—

As we all know, printed circuit board (PCB) cleaning technology plays a crucial role in PCB replication. Ensuring the cleanliness of the circuit board is essential for accurate scanning and generation of the document map, making PCB cleaning technology a significant technical activity. Wang Gaogong, an engineer at Jieduobang, has extensively reviewed current technologies and summarized four emerging methods of next-generation PCB cleaning technology.

1. Water Cleaning Technology for PCB Replication:

Water cleaning technology represents the future direction of cleaning methods. It requires the establishment of dedicated facilities for sourcing pure water and treating discharge water. This method employs water as the cleaning medium, enriched with surfactants, additives, corrosion inhibitors, chelating agents, and other components to formulate a range of water-based cleaning agents. These agents effectively remove aqueous solvents and non-polar contaminants. Key features of this cleaning process include:

– Safety: Non-flammable, non-explosive, and generally non-toxic.

– Versatility: The formulation of cleaning agents allows for effective removal of both polar and non-polar pollutants, ensuring a broad cleaning capability.

– Multiple Mechanisms: Water, being a polar solvent, dissolves contaminants and employs mechanisms such as saponification, emulsification, displacement, and dispersion. Ultrasonic cleaning in water is notably more effective than in organic solvents.

– Cost-Effectiveness: As a natural solvent, water is relatively inexpensive and widely applicable.

—

The disadvantages of water cleaning are:

1. In areas where water resources are scarce, this method consumes significant amounts of water, thus being restricted by local natural conditions.

2. Some components, especially metal parts, are prone to rust and cannot be effectively cleaned with water.

3. Due to its high surface tension, water cleaning struggles to reach and clean small gaps thoroughly, often leaving behind residual surfactants.

4. Drying after water cleaning is challenging and energy-intensive.

5. Water cleaning requires high equipment costs, necessitating wastewater treatment facilities and occupying large areas.

2. Semi-water cleaning technology for PCB replication:

Semi-aqueous cleaning primarily utilizes organic solvents, deionized water, and specific active agents and additives. This method bridges the gap between solvent and water cleaning. The organic solvents used are flammable but have high flash points and low toxicity, ensuring safety during use. Nevertheless, rinsing with water and subsequent drying are necessary. Some formulations incorporate 5% to 20% water and small amounts of surfactants to reduce flammability and facilitate rinsing. Key characteristics of semi-aqueous cleaning include:

1. Effective cleaning ability against both polar and non-polar contaminants, ensuring durable cleaning results.

2. Utilization of two different media for cleaning and rinsing, typically using pure water for the rinsing stage.

3. Drying process follows rinsing. However, the complexity of treating waste liquids and wastewater remains a challenge for this technology.

3. No-clean technology for PCB replication:

No-clean flux or solder paste is employed during the soldering process, eliminating the need for subsequent cleaning. This technology is increasingly popular, particularly in mobile communication products, as an alternative to traditional cleaning methods. Various types of no-clean fluxes exist, including:

1. Rosin-type fluxes, which use inert rosin solder (RMA) for reflow soldering, requiring no post-soldering cleaning.

2. Water-soluble fluxes that necessitate cleaning with water after soldering.

3. Low-solid-content fluxes that do not require cleaning post-soldering. No-clean technology offers several advantages, including streamlined process flows, reduced manufacturing costs, and minimized environmental impact.

The widespread adoption of no-clean soldering technology and fluxes has been a prominent trend in the electronics industry since the late 20th century, particularly as a means to replace CFCs.

4. Solvent cleaning technology for PCB replication:

Solvent cleaning relies on the solvent’s dissolving properties to remove contaminants efficiently. Solvent cleaning is favored for its rapid evaporation and strong dissolving capabilities, requiring relatively simple equipment setups. Depending on the solvent used, it can be categorized into flammable and non-flammable types:

– Flammable solvents include organic hydrocarbons and alcohols (e.g., glycol esters), while non-flammable solvents encompass chlorine-substituted hydrocarbons and fluorohydrocarbons (e.g., HCFCs and HFCs).

HCFCs are chlorine-containing fluorocarbons with low latent heat of evaporation, good volatility, and minimal ozone layer impact. However, due to environmental concerns, their use is restricted, with a phase-out mandated by 2040. Issues include high costs and limited cleaning efficacy. Other non-ODS solvents, such as dichloromethane and trichloroethane, are notable for their:

– Strong ability to clean oily residues,

– Suitability for steam cleaning and vapor phase drying,

– Non-flammability and safety in use,

– Reusability through distillation, enhancing economic viability.

However, chlorinated hydrocarbons pose challenges such as high toxicity, poor compatibility with plastics and rubber, and stability concerns necessitating stabilizer additives. Hydrocarbon solvents, derived from crude oil distillation (e.g., gasoline, kerosene), offer:

– Strong cleaning capabilities against oily residues,

– Reusability through distillation,

– Low toxicity and environmental impact.

However, safety considerations, particularly regarding flammability, require stringent precautions. Within the alcohol category, ethanol and isopropanol are commonly used for their:

– Effective dissolving capabilities against ionic pollutants,

– Compatibility with metals and plastics without corrosion or expansion,

– Rapid evaporation without requiring hot air,

– Dehydrating properties, often used as desiccants.

However, alcohol-based solvents are highly volatile, with low flash points necessitating explosion-proof measures for equipment and facilities used in PCB cleaning.