The so-called carbon printing ink actually refers to the use of screen printing technology ,to print carbon printing ink on the designated position of the PCB board, and after the oven curing test OK, a qualified carbon film with a certain resistance value is formed to replace the original resistance element. The production process is actually similar to silk screen printing. If you want to say the difference, it is that the carbon printing ink has better conductivity performance. On the other hand, the character is only a semiconductor material, which only plays the role of solder insulation..
Carbon printing ink production capacity
Carbon ink gap: Because carbon ink has good conductive properties, the carbon ink on the finished board needs a certain gap to ensure no short circuit. Generally, the minimum required product has 8mil gap (HOZ bottom copper) and 12mil gap (1- 3OZ bottom copper), if the production film can increase the gap, try to increase the gap of the finished product to ensure that there is no short circuit.
Minimum alignment tolerance of carbon ink: +/- 6mil
The size of the carbon ink window and the gap with the copper pattern: Considering factors such as alignment tolerances and ink leakage, the carbon ink needs to be 6mil (hoz bottom copper) and 8mil (1-3OZ bottom copper) larger than the unilateral copper PAD to guaranteed not to reveal copper. Correspondingly, the carbon ink window also needs 6mil (HOZ bottom copper) and 8mil (1-3OZ bottom copper) gaps from the surrounding copper pattern to avoid carbon ink covering the surrounding copper pattern, thus avoiding short circuit.
Carbon ink thickness: primary printing ink thickness: 0.3-1.0mil, primary printing carbon ink thickness tolerance: +/- 0.3mil; if the carbon ink thickness is required to be 1.0mil or more, the secondary printing carbon ink is required, and the secondary return Thickness of carbon printing ink: 1.0-2.0mil, thickness tolerance: +/- 0.4mil, the second reprinted carbon ink film is 3mil smaller than the first carbon printing ink unilateral film, so two sets of tools need to be written on MI.
Technical process of carbon oil board
The process flow of carbon oil board can be simply represented by a picture:
Process control of carbon ink board in screen printing room
1. The process control of the carbon ink board of the screen printing room is actually not simple, and it is not complicated. Let’s take a look at some aspects:
2. The operator must wear gloves to work.
3. During the production operation, the process parameters of each machine and equipment must be carried out according to the relevant operation instructions, and cannot be changed at will.
4. Each machine must be clean, and the surface must be free of dust, dirt, oil and other debris.
5. Screen printing speed and ink return speed the suction pressure is controlled in the optimal range. (Take printing effect as the inspection basis).
6. The wire mesh, scraper, and carbon ink are selected according to the MI requirements of the project.
7. The carbon ink must be stirred well before use. Use a viscometer to check that the viscosity is within the required range. After the ink is used, seal it in time.
8. Be sure to clean the grease, oxide and other contaminants on the surface of the board before printing. All carbon-filled carbon ink boards must be confirmed by the QA first board before they can be officially produced.
9. During the screen printing process, the operator must self-check at least 2PNL for each board printed, in particular, the number of self-checks should be increased. The drying temperature of carbon ink board is 150 ℃ for 45 minutes. Carbon ink hole drying temperature 150 ℃ for 20 minutes
9. Carbon ink resistance measurement, the resistance value of the carbon ink via hole should be less than 100 ohms, the resistance of the carbon wire should be less than 25Ω / port (carbon wire length ÷ carbon wire width × 25Ω), the ink in the carbon ink filling hole should be more than 2/3, It can be tested according to the drawings of the engineering department and the points required by the MI.
10. The baked plate operator fills in the time and temperature of the baked plate for each baked plate, etc. After cooling, the operator should inform QA to carry out the random inspection of carbon resistance and the adhesion test.
11. Each carbon ink screen used to reach 2500 prints, must be returned to the net room to request a new screen.
1. Don’t put your hands and body under the screen when you start carbon filling and carbon printing.
2. Bake plate workers should wear thick wire gloves to prevent skin burns.