Preface
Printed circuit board manufacturing technology is a very complex and comprehensive processing technology. It can be divided into dry processing (design and cloth line, template making, drilling, film sticking, exposure and shape processing) and wet processing (inner layer board black film oxidation, removing grease and grease of, copper deposition, electroplating, development, etching, film stripping, silk screen printing, hot air leveling, etc.). Especially in the wet process process, a large amount of water is needed, so there are many kinds of heavy metal wastewater and organic wastewater discharged, the composition is complex and the treatment is difficult. If the utilization rate of copper foil in printed circuit board is 30% ~ 40%, the copper content in waste liquid and waste water is considerable. According to the calculation of 10000 square meters of double-sided plate (the thickness of copper foil on each side is 35 microns), the copper content in waste liquid and waste water is about 4500 kg, and there are many other heavy metals and precious metals. These metals in waste liquid and waste water are discharged without treatment, which not only causes waste but also pollutes the environment. Therefore, the treatment of wastewater and the recovery of copper and other metals in PCB production process are very meaningful, and they are indispensable parts in PCB production.
It is well known that a large amount of waste water in the production process of printed circuit board is copper, and a very small amount is lead, tin,gold, silver, fluorine, ammonia, organic compounds and organic complexes.
As for the process of producing copper wastewater, the main processes are: copper precipitation, full board copper plating, graphic copper plating, etching and various printing plate making pretreatment processes (chemical pretreatment, brush board pretreatment, pozzolan grinding pretreatment, etc.).
According to its composition, the copper containing wastewater produced by the above processes can be roughly divided into complex wastewater and non complex wastewater. In order to make the wastewater treatment meet the national discharge standard, the maximum allowable discharge concentration of copper and its compounds is 1mg / L (calculated according to copper), different wastewater treatment methods must be adopted for different copper containing wastewater.
2.Treatment of wastewater containing copper complex
2.1 source and composition of wastewater
2.1.1 chemical precipitation of copper:
The wastewater mainly contains complexing agents EDTA, sodium tartrate or other complexing agents and Cu2 +. Among them, Cu2 + forms a very stable complex with complexing agent, which cannot be treated by conventional neutralization precipitation method.
2.1.2 alkaline etching process:
The wastewater mainly contains Cu2 + and NH3 · H2O. When the content of NH4 + is high and under alkaline conditions, Cu2 + and NH4 +can form copper ammonia complex, which can not be treated by neutralization precipitation method.
2.1.3 micro etching (ammonium persulfate sulfuric acid) process:
The wastewater mainly contains Cu2 + and NH4 +. Under acidic condition, Cu2 + and NH4 + in wastewater can not form complex, but can form complex under alkaline condition.
2.1.4 Other processes:
For acid deoiling, alkaline degreasing, degumming, de drilling, swelling and other processes, the wastewater may contain complexing agents according to the chemicals used. Therefore, it can not be treated by general neutralization precipitation.
2.2 The main method of complex wastewater treatment at home and abroad
2.2.1 ion exchange method
Uses ion exchange method to treat complex heavy metals, which has many advantages: less land occupation, no need to classify wastewater treatment cost is relatively low. However, this method has many disadvantages, such as large investment, high requirements for resin and inconvenient control and management.the treatment process is as follows:
2.2.2 complex breaking treatment
is mainly to destroy the structure of complexing agent through strong oxidation to form non complex. In this way, the complex wastewater can be treated by general neutralization sedimentation after complex breaking treatment. The treatment process is as follows:
2.2.3 displacement treatment
uses the heavy metal complex to be unstable and dissociated under acidic conditions. Cu2 + is replaced by adding Ca2 + and Fe2 +, and then Cu2 + is precipitated by increasing pH value.
2.2.4 chemical precipitation method
uses chemicals that can form more stable precipitates with heavy metals than their complexes, such as Na2S, CAS and H2S, so as to achieve the purpose of removing heavy metals.
2.2.5 heavy metal collector precipitation method
uses polymer heavy metal collector, which can chelate with heavy metal ions strongly, and is not affected by the concentration of heavy metal ions, and can form precipitation with it to achieve the purpose of removing heavy metals.
3. non complex containing copperWastewater treatment method
3.1 the main source of wastewater
is rinsing water produced by whole plate electroplating, pattern electroplating, acid etching and other processes.
3.2 the main method to treat non complex wastewater
is chemical precipitation. When the waste liquid is alkaline, it becomes insoluble hydroxide precipitation, carbonate precipitation or sulfide precipitation. Generally, lime (calcium oxide) is added to the acid wastewater to make the wastewater alkaline and form hydrogen oxygen compound precipitation.
4 .A Brief Introduction of Comprehensive Treatment Technology of Printed Board Wastewater
The author of this article has been engaged in printed board materials, production, technology and quality management for more than ten years. He has accumulated certain experience in foreign printed board manufacturing companies, domestic printed board joint ventures, and currently engaged in state-owned printed board enterprises. Here are some tips on the treatment of printed board wastewater, as follows:
4.1 overall idea of PCB wastewater treatment
the quality of PCB wastewater treatment is directly related to the classification of PCB wastewater treatment. According to the author of this paper,should be considered comprehensively according to the source of wastewater, the size of copper content, the amount of waste water produced per unit time and whether it is worth treating. According to the above ideas, the author thinks that the printed circuit board waste water can be divided into the following types of wastewater and treated by different methods.
(1) copper containing complex wastewater;
(2) copper containing non complex wastewater;
(3) general copper containing rinsing water;
(4) acid-base wastewater containing other heavy metals;
(5) general acid-base wastewater without copper;
(6) alkaline etching wastewater with high copper content.
4.2 Treatment methods of the above sewage
(1) Treatment of wastewater containing copper complex：
(2) Treatment method of copper containing non complex wastewater:
(3) The treatment methods of general copper containing rinsing water are as follows:
(4) Treatment methods for acid-base wastewater containing other heavy metals:
(5) Treatment methods for general acid-base wastewater without copper:
(6) Treatment method for alkaline etching wastewater with high copper content:
For the etching waste liquid with high copper content (generally up to 130 ~ 150g / L), cooperate with relevant manufacturers and adopt various methods for outward transportation and treatment, instead of self-treatment. It's waste liquid for us, but raw material for other manufacturers. This not only saves the cost of sewage treatment, but also creates certain economic benefits.
4.3 Several measures to ensure the standard of sewage treatment
(1)Ensure that all copper containing wastewater is treated by sewage treatment station：
Some main production processes, such as electroless copper deposition, full plate plating and graphic plating, should be equipped with water collecting pan in the production site, so that the solution leakage caused by carelessness in the normal production process or during the maintenance of production line can be collected, so as to effectively avoid the running, emitting, dripping and leakage of electroplating solution, and ensure that the sewage treatment meets the standard.
(2)Ensure that different types of wastewater flow to the sewage treatment station through their respective pipelines：
Strictly distinguish different types of waste water, and according to the equipment layout of the production site, discharge pipes and mark them accordingly. In this way, even if the production process is changed, all kinds of waste water can be re introduced into the corresponding pipelines according to the composition of each medicine solution, so as to ensure that the sewage treatment reaches the standard.
(3) Strictly operate the process and prohibit dumping copper containing wastewater everywhere：
PCB manufacturers have different production conditions and processing processes. Due to the constraints of PCB processing equipment or production environment, some temporary measures are sometimes taken. For example, in order to avoid the oxidation of copper layer on the surface of printed circuit board, it is necessary to put it in the plastic tank containing dilute acid solution when the parts of printed circuit board are in turnover between working procedures; the different maintenance and cleaning operation of phosphor copper ball used for copper electroplating.
In this case, the process operation discipline must be strictly enforced, and the above copper containing wastewater should be poured into the corresponding treatment tank. It is forbidden to dump anywhere to ensure that the sewage treatment meets the standard.
(4) Continuously strengthen equipment progress to reduce unnecessary copper containing wastewater treatment capacity:
for example, the brush machine used in the pretreatment of printed circuit boards has not only a large amount of water, but also a high amount of copper powder. If it is included in the treatment, it is very uneconomical. In order to reduce the burden of sewage treatment and ensure the standard of sewage treatment, the equipment transformation should be strengthened, and the copper powder recycling machine should be used in the process to recover the waste water.
(5) continuously strengthen the process progress and reduce the treatment capacity of copper complex wastewater：
carry out process reform under the conditions of economy and supply conditions. For example, the ammonium persulfate used in the chemical pretreatment of printed circuit boards is replaced by sodium persulfate. Although the price of sodium persulfate is higher than that of ammonium persulfate, the treatment capacity of copper containing complex wastewater can be greatly reduced by using sodium persulfate, and the cost of wastewater treatment can be saved. It should be cost-effective. What's more important is that it can further ensure the standard of sewage treatment.
5. Conclusion
To sum up, the treatment of wastewater from printed circuit board production is more complex, and it is difficult to ensure that the wastewater treatment meets the standard. However, as long as the leaders at all levels pay attention to it, strengthen the publicity and education of environmental protection laws and decrees for employees, and improve the environmental protection awareness of the majority of employees, the environmental protection level of our country will certainly reach a new level. On the other hand, the manufacturers should increase the investment in wastewater treatment, transform the old equipment, and ensure the normal operation of wastewater treatment equipment. In addition, we should actively introduce new wastewater treatment technology, only in this way, can we truly ensure that the wastewater treatment standards, and create a pollution-free environment for us.
