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PCB Technology

PCB Technology - Circuit Board Printing Process

PCB Technology

PCB Technology - Circuit Board Printing Process

Circuit Board Printing Process
Author:Circuit Boarder

Circuit board printing is now a very developed new industry, and the rapid development of screen printing and injected vitality into this industry, to the electronics industry has brought about significant changes. The current circuit board screen printing process is fully capable of adapting to the production of high-density circuit boards.

Silk Screen for Circuit Board Printing

Silk screen is the most important part of the screen printing plate, it is the key to control the ink flow and printing thickness, and determines the durability of the screen plate. In addition, an excellent bond between the silk screen and the photographic material of the screen plate is also an important factor in the production of high-quality, high-precision screen printing plates. In order to ensure a good bond between the silk screen and the photographic material, the traditional practice is to roughen and degrease the new silk screen, so as to ensure the quality of the screen plate and prolong the service life of the silk screen. At the same time, it is also important to choose the correct mesh size for the screen. 160 mesh nylon silk screen made of printing plates often appear photopolymer film and silk screen adhesion is not good enough, the printed line is easy to become thick and burrs, squeegee scraping effort and other problems. Using 250 mesh nylon silk screen to make the printing plate, the printing accuracy is improved, the scraping effort is saved, and the burr is reduced. With 360 mesh nylon silk screen, the photopolymer film is firmly bonded to the silk screen, the squeegee is less labour-intensive, the printing accuracy is significantly improved, and the lines and text edges are neat. Lines and spacing up to No.2-0.15mm.

Photographic materials for circuit board printing

Commonly used photographic materials for printing plates include diazo emulsions and photographic films. The diazo photographic emulsion is commonly used in screen plate production. Photographic film has the characteristics of uniform and controllable film thickness, high resolution, high definition, wear resistance, and strong adhesion with silk screen, etc., which is widely used in the character printing of printed boards. The requirements of circuit board screen printing plate for photosensitive materials are. Good printability, such as easy coating. There is a suitable range of light-sensitive spectrum, generally 340 ~ 440nm is appropriate, light-sensitive wavelength is too long, plate-making operations and storage of printing plates need to be in strict darkroom conditions. If the wavelength is too short, the selection of light source and protection of personnel will become more difficult. High sensitivity can achieve the purpose of energy saving and fast plate making. Good development efficiency, high resolution. Good stability, easy to store, reduce waste. Economical, hygienic, non-toxic and harmless.

Stencil for Printed Circuit Boards

Stencil material and cross-section shape are very important. If the frame is not strong enough for a certain size of stencil, then tension uniformity cannot be guaranteed. Tension uniformity cannot be guaranteed. Generally, high tensile aluminium stencil are used.

How are circuit boards made? When we open the keyboard of a general-purpose computer, we see a piece of flexible film (flexible insulating substrate) with a silver-white (silver paste) conductive pattern and a Kenbit pattern printed on it. Because the general screen leakage printing method to get this pattern, so we call this printed circuit board for flexible silver paste printed circuit board. We go to the computer city to see a variety of computer motherboards, graphics cards, network cards, modems, sound cards and home appliances on the printed circuit board is different. It is used by the substrate is made of paper-based (commonly used in single-sided) or glass cloth-based (commonly used in double-sided and multi-layer), pre-impregnated with phenolic or epoxy resin, surface layer on one side or both sides of the book glued to the copper laminate and then laminated and cured into. This kind of circuit board laminated copper book sheet, we call it rigid board. Then made into printed circuit boards, we call it rigid printed circuit boards. A printed circuit board with a printed circuit pattern on one side is called a single-sided printed circuit board, while a printed circuit board with a printed circuit pattern on both sides and interconnected on both sides through the metallisation of holes is called a double-sided printed circuit board. If a double-sided for the inner layer, two single-sided for the outer layer or two double-sided for the inner layer, two single-sided for the outer layer of the printed circuit board, through the positioning system and insulating bonding data alternately together and conductive patterns according to the design requirements of the interconnected printed circuit boards become four, six-layer printed circuit boards, also known as multi-layer printed circuit boards. Nowadays, there are more than 100 layers of practical printed circuit boards.

Printed circuit board production process is more complex, it involves a wider range of processes, from simple mechanical processing to complex mechanical processing, there are ordinary chemical reactions and photochemical electrochemical thermochemical processes, computer-aided design CAM and other aspects of knowledge. And in the production process in the process of a lot of problems and will meet from time to time new problems and part of the problem in the absence of a clear understanding of the causes of the problem disappeared, due to its production process is a non-continuous assembly line form, any one of the links out of the problem will result in the whole line of production or a large number of consequences of the scrap, printed circuit boards, if the scrap is unable to be recycled and reuse, process engineers work under pressure, so many engineers left the industry to switch to a more complex mechanical processing. Engineers left the industry to the printed circuit board equipment or data vendors to do sales and technical services.

circuit board

Printed Circuit Board

Printing process for circuit boards

Circuit board printing processes usually include single-sided, double-sided printed circuit boards and ordinary multi-layer circuit boards.

Single Sided Rigid Printed Board

Single-sided rigid printing board -> single-sided laminating board -> unloading -> (brushing, drying) -> drilling or punching -> screen-printed circuit resist etching pattern or use dry film -> curing inspection repair board -> etching copper -> to resist etching material, drying -> brushing, drying -> screen-printed solder resist pattern (commonly used green oil), UV curing -> screen-printed character marking pattern, UV curing -> preheating, punching and shape -> power open and short-circuit test -> brushing and drying -> pre-application of flux antioxidant (drying) or tin spray hot air levelling -> inspection and packaging -> finished products out of the factory. Pre-coating flux antioxidant (drying) or tin spray hot air levelling -> inspection and packaging -> finished products out of the factory.

Double-sided rigid printing board

Double-sided rigid board->Double-sided laminates->Unloading->Stacking->Digital drilling of via holes->Inspection, deburring and brushing->Chemical plating (via holes metallisation)->(full-board electroplating of thin copper)->Inspection and brushing->Screen printing of negative circuit graphics, curing (dry or wet film, exposure, development)->Inspection, board repair->Wire graphic plating->Stainless steel plating (corrosion-resistant nickel/gold)->Removal of printed material (photographic film)->Etching of copper->(desoldering)->Cleaning Brushing -> screen printing solder resist pattern commonly used heat curing green oil (paste light-sensitive dry film or wet film, exposure, developing, heat curing, commonly used light-sensitive heat curing green oil) -> cleaning, drying -> screen printing marking character pattern, curing -> (spray tin or organic soldering film) -> shape processing -> cleaning, drying -> power on and off test -> inspection and packaging -> finished products out of the factory.

Through-hole metallisation process for multilayer boards -> internal laminates double-sided opening -> brushing -> drilling positioning holes -> photoresist dry film or photoresist coating -> exposure -> developing -> etching and de-embossing -> internal roughing, de-oxidisation -> internal inspection -> (external single-sided laminates line production, B-stage bonding sheet, sheet bonding sheet inspection, drilling positioning holes) -> laminating -> digital control Drilling -> Hole inspection -> Hole pre-treatment and chemical copper plating -> Thin copper plating on the whole board -> Layer inspection -> Photoresist dry film or photoresist coating -> Exposure of the top layer backing board -> Developing and repairing the board -> Line pattern plating -> Tin-lead alloy plating or nickel/gold plating -> De-filming and etching -> Inspection -> Screen-printing of soldermask or photoresist pattern -> Printing of character pattern -> (Hot air levelling or organic soldermask) -> Digitally controlled shape washing -> Cleaning, Drying -> Power on/off inspection -> Finished product inspection -> Packaging for shipment. Double-sided rigid printing board

With the development trend of high-density circuit boards, circuit board printing process requires more and more high, more and more new technologies applied to circuit board printing process, sh as laser technology, photopolymerised resin and so on.