JPH0513936A - Recoverying method for water from thin drain of cleaning water for printed substrate - Google Patents

Abstract

PURPOSE:To reproduce the processed water in a sterilized state at a reusable level for rinse shower in the title water recovery method from thin drain produced by the cleaning step of soldered printed substrate. CONSTITUTION:Within the title water recovery method from the thin drain containing respective removal steps such as the fine particle removing step using microfilms 2 and/or 9; the organic matter removing step using an active carbon adsorption tower 3; and the metallic ion content and organic acid content removing step using an ion-exchange resin towers 4 and 5 or a mixed bed tower 10, the other step ultraviolet sterilizing the processed water by said organic matter removing step and metallic ion content, organic acid content removing step using UV sterilizer 7 is further added to the title water recovery method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering water from diluted waste water for cleaning printed circuit boards, and more specifically, to a method for recovering water from diluted waste water produced by cleaning the printed circuit board with water using a soldering process using flux. It relates to a method of collecting water.

[0002]

2. Description of the Related Art Conventionally, a chlorofluorocarbon solvent (in particular, chlorofluorocarbon 113) has been widely used as a cleaning agent for washing off flux residue used in a soldering process of a printed circuit board in the electronic industry. However, the depletion of the ozone layer of CFC-based solvents has become a major environmental issue worldwide, and it has become certain that the use of CFC-based solvents will be regulated. Law concerning the protection of the ozone layer "). Regarding this environmental problem, various countermeasures are being investigated and examined, but there are various problems such as economic efficiency and long-term practical application. Development of flux and cleaning of printed circuit boards with water (mainly in the US),
Alkali saponification agents and the like as alternative cleaning agents for CFC-based solvents are being studied and implemented.

Here, the contents of the flux will be briefly described. As is well known, the action of flux is
(1) Soluble compound such as chloride, bromide, organic acid salt, amine complex salt, etc., which reacts with an oxide or the like existing on the surface of the solder or the base metal or generated during soldering And (2) at the soldering working temperature, to cover the surface of the soldered portion in a liquid state to create a non-oxidizing environment and prevent oxidation that hinders the flow and bonding of the solder.

Among various conventional fluxes, rosin flux is a non-corrosive resin flux. This includes dip-type solder flux (component: rosin, organic acid, organic amine, organic solvent, etc.), cream solder prepared by mixing flux and powdered solder (component: solder approximately 90%, rosin-based flux approximately 10%). A method of printing cream solder on the printed circuit board part on which the chip is placed and soldering it in a far infrared furnace). In this case, an alkali saponifying agent is used to wash off the flux residue from the soldered printed circuit board. In addition, rosin mainly plays the above-mentioned function (2).

Recently developed water-soluble fluxes include organic acid fluxes and water-soluble rosin fluxes.

When the soldering process is performed with the rosin flux, the rosin is a component that does not easily drop when the printed board is washed with an alkali saponifying agent to remove the flux residue. Therefore, the composition of the alkali saponifying agent contains, in addition to the organic amine, a large amount of alcohol as an organic solvent, a surfactant and the like, and is used for washing at a concentration of about 5 to 25% by weight.

In the above case, the printed circuit board is cleaned by first removing the flux residue with a cleaning agent shower using an alkali saponifying agent, and then roughly washing with a rinsing shower.
Subsequently, finish washing is performed with a rinse shower, and it has been attempted to treat the wastewater of this finish washing to make water that can be used again for the rinse shower.

Further, in the case of water-soluble flux, the same as the above except that the cleaning step in the above-mentioned cleaning agent shower is not necessary, and in this case also, the waste water of finish cleaning is treated and reused in the rinse shower. Is being attempted.

The basic constitution of the wastewater treatment / regeneration system used for such wastewater treatment is a fine particle removing process, an organic substance removing process, and an ionic substance removing process (separating into a metal ion content removing process and a halogen substance / organic acid removing process). In some cases, both components may be removed in one step.)
Consists of.

However, since the printed circuit board is washed at a relatively high temperature of about 40 ° C. to about 70 ° C., the treated water (substantially pure water) obtained through the above-mentioned steps is prone to bacterial growth and slime. It often happens. When such treated water is used again in the rinse shower, problems such as clogging of the shower nozzle and contamination of the printed circuit board and a reduction in the pass rate thereof occur.

[0011]

SUMMARY OF THE INVENTION In view of the above-mentioned drawbacks of the prior art, the present invention provides a method for recovering water from diluted wastewater for cleaning a printed circuit board, which provides sterilized treated water at a level that can be reused in a rinse shower. The purpose is to provide.

[0012]

In order to achieve the above object, the present invention provides a method for recovering water from dilute wastewater produced by cleaning a printed circuit board, the step of removing organic matter from the wastewater, and the removal of organic matter. A step of removing metal ions and organic acids from the treated water that has gone through the steps, and a step of sterilizing the treated water after the steps of removing metal ions and organic acids with ultraviolet rays, and further removing fine particles from the wastewater or any of the treated water. The present invention provides a method of recovering water from diluted wastewater for cleaning a printed circuit board, which includes the step of:

[0013]

[Function] When normal oxidizing bactericidal agents (for example, ozone, hydrogen peroxide, free chlorine, hypochlorite ion) are used for sterilizing waste water or treated water, the pure water obtained is reused for cleaning the printed circuit board. In use, the problem of corroding the metal parts of the printed circuit board is unavoidable. On the other hand, when the ultraviolet sterilization is performed according to the present invention, the above problem of corrosion can be avoided. It should be noted that the term "sterilization" used herein also includes the meaning that the organic matter remaining in the treated water that has undergone the organic matter removal step is oxidized by ultraviolet rays to sterilize and reduce COD (chemical oxygen consumption) sufficiently.

The present invention will be described in detail below.

The alkali saponifying agent used for cleaning the printed circuit board when rosin flux is used has a very high concentration in consideration of waste water treatment equipment. To give an example of the undiluted solution, TOC (total organic Carbon) About 480,000 mg / l
Before and after, BOD (biological oxygen demand) around 130000 mg / l, COD around 67,000 mg / l, pH 10 to 1
1.7, which is diluted with water about 4 times and used for actual cleaning.

This diluted alkaline saponification agent is supplied as a cleaning agent shower onto the soldered printed circuit board to remove flux residue, rinse the printed circuit board with a rinse shower, and then carry out a final wash with a rinse shower to produce this finish. Wash effluent is one of the effluents treated by the method of the present invention. Therefore, such wastewater contains contaminants derived from flux, contaminants derived from printed circuit boards, contaminants derived from alkali saponification agents, etc., and its water quality is about 15 ml / l of TOC, About 1 mg / l, conductivity about 40 μs / cm, metal about 5 mg / l,
The pH is around 9.

When the water-soluble flux is used, the printed circuit board is not washed with the cleaning agent shower as described above. Therefore, in this case, the drainage is a contaminant derived from the flux and a contaminant derived from the printed circuit board. Etc., but does not include contaminants derived from the cleaning agent.

From such drainage, first, for example, 10 μm
A micro filter with front and rear pore size
Rosin, solder balls, etc.) are removed. This step is not essential. For example, when relatively large particles are not included in the waste water, such as when using a water-soluble flux, omit it and only perform the relatively small particle removal step described later. There are cases where you can do it.

Next, the wastewater that has or has not passed through the fine particle removal step is passed through, for example, an activated carbon adsorption tower filled with activated carbon to remove organic substances (mainly nonionic organic substances such as organic solvents). Yes (TOC reduction).

Next, metal ions and organic acids are removed from the treated water from which organic substances have been removed. The metal ion component is the dissolved metal part of the printed circuit board.
Contains ions such as copper, zinc, tin, and aluminum. on the other hand,
Organic acid is derived from flux.

The removal of the metal ion component / organic acid component is carried out by, for example, passing the organic substance-removing treated water through an ion exchange resin tower having a mixed bed filled with a mixed resin composed of a cation exchange resin and an anion exchange resin, Both may be removed at the same time, passing through an ion exchange resin column having a cation exchange resin bed and an ion exchange resin column having an anion exchange resin bed,
Each may be removed. In the latter case, the order of both resin beds is arbitrary, and either resin bed may be passed through first. The organic acid component is usually adsorbed on the anion exchange resin, but if inorganic acid such as halogen acid is contained in the organic acid component removal treatment, it is simultaneously removed by the anion exchange resin.

The treated water from which the metal ions and organic acids have been removed is then subjected to ultraviolet sterilization. As previously mentioned,
An integrated system for cleaning printed circuit boards and recycling wastewater
8 to 1 per day at a water temperature of about 40 ° C to about 70 ° C
It is usually operated for 6 hours, and bacteria are often proliferated in the treated water, and the above-mentioned troubles are likely to occur. Therefore, sterilization is necessary.

The treated water after the above treatment is preferably passed through, for example, a microfilter having a pore size of about 3 μm to remove the remaining fine particles before being sent to the rinse shower nozzle. If not, it is necessary to remove fine particles at this stage.

A heat exchanger may be incorporated in the waste water treatment system as described above. For example, at least a part of the treated water that has undergone at least the metal ion / organic acid removal step is returned to the heat exchanger provided at least before the organic matter removal step, and exchanges heat with waste water. For example, the waste water having a temperature of about 60 ° C. and the treated water whose temperature has been lowered to about 45 ° C. due to heat dissipation through several steps are heat-exchanged to reduce the temperature of the waste water to about 50 ° C.
Lower it back and forth and send it to the next step. This is because (1) the activated carbon used in the organic matter removal step has a higher adsorption efficiency at lower temperatures, so it is better to lower the drainage temperature as much as possible. (2) Anion exchange resin used for organic acid removal It is possible to suppress the tendency for the exchange capacity to decrease over time by passing a liquid with a low temperature, and (3) increase the temperature of the treated water (pure water) reused for the rinse shower partially by the heat exchange. This is for the reason that energy saving can be achieved.

Next, the water quality analysis management of the treated water will be described.

In order to know the total amount of organic substances, COD measurement cannot measure those that cannot be decomposed by an oxidizing agent such as potassium permanganate, while TOC measurement measures the amount of carbon constituting the organic substances. Convenient for
In the case of the method of the present invention, TOC should be a measure of the cleanliness of the treated water. The TOC measurement may be performed using a combustion type TOC analyzer used for ordinary water quality analysis, but in the method of the present invention, a UV measuring device that is inexpensive, inexpensive to maintain, and easy to manage is used. It can also be carried out by the conventional UV analysis method. Normally, the UV analysis method is not used for measuring and managing TOC, but in the method of the present invention, the UV analysis method can be used for measuring and managing TOC because the amount of organic solvent in the waste water is large and the TOC and UV absorbance are large. It seems that the causal relationship of is high.

The TOC analyzer such as a UV measuring device may be placed at any position after the organic substance removing step, but it is preferably placed after the ultraviolet sterilization step. T in treated water
If the OC exceeds the upper limit of the target value, take measures such as replacing the activated carbon.

Management of ionic substances such as metal ions and organic acids in the treated water may be carried out by utilizing electric conductivity measurement. Although an ionic substance can be controlled with an inexpensive electric conductivity meter, in this case, since the measurement is performed at about 25 ° C, a cooling mechanism for the treated water is required. When the amount of these ionic substances in the treated water exceeds the upper limit of the target value, measures such as replacement of exchange resin are taken.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings, but the present invention is not limited to the embodiments.

Example 1 FIG. 1 is a flow chart showing an example of a preferred embodiment of the method of the present invention.

Waste water L1 of about 60 ° C. discharged from the printed board cleaning system 1 is stored in a waste water receiving tank R1 and is passed by a pump P1 through a valve V1 to a micro filter 2 having a pore diameter of about 10 μm. Fine particles are removed from the wastewater L1.

Next, the waste water from which the fine particles have been removed is passed through the activated carbon adsorption tower 3 to remove organic substances (this is performed after the waste water temperature has been lowered by heat exchange described later).

Next, the treated water leaving the activated carbon adsorption tower 3 is
It is passed through the cation exchange resin tower 4 to remove the metal ion content. Further, the treated water is passed through the anion exchange resin tower 5 to remove the organic acid content. Instead of providing these two exchange resin columns, one mixed bed column 10 (shown by a broken line) in which a cation exchange resin and an anion exchange resin are mixed and packed may be provided. In this case, the two-step process need be one-step process.

The treated water from which the metal ions and organic acids have been removed is stored in the treated water receiving tank R2. Since this treated water is cooled to about 45 ° C., it is returned to the heat exchanger 6 by the pump P2, and heat exchange is performed with the wastewater that has passed through the microfilter 2. Therefore, the wastewater entering the activated carbon adsorption tower 3 in the above description is cooled to about 50 ° C.

The treated water discharged from the heat exchanger 6 is sent to the UV sterilizer 7 and sterilized. As the UV sterilizer, a UV sterilizer that emits UV light having a wavelength corresponding to the range of UV-B and UV-C is preferable, and a UV sterilizer that emits UV light having a main wavelength of about 250 to 260 nm is particularly preferable. A running water type UV sterilizer is preferable in that continuous sterilization can be performed.
The externally illuminated running water type or the internally illuminated running water type may be used, but the internally illuminated running water type suitable for large-capacity treatment is preferable in terms of energy efficiency.

Next, the TOC of the substantially pure water obtained is analyzed by the UV automatic measuring device 8 and is sent to the microfilter 9 having a pore diameter of about 3 μm via the flowmeter F.

The microfilter 9 removes the remaining fine particles from the substantially pure water, and the pure water L2 obtained is sent to the rinse shower nozzle of the printed circuit board cleaning system and used again for the final cleaning of the printed circuit board.

FIG. 2 demonstrates that the TOC analysis can be sufficiently carried out in the case of the method of the present invention by the above-mentioned UV automatic measuring device 8.

That is, FIGS. 2 (a), 2 (b), 2 (c) and 2 (d) are UV absorption curves obtained under the same conditions (cell length: 50 mm), and FIG. TOC 2.5 mg /
Fig. 2 (b) shows TOC 5.0 mg / l when measuring 1 l of water.
2 (c) shows the case of measuring TOC 7.5 mg / l water, and FIG. 2 (d) shows the case of measuring TOC 15.0 mg / l water (these waters). The pollutants are almost the same as the pollutants in the water treated by the method of the present invention). It can be seen that there is a high correlation between the peak height of the ultraviolet wavelength of 254 nm and TOC, which is sufficient for the purpose of TOC control in the method of the present invention.

Although not shown in FIG. 1, a conductivity meter may be provided at some position after the metal ion / organic acid content removing step to control the ionic substance. For example, 5μ
When s / cm is set as the upper limit of the target value, when the electric conductivity exceeds this value, the ion exchange resin must be regenerated with a chemical solution, or if the ion exchange resin tower is a cartridge type, the ion exchange resin must be replaced. take.

The flow rate in the waste water treatment system is based on the measured value of the flow meter F and the like, and the valves V1, V
2, V3, V4 and other valves not shown are controlled and adjusted.

[0042]

The ultraviolet sterilization process is incorporated in the system for diluting the printed circuit board cleaning diluted wastewater by the method of the present invention, so that the treated pure water can be reused as a rinse shower in the printed circuit board cleaning system. Problems such as clogging of the shower nozzle and recontamination of the cleaned printed circuit board and a decrease in the acceptance rate can be eliminated. Further, unlike the case of using a normal oxidant type germicide, since ultraviolet rays are used, it is possible to avoid the problem that the metal portion of the printed circuit board is corroded.

Further, in the case of the method of the present invention, the detection and measurement of TOC in the treated water can be carried out by an ultraviolet analysis method using a UV measuring instrument which is inexpensive, low in maintenance cost and easy to manage. It has an advantage that the water quality can be controlled at low cost.

When a heat exchanger is incorporated in the system for diluting the printed circuit board cleaning diluted wastewater by the method of the present invention,
Activated carbon can be used in the organic substance removal step to use its adsorption efficiency at a high level, and anion exchange resin can be used in the organic acid removal step to suppress the tendency of the exchange capacity to decrease over time. Energy can be saved when pure water is used for the rinse shower.

[Brief description of drawings]

FIG. 1 is a flow chart showing an example of a preferred embodiment of the method of the present invention.

FIGS. 2 (a), (b), (c) and (d) are UV absorption curves of treated water of different TOCs obtained from diluted waste water for cleaning printed circuit boards (determined under the same conditions). It is a figure showing.

[Explanation of symbols]

1 Printed circuit board cleaning system 2 micro filters 3 Activated carbon adsorption tower 4 Cation exchange resin tower 5 Anion exchange resin tower 6 heat exchanger 7 UV sterilizer 8 UV automatic measuring instrument 9 Micro filter 10 mixed bed tower L1 drainage L2 pure water

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication C02F 1/42 G 7158-4D 9/00 Z 6647-4D // B01D 61/14 500 C02F 1 / 44 K 8014-4D (72) Inventor, Yoyo Yoshitani, 1-4-9 Kawagishi, Toda City, Saitama Prefecture Organo Research Institute

Claims (5)

[Claims] 1. A method of recovering water from dilute wastewater generated by cleaning a printed circuit board, a step of removing organic matter from the wastewater, a step of removing metal ions and organic acids from the treated water that has undergone the organic matter removing step, And water from diluted wastewater for cleaning printed circuit boards, characterized by including a step of sterilizing the treated water after the metal ion / organic acid removal step with ultraviolet rays, and a step of removing fine particles from the wastewater or any of the treated water. Recovery method. 2. The print according to claim 1, wherein the step of removing the metal ion / organic acid content is performed by passing the solution through a mixed bed composed of a mixed resin of a cation exchange resin and an anion exchange resin. Substrate cleaning Method for recovering water from dilute wastewater. 3. The diluted wastewater from printed circuit board cleaning according to claim 1, wherein the step of removing the metal ion / organic acid content is performed by passing the solution through a cation exchange resin bed and an anion exchange resin bed. Water recovery method. 4. The water quality control of the recovered water is carried out by detecting and measuring the total organic matter content of the treated water that has undergone at least the organic matter removing step by an ultraviolet analysis method. 5. A method for recovering water from diluted wastewater for cleaning printed circuit boards according to any one of 1. 5. The organic water removing step is performed by returning the treated water that has undergone at least the metal ion / organic acid removing step to at least a heat exchanger provided before the organic material removing step and performing heat exchange with waste water. The method for recovering water from diluted wastewater for cleaning printed circuit boards according to claim 1, wherein the temperature of the wastewater entering is lowered.