PCB Tech - PCB high concentration organic waste disposal

Looking at the current environmental protection situation, it is imperative to recycle waste water from PCB production, and the government oversees the up-to-standard discharge of recycled residual water and waste water with no recycling value. Combined with the current national environmental protection administrative agency's outstanding attention to COD in total control projects. This article mainly deals with the recycling and treatment of high-concentration organic waste liquid from circuit boards.

Disposal status of high-concentration organic waste liquid

There is no authoritative pollutant survey statistics for the high-concentration organic waste liquid (non-cleaning water) produced by PCB production. The following table shows the survey results of overseas environmental protection companies on the pollutant emissions of PCB companies.

Mixed collection, acidification destabilization, solid-liquid separation. After the CODcr of the clear liquid is reduced to 10-20% of the original waste liquid, chemical treatment is used in conjunction with the rinsing wastewater of each process. The chemical treatment process will also absorb part of it due to coagulation. The total drainage CODcr fluctuates up and down at the 110mg/L compliance line, and the fluctuation range varies with the treatment process, the amount of dilution water and the specific operation.

Most of the fluffy waste liquid, degreasing waste liquid, copper sinking waste liquid, and OSP waste liquid are entrusted for disposal, and there may also be individual cases of co-processing and discharge with wastewater.

Organic pollutants in high-concentration organic waste liquid

Development and unwinding waste liquid

The main organic pollutants of the developing and removing film waste liquid are photosensitive coatings, and the main component of the photosensitive coatings is photosensitive resin. The photosensitive resin undergoes a photocrosslinking or entanglement reaction after UV exposure, and the solubility of the reaction product is significantly different from that of the unreacted substance. Photosensitive coatings are divided into two categories: positive image type and negative image type. The commodity supply state includes photosensitive dry film and water-based paint. Its uses are divided into anti-etching and anti-electroplating. The developing operation is divided into solvent-based and water-based. Two kinds. At present, in the production of PCBs, especially multilayer PCBs, negative image, water-developing dry film or wet film are mostly used. Representative products are mostly acrylic unsaturated polyester, acrylic polyether, acrylic epoxy, acrylic polyurethane, etc.

The photosensitive film partially dissolved, swollen, stripped, and broken into the developing or de-filming waste liquid is the main organic pollutant in the developing and de-filming waste liquid. The COD of the part that can be acidified, destabilized and separated accounts for about 80 ~ of the total COD of the mixed waste liquid. 90%, so the acidification destabilization separation operation in the environmental protection treatment of the development and film removal waste liquid is necessary.

The development and stripping waste liquid discharged from PCB production is a suspended liquid. This suspension will deposit suspended solids in the corners of the rectangular section of the working liquid tank. This deposit needs to be removed before the development and stripping working solution is updated. The industry currently uses the so-called tank washing water for this operation. The tank washing water is generally 2 to 5% hydrochloric acid or 5 to 10% EDTA tetrasodium salt. The waste liquid of film removal is discarded together. If the washing tank water is the latter or a mixture of the two, EDTA is undoubtedly an organic pollutant in high-concentration organic waste liquid.

Fluffy waste

The pre-treatment process of the hole metallization operation in PCB production includes the fluffing treatment. The object of fluffing treatment is the hole wall part of the film material such as the epoxy glass substrate of the rigid board or the polyimide of the flexible board. The essence of this operation is For the slight swelling process of cured epoxy resin or polyimide, the data reported that the medium used is alkaline alcohol ether or amide organic solvent. The working medium for fluffy treatment needs to be discarded and replaced regularly. The CODcr of the waste fluffy treatment medium is as high as 200g/L. It should be collected separately and commissioned for disposal. Do not mix into the high-concentration organic waste liquid system.

Copper sinking waste

The copper sinking working solution for the hole metallization process of PCB production also has the problem of discarding and updating. The Cu2+ in this waste mother liquor is about 1.4～4.5g/L, CODcr is about 30～100g/L, and COD comes from the autocatalytic system. The complexing ligand-EDTA and reducing agent-formaldehyde. At present, most of the sewage treatment processes dilute it with complexed wastewater and then co-process it. There is basically no technical difficulty in meeting the copper standard, but the COD meeting the standard depends on the process arrangement.

Degreasing waste liquid

There are many degreasing operations in the PCB production process with water. The degreasing agents are divided into two types: alkaline and acidic. The CODcr of the waste working solution is about 3000-5000mg/L. In addition, the whole hole waste liquid, which is generally regarded as an oil removal working solution, contains a small amount of organic solvents in addition to surfactants, and the CODcr of the waste liquid is about 100,000 to 150,000 mg/L. It can be seen that after most of the original dilution water is collected and reused, the disposal of the degreasing waste liquid also needs to find a new way out.

OSP waste

The PCB production process is equipped with an anti-oxidation treatment unit. The anti-oxidation treatment solution contains imidazole organics and corresponding solvents, and the waste solution may also contain copper complexes. It can be seen that the waste liquid should also be identified and properly disposed of organic pollutants and copper pollutants.

At present, the design goal of most of the sewage treatment plants of printed circuit enterprises is to meet the copper standard. The COD in the sewage of enterprises with double-sided panels as the main product depends on the dilution effect. After the implementation of sewage resource requirements, 60-65% of the workshop's drainage becomes recycled water and returns to the workshop. This creates a situation where the water entering the sewage treatment system is only 35-40% of the original design water volume, and the total amount of pollutants entering the sewage treatment system is basically unchanged. In the new situation, the metal pollutants in the sewage can still be separated and purified according to the principle of solubility product, but it is impossible to achieve the COD standard that is diluted by the amount of water.