Pay Attention to The Wastewater Treatment during PCB Fabrication Process

Why Pay Attention to Treat The Wastewater Produced by PCB Fabrication Process

PCB fabrication process is a very complex and highly integrated technology, during which a large amount of wastewater is produced. The wastewater has a complex composition, contains a variety of heavy metals ions, metal complexes, organic polymer compounds, and various organic additives. 
A large number of metal ions and complexes such as Cu2+, Ni2+, Ag+, Au+, Sn2+/Sn4+, and Pb+ in PCB wastewater are harmful to animals, plants and the environment. The wastewater produced by PCB fabrication process also contains plenty of organic substances, such as surfactants, inks, resists, organic dispersants, brighteners, degreasers and other high concentrations of organic compounds, as well as ammonia, cyanide, fluoride, phosphorus and other pollutants. These substances can affect the function of water bodies and destroy the ecology. For humans, they are the cause of various diseases. 

If the PCB wastewater is allowed to polluted, the consequences will be unimaginable.

China PCB fabrication industry value has accounted for more than 25% of the world's total output value, becoming the world's first PCB fabrication site, but the rapid development also has exacerbated the wastewater emissions during PCB fabrication process. 
For China PCB fabrication factories properly handling the wastewater generated by the PCB fabrication process is an important aspect to achieve sustainable development.

How The Wastewater is Produced? - Analysis Based on Single-sided PCB Fabrication Process

(1) Cutting and Drilling: Cut the single CCL into the required size as needed, and then drill on the copper foil according to the PCB Gerber data. 

• Copper foil scrap and dust are produced here.

(2) Cleaning: Before the PCB imaging, there will be a pre-treatment process, which is to clean the copper surface with a dilute sulfuric acid solution and polish it with machines, in order to remove oxides. 

• Organic wastewater and sulfuric acid mist gas get produced here.

(3) Exposure: Rolling the photosensitive dry film onto the copper foil substrate. Then the circuit pattern negative film is placed on the photosensitive dry film, the dry film forms a collective reaction when irradiated by ultraviolet light, and is exposed and developed under the irradiation of ultraviolet light, so that the dry film on the circuit pattern is hardened, and the designed pattern is transferred to the PCB.
(4) Development: Also known as pattern transfer. With a developing solution containing the sodium carbonate outside line is not hardened photosensitive dry film was removed, washed and dirt and countercurrent washing. 

• This process produces organic waste and wastewater.

(5) Etching: The copper surface not covered with the etching resist is completely etched away by an alkaline etching solution (ammonium chloride + ammonia water) etching solution, and only the copper lines protected by the hardened dry film are left. And carry out countercurrent washing. 

• This process produces acidic copper-containing waste liquid, copper-containing wastewater, and ammonia. 

(6) Fading: Dissolve the hardened dry film on the copper line with an aqueous solution containing sodium hydroxide or an organic solvent to expose the copper line and wash it with water. 

• This process produces organic wastewater and waste.

(7) Pressing or Stiffening: The PCB with circuit pattern and cover film with exposures are pressed together by a high-temperature vacuum press. The cover film acts as a permanent protective film on the PCB. 

• This process produces a resin decomposition gas. 

(8) Punching: Punch the holes used for fixing the nuts on circuit boards. 
(9) Residue Removing: The oil and organic matter on the circuit board are removed by a degreasing agent and dilute sulfuric acid, and washed by countercurrent washing, washing with water, and drying. 

• This process produces copper-containing wastewater, sulfuric acid mist. 

(10) Soldermask (Green): Its function is to prevent bridging during wave soldering, improve soldering quality and save solder. It is also a permanent protective layer for printed boards that protects against moisture, corrosion, mildew and mechanical abrasion. 

• Organic waste gas, weak acid waste liquid/gas, wastewater are produced.

(11) Screen Printing: Print the overlay.

• This process produces organic waste gas, waste ink. 

(12) Spray Tin (lead-free): Preheat, rosin and then tin. 

• This process produces organic gases.

(13) Shape Processing, then E-Testing.

• This process produces corner scraps.

(14) PCB Surface Finish: Cover the copper layer with nickel alloy for protecting the copper foil from oxidation and providing a solderable surface for PCB assembly.

• This process produces concentrated waste liquid and organic wastewater. 

(15) FQC, Packaging, and Shipment.

How to Deal with The Wastewater Produced by PCB Fabrication Process?

PCB wastewater treatment is mainly divided into the chemical method and physical method. Chemical method is to convert pollutants in wastewater into the easily separable physical state (solid or gaseous), including chemical precipitation method, redox method, ion exchange method, and electrolysis method. Etc., the physical method is to enrich the pollutants in the wastewater or separate them easily separated physical state from the wastewater, so that the wastewater can reach the discharge standard, mainly including decanting method, electrodialysis, reverse osmosis and the like.

1. Redox method

The redox method is to convert harmful substances into harmless substances by using an oxidizing agent or a reducing agent, and to precipitate and precipitate them, and the cyanide-containing wastewater and the chromium-containing wastewater in the circuit board are often subjected to a redox method.

2. Chemical precipitation

Chemical precipitation is the use of one or several chemicals to convert harmful substances into easily separated precipitates or precipitates. There are many kinds of chemical agents used for circuit board wastewater treatment, such as NaOH, CaO, Ca(OH)2, Na2S, etc. The precipitant can convert heavy metal ions into precipitates and then pass through an inclined plate sedimentation tank, sand filter, and filter press. Etc., to separate the solid and liquid.

3. Ion exchange method

Chemical precipitation treatment of high concentration wastewater is difficult, often combined with ion exchange. First, the chemical precipitation method is used to reduce the content of heavy metal ions to about 5 mg/L, and then the ion exchange method is used to reduce the heavy metal ions to the discharge standard.

4. Electrolysis

Electrolytic treatment of high-concentration circuit board wastewater can reduce the content of heavy metal ions, but the electrolysis method is effective only for the treatment of high-concentration heavy metal ions, and consumes a large amount of electricity, and can only process a single metal.

5. Gaseous condensation-electric filtration

This novel approach consists of three parts. The first part is an ionized gas generator. Air is drawn into the generator, which can change the chemical structure of the ionized magnetic field into highly activated magnetic oxygen ions and nitrogen ions. The gas is introduced into the wastewater by a jet device. Harmful substances such as metal ions and organic substances in the wastewater are oxidized and aggregated and are easily removed by filtration.
The second part is an electrolyte filter that filters out the agglomerates produced in the first part. The third part is a high-speed ultraviolet irradiation device. The ultraviolet light is injected into the water to oxidize organic matter and chemical complexing agent to reduce CODcr and BOD5.