Printed Circuit Board (PCB)

A brief history of development

History

Before the advent of printed circuit boards, the interconnection between electronic components relied on the direct connection of wires to form a complete circuit . In modern times, the circuit panel only exists as an effective experimental tool, and the printed circuit board has become an absolute dominant position in the electronics industry.

Printed circuit boards (5 sheets)

At the beginning of the 20th century, people began to simplify the production of electronic equipment, reduce the wiring between electronic parts, and reduce production costs. Delve into the method of replacing wiring with printing. Over the past 30 years, engineers have repeatedly proposed to use metal conductors for wiring on insulated substrates. The most successful was in 1925, Charles Ducas of the United States printed circuit patterns on an insulating substrate, and then used electroplating to successfully establish conductors for wiring.

Until 1936, Austrian Paul Eisler (Paul Eisler) published foil technology in the United Kingdom, he used a printed circuit board in a radio device; and in Japan, Miyamoto helped The spray-attached wiring method "Metalcon method blowing wiring method (Patent No. 119384)" successfully applied for a patent. Among the two, Paul Eisler’s method is the most similar to today’s printed circuit boards. This type of method is called subtraction, which removes unnecessary metal; while Charles Ducas and Miyamoto Kinosuke’s method is to add only what is needed. The wiring is called the additive method. Even so, because the electronic components at that time generated a lot of heat, the substrates of the two were difficult to use together, so there was no formal practical use, but it also made the printed circuit technology further.

Development

In the past ten years, my country's printed circuit board (PCB) manufacturing industry has developed rapidly, and its total output value and total output have both ranked first in the world. Due to the rapid development of electronic products, price wars have changed the structure of the supply chain. China has both industrial distribution, cost and market advantages, and has become the world's most important printed circuit board production base.

Printed circuit boards have developed from single-layer to double-sided, multi-layer and flexible boards, and continue to develop in the direction of high precision, high density and high reliability. Continuously shrinking volume, reducing costs, and improving performance have enabled printed circuit boards to maintain strong vitality in the development of electronic products in the future.The development trend of future printed circuit board manufacturing technology is to develop in the direction of high density, high precision, fine aperture, fine wire, small pitch, high reliability, multilayer, high-speed transmission, light weight and thinness in performance.

Classification

Single panel

On the most basic PCB, the parts are concentrated on one side, and the wires are concentrated on the other side. Because the wires only appear on one side, this kind of PCB is called a single-sided (Single-sided). Because single-sided boards have many strict restrictions on the design of the circuit (because there is only one side, the wiring cannot cross and must be around a separate path), so only early circuits use this type of board.

Double-sided board

This kind of circuit board has wiring on both sides, but to use two-sided wires, there must be a proper circuit connection between the two sides. The "bridge" between such circuits is called a via. A via is a small hole filled or coated with metal on the PCB, which can be connected with the wires on both sides. Because the area of ​​the double panel is twice as large as the single panel, the double panel solves the difficulty of the single panel due to the interlacing of wiring (it can be passed to the other side through via holes), and it is more suitable for use in more complicated circuits than the single panel.

Multilayer boards

In order to increase the area that can be wired, multilayer boards use more single or double-sided wiring boards. Use one double-sided as the inner layer, two single-sided as the outer layer, or two double-sided as the inner layer and two single-sided as the outer layer of the printed circuit board. The positioning system and the insulating bonding material alternately together and the conductive pattern Printed circuit boards that are interconnected according to design requirements become four-layer and six-layer printed circuit boards, also known as multilayer printed circuit boards. The number of layers of the board does not mean that there are several independent wiring layers. In special cases, empty layers are added to control the thickness of the board. Usually, the number of layers is even and includes the two outermost layers. Most motherboards have a 4 to 8 layer structure, but technically, it can be a PCB of nearly 100 layers in theory. Most large supercomputers use fairly multi-layered motherboards, but because these types of computers can already be replaced by clusters of many ordinary computers, super-multilayered boards have gradually ceased to be used. Because the various layers in the PCB are tightly integrated, it is generally not easy to see the actual number, but if you look closely at the motherboard, you can still see it.

Information

Composition

Current circuit boards are mainly composed of the following

Lines and patterns (Pattern): Lines are made It is a tool for continuity between the originals. In the design, a large copper surface will be additionally designed as a ground and power layer. The route and the drawing are made at the same time.

Dielectric layer (Dielectric): Used to maintain the insulation between the circuit and each layer, commonly known as the substrate.

Hole (Through hole / via): The through hole can make the lines of more than two levels connect to each other. The larger through hole is used as a part plug-in. In addition, there are non-through holes (nPTH ) Usually used for surface mount positioning and fixing screws during assembly.

Solder resistant /Solder Mask: Not all copper surfaces have to eat tin parts, so the non-tin area will be printed with a layer of material that isolates the copper surface from eating tin (usually It is epoxy resin) to avoid short circuits between non-tinned circuits. According to different processes, it is divided into green oil, red oil and blue oil.

Silk screen (Legend /Marking/Silk screen): This is a non-essential composition. The main function is to mark the name and position frame of each part on the circuit board, which is convenient for maintenance and identification after assembly.

Surface Finish: Because the copper surface is easily oxidized in the general environment, it can not be tinned (poor solderability), so it will be protected on the copper surface that needs to be tinned. The protection methods include HASL, ENIG, Immersion Silver, Immersion Tin, and Organic Solder Preservative (OSP). Each method has its advantages and disadvantages, which are collectively referred to as surface treatment.

Appearance

Bare board (no parts on top) is also often called "Printed Wiring Board (PWB)". The base plate of the board itself is made of materials that are insulated and heat-insulated, and not easy to bend. The small circuit material that can be seen on the surface is copper foil. The copper foil was originally covered on the entire board, but part of it was etched away during the manufacturing process, and the remaining part became a network of small lines. . These lines are called conductor patterns or wiring, and are used to provide circuit connections for parts on the PCB.

Usually the color of PCB is green or brown, which is the color of solder mask. It is an insulating protective layer that can protect the copper wire, prevent short circuits caused by wave soldering, and save the amount of solder. A silk screen is also printed on the solder mask. Usually words and symbols (mostly white) are printed on this to mark the position of each part on the board. The screen printing surface is also called the legend surface.

When the final product is made, integrated circuits, transistors, diodes, passive components (such as resistors, capacitors, connectors, etc.) and various other electronic parts will be installed on it. Through the wire connection, the electronic signal connection can be formed and the application function can be formed.

Advantages

The main advantages of using printed boards are:

⒈Due to the repeatability (reproducibility) and consistency of the graphics, the wiring and assembly are reduced It saves the maintenance, debugging and inspection time of the equipment;

⒉The design can be standardized, which is beneficial to interchange; 3. High wiring density, small size and light weight are conducive to the miniaturization of electronic equipment;

⒋Conducive to mechanized and automated production, improves labor productivity and reduces the cost of electronic equipment.

Printed board manufacturing methods can be divided into two major categories: subtractive method (subtractive method) and additive method (additive method). At present, large-scale industrial production is still dominated by the method of corroding copper foil in the subtractive method.

(Overview picture)

⒌Especially the bending resistance and precision of the FPC flexible board, it is better applied to high-precision instruments. (such as cameras, mobile phones. Cameras, etc.)

Manufacturing

Substrate

Substrates are generally classified based on the insulating part of the substrate. Common raw materials are bakelite and fiberglass board. And all kinds of plastic boards. And PCB manufacturers generally use a kind of insulating part composed of glass fiber, non-woven material, and resin, and then use epoxy resin and copper foil to press the "adhesive sheet" (prepreg) for use.

Common substrates and main components for the circuit design of Xgs game consoles are:

FR-1 ──Phenolic cotton paper, this substrate is generally called bakelite (compared to FR-2 High economy)

FR-2 ──Phenolic cotton paper,

FR-3 ──Cotton paper, epoxy resin

FR -4 ──Woven glass, epoxy resin

FR-5 ──Glass cloth, epoxy resin

FR-6 ──Frosted glass, polyester

G-10 ──Glass cloth, epoxy resin

CEM-1 ──Tissue paper, epoxy resin (flame retardant)

CEM-2 ──Cotton paper, epoxy resin (non-flame retardant)

CEM-3 ──Glass cloth, epoxy resin

CEM-4 ──Glass cloth, epoxy resin< /p>

CEM-5 ──Glass Cloth, Polyester

AIN ──Aluminum Nitride

SIC ──Silicon Carbide

Metal coating The layer

The metal coating is not only the wiring on the substrate, but also the place where the circuit of the substrate is soldered to the electronic components. In addition, because different metals have different prices, they directly affect the cost of production. In addition, the solderability, contactability, resistance value, etc. of each metal are different, which will directly affect the performance of the device.

Commonly used metal coatings are: copper, tin (the thickness is usually 5 to 15μm), lead-tin alloy (or tin-copper alloy, that is, solder, the thickness is usually 5 to 25μm, the tin content is about 63 %), gold (usually only plated on the interface), silver (usually only plated on the interface, or an alloy that is also silver as a whole).

Circuit design

The design of the printed circuit board is based on the circuit schematic diagram to realize the functions required by the circuit user. The design of the printed circuit board mainly refers to the layout design, which requires various factors such as the layout of internal electronic components, metal connections, through holes and external connections, electromagnetic protection, heat dissipation, and crosstalk. Excellent circuit design can save production costs and achieve good circuit performance and heat dissipation performance. Simple layout design can be realized by hand, but complex circuit design generally needs to be realized by computer-aided design (CAD), and well-known design software includes OrCAD, Pads (also known as PowerPCB), Altium designer (also known as Protel), FreePCB , CAM350, etc.

Basic production

According to different technologies, it can be divided into two major types of processes: elimination and addition.

Subtractive method

Subtractive method is to use chemicals or machinery to remove a blank circuit board (that is, a complete piece of metal The unnecessary places on the foil circuit board are removed, and the remaining place is convenient for the required circuit.

Screen printing: Make the pre-designed circuit diagram into a screen mask, the unnecessary circuit parts on the screen will be covered by wax or impermeable materials, and then put the screen mask in the blank On the circuit board, oil on the screen with a protective agent that will not be corroded. Put the circuit board in the corrosive liquid, and the parts that are not covered by the protective agent will be eroded away. Finally, the protective agent is cleaned.

Photosensitive plate: Print the pre-designed circuit diagram on the transparent film mask (the easiest way is to use the transparencies printed by the printer), and the required parts should be printed as opaque Then apply photosensitive paint on the blank circuit board, put the prepared film mask on the circuit board and irradiate it with strong light for several minutes. After removing the mask, use the developer to display the pattern on the circuit board, and finally it looks like Corroded the circuit in the same way as screen printing.

Engraving: Use a milling machine or laser engraving machine to directly remove the unnecessary parts on the blank circuit.

Additive method

Additive method (Additive), now it is common to cover a photoresist on a substrate pre-plated with thin copper ( D/F), after UV exposure and then develop, expose the necessary places, and then use electroplating to increase the thickness of the official circuit on the circuit board to the required specifications, and then plate a layer of anti-etching resist-metal thin tin , Finally remove the photoresist (this process is called film removal), and then etch away the copper foil layer under the photoresist.

Layer method

Layer method is one of the methods for making multilayer printed circuit boards. The outer layer is wrapped after the inner layer is made, and then the outer layer is processed by subtraction or addition. The operation of the build-up method is repeated continuously to obtain a multilayer printed circuit board with multiple layers, which is the sequential build-up method.

1. Inner layer production

2. Laminate formation (that is, the action of bonding different layers)

3. Laminate completion (minus The outer layer of the method contains a metal foil film; additive method)

4. Drilling

Panel method

1. Full Block PCB electroplating

2. Add a resist layer (resist to prevent it from being etched) where the surface should be kept

3. Etching

4. Remove Barrier layer

Pattern method

1. Add a barrier layer where the surface should not be kept

2. Surface required for electroplating To a certain thickness

3. Remove the barrier layer

4. Etch until the unnecessary metal foil film disappears

Complete addition method

1. Add a barrier layer where no conductor is needed

2. Use electroless copper to form a circuit

Partial addition method

b>

1. Cover the entire PCB with electroless copper

2. Add a barrier layer where no conductor is needed

3. Electrolytic copper plating< /p>

4.Remove the barrier layer

5. Etch until the electroless copper disappears under the barrier layer

ALIVH

ALIVH (Any Layer Interstitial Via Hole, Any Layer IVA) is a layer-added technology developed by Matsushita Electric. This is using Aramid fiber cloth as the base material.

1. Immerse the fiber cloth in epoxy resin to become "prepreg"

2. Laser drilling

3. Drilling Fill the conductive paste

4. Paste copper foil on the outer layer

5. Make circuit patterns on the copper foil by etching

6. Finish the first The two-step semi-finished product is glued on the copper foil

7. Laminated weaving

8. Repeat the fifth to seventh steps again and again until it is completed

B2it

B2it (Buried Bump Interconnection Technology) is a build-up technology developed by Toshiba.

1. First make a double-sided or multi-layer board

2. Print the cone silver paste on the copper foil

3. Put the adhesive sheet on the silver paste And make the silver paste penetrate through the adhesive sheet

4. Stick the adhesive sheet from the previous step on the board of the first step

5. Use the etching method to etch the copper of the adhesive sheet The foil is made into a circuit pattern

6. Repeat the second to fourth steps again and again, until the completion of the

functional test

Dense PCB, higher Bus speeds and analog RF circuits have all presented unprecedented challenges to testing. Functional testing in this environment requires careful design, well-thought-out test methods, and appropriate tools to provide credible test results.

When dealing with fixture suppliers, keep these issues in mind, and at the same time think about where the product will be manufactured. This is a place that many test engineers will ignore. For example, we assume that the test engineer is in California in the United States, but the product is manufactured in Thailand. Test engineers will think that products need expensive automated fixtures, because the California plant is expensive, requiring as few testers as possible, and automated fixtures are needed to reduce the employment of high-tech and high-paid operators. But in Thailand, these two problems do not exist. It is cheaper to let people solve these problems because the labor cost here is very low, and the land price is also very cheap. Large factories are not a problem. Therefore, sometimes first-class equipment may not be popular in some countries.

Technology level

In high-density UUT, if calibration or diagnosis is required, it is likely to need to be explored manually. This is due to the contact between the needle and the bed. Limitations and faster testing (using probes to test UUTs can quickly collect data instead of feeding information back to the edge connector) and other reasons, so the operator is required to explore the test points on the UUT. No matter where it is, make sure that the test point is clearly marked.

The probe type and ordinary operators should also pay attention to the issues that need to be considered:

Is the probe larger than the test point? Is the probe in danger of short-circuiting several test points and damaging the UUT? Is there an electric shock hazard to the operator?

Can each operator quickly find the test point and conduct an inspection? Are the test points large and easy to identify?

How long does it take for the operator to press the probe on the test point to get an accurate reading? If the time is too long, some troubles will occur in the small test area, such as the operator’s hand sliding due to the long test time, so it is recommended to expand the test area to avoid this problem.

After considering the above problems, the test engineer should re-evaluate the type of test probe, modify the test file to better identify the location of the test point, or even change the requirements for the operator.

Automatic detection

In some cases, automatic detection is required. For example, it is difficult to use manual detection for PCB, or the technical level of operators is limited. When the test speed is greatly reduced, automated methods should be considered at this time.

Automatic detection can eliminate human error, reduce the possibility of short circuit of several test points, and speed up the test operation. But be aware that automatic detection may also have some limitations, which vary according to the supplier’s design, including:

UUT size

number of sync probes

Test the positioning accuracy of the probe

Can the system detect UUT on both sides?

How quickly does the probe move to the next test point?

What is the actual interval required by the probe system? (Generally speaking, it is larger than the offline functional test system)

Automatic detection usually does not use needle bed fixtures to contact other test points, and generally it is slower than the production line, so two steps may be taken: if The detector is only used for diagnosis. You can consider using a traditional functional test system on the production line, and place the detector as a diagnostic system on the side of the production line; if the purpose of the detector is UUT calibration, then the only real solution is to use multiple A system, it is still much faster than manual operation.

How to integrate into the production line is also a key issue that must be studied. Is there still room for the production line? Can the system be connected to the conveyor belt? Fortunately, many new detection systems are compatible with SMEMA standards, so they can work in an online environment.

Boundary Scan

This technology should be discussed as early as the product design stage, because it requires specialized components to perform this task. In UUTs based on digital circuits, devices with IEEE1194 (boundary scan) support can be purchased, so that most diagnostic problems can be solved with little or no detection. Boundary scan will reduce the overall functionality of UUT, because it will increase the area of ​​each compatible device (each chip adds 4 to 5 pins and some lines), so the principle of choosing this technology is the cost. Should be able to improve the diagnosis results. It should be remembered that boundary scan can be used to program flash memory and PLD devices on the UUT, which further increases the reason for choosing this test method.

How to deal with a limited design?

If the UUT design has been completed and finalized, the options are limited at this time. Of course, you can also request modifications in the next revision or new product, but process improvement always takes a certain amount of time, and you still have to deal with the current situation.

Design

With the rapid development of electronic technology, printed circuit boards are widely used in various fields, and almost all electronic devices contain corresponding printed circuit boards. In order to ensure the normal operation of electronic equipment, reduce mutual electromagnetic interference, and reduce the adverse effects of electromagnetic pollution on humans and the ecological environment, electromagnetic compatibility design cannot be ignored. This article introduces the design methods and skills of printed circuit boards.

In the design of printed circuit boards, the layout of components and the wiring of circuit connections are the two key links.

Layout

Layout means placing circuit components in the wiring area of ​​the printed circuit board. Whether the layout is reasonable not only affects the subsequent wiring work, but also has an important impact on the performance of the entire circuit board. After ensuring circuit functions and performance indicators, to meet the requirements of manufacturability, testing and maintenance, the components should be evenly, neatly and compactly placed on the PCB, and the leads and connections between the components should be minimized and shortened to obtain Uniform packing density.

Arrange the position of each functional circuit unit according to the circuit process, so that the input and output signals, high-level and low-level parts do not cross as much as possible, and the signal transmission route is the shortest.

Functional distinction

The location of components should be grouped according to power supply voltage, digital and analog circuits, speed, current size, etc., to avoid mutual interference.

When the digital circuit and the analog circuit are installed on the circuit board at the same time, the ground wire and power supply system of the two circuits are completely separated. If possible, the digital circuit and the analog circuit are arranged in different layers. When fast, medium-speed and low-speed logic circuits need to be arranged on the circuit board, they should be placed close to the connector; and low-speed logic and memory should be placed far away from the connector. In this way, it is beneficial to reduce the reduction of common impedance coupling, radiation and crosstalk. Clock circuits and high-frequency circuits are the main sources of harassment radiation and must be arranged separately and away from sensitive circuits.

Thermal and magnetic considerations

The heating element and the thermal element are as far away as possible, and the influence of electromagnetic compatibility should be considered.

Manufacturability

⑴Level

Place the components on one side as much as possible to simplify the assembly process .

⑵Distance

The minimum limit of the distance between the components is determined according to the shape of the component and other related properties. The current components The distance between them is generally not less than 0.2 mm ~ 0.3mm, and the distance between the components and the edge of the printed board should be greater than 2 mm.

⑶Direction

The direction and density of the element arrangement should be conducive to air convection. Consider the assembly process, and the component orientation should be as consistent as possible.

Wiring

1, wire

⑴width p>

The minimum width of the printed wire is mainly determined by the adhesion strength between the wire and the insulating substrate and the current value flowing through them. The printed wire can be as wide as possible, especially the power line and ground wire, as wide as possible under the condition of the board surface, even if the area is tight, it is generally not less than 1mm. Especially the ground wire, even if it is not allowed to be widened locally, it should be widened where it is allowed to reduce the resistance of the entire ground wire system. For wires longer than 80mm, even if the working current is not large, they should be widened to reduce the influence of the voltage drop of the wires on the circuit.

⑵Length

To minimize the length of the wiring, the shorter the wiring, the less interference and crosstalk, and it The lower the parasitic reactance, the less radiation. Especially the grid of the field effect tube, the base of the triode and the high-frequency circuit should pay attention to the wiring to be short.

⑶Spacing

The distance between adjacent wires should meet the requirements of electrical safety. Crosstalk and voltage breakdown are The main electrical characteristics that affect the wiring spacing. In order to facilitate operation and production, the spacing should be as wide as possible, and the minimum spacing should be at least suitable for the applied voltage. This voltage includes working voltage, additional fluctuating voltage, overvoltage and peak voltage due to other reasons. When there is mains voltage in the circuit, the distance should be wider for safety.

⑷Path

The width of the signal path, from drive to load, should be constant. Changing the path width changes the path impedance (resistance, inductance, and capacitance), which will cause reflection and cause unbalanced line impedance. Therefore, it is best to keep the width of the path constant. In the wiring, it is best to avoid using right angles and sharp angles, generally the corners should be greater than 90°. The edges inside the right-angle path can generate a concentrated electric field, which generates noise coupled to the adjacent path. The 45° path is better than the right-angle and acute-angle paths. When two wires meet and connect at an acute angle, the acute angle should be changed to a circle.

2. Aperture and pad size

The diameter of the component mounting hole should match the lead diameter of the component, so that the diameter of the mounting hole is slightly (0.15～0.3)mm larger than the diameter of the component lead. Usually DIL package pins and most small components use 0.8mm aperture, and the diameter of the pad is about 2mm. In order to obtain better adhesion for large-aperture pads, the ratio of the diameter of the pad to the aperture is about 2 for epoxy glass substrates, and (2.5 to 3) for phenol cardboard substrates.

Vias are generally used in multi-layer PCBs. Its minimum usable diameter is related to the thickness of the board base. Usually, the ratio of the board base thickness to the via diameter is 6:1. In the case of high-speed signals, the vias produce a path of (1～4)nH inductance and (0.3～0.8)pF capacitance. Therefore, when laying high-speed signal channels, vias should be kept to an absolute minimum. For high-speed parallel lines (such as address and data lines), if layer changes are unavoidable, ensure that the number of vias for each signal line is the same. And the number of vias should be minimized, and if necessary, a printed wire protection ring or protection line should be set to prevent oscillation and improve circuit performance.

3. Ground wire design

Unreasonable ground wire design will cause interference to the printed circuit board, fail to meet the design index, or even fail to work . The ground wire is the reference point of the electric potential in the circuit, and it is the common channel of the electric current. The ground potential is theoretically zero potential, but in fact, due to the existence of wire impedance, the potential of the ground wire is not all zero. As long as the ground wire has a certain length, it is not a zero equipotential point everywhere. The ground wire is not only an essential circuit common channel, but also a channel for interference.

One point grounding is the basic principle to eliminate ground interference. The ground wires of all circuits and equipment must be connected to a uniform grounding point, which is used as the zero potential reference point (surface) of the circuit and equipment. One-point grounding consists of a common ground wire in series with one-point grounding and an independent ground wire in parallel with one-point grounding.

The common ground wire is connected in series with one point grounding method. The grounding leads of each circuit are relatively short and the resistance is relatively small. This grounding method is often used for grounding in equipment cabinets. An independent ground wire is connected in parallel with one point grounding. Only one physical point is defined as the ground reference point. All other points that need to be grounded are directly connected to this point. The ground potential of each circuit is only related to the ground current base impedance of the circuit. The influence of other circuits.

Pay attention to the following points during the specific wiring:

⑴The length of the trace should be as short as possible to minimize the lead inductance. In low-frequency circuits, because the ground currents of all circuits flow through a common ground impedance or ground plane, avoid the use of multi-point grounding.

⑵The public ground wire should be arranged at the edge of the printed circuit board as much as possible. The circuit board should keep as much copper foil as the ground wire to enhance the shielding ability.

⑶The double-layer board can use the ground plane, the purpose of the ground plane is to provide a low impedance ground wire.

⑷In the multilayer printed circuit board, a grounding layer can be set, and the grounding layer is designed into a mesh. The spacing of the ground wire grid should not be too large, because one of the main functions of the ground wire is to provide a signal return path. If the grid spacing is too large, a larger signal loop area will be formed. Large loop areas can cause radiation and sensitivity issues. In addition, the signal return actually takes a path with a small loop area, and other ground wires do not work.

⑸The ground plane can minimize the radiation loop.

Recycling

Printed circuit board manufacturing technology is a very complex and highly comprehensive processing technology. Especially in the wet processing process, a large amount of water is needed, so a variety of heavy metal wastewater and organic wastewater are discharged, the composition is complicated, and the treatment is difficult. Calculate according to the utilization rate of printed circuit board copper foil of 30% to 40%, then the copper content in the waste liquid and wastewater is quite considerable. According to the calculation of 10,000 square meters of double-sided panels (the thickness of each side of the copper foil is 35 microns), the copper content in the waste liquid and wastewater is about 4,500 kg, and there are many other heavy metals and precious metals. If these metals in the waste liquid and waste water are discharged without treatment, it will not only cause waste but also pollute the environment. Therefore, the waste water treatment and the recovery of copper and other metals in the printed board production process are of great significance, and they are an indispensable part of the printed board production.

As we all know, a large amount of waste water in the production process of printed circuit boards is copper, and a very small amount is lead, tin, gold, silver, fluorine, ammonia, organics and organic complexes.

As for the processes that produce copper wastewater, there are mainly: copper immersion, full-board copper electroplating, pattern copper electroplating, etching, and various printed board pre-treatment procedures (chemical pre-treatment, brushing pre-treatment, volcanic ash grinding board Processing etc.).The copper-containing wastewater produced by the above process can be roughly divided into complex wastewater and non-complex wastewater according to its composition. In order to make wastewater treatment meet the national discharge standards, the maximum allowable discharge concentration of copper and its compounds is 1mg/l (calculated as copper), and different wastewater treatment methods must be adopted for different copper-containing wastewater.