How to remove PCB welded residues

 The welded residue on the PCB is mainly salt substances that are not completely volatile or reaction to the solder reactions during the welding process. These residues may have adverse effects on the performance and service life of PCB, so they need to be removed in time.

Common welded residues include residues of rosin welds and residues of organic acid welds. The residue of the rosin welded is mainly composed of polymer pine fragrance, undesirable activation agent, and salt generated between the rosin and melting welded welded during welding. These substances swell after the moisture absorption, and some substances also respond to water with water. The residues of organic acid welds are mainly composed of a variety of organic acids, and also contain some compounds that can produce halogen ions at high temperatures. This type of residue is the most difficult to remove salt formed by organic acids and solder formation. They have strong adsorption properties and poor solubility.

In order to remove the residue on the PCB, the method of cleaning agent, alcohol, hot air gun, ultrasonic cleaning machine or professional welder removal can be used. During the processing process, be careful not to damage the PCB surface and components, and keep it safe to avoid contact with harmful chemicals.

Solvent Cleaning Agents Used

Solvent cleaning refers to using organic chemical solutions to dissolve then rinse away flux residues. Some typcal solvents include:

Isopropyl alcohol (IPA) – Rapidly evaporates with wide materials compatibility

Acetone – Stronger solvency but more aggressive requiring dilution

Terpenes – Plant derived citrus cleaners with reduced environmental impact

Solvent cleaning can be performed by manual wiping, immersion tanks, inline conveyors and ultrasonic or pressure spray systems with vacuum drying.

Some benefits of solvent cleaning include:

Removes diverse flux chemistries like rosin mildly, no-clean, water soluble types

Penetrates tight gaps under components to access hidden residues

Quickly dissolves both ionic and non-ionic contamination

Enables isolated spot cleaning of small areas when needed

Wide availability of chemical compatibility data to guide material selections

However, solvents also pose flammability, waste disposal and regulatory emission control challenges. This motivates aqueous process alternatives.

Aqueous Flux Residue Cleaning Processes

Water-based cleaning relies on ionized water’s natural solvency power combined with detergents at elevated temperatures and impingement pressures to reliably remove residues.

Some common aqueous cleaning systems include:

Immersion washers – Features multiple staged baths for gross soil removal down to rinses

Inline washers – Continuous conveyors passing boards through spray detergent zones + rinses

Ultrasonic systems – Energized baths generating focused cavitation shockwaves hitting board surfaces

Pressure spray washers – Direct high impingement jets + mechanical scrubbing on boards

Condensation washers – Controlled condensing humidity enclosures to lift residues

Water cleaning is attractive because it avoids hazardous chemical disposal requirements and utilizes lower cost aqueous detergents. Thermal energy efficiently substitutes harsh solvents.

Key benefits of aqueous cleaning encompass:

Eco/worker friendly with simpler waste water treatment

Readily accessible and plentiful water media

Heated spray and ultrasonics provide excellent cleaning power

Programmable automation adaptable for high volume applications

Reliable reproducibility following validated cycles

On the downside, aqueous processes lack penetration into tight spaces. Water sensitivity limits components exposure allowances too. Despite such constraints, appropriate water-based cleaning systems prove highly effective for suitable PCB assembly applications when engineered properly.

Now that we distinguished solvent versus water-based options, let’s elaborate best practice process considerations to deploy either approach effectively.

Optimizing Process Parameters for Flux Removal Efficiency

Successfully removing flux residues depends greatly on selecting optimal equipment settings and following disciplined operating protocols tailored to your boards.

Here are some key process parameters to optimize:

Cleaning Media – Match solvent or water-based detergent chemistry to flux type and processing goals. Start with manufacturers recommended formulations.

Concentration – For aqueous cleaners, calibrate detergent % dilution carefully for target soils. Excessive concentrations waste chemicals whereas low concentrations risk cleaning shortfalls.

Exposure Time – Ensure adequate dwell time for cleaning agents to penetrate, solubilize and detach all residues present. Complex boards need longer durations.

Temperature – Heated media between 50-80°C boosts cleaning dynamics substantially compared to room temperatures for dried residues. But don’t overheat beyond chemical or component limits.

Flow Rate (solvent) – Adjust solvent spray flow to flood boards without excessive impingement pressure causing component blow-off defects.

Impingement Pressure (aqueous) – Steam and spray jets help blast off hardened residues mechanically when delicately optimized in psi/bar units without deforming boards.

Frequency – Replenish baths regularly based on accumulated soil loading quantified in microSiemens to maintain cleaning efficiency as contaminants saturate solutions.

Careful process testing starting from baseline presets then gradually adjusting within equipment safe ranges determines optimums empirically case-by-case based on cleaner qualifications.

Next we’ll highlight some practical challenges working with either cleaning technique.