CHINA Printed circuit board manufacturers

In recent years, electronic products have already covered military weapons, computers, communication equipment, mobile storage equipment, mobile communication equipment and other related fields, and have higher and higher requirements in terms of volume, integration, and functions. As an important part of electronic products, circuit board proofing is also constantly established and updated. China is already the largest country in the world in terms of output value of printed circuit boards (PCB). Up to HDI (High) Zhucheng's internal interconnection technology, the technical level is constantly improving. There are also endless means of plate making, and different plate making processes also have their own advantages and disadvantages according to their different application objects. At present, the production of printed circuit boards is mainly used in two aspects, one is the mass production of enterprises, and the other is teaching and scientific research in middle schools.

1 Development of printed circuit boards

Printed circuit board (Board) referred to as PCB, also known as printed circuit board, is one of the important components of electronic products. A printed circuit is a conductive pattern for connection between components produced on the surface or inside of an insulating substrate by means of a color printing method according to a pre-designed circuit. Electronic products made of printed circuit boards have the advantages of high reliability, good consistency, high mechanical hardness, light weight, small size, and easy standardization. Almost every kind of electronic equipment, ranging from small electronic watches and calculators to large computers, communication equipment, and electronic radar systems, as long as there are electronic components, the electrical interconnection between them will use printed circuit boards. In the research and development process of electronic products, one of the most basic factors that affect the success of electronic products is the design and manufacture of the printed circuit board of the product.

The invention of single-sided copper-clad board has become a symbol of a new era of circuit board design and manufacturing. Wiring design and manufacturing technology have matured. First, use a template to print the anti-corrosion film on the copper-clad board, and then corrode the reticle. These technologies are as simple as color printing on paper, hence the name " printed circuit board ". The application of printed circuit boards greatly increases the production cost. With the development of electronic technology and the advancement of printed circuit board technology, double-sided panels have appeared, that is, copper is deposited on both sides of the board, and the scribe lines can be etched on both sides.

With the development of electronic product production technology, people began to develop interlayers on the basis of double-sided circuit boards. Of course, a single-sided board is superimposed on the basis of double-sided boards. This is a multi-layer circuit board. Originally, the interlayer was mostly used for the wiring of large-area phase lines and power lines, and the surface layer was used for signal wiring. Later, more and more interlayers were required for signal wiring, which increased the number of layers of the circuit board. However, the interlayer cannot be reduced indefinitely, mainly due to cost and length issues.

Printed circuit boards are from double-layer to double-sided, multi-layer boards and flexible boards, as well as soft and hard boards (PCB), and are constantly developing in the direction of high precision, high density and high reliability. Continuously reduce volume, reduce cost and improve performance.

2 Classification and functions of printed circuit boards

Printed circuit boards can be divided into rigid printed circuit boards and flexible printed circuit boards according to the materials they are made of, also called hard boards and soft boards. Rigid printed circuit boards include thermosetting paper laminates, epoxy paper laminates, polyester glass felt laminates, and epoxy glass cloth laminates. Flexible printed circuit board is also called flexible printed circuit board or FPC (), flexible circuit board is a kind of high reliability and high flexibility made of copolymer or polyester film as the base material. printed circuit board. These circuit boards have good heat dissipation, can be bent, folded, curled, and can be freely connected and stretched in three-dimensional space. The FPC can be used to reduce the volume, realize lightweight, miniaturization, and thinning, and then realize the integration of device devices and wire connections. FPC is widely used in industries such as electronics, computers, communications, aerospace and electrical appliances.

Printed circuit boards provide mechanical support for the fixing and assembly of various electronic components such as integrated circuits in electronic equipment, realize the wiring and electrical connection or electrical insulation between various electronic components such as integrated circuits, and provide the required electrical characteristics . Provide solder mask graphics for manual spot welding, and provide identification characters and graphics for device insertion, inspection, and maintenance.

3 Basic process classification of printed circuit boards

There are many ways to make printed circuit boards, but they can be roughly divided into three types in theory:

1) Subtraction method: first use physical method or screen printing method or nickel plating method to transfer a certain circuit pattern on the copper surface of the copper clad strip (this pattern is composed of a certain anti-corrosion material), and then Then use physical etching to etch away the unnecessary parts of the circuit board design and manufacture , leaving the required circuit patterns.

2) Semi-additive method: If you want to make more fine lines, you can use the semi-additive method. These processes first use photoresist to generate graphics on the surface, then design and manufacture graphic nickel-plated circuit boards , and then go through film removal and differential etching processes to obtain the fine lines we need. The base material of the semi-additive method mostly uses a thin copper strip of 5mm or less, and a thicker resist layer can be used to make a circuit below 20?m.

3) Additive method: The additive method is a method in which conductor circuit patterns are generated by direct processing of insulating substrates. Additive method process: laminate blanking→coating catalytic adhesive→negative image transfer (sticking dry film→exposure→developing)→roughening→electroless nickel plating→dry film removal→fine line, because the additive method Physical methods are used to thicken copper, so the production efficiency is low.

In the current production, the subtractive method is still used as the basic process.

4 Manufacturing methods of printed circuit boards

4.1 Thermal transfer method

This is a simple circuit board manufacturing process that was often used by colleges and universities in the past. The main process is: use a copier to copy the circuit pattern on the heat transfer paper, and then cover the heat transfer paper with the pattern on the copper clad board through heat transfer. The printing machine tears the thermal transfer paper and uses water to corrode the graphics. Use a bench drill to drill holes manually and use sandpaper to polish off the toner on the surface of the circuit. The advantages of these processes are: the speed of making a single panel is fast, the cost is relatively low, and it is easy to realize. weakness is:

1) Drilling cannot be done manually, the screw holes of the circuit and the hole have already been corroded and formed, how to make the hole in the center of the via hole? Only a manual bench drill can be used to align the tip of the reamer with the center of the via hole completely by vision Alignment, if the PCB has many holes, it will be a very cumbersome process, which is basically not feasible for complex boards;

2) Only very simple circuits can be made, such as the line width and spacing are usually above 0.25mm, which is very different from the current industrial level of PCB manufacturing;

3) It is impossible to transfer the lines on both sides to the copper clad board at the same time, let alone align the lines on both sides, so it is impossible to make a double-sided circuit board;

4) The hole metallization of double-sided panels cannot be completed;

5) Can not solve the problem of solder resistance, usually only bare boards are made, which is prone to spot welding leakage problems; can not solve the problem of solderability, spot welding is difficult after the copper surface is oxidized, and it is necessary to use physical potions to remove the oxides on the copper surface Then spot weld.

4.2 Current industrial level PCB manufacturing process

At present, the process flow commonly used by PCB shoe factories is:

Drilling brush plate with physical nickel plating to complete the hole Metallization brush plate paste dry film exposure Baking hot air leveling (or physical copper plating, chemical nickel gold, OSP, etc.) milling appearance continuity test.

These processes are currently the most widely used methods by PCB manufacturers . This method has many advantages and is suitable for the production of precision circuit boards. Usually, the line width can reach 0.12mm (can be made to 0.1mm); it is suitable for mass production of enterprises; The cost of mass production is not high; but there are many insurmountable shortcomings for middle school teaching and scientific research, mainly:

1) The process is complex and the cost of ordering equipment is very high;

2) The process operation is very complicated and requires very professional and experienced personnel to operate and use;

3) Need to use a lot of toxic and harmful substances, such as formaldehyde, EDTA, heavy metals, etc.;

4) Special workplaces are required, such as cold storage for dry film storage, purified space and yellow light environment for film application, darkroom for film production, etc.;

5) The cost is very high for discontinuous production and use. For example, the chemical stability of physical tin plating is poor, and the shelf life of the dry film is particularly short. If it is not used continuously, the cost of making circuit boards will be high;

6) Need to be equipped with a professional sewage treatment workshop; need to be equipped with a professional physical analysis laboratory.

Those who are engaged in the design of electronic circuits are deeply aware that the most troublesome thing in designing a product is the board test, and the most troublesome thing in the board test is the production of color printed circuit boards. Even though most people leave this hateful thing to the circuit board factory to deal with, it takes too long to wait 3 to 7 days for each board, but the cost of board manufacturing is not low. New design inspirations are often discarded because of these troubles and so on. In the actual teaching of colleges and universities, both teachers and middle school students hope to independently complete a design work or electronic product in their own hands. But the biggest hurdle preventing electronics from taking shape is the printed circuit board, and in these cases the advent of mechanical board-making processes has solved the problem. The design completed on the computer can be realized immediately, which undoubtedly stimulates the enthusiasm for scientific research and learning of the teachers and students of the college.

4.3 Mechanical plate making process

These processes are suitable for the production of high-precision double-sided circuit boards. The main process flow is: the random software of the circuit board engraving machine directly reads the design data and manually estimates the engraving machine. Manual drilling adopts advanced direct nickel plating process to complete the conduction of the hole Use the engraving machine to manually complete the milling of the double-sided circuit. Use the engraving machine to manually complete the appearance cutting of the PCB. The advantages of these processes are:

1) The speed of making single pieces and samples is relatively fast, which is suitable for teachers and students in colleges and universities to conduct research, teach, and participate in various electronic competitions;

2) The precision of making the circuit is relatively high, usually the model can be made with a line width and width of 0.1mm, which is at the same level as the current industrialized PCB;

3) The scalability of the system is relatively good. You can choose to reduce the solder mask and character functions, or upgrade to a multi-layer board manufacturing system. At the same time, you can also manufacture multi-layer boards with buried holes and through holes;

4) Random CAM is a real CAM software, which has the same function as the CAM software commonly used in PCB shoe factories, and plays the role of receiving design data and data processing. This software can be installed on the notebooks of every middle school student, and can be used to let middle school students understand how the PCB data designed by circuit board EDA design software such as PowerPCB is converted, output, and processed in the PCB shoe factory. How each type of data is used and how the data is converted into various manufacturing data.

The disadvantages of these processes are:

1) Not suitable for mass production. The board-making time of a single circuit board or even several circuit boards is relatively short, and as the number of boards decreases, the board-making time is also doubled;

2) The board making process is not as good as that of the PCB board factory , and the appearance of the circuit board is not as beautiful as that of the board factory.

It can be seen that for the mass production of printed circuit boards in enterprises, the traditional chemical board-making process should be used, and the mechanical board-making process can be used for the teaching and scientific research of colleges and scientific research institutions. At present, out of the concept of energy saving, environmental protection and high efficiency, both the chemical plate making process and the mechanical plate making process are constantly being improved. Among them, the laser cutting machine is introduced in the mechanical board, and different circuit patterns can be carved out with the help of laser beams. In the near future, people may develop a more robust method for the manufacture and production of printed circuit boards.