The characteristics and development prospects of multilayer circuit boards

Multilayer boards are typically first fabricated from internal graphics and then printed and etched into a single or double sided substrate, bonded to a designated intermediate layer, and then heated, pressurized and bonded. The drilling method is the same as the through-hole plating on the double-sided board. These basic manufacturing methods have not changed much from the 1960s, but with the maturity of materials and process technology (for example, bonding technology, drilling, film production, improvement of rubber residue production) Laminates have become more diverse.
Plated through hole
Original copper
After the interlayer conductive channel is formed, a copper layer should be laid thereon to complete the conduction of the interlayer circuit. First, the powder in the pores and the pores on the pores were washed by re-brushing and high-pressure cleaning, and then the residue of the copper on the surface of the pore wall copper was removed with a potassium permanganate solution. The tin-palladium colloid layer adheres to the cleaned pore walls and is then reduced to palladium metal. The circuit board is immersed in a chemical copper solution, and copper ions in the solution are reduced and deposited on the pore walls by catalytic action of palladium metal to form a via circuit. The copper layer in the through-holes is thickened by copper sulfate bath plating to withstand the dynamic impact of subsequent processing and use environments.
External circuit
Twice copper
Line image transfer printing is similar to internal line printing, but in online etching, it is divided into two production modes, positive and negative. Negative films are produced in the same way as internal circuits. After development, the copper is etched and the film is directly removed. The positive electrode film is produced by secondary copper and tin-lead plating after development (the tin-lead in this region will remain as an etch inhibitor in the subsequent copper etching step). After the film is removed, the exposed copper foil is etched by a mixed solution of alkaline ammonia and copper chloride to form an electric circuit. Finally, the successful retreating tin-lead layer was stripped with a tin-lead stripping solution (in the early days, there was a way to preserve the tin-lead layer, which was used to cover the circuit as a large-capacity household protective layer, but it is not currently used).
Anti-welding edge paint
When the external circuit is completed, an insulating resin layer is applied to avoid oxidation and short-circuit soldering. Prior to painting, the copper surface of the PCB should be roughened and cleaned by brushing, microetching and other methods. Then use steel plate printing, curtain coating and electrostatic spraying. The liquid photosensitive green paint is applied to the surface of the board by other methods, and then pre-baked and dried (coating a dry film photosensitive green paint on the surface by vacuum film pressing). When it is cooled and exposed in an ultraviolet exposure machine, the green paint will react with the UV radiation in the transparent area of ​​the film (the green paint in this area will remain in the subsequent development step), and the area on the film is not illuminated. It will be removed by an aqueous solution of sodium carbonate. Finally, the resin in the green paint is completely hardened by high temperature baking.
An earlier green paint is produced by direct heating (or ultraviolet irradiation) after screen printing to harden the film. However, during printing and hardening, green paint often penetrates the copper surface of the line terminal contacts, which causes trouble in soldering and using the components. Now, in addition to simple and rough boards, there are more green paints for production.
Character printing
Print the letter, logo or part label requested by the customer on the board by screen printing and then harden the letters by hot baking (or UV irradiation).
Contact processing
The solder mask green coating covers most of the copper surface of the circuit, exposing only the terminal contacts for part soldering, electrical testing and board insertion. The terminals should be properly protected to avoid oxides on the terminals connected to the anode (+) during long-term use, which can affect the stability of the circuit and cause safety problems. [Gold plating] A high hardness and wear resistant nickel layer and a high chemical passivation gold layer are applied to the insertion terminals of the circuit board (commonly referred to as a gold finger) to protect the terminals and provide good connection performance.
[Silver Spray] A layer of tin-lead alloy is applied to the soldered end of the board by hot air flattening to protect the board end and provide good solderability.
[Pre-welding] The anti-oxidation pre-welding skin is used to cover the welding end of the circuit board, and the welding end is temporarily protected. The welding surface is smooth before welding and the welding performance is good.
[Carbon Ink] A carbon ink layer is printed on the contact end of the board by screen printing to protect the end points and provide good connection performance.
Forming a cut
The PCB is cut to the customer's required size by a CNC forming machine (or die punch). When cutting, the PCB is formed by fixing the previously drilled positioning holes on the bed (or mold). After cutting, the gold finger is ground to facilitate insertion into the PCB. X-shaped break lines are usually added to the circuit board formed by the multi-joint chip to facilitate the customer to split and disassemble after insertion. Finally, clean the dust and surface ionic contaminants on the board.
Final inspection package
Perform final board conductivity, impedance testing, solderability and thermal shock resistance testing prior to packaging. The humidity and accumulated thermal stress absorbed by the board during the process are eliminated by proper baking. Finally, the board is packaged and shipped in a vacuum bag.
The PCB market continues to evolve, benefiting mainly from two aspects of electricity. First of all, the market space of the PCB application industry continues to expand, and the application of the communication industry and the notebook computer industry continues to improve, making the high-end multilayer PCB market grow rapidly, with an application rate of up to 50%. At the same time, the proportion of digital circuit boards such as color TVs, mobile phones, and automotive electronics has also increased significantly, which has led to an ever-expanding space in the circuit board industry. In addition, the global PCB industry is shifting to China, which has also led to the rapid expansion of China's PCB market space. Recently, PCB's purely published earnings data revealed a growing market environment in which PCB order-to-delivery rates have steadily exceeded one in the past year. On the other hand, due to fierce competition in the PCB industry, some large PCB factories have been forced to exit the market by actively developing new technologies, increasing the number of PCB layers or promoting the marketization of FPC. Technical requirements to meet changing market demands. At the same time, some small non-competitive factories were forced to withdraw from the market through technology “suppression”, which is also a large part of the good market situation this year. Concerns about PCB small factories.
With the increasing use of FPC, FPC is widely used in computers and communications, consumer electronics, automotive, military and aerospace, medical and other fields, so the market demand has increased significantly. According to dealers, FPC shipments this year are also significantly higher than in previous years, while gross margins continue to be maintained, and distributors show confidence in the investment market.