Cleaner production refers to continuously adopting measures such as improving design, using clean energy and raw materials, adopting advanced technology and equipment, improving management and comprehensive utilization, etc., to reduce pollution from the source, improve resource utilization rate, and reduce or avoid the generation and discharge of pollutants in the process of PCB production, service and product use, so as to reduce or eliminate its harm to human health and the environment.
This paper will briefly introduce the cleaner production measures of flexible printed circuit boards, which aim at cleaner production, comprehensive utilization of resources and reduction of environmental pollution.
Production process of FPC
At present, the production process of flexible circuit board mainly includes cutting, punching, black hole, copper plating, dry film sticking, exposure, development, etching, dry film drying, decontamination and cleaning, protective film sticking, lamination, pure tin, gold plating, silk screen printing, die cutting, electrical testing, reinforcing film sticking and functional testing. See the figure for the specific process flow:
Clean production process of FPC
1. Direct Metallization (DMS)
At present, the more advanced method is that instead of direct metallization (DMS) of chemical copper deposition, fine carbon powder is dip-coated on the hole wall to form a conductive layer. After micro-etching, the carbon group on the copper layer is removed, and only the conductive carbon film is left on the non-conductor (insulated epoxy resin substrate) inside the hole wall, and then directly electroplated. In the electroplating stage, a new type of fully enclosed equipment is adopted. Compared with the traditional electroplating bath, the amount of waste gas spilling to the outside is reduced by more than 95%, the amount of sewage discharge is reduced by about 1/3, and the concentration of pollutants in the waste liquid is low. At the same time, the noise pollution is greatly reduced because the equipment has a good sound insulation effect and a blower silencer is installed.
2. Pure tin electroplating method
Using pure tin electroplating instead of tin-lead electroplating can eliminate the pollution of heavy metal lead. If the thickness of the lead-tin plating layer on the circuit board is 10μm, the amount of lead in 1t waste liquid will reach 18 ~ 20kg. If the amount of tin-stripping waste liquid is 52.1t/a, the lead discharge can be reduced by 937.8 ~ 104 2.0kg/a.
3. Add water roller and air knife.
Between the ammonia-copper etching section and the water washing section, a water absorption roller and an air knife are arranged, so that the etching solution is fully utilized in the etching tank, and the amount of ammonia-copper brought by the discharged sewage can be reduced by 80% compared with the traditional method, thus reducing the difficulty and cost of wastewater treatment. Between the developing machine section and the washing section, there are water absorption rollers and air knives, which make the developer fully utilized in the developing tank and greatly reduce the amount of potassium carbonate brought out by the discharged sewage. The relevant exhaust positions are equipped with exhaust vents, which are directly connected with the exhaust pipeline when exhausting, and the exhaust gas enters the treatment facilities to avoid leakage. At the same time, the water from the last washing of the developing machine is reused in the etching section, which saves a lot of fresh water.
4. Fully enclosed equipment is adopted.
The oxidation section adopts fully closed equipment, and the emission of waste gas is more than 95% lower than that of traditional blackening tank. The front section of the system is equipped with a drying oven. Compared with the usual blackening line which is separated from the oven, the organic waste gas can be collected and treated better, thus reducing its spillage. The equipment has a good sound insulation effect, and the noise pollution can be greatly reduced by adding a blower silencer.
5. Replace the hanger.
Changing the rack and using tin-coated rack can prolong the slot changing frequency of nitric acid solution of rack from 2d/ time to 7d/ time, thus reducing the pollution discharge.
6. Use nitric acid instead of fluoroboric acid.
Using nitric acid instead of fluoroboric acid to remove tin can eliminate fluorine pollution.
7. Use CAD and photo-painting to make plate.
Adopting CAD and photo-drawing technology can improve the quality of the base plate and reduce the waste and pollution of the photographic base plate.
8. Adopt laser direct imaging technology.
Using laser direct imaging technology can save the process of photographic plate making, thus avoiding the waste and pollution of photographic negatives.
Cleaner production process control of FPC
It is a traditional habit of electroplating industry to wash the plated parts in regular flow, which wastes water resources and greatly increases the load of sewage treatment. The following improvement measures can be adopted:
(1) Automatic assembly line operation: the circuit board is input into each sealed electroplating bath by the unwinder, which reduces the water consumption and waste water production to a certain extent.
(2) Deionized water is used to prepare electroplating solution, which can reduce impurities from entering electroplating bath, prolong the service life of electroplating solution and reduce the amount of waste liquid.
(3) The electroplating solution (concentrated wastewater) carried out by the plated parts enters the recovery tank, and the plated parts are cleaned by deionized water in stages, so that the volatilization of the solution is reduced, the phenomena of running, bubbling, dripping and leakage caused by manual operation are prevented, the pollution is reduced, the loss of electroplating solution is reduced, and the smooth production is ensured.
(4) Deionized water is used to prepare and clean the solution, which avoids the impurity pollution in the solution, prolongs the service life of the electroplating solution, ensures the product quality and reduces the waste water treatment cost.
(5) The intermediate products and solvents in the production process are recycled in time, which greatly reduces the generation and discharge of pollutants.
energy-saving measures
1, countercurrent rinsing
The washing tank adopts a counter-current rinsing tank, that is, it passes through the interlayer with upper and lower falls on the middle second floor, and the water in the back channel flows counter-current to the water in the front channel, and the floating objects in the water are discharged along with the overflow port. The water consumption of two tanks is equivalent to that of one tank, thus saving water.
2. Intelligent spraying
When the workpiece is put into the tank, a signal will be given to the computer, and the electromagnetic valve will automatically open, and then spraying will begin; When the workpiece is removed, the spraying stops immediately, thus saving water.
3, purification tertiary treatment
At the flat mouth of the low-load surface with hot gas and waste gas tank edge, the plug-in suction hood and the whole suction at the tank edge are adopted. Through the three-stage treatment of absorption, purification and spraying of the combined waste gas purification tower, the main suction pipe is provided with a branch pipe, and the branch pipe is provided with a valve for controlling the air volume to control the air volume so as to reduce the energy consumption.
Cyanide-containing wastewater treatment
In the production process of flexible circuit board, some sections involve cyanide-containing gold plating process. Because the cyanide-free gold plating process is not mature at home and abroad at present, and because of the special requirements of products, cyanide-containing electroplating can only be used to make the gold plating layer evenly distributed and compact with high wear resistance. The micro-cyanide citric acid bath process was selected, and the toxic drugs such as potassium cyanide and sodium cyanide were replaced by gold potassium cyanide. Hydrogen cyanide was not produced in the bath, and the cyanide content was only about 0.5g/L. The treatment method of cyanide-containing wastewater is alkaline chlorination, that is, under alkaline conditions (pH= 8.5～ 11), liquid chlorine can oxidize cyanide into cyanate, making its toxicity only 0.1% of that of cyanide. If excessive oxidant is added, cyanate can be further oxidized into CO2 and N2, and the water quality can be further purified.
Because the micro-cyanide citric acid bath process is adopted, the cyanide content in the plating solution is very low, so the concentration of cyanide in the cyanide-containing wastewater is also low. After the pretreatment of oxidizing and breaking cyanide, the treatment efficiency of cyanide pollutants in the wastewater can reach more than 97%, which ensures the standard discharge.