CN116446029A - A method and device for removing tin from PCB in one step and recovering tin at the same time - Google Patents

Abstract

The invention discloses a method and a device for recovering tin while removing tin from PCB in one step. The etched circuit board is passed through an acidic system solution in an electrolytic reaction device for continuous tin removal, and is carried out under the conditions of external field coupling strengthening and pulse electric field simultaneous action. Electrolytic tin stripping and tin recovery; as the reaction progresses, the tin coating on the circuit board is completely dissolved into the solution, and the tin ions in the solution are deposited and precipitated at the cathode to obtain high-quality cathode tin. While effectively shortening the tin stripping time and efficiently recovering tin, the present invention effectively solves the problem that the current nitric acid tin stripping system has a large output of ammonia nitrogen wastewater and is difficult to utilize as resources, and has the advantages of cleanliness, high efficiency and strong selectivity. The device of the present invention is simple and practical, and can achieve better tin stripping and recovery effects when used as a set.

Description

A method and device for removing tin from PCB in one step and recovering tin at the same time

technical field

The invention specifically relates to a method and a device for removing tin from a PCB in one step and recovering tin at the same time, and belongs to the field of nonferrous metal metallurgy.

Background technique

Printed circuit board (PCB) is the support of electronic components. Its main function is to connect various types of electronic components to form specific circuits. It is the key electronic interconnection of electronic products. Any electronic product or equipment needs to use printed circuit boards. To equip. Printed circuit boards are of great significance to the development of the times, and its downstream industries have covered all consumer electronics products, including information, communications, medical care, and even aerospace technology products. Printed circuit boards are inseparable from each other.

The production of PCB includes more than 20 processes such as cutting, drilling, grinding, copper sinking, electroplating, pattern transfer, copper plating, stripping, and etching. Lines and other conditions lead to scrapping, the tin plating process is essential, and the tin plating layer is removed after the graphic production is completed. At present, most domestic PCB manufacturers use nitric acid or nitric acid-alkylsulfonic acid type tin stripping water for tin stripping.

However, due to the instability and poor selectivity of nitric acid itself, the properties of the tin stripping water will change greatly after repeated tin stripping. The tin stripping water not only contains higher concentrations of tin ions (100-150g /L), also contains a certain concentration of copper ions and iron ions (20 ~ 30g/L), in addition, heterocyclic compounds, polycyclic aromatic compounds and other polymers will gradually accumulate because they cannot be opened. At this time, the tin stripping solution can no longer effectively dissolve the tin coating on the PCB, and needs to be replaced with an open circuit. The decommissioned tin stripping solution not only contains a large amount of valuable metals, but also contains a relatively high concentration of nitric acid and other organic components, which is a hazardous waste. If it is not treated effectively, it will not only cause a lot of waste of resources, but also bring a huge potential risk of environmental pollution. So far, the treatment methods of waste tin stripping water mainly include: precipitation method, distillation method, electrolysis method and so on.

Generally speaking, there are still two major problems in the tin stripping water of the current nitric acid or nitric acid-alkylsulfonic acid system in the tin stripping process and the treatment of the tin stripping waste liquid: (1) the tin stripping process mainly uses nitric acid to dissolve tin and copper. Mainly, there are problems of heavy NOx gas pollution, large amount of sludge and residual acid, and high cost; (2) the process of treating tin stripping water with precipitation, electrolysis, and distillation has large reagent consumption, low metal recovery, Serious problems such as large amount of waste water.

In order to solve the above problems, the applicant has developed "a tin stripping water based on hydrochloric acid-tin salt system and a method for removing tin from waste tin stripping water (application number 201410011267.0)" and provided a system based on hydrochloric acid-tin salt The non-nitric acid type tin stripping water, and the method of recovering tin from such waste tin stripping water after stripping tin and regenerating the tin stripping water at the same time, although the small-scale test results show that the use of this tin stripping water can effectively remove the tin on the tinplate Retire. However, in the subsequent application of this method to the industrial practice of stripping tin from printed circuit boards and recycling tin, they encountered slow tin stripping speed (more than 10 minutes), severe corrosion of PCB copper substrates, and "tin crystals" when tin was extracted by diaphragm electrodeposition. Muster phenomenon, low electrowinning efficiency and other serious problems. The reason is that, compared with the current nitric acid or nitric acid-alkyl sulfonic acid system tin stripping water, the tin stripping water of the hydrochloric acid-tin salt system has relatively weak oxidation performance and weaker solubility for tin plating on PCBs. The speed is also slower. If you want to use this tin stripping water to remove more tin on the PCB, you must prolong the tin stripping time. However, because the corrosion of ^Cl- in the tin stripping water of the hydrochloric acid-tin salt system belongs to "pitting corrosion", it tends to be on the PCB Many small holes distributed in dots are formed on the board, resulting in very uneven surface of the copper substrate after tin stripping, which affects the subsequent electronic processing performance of the PCB.

In order to effectively improve the speed of tin stripping, the applicant has also developed "a two-stage method for stripping tin from PCB boards (application number 201811126057.0)", which provides a system based on hydrochloric acid-tin salt in the first stage and nitric acid in the second stage -The compound two-stage tin stripping water with nitrate system further efficiently recovers tin on-line and effectively reduces the discharge of ammonia nitrogen wastewater during the treatment of waste tin stripping water. However, outstanding environmental problems such as NOx gas pollution, sludge and residual acid cannot be completely resolved.

Contents of the invention

Aiming at the problems and deficiencies in the above-mentioned prior art, the technical problem to be solved by the present invention is: to provide a method for recovering tin while removing tin from PCB in one step. The method provided by the present invention can effectively shorten the time for stripping tin and improve the efficiency of stripping tin At the same time, the tin in the solution can be recovered. In addition, it can also effectively avoid the discharge of ammonia nitrogen wastewater during the treatment of waste tin stripping water. Realize the purpose of clean and efficient production of PCB tin stripping.

Another object of the present invention is to provide a simple and practical device that is compatible with the above-mentioned method for one-step stripping of PCB and simultaneously recovering tin, and can comprehensively obtain better effects of stripping tin and recovering tin.

In order to achieve the above object, the present invention adopts the following technical solutions:

A method for removing tin from PCB in one step and recovering tin at the same time. The etched circuit board is passed through an acidic system solution in an electrolytic reaction device for continuous tin removal, and electrolytic tin removal and tin recovery are carried out under the condition of external field coupling strengthening and the simultaneous action of an electric field; As the reaction proceeds, the tin coating on the circuit board dissolves into the solution, and the tin ions in the solution are deposited and precipitated at the cathode.

The acidic system solution is a solution consisting of a single acid or a mixed acid selected from sulfuric acid, methanesulfonic acid, hydrochloric acid, and a tin stripping accelerator, a tin stripping corrosion inhibitor, an electrolytic stabilizer, and a solution dispersant, preferably sulfuric acid or methyl sulfonic acid.

The tin stripping accelerator is one of tetraethylammonium bromide, sodium methanesulfonate, tartaric acid, sodium citrate, sulfosalicylic acid; the tin stripping corrosion inhibitor is benzotriazole, One of tolyl benzotriazole, sebacic acid or sodium benzoate; the electrolytic stabilizer is one of animal bone glue, cresol sulfonic acid, phenol sulfonic acid, β-naphthol; the solution dispersant is One of ethylene oxide, polyethylene glycol, alkylphenol polyoxyethylene ether, the preferred tin stripping accelerator is sodium methanesulfonate, the preferred tin stripping corrosion inhibitor is benzotriazole, preferably The preferred electrolytic stabilizer is animal bone glue, and the preferred solution dispersant is ethylene oxide.

The acidity of the acidic system is 1mol/L-5mol/L; the concentration of the tin-removing accelerator is 0.1-5g/L; the concentration of the tin-removing corrosion inhibitor is 0.01-2g/L; the concentration of the electrolytic stabilizer is 0.05-20g/L; The concentration of the solution dispersant is 0.01-5g/L, the preferred acidity is 2-4mol/L, the preferred concentration of the tin-removing accelerator is 0.5-3mol/L, and the preferred concentration of the tin-removing corrosion inhibitor is 0.5-1mol/L, The preferred concentration of the solution dispersant is 0.05-3 mol/L.

The external field coupling strengthening condition is ultrasonic coupling strengthening, the ultrasonic frequency is 20-500kHz, the ultrasonic power is 10-200W, the preferred ultrasonic frequency is 40kHz, and the preferred ultrasonic power is 100W.

The electrolytic tin stripping electric field is a pulse electric field, the pulse frequency of the pulse electric field is 50-2000 Hz, the duty ratio is 50%-90%, the average current density of the electrolytic initial pulse is 10-500A/m ² , and the preferred pulse frequency is 100 ~500 Hz, the preferred duty cycle is 70-80%, and the preferred average current density is 50-150 A/m ² .

The time for the etched circuit board to pass through the continuous tin stripping electrolytic reaction device is 15s-120s, and the preferred reaction time is 45-90s.

A device for removing tin from PCB in one step and recovering tin at the same time, comprising a tin removal tank, a liftable anode tank, an anode guide rod, a cathode guide rod, a graphite anode, a transmission device, an ultrasonic generator, a cathode sheet and a pulse power supply; The bottom of the tin bath is provided with a groove for placing the cathode and solution inlet/outlet; one end of the anode guide rod is connected to the graphite anode, the other end is connected to the positive electrode of the pulse power supply through a wire, one end of the cathode guide rod is connected to the cathode sheet, and the other end is connected to the graphite anode through a wire. The negative pole of the pulse power supply is connected.

In the device, the material of the cathode guide rod and the anode guide rod is stainless steel.

In the said device, the cathode piece is made of stainless steel, titanium plate or refined copper.

Principles and advantages

The method and equipment of the present invention replace the addition of the oxidant in the original tin stripping system by introducing a pulsed electric field. When the anode contacts the PCB coating, a closed circuit is formed, and an oxidation reaction occurs on the coating surface so that tin enters the solution in the form of tin ions. (such as formula 1), the reduction reaction on the surface of the cathode causes tin ions to precipitate at the cathode in the form of metal tin (such as formula 2), and more unexpectedly, after adding the ultrasonic coupling external field, the energy brought by the ultrasonic further accelerates the tin ions When the coating is dissolved, the concentration polarization in the solution is reduced, and the distribution of tin ions in the solution is more uniform, especially the concentration polarization of each ion near the cathode sheet is significantly reduced, so that tin can be deposited in a more flat form on the on the cathode sheet. In addition, the pulse current used in the present invention dissolves the PCB tin coating, and there is no oxidizing substance in the solution itself. When controlled under specific current and voltage conditions, it can dissolve the tin while avoiding the dissolution of copper on the PCB, and can selectively Dissolve tin to achieve efficient and selective separation of tin on PCB.

Sn-2e=Sn ²⁺ (1)

Sn ²⁺ +2e＝Sn (2)

Compared with the current nitric acid or nitric acid-alkane sulfonic acid system, the present invention avoids the use of nitric acid as a solution and an oxidant, effectively avoids environmental problems such as heavy NOx gas pollution, large amount of sludge and residual acid, and high cost. The process problems of large reagent consumption, low metal recovery rate and large amount of waste water in the process of treating tin stripping water are reduced, and tin stripping and tin recovery are realized in one step. The invention has great significance for promoting the technological progress of PCB production in my country, saving energy and reducing consumption, and protecting the environment.

Description of drawings

Fig. 1 is a schematic diagram of a device for removing tin in one step and recovering tin simultaneously in the present invention.

In the figure 1-anode guide rod, 2-graphite anode, 3-liftable anode tank, 4-PCB transmission device, 5-ultrasonic generator, 6-solution inlet/outlet, 7-cathode sheet, 8-cathode guide rod, 9-Sn stripping solution, 10-Pulse power supply.

specific implementation plan

The following examples are intended to further illustrate the present invention, but not to limit the present invention.

The device for removing tin in one step and reclaiming tin simultaneously in the present invention includes a tin removing tank, a liftable anode tank, an anode guide rod, a cathode guide rod, a graphite anode, a transmission device, an ultrasonic generator, a cathode sheet and a pulse power supply; The bottom of the tank is provided with a groove for placing the cathode and solution inlet/outlet; one end of the anode guide rod is connected to the graphite anode, the other end is connected to the positive electrode of the pulse power supply through a wire, one end of the cathode guide rod is connected to the cathode sheet, and the other end is connected to the pulse power supply through a wire. The negative pole of the power supply is connected; the cathode material is a titanium plate.

Example 1

For a tinned PCB provided by a company, the surface of the PCB is tinned with 30g per square meter.

Configure sulfuric acid solution in the one-step tin removal and recovery tin device, the mixed solution sulfuric acid acidity is 1.5mol/L, sodium methanesulfonate 0.5g/L, benzotriazole 0.2g/L, animal bone glue 0.1g/L, Polyethylene glycol 0.1g/L, react under the condition that the ultrasonic frequency is 100kHz, the ultrasonic frequency is 100W, the pulse frequency is 200Hz, the duty cycle is 70%, and the pulse average current density is 100A/ ^m2 , and the conveyor belt speed is adjusted After the PCB is stripped in the solution for 60s, a PCB with a flat and smooth surface is obtained. Observation by an optical microscope shows that the surface of the stripped tin plate obtained has no tin coating, and the surface of the substrate is flat and smooth. The PCB after stripping tin was analyzed by chemical analysis method, and it was found that the tin content on the surface of the PCB after stripping tin was zero. After the continuous stripping test, the cathode obtained the tin element with a current efficiency of 90.51%. After taking out the cathode plate for observation, it was found that the surface of the cathode obtained was flat and smooth. The obtained cathode was analyzed by chemical analysis and found to contain 99.99% tin.

Example 2

For a tinned PCB provided by a company, the surface of the PCB is tinned with 32g per square meter.

Configure sulfuric acid solution in a one-step tin removal and tin recovery device. The acidity of the mixed solution is 2mol/L methanesulfonic acid, 0.5g/L tartaric acid, 0.2g/L tolylbenzotriazole, and 10g/L cresolsulfonic acid. , Ethylene oxide 0.1g/L, react under the conditions of ultrasonic frequency of 200kHz, ultrasonic frequency of 200W, pulse frequency of 500Hz, duty cycle of 75%, pulse average current density of 50A/ ^m2 , and adjust the conveyor belt After the PCB is stripped at a rate of 40s in the solution, a PCB with a flat and smooth surface is obtained. Observation by an optical microscope shows that the surface of the stripped tin plate obtained has no tin coating, and the surface of the substrate is flat and smooth. The PCB after stripping tin was analyzed by chemical analysis method, and it was found that the tin content on the surface of the PCB after stripping tin was zero. After the continuous stripping test, the cathode obtained tin element with a current efficiency of 91.02%. After taking out the cathode plate for observation, it was found that the surface of the obtained cathode was flat and smooth. The obtained cathode was analyzed by chemical analysis and found to contain 99.98% tin.

Example 3

For a tinned PCB provided by a company, the surface of the PCB is tinned with 31g per square meter.

Configure sulfuric acid solution in the one-step tin removal and tin recovery device, the acidity of the mixed solution hydrochloric acid is 5mol/L, sulfosalicylic acid 0.1g/L, sodium benzoate 0.01g/L, β-naphthol 0.05g/L, alkyl Phenol polyoxyethylene ether 0.01g/L, react under the condition that the ultrasonic frequency is 20kHz, the ultrasonic frequency is 10W, the pulse frequency is 50Hz, the duty ratio is 50%, and the pulse average current density is 50A/ ^m2 , and the conveyor belt is adjusted After the PCB is stripped at a rate of 120s in the solution, a PCB with a flat and smooth surface is obtained. Observation by an optical microscope shows that the surface of the stripped tin plate obtained has no tin coating, and the surface of the substrate is flat and smooth. The PCB after stripping tin was analyzed by chemical analysis method, and it was found that the tin content on the surface of the PCB after stripping tin was zero. After the continuous stripping test, the cathode obtained a tin element with a current efficiency of 84.45%. After taking out the cathode plate for observation, it was found that the surface of the cathode obtained was flat and smooth. The obtained cathode was analyzed by chemical analysis and found to contain 99.95% tin.

Comparative Example 1 (solder stripping water under configured non-invention parameter conditions)

Configure the solution as described in Example 1, the difference is that no tin stripping accelerator, tin stripping corrosion inhibitor, electrolytic stabilizer and solution dispersant are added, ultrasonic frequency, ultrasonic power, pulse as described in Example 1 The reaction was carried out under frequency, duty cycle and pulse average current density, and the tin removal time was 120s. It was found that the tin layer on the PCB was difficult to remove completely. After analysis, it was found that 19.14% of the tin remained on the PCB. The cathode has no specific morphology generated.

Comparative Example 2 (without applying ultrasonic external field coupling enhancement)

Configure the solution as described in Example 2, the difference is that no ultrasonic external field coupling strengthening is applied, and the reaction is carried out under the pulse frequency, duty cycle and pulse average current density as described in Example 2, and the tin stripping time is 120s. It was found that the tin layer on the PCB was difficult to completely remove, and after analysis, it was found that 8% of the tin remained on the PCB. A large number of "whiskers" grow on the tin on the surface of the cathode, the cathode gas is precipitated seriously, and the current efficiency is only 42.18%. Comparative example 3 (do not adopt pulsed electric field)

Configure the solution as described in Example 2, the difference is that no ultrasonic external field coupling strengthening is applied, and the reaction is carried out at the ultrasonic frequency and ultrasonic power as described in Example 2. The tin stripping time is 120s, and the tinned layer on the PCB is found. It is difficult to remove completely, and after analysis, it is found that 64% of tin remains on the PCB. No product was formed at the cathode.

Claims (7)

1. A method and a device for withdrawing tin and recovering tin of a PCB in one step are characterized in that: in the continuous tin stripping electrolytic reaction device for the etched circuit board through the acid system solution, electrolytic tin stripping and tin recovery are carried out under the simultaneous actions of an external field coupling strengthening condition and an electric field; along with the progress of the reaction, the tin plating layer on the circuit board is dissolved into the solution, and tin ions in the solution are deposited and separated out at the cathode.

2. The method according to claim 1, characterized in that: the acidic system solution is a solution composed of single acid or mixed acid selected from sulfuric acid, methanesulfonic acid and hydrochloric acid, a tin stripping accelerator, a tin stripping corrosion inhibitor, an electrolytic stabilizer and a solution dispersing agent.

3. Acidic system solution according to claims 1 and 2, characterized in that: the tin stripping accelerant is one of tetraethylammonium bromide, sodium methylsulfonate, tartaric acid, sodium citrate and sulfosalicylic acid; the tin stripping corrosion inhibitor is one of benzotriazole, methylbenzotriazole, sebacic acid or sodium benzoate; the electrolytic stabilizer is one of animal bone glue, cresol sulfonic acid, phenol sulfonic acid and beta-naphthol;

the solution dispersing agent is one of ethylene oxide, polyethylene glycol and alkylphenol polyoxyethylene.

4. An acidic system solution according to claims 1-3, characterized in that: the acidity of the acid system is 1 mol/L-5 mol/L; the concentration of the tin stripping accelerator is 0.1-5 g/L; the concentration of the tin stripping corrosion inhibitor is 0.01-2 g/L; the concentration of the electrolytic stabilizer is 0.05-20 g/L; the concentration of the solution dispersing agent is 0.01-5 g/L.

5. The method according to claim 1, characterized in that: the external field coupling strengthening condition is ultrasonic coupling strengthening, the ultrasonic frequency is 20-500 kHz, and the ultrasonic power is 10-200W.

6. The method according to claim 1, characterized in that: the electrolytic tin stripping electric field is a pulse electric field, the pulse frequency of the pulse electric field is 50-2000 Hz, the duty ratio is 50-90%, and the average current density of the initial electrolytic pulse is 10-500A/m ² 。

7. The method according to claim 1, characterized in that: the time for the etched circuit board to pass through the continuous tin stripping electrolytic reaction device is 15-120 s.