Manufacturing Technology of Carbon Ink PCB

1. Overview

The Carbon Ink PCB is made of carbon paste screen hole filling process. Carbon particles are evenly distributed in thermoplastic resin to make conductive ink, and then covered with soldermask. Its toughness is high, its thickness is thin, its insulation is good, and its price is lower than that of gold plating. It is often used in high voltage, pulse and high frequency circuits.

The most common methods of making circuits on printed circuit boards are subtractive method and additive process method. Additive process uses electroless copper or electroplated copper to generate circuits, and making conductive Carbon Ink PCB is also a kind of additive process. Conductive carbon ink is used to make wires, which are printed on insulators. With this method, it is easy and effective to make conductive Carbon Ink PCB with various shapes for printing.

The production process of Carbon Ink PCB is a combination of subtractive method and additive process's PCB board manufacturing method. At present, conductive Carbon Ink PCB have made breakthrough progress in application fields, especially in electronic products with low electric power. As a permanent conductive coating on conductive Carbon Ink PCB, conductive Carbon Ink PCB have been adopted and popularized by many electronic designers.

Conductive Carbon ink, with mature and stable production technology, leading product quality, excellent printability, heat resistance and moisture resistance, and stable heating performance, is widely used in far infrared drying oven, incubator, electric blanket, sauna room, floor heating board for electric heating, and electric heating in greenhouse. It has broad development prospects.

At present, the conductive inks include: Carbon Ink, silver oil, high-resistance Carbon Ink, silver paste, transparent conductive oil, far infrared electrothermal ink, far infrared electrothermal paint (low, medium and high), strippable protective ink (circuit board, ITO touch screen, anti-engraving), electromagnetic shielding and anti-static paint, infrared thermal imager, Japan's TIONVT-04 particle size meter, temperature measurement patch and other testing instruments.

2. Production process characteristics of Carbon Ink PCB

With the rapid development of electronic industry, conductive Carbon Ink PCB are gradually adopted in common electrical appliances and instruments, which tend to be multifunctional and miniaturized. Such as television, telephone, electronic organ, game machine and video recorder. Its new technology and new functions are constantly being developed and utilized, and the electronic fields such as computer keyboards, card calculators, mini-recorders, electronic measuring devices and SMT are also beginning to choose conductive carbon Carbon Ink PCB, thus enhancing its reputation and expanding its demand.

The conductive Carbon Ink PCB adopts a simple screen printing process, and one or two layers of conductive carbon ink patterns are added on a single-sided printed circuit board to realize high-density wiring. The printed conductive patterns are used as resistors, key switch contacts and electromagnetic shielding layers, etc., which adapts to the development trend of miniaturization, light weight and multifunction of electronic products.

Conductive ink has a wide range of applications, and is the first choice of most electronic enterprises: conductive carbon paste screen for silica gel keys, conductive Carbon Ink PCB, high-resistance carbon ink oil for potentiometer sliders, low-resistance carbon ink oil for remote controllers, high-resistance carbon ink oil for electronic organ tuning film, low-resistance carbon ink oil for PCB keys, conductive carbon ink for PET film switches, high-resistance carbon paste for electronic drums, antenna Carbon Ink for touch screens, carbon paste for inductive pens for capacitive screens, and conductive circuit boards.

The characteristics of this process have the advantages of previous PTH PCB boards and single-sided PCB, forming a single-sided double-layered PCB board without interconnection holes; Simplifies the production process of PTH PCB boards, which can be realized by steel mesh printing directly, is easy to master, light in weight, and can be thinned, even phenolic cardboard can be used; Parts mounting holes can also be processed; It is suitable for high volume PCB assembly production, shortens the production cycle, reduces the production cost, and has no three wastes pollution--Waste water, waste gas and solid waste.

Carbon Ink PCB can shorten the production cycle of double-sided PCB board by two thirds; The volume of the whole machine is reduced by one quarter to one third; The assembly efficiency of the whole machine is increased by 30%; The production cost is reduced by one-third, so that more double-sided PCB boards or simple multi-layer PCB boards are transformed into conductive carbon Ink PCB. As far as the technical specifications of conductive Carbon Ink PCB are concerned, IEC1249-5-4 contains some technical instructions on conductive coatings; Japan's Hitachi, Toshiba, Panasonic and other famous companies also have some technical specifications for conductive Carbon Ink PCB; Some ink manufacturers, such as Coates, Acheson, Asahi and so on, also have the technical conditions of conductive ink; But these are only some simple explanations and introductions; In 1998 (Shenzhen Sheng Tian Feng Technology Co., Ltd. was established), the standard SJ/T11171-98 "Specification for NPTH Single-sided and Double-sided Conductive Carbon Ink PCB" issued by China's electric industry comprehensively discussed the technical conditions and testing methods of conductive carbon ink PCB boards.

Definition of Carbon Printing

The Carbon Printing actually refers to printing Carbon Ink oil on the designated position by Screen Printing technology, and forming a qualified carbon film with a certain resistance value after oven curing test is OK to replace the original resistance electronic components. In fact, the production process is similar to that of Silkscreen Printing. If there is any difference, it is that the Carbon Printing has better conductivity. On the other hand, the silkscreen are just a semiconductor material, which only plays the role of solder insulation.

Production capacity of Carbon Printing

Let's take a look at the production capacity of Carbon Printing.

1.Carbon Ink gap: Because Carbon Ink has good electrical conductivity, the Carbon Ink on the finished product board must have a certain gap to ensure no short circuit. Usually, the finished product should have a minimum gap of 8mil (HOZ bottom copper) and 12mil (1-3OZ bottom copper). If the gap can be increased in film production, try to increase the gap of the finished product to ensure no short circuit.

2.Minimum alignment tolerance of Carbon Ink: +/-6mil

3.Size of oil opening and gap between oil opening and copper PATTERN: Considering factors such as alignment tolerance and oil leakage, Carbon Ink should be 6mil(HOZ bottom copper) and 8mil(1-3OZ bottom copper) larger than copper PAD, so as to ensure no copper exposure. Accordingly, the gap between the Carbon Ink opening and the surrounding copper PATTERN should be 6mil(HOZ bottom copper) and 8mil(1-3OZ bottom copper), so as to prevent the Carbon Ink from covering the surrounding copper PATTERN, thus avoiding short circuit.

4.The thickness of Carbon Ink : 0.3-1.0mil for one-time screen printing, and+/-0.3 mil for one-time screen printing; If the thickness of Carbon Ink is required to be more than 1.0mil, it is necessary to print the Carbon Ink twice. The thickness of the Carbon Ink for the second printing is 1.0-2.0mil, and the thickness tolerance is +/-0.4mil. The Carbon Ink film for the second printing is 3mil smaller than that for the first screen printing, so two sets of tools need to be written on MI.

Process control of Carbon Ink PCB in screen printing room

In fact, the process control of Carbon Ink PCB in screen printing room is neither simple nor complex. Let's take a look at the following aspects:

1.Operators must wear gloves to work.

2.During production, the process parameters of each machine and equipment must be carried out according to the relevant operation instructions, and shall not be arbitrarily changed.

3.All machines and equipment must be clean, and there must be no dust, garbage, oil and other sundries on the surface.

4.Screen printing speed and ink returning speed and suction pressure should be controlled in the best range. (Take the printing effect as the inspection basis).

5.Screen, scraper and Carbon Ink shall be selected according to the requirements of engineering MI.

6.The oil must be stirred evenly before use, the viscosity detected by viscometer is within the required range, and the ink should be sealed in time after use.

7.Before printing, the grease, oxide and other pollutants on the board surface must be cleaned, and all carbon-filled Carbon Ink boards must be confirmed by the first board of QA before they can be officially produced.

8.In the process of silk-screen printing, the operator should check at least 2PNL per printing plate, and increase the number of self-checks in special circumstances. 4.9 Drying temperature of Carbon Ink plate is 150℃ for 45 minutes. The drying temperature of the oil-filled hole is 150℃ for 20 minutes, and then

9.For oil resistance measurement, the resistance value of Carbon Ink via hole should be less than 100 ohms, the square resistance of carbon wire should be less than 25Ω/ port (the length of carbon wire ÷ the width of carbon wire× 25 Ω), and more than 2/3 of the oil in the Carbon Ink irrigation hole can be detected according to the drawings of engineering department and the points required by MI.

10.The operator of the baking sheet shall fill in the time when the baking sheet is put into the furnace, the time when the baking sheet is put out of the furnace, the temperature quantity, etc. After being put out of the furnace and cooled, the operator shall inform QA to carry out random inspection of carbon resistance and adhesion test.

11.Each Carbon Ink screen has reached 2,500 prints, so it must be returned to the net room for re-drying the new screen.

Safety precautions

There are many safety precautions for Carbon Ink PCB board in screen printing room. Let's talk about two of them below.

1.Don't put your hands and body under the screen printing when turning on carbon printing.

2.Operators should wear thick gloves to avoid scalding their skin.

With the development of PCB and its component mounting in the direction of short and thin, more and more manufacturers are involved in the development wave of integrated manufacturing of components and PCB, among which conductive Carbon Ink PCB is one of the earlier integrated products. Under the condition of low requirements of PCB working environment and resistance precision, the production and application of conductive Carbon Ink PCB are very extensive. However, the printing technology of conductive Carbon Ink PCB has been replaced by materials and technologies with higher resistance precision, and gradually faded out of people's sight. Even so, because the manufacturing process of the conductive Carbon Ink PCB is relatively simple and the processing cost is low, if the manufacturing process of the conductive Carbon Ink PCB can be optimized, the controlled precision of its resistance value and the yield of finished products can be improved, the products still have a wide market space.