reduces cleaning activity and may precipitate insoluble amine salts that redeposit on board surfaces. The product is also unsuitable for assemblies containing bare aluminium stiffeners, zinc-nickel electroplated fasteners, or silver-frit die-attach materials. New solder mask formulations must be qualified before use because some low-crosslink-density solder masks exhibit surface gloss changes after repeated immersion at 50°C for 10 min. The process should be validated for each board design using solder paste and surface finish combinations specified by the assembler, and the final cleaning recipe should be locked through ionic cleanliness testing under IPC-TM-650 2.3.25 and 2.3.28 before production release.